Measurement of Tensile Strength
Okra bast fibres were cut into small pieces of length 30 cm and the length of each specimen between the jaws of the machine was maintained 10 cm. One twist per 2 cm was given along the length of the fibre between the jaws of the machine for measuring breaking strength of okra bast fibre. 0.5 gm of each specimen was weight out and the tensile strength of it was measured (by Torsee,s Scopper Type-OS-100). The breaking load was gradually increased after starting the machine and at a particular point the specimen was broken down. The machine was stopped at the point of break. The breaking load was shown on the scale of the tensile tester in N. In each experiment tensile strength for 10 cm specimens were taken and the mean of 10 readings was the breaking strength of okra bast fibre.
Knowing the breaking load, the tensile strength/tenacity was calculated by the following formula:
Tenacity = Average breaking load /Denier (gm/denier)
From the weight and length, the denier of okra bast fibre sample was calculated according to the formula:
Denier = Weight of sample in gm/Length of the sample in meter x 9000
Weight and length of the sample were measured between the jaws of the tensile strength tester. By calculating average breaking strength and denier, tensile strength or tenacity of undyed and dyed bleached and modified okra bast fibres were measured.
Tuesday, June 28, 2011
Degradation Method
Degradation Method
Thermo-oxidative Degradation
The thermo-oxidative degradation of undyed, bleached dyed and modified okra bast fibres were studied. Okra bast fibres were cut into equal length of 30 cm and placed in an electric oven in presence of air. After heating the experimental samples at 50, 100, 150, 200 and 250°C for 1 h, the fibre samples were collected. The change in colour of samples were assessed with Grey Scale.
Photo-Oxidative Degradation
Both undyed and bleached dyed and modified okra bast fibres were attached on a flat board separately and placed on the roof of a building for exposure in open air under the sun for 50, 100, 150, 200 and 250 hours without any protection from weather. Care was taken so that the effect of weathering would be confined to the surface of the fibre. After exposing the fibres were collected from the board for experimental purpose. The change in colour of samples was assessed with Grey Scale.
Thermo-oxidative Degradation
The thermo-oxidative degradation of undyed, bleached dyed and modified okra bast fibres were studied. Okra bast fibres were cut into equal length of 30 cm and placed in an electric oven in presence of air. After heating the experimental samples at 50, 100, 150, 200 and 250°C for 1 h, the fibre samples were collected. The change in colour of samples were assessed with Grey Scale.
Photo-Oxidative Degradation
Both undyed and bleached dyed and modified okra bast fibres were attached on a flat board separately and placed on the roof of a building for exposure in open air under the sun for 50, 100, 150, 200 and 250 hours without any protection from weather. Care was taken so that the effect of weathering would be confined to the surface of the fibre. After exposing the fibres were collected from the board for experimental purpose. The change in colour of samples was assessed with Grey Scale.
Colour Fastness to Spotting: Acid and Alkali
Colour Fastness to Spotting: Acid and Alkali
Undyed and dyed (bleached & modified) okra bast fibres were combed and compressed enough to form a sheet of 10 cm × 4 cm. The specimens were spotted with two drops of acid or alkali solution at room temperature. The surface of the specimens were gently rubbed with the glass rod to ensure penetration. The specimens were dried by hanging them in open air at room temperature. The change in colour of the specimens was assessed after drying with Grey Scale. In the same way, the change in colour was assessed by the solution given below.
(i) Acetic acid solution containing 10 g/l.
(ii) Nitric acid solution containing 10 g/l.
(iii) Sulphuric acid solution containing 10 g/l.
(iv) Sodium carbonate solution containing 10 g/l.
(v) Ammonia solution containing 10 g/l.
(vi) Sodium hydroxide solution containing 10 g/l.
Undyed and dyed (bleached & modified) okra bast fibres were combed and compressed enough to form a sheet of 10 cm × 4 cm. The specimens were spotted with two drops of acid or alkali solution at room temperature. The surface of the specimens were gently rubbed with the glass rod to ensure penetration. The specimens were dried by hanging them in open air at room temperature. The change in colour of the specimens was assessed after drying with Grey Scale. In the same way, the change in colour was assessed by the solution given below.
(i) Acetic acid solution containing 10 g/l.
(ii) Nitric acid solution containing 10 g/l.
(iii) Sulphuric acid solution containing 10 g/l.
(iv) Sodium carbonate solution containing 10 g/l.
(v) Ammonia solution containing 10 g/l.
(vi) Sodium hydroxide solution containing 10 g/l.
Colour Fastness to Sunlight
Colour Fastness to Sunlight
Light fastness test was carried out of both the bleached dyed and modified dyed fibres. Specimens of the fibre were attached separately on a board by a glass rod and placed on the roof of a building for exposure in the open air under the sun without any protection from weathering, but was protected form rain, dews,dust etc. The specimens were exposed under the sun for seven hours each day and continued for 250 h. After every 50 h, the fastness was assessed by comparing the change in colour of specimen with that of the standard or original.
Measurement of DL*, Da*and Db*
In addition to visual assessments, the samples were evaluated objectly by measuring the CIE Lab values (DL*, Da*and Db*) of dyed samples before and after washing using a Macbath CE-3100 spectrometer and then calculating the colour change. Illuminant D65 and 10° observer geometry were used throughout for the colour measurement.
Light fastness test was carried out of both the bleached dyed and modified dyed fibres. Specimens of the fibre were attached separately on a board by a glass rod and placed on the roof of a building for exposure in the open air under the sun without any protection from weathering, but was protected form rain, dews,dust etc. The specimens were exposed under the sun for seven hours each day and continued for 250 h. After every 50 h, the fastness was assessed by comparing the change in colour of specimen with that of the standard or original.
Measurement of DL*, Da*and Db*
In addition to visual assessments, the samples were evaluated objectly by measuring the CIE Lab values (DL*, Da*and Db*) of dyed samples before and after washing using a Macbath CE-3100 spectrometer and then calculating the colour change. Illuminant D65 and 10° observer geometry were used throughout for the colour measurement.
Measurement of Colour Strength (K/S value)
Measurement of Colour Strength (K/S value)
The colour yield of both bleached and grafted dyed fibres was evaluated by light reflectance measurements using Macbeth CE-3100 spectrometer.
The colour strength (K/S) value was assesed using the Kubelka-Munk equation:
(1-R)(1-R)
K/S =-------------
2R
Where R is the decimal fraction of the reflectance of dyed fibre.
The colour yield of both bleached and grafted dyed fibres was evaluated by light reflectance measurements using Macbeth CE-3100 spectrometer.
The colour strength (K/S) value was assesed using the Kubelka-Munk equation:
(1-R)(1-R)
K/S =-------------
2R
Where R is the decimal fraction of the reflectance of dyed fibre.
Method of Dyeing
Method of Dyeing
Direct green 27 and Direct Red 28 were dissolved at first by making paste with little distilled water and then by adding cold distilled water, the dye baths were prepared by taking 5 % dye concentration and 5% electrolyte (Na2SO4) concentration (on the basis of weight of okra fibre). The fibre-liquor ratio was maintained at 1:50. Before immersing the fibre in the dye bath it was treated well in distilled water and squeezed for even absorption of dye particles. Dyeing temperature was fixed at 70°C and it was continued for 60 min. The dye bath was occasional stirring by a glass rod and then allowed for further 30 min as the bath cools down. During dyeing the dye bath were slightly alkaline with 2% sodium carbonate solution to attain the fast reaction and also hot distilled water was added to the dye bath in order to maintain the fibre-liquor ratio 1:50 throughout the experiment.
Direct green 27 and Direct Red 28 were dissolved at first by making paste with little distilled water and then by adding cold distilled water, the dye baths were prepared by taking 5 % dye concentration and 5% electrolyte (Na2SO4) concentration (on the basis of weight of okra fibre). The fibre-liquor ratio was maintained at 1:50. Before immersing the fibre in the dye bath it was treated well in distilled water and squeezed for even absorption of dye particles. Dyeing temperature was fixed at 70°C and it was continued for 60 min. The dye bath was occasional stirring by a glass rod and then allowed for further 30 min as the bath cools down. During dyeing the dye bath were slightly alkaline with 2% sodium carbonate solution to attain the fast reaction and also hot distilled water was added to the dye bath in order to maintain the fibre-liquor ratio 1:50 throughout the experiment.
Measurement of Water Absorption
Method for the measurement of water absorption
Water absorption tests of untreated and chemically modified okra bast fibres are carried out by taking a small amount (about 0.5 g) of the fibre. Fibre samples were first dried by heating in an electric oven at 70°C for about 2 h, weighed and then soaked in a bath of conductivity water at room temperature. After 24 h, the fibre samples were removed from water, dried by a cotton cloth and weighed again.
A-B
Percentage of water absorption by fibres =------------100
B
Where,
A = The weight of the fibres after water absorption.
B = The weight of the fibres before water absorption
(drying sample).
Water absorption tests of untreated and chemically modified okra bast fibres are carried out by taking a small amount (about 0.5 g) of the fibre. Fibre samples were first dried by heating in an electric oven at 70°C for about 2 h, weighed and then soaked in a bath of conductivity water at room temperature. After 24 h, the fibre samples were removed from water, dried by a cotton cloth and weighed again.
A-B
Percentage of water absorption by fibres =------------100
B
Where,
A = The weight of the fibres after water absorption.
B = The weight of the fibres before water absorption
(drying sample).
Scanning Electron Microscopy (SEM)
Scanning Electron Microscopy (SEM)
A scanning electron microscopy (SEM) machine was used to study the surface morphology of the acrylonitrile treated OBF. The microscopic utmost importance in characterizing the structural changes that have occurred upon treatment.
Scanning Electron Microscope:
Model: Philips XL-30
Specification of SEM: Magnification 100000X
Excitation voltage 30 kv
Equipped with vacuum pump
Equipped with EDS
A scanning electron microscopy (SEM) machine was used to study the surface morphology of the acrylonitrile treated OBF. The microscopic utmost importance in characterizing the structural changes that have occurred upon treatment.
Scanning Electron Microscope:
Model: Philips XL-30
Specification of SEM: Magnification 100000X
Excitation voltage 30 kv
Equipped with vacuum pump
Equipped with EDS
Fourier Transform Infrared Spectroscopy (FTIR) measurement
Fourier Transform Infrared Spectroscopy (FTIR) measurement
The measurements were performed using a Shemazdu Spectrometer. A total 100 scans were taken with a resolution of 2 cm-1 for each sample. The fibre was cut in a size range between 106 and 212 micrometer. A mixture of 5.0 mg of dried fibres and 200 mg of KBr was pressed into a disk for FTIR measurement.
The measurements were performed using a Shemazdu Spectrometer. A total 100 scans were taken with a resolution of 2 cm-1 for each sample. The fibre was cut in a size range between 106 and 212 micrometer. A mixture of 5.0 mg of dried fibres and 200 mg of KBr was pressed into a disk for FTIR measurement.
Method of Modification of Okra Bast Fiber
Method of Modification of Okra Bast Fiber
Vinyl monomer (Acrylonitrile) was dissolved in cold distilled water. Initiator and catalyst solutions were also prepared with cold distilled water. The modifying baths were prepared by adding required amount of monomer, initiator and catalyst. The fibre-liquor ratio was maintained at 1:50. Modification was started at 30°C and then the temperature was slowly increased upto 90°C with 30 min and continued for 240 min with occasional stirring by a glass rod and allowed for further 30 min as the bath cools down. Hot distilled water was added to the modifying baths in order to maintain the fibre-liquor ratio 1:50 throughout the experiment. After modification the fibres were washed with hot distilled water to remove the suspended homopolymer on the okra bast fibre sample and dried at room temperature.
Percentage of grafting was calculated according to the following formula:
A-B
Percentage of grafting = ---------- 100
B
Where,
A = The weight of the okra bast fibre after modification
B = The weight of bleached okra bast fibre before modification
Selection of Optimum Modification Conditions
In order to select the optimum conditions of modification of okra bast fibre, monomer concentration, initiator concentration, catalyst concentration, modification time and modification temperature were selected accordingly.
Selection of Monomer Concentration
Ten baths were prepared with 0.01M, 0.02M, 0.03M, 0.04M, 0.05M, 0.06M, 0.07M, 0.08M, 0.09M and 0.1M acrylonitrile monomer. Keeping constant all other parameters (Initiator 0.1M, catalyst-0.1M, time 90 min, temperature 70°C, fibre-liquor ratio1:50), the monomer concentration which gave the maximum percentage of grafting was selected for modification.
