Die evaluering van peroksiedbleiking van Gonometa postica-sy
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Date
2007-11
Authors
Olivier, Yolande
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
English: Degradation of Gonometa postica silk, which occurs during bleaching, is not only a problem for the consumer but also for the producer. The purpose of this study was to determine the effect of hydrogen peroxide bleaching on Gonometa postica silk. The specific goal was to determine the influence that temperature, pH and time duration has on the releasing of hydrogen peroxide, colour change, breaking strength, stiffness and shrinkage. A literature study was undertaken to describe the physical properties, chemical and molecular structure of Gonometa postica silk. Research on the degradation effect of hydrogen peroxide on silk was investigated and the factors that influenced the bleaching effect, were identified. An experimental study was carried out to determine the releasing of hydrogen peroxide at 50˚C, 60˚C, 70˚C and 90˚C at a pH 8 and pH 10. The Gonometa postica silk was bleached with hydrogen peroxide in a 5 l water bath and dried afterwards. The samples were kept in standard atmosphere conditions of 20 ± 1˚C and 65 ± 2% relative humidity before and during testing. The colour change, breaking strength, stiffness and shrinkage of Gonometa postica silk were determined after hydrogen peroxide bleaching. The release of hydrogen peroxide was determined by potassium permanganate titrations during the bleach action, while the colour changes (delta E) of the samples were determined by a colorimeter. The instron tensile tester was used to determine the breaking strength of bleached and unbleached samples according to the SABS method 13934 – 1:1999. The breaking strength was measured in Newton and elongation in mm. The stiffness of the silk was measured by a Shirley stiffness tester. Shrinkage caused during bleaching was determined in grain difference and expressed in percentages. To illustrate the degradation caused by bleaching, scanning electron microscope photos were taken. 90 The results indicated that temperature, pH and time duration plays an important role in the bleaching of Gonometa postica silk. At a pH 10, the colour change (bleaching effect) increased rapidly as the temperature increased. More bleaching (colour change) could be seen at low temperatures at a pH value of 8. High temperatures damaged the fibre, which lowered the breaking strength, and caused an increase in the stiffness of the fibre as the temperature incresed. Hydrogen peroxide released quicker at high temperatures. Different temperatures did not influence shrinkage. The pH-value was the factor with the highest influence on the release of hydrogen peroxide. More bleaching and release of hydrogen peroxide could be seen at a pH value of 8 and better results were obtained in colour change at a pH value of 10 at low temperatures. The pH-value had no significant influence on breaking strength, stiffness and shrinkage. Better results could be seen with an increase in time of bleaching. The results showed that 70˚C for 3 hours at a pH value of 8 are the best conditions for bleaching Gonometa postica silk. Althought some damage to the fibres was evident under these treatment conditions, an effective white colour was obtained. The conclusion that can thus be made is that factors, such as temperature and pHvalue, have the biggest influence on colour change, tensile strength and stiffness of Gonometa postica silk.
Afrikaans: Degradation of Gonometa postica silk, which occurs during bleaching, is not only a problem for the consumer but also for the producer. The purpose of this study was to determine the effect of hydrogen peroxide bleaching on Gonometa postica silk. The specific goal was to determine the influence that temperature, pH and time duration has on the releasing of hydrogen peroxide, colour change, breaking strength, stiffness and shrinkage. A literature study was undertaken to describe the physical properties, chemical and molecular structure of Gonometa postica silk. Research on the degradation effect of hydrogen peroxide on silk was investigated and the factors that influenced the bleaching effect, were identified. An experimental study was carried out to determine the releasing of hydrogen peroxide at 50°C, 60°C, 70°C and 90°C at a pH 8 and pH 10. The Gonometa postica silk was bleached with hydrogen peroxide in a 5 l water bath and dried afterwards. The samples were kept in standard atmosphere conditions of 20 ± 1°C and 65 ± 2% relative humidity before and during testing. The colour change, breaking strength, stiffness and shrinkage of Gonometa postica silk were determined after hydrogen peroxide bleaching. The release of hydrogen peroxide was determined by potassium permanganate titrations during the bleach action, while the colour changes (delta E) of the samples were determined by a colorimeter. The instron tensile tester was used to determine the breaking strength of bleached and unbleached samples according to the SABS method 13934 – 1:1999. The breaking strength was measured in Newton and elongation in mm. The stiffness of the silk was