Characterization of linen modified by low temperature plasma and enzymatic hydrolysis

Abstract

This thesis is concerned with a study on the effects of low temperature plasma pretreatment and enzyme treatment as well as their synergy in order to modify the properties of linen. Linen is more expensive due to the difficulties in processing and it faces strong competition with other natural fibers. Fiber modification, preparation and finishing treatments by environmentally friendly processes are essential in order to minimize the chemical waste and associated disposal problem. Characterizations of the modified linen have been carried out and the effects of the treatments have been experimentally determined. Fiber bulk structure and properties have been studied along with the mechanical properties, surface morphology and properties, and dyeing properties of linen. A number of modern characterization techniques have been applied such as the Environmental Scanning Electron Microscopy, Atomic Force Microscopy, X-ray Photoelectron Spectroscopy and a downward wicking measurement. Low temperature plasma treatments were applied to linen with oxygen and argon gases, various levels of discharge power and exposure time. It was discovered by X-ray Photoelectron Spectroscopy that the surface oxygen content of the low temperature plasma treated linen was increased, along with the formation of voids and cracks on the fiber surface. The fabric weight loss increased with the exposure time. No significant change in x-ray crystallinity and cuprammonium fluidity was found. A slight reduction of the moisture regain was detected. Fabric water uptake and strength first were increased and then decreased with the prolonged exposure whereas fabric bending rigidity, hysteresis and wrinkle recovery were slightly improved. Environmental Scanning Electron Microscopy illustrated the time series images of flax surface appearance changed by the low temperature plasma treatment for the first time. With the image processing techniques and Atomic Force Microscopy, a comprehensive understanding of the surface morphology of low temperature plasma treated flax fibers was achieved. The wetting properties of low temperature plasma treated linen were studied by a downward wicking experiment. Wicking properties of linen were greatly improved by the application of low temperature plasma treatment. Further investigation was conducted in order to study the synergy of low temperature plasma and enzyme treatment. Enzymes have been used extensively in cotton textiles to remove small fiber ends from fabric surface, create a smooth fabric appearance and introduce a degree of softness without using traditional chemical treatments. The low temperature plasma pretreatment enhanced the effectiveness of enzyme treatment. With an oxygen gas for 2.5 minutes exposure time, a faster reaction rate and acceptable strength loss percentage were achieved. The surface roughness created by the low temperature plasma treatment were further deepened and smoothed by the enzyme treatment. Fabric yellowing occurred after plasma exposure and the whiteness was almost recovered after the enzyme treatment. An increase of fabric water uptake was further provided by the enzyme treatment. Fabric bending rigidity, hysteresis and wrinkle recovery were slightly improved by both treatments. Low temperature plasma pretreatment improved dyeing performance for a direct dye of small molecule size. However, an adverse effect of dyeing performance was obtained after the enzyme treatment. As a comparison, the study of enzyme treatment on mercerized linen was also carried out. The factors concerned were the mercerization tension, concentration of cellulase, incubation time and mechanical agitation. Experimental results confirmed that the effectiveness of enzyme treatment was strengthened by the mercerization pretreatment. Higher reduction of fabric stiffness, minimization of the loss of tensile strength, shortening of the original treatment time, complete removal of surface fibrils and improvement of dyeing performance for direct dyes were achieved. On the other hand, the effect of mechanical agitation on the efficiency of enzyme treatment has been studied and the results revealed that the reduction of both bending rigidity and hysteresis were achieved by applying a higher mechanical agitation during the enzyme treatment. It was found that low temperature plasma pretreatment was more effective than the mercerization pretreatment in improving the effectiveness of enzyme treatment. The present thesis illustrates that the application of two environmentally friendly processing technologies can achieve significant improvements of fiber properties in terms of fabric wetting and dyeability, and moderate improvement of fabric strength, wrinkle recovery, bending rigidity and hysteresis.