Selection of Initiator Concentration
The selected monomer concentration and other parameters (catalyst 0.1M, time 90 min, temperature 70°C, fibre-liquor ratio 1:50) were kept constant and the ten modifying baths were prepared with 0.001M, 0.005M, 0.01M, 0.015M, 0.02M, 0.025M, 0.03M, 0.035M, 0.04, and 0.045M potassium persulphate (K2S2O8) initiator solution. The initiator concentration which gave the maximum grafting was selected for modification.
Selection of Catalyst Concentration
The selected monomer and initiator concentration and other parameters (time 90 min, temperature 70°C, fibre-liquor ratio 1:50) were kept constant and then ten modifying baths were prepared with 0.001M, 0.002M, 0.003M,
0.004M, 0.006M, 0.007M, 0.008M, 0.009M, 0.01M,and 0.02M ferrous sulphate (FeSO4) as catalyst to catalyse the initiator. The catalyst concentration which gave the maximum grafting was selected for modification.
Selection of Modification Time
Eight modifying baths each containing selected monomer, initiator and catalyst concentrations were prepared and the fibres were modified at 70°C for 30, 60, 90, 120, 150, 180, 210 and 240 min. The time of modification which gave maximum grafting was selected for modification.
Selection of Modification Temperature
Seven modifying baths, each containing selected monomer, initiator and catalyst concentrations were prepared and then the okra fibre were modified at 30° (room temperature), 40°, 50°, 60°, 70°, 80° and 90°C for selected time. The temperature, which gave maximum grafting, was selected for modification.
Vinyl monomer (Acrylonitrile) was dissolved in cold distilled water. Initiator and catalyst solutions were also prepared with cold distilled water. The modifying baths were prepared by adding required amount of monomer, initiator and catalyst. The fibre-liquor ratio was maintained at 1:50. Modification was started at 30°C and then the temperature was slowly increased upto 90°C with 30 min and continued for 240 min with occasional stirring by a glass rod and allowed for further 30 min as the bath cools down. Hot distilled water was added to the modifying baths in order to maintain the fibre-liquor ratio 1:50 throughout the experiment. After modification the fibres were washed with hot distilled water to remove the suspended homopolymer on the okra bast fibre sample and dried at room temperature.
Percentage of grafting was calculated according to the following formula:
A-B
Percentage of grafting = ---------- 100
B
Where,
A = The weight of the okra bast fibre after modification
B = The weight of bleached okra bast fibre before modification
Selection of Optimum Modification Conditions
In order to select the optimum conditions of modification of okra bast fibre, monomer concentration, initiator concentration, catalyst concentration, modification time and modification temperature were selected accordingly.
Selection of Monomer Concentration
Ten baths were prepared with 0.01M, 0.02M, 0.03M, 0.04M, 0.05M, 0.06M, 0.07M, 0.08M, 0.09M and 0.1M acrylonitrile monomer. Keeping constant all other parameters (Initiator 0.1M, catalyst-0.1M, time 90 min, temperature 70°C, fibre-liquor ratio1:50), the monomer concentration which gave the maximum percentage of grafting was selected for modification.
Selection of Initiator Concentration
The selected monomer concentration and other parameters (catalyst 0.1M, time 90 min, temperature 70°C, fibre-liquor ratio 1:50) were kept constant and the ten modifying baths were prepared with 0.001M, 0.005M, 0.01M, 0.015M, 0.02M, 0.025M, 0.03M, 0.035M, 0.04, and 0.045M potassium persulphate (K2S2O8) initiator solution. The initiator concentration which gave the maximum grafting was selected for modification.
Selection of Catalyst Concentration
The selected monomer and initiator concentration and other parameters (time 90 min, temperature 70°C, fibre-liquor ratio 1:50) were kept constant and then ten modifying baths were prepared with 0.001M, 0.002M, 0.003M,
0.004M, 0.006M, 0.007M, 0.008M, 0.009M, 0.01M,and 0.02M ferrous sulphate (FeSO4) as catalyst to catalyse the initiator. The catalyst concentration which gave the maximum grafting was selected for modification.
Selection of Modification Time
Eight modifying baths each containing selected monomer, initiator and catalyst concentrations were prepared and the fibres were modified at 70°C for 30, 60, 90, 120, 150, 180, 210 and 240 min. The time of modification which gave maximum grafting was selected for modification.
Selection of Modification Temperature
Seven modifying baths, each containing selected monomer, initiator and catalyst concentrations were prepared and then the okra fibre were modified at 30° (room temperature), 40°, 50°, 60°, 70°, 80° and 90°C for selected time. The temperature, which gave maximum grafting, was selected for modification.
Bleaching of Okra with Sodium Chlorite
Bleaching of Okra Bast Fibre With Sodium Chlorite
For bleaching, about 1 gm dewaxed okra bast fibre dried at 105°C was treated with 0.7% sodium chlorite (NaClO2) solution buffered at pH 4. Required amount of sodium chlorite was dissolved in a known volume of water, and its pH, which was 10.6, was lowered to 4 by the gradual addition of 0.2N acetic acid. pH readings were taken with pH meter (Pocket). The pH meter was standardized with a buffer solution of known pH and was checked
with another buffer solution of known pH. A buffer mixture of pH 4 (acetic acid-sodium acetate) was prepared and added to the chlorite CH3COOH-CH3COONa buffer solution in the proportion of 1 ml of buffer solution for every 10 ml of chlorite solution, to ensure that pH remained at 4 throughout the progress of the reaction. This pH maintaining is necessary because many organic acids are liberated during bleaching and unless the mixture is buffered the pH of the medium would change. The bleaching process was carried out by digesting the fiber for about 2 h at 90-95°C. For each gram of the fiber 80 ml of the mixture was used. After bleaching the fibre was filtered over a sintered funnel and washed thoroughly with distilled water. It was then treated with 2% sodium metabisulphite solution for 15 min. The fiber-liquor ratio was 1:50. Again the fiber was filtered and washed thoroughly with distilled water. The bleached okra bast fibre on the sintered funnel was then dried and preserved in a desicator.
For bleaching, about 1 gm dewaxed okra bast fibre dried at 105°C was treated with 0.7% sodium chlorite (NaClO2) solution buffered at pH 4. Required amount of sodium chlorite was dissolved in a known volume of water, and its pH, which was 10.6, was lowered to 4 by the gradual addition of 0.2N acetic acid. pH readings were taken with pH meter (Pocket). The pH meter was standardized with a buffer solution of known pH and was checked
with another buffer solution of known pH. A buffer mixture of pH 4 (acetic acid-sodium acetate) was prepared and added to the chlorite CH3COOH-CH3COONa buffer solution in the proportion of 1 ml of buffer solution for every 10 ml of chlorite solution, to ensure that pH remained at 4 throughout the progress of the reaction. This pH maintaining is necessary because many organic acids are liberated during bleaching and unless the mixture is buffered the pH of the medium would change. The bleaching process was carried out by digesting the fiber for about 2 h at 90-95°C. For each gram of the fiber 80 ml of the mixture was used. After bleaching the fibre was filtered over a sintered funnel and washed thoroughly with distilled water. It was then treated with 2% sodium metabisulphite solution for 15 min. The fiber-liquor ratio was 1:50. Again the fiber was filtered and washed thoroughly with distilled water. The bleached okra bast fibre on the sintered funnel was then dried and preserved in a desicator.
Scouring of Okra Bast Fiber
Scouring of Okra Bast Fibre
The removal of impurities such as dirty materials, fatty, waxy and gummy substances from textile materials is called scouring. It is carried out by the use of surface-active agents, such as soda and detergents.
About 30 cm from the bottom of the fibre was discarded and it was then cut into three equal parts (20 cm) viz. the top, the middle and the bottom. Middle portion of the fiber was used for investigation. Okra bast fibre was scoured in a solution containing 5 mg Na2CO3 and 5 gm detergent per liter of water in a large beaker. The ratio of the fiber to solution was 1:50. The solution with okra fibre was heated at 60°C for 30 min. Then the fiber was thoroughly washed with distilled water for several times. Finally it is dried at 80-90°C in an electric oven and stored in a desiccator.
The removal of impurities such as dirty materials, fatty, waxy and gummy substances from textile materials is called scouring. It is carried out by the use of surface-active agents, such as soda and detergents.
About 30 cm from the bottom of the fibre was discarded and it was then cut into three equal parts (20 cm) viz. the top, the middle and the bottom. Middle portion of the fiber was used for investigation. Okra bast fibre was scoured in a solution containing 5 mg Na2CO3 and 5 gm detergent per liter of water in a large beaker. The ratio of the fiber to solution was 1:50. The solution with okra fibre was heated at 60°C for 30 min. Then the fiber was thoroughly washed with distilled water for several times. Finally it is dried at 80-90°C in an electric oven and stored in a desiccator.
Collection and Preparation of Okra Fiber
Collection and Preparation of Okra Fibre
The okra fibre of different species are found in the various regions in Bangladesh. For our investigation the okra fiber was collected from Jhenidah district region. The plant is first retted into water for 13 to 15 days, the fibre was then separated from cementing and gummy materials. The fibre was washed in clean water for several times and dried in air without exposing sunlight. Finally the fibre was dried in an electric oven at 105°C and stored in a desicator.
The okra fibre of different species are found in the various regions in Bangladesh. For our investigation the okra fiber was collected from Jhenidah district region. The plant is first retted into water for 13 to 15 days, the fibre was then separated from cementing and gummy materials. The fibre was washed in clean water for several times and dried in air without exposing sunlight. Finally the fibre was dried in an electric oven at 105°C and stored in a desicator.
Sunday, June 26, 2011
My Investigation on Natural Okra Fiber
MY OF THE PRESENT INVESTIGATION
Okra bast fibre is a lignocellulosic fibre which contains higher percentage of α-cellulose. So it is indeed a very fascinating field of research with unlimited future possibilities for improving the desired properties of the fibre. They are generally biodegradable but do not possess the necessary and sufficent properties desirable for engineering or commodity plastics. Besides, like other vegetable fibres okra bast fibre possess few weak points i.e., rub resistance, colour fastness, wash and wear properties and very much prone to creasing, possibly because of high degree of orientation of cellulose in the fibre. This defect of creasing of cellulosic fiber may be remedied remarkably by the crease-resisting process in which resins are synthesized within the cellulosic materials in different proportions. In order to improve the textile properties of okra bast fibre it is an urgent need to improve several properties such as whiteness, softness, washing, dyeing behaviour, colour fastness, light resistance, thermal resistance, etc. So an attempt has been made to improve those characteristics of okra fiber through chemical modification and dyeing.
In the view of the above considerations, the following efforts have been exerted in the present investigation:
> To synthesize acrylonitrile resin onto okra bast fibre are focused on fiber-surface treatment methods and the resultant effects on the physical and mechanical properties of the fibre. The modification of okra bast fibre with acrylonitrile was carried out at varying initiator concentration, catalyst concentration, modification time, modification temperature.
> FTIR was employed to assess the relation between structure and properties after modification.
> SEM was used to observe the microstructure and the surface morphology of treated and untreated okra bast fibre.
> The bleached and modified okra bast fibres have been dyed with Direct Red 28 and Direct Green 27 in presence of sodium sulphate as an electrolyte. Electrolyte is used for obtaining better hue and level dyeing.
> The colour strength and CIE lab values of dyed samples are measured in Macbeth CE-3100 spectrophotometer.
> The colour fastness undyed and dyed (bleached and modified) okra bast fibre have been studied on the exposure to sunlight, wishing, acid spotting, alkali spotting and heat.
> The effect of various influences such as heat and light on tensile strength of bleached and modified okra bast fibre and their dyed fibre has been studied.
Okra bast fibre is a lignocellulosic fibre which contains higher percentage of α-cellulose. So it is indeed a very fascinating field of research with unlimited future possibilities for improving the desired properties of the fibre. They are generally biodegradable but do not possess the necessary and sufficent properties desirable for engineering or commodity plastics. Besides, like other vegetable fibres okra bast fibre possess few weak points i.e., rub resistance, colour fastness, wash and wear properties and very much prone to creasing, possibly because of high degree of orientation of cellulose in the fibre. This defect of creasing of cellulosic fiber may be remedied remarkably by the crease-resisting process in which resins are synthesized within the cellulosic materials in different proportions. In order to improve the textile properties of okra bast fibre it is an urgent need to improve several properties such as whiteness, softness, washing, dyeing behaviour, colour fastness, light resistance, thermal resistance, etc. So an attempt has been made to improve those characteristics of okra fiber through chemical modification and dyeing.
