Processing and performance properties of polypropylene sisal fibre composites and their foams

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“PROCESSING AND PERFORMANCE PROPERTIES OF POLYPROPYLENE/SISAL FIBRE COMPOSITES

AND THEIR FOAMS”

AJIT BABARAO BHAGAT

DEPARTMENT OF MATERIALS