INFLUENCE OF FIBRE CHARACTERISTICS ON SPINNING STABILITY AND STRUCTURE PROPERTY RELATIONSHIPS OF ROTOR AND RING SPUN YARNS

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1 INFLUENCE OF FIBRE CHARACTERISTICS ON SPINNING STABILITY AND STRUCTURE PROPERTY RELATIONSHIPS OF ROTOR AND RING SPUN YARNS By P. K. MAJUMDAR A thesis submitted to the Indian Institute of Technology, New Delhi for the award of the degree of DOCTOR OF PHILOSOPHY o E LM% DEPARTMENT OF TEXTILE TECHNOLOGY INDIAN INSTITUTE OF TECHNOLOGY, DELHI -MARCH,-1993_

2 CERTIFICATE This is to certify that the thesis entitled "Influence of Fibre Characteristics on Spinning Stability and Structure-property Relationships of Rotor and- Ring Spun Yarns", submitted by Mr. P.K. Majumdar to the Indian Institute of Technology,Delhi, for the award of Degree of Doctor of Philosophy is a record of the bonafide research work carried out by Mr. P.K. Majumdar. He has worked under our guidance for the submission of this thesis, which to our knowledge has reached the requisite standard. This thesis or any part thereof, has not been submitted to any other University or Institution for the award of any degree or diploma. cç- (A.K. Sengupta) (R. Chattopadhya ) Thesis Supervisors Department of Textile Technology Indian Institute of Technology New Delhi

3 ACKNOWLEDMENTS I place on record my profound gratitude to my Research Supervisors, Prof. A.K. Sengupta, and Dr. R. Chattopadhyay, Department of Textile Technology, Indian Institute of Technology, Delhi, for all their insightful guidance, active cooperation and encouragement throughout the period of my research project. It is my privilege to have Prof. M.L. Gulrajani, Prof. B. Dutta and Prof. P.K. Hari as Heads of Department during the tenure of my research and I gratefully acknowledge their help and encouragement at every stage of my work. I am also grateful to Dr. S.M. Ishtiaque for his active help and cooperation in conducting my research work. My sincere thanks are due to Dr. P.C. Dasgupta, ex-principal, Institute of Jute Technology, Calcutta for providing me facilities for carrying out a part of my research work at their institution. I am very much indebted to Dr. D. Sur and Mr. A. Mukherjee for evincing a keen interest in my work and rendering me all possible help during my stay at the laboratory. I am very much thankful to Dr. B. Chatterjee, College of Textile Technology, Serampore, for his active help and valuable suggestions at different stages of my work. I am indebted to Mr. N.L. Tarafdar, Mr. Satayaki Bhattacharya and Mr. A. Banerjee for taking additional burden during my absence from my institution for more than three years. i

4 I gratefully acknowledge the financial support provided for my research project by the Ministry of Human Resource and Development, Govt. of India, under Quality Improvement Programme. I am also grateful to Dr. S.M. Chatterjee, Principal, College of Textile Technology, Serampore and Secretary, Education Department, Govt. of West Bengal, for sponsoring my research programme. For all their help extended to me in one way or another in accomplishing my task, I wish to thank my friends and colleagues, especially, Mr. A. Das, Mr. J.K. Sensarma and Mr. P.K. Dey. I wish to acknowledge the assistance rendered by M/s J.K. Dang, V.A. Passi, R. Khattar, M.L. Khanna and all other laboratory staff of the Department. I am also very much thankful to Mr. R. Arora for neatly typing the thesis and to Mr. K.G. Padam for neatly tracing all the figures. With deep sense of gratitude, I acknowledge the neverfailing loving care, concern and encouragement of Late S.K. Sengupta, Mr. S.K. Sengupta and Mrs. M. Sengupta and the cooperation and concern of Mr. S. Sengupta, Mrs. S. Sengupta and Mr. B. Sengupta. ii

5 Finally, I appreciate the understanding and patience of my wife Mrs. Sunanda Majumdar and my little daughter Sanghamitra, in enduring my absence for three long years, which act has been a source of strength and inspiration for me in pursuing my research programme. March 1993 New Delhi (P.K. MAJUMDAR) iii