In the view of the above considerations, the following efforts have been exerted in the present investigation:
> To synthesize acrylonitrile resin onto okra bast fibre are focused on fiber-surface treatment methods and the resultant effects on the physical and mechanical properties of the fibre. The modification of okra bast fibre with acrylonitrile was carried out at varying initiator concentration, catalyst concentration, modification time, modification temperature.
> FTIR was employed to assess the relation between structure and properties after modification.
> SEM was used to observe the microstructure and the surface morphology of treated and untreated okra bast fibre.
> The bleached and modified okra bast fibres have been dyed with Direct Red 28 and Direct Green 27 in presence of sodium sulphate as an electrolyte. Electrolyte is used for obtaining better hue and level dyeing.
> The colour strength and CIE lab values of dyed samples are measured in Macbeth CE-3100 spectrophotometer.
> The colour fastness undyed and dyed (bleached and modified) okra bast fibre have been studied on the exposure to sunlight, wishing, acid spotting, alkali spotting and heat.
> The effect of various influences such as heat and light on tensile strength of bleached and modified okra bast fibre and their dyed fibre has been studied.
Moisture Absorption, Desorption and Swelling
Moisture Absorption, Desorption and Swelling
Moisture sorption is a physicochemical phenomenon. The hydroxyl groups of the carbohydrate fraction attract water molecules and attachment occurs due to hydrogen bonding. In a bone-dry fiber, water molecules can diffuse in to form such bonds ini-tially. Late-arriving molecules can attach themselves either to existing water molecules (indirect attachment) or to the other hydroxyl groups (direct attachment). Diffusion of water molecules does not take place in the crystalline regions of native cellulose in the fiber because of the relatively tight packing of the molecules therein. Thus, absorp¬tion of water is proportional to the extent of the fiber’s noncrystalline, less-oriented regions. Since hemicelluloses and polyuronides are not crystalline, their presence in the fiber will increase its regain. On the other hand, the presence of lignin decreases moisture absorption, since lignin is hydrophobic. In addition, layers of lignin in the inner middle lamella and close to the fiber surface will hinder penetration of moisture into the cellulosic cell wall.
According to Lewin, the small affinity of the lignin for moisture was, according to these investigators in accordance with the small changes in swelling behavior of the jute fiber after a considerable part of the lignin was removed. This is also the obvious explanation of the high moisture absorption in flax in spite of its well known high degree of crystallinity. If it is assumed that the regain of nonlignin middle lamella components in jute and flax is similar, it follows that, in the light of the much lower lignin content of flax, a higher regain should be expected for flax than jute. The lower crystallinity of a-cellulose in jute explains this discrepancy. It should be pointed out that the information on the contribution of the middle lamella and its constituents toward moisture absorption in bast and leaf fibers, other than flax and jute, is very scarce and limited.
Conventionally, the moisture sorption characteristics of fibers are depicted by ab-sorption/desorption isotherms. In practice, it is difficult to compare isotherms of dif-ferent fibers over the whole range of rh (relative humidity) and temperature values. It is often sufficient to compare their regains at the standard conditions of 65% rh and 21 °C (70°F). List gives absorption regains for a few fibers, together with the differences between absorption and desorption regains.
Fiber Absorption regain (%)
At 65% rh 700 F Difference between
desorption and absorption regains 65% rh 700 F
Abaca 9.5 --
Sisal 11.0 --
Cotton 7-8 0.9
Hemp 8 --
Jute 12 1.5
Kapok 10 --
Ramie (bleached) 6 --
Wool (scoured) 14 20
Coir 10 --
Banana 15.2 --
Okra Bast Fiber 9 1.2
Moisture sorption is a physicochemical phenomenon. The hydroxyl groups of the carbohydrate fraction attract water molecules and attachment occurs due to hydrogen bonding. In a bone-dry fiber, water molecules can diffuse in to form such bonds ini-tially. Late-arriving molecules can attach themselves either to existing water molecules (indirect attachment) or to the other hydroxyl groups (direct attachment). Diffusion of water molecules does not take place in the crystalline regions of native cellulose in the fiber because of the relatively tight packing of the molecules therein. Thus, absorp¬tion of water is proportional to the extent of the fiber’s noncrystalline, less-oriented regions. Since hemicelluloses and polyuronides are not crystalline, their presence in the fiber will increase its regain. On the other hand, the presence of lignin decreases moisture absorption, since lignin is hydrophobic. In addition, layers of lignin in the inner middle lamella and close to the fiber surface will hinder penetration of moisture into the cellulosic cell wall.
According to Lewin, the small affinity of the lignin for moisture was, according to these investigators in accordance with the small changes in swelling behavior of the jute fiber after a considerable part of the lignin was removed. This is also the obvious explanation of the high moisture absorption in flax in spite of its well known high degree of crystallinity. If it is assumed that the regain of nonlignin middle lamella components in jute and flax is similar, it follows that, in the light of the much lower lignin content of flax, a higher regain should be expected for flax than jute. The lower crystallinity of a-cellulose in jute explains this discrepancy. It should be pointed out that the information on the contribution of the middle lamella and its constituents toward moisture absorption in bast and leaf fibers, other than flax and jute, is very scarce and limited.
Conventionally, the moisture sorption characteristics of fibers are depicted by ab-sorption/desorption isotherms. In practice, it is difficult to compare isotherms of dif-ferent fibers over the whole range of rh (relative humidity) and temperature values. It is often sufficient to compare their regains at the standard conditions of 65% rh and 21 °C (70°F). List gives absorption regains for a few fibers, together with the differences between absorption and desorption regains.
Fiber Absorption regain (%)
At 65% rh 700 F Difference between
desorption and absorption regains 65% rh 700 F
Abaca 9.5 --
Sisal 11.0 --
Cotton 7-8 0.9
Hemp 8 --
Jute 12 1.5
Kapok 10 --
Ramie (bleached) 6 --
Wool (scoured) 14 20
Coir 10 --
Banana 15.2 --
Okra Bast Fiber 9 1.2
Auto-oxidation mechanism
Auto-oxidation mechanism
Degradation of polymers by chemical reactions is a typical consecutive property and chemical changes occur due to reaction with components in the environment. The most important of these degrading reagents is oxygen. Oxidation may be induced and accelerated by radiation (photo-oxidation) or by thermal energy (thermal oxidation). Thermal oxidation, like photo-oxidation is caused by auto-oxidation. In photochemical degradation the energy of activation is supplied by sunlight. In the most ordinary chemical reactions, the activation energy changes between 60 to 270 KJ/mol ranges. This is energetically equivalent to radiation of wavelengths between 1900 and 440 nm. Above room temperature, polymers degrade in air after an induction period by thermal aging.
Oxidation phenomenon of polymers was investigated very early in connection with the aging of natural rubber. Hofmann realized the connection between aging and the absorption of oxygen. Based on the fact that hydrocarbon compounds react with molecular oxygen forming oxidation products, the auto-oxidation developed by a free-radical chain reaction. Boland and Gee showed that the oxidation of hydrocarbons proceeds autocatalytically. The reaction is slow at the start, generally associated with shorter induction period. In this period, the polymer does not show any obvious changes and there is no evidence of oxygen absorption.
This period is nevertheless important in the process of polymer oxidation, because small amounts of hydroperoxides are formed which initiate the subsequent rapid auto-oxidation of the polymer. As a rule an increase in temperature reduces the induction period and accelerates the auto-oxidation. In some cases, when the polymer contains trace amounts of peroxide impurities or catalysts such as metallic salts, the induction period is not observed at all and the process of catalytic oxidation begins immediately. The decomposition of the hydroperoxides is commonly recognized as the process for the further rapid oxidation. The free-radical initiated chain reaction of auto-oxidation is depicted schematically in Figure . The radical processes during the thermal or photo-degradation of polypropylenes are identical. The basic oxidation mechanism has generally been believed to consist of the following three steps:
(i) Initiation:
RH > R.
(ii) PropagatioO2n:
R. + O2 > ROO.
(Peroxy radical)
This reaction is very fast and quickly converted into-
ROO. + RH > R. + ROOH
ROOH is very important species (unstable) which is responsible for degradation.
Chain branching:
ROOH > RO. + .OH
Termination:
2ROO. > ROOR + O2
Degradation of polymers by chemical reactions is a typical consecutive property and chemical changes occur due to reaction with components in the environment. The most important of these degrading reagents is oxygen. Oxidation may be induced and accelerated by radiation (photo-oxidation) or by thermal energy (thermal oxidation). Thermal oxidation, like photo-oxidation is caused by auto-oxidation. In photochemical degradation the energy of activation is supplied by sunlight. In the most ordinary chemical reactions, the activation energy changes between 60 to 270 KJ/mol ranges. This is energetically equivalent to radiation of wavelengths between 1900 and 440 nm. Above room temperature, polymers degrade in air after an induction period by thermal aging.
Oxidation phenomenon of polymers was investigated very early in connection with the aging of natural rubber. Hofmann realized the connection between aging and the absorption of oxygen. Based on the fact that hydrocarbon compounds react with molecular oxygen forming oxidation products, the auto-oxidation developed by a free-radical chain reaction. Boland and Gee showed that the oxidation of hydrocarbons proceeds autocatalytically. The reaction is slow at the start, generally associated with shorter induction period. In this period, the polymer does not show any obvious changes and there is no evidence of oxygen absorption.
This period is nevertheless important in the process of polymer oxidation, because small amounts of hydroperoxides are formed which initiate the subsequent rapid auto-oxidation of the polymer. As a rule an increase in temperature reduces the induction period and accelerates the auto-oxidation. In some cases, when the polymer contains trace amounts of peroxide impurities or catalysts such as metallic salts, the induction period is not observed at all and the process of catalytic oxidation begins immediately. The decomposition of the hydroperoxides is commonly recognized as the process for the further rapid oxidation. The free-radical initiated chain reaction of auto-oxidation is depicted schematically in Figure . The radical processes during the thermal or photo-degradation of polypropylenes are identical. The basic oxidation mechanism has generally been believed to consist of the following three steps:
(i) Initiation:
RH > R.
(ii) PropagatioO2n:
R. + O2 > ROO.
(Peroxy radical)
This reaction is very fast and quickly converted into-
ROO. + RH > R. + ROOH
ROOH is very important species (unstable) which is responsible for degradation.
Chain branching:
ROOH > RO. + .OH
Termination:
2ROO. > ROOR + O2
Degradation and Degrading Agents
DEGRADATION OF TEXTILE FIBRE
Concept of degradation
Polymer degradation involving light and heat is defined as a combination of chemical and physical changes occurring during the processing, storage and usage. This results in the loss of some useful properties of the polymeric material. These changes are mainly due to the competing chemical processes of macromolecular degradation and cross-linking. Polymer degradation and cross-linking involve a variety of conjugated chain-radical, ionic and molecular reactions.
The degradation reaction is broadly of two types: (1) Chain-end degradation and (2) random degradation. In the first type, the degradation starts from the chain-ends, resulting in a successive release of the monomeric units. This type of degradation is also called depolymerization (unzipping), the reverse of the propagation step in chain polymerization. The second type of degradation occurs at any random point along the polymer chain is called random degradation (zipping) which is the reverse of the polycondensation process. A distinguishing characteristic between the two types of degradation is that generally in the random process the molecular weight falls rapidly but considerably more slowly than in depolymerization.
Degrading agents
Types of degradation in the presence of various influences
Degrading Agents Types of degradation
1.Light (UV, visible) 1. Photochemical degradation
2. X-ray, gama-ray, fast electrous etc. 2. High energy radiation induced
degradation.
3. Laser light 3. Ablative photo degradation
4. Electrical field 4. Electrical Aging.
5. Plasma 5. corrosive degradation, etching.
6. Microorganism 6. Bio degradation.
7. Enzymes 7. Bio crosion.
8. Stress forces 8. Mechanical degradation
9. Ultra sound 9. Ultrasonic degradation
10. Chemicals (Acid, base etc.) 10. Chemical degradation
11. Heat 11. Thermal degradation and/or
decomposition
12. Oxygen, Ozone 12. Oxidative degradation (oxidation),
ozonolysis
13. Heat and oxygen 13. Thermoxidative degradation and/or
decomposition combustion
14. Light and O2 14. Photo oxidation
Concept of degradation
Polymer degradation involving light and heat is defined as a combination of chemical and physical changes occurring during the processing, storage and usage. This results in the loss of some useful properties of the polymeric material. These changes are mainly due to the competing chemical processes of macromolecular degradation and cross-linking. Polymer degradation and cross-linking involve a variety of conjugated chain-radical, ionic and molecular reactions.