measured by a Shirley stiffness tester. Shrinkage caused during bleaching was determined in grain difference and expressed in percentages. To illustrate the degradation caused by bleaching, scanning electron microscope photos were taken. The results indicated that temperature, pH and time duration plays an important role in the bleaching of Gonometa postica silk. At a pH 10, the colour change (bleaching effect) increased rapidly as the temperature increased. More bleaching (colour change) could be seen at low temperatures at a pH value of 8. High temperatures damaged the fibre, which lowered the breaking strength, and caused an increase in the stiffness of the fibre as the temperature incresed. Hydrogen peroxide released quicker at high temperatures. Different temperatures did not influence shrinkage. The pH-value was the factor with the highest influence on the release of hydrogen peroxide. More bleaching and release of hydrogen peroxide could be seen at a pH value of 8 and better results were obtained in colour change at a pH value of 10 at low temperatures. The pH-value had no significant influence on breaking strength, stiffness and shrinkage. Better results could be seen with an increase in time of bleaching. The results showed that 70°C for 3 hours at a pH value of 8 are the best conditions for bleaching Gonometa postica silk. Althought some damage to the fibres was evident under these treatment conditions, an effective white colour was obtained. The conclusion that can thus be made is that factors, such as temperature and pHvalue, have the biggest influence on colour change, tensile strength and stiffness of Gonometa postica silk.
Afrikaans: Degradation of Gonometa postica silk, which occurs during bleaching, is not only a problem for the consumer but also for the producer. The purpose of this study was to determine the effect of hydrogen peroxide bleaching on Gonometa postica silk. The specific goal was to determine the influence that temperature, pH and time duration has on the releasing of hydrogen peroxide, colour change, breaking strength, stiffness and shrinkage. A literature study was undertaken to describe the physical properties, chemical and molecular structure of Gonometa postica silk. Research on the degradation effect of hydrogen peroxide on silk was investigated and the factors that influenced the bleaching effect, were identified. An experimental study was carried out to determine the releasing of hydrogen peroxide at 50°C, 60°C, 70°C and 90°C at a pH 8 and pH 10. The Gonometa postica silk was bleached with hydrogen peroxide in a 5 l water bath and dried afterwards. The samples were kept in standard atmosphere conditions of 20 ± 1°C and 65 ± 2% relative humidity before and during testing. The colour change, breaking strength, stiffness and shrinkage of Gonometa postica silk were determined after hydrogen peroxide bleaching. The release of hydrogen peroxide was determined by potassium permanganate titrations during the bleach action, while the colour changes (delta E) of the samples were determined by a colorimeter. The instron tensile tester was used to determine the breaking strength of bleached and unbleached samples according to the SABS method 13934 – 1:1999. The breaking strength was measured in Newton and elongation in mm. The stiffness of the silk was measured by a Shirley stiffness tester. Shrinkage caused during bleaching was determined in grain difference and expressed in percentages. To illustrate the degradation caused by bleaching, scanning electron microscope photos were taken. The results indicated that temperature, pH and time duration plays an important role in the bleaching of Gonometa postica silk. At a pH 10, the colour change (bleaching effect) increased rapidly as the temperature increased. More bleaching (colour change) could be seen at low temperatures at a pH value of 8. High temperatures damaged the fibre, which lowered the breaking strength, and caused an increase in the stiffness of the fibre as the temperature incresed. Hydrogen peroxide released quicker at high temperatures. Different temperatures did not influence shrinkage. The pH-value was the factor with the highest influence on the release of hydrogen peroxide. More bleaching and release of hydrogen peroxide could be seen at a pH value of 8 and better results were obtained in colour change at a pH value of 10 at low temperatures. The pH-value had no significant influence on breaking strength, stiffness and shrinkage. Better results could be seen with an increase in time of bleaching. The results showed that 70°C for 3 hours at a pH value of 8 are the best conditions for bleaching Gonometa postica silk. Althought some damage to the fibres was evident under these treatment conditions, an effective white colour was obtained. The conclusion that can thus be made is that factors, such as temperature and pHvalue, have the biggest influence on colour change, tensile strength and stiffness of Gonometa postica silk.
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Keywords
Bleaching, Silk -- Dyes and dyeing, Peroxides, Dissertation (M.Sc. (Home Ec.) (Microbial, Biochemical and Food Biotechnology))--University of the Free State, 2007