6 DEDICATED TO MY MOTHER

7 ABSTRACT Amongst the many yarn formation techniques developed so far, only rotor spinning has been able to establish itself as an alternative to ring spinning particularly in the coarse to medium count ranges. Though initially used for processing cotton only, spinning of manmade fibres and blends is also being carried out today using this system incorporating some design modifications in rotor and opening roller to suit the synthetic fibres. Of late, it has been realized that some modifications in fibres may also be necessary for successful spinning of synthetic fibres. In this regard, cross-sectional shape of fibres and also surface frictional characteristics are likely to be of paramount importance. The mechanism of yarn formation in rotor is different from that of ring spinning and, as a result, the structure of rotor spun yarn varies considerably from that of ring spun yarns. In ring spinning fibres are held at one end by the front roller nip while being twisted, but in rotor spinning there is no such positive grip over the fibres. The fibres are pressed against the rotor wall by centrifugal force. Being open-end system of spinning, fibre characteristics are likely to have significant influence on the spinning performance and structure-property relationship of these yarns. A large volume of research work published on rotor spinning has shown that the difference in tensile

8 behaviour between rotor and ring spun yarns is mainly due to their structure. While the effects of various fibre and process parameters on structure and properties of rotor spun yarns have been reported, the effect of the cross-sectional shape of fibres and fibre surface frictional characteristics on structure and tensile behaviour of rotor and ring spun yarns have not been studied so far. In the present work, attempts have been made to investigate these aspects in detail. Amongst the different parameters through which the yarns are characterized, twist is the most important, particularly when the properties of different yarns are being compared. In case where comparisons are made between the properties of ring and rotor spun yarns it is very much essential that their level of twist must be specified. Measurement of twist of rotor spun yarn is difficult due to its structure. The untwist-twist method of twist measurement was used in the present study with a tension of 1.5 gf/tex. The accuracy of this method was verified by studying the total twist to break (measured twist + added twist to break) at various twist levels. In case of ring spinning there is hardly any loss of twist as the fibres are held firmly at one end by the front roller nip while being twisted. But in case of rotor spinning there is considerable loss in twist as has already been reported by many authors. As there is no positive grip over the fibres during spinning it is very much likely that both the minimum twist to spin and the twist transmission efficiency which ii

9 determine the spinning stability would be affected by many of the fibre properties. Spinning stability has been determined in terms of twist transmission efficiency and the minimum twist which would allow an uninterrupted spinning of 200 metres of yarn. The minimum twist to spin continuously is likely to be influenced mainly by the minimum amount of torque required to be generated to consolidate the fibres and also the level of fibre to fibre friction (cohesive force) which would help the forming yarn to withstand the spinning tension. The twist transmission efficiency is affected by the leakage of twist in the rotor groove and this in turn is likely to be influenced by the amount of torque transmitted in the rotor groove. The propagation of torque in the rotor groove is, however, restricted by higher fibre to metal friction. In the present study polyester and acrylic fibres of different cross-sectional shapes were taken. Fibre torsional rigidity and surface frictional characteristics were found to vary due to their differences in the cross-sectional shapes. The torsional rigidity and fibre surface friction (fibre to fibre and fibre to metal) were found to influence both minimum twist and twist transmission efficiencies. Trilobal polyester with the lowest torsional rigidity and the highest fibre to fibre and fibre to metal friction was found to give the lowest minimum twist and the highest twist transmission efficiency. In case of acrylic fibres, the torsional rigidity values did not differ significantly and, thus, the iii

10 spinning stability was mainly influenced by fibre surface friction. Acrilan with the highest cohesive force required the lowest minimum twist to spin continuously and Creslan with the highest fibre to metal friction showed the highest twist transmission efficiency. The fibre surface friction, altered by varying the nature and amount of spin finishes applied, was also found to influence the minimum twists and twist transmission efficiencies in a similar manner. The structures of rotor and ring spun yarns have been well researched. However, there is little information as to how these structures are affected by cross-sectional shape and surface friction of fibres. In the present study the structure has been characterized mainly by packing factor and migrational parameters. Packing coefficient which is generally less for rotor spun yarns, has been found to be maximum for trilobal polyester fibres in comparison to circular and hollow fibres. In case of acrylic fibres, Acrilan with kidney bean cross-section has shown maximum packing for rotor spun yarns. However, differences in packing is not so much visible in ring spun yarns. While studying the influence of fibre surface friction, altered by the application of varying nature and amount of spin finish, roving separation force has been found to be well correlated with packing factor especially for rotor spun yarns. Cotton fibres were also used in this study. Cotton fibres were mercerized in the loose state to change the surface frictional characteristics. Rotor spun yarns with mercerized cotton have shown higher packing factor in iv