The degradation reaction is broadly of two types: (1) Chain-end degradation and (2) random degradation. In the first type, the degradation starts from the chain-ends, resulting in a successive release of the monomeric units. This type of degradation is also called depolymerization (unzipping), the reverse of the propagation step in chain polymerization. The second type of degradation occurs at any random point along the polymer chain is called random degradation (zipping) which is the reverse of the polycondensation process. A distinguishing characteristic between the two types of degradation is that generally in the random process the molecular weight falls rapidly but considerably more slowly than in depolymerization.
Degrading agents
Types of degradation in the presence of various influences
Degrading Agents Types of degradation
1.Light (UV, visible) 1. Photochemical degradation
2. X-ray, gama-ray, fast electrous etc. 2. High energy radiation induced
degradation.
3. Laser light 3. Ablative photo degradation
4. Electrical field 4. Electrical Aging.
5. Plasma 5. corrosive degradation, etching.
6. Microorganism 6. Bio degradation.
7. Enzymes 7. Bio crosion.
8. Stress forces 8. Mechanical degradation
9. Ultra sound 9. Ultrasonic degradation
10. Chemicals (Acid, base etc.) 10. Chemical degradation
11. Heat 11. Thermal degradation and/or
decomposition
12. Oxygen, Ozone 12. Oxidative degradation (oxidation),
ozonolysis
13. Heat and oxygen 13. Thermoxidative degradation and/or
decomposition combustion
14. Light and O2 14. Photo oxidation
General Theory of Dyeing
The General Theory of Dyeing
Dyeing is the process of coloring textile materials by immersing them in an aqueous solution of dye, called dye liquor. Normally the dye liquor consists of dye, water and an auxiliary. To improve the effectiveness of dyeing, heat is usually applied to the dye liquor. The theory of aqueous dyeing, as explained below, is modified when an organic solvent is substituted for water. The general theory of dyeing explains the interaction between dyes, fiber, water and dye auxiliary. More specifically, it explains:
Forces of repulsion which are developed between the dye molecules and water. Forces of attraction which are development between the dye molecules and fibers.
These forces are responsible for the dye molecules leaving the aqueous dye liquor and entering and attaching themselves to the polymers of the fiber.
Dye molecules are organic molecules which can be classified according to the causing part of the color are listed bellow:
i) Anionic: In which the color is caused by the anionic part of the dye molecule.
ii) Cationic: In which the color is caused by the cationic part of the dye molecule.
iii) Disperse: In which the color is caused by the whole molecule.
Dyeing is the process of coloring textile materials by immersing them in an aqueous solution of dye, called dye liquor. Normally the dye liquor consists of dye, water and an auxiliary. To improve the effectiveness of dyeing, heat is usually applied to the dye liquor. The theory of aqueous dyeing, as explained below, is modified when an organic solvent is substituted for water. The general theory of dyeing explains the interaction between dyes, fiber, water and dye auxiliary. More specifically, it explains:
Forces of repulsion which are developed between the dye molecules and water. Forces of attraction which are development between the dye molecules and fibers.
These forces are responsible for the dye molecules leaving the aqueous dye liquor and entering and attaching themselves to the polymers of the fiber.
Dye molecules are organic molecules which can be classified according to the causing part of the color are listed bellow:
i) Anionic: In which the color is caused by the anionic part of the dye molecule.
ii) Cationic: In which the color is caused by the cationic part of the dye molecule.
iii) Disperse: In which the color is caused by the whole molecule.
Why Okra Bast Fiber is Dyed
Why a (Okra Bast Fiber) textile fiber is dyed
A textile material is dyed generally in order to enhance its appearance by the attraction of hue. Textiles may also be dyed for other special purposes, not necessarily involving attractive hues, e.g. camouflage, identification etc. The color is expected to withstand those agencies (exposure to light, weather, moisture, washing etc) which is likely to meet in use to a reasonable degree. In other words, dyeing are expected to be fast to a dyed textiles is that the hue should be uniform over the whole. The satisfactory achievement of these three attributes correct hue, satisfactory fastness and uniformity of hue comprises the art of dyeing.
A textile material is dyed generally in order to enhance its appearance by the attraction of hue. Textiles may also be dyed for other special purposes, not necessarily involving attractive hues, e.g. camouflage, identification etc. The color is expected to withstand those agencies (exposure to light, weather, moisture, washing etc) which is likely to meet in use to a reasonable degree. In other words, dyeing are expected to be fast to a dyed textiles is that the hue should be uniform over the whole. The satisfactory achievement of these three attributes correct hue, satisfactory fastness and uniformity of hue comprises the art of dyeing.
Colour and Vision
Color and vision
The ordinary light is composed of electromagnetic radiation of varying wavelength. On the basis of wavelength of light, the electromagnetic radiation can be divided into three types which are as follows:
Range of wave length of light (˚A) Part of time
1000 – 4000 Ultraviolet
4000 – 7500 Visible part (White light)
7500 – 1000000 Infra – red
Since our eyes are sensitive only to the electromagnetic radiation of wavelengths 4000 – 7500 ˚A., it is this region which produces a definite color in a particular substance. The UV radiation (wave length more than 7500 A) are not visible to human eyes.
When white light falls on a substance the color is obtained in different ways as:
• When the white light is reflected completely the substance will appear white.
• When the white light is absorbed completely the substance will appear black.
• When all the wavelengths of white light is absorbed except one single narrow bond which is reflected. Then the color of the substance will correspond to the color of the reflected band of light.
• When only a single bond of white light is absorbed the substance will have the complimentary color of the absorbed band of the light e.g. If the color absorbed lies in the range 4000 – 4350˚A. Then the color absorbed is violet and so the complementary color obtained will be yellow green.
The ordinary light is composed of electromagnetic radiation of varying wavelength. On the basis of wavelength of light, the electromagnetic radiation can be divided into three types which are as follows:
Range of wave length of light (˚A) Part of time
1000 – 4000 Ultraviolet
4000 – 7500 Visible part (White light)
7500 – 1000000 Infra – red
Since our eyes are sensitive only to the electromagnetic radiation of wavelengths 4000 – 7500 ˚A., it is this region which produces a definite color in a particular substance. The UV radiation (wave length more than 7500 A) are not visible to human eyes.
When white light falls on a substance the color is obtained in different ways as:
• When the white light is reflected completely the substance will appear white.
• When the white light is absorbed completely the substance will appear black.
• When all the wavelengths of white light is absorbed except one single narrow bond which is reflected. Then the color of the substance will correspond to the color of the reflected band of light.
• When only a single bond of white light is absorbed the substance will have the complimentary color of the absorbed band of the light e.g. If the color absorbed lies in the range 4000 – 4350˚A. Then the color absorbed is violet and so the complementary color obtained will be yellow green.
Requirements of True Dye
Requirements of True Dye
For a substance to act as a dye certain conditions must be fulfilled and these are as follows.
• It must have a suitable color
• It must have an attractive color
• It must be able to fix itself or be capable of being fixed to the fabric
• The substrate to be dyed must have affinity for an appropriate dye and must be able to absorb it from solution or aqueous dispersion, if necessary in the presence of auxiliary substances under suitable conditions of concentration, temperature and pH
• It must be soluble in water or must form a stable and good dispersion in water. Alternatively, it must be soluble in the medium other than water. However, it is to be remembered that the pick up of the dye from the medium should be good.
The fixed dye must have fastness properties, e.g.,
• Fastness to light,
• Fastness to temperature,
• Resistance to the action of water, dilute acids, alkalis and various organic solvents and soap solution.
For a substance to act as a dye certain conditions must be fulfilled and these are as follows.
• It must have a suitable color
• It must have an attractive color
• It must be able to fix itself or be capable of being fixed to the fabric
• The substrate to be dyed must have affinity for an appropriate dye and must be able to absorb it from solution or aqueous dispersion, if necessary in the presence of auxiliary substances under suitable conditions of concentration, temperature and pH
• It must be soluble in water or must form a stable and good dispersion in water. Alternatively, it must be soluble in the medium other than water. However, it is to be remembered that the pick up of the dye from the medium should be good.
The fixed dye must have fastness properties, e.g.,
• Fastness to light,
• Fastness to temperature,
• Resistance to the action of water, dilute acids, alkalis and various organic solvents and soap solution.
Dyeing and Dyes
Dyeing
The most important view of dyeing is for colouring textile material. Other than textiles there are other materials that are coloured by dyeing viz. paper products, leather products, cosmetics, foods etc. The dyeing usually is done to make the product attractive. Dyeing of textile materials is a process of applying a dye so that the materials not only change their color but also lastly retain the dye. The process that results in the materials acquiring one color is called plain dyeing or simply dyeing; the application of color to the material at separate places or of several colors forming a design is called pattern printing. The subject of dyeing includes two objects: the dyestuffs and the fiber and relation between them at certain conditions.
Dyes
Generally, a dye may be defined as a color substance which when applied to the fabrics a permanent color and the color is not usually removed by washing with water, soap or no exposure to sunlight. In other words, compounds containing charomophore and auxochrome groups are called dyes. Chromophore group is responsible for dye colour due to their unsaturation or multiple bonds e.g. --NO2, – N=O, --N = N--, quinonoid structure, >C = O etc.
Auxochrome group is responsible for dye fiber reaction e.g –OH, COOH, SO3H, –NH2, Cl- etc.
All colored substances are not necessarily dyes. For example, though both picric acid and trinitrotoluene are yellow in color but only picric acid can fix to a cloth where trinitrotoluene does no fix to a cloth and so it is not a dye.
Direct dyes
The characteristic features of direct dyes are:
(1) The shapes are long, narrow and flat
(2) The constitutive groups are -OH, -NH2 , -N=N– which may form hydrogen bond with --OH groups of the cellulosic chain and
(3) Two or more ion forming groups usually SO3Na which help the dissolution of dyes in water.
Direct dyes are used to dye animal fibers as well as cotton or the vegetable fibers without mordant directly. Some of them are also employed for dyeing union goods (cotton and wool or cotton and silk). These dyes are also called salt dyes, because of the fact that dyeing is usually carried out in presence of common salt or Glauber’s salt to the dye bath. The dye is applied to the fabric by immersing the fabric in hot boiling solution and then removing and drying the fiber. Addition of common salt increases the solubility of the dye and hence cause better exhaustion of it forms the dyeing solution.
The most important view of dyeing is for colouring textile material. Other than textiles there are other materials that are coloured by dyeing viz. paper products, leather products, cosmetics, foods etc. The dyeing usually is done to make the product attractive. Dyeing of textile materials is a process of applying a dye so that the materials not only change their color but also lastly retain the dye. The process that results in the materials acquiring one color is called plain dyeing or simply dyeing; the application of color to the material at separate places or of several colors forming a design is called pattern printing. The subject of dyeing includes two objects: the dyestuffs and the fiber and relation between them at certain conditions.
Dyes
Generally, a dye may be defined as a color substance which when applied to the fabrics a permanent color and the color is not usually removed by washing with water, soap or no exposure to sunlight. In other words, compounds containing charomophore and auxochrome groups are called dyes. Chromophore group is responsible for dye colour due to their unsaturation or multiple bonds e.g. --NO2, – N=O, --N = N--, quinonoid structure, >C = O etc.
Auxochrome group is responsible for dye fiber reaction e.g –OH, COOH, SO3H, –NH2, Cl- etc.
All colored substances are not necessarily dyes. For example, though both picric acid and trinitrotoluene are yellow in color but only picric acid can fix to a cloth where trinitrotoluene does no fix to a cloth and so it is not a dye.
Direct dyes
The characteristic features of direct dyes are:
(1) The shapes are long, narrow and flat
(2) The constitutive groups are -OH, -NH2 , -N=N– which may form hydrogen bond with --OH groups of the cellulosic chain and
(3) Two or more ion forming groups usually SO3Na which help the dissolution of dyes in water.
Direct dyes are used to dye animal fibers as well as cotton or the vegetable fibers without mordant directly. Some of them are also employed for dyeing union goods (cotton and wool or cotton and silk). These dyes are also called salt dyes, because of the fact that dyeing is usually carried out in presence of common salt or Glauber’s salt to the dye bath. The dye is applied to the fabric by immersing the fabric in hot boiling solution and then removing and drying the fiber. Addition of common salt increases the solubility of the dye and hence cause better exhaustion of it forms the dyeing solution.
