STUDIES IN SINGLE-STAGE PREPARATORY PROCESSES FOR COTTON FABRICS

Transcription

1 STUDIES IN SINGLE-STAGE PREPARATORY PROCESSES FOR COTTON FABRICS A thesis submitted in fulfilment of the requirements for the award of the degree of DOCTOR OF PHILOSOPHY by N. SUKUMAR ORLK DEPARTMENT OF TEXTILE TECHNOLOGY INDIAN INSTITUTE OF TECHNOLOGY, DELHI December 1985

2 )1.:1) ICATED rr() NI LOV MO`Fil N, IKA 1,,,AN'S1 1

3 C: R T I q' ICA TE rhis is to cc rtify that the thesis entitled "STUDIES IN SING LE -STUA GE PREPA RA TORY PROCESSES FOR COTTON FA I3RICS", Ltp' ubutittta] by Mr, N. SW:KUMAR, to the Indian Institute of 'rechnology, Dulhi for the award of the degree of DOCTOR OF PH ILOSOPH V in the Department of Textile Technology, is a record of honalide research work carried out by him. Mr. N. Sukumar has 'hi 'd with my guidance and supervision and has fulfilled all the roqui roll-writs for the submission of the thesis. The results contained in this thesis have not been submitted part or in full, to any other University or Institute for the award or dip I,oxna. M, L. OULRAjANI, Professor and Bead, Dept. of Textile Technology, I. I. T., New Delhi.

4 ACKNOWLEDGEMENTS I wish to acknowledge gratefully all those who assisted me in the completion of the dissertation. I offer my sincere gratitude to my research adviser Prof. ivi.l.gulrajani, Head, Department of Textile Technology for his meticulous guidance and his constructive personal involvement in my work till its completion which incited me to accomplish it in a good manner. I acknowledge may indebtedness to my cooperative colleagues and friends specially to Mr. R. Venkatraj, Miss Manjeet Bhatia, Mr M. E. Vincent Vinoba ind Mr. R.K. Suresh who envinced unstinted interest in ray work. I also acknowledge the untiring enthusiasm with which Mrs. P.N. Revathi and Mr. P. Ravi who helped in bringing out the thesis to a presentable form. I wish to record my appreciation to ray wife Mrs. S. Rajeswari for the patience, cooperation and encouragement extended during my research work. AILA--il:-/s - ( N. SUKUIVIAR

5 ABSTRACT Fabric preparation has been considered as the back-bone of the chemical processing of cotton textiles. Elaborate procedures have been evolved to ensure perfect fabric preparation, with the result this has become the most time consuming, energy-intensive and laborious step in the chemical processing of cotton fabrics. Dowever, with the mounting energy crisis, during last five years many investigations have been directed to either shorten the fabric preparation sequence or to make it less energy intensive. A single-stage preparatory (SSP) process involving the use of emulsified solvent as the scouring agent and hydrogen peroxide as the bleaching cum desizing agent has been standardised by the author. This thesis is an extension of the previous study and is concerned with the further optimisation of the process as well as with the mechanism of decomposition of hydrogen peroxide. The system has also been investigated with respect to its suitability for low-temperature fabric preparation using hydrogen peroxide as well as sodium hypochlorite. A critical examination of the above mentioned single-stage preparatory (SSP) process indicated that the phi of the fabric lowered from to near neutral during the treatment and a substantial quantity of hydrogen peroxide remained undecomposed on the fabric. In 'der to further optimise the process and to fully utilise the hydrogen peroxide on the padded fabric, a study was undertaken to investigate

6 the effect of ph buffers on the SSP process as well as on the decomposition of hydrogen peroxide on the fabric. Two kinds of cotton fabric, one containing acrylic size (Cambric 1) and the other containing starch size (Cambric 2) were subjected to the SSP process with the buffered and unbuffered solution. From the results of these measurements it has been observed that the SSP process is accelerated by the phi buffers, with the result the process can be completed in a shorter time period. Alternatively, one can reduce the quantity of hydrogen peroxide from 1-2% to 0.5-1% and achieve the similar properties of the prepared fabric. Since it is not known how the decomposition of hydrogen peroxide in the SSP process proceeds, an investigation was undertaken to follow the pattern of decomposition of hydrogen peroxide. The decomposition of hydrogen peroxide is found to follow pseudo- first order reaction kinetics. It has also been observed that the hydrogen peroxide decomposes at a faster rate from the buffered solutions. Furthermore, the acrylic size of the Cambric 1 seems to stabilize hydrogen peroxide. However, the damage to cellulose is more in Cambric 1 than in Cambric 2 fabric. Since the SSP process is a solvent-assisted scouring process, it was surmised that it should be effective in removing wax from grey cotton at low -temperature. Moreover, since hydrogen peroxide

7 is capable of bleaching at a low-temperature, an attempt was made to develop a low-temperature SSP process. Of the five different compounds investigated for their suitability to activate/stabilise the hydrogen peroxide in low-temperature SSP process, only trisodium phosphate and tetrasodium pyrophosphate were found to be suitable, and a recipe for the low-temperature SSP process has been suggested. From a study of the mechanism for the activation/stabilisation of peroxide with sodium silicate, it is concluded that the stabilisation of peroxide is by the precipitated silica gel and not by sodium silicate. Baying established that a low-temperature SSP process was feasible, attention was given to the sodium hypochlorite bleaching. An investigation was undertaken to optimise the process conditions for process utilising sodium hypochlorite as desizing cum bleaching :igent. A miniature cistern was fabricated and used. A second-order response surface design of five levels, four variables and utilising :31 different conditions, was chosen to ascertain the optimum process conditions and to evaluate the effect of various bleaching conditions on the properties of the bleached fabrics. A comparison of the properties of the fabric samples bleached with the SSP process with that of the properties of the fabric prepared by the conventional hypochlorite process has been made and the economically practicable optimum process coudit4id,1, have been reported.

