A Study On The Degumming And Modification Of Kenaf Bast Fiber By Bio-enzyme Degradation

Based on the analysis of the characteristics of kenaf's intergrowth a technology of bio-enzyme degradation used for degumming and modification of kenaf bast fiber is proposed in the paper.The technology is aimed at resolving the long-standing problems of environmental pollution which is caused by the chemical residue existed in both the degumming and modifying process.The work includes the following parts:the selection and domestication of the strain specially suitable for degumming the kenaf fiber;the systematic experiments of degumming and modification of kenaf fibers using the pactinase secreted by the selected strain and hemicellulase;the analysis of the action mechanisms of the pectinase and hemicellulase on kenaf fiber during the degumming and modifying process;the treatment of degumming wastewater using bio-membrance method;and the study of the application of all the results obtained in laboratory to the medium-duty of kenaf products.The contents of each chapter are as follows:The first chapter gives out an introduction to the present status of research for degumming and modification of bast fibers and degumming wastewater treatment using biological technique at home and abroad.In the second chapter,the strain suitable for kenaf degumming is selected at first. According to the morphology of colony and strain body the selected strain is considered to be Aspergillus Niger family.With the aid of DNA determination and in the light of DNA description of the strain in 18S RNA coding region the strain can be further identied with Aspergillus Niger family.Then the pectinase secreted by the strain is extracted,also its activity is measured.By using DNS method and viscosity dropping method the activities of exo-pectase and endo- pectase are measured to be 565u/mL and 414u/mL respectively when acting on pectin,but only to be 99u/mL and 261u/mL when acting on cellulose. Therefore,the enzyme secreted by the strain is suitable for degumming the kenaf,but it will not damage the fibers.The following work is to investigate the variation of both the bacteria amount and zymogenic activity with the strain growing.It is found that both of them all reach the highest level at 52-56 hour after the strain starting growth,and the relationship between the bacteria amount increasing and zymogenic activity heightering is characteristic of synchronous synthesis.Therefore,it is reasonable for extracting the pactinase secreted by the strain at the time mentioned above.The third chapter covers the systematic experiments of degumming and modification of kenaf fibers using bio-enzymatic technology and the testing of the properties of the degummed and modified fibers.By single-factor test and orthogonal test,the optimum process parameters for degumming are:temperature 36℃,pH value 8,bath ratio 1:25, degumming time 60h,amount of enzymatic solution for each 10g kenaf fiber being 3 mL/10g bast.After being degummed,the residual gum rate and weight-loss ratio of the fibers are 16.1%and 23%respectively,and the fiber separability and flexibility are better then that of before.To improve the spinning performance,the fibers are further modified in the same reactor as that in degumming by using the combination of cellulase and hemicellulase so as to remove the residual hemicellulose,part of lignin and other impurities in the degummed fibers. The experimental results show that the optimum process parameters for modification are: temperature 40℃,pH value 5.5,modifying time 18h,the conbination proportion being 10g of cellulase and 30g of hemicellulase per 1kg of bast.The results obtained from fiber cross-sectional microscopic image,fiber longitudinal SEM photos,fiber infrared spectrums and textile routine testing show that the kenaf fibers treated with bio-enzyme technique have superiority over the one treated by traditional retting method due to lower residual gum rate and weight-loss ratio,better breaking strength,breaking elongation and flexibility,more smooth fiber surface,better fiber separability and less fiber damage.In fourth chapter the mechanism of degumming and modification of kenaf fibers using bio-enzyme technique,the bio-enzymatic degumming processing,the cutting position of pectinase and hemicellulase and the degradation of large molecular chain are all expound in detail.Pectinase degumming is a continuous process including three stages:first,the insoluble pectin is changed into soluble pectin;second,the soluble pectin is demethylated to pectic acid; finally,1,4-glycosidic linkages between galacturonic acid monomers are hydrolyzed making the large molecules degraded.During the degumming process,Methoxylation polygalacturonlase and Polygalacturonlase play a major role.They both exist as endo-pectase and exo-pectase or Endo-MPG/PG and Exo-MPG/PG for short.Endo-pectase cuts the large pectic molecule at the arbitrary position in the middle part of the molecule,while exo-pectase degrades the large pectic molecule at the end of the molecule.Both Endo-MPG and Exo-MPG take priority of acting on pectin,but Endo-PG and Exo-PG on pectic acid. Endo-1,4-β-D-xylanase and exo-1,4-β-D-xylanase play a major role in the process of kenaf fiber modification using hemicellulase.Endo-1,4-β-D-xylanase cuts the molecular chain frame randomly,thus results in generating xylooligosaccharide and decreasing the polymerization degree.Then the exo-1,4-β-D-xylanase decomposes the xylooligosaccharide and xylobiose into xylose.After the enzymolysis,there are mainly galacturonic acid, galacturonic acid methyl ester,galactose,xylose,glucose,arabinose and a small number of rhamnose and mannose in the degumming and modification wastewater.They are all monose with low molecular weight and easier to degrade when the wastewater needs to be treated.In fifth chapter the treatment of wastewater originated from the degumming and modification of kenaf fiber using bio-enzyme technology is studied.Based on the analysis of ingredients in the wastewater by using gas chromatography,the content and proportion of each monose are determined.By taking chitin as carriers to immobilize the bio-membrane,the chitin bio-membrane method is used to treat the wastewater.The optimum process parameters are determined by test as follows:treatment time 18h,pH value 7,initial COD 450, temperature 27℃.After treatment the quality indexes of the treated water are COD value 208, BOD₅ value 61,PH value 6.9,solid amount 73 and color 10,which have reached the second standard grade according to the Integrated Wastewater Discharge Standard.In sixth chapter the application of the results obtained in laboratory to the medium-duty of kenaf products is studied.Apparel fabrics and automotive trim materials are developed by using the kenaf fiber being degummed and modified.Also the possibility of using supercritical CO₂ non-water dyeing technique to dye the treated kenaf fiber is explored.The seventh chapter gives out the conclusion and prospect.The main contributions of the work are summed and an outline of the problems which need to be further sthdied is made as well.