Studies on drawing of polyethylene terephthalate by the prototype incremental drawing process

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STUDIES ON DRAWING OF POLYETHYLENE

TEREPHTHALATE BY THE PROTOTYPE INCREMENTAL DRAWING PROCESS

By

ANJAN KUMAR MUKHOPADHYAY

Centre for Materials Science and Technology

SUBMITTED

IN FULFILMENT OF THE REQUIREMENTS OF THE DEGREE OF

DOCTOR OF PHILOSOPHY

6.14%

to the

INDIAN INSTITUTE OF TECHNOLOGY, DELHI

SEPTEMBER, 1990

CERTIFICATE

This is to certify that the thesis entitled

"STUDIES ON DRAWING OF POLYETHYLENE TEREPHTHALATE BY THE PROTOTYPE INCREMENTAL DRAWING PROCESS" being submitted by Mr.Anjan Kumar. Mukhopadhyay, to the Indian Institute of Technology, Delhi, for the award of the degree of Doctor of Philosophy in the Centre for Materials Science and Technology, is a record of bonafide research work carried out by him. Mr. Anjan Kumar Mukhopadhyay has worked under our guidance and supervision and fulfilled the requirements for the submission of the thesis.

The results contained in this thesis have not been submitted, in part or in full, to any other University or Institute for the award of any degree or diploma.

---

Centre for Materials Science and Technology,

Indian Institute of Technology Delhi, New Delhi-110016

(Bhaskar Dutta) Professor and Head

Department of Textile Tech.

Indian Institute of Technology Delhi, New Delhi - 110 016

ACKNOWLEDGEMENT

I wish to express my deep sense of gratitude and indebtness to Prof. Ashok Misra, Centre for Materials Science and Technology and to Prof. Bhaskar Dutta, Head, Department of Textile Technology, for their keen interest, valuable guidance and constant encouragement throughout the course of this research work. They provided me the opportunity to work in an entirely new area of research which was extremely challenging.

I express my sincere thanks to Prof. S.

Krishnamoorthy, Head, Centre for Materials Science and Technology, for his co-operation and encouragement.

I gratefully acknowledge the financial support provided for this research programme by the Department of Science and Technology, Govt. of India which made this research work feasible.

I would hereby like to thank Dr. L.R. Subbaraman, Senior Manager (Research and Development), Indian Organic Chemicals Limited for his interest in my work on Incremental drawing. I am thankful to him for his promptness in supplying us with PET samples and information whenever required.

I take this opportunity to thank Prof. M.V.

Sussman, Department of Chemical Engineering, Tufts

University, Massachusetts, USA, for his encouragement and the useful discussion that I had with him during my visit to the USA.

I am thankful to the Director, The Bombay Textile Research Association for his permission in getting some experimental work done in his laboratory.

I am very grateful to the staff members of various laboratories in the Textile Department and Centre for Materials Science and Technology for their help and co-operation.

I am very much indebted to Dr. S.K. Sett, Mr. A.K.

Rakshit, Mr. K.N. Bhaumik and Dr. S.K. Bhattacharya for their help and useful discussion that I had with them during the period of my research work.

I thank Mr. Sanchay Das for taking excellent photographs of the machine set-up. Thanks are due to my friends and colleagues for their help and co-operation.

I am thankful to Mr. Sanjay Arora, Mr. Vinod Kumar and Ch. Venugopal for their excellent work in the preparation of this thesis and to Mr. A.K. Biswas for neatly tracing out the figures.

Words are too poor to express the contribution of my parents who are the sole source of inspiration and

encouragement in my day to day life. I do feel from the core of my heart that it is only their constant blessings because of which the present research work is successfully completed.

(Anjan Kumar Muk

ABSTRACT

The Incremental Drawing Process (IDP) is a novel technique where the molecular structure of spun fibres are oriented by incremental stretching over several successive steps. The synthetic fibre is drawn between two bodies, one or both of which have a continuously increasing diameter.

Two different drawing body profiles have been used in the present investigation to get different drawing sequences.

Earlier work has shown that a significant improvement in the properties of Nylon-6 could be obtained by drawing at ambient temperatures. The latter phenomenon was ascribed to the better molecular alignment achieved by the IDP process as compared to the conventional drawing

v'

process (CDP) under identical processing conditions. The present work is an attempt towards exploring the potential of the IDP process for the drawing of PET spun at low as well as high speeds.

Since, the glass transition temperature (T ) of PET g

0 0

is in the range of 70 -80 C, it is necessary to draw PET fibre at elevated temperatures. As a first attempt, a chamber type of heating system with hot air blowing attachment was fabricated. Polyethylene Terephthalate partially oriented yarn (PET-POY) was successfully drawn by IDP at draw-ratios of 1.76, 1.84 and 2.00 with 12,13 and 15 steps respectively at a drawing speed of 300 m/min.

ii

Correspondingly, PET-POY was also drawn by CDP at equivalent draw-ratios and speed. At an equivalent draw-ratio of 2.0, the tenacity and initial modulus values for IDP were 0.50 and 9.38 N/tex respectively as compared to 0.39 and 8.33 N/tex for CDP. This showed that IDP registered tenacity values higher than CDP by about 28%. The higher tenacity of the fibre drawn by IDP as compared to CDP can be attributed to the existence of highly oriented amorphous regions in IDP drawn fibres. A model has also been proposed to explain the significant improvement in properties in IDP as compared to CDP.