Monomer, Initiator and Catalyst
MONOMER
Low molecular weight compounds having a functionality of two or more from which polymers are formed are called monomers. To polymerise them, it only renders a suitable reaction conditions. Then, these monomer molecules add each other to form fewer but higher molecular weight compound.
The functionality of a monomer depends on the number of reactive sites it has. A compound assumes functionality because of the presence of reactive functional groups like -OH, -COOH, - NH2 etc. The number of functional groups per molecule of the compound defines its functionality.
Some compounds which do not contain any reactive functional group but the presence of double or triple bonds in molecule bestows poly-functionality on them are called vinyl monomers. For example, ethylene which can take on two atoms of hydrogen, because of the presence of a double bond and hence, functionality two.
CH2=CH2 + H2 = CH3-CH3
Similar is the ease with other homologous of ethylene and vinyl compounds such as methacrylic acid [H2C=C(CH3)COOH], acrylamide [H2C=CH-CONll2], methyl methacrylate [H2C=C(CH3)COOCH3], methyl acrylate [H2C=CHCOOCH3], acrylonitrile [CH2=CH-CN], etc. Acetylene has a functionality of four i.e. [HC CH].
There are some other compounds in which the presence of easily replaceable hydrogen atoms contributes functionality. Phenol is an example of such type.
INITIATIOR
The initiation reaction of polymerisation is carried out by initiators. Initiators are thermally unstable compounds and decompose into products called free radicals. These free radicals can attack monomers and initiate the polymerisation reaction.
If R- R is an initiator and the pair of electrons forming the bond between two ‘R’ can be represented by dots, the initiator can be written as R:R. Initiators are decomposed by homolytic dissociation and are splited into two symmetrical components. Each component carries with it one of the electrons from the electron pair, is called free-radieal, i.e. R – R 2R•. The decomposition of the initiator to form free radicals can be introduced by heat energy, light, catalyst etc. Potassium persulphate (K2S2O8), azo compounds, peroxides, hydroxides, peracids and peresters are useful initiators.
CATALYST
The catalyst may be responsible for peculiar chain initiation and possess a metal atom with some + ionic character. The reason for their presence varies from reaction to reaction. For instance, in the vinyl type reactions, the catalysis are required to produce initiating centres. Many metallic salts such as FeSO4, FeCl3, Fe2(SO4)3, CuSO4, ZnSO4, K2SO4, CoSO4 , H2SO4 etc. are used as catalyst for graft copolymerisation of cellulosic materials.
Low molecular weight compounds having a functionality of two or more from which polymers are formed are called monomers. To polymerise them, it only renders a suitable reaction conditions. Then, these monomer molecules add each other to form fewer but higher molecular weight compound.
The functionality of a monomer depends on the number of reactive sites it has. A compound assumes functionality because of the presence of reactive functional groups like -OH, -COOH, - NH2 etc. The number of functional groups per molecule of the compound defines its functionality.
Some compounds which do not contain any reactive functional group but the presence of double or triple bonds in molecule bestows poly-functionality on them are called vinyl monomers. For example, ethylene which can take on two atoms of hydrogen, because of the presence of a double bond and hence, functionality two.
CH2=CH2 + H2 = CH3-CH3
Similar is the ease with other homologous of ethylene and vinyl compounds such as methacrylic acid [H2C=C(CH3)COOH], acrylamide [H2C=CH-CONll2], methyl methacrylate [H2C=C(CH3)COOCH3], methyl acrylate [H2C=CHCOOCH3], acrylonitrile [CH2=CH-CN], etc. Acetylene has a functionality of four i.e. [HC CH].
There are some other compounds in which the presence of easily replaceable hydrogen atoms contributes functionality. Phenol is an example of such type.
INITIATIOR
The initiation reaction of polymerisation is carried out by initiators. Initiators are thermally unstable compounds and decompose into products called free radicals. These free radicals can attack monomers and initiate the polymerisation reaction.
If R- R is an initiator and the pair of electrons forming the bond between two ‘R’ can be represented by dots, the initiator can be written as R:R. Initiators are decomposed by homolytic dissociation and are splited into two symmetrical components. Each component carries with it one of the electrons from the electron pair, is called free-radieal, i.e. R – R 2R•. The decomposition of the initiator to form free radicals can be introduced by heat energy, light, catalyst etc. Potassium persulphate (K2S2O8), azo compounds, peroxides, hydroxides, peracids and peresters are useful initiators.
CATALYST
The catalyst may be responsible for peculiar chain initiation and possess a metal atom with some + ionic character. The reason for their presence varies from reaction to reaction. For instance, in the vinyl type reactions, the catalysis are required to produce initiating centres. Many metallic salts such as FeSO4, FeCl3, Fe2(SO4)3, CuSO4, ZnSO4, K2SO4, CoSO4 , H2SO4 etc. are used as catalyst for graft copolymerisation of cellulosic materials.
Grafting Sites on the Cellulose and Mechanism for Okra Bast Fiber
GRAFTING SITES ON THE CELLULOSE AND MECHANISM
Okra bast basically is a cellulosic fibre. The structural unit of cellulose is C6H10O5 or anhydroglucose unit. In the presence of monomer, chain radicals such as (I), (II) and (III) load to graft copolymers, whereas (IV), (V) will give rise to block copolymers.
Actually both types of reactions are found to take place. In addition there will be radicals formed by radiolysis of the monomer and if there is a solvent present by radiolysis of the solvent, these monomer and solvent radicals lead to formation of homopolymer.
Cellulose is not simply possible to modified the properties owing to the fact that the cellulose chains become part of a three dimensions network, the material becomes harder and more rigid.
Grafting onto cellulose is therefore of necessity a heterogeneous reaction in which the physical structures and states of aggregation of the cellulose plays a significant role. The synthesis of cellulose graft copolymer differs from the fully synthetic graft copolymer by the fact that cellulose insoluble in all common organic solvents. Okra bast cellulose is a naturally occurring polymer which is not simply possible to modify in its properties. However, since the greatest number of synthesis involved heterogeneous grafting reactions these will form the first and most important part of the discussion of grafting methods. The polymerization of vinyl monomers may be initiated by free radicals or by certain ions. Free radicals can be generated on a cellulose chain by hydrogen abstraction oxidation, ceric-ion method, diazotisation and introduction of unsaturated groups or by irradiation. If a vinyl monomer is polymerized in the presence of cellulose by a free radical process, a hydrogen atom may be abstracted from the cellulose by growing chain radical or by a radical formed by the polymerization catalyst. This leads to an unshared electron on the cellulosic chain is capable of grafting.
It should be pointed out here that cellulose is a very poor transfer agent (1) and that very little graft copolymer results from the abstraction of hydrogen atoms by a growing chain radical. In most cases it is not the growing chain radical but a radical produced by the initiator which is responsible for formation of graft copolymer.
Thus in case of redox initiation with potassium persulphate (K2S2O8) and ferrous sulphate (FeSO4), •OH free radicals are generated which abstracts a hydrogen atom from the cellulose and thereby leads to grafting.
1 i) K2 S2O8 = 2K+ + S2 O8=
ii) FeSO4 = Fe++ + SO4=
2 i) S2 O8= + Fe (II) Adduct
ii) Adduct Fe (III) + 2SO4-
3 i) Fe (III) + H2O Fe (II) + + H+ HO.
ii) SO4- + H2O SO=4 + + H+
Okra bast basically is a cellulosic fibre. The structural unit of cellulose is C6H10O5 or anhydroglucose unit. In the presence of monomer, chain radicals such as (I), (II) and (III) load to graft copolymers, whereas (IV), (V) will give rise to block copolymers.
Actually both types of reactions are found to take place. In addition there will be radicals formed by radiolysis of the monomer and if there is a solvent present by radiolysis of the solvent, these monomer and solvent radicals lead to formation of homopolymer.
Cellulose is not simply possible to modified the properties owing to the fact that the cellulose chains become part of a three dimensions network, the material becomes harder and more rigid.
Grafting onto cellulose is therefore of necessity a heterogeneous reaction in which the physical structures and states of aggregation of the cellulose plays a significant role. The synthesis of cellulose graft copolymer differs from the fully synthetic graft copolymer by the fact that cellulose insoluble in all common organic solvents. Okra bast cellulose is a naturally occurring polymer which is not simply possible to modify in its properties. However, since the greatest number of synthesis involved heterogeneous grafting reactions these will form the first and most important part of the discussion of grafting methods. The polymerization of vinyl monomers may be initiated by free radicals or by certain ions. Free radicals can be generated on a cellulose chain by hydrogen abstraction oxidation, ceric-ion method, diazotisation and introduction of unsaturated groups or by irradiation. If a vinyl monomer is polymerized in the presence of cellulose by a free radical process, a hydrogen atom may be abstracted from the cellulose by growing chain radical or by a radical formed by the polymerization catalyst. This leads to an unshared electron on the cellulosic chain is capable of grafting.
It should be pointed out here that cellulose is a very poor transfer agent (1) and that very little graft copolymer results from the abstraction of hydrogen atoms by a growing chain radical. In most cases it is not the growing chain radical but a radical produced by the initiator which is responsible for formation of graft copolymer.
Thus in case of redox initiation with potassium persulphate (K2S2O8) and ferrous sulphate (FeSO4), •OH free radicals are generated which abstracts a hydrogen atom from the cellulose and thereby leads to grafting.
1 i) K2 S2O8 = 2K+ + S2 O8=
ii) FeSO4 = Fe++ + SO4=
2 i) S2 O8= + Fe (II) Adduct
ii) Adduct Fe (III) + 2SO4-
3 i) Fe (III) + H2O Fe (II) + + H+ HO.
ii) SO4- + H2O SO=4 + + H+
Polymer, Homopolymer, Copolymer and Graft Copolymer
POLYMER, HOMOPOLYMER, COPOLYMER AND GRAFT COPOLYMER
Polymer
A polymer is large molecule formed by repeating linking of small molecules called monomers. For example, polyethylene is a polymer formed by repeating linking of ethylene molecules. Thus:
nCH2 = CH2 [-CH2-CH2-]n
Ethylene (monomer) Polyethylene (polymer)
The number of repeating unit (n) in the chain formed the polymer is known as degree of polymerisation (DP). Polymer with high DP is called high polymers. Molecular weight of polymer may vary from 104 up to several millions.
Homopolymer
A polymer which has a single or same type of repeating unit, may be referred to an homopolymer. The backbone of homopolymer entirely builds up the same repeating units.
M1 - M1 - M1- M1 - M1 - M1 - M1
Copolymer
A polymer which has two different repeating units is called copolymer and the process by which it is synthesised is referred to as copolymerisation.
---------M1 – M2 ¬– M1¬ – M2 – M1 – M2– M1 – M2 – M1 – M2 – M1---------
Graft Copolymer
Graft copolyerisation results from the formation of an active site at a point on a polymer molecule other than its end, exposure to second monomer. Most graft copolymers are formed by radical polymerisation. The major active reaction is chain transfer to polymer. In many instances the transfer reaction involves subtraction of a hydrogen atom. Ultraviolet or ionising radiation or redox initiation among other methods can also use to produce polymer radicals leading to graft copolymer. A graft copolymer is a branched copolymer with a backbone of a linear or homopolymer.
------M1 – M1 ¬– M1¬ – M1 – M1 – M1– M1 – M1 – M1 – M1 – M1------
POLYMER, HOMOPOLYMER, COPOLYMER AND GRAFT COPOLYMER
Polymer
A polymer is large molecule formed by repeating linking of small molecules called monomers. For example, polyethylene is a polymer formed by repeating linking of ethylene molecules. Thus:
nCH2 = CH2 [-CH2-CH2-]n
Ethylene (monomer) Polyethylene (polymer)
The number of repeating unit (n) in the chain formed the polymer is known as degree of polymerisation (DP). Polymer with high DP is called high polymers. Molecular weight of polymer may vary from 104 up to several millions.
Homopolymer
A polymer which has a single or same type of repeating unit, may be referred to an homopolymer. The backbone of homopolymer entirely builds up the same repeating units.
M1 - M1 - M1- M1 - M1 - M1 - M1
Copolymer
A polymer which has two different repeating units is called copolymer and the process by which it is synthesised is referred to as copolymerisation.
---------M1 – M2 ¬– M1¬ – M2 – M1 – M2– M1 – M2 – M1 – M2 – M1---------
Graft Copolymer
Graft copolyerisation results from the formation of an active site at a point on a polymer molecule other than its end, exposure to second monomer. Most graft copolymers are formed by radical polymerisation. The major active reaction is chain transfer to polymer. In many instances the transfer reaction involves subtraction of a hydrogen atom. Ultraviolet or ionising radiation or redox initiation among other methods can also use to produce polymer radicals leading to graft copolymer. A graft copolymer is a branched copolymer with a backbone of a linear or homopolymer.
