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
)1.:1) ICATED rr() NI
LOV MO`Fil N, IKA 1,,,AN'S1 1
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.
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.
AIL
A--il:-/s„ - ( N. SUKUIVIARABSTRACT
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 10. 5 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
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
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.
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.
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CONTENTS
-age No.
PART
1
INTRODUCTION AND REVIEW OF LITERATURE1.1. Introduction 2
1,2 Process De v e lo pm c nt s , '
1.2.1 Desizing Processes 3
1,2.2 Scouring Processes 8
1.2.3 Bleaching Processes 12
1. 3 Auxiliaries used in Textile Preparation 17
1_ 3,1 Surface Active Agents 17
1.3.2 Sequestering Agents in Scouring and Bleaching 22
1.
3.3 Miscellaneous Scouring Assistants 23 1.3.4 Stabiliser in Peroxide Bleaching 24 1.4 Recent Trendsin Fabric Preparation 261.4.1 Cold Bleaching Processes 27
1.4.
2 Combined Preparatory Processes 20PART 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 362A
1,2 Effect of pH in Peroxide Bleaching 402A.1 3 Aim of the Work 44
2A . 2 Experimental 45
2A . 2. 1 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 . 3. 3 Wetting Time 56
2A . 3. 4 Starch Content 56
2A . 3. 5 Stability of Bleach Baths 57
2A . 3.6 Optimisation 57
Section 213 Kinetics of Peroxide 1-.)ecomposition in the SS') Process
213, 1 Introduction 62
213. 1.1 Chemical Kinetics 62
213. 1. 2 Kinetics of Thermal Decomposition of 63 Hydrogen Peroxide
213. 1. 3 Aim of the Work 65
213.2 Experimental 66
213.2.1 Materials 66
213. 2, 2 Chemicals 66
213, 2, 3 Fabric Treatment 66
213. 2. 4 Test Methods 67
213. 3 Results and Discussion 71
213, 3. 1 Kinetics of Decomposition 71
213. 3.2 Copper Number and Carboxyl content 76
Section 2C A Low-Tempsrature SSP Process
2C, 1 Introduction 80
2C. 1. 1 Cold-Bleaching Process 80
1. 2 A ctivation/Stabilisation of Hydrogen Peroxide in 83 Cold-Bleaching Process
2C, 1, 3 Aim of the Work 04
2C. 2 Experimental 84
2C. 2. 1 Materials 84
2C. 2. 2 Chemicals 84
2(..:. 2. 3 Fabric Treatinent 8 5
2C. 2.4 Test Methods 85
2C. 3 Results and Discussion 89
2G. 3. 1 Whiteness Index 89
2C. 3, 2 Strength Loss 80
2C. 3.3 Ash Content 90
2C. 3,4 Wetting Time 92
2C. 3. 5 Optimised Process Conditions 92
2C. 3. 6 Me chanisam of Stabilisation/A ctivation. of 93 Peroxide
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 98
. 1.2 Bleaching Process 99
3A, 1., 3 Developments in Ilypochloritc., Bleaching 101
3A A. 1.4 Aim of the Work 104
3.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
Section 3B Kinetics of Hypochlorite Decomposition in the SSP Process
313.1 Introduction 122
313.1.1 Self-Decomposition of Sodium Hypochlorite 122 313.1.2 A ction of Hypo chlorite on Cellulose 123
313.1.3 A int of the Work 125
313.2 Experimental 120
313.2.1 Materials 126
313.2,2 Chemicals 126
3B. 2.3 Bleaching Procedure 126
313.2.4 Test Methods 127
313,3 Results and Discussion 129
313.3.1 Kinetics of Sodium ilypochlorite Decomposition 129 313,3,2 Chlorate Formation and Oxygen Evolution 133
313,3.3 Damago to Cellulose 136
313.3,4 Conventional Bleaching 137
PART 4 CONCLUSIONS
4,1 Conclusions 139
REFERENCES 143
LIST OF PUBLICATIONS 152