11 comparison to yarns with unmercerized cottons. All migrational parameters except mean fibre position have been found to be highly -influenced by cross-sectional shape and surface frictional characteristics of fibres in case of ring spun yarns. Trilobal has shown maximum migration followed by circular and hollow- fibres in case of polyester and Acrilan has shown maximum migration followed by Creslan and Orlon in case of acrylic fibres. Fibre bending rigidity and cohesive force have been found to mainly influence the migration in yarns. In case of fibres with different surface frictional characteristics, interfibre coefficient of friction as expressed by roving cohesive force has been found to influence the migrational parameters studied. Rotor spun yarns in general have shown poorer migration in comparison to ring spun yarns. However, here also migrational parameters have been found to be influenced by cross-sectional shape and surface frictional characteristics of fibres though their influences have been found to be less pronounced as compared to ring spun yarns. It is well known that tensile strength of rotor spun yarns are lower than that of corresponding ring spun yarns. The reason for this has been ascribed to lesser contribution of fibres in sharing the loads which ultimately results in lesser number of fibres rupturing during yarn failure. In the contribution to tensile load registered during failure, apart from the number of fibres rupturing, an equally important factor is whether the fibres fail u

12 simultaneously at the same location in the yarn crosssection, in which case the failure is instantaneous and catastrophic and the rupture zone is very short and sharp. This would then result in a more even load sharing between fibres, thus causing a high strength translation efficiency from fibre to yarn. On the other hand, if the number of fibres rupturing is much lower and also if the fibres are not rupturing simultaneously at the same place, the rupture zone is going to be elongated which would lower the strength of the yarn. Therefore, a detailed study of the phenomenon of rupture is necessary for proper understanding of the way the fibres participate in sharing load during tensile failure. Yarn strength has been found to relate well with the number of fibres broken at the rupture point. The rupture zone was studied using two methods. In one method the number of broken fibres was estimated by tracer fibre technique. Since the estimation of broken fibres through tracer fibre technique is a tedious process, a new method has been used where the weight of the fibre material in the rupture zone, taken from the two ends of a broken yarn, has been recorded. The weight of the rupture zone has an inverse relation with the number of broken fibres and so with the yarn strength. A good correlation was found between these two methods. Tensile behaviour of rotor spun yarns has been found to be highly influenced by cross-sectional shape of fibres and also fibre surface frictional characteristics. Ring spun vi

13 yarns have shown higher strength translation efficiency than rotor spun yarns. Fibre cross-sectional shapes have been found to influence strength translation efficiency significantly for rotor spun yarns. Trilobal and Acgilan showed highest packing factors as well as translation efficiency for polyester and acrylic yarns respectively. Surface friction altered through application of spin finish has a pronounced effect on cohesive force and packing and in turn on tenacity of rotor spun yarns. In case of ring spun yarns, neither cross-sectional shapes of fibres nor the level of interfibre friction have any pronounced effect on strength translation efficiency. The influence of stress-strain characteristics of fibres on strength translation efficiency has been studied in some detail. It is well known that all fibres constituting a yarn do not rupture during tensile failure of a yarn. Some fibres rupture while some slip. Moreover, the fibres that rupture do not fail simultaneously. The strength of the yarn is, thus, governed by the manner of load sharing of the fibres in a yarn. When a group of fibres fails, the contribution of other fibres towards load sharing would depend on the levels of strain reached by them. Thus the shape of stress-strain curve of a fibre, particularly in the vicinity of failure strain of yarn, is likely to have a considerable influence on the contribution of stress by individual fibres which would ultimately determine the failure stress of the yarns. This has been found to be so particularly in the case of rotor spun yarns. vii

14 CONTENTS Page No. CHAPTER 1 INTRODUCTION 1 CHAPTER 2 REVIEW OF LITERATURE 2.1 structure of rotor and ring spun yarns Wrapper fibres A Classification of wrapper fibres or belts B Theory and mechanism of formation of wrapper 10 fibres or belts Fibre migration Geometry of yarn twisting and 21 migration Mechanism of axial migration A Tension mechanism B Geometric mechanism Combination of tension and geometric 30 mechanism Random causes A Migration in ring spun yarns B Migration in rotor spun yarns Twist structure of yarn Definition of twist Purpose of twist The mechanism of twist Theoretical and measured twist in 37 rotor and ring spun yarns Twist measurement 41 (i)