------M1 – M1 ¬– M1¬ – M1 – M1 – M1– M1 – M1 – M1 – M1 – M1------
POLYMER, HOMOPOLYMER, COPOLYMER AND GRAFT COPOLYMER
Polymer
A polymer is large molecule formed by repeating linking of small molecules called monomers. For example, polyethylene is a polymer formed by repeating linking of ethylene molecules. Thus:
nCH2 = CH2 [-CH2-CH2-]n
Ethylene (monomer) Polyethylene (polymer)
The number of repeating unit (n) in the chain formed the polymer is known as degree of polymerisation (DP). Polymer with high DP is called high polymers. Molecular weight of polymer may vary from 104 up to several millions.
Homopolymer
A polymer which has a single or same type of repeating unit, may be referred to an homopolymer. The backbone of homopolymer entirely builds up the same repeating units.
M1 - M1 - M1- M1 - M1 - M1 - M1
Copolymer
A polymer which has two different repeating units is called copolymer and the process by which it is synthesised is referred to as copolymerisation.
---------M1 – M2 ¬– M1¬ – M2 – M1 – M2– M1 – M2 – M1 – M2 – M1---------
Graft Copolymer
Graft copolyerisation results from the formation of an active site at a point on a polymer molecule other than its end, exposure to second monomer. Most graft copolymers are formed by radical polymerisation. The major active reaction is chain transfer to polymer. In many instances the transfer reaction involves subtraction of a hydrogen atom. Ultraviolet or ionising radiation or redox initiation among other methods can also use to produce polymer radicals leading to graft copolymer. A graft copolymer is a branched copolymer with a backbone of a linear or homopolymer.
Polymer
A polymer is large molecule formed by repeating linking of small molecules called monomers. For example, polyethylene is a polymer formed by repeating linking of ethylene molecules. Thus:
nCH2 = CH2 [-CH2-CH2-]n
Ethylene (monomer) Polyethylene (polymer)
The number of repeating unit (n) in the chain formed the polymer is known as degree of polymerisation (DP). Polymer with high DP is called high polymers. Molecular weight of polymer may vary from 104 up to several millions.
Homopolymer
A polymer which has a single or same type of repeating unit, may be referred to an homopolymer. The backbone of homopolymer entirely builds up the same repeating units.
M1 - M1 - M1- M1 - M1 - M1 - M1
Copolymer
A polymer which has two different repeating units is called copolymer and the process by which it is synthesised is referred to as copolymerisation.
---------M1 – M2 ¬– M1¬ – M2 – M1 – M2– M1 – M2 – M1 – M2 – M1---------
Graft Copolymer
Graft copolyerisation results from the formation of an active site at a point on a polymer molecule other than its end, exposure to second monomer. Most graft copolymers are formed by radical polymerisation. The major active reaction is chain transfer to polymer. In many instances the transfer reaction involves subtraction of a hydrogen atom. Ultraviolet or ionising radiation or redox initiation among other methods can also use to produce polymer radicals leading to graft copolymer. A graft copolymer is a branched copolymer with a backbone of a linear or homopolymer.
------M1 – M1 ¬– M1¬ – M1 – M1 – M1– M1 – M1 – M1 – M1 – M1------
POLYMER, HOMOPOLYMER, COPOLYMER AND GRAFT COPOLYMER
Polymer
A polymer is large molecule formed by repeating linking of small molecules called monomers. For example, polyethylene is a polymer formed by repeating linking of ethylene molecules. Thus:
nCH2 = CH2 [-CH2-CH2-]n
Ethylene (monomer) Polyethylene (polymer)
The number of repeating unit (n) in the chain formed the polymer is known as degree of polymerisation (DP). Polymer with high DP is called high polymers. Molecular weight of polymer may vary from 104 up to several millions.
Homopolymer
A polymer which has a single or same type of repeating unit, may be referred to an homopolymer. The backbone of homopolymer entirely builds up the same repeating units.
M1 - M1 - M1- M1 - M1 - M1 - M1
Copolymer
A polymer which has two different repeating units is called copolymer and the process by which it is synthesised is referred to as copolymerisation.
---------M1 – M2 ¬– M1¬ – M2 – M1 – M2– M1 – M2 – M1 – M2 – M1---------
Graft Copolymer
Graft copolyerisation results from the formation of an active site at a point on a polymer molecule other than its end, exposure to second monomer. Most graft copolymers are formed by radical polymerisation. The major active reaction is chain transfer to polymer. In many instances the transfer reaction involves subtraction of a hydrogen atom. Ultraviolet or ionising radiation or redox initiation among other methods can also use to produce polymer radicals leading to graft copolymer. A graft copolymer is a branched copolymer with a backbone of a linear or homopolymer.
------M1 – M1 ¬– M1¬ – M1 – M1 – M1– M1 – M1 – M1 – M1 – M1------
POLYMER, HOMOPOLYMER, COPOLYMER AND GRAFT COPOLYMER
Polymer
A polymer is large molecule formed by repeating linking of small molecules called monomers. For example, polyethylene is a polymer formed by repeating linking of ethylene molecules. Thus:
nCH2 = CH2 [-CH2-CH2-]n
Ethylene (monomer) Polyethylene (polymer)
The number of repeating unit (n) in the chain formed the polymer is known as degree of polymerisation (DP). Polymer with high DP is called high polymers. Molecular weight of polymer may vary from 104 up to several millions.
Homopolymer
A polymer which has a single or same type of repeating unit, may be referred to an homopolymer. The backbone of homopolymer entirely builds up the same repeating units.
M1 - M1 - M1- M1 - M1 - M1 - M1
Copolymer
A polymer which has two different repeating units is called copolymer and the process by which it is synthesised is referred to as copolymerisation.
---------M1 – M2 ¬– M1¬ – M2 – M1 – M2– M1 – M2 – M1 – M2 – M1---------
Graft Copolymer
Graft copolyerisation results from the formation of an active site at a point on a polymer molecule other than its end, exposure to second monomer. Most graft copolymers are formed by radical polymerisation. The major active reaction is chain transfer to polymer. In many instances the transfer reaction involves subtraction of a hydrogen atom. Ultraviolet or ionising radiation or redox initiation among other methods can also use to produce polymer radicals leading to graft copolymer. A graft copolymer is a branched copolymer with a backbone of a linear or homopolymer.
Chemical Treatment of Okra Bast Fiber
CHEMICAL Treatment OF OKRA BAST FIBRE
Okra bast fibre is a lignocellulosic fibre, which obtained from okra bast plant that grows everywhere abundantly in Bangladesh. Therefore, okra fiber can play an important role in the field of our national economy in finding various applications. They are generally biodegradable but do not possess the necessary and sufficient properties desirable for engineering or commodity plastics. Besides, like other vegetable fibers, okra fiber possess few weak points i.e., rub resistance, colour fastness, wash and wear properties and very much prone to creasing, possibly because of high degree of orientation of cellulose in the fibre. This defect of creasing of cellulosic fiber may be remedied remarkably by the crease-resisting process in which resins are synthesized within the cellulosic materials in different proportions. In order to improve the textile properties of okra fiber it is an urgent need to improve several properties such as whiteness, softness, washing, dyeing behavior, colour fastness, light resistance, thermal resistance, etc. So an attempt has been made to improve those characteristics of okra bast fibre through chemical modification and dyeing.
The chemical modification means to change the cellulose structure of okra fiber. The chemical structure of cellulose can be changed in three ways:
i) By preparing a derivative, e.g. an ester or ether
ii) By preparing a crosslinked cellulose i.e. a network structure or
iii) By preparing branched cellulose i.e. a graft copolymer of cellulose (grafting process).
The chemical modification of okra bast fibre with acrylonitrile under the influence of catalytic action induces cross-linking of resins on to okra fibre. The sequence of reactions would be expected to take place, ultimately leading to notable weight gain and changes in the chemical nature of fibre.
Okra bast fibre is a lignocellulosic fibre, which obtained from okra bast plant that grows everywhere abundantly in Bangladesh. Therefore, okra fiber can play an important role in the field of our national economy in finding various applications. They are generally biodegradable but do not possess the necessary and sufficient properties desirable for engineering or commodity plastics. Besides, like other vegetable fibers, okra fiber possess few weak points i.e., rub resistance, colour fastness, wash and wear properties and very much prone to creasing, possibly because of high degree of orientation of cellulose in the fibre. This defect of creasing of cellulosic fiber may be remedied remarkably by the crease-resisting process in which resins are synthesized within the cellulosic materials in different proportions. In order to improve the textile properties of okra fiber it is an urgent need to improve several properties such as whiteness, softness, washing, dyeing behavior, colour fastness, light resistance, thermal resistance, etc. So an attempt has been made to improve those characteristics of okra bast fibre through chemical modification and dyeing.
The chemical modification means to change the cellulose structure of okra fiber. The chemical structure of cellulose can be changed in three ways:
i) By preparing a derivative, e.g. an ester or ether
ii) By preparing a crosslinked cellulose i.e. a network structure or
iii) By preparing branched cellulose i.e. a graft copolymer of cellulose (grafting process).
The chemical modification of okra bast fibre with acrylonitrile under the influence of catalytic action induces cross-linking of resins on to okra fibre. The sequence of reactions would be expected to take place, ultimately leading to notable weight gain and changes in the chemical nature of fibre.
Chemistry of Sodium Chlorite Bleaching
Chemistry of Sodium Chlorite Bleaching
Sodium Chlorite ((NaClO2) is known as anhydrous salt. Anhydrous sodium chlorite is a colourless hygroscopic substance. It is stable and when heated sodium chlorite decomposes according to the following reaction:
NaClO2 = NaCl + O2
Sodium chlorite may explode under impact only in the presence of traces of organic substances. It is readily dissolved in water. As an oxidizing agent, sodium chlorite occupies the place somewhere between hypochlorite and chlorite. Thus, for instance, the oxidation-reduction potential of the reaction.
Cl+4O2 + 4H+ + 4e- = Cl0 + 2H2O
In a strong alkaline medium (pH-11) hypochlorite quickly oxidizes to chlorate as
NaClO2 + NaOCl = NaClO3 + NaCl
However, oxidation proceeds only to chlorine dioxide:
2NaClO2 + NaOCl + H2O = ClO2 + NaCl + 2 NaOH
Chlorine reacts with chlorite in the same way
2NaOClO2 + Cl2 = 2 NaCl + 2 ClO2
By simple acidifying of chlorite solution chlorine dioxide is obtained.
5NaClO2 + 4HCl = 2ClO2 + 5 NaCl + 2H2O
Acidic Sodium chlorite bleaching solution have a pH 4.
Hefti gives the following schemes of sodium Chlorite decomposition in an acid medium.
i) 5ClO-2 + 2H+ = 4ClO2 + Cl- + 2OH-
ii) 3ClO-2 = 2 ClO3 + Cl-
iii) ClO2 = Cl + 2O
Sugar oxidation was taken as an example to study the effect of sodium chlorite on fibrous material and particularly on cellulose. The sugar oxidation are shown by the following reaction:
R—CH2OH + 3ClO2 = R—CHO + Cl +2OH
Sodium chlorite oxidation potential is insufficient for breaking the link between the carbon atoms in the chain of the main valencies of cellulose.
Sodium Chlorite ((NaClO2) is known as anhydrous salt. Anhydrous sodium chlorite is a colourless hygroscopic substance. It is stable and when heated sodium chlorite decomposes according to the following reaction:
NaClO2 = NaCl + O2
Sodium chlorite may explode under impact only in the presence of traces of organic substances. It is readily dissolved in water. As an oxidizing agent, sodium chlorite occupies the place somewhere between hypochlorite and chlorite. Thus, for instance, the oxidation-reduction potential of the reaction.
Cl+4O2 + 4H+ + 4e- = Cl0 + 2H2O
In a strong alkaline medium (pH-11) hypochlorite quickly oxidizes to chlorate as
NaClO2 + NaOCl = NaClO3 + NaCl
However, oxidation proceeds only to chlorine dioxide:
2NaClO2 + NaOCl + H2O = ClO2 + NaCl + 2 NaOH
Chlorine reacts with chlorite in the same way
2NaOClO2 + Cl2 = 2 NaCl + 2 ClO2
By simple acidifying of chlorite solution chlorine dioxide is obtained.