In order to study the development of orientation, the fibres were collected from selected steps and analysed.

An advantage of using IDP for such a study is that the fibres obtained at different steps are part of the same continuous process and samples at different draw-ratios are obtained in one single experiment. In this study, PET-POY was drawn by IDP to a draw-ratio of 1.89 at a temperature of

0

85 C maintained with a heated chamber coupled to a hot air blowing system. It was demonstrated that IDP is an excellent technique to follow and analyse the process of drawing. The structural development could be correlated with the development of mechanical properties.

0

The attainment of temperature above 120 C was difficult in the chamber type of heating system whereas

111 0 0

high temperatures in the range of 200 -250 C was necessary for achieving high tenacity and high modulus fibre. Hence, a plate type heating system was used to attain the dual objectives. To achieve high tenacity fibre, PET filaments spun at different spinning speeds were drawn to equivalent _ draw-ratios with the two plate heaters with independent temperature control designed for IDP. PET-POY was drawn

0

keeping the (a) first heater temperature at 90 C and ranging 0 0

the second heater temperature from 140 C to 200 C (b) first 0

heater temperature at 85 C and ranging the second heater 0 0

temperature from 140 C to 200 C respectively. Similarly, low oriented PET was drawn with the first heater temperature

0 0

at 85 C and the second heater temperature varying from 140 C 0

to 200 C. It was observed that pre-orientation of the parent material was responsible for the change in properties. Highest value of tenacity was obtained in low oriented PET samples drawn to a draw ratio of 5.2 with the

0 0

temperature combination of 85 C/200 C. It registered a tenacity of 0.6 N/tex in IDP whereas tenacity of 0.49 N/tex was registered when drawn by the CDP under identical processing conditions. Thus an increase of 22% in tenacity value was evidenced.

Effect of drawing speed on the properties of PET-POY was also studied. The residence time in IDP is much higher than CDP and thus high speeds of drawing are possible by IDP. The multifilament PET-POY was drawn at 100, 200,

i

300, 500, 700 and 900 m/min at a draw ratio of 1.76 with the 0

temperature of 80 C. The properties increased upto a speed of 300 m/min, but no significant change was seen beyond 300 m/min. This was explained on the basis of rate of crystallisation and relaxation with respect to the residence time. It has been shown that IDP is capable of attaining high drawing speeds without affecting the properties or fibre breakage.

It has been clearly shown that the prototype system developed provides fibres with superior properties than those obtained by CDP. Furthermore, IDP can be used to prepare high strength fibres from commercially available conventional semi-crystalline polymers. It has also proved to be an excellent technique for following the process of structure development in oriented system. Hence it has excellent scope for commercial exploitation as well as a tool for scientific investigation.

CHAPTER I

CONTENTS

INTRODUCTION AND LITERATURE SURVEY 1.1 General Introduction

1.2 Drawing of Polyethylene Terephthalate 1.2.1 Use of considere construction 1.2.2 Mechanism of neck drawing

Page No

1 5 10 14 1.3 Low Temperature Drawing of PET 16 1.4 Importance of Stretching Temperature

in PET 18

1.4.1 High temperature and multistage

stretching 22

1.5 Effect of drawing rate on properties

of PET fibre 28

1.6 Effect of orientation on the properties

of PET 30

1.7 Partially oriented yarn (POY) and Low

oriented PET 31

CHAPTER II DESIGN DETAILS OF INCREMENTAL DRAWING

2.1 Description of typical IDP set-up 33 2.2 Incremental drawing "chine 33 2.2.1 Machine assembly 35 2.3 Involvement of parameters in designing

drawing body (cone) in incremental drawing process

2.3.1 Maximum and minimum diameters of

the cone 36

2.3.2 Angle of the cone 38 2.3.3 Size and shape of steps 39 2.3.4 Number of steps 39

CHAPTER

2.4 2.5

Take-up unit

Design of drawing body profiles

ii

40

2.5.1 Linear profile drawing body 40 2.5.2 Non-linear profile drawing body 41 2.5.3 Wrapping of fibres on the

drawing body 43

2.5.4 Possible methods of heating in

IDP 44

2.5.4.1 Chamber heating system 45 2.5.4.2 Temperature control

2.5.4.2.1 Thermo-electric

sensors 47

2.5.4.2.2 Temperature controlling

unit 49

2.5.4.3 Plate heating system 50

III EXPERIMENTAL DETAILS

3.1 Material 53

3.2 Sample Preparation

3.2.1 PET-POY drawn by chamber heating system with non-linear profile

drawing body 55

3.2.2 PET-POY drawn by plate heating system with linear profile

drawing body 56

3.2.3 Low oriented PET drawn by plate heating system with linear profile

drawing body 56

3.3 Residence Time 57

3.4 Measurement of Linear Density 59 3.5 Measurement of Diameter 59

CHAPTER

3.6 3.7

Measurement of Draw-Ratio Mechanical Properties

3.7.1 Evaluation of mechanical properties

iii

60

60

3.7.1.1 Tenacity 61

3.7.1.2 Breaking extension (%)

(strain %) 61

3.7.1.3 Initial modulus 61 3.7.2 Sonic modulus 62 3.8 Structural Properties

3.8.1 Birefringence 63

3.8.2 X-ray diffraction

3.8.2.1 Crystallinity 64 3.8.2.2 Crystalline orientation 65 3.8.2.3 Amorphous orientation 66 3.8.2.4 Crystal size 67 3.8.2.5 Density measurement 68 3.8.2.6 % Shrinkage measurement 69

IV COMPARISON OF PROPERTIES OF PET-POY DRAWN BY CONVENTIONAL AND INCREMENTAL DRAWING

4.1 Sample Preparation 70

4.2 Experimental 72

4.3 Results

4.3.1 Variation of tensile properties

with draw-ratios 73

4.3.2 Actual draw-ratio 73 4.3.3 Variation of sonic modulus with

the draw-ratio 74

iv

4.3.4 Birefringence 74

4.3.5 Variation of % X-ray crystallinity

with the draw-ratio 75 4.3.6 Variation of orientation functions

with the draw-ratio 75

4.4 Discussions 76

4.5 Structural Model 79

CHAPTER V HIGH TEMPERATURE DRAWING

5.1 Introduction 84

5.2 Experimental

5.2.1 The starting materials 85 5.2.2 Sample preparation 86 5.2.3 Testing and characterisation 87 5.3 Results

5.3.1 POY(3000m/min) drawn material 5.3.1.1 Variation in tenacity

and % breaking extension as a function of second

heater temperature 87 5.3.1.2 Variation in initial

modulus and % crystallinity (by density) as a function

of second heater temperature 88 5.3.1.3 Variation in birefringence

and sonic modulus as a function of second heater

temperature 88

5.3.1.4 Variation in % X-ray

crystallinity as a function

of second heater temperature 88 5.3.1.5 Variation in crystal size

as a function of second

heater temperature 89

V

5.3.1.6 Variation in orientation

function with temperature 89 5.4 PET-POY (2000m/min) and low-oriented

(1000 m/min) PET drawn by IDP and CDP

5.4.1 Variation in tenacity as a function

of second heater temperature 90 5.4.2 Variation in % breaking extension

as a function of second heater

temperature 90

5.4.3 Variation in initial modulus as a function of second heater

temperature 90

5.4.4 Variation in birefringence as a function of second heater

temperature 91

5.4.5 Variation in sonic modulus as a function of second heater

temperature 91

5.4.6 Variation in % crystallinity (by density) and % crystallinity (by X-ray) as a function of second

heater temperature 92

5.4.7 Variation in crystal size as a

function of temperature 92 5.4.8 Variation in orientation function

as a function of temperature 92

5.5 Discussions 93

5.6 Structural Model 97

CHAPTER VI ANALYSIS OF DRAWING MECHANISM FOR PET-POY FIBRES AVAILABLE FROM STEPS IN IDP

6.1 Introduction 101

6.2 Sample Preparation 103

6.3 Experimental

6.3.1 Denier, draw-ratio and % shrinkage 103

vi 6.3.2 Diameter measurement 104 6.3.3 Property measurement 105 6.4 Results

6.4.1 Variation in denier along the

number of steps 106

6.4.2 Variation in % shrinkage along

the number of steps 106 6.4.3 Variation of draw-ratio along

the number of steps 106 6.4.4 Variation of diameter (microns)

along the number of steps 107 6.4.5 Stress-strain curves for fibres

obtained from different steps 107 6.4.6 Variation in tensile properties

along the number of steps 108 6.4.7 Variation in birefringence along

the number of steps 108 6.4.8 Variation in % Crystallinity (by

density and X-ray) along the

number of steps 109

6.4.9 Variation in sonic modulus along

the number of steps 109 6.4.10 Variation in orientation factors

along the number of steps 109

6.5 Discussions 110

CHAPTER VII EFFECT OF DRAWING RATES ON THE PROPERTIES OF PET-POY

7.1 Sample Preparation ₁₁₆

7.2 Results

7.2.1 Variation in tensile properties

with the drawing rates 117

vii 7.2.2 Variation in birefringence with

the drawing rates 118

7.2.3 Variation in % X-ray crystallinity

with the drawing rates 118 7.2.4 Variation in orientation functions

with the drawing rates 118 7.2.5 Variation of residence time with

the drawing rates 119

7.3 Discussions 119

CHAPTER VIII SUMMARY AND CONCLUSIONS 123

CHAPTER IX SUGGESTION FOR FURTHER WORK 131

REFERENCES

APPENDIX