8 In order to ascertain the mode of decomposition of sodium hypochlorite in the SSP bleach baths, an investigation on kinetics of decomposition of sodium hypochlorite was carried out. From the results of this study, it is found that the hypochlorite decomposition follows as second order reaction kinetics. The extent of decomposition. of sodium hypochlorite in SSP process is higher at ph 9 as compared to ph 10 and 11, both in the presence and absence of cotton, The rate constant values are high when cotton is present in the bleach bath, The copper number and carboxyl content of the bleached samples increase with decrease in ph of the bleach bath. * fol **** 0 *****

9 CONTENTS -age No. PART 1 INTRODUCTION AND REVIEW OF LITERATURE 1.1. Introduction 2 1,2 Process De v e lo pm c nt s,' Desizing Processes 3 1,2.2 Scouring Processes Bleaching Processes Auxiliaries used in Textile Preparation 17 1_ 3,1 Surface Active Agents Sequestering Agents in Scouring and Bleaching Miscellaneous Scouring Assistants Stabiliser in Peroxide Bleaching Recent Trendsin Fabric Preparation Cold Bleaching Processes Combined Preparatory Processes 20 PART 2 THE SINGLE STAGE PREPARATORY PROCESSES BASED ON HYDROGEN PEROXIDE Section 2A Effect of ph Buffers on the SSP Process 2A. 1 Introduction $6 2A 1, 1 Concept of ph Buffers 36 2A 1,2 Effect of ph in Peroxide Bleaching 40

10 2A.1 3 Aim of the Work 44 2A. 2 Experimental 45 2A Materials 45 2A, 2, 2 Chemicals 46 2A. 3 Fabric 'I' reatment 46 2A, 2.4 Test Methods 48 2A. 3 Results and Discussion 50 2A. 3, 1 Whiteness Index 53 2A, 3. 2 Percent Strength Loss 54 2A Wetting Time 56 2A Starch Content 56 2A Stability of Bleach Baths 57 2A. 3.6 Optimisation 57 Section 213 Kinetics of Peroxide 1-.)ecomposition in the SS') Process 213, 1 Introduction Chemical Kinetics Kinetics of Thermal Decomposition of 63 Hydrogen Peroxide Aim of the Work Experimental Materials , 2 Chemicals , 2, 3 Fabric Treatment 66

11 Test Methods Results and Discussion , 3. 1 Kinetics of Decomposition Copper Number and Carboxyl content 76 Section 2C A Low-Tempsrature SSP Process 2C, 1 Introduction 80 2C Cold-Bleaching Process A ctivation/stabilisation of Hydrogen Peroxide in 83 Cold-Bleaching Process 2C, 1, 3 Aim of the Work 04 2C. 2 Experimental 84 2C Materials 84 2C Chemicals 84 2(..: Fabric Treatinent 8 5 2C. 2.4 Test Methods 85 2C. 3 Results and Discussion 89 2G Whiteness Index 89 2C. 3, 2 Strength Loss 80 2C. 3.3 Ash Content 90 2C. 3,4 Wetting Time 92 2C Optimised Process Conditions 92 2C Me chanisam of Stabilisation/A ctivation. of 93 Peroxide

12 PART 3 A SINGLE-STAGE PREPATORY PROCESS BASED ON SODIUM HYPOCHLoRITE Section 3A Optimisation of SSP Process Conditions 3A,1 Introduction 98 3A.1. 1 Sodium Ilypochlorite Bleaching Process 99 3A, 1., 3 Developments in Ilypochloritc., Bleaching 101 3A. 1.4 Aim of the Work A, 2 Experimental 105 3A 2.1 Materials 105 3A. 2.2 Chemicals 105 3A, 2.3 Design of Experiments 105 3A. 2.4 Fabric Treatment 110 3A, 2.5 Conventional Process 110 3A. 2.6 Testing Methods 111 3A, 3 Results and Discussion 112 3A. 3.1 Whiteness Index 117 3A. 3,2 Tensile Strength 117 3A 3,3 Wetting Time 118 3A 3.4 Statistical Analysis 119 3A 3,5 Optimisation 119 3A. 3.6 Yellowness During Storage 120

13 Section 3B Kinetics of Hypochlorite Decomposition in the SSP Process Introduction Self-Decomposition of Sodium Hypochlorite A ction of Hypo chlorite on Cellulose A int of the Work Experimental Materials ,2 Chemicals 126 3B. 2.3 Bleaching Procedure Test Methods ,3 Results and Discussion Kinetics of Sodium ilypochlorite Decomposition ,3,2 Chlorate Formation and Oxygen Evolution ,3.3 Damago to Cellulose ,4 Conventional Bleaching 137 PART 4 CONCLUSIONS 4,1 Conclusions 139 REFERENCES 143 LIST OF PUBLICATIONS 152