15 2.2 Structure-strength relation Fibre rupture Influence of fibre properties 48 CHAPTER 3 TWIST TRANSMISSION EFFICIENCY AND REQUIREMENTS OF MINIMUM TWIST IN ROTOR SPINNING 3.1 Introduction Experimental Materials used Sample preparation Spin finish application Fibre dyeing A Preparation of rotor yarn samples E Preparation of roving C Preparation of rotor yarn for 62 cluster studies Test methodology Measurement of tensile properties of 62 fibres Evaluation of bending rigidity of 62 fibres Measurement of torsional rigidity of 63 fibres Measurement of fibre surface friction Measurement of cohesive force Estimation of minimum twist to spin Measurement of cluster size Measurement of yarn twist Measurement of yarn irregularities 70

16 3.3 Test Results and discussions Characterization of fibre property Requirement of minimum twist Influence of fibre cross-sectional 72 shape Influence of rotor speed Twist loss during spinning 80 CHAPTER'4 INFLUENCE OF FIBRE CROSS-SECTIONAL SHAPE AND SURFACE FRICTION ON STRUCTURE OF ROTOR AND RING SPUN YARNS 4.1 Introduction Experimental Materials used Sample preparation Cotton fibre mercerization A Preparation of rotor spun yarn samples B Preparation of roving C Preparation of ring spun yarn samples Test methodology Measurement of cohesive force Measurement of packing factor A Observation of axial migration 104 by tracer fibre technique B Characterization of migration Test results and discussions Packing factor Influence of fibre cross-sectional 111 shape

17 Influence of fibre surface friction Influence of cross-sectional shape and 121 surface friction of cotton altered by mercerization Fibre migration 124 CHAPTER Effect of cross-sectional shape A Mean fibre position B R.M.S. deviation C Mean migration intensity D Coefficient of migration Effect of spin finish 138 STUDIES ON FAILURE BEHAVIOUR OF YARNS 5.1 Introduction Experimental Materials used Sample preparation Test methodology Measurement of cohesive force Measurement of tensile properties 152 of yarns Estimation of fibre rupture Tracer fibre technique A Observation of tracers B Identification of broken or 153 slipped ends of fibre Weight of the rupture zone Test results and discussion Study of yarn failure behaviour 155 (iv)

18 5.3.2 Effect of cross-sectional shape of fibres Effect of spin finish Effect of mercerization of cotton fibres 178 CHAPTER 6 INFLUENCE OF FIBRE CHARACTERISTICS STRUCTURAL PARAMETERS ON MECHANICAL BEHAVIOUR OF ROTOR AND RING SPUN YARNS 6.1 Introduction Experimental Materials used Sample preparation Test methodology Measurement of tensile properties 183 of yarns Measurement of tensile properties 191 of fibres 6.3 Results and discussions Yarn tenacity Effect of fibre cross-sectional shape Effect of fibre surface friction Effect of mercerization of cotton 225 fibres Elongation at break Effect of fibre cross-sectional shape Effect of fibre surface friction Effect of mercerization of cotton 239 fibres Initial modulus Effect of fibre cross-sectional shape Effect of fibre surface friction 244 (v)

19 Effect of mercerization of cotton 249 fibres Specific work of rupture 249 CHAPTER Effect of fibre cross-sectional shape Effect of fibre surface friction Effect of mercerization of cotton 255 fibre EFFECT OF FIBRE TENSILE CHARACTERISTICS ON TENSILE BEHAVIOUR OF YARNS 7.1 Introduction Experimental Materials used Sample preparation Test methodology Measurement of fibre to fibre 265 and fibre to metal coefficient of friction Measurement of cohesive force Measurement of tensile properties 267 of fibres & yarns Estimation of fibre rupture Measurement of packing factor Test results and discussion Characterization of fibre properties Yarn packing Tensile behaviour of yarns Tenacity Elongation at break 279 (vi)

20 Initial modulus Specific work of rupture 282 CHAPTER 8 SUMMARY AND CONCLUSIONS 288 BIBLIOGRAPHY 305 APPENDIX I 312 APPENDIX II 314 APPENDIX III 315 APPENDIX IV 317