5NaClO2 + 4HCl = 2ClO2 + 5 NaCl + 2H2O
Acidic Sodium chlorite bleaching solution have a pH 4.
Hefti gives the following schemes of sodium Chlorite decomposition in an acid medium.
i) 5ClO-2 + 2H+ = 4ClO2 + Cl- + 2OH-
ii) 3ClO-2 = 2 ClO3 + Cl-
iii) ClO2 = Cl + 2O
Sugar oxidation was taken as an example to study the effect of sodium chlorite on fibrous material and particularly on cellulose. The sugar oxidation are shown by the following reaction:
R—CH2OH + 3ClO2 = R—CHO + Cl +2OH
Sodium chlorite oxidation potential is insufficient for breaking the link between the carbon atoms in the chain of the main valencies of cellulose.
Association of Cellulose, Hemicellulose and Lignin in Okra bast Natural Fiber
Association of Cellulose, Hemicellulose and Lignin
There is no conclusive proof with regard to the chemical union of hemicellulose with cellulose in the okra fiber. In case of ligno-cellulosic fiber the opinion is that hemicellulose except xylan can not enter cellulose crystallites due to spacing difficulty. The cellulosans (mainly xylan) associated with the true cellulose in the cellulosic structure, are relatively short chain compounds, and occupy longitudinally the same space as the glucose units in the cellulosic chains. Xylan and cellulose are laid as a mixed crystallite structure probably with an incrusting cement consisting of lignin and hemicellulose.
It was elsewhere reported that a trisaccharide “gruce-xylo-arabinose” was isolated from delignified okra holocellulose supporting some chemical bonding affinity between cellulose and hemicellulose. But physical data from x-ray study do not appear to justify any chemical union between cellulose and hemicellulose.
Regarding the possibility of cellulose-lignin combination, the view is that the lignin cannot enter the cellulose crystallite due to the same spacing difficulties, but a small amount of lignin is intimately associated at the cell wall boundaries of cellulose. Chemical union exists between lignin and hemicellulose and it is the ester type linkage between the alcoholic hydroxyl group of lignin and the carboxyl group of polyuronic acid of hemicellulose appear, and the other type linkage between phenolic hydroxyl group of lignin and hydroxyl group of hemicellulose.
Hemi-COOH+HO-lignin= Hemi-COO-lignin ester linkage
Hemi-OH+HO-lignin= Hemi-O-lignin ether linkage
Thus, the main constituents of okra and other cellulosic fibre, alpha-cellulose, hemicellulose and lignin, are in closest physical association and because of their chemical properties overlap, sharp separation is a matter of extreme difficulty. -Cellulose which is the supreme structural element of the fibre while lignin and hemicellulose are distributed throughout the entire body of the fibre. The major portion of lignin is located in the intercellulose spaces, which in combination with hemicelluloses, serves as a cementing material for the ultimate cell units.
There is no conclusive proof with regard to the chemical union of hemicellulose with cellulose in the okra fiber. In case of ligno-cellulosic fiber the opinion is that hemicellulose except xylan can not enter cellulose crystallites due to spacing difficulty. The cellulosans (mainly xylan) associated with the true cellulose in the cellulosic structure, are relatively short chain compounds, and occupy longitudinally the same space as the glucose units in the cellulosic chains. Xylan and cellulose are laid as a mixed crystallite structure probably with an incrusting cement consisting of lignin and hemicellulose.
It was elsewhere reported that a trisaccharide “gruce-xylo-arabinose” was isolated from delignified okra holocellulose supporting some chemical bonding affinity between cellulose and hemicellulose. But physical data from x-ray study do not appear to justify any chemical union between cellulose and hemicellulose.
Regarding the possibility of cellulose-lignin combination, the view is that the lignin cannot enter the cellulose crystallite due to the same spacing difficulties, but a small amount of lignin is intimately associated at the cell wall boundaries of cellulose. Chemical union exists between lignin and hemicellulose and it is the ester type linkage between the alcoholic hydroxyl group of lignin and the carboxyl group of polyuronic acid of hemicellulose appear, and the other type linkage between phenolic hydroxyl group of lignin and hydroxyl group of hemicellulose.
Hemi-COOH+HO-lignin= Hemi-COO-lignin ester linkage
Hemi-OH+HO-lignin= Hemi-O-lignin ether linkage
Thus, the main constituents of okra and other cellulosic fibre, alpha-cellulose, hemicellulose and lignin, are in closest physical association and because of their chemical properties overlap, sharp separation is a matter of extreme difficulty. -Cellulose which is the supreme structural element of the fibre while lignin and hemicellulose are distributed throughout the entire body of the fibre. The major portion of lignin is located in the intercellulose spaces, which in combination with hemicelluloses, serves as a cementing material for the ultimate cell units.
Cellulose, Hemicellulose and Lignin
Cellulose:
Cellulose is the principal constituent of all plant life. It is a linear polymer of anhydroglucose units linked in 1 and 4 position by a alpha-glucoside links. The empirical formula of cellulose (C6H10O¬5)n corresponds to a polyanhydride of glucose. The two terminal glucose residues of cellulose molecule contain two different end groups; one contains a reducing end group, where as the other contains an extra secondary hydroxyl group in the position C4 and is known as the non-reducing end group.
There are two secondary and one primary alcoholic hydroxyl groups in each basic anhydro-D-glucose unit (C6H10O¬5)n which are arranged in positions 2, 3 and 6 respectively, on the basic unit. The reactivity of the hydroxyl groups varies in different reactions. In many reactions the primary hydroxyl groups have a greater reactivity. The two secondary hydroxyls, at the second and third carbon atoms, differ somewhat in their reactivity, the primary hydroxyls of cellulose elementary units are responsible for the sorbability and dye-ability of cellulose materials. The high hydroxyl content of cellulose might suggest high water solubility. The because of stiffness of the chains and hydrogen bonding between hydroxyl groups of adjacent chains.
Besides hydrogen bonding, another type of linkages called semiacetal linkages is present between the adjacent chain molecules of cellulose.
From X-ray diffraction diagram, it has been concluded that cellulose has two regions: crystalline and amorphous. In the amorphous region the polymer chains end to be folded, and consequently, they will have rather different properties than the crystalline region. The most of the chemical reactions take place in disordered region of with cellulose. Again, polymeric fibers are never completely crystalline. This interconnection of crystalline and amorphous regions enhances the strength of the polymer.
Hemicellulose
The isolated hemicelluloses are amorphous substances. A mixture of polysaccharides called hemicellulose closely interpenetrates the cellulose and lignin of plant cell walls. It is a group of cell wall polysaccharides which unlike cellulose, are soluble in dilute alkali and are readily hydrolysed to pentose and hexose with some uronic acids.
Chowdhry and Saha identified a number of simple sugars and galacturonic acid from the hydrolysate of delignified jute hemicellulose. Norman found about 15 to 18 xylan type hemicellulose. He also classified hemicellulose into polyuronides and cellulosan. The xylan is a cellulosan type hemicellulose and is free from uronic acid while polyuronides invariable contain uronic acids. High xylan contend fiber usually means a high lignin content and is a characteristic of a fiber of poor quality and vice-versa. Sarker and others showed xylose linked with methyluronic acid formed the basic building units of hemicellulose in okra. It appeared that six xylose units were linked with one methyl glucouronic acid unit.
Lignin
Most plant tissues contain in addition to carbohydrate and extractives, an amorphous polymeric gummy material is known as lignin. The nature of lignin and its relationship to cellulose and other constituents of jute, banana, PALF, okra bast fiber etc are still uncertain. Unlike cellulose and hemicellulose, lignin gives a series of color reactions that indicate the presence of compounds for which these reactions are typical. Isolated lignin is generally an amorphous material having an average high molecular weight.
Lignin is an insoluble, resin like substance of phenolic character. It is built up to a large extent, of phenyl propane building stones, of ten having a hydroxyl group in the para position and methoxyl group/groups in meta position/positions to the side chain. Besides, there may be carbon to carbon or carbon to oxygen bonds joining the aromatic ring to the other portions of the structure. The recent opinion is that the major portion of the lignin is combined with carbohydrate materials, probably with hemicellulose through two types of linkages, one being alkali sensitive and the other alkali-resistant.
The alkali sensitive linkage is an ester type of combination existing between hydroxyl groups of lignin and carboxyl groups of uronic acids of hemicelluloses. The other one is believed to be of ether or similar type occurs through he hydroxyl groups of lignin. The lignin molecule, thus being polyfunctional due to the presence of alcoholic and phenolic hydroxyl groups, may exist in combination with two more neighbouring chain molecules, cellulose or hemicellulose, serving the function of a cross-linking agent.
Cellulose is the principal constituent of all plant life. It is a linear polymer of anhydroglucose units linked in 1 and 4 position by a alpha-glucoside links. The empirical formula of cellulose (C6H10O¬5)n corresponds to a polyanhydride of glucose. The two terminal glucose residues of cellulose molecule contain two different end groups; one contains a reducing end group, where as the other contains an extra secondary hydroxyl group in the position C4 and is known as the non-reducing end group.
There are two secondary and one primary alcoholic hydroxyl groups in each basic anhydro-D-glucose unit (C6H10O¬5)n which are arranged in positions 2, 3 and 6 respectively, on the basic unit. The reactivity of the hydroxyl groups varies in different reactions. In many reactions the primary hydroxyl groups have a greater reactivity. The two secondary hydroxyls, at the second and third carbon atoms, differ somewhat in their reactivity, the primary hydroxyls of cellulose elementary units are responsible for the sorbability and dye-ability of cellulose materials. The high hydroxyl content of cellulose might suggest high water solubility. The because of stiffness of the chains and hydrogen bonding between hydroxyl groups of adjacent chains.
Besides hydrogen bonding, another type of linkages called semiacetal linkages is present between the adjacent chain molecules of cellulose.
From X-ray diffraction diagram, it has been concluded that cellulose has two regions: crystalline and amorphous. In the amorphous region the polymer chains end to be folded, and consequently, they will have rather different properties than the crystalline region. The most of the chemical reactions take place in disordered region of with cellulose. Again, polymeric fibers are never completely crystalline. This interconnection of crystalline and amorphous regions enhances the strength of the polymer.
Hemicellulose
The isolated hemicelluloses are amorphous substances. A mixture of polysaccharides called hemicellulose closely interpenetrates the cellulose and lignin of plant cell walls. It is a group of cell wall polysaccharides which unlike cellulose, are soluble in dilute alkali and are readily hydrolysed to pentose and hexose with some uronic acids.
Chowdhry and Saha identified a number of simple sugars and galacturonic acid from the hydrolysate of delignified jute hemicellulose. Norman found about 15 to 18 xylan type hemicellulose. He also classified hemicellulose into polyuronides and cellulosan. The xylan is a cellulosan type hemicellulose and is free from uronic acid while polyuronides invariable contain uronic acids. High xylan contend fiber usually means a high lignin content and is a characteristic of a fiber of poor quality and vice-versa. Sarker and others showed xylose linked with methyluronic acid formed the basic building units of hemicellulose in okra. It appeared that six xylose units were linked with one methyl glucouronic acid unit.
Lignin
Most plant tissues contain in addition to carbohydrate and extractives, an amorphous polymeric gummy material is known as lignin. The nature of lignin and its relationship to cellulose and other constituents of jute, banana, PALF, okra bast fiber etc are still uncertain. Unlike cellulose and hemicellulose, lignin gives a series of color reactions that indicate the presence of compounds for which these reactions are typical. Isolated lignin is generally an amorphous material having an average high molecular weight.
Lignin is an insoluble, resin like substance of phenolic character. It is built up to a large extent, of phenyl propane building stones, of ten having a hydroxyl group in the para position and methoxyl group/groups in meta position/positions to the side chain. Besides, there may be carbon to carbon or carbon to oxygen bonds joining the aromatic ring to the other portions of the structure. The recent opinion is that the major portion of the lignin is combined with carbohydrate materials, probably with hemicellulose through two types of linkages, one being alkali sensitive and the other alkali-resistant.
The alkali sensitive linkage is an ester type of combination existing between hydroxyl groups of lignin and carboxyl groups of uronic acids of hemicelluloses. The other one is believed to be of ether or similar type occurs through he hydroxyl groups of lignin. The lignin molecule, thus being polyfunctional due to the presence of alcoholic and phenolic hydroxyl groups, may exist in combination with two more neighbouring chain molecules, cellulose or hemicellulose, serving the function of a cross-linking agent.
Chemical Composition of Okra Bast Fiber
1.1.2 Chemical Composition and structure of the fibre ( Natural Things)
Chemically speaking, okra bast fibre is a composite fibre extracted from the okra bast plant by retting in water. Okra bast fibre is a complex mixture of chemical compound, which a no built up by natural process during the growth of okra fibre in the plant stem. The composition of okra fibre is not uniform. The condition of soil, climate, maturity of the plant, retting etc. makes considerable variation in the constituents of the fibre.
The general compositions of the Abelmoschus esculentus fibre are more or less same with minor deference in constituents. The average composition of fairly a good quality of okra bast fibre is as follows.
List-1: Chemical Composition of okra bast fibre
Constituents Amounts ( Percentage)
1.alpha-cellulose 59.2
2. Hemicellulose 19.0
3. Lignin 9.8
4.Pectins 3.7
5. Fatty and waxy matters 5.3
6. Aqueous extract 3.0
7.Total 100
It is evident from the composition of okra bast fibre that the main constituents are alpha-cellulose, hemicellulose and lignin and the rest are very little influence to the structure of okra bast fibre.
Chemically speaking, okra bast fibre is a composite fibre extracted from the okra bast plant by retting in water. Okra bast fibre is a complex mixture of chemical compound, which a no built up by natural process during the growth of okra fibre in the plant stem. The composition of okra fibre is not uniform. The condition of soil, climate, maturity of the plant, retting etc. makes considerable variation in the constituents of the fibre.
The general compositions of the Abelmoschus esculentus fibre are more or less same with minor deference in constituents. The average composition of fairly a good quality of okra bast fibre is as follows.
List-1: Chemical Composition of okra bast fibre
Constituents Amounts ( Percentage)
1.alpha-cellulose 59.2
2. Hemicellulose 19.0
3. Lignin 9.8
4.Pectins 3.7
5. Fatty and waxy matters 5.3
6. Aqueous extract 3.0
7.Total 100
It is evident from the composition of okra bast fibre that the main constituents are alpha-cellulose, hemicellulose and lignin and the rest are very little influence to the structure of okra bast fibre.
Natural Fiber : Okra Bast Fiber
THE OKRA BAST FIBRE
Okra plant, okra bast fibre and uses
Okra plant (Abelmoschus esculentus) is of the Malvaceae or mallow family along with cotton, hollyhock, rose of Sharon and hibiscus. It is know by many names: Lady Fingers, Gombo, Okro, Ochro, Okoro, Quimgombo, bhindi, bindi, bamia bamiya, bamieh. A tall-growing, warm-season, annual vegetable, okra has large, attractive, hibiscus like yellow flowers; heart-shaped, lobed leaves with long stems attached to a thick woody stem. The fruit, a long generally ribbed fuzzy pod developing in the leaf axil, grows rapidly after flowering. The edible part is the fruit pod, which varies in color from yellow to red to green.
The upright plant averages between 3-6 feet or more with varieties for both temperate and tropical areas. Indigenous African varieties can grow to 12 feet tall, with a base stem 4 inches in diameter. Its lobed leaves are generally hairy and may reach 11 inches in length. Okra is often grown as a perennial in many tropical areas. Cultivators vary in plant height, shape and color of the pod. Most cultivators are adapted to high temperatures and a wide range of soil types. Average temperatures of 68-80F are best for growth, flowering and pod development. Okra is tolerant to wide variation in rainfall.
Okra is a plant that produces an edible pod that is eaten as a vegetable. It originated in Africa, perhaps Ethiopia, and was brought to the Americas with the slave trade. The pods are green, have a ridged skin, and generally a narrow, tapering shape, although some can be almost round. Pods longer than about 4 inches are likely to be tough and fibrous. In cooking, okra exudes a gummy fluid that is often thickens whatever dish it’s in.
Okra is most popular in the south of United States, and is available year-round there. Fresh, it available in the rest of the country generally from May to October. It is also available canned and frozen. Okra is best known as being an ingredient in southern gumbos, where both its flavor and thickening qualities are appreciated. It can be prepared in many ways, though sautéed, braised, and baked.
Okra plant is grown abundantly in Bangladesh. At present, these are waste after collecting fruits. The fibers are obtained mainly from the stem of the plant. About 37 kg (average weight) of stem yields about 2 kg of good quality fiber; the yield is 2-2.5% of dry fibre. The fiber has not been exploited much commercially hitherto, as it was consid¬ered inferior to abaca and other available hard fibers. It can be extracted by hand¬scraping, by retting, or by using raspador machines; it can also be extracted chemically, for example by boiling in NaOH solution. Extraction of the fibre for local use (in cordage) or for cottage industries is due to high cellulose and low lignin content, its use in the paper industry (tissue, filters, specialty nonwoven, document, printing, sur¬gical and hygienic applications, coffee bags, meat casings, etc.) have been reported. Over the years, there has been considerable interest in exploiting it for a variety of household and industrial uses on a commercial scale. For instance, the use of as reinforcement with autoclaved cement mortar, with air-cured cement, or with air-cured plaster is being investigated. Therefore, the development of mechanical decorticating methods is reported to be in progress. The potential yield of the okra bast fibre in India is estimated to be 1102 tons annually. Unfortunately there is no work or utilization of okra bast fiber so far in our country. Immediate attention must be given for proper utilization of this high cellulose and low lignin content fibre.
Okra plant, okra bast fibre and uses
Okra plant (Abelmoschus esculentus) is of the Malvaceae or mallow family along with cotton, hollyhock, rose of Sharon and hibiscus. It is know by many names: Lady Fingers, Gombo, Okro, Ochro, Okoro, Quimgombo, bhindi, bindi, bamia bamiya, bamieh. A tall-growing, warm-season, annual vegetable, okra has large, attractive, hibiscus like yellow flowers; heart-shaped, lobed leaves with long stems attached to a thick woody stem. The fruit, a long generally ribbed fuzzy pod developing in the leaf axil, grows rapidly after flowering. The edible part is the fruit pod, which varies in color from yellow to red to green.
The upright plant averages between 3-6 feet or more with varieties for both temperate and tropical areas. Indigenous African varieties can grow to 12 feet tall, with a base stem 4 inches in diameter. Its lobed leaves are generally hairy and may reach 11 inches in length. Okra is often grown as a perennial in many tropical areas. Cultivators vary in plant height, shape and color of the pod. Most cultivators are adapted to high temperatures and a wide range of soil types. Average temperatures of 68-80F are best for growth, flowering and pod development. Okra is tolerant to wide variation in rainfall.
Okra is a plant that produces an edible pod that is eaten as a vegetable. It originated in Africa, perhaps Ethiopia, and was brought to the Americas with the slave trade. The pods are green, have a ridged skin, and generally a narrow, tapering shape, although some can be almost round. Pods longer than about 4 inches are likely to be tough and fibrous. In cooking, okra exudes a gummy fluid that is often thickens whatever dish it’s in.
Okra is most popular in the south of United States, and is available year-round there. Fresh, it available in the rest of the country generally from May to October. It is also available canned and frozen. Okra is best known as being an ingredient in southern gumbos, where both its flavor and thickening qualities are appreciated. It can be prepared in many ways, though sautéed, braised, and baked.
Okra plant is grown abundantly in Bangladesh. At present, these are waste after collecting fruits. The fibers are obtained mainly from the stem of the plant. About 37 kg (average weight) of stem yields about 2 kg of good quality fiber; the yield is 2-2.5% of dry fibre. The fiber has not been exploited much commercially hitherto, as it was consid¬ered inferior to abaca and other available hard fibers. It can be extracted by hand¬scraping, by retting, or by using raspador machines; it can also be extracted chemically, for example by boiling in NaOH solution. Extraction of the fibre for local use (in cordage) or for cottage industries is due to high cellulose and low lignin content, its use in the paper industry (tissue, filters, specialty nonwoven, document, printing, sur¬gical and hygienic applications, coffee bags, meat casings, etc.) have been reported. Over the years, there has been considerable interest in exploiting it for a variety of household and industrial uses on a commercial scale. For instance, the use of as reinforcement with autoclaved cement mortar, with air-cured cement, or with air-cured plaster is being investigated. Therefore, the development of mechanical decorticating methods is reported to be in progress. The potential yield of the okra bast fibre in India is estimated to be 1102 tons annually. Unfortunately there is no work or utilization of okra bast fiber so far in our country. Immediate attention must be given for proper utilization of this high cellulose and low lignin content fibre.
Friday, June 24, 2011
Studies on Chemical Modification of Okra Bast Fiber with Acrylonitrile and its Physicochemical Characteristics
The world’s supply of bio-fibres i.e., natural polymers is being depleted, the demand for renewable raw materials continues to rise. So responsible use of available bio-fibres has become an inevitable task for scientists. Okra bast fibre is a lignocellulosic plant fibre which obtained from okra plant that grows everywhere abundantly in Bangladesh. Now-a-days, it is rejected as an agricultural waste products. Therefore, okra bast fibre can play an important role in the field of our national economy in finding various applications. They are generally biodegradable but do not possess the necessary and sufficient properties desirable for engineering or commodity plastics. Besides, like other vegetable fibres okra bast fibre possess few weak points i.e., rub resistance, colour fastness, wash and wear properties and very much prone to creasing, possibly because of high degree of orientation of cellulose in the fibre. This defect of creasing of cellulosic fibre may be remedied remarkably by the crease-resisting process in which resins are synthesized within the cellulosic materials in different proportions. In order to improve the textile properties of okra bast fibre it is an urgent need to improve several properties such as whiteness, softness, washing, dyeing behavior, colour fastness, light resistance, thermal resistance, etc. So, an attempt has been made to improve those characteristics of okra bast fibre through chemical modification and dyeing.
The constituents of okra bast fibre are 59.2% α-cellulose, 19.0% hemicellulose, 9.8% lignin, 3.7% pectin, 5.3% fatty and waxy matters and 3.0% aqueous extract.
The modification has been carried out in aqueous medium using potassium persulphate (K2S2O8) as an initiator under the catalytic influence of ferrous sulphate (FeSO4) in presence of air. To attain the maximum graft level, optimum conditions, viz., monomer concentration, initiator concentration, catalyst concentration, as well as reaction time and temperature have been determined. The percentage of grafting increases with the increase of monomer concentration, initiator concentration, catalyst concentration, time and temperature up to certain limits and thereafter it decreases.
The optimum conditions of modification for acrylonitrile are 0.03 M monomer, 0.005 M initiator, 0.005 M catalyst, reaction time 90 min and temperature 70ºC. The maximum percentage of grafting at optimum condition is 7.38%. Again, the formation of composite by the incorporation of monomer with okra bast fibre is confirmed by Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) measurements.
The bleached and modified okra bast fibres have been dyed with Direct Green 27 and Direct Red 28 in presence of sodium sulphate as an electrolyte. The conditions of dyeing are 5% dye, 5% electrolyte, time 60 min and temperature 70ºC for both Direct Green 27 and Direct Red 28. The dye absorption is decreased with the increase of grafting due to the increases of hydrophobicity of fibres.
The absorption of dyes and colour strength (K/S value) by bleached fibre is comparatively higher than that of modified fibre. Due to the hydrophobic nature of modified fibre absorb the less amount of dye from the dyebath.
The colourfastness onto sunlight of modified dyed fibre is comparatively higher than that of bleached dyed fibre, this is perhaps, modification and dyeing together inhibit the UV-irradiation save the fibre from photo-oxidation. The colourfastness tests to spotting of okra bast fibre with acids and alkalis are remarkable. Sulphuric acid and sodium hydroxide give unsatisfactory results by changing colour but in most of the cases, such as acetic acid, sodium carbonate and ammonium hydroxide give satisfactory results.
The tensile strength of bleached fibre is comparatively lower than that of modified fibre. On the other hand, the percentage of tensile strength losses lower in case of modified fibre than bleached fibre on exposure to sunlight and heat. The percentage loss of tensile strength of bleached fibre increases than modified fibre.
The effect of temperature on the tensile strength of bleached fibre is more pronounced than that of modified fibre. This means that modified fibre is more heat resistant than the bleached fibre.
It can be concluded considering all the parameters used in the present investigation that depending upon the effect of various external influences on the bleached and modified okra bast fibres, the modified fibre is more resistant than bleached fibre. Between the dyes Direct Red 28 exhibits better results than Direct Green 27 in most of the cases.
Keywords: Okra Bast Fibre; Chemical Modification; Acrylonitrile monomer; Fourier Transform Infrared Spectroscopy (FTIR); Scanning Electron Microscopy (SEM); Dyeing Behaviour; Colour Strength; Degradation Behaviour; Colourfastness; Tensile Strength.
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