A STUDY OF THE REASONS FOR SHRINK-RESISTANCE AND MACHINE WASHABILITY OF SUPERLIGHT WEIGHT, WOVEN, PURE WOOL FABRICS BY CATHRYN ELIZABETH LEE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING UNIVERSITY OF NEW SOUTH WALES SUPERVISORS: ASSOCIATE PROFESSOR MARK HOFFMAN, EMERITUS PROFESSOR MIKE PAILTHORPE, DR SURINDER TANDON A Thesis Submitted for Fulfillment of the Degree of Doctor of Philosophy FEBRUARY, 2006 “Woollens should be washed early in the morning, on a bright, breezy day for preference. The more quickly they are dried the less they will shrink” Common-Sense Laundry Book, p50, The NSW Cookery Teachers’ Association, George B. Philip & Son, Sydney (circa 1920). i ABSTRACT The washing of wool textiles has been an ongoing problem for the wool industry as the conditions of washing, especially in an automatic washing machine invariably lead to the felting shrinkage of the fabric. Much research effort has gone into the prevention of felting shrinkage to make wool fabrics ‘machine washable’, however the processes which have been most effective in achieving this alter the properties of the fibres. This project has been an investigation into the reasons for the shrink-resistance of a woven, pure wool, fabric that has not been treated with any chemical shrink-resist treatments. The fabric was developed by Canesis Network Limited, as part of ongoing research into weavable singles yarns. It has been found that, for the fabrics in this project, felting shrinkage resistance is dependent upon a unique yarn structure with high levels of twist, tight fabric construction with high end and pick density and short float lengths, and finishing processes which permanently set the fabric using heat and steam under lateral compression. This combination of factors means that the individual fibres are so tightly bound in the yarns and the fabric structure, and so well set in their close configuration that they are unable to move in washing and cause felting. The density of the fabric was found to be the measure that best described the reasons for the changes the felting shrinkage of the fabric. Due to the recognised importance of the scales and the directional frictional effect in felting experiments were carried out to determine if there had been any change in the frictional properties of the fibres through low stress mechanical testing. Furthermore, as changes to wool chemistry have been used extensively in other shrink-resistance treatments, chemical testing was carried out. It was found that changes took place in the parameters measured in these tests; however, they were unable to explain the changes in felting shrinkage. 1 CONTENTS STATEMENT OF ORIGINALITY..................................................................................ii COPYRIGHT STATEMENT..........................................................................................iii ABSTRACT...................................................................................................................... 1 CONTENTS...................................................................................................................... 2 ACKNOWLEDGEMENTS............................................................................................ 18 ABBREVIATIONS ........................................................................................................ 21 CHAPTER 1 PROJECT BACKGROUND ....................................................................22 CHAPTER 2 HYPOTHESIS..........................................................................................23 CHAPTER 3 LITERATURE REVIEW, FELTING AND OTHER FORMS OF WOOL SHRINKAGE AND FINISHING OF WOOL FABRICS................................. 25 3.1 INTRODUCTION .......................................................................................... 25 3.2 THE FELTING PROCESS............................................................................. 25 3.3 FRICTION IN WOOL.................................................................................... 26 3.4 THEORIES ON SCALES AND FRICTION ................................................. 27 3.4.1 “The Ratchet Mechanism”...................................................................... 27 3.4.2 “The Ploughing Mechanism”.................................................................. 28 3.4.3 Other Theories ........................................................................................ 28 3.5 CONDITIONS OF FELTING ........................................................................ 29 3.5.1 Temperature ............................................................................................ 29 3.5.2 pH and The Action Of Soaps And Detergents........................................ 30 3.6 FIBRE PROPERTIES AFFECTING FELTING............................................ 31 3.6.1 Fibre Length............................................................................................ 31 3.6.2 Fibre Diameter ........................................................................................ 32 3.6.3 Fibre Crimp............................................................................................. 33 3.6.4 Elastic Properties/Elasticity .................................................................... 34 3.7 YARN AND FABRIC PROPERTIES AFFECTING FELTING................... 35 3.8 THEORIES ON WOOL FRICTION AND FELTING................................... 36 3.9 WOOL FABRIC FINISHING PROCESSES ................................................. 38 3.9.1 Scouring .................................................................................................. 38 3.9.2 Milling..................................................................................................... 40 3.9.3 Drying ..................................................................................................... 41 3.9.4 Carbonising............................................................................................. 42 2 Contents 3.9.5 Raising and Brushing.............................................................................. 43 3.9.6 Setting and Pressing Processes ............................................................... 43 3.9.6.1 Crabbing.............................................................................................. 43 3.9.6.2 Potting................................................................................................. 44 3.9.6.3 Beaming .............................................................................................. 44 3.9.6.4 Decatising ........................................................................................... 45 3.9.6.5 Pressing............................................................................................... 47 3.9.7 Singeing And Shearing ........................................................................... 48 3.9.8 London Shrinkage................................................................................... 48 3.10 CONVENTIONAL SHRINKPROOFING METHODS................................. 49 3.10.1 Degradative Processes ............................................................................ 50 3.10.1.1 Chlorination Processes........................................................................ 51 3.10.1.2 Other Degradative Processes .............................................................. 52 3.10.2 Electrical Discharge Treatments Or Plasma Treatments ........................ 53 3.10.2.1 Glow Discharge Treatments ............................................................... 53 3.10.2.2 Corona Treatments.............................................................................. 54 3.10.3 Enzyme Processes................................................................................... 54 3.10.4 Polymer Treatments ................................................................................ 55 3.10.5 Other Methods Of Preventing Shrinkage................................................ 57 3.11 OTHER FORMS OF SHRINKAGE IN WOOL FABRICS........................... 57 3.11.1 Relaxation Shrinkage.............................................................................. 57 3.11.2 Hygral Expansion.................................................................................... 57 3.12 SETTING OF WOOL FABRICS ................................................................... 59 3.13 SUMMARY.................................................................................................... 61 CHAPTER 4 MATERIALS AND METHODS ............................................................. 62 4.1 FABRIC PRODUCTION: WEAVING, FINISHING, AND SAMPLING.... 62 4.1.1 Weaving .................................................................................................. 62 4.1.2 Finishing And Sampling ......................................................................... 64 4.1.2.1 Plain Weave: Pilot Production............................................................ 65 4.1.2.1.1 Pressure Decatising Cycle................................................................... 67 4.1.2.2 Plain Weave: Bulk Production ............................................................ 67 4.1.2.3 Twill Fabric Production ...................................................................... 70 4.2 SAMPLE PREPARATION AND TEST METHODS.................................... 74 3 Contents 4.2.1 Measurement Errors................................................................................ 74 4.2.2 Sample Preparation................................................................................