Degumming Gonometa postica cocoons using environmentally conscious methods Ismari van der Merwe February 2015 Degumming Gonometa postica cocoons using environmentally conscious methods Ismari van der Merwe Thesis submitted in accordance with the requirement for the degree Philosophiae Doctor in the Faculty of Natural and Agricultural Sciences Department of Consumer Science at the University of the Free State, Bloemfontein, South Africa February 2015 Promoter: Prof H J H Steyn Co-promoter: Prof C Hugo Declaration “I declare that this dissertation, which I hereby submit for the degree Philosophiae Doctor at the University of the Free State, is my own work and has not previously been submitted by me for a degree at this or any other tertiary institution. I further more cede copyright of the thesis in favour of the University of the Free State.” ________________________________ Ismari van der Merwe 2 February 2015 ii The establishment of a sustainable wild silk industry in Africa could pave the way for similar Africa-unique projects to capture the true spirit of the continent. That spirit that determines her worth and echoes in her truths: “Every morning in Africa, a gazelle wakes up. It knows it must run faster than the fastest lion or it will be killed. Every morning a lion wakes up. It knows it must outrun the slowest gazelle or it will starve to death. It doesn’t matter whether you are a lion or a gazelle… when the sun comes up, you’d better be running.” (Author: Unknown) iii Acknowledgements Research is never the work of one person alone. There are always a lot of people that in their own way, however small, helped to make a project like this possible. First and foremost, praise to our Heavenly Father, for giving me the ability to undertake and complete this study. I wish to thank Professor Steyn, my supervisor and mentor, of the Department Consumer Science, University of the Free State, for introducing me to this field of study, for her input, time, encouragement and patience. Her knowledge of research and textiles is an inspiration. We are all privileged to be under her guidance. I also wish to thank my co-supervisor, Professor Hugo, Department of Microbial, Biochemical and Food Biotechnology, University of the Free State, for her advice on the microbiology analysis of this dissertation, for her constant interest during my study and for her invaluable criticism. Thank you for your guidance. Thank you to Dr Van Biljon, Department of Plant Science, University of the Free State, for all the help and assistance with the SDS-PAGE tests and the revision of that part of the dissertation. I wish to acknowledge Professor Schall for the statistical analysis and interpretation of the results obtained in this study. To Mrs Adine Gericke from the University of Stellenbosch, Textile Science, thanks are due for her assistance with the strength tests. iv Thanks are also due to Dr Bothma of the Department of Food Science, for all her help with technical aspects of this dissertation. Thank you for your time and friendship. To Fransie van Tonder and her husband, Dr Gerrit van Tonder (who passed away recently), for providing the vermicompost for my laboratory work. To Mrs Gina Olivier for providing the cocoons for the laboratory work. To all my friends and colleagues at the Department of Consumer Science, thank you for your never-ending support and interest throughout my studies. To my dearest friends, Professor Louis and Lotte Venter – I do not have the words to express my gratitude; thank you for everything! To my family and friends: Thank you for being there. Especially to my Father and Mother for all their help and endless love. Words cannot describe my thankfulness. Last but not least, to my husband, Willem, my daughters, Ané, Karin and Marina, and my sons Willem and Louis. Thank you for all your love, understanding and support, it carried me during this time. A special word of thanks to you, Ané, for all assistance with the technical work of this dissertation; all the coffee you made and just being there for me. v Table of contents ______________________________________________________________________ CHAPTER 1…………………………………………………………………………1 GENERAL INTRODUCTION…………………………………………………..1 1.1 Introduction…………………………………………………………………….2 1.2 Problem statement…………………………………………………………..5 1.3 Aim…………………………………………………………………………………5 1.4 Objectives……………………………………………………………………….6 1.5 Structure of the dissertation……………………………………………..6 CHAPTER 2…………………………………………………………………………8 LITERATURE REVIEW…………………………………………………………..8 2.1 Introduction……………………………………………………………………….9 2.2 Silkworm varieties…………………………………………………………….10 2.3 The life-cycle and ecology of the silkworm………………………….22 2.4 The cocoon……………………………………………………………………….32 2.5 Cocoon processing…………………………………………………………….34 2.5.1 Chemical degumming of wild silk………………………………….38 2.5.1.1 Alkali degumming………………………………………….38 2.5.1.1.1 Orvus paste…………………………………39 2.5.1.1.2 Other alkali methods……………………..40 2.5.1.2 Acid degumming…………………………………………..41 2.5.1.3 Enzymatic degumming……………………………………43 2.5.1.4 Quality of the water……………………………………….44 2.5.1.5 Acceleration of the degumming process………………45 2.5.2 Biological degumming of wild silk………………………………….47 vi 2.5.2.1 Vermicompost………………………………………………47 2.5.2.2 Distilled water………………………………………………54 2.5.2.3 Catholyte…………………………………………………….55 2.5.2.4 Eucalyptus oil……………………………………………….57 2.6 Determination of silk quality………………………………………………60 2.6.1 Size and weight of the cocoon……………………………………..60 2.6.2 Morphological structure of the fibre……………………………….64 2.6.3 Physical properties of the silk………………………………………67 2.6.4 Mechanical properties………………………………………………..68 2.6.5 Chemical composition of the filament…………………………….70 2.6.5.1 Sericin………………………………………………………..71 2.6.5.2 Fibroin………………………………………………………..75 2.7 Conclusion………………………………………………………………………..81 CHAPTER 3………………………………………………………………………83 MATERIALS AND METHODS……………………………………………….83 3.1 Cocoons…………………………………………………………………………..84 3.2 Preparation of degumming liquors……………………………………..85 3.2.1 Orvus paste…………………………………………………………...85 3.2.2 Vermicompost…………………………………………………………86 3.2.3 Catholyte……………………………………………………………….87 3.2.4 Distilled water…………………………………………………………89 3.2.5 Eucaluptus oil………………………………………………………….89 3.3 Degumming methods………………………………………………………..89 3.3.1 Orvus paste………………………………………………………......89 3.3.2. Vermicompost………………………………………………………..91 3.3.3 Catholyte……………………………………………………………....92 vii 3.3.4 Distilled water…………………………………………………………92 3.3.5 Eucalyptus oil and distilled water…………………………………92 3.3.6 Eucalyptus oil and catholyte……………………………………….93 3.3.7 Eucalyptus oil and Orvus paste……………………………………93 3.4 Physical fibre property analysis after different degumming methods………………………………………………………………………….94 3.4.1 Weight loss…………………………………………………………….94 3.4.2 Degumming efficiency………………………………………………95 3.4.3 Morphology of silk fibre analysis…………………………………..95 3.5 Mechanical fibre property analysis………………………………………96 3.5.1 Tensile strength……………………………………………………….96 3.6 Chemical fibre analysis……………………………………………………..98 3.6.1 Silk fibre solution preparation……………………………………..98 3.6.2 One-dimensional SDS-PAGE………………………………………..99 3.7 Microbial analysis and identification of silk fibres……………….100 3.7.1 Microbial analysis……………………………………………………100 3.7.2 Microbial identification……………………………………………..100 3.8 Statistical analysis…………………………………………………………..101 3.8.1 Degumming data set……………………………………………….102 3.8.2 Maximum load data set…………………………………………….102 CHAPTER 4………………………………………………………………………103 RESULTS AND DISCUSSION……………………………………………..103 4.1 Physical fibre properties after different degumming methods………………………………………………………………………….104 4.1.1 Weight loss…………………………………………………………….104 viii 4.1.2 Degumming efficiency………………………………………………111 4.1.3 Morphology of silk fibres……………………………………………114 4.2 Mechanical fibre properties after different degumming methods………………………………………………………………………….123 4.2.1 Maximum load………………………………………………………..123 4.2.2 Displacement………………………………………………………….130 4.3 Chemical fibre properties after different degumming methods………………………………………………………………………….135 4.4 Microboal analysis and identification of silk fibres after different degumming methods…………………………………………..142 CHAPTER 5………………………………………………………………………145 GENERAL CONCLUSIONS AND RECOMMENDATIONS…….146 5.1 General conclusion…………………………………………………………..146 5.2 Recommendation……………………………………………………………..150 REFERENCES………………………………………………………………………151 ABSTRACT…………………………………………………………………………..198 OPSOMMING………………………………………………………………………201 ix List of figures _________________________________ Figure Description Page number 1.1 G. postica cocoons in the trees looking very similar to 3 the pods of the Acacia tree (Dreyer, 2013). 2.1 Mulberry silkworm (International Sericultural 11 commission, 2013). 2.2 Mulberry silk cocoons (International Sericultural 11 commission, 2013). 2.3 Eri silk worm (International Sericultural commission, 12 2013). 2.4 Eri silkworm cocoon (a) and silk (b) (International 12 Sericultural commission, 2013). 2.5 Muga silk worm (International Sericultural commission, 13 2013). 2.6 Muga silk cocoon and silk (International Sericultural 13 commission, 2013). 2.7 Tasar silk worm (International Sericultural commission, 14 2013). 2.8 Tasar silk cocoons (a) and silk (b) (International 15 Sericultural commission, 2013). 2.9 16 Anaphae silk worm (International Sericultural x commission, 2013). 2.10 Anaphae silk cocoon (a) and silk (b) (International 16 Sericultural commission, 2013). 2.11 Fagara silk worm (a); Fagara silk cocoon (b) and silk (c) 16 (International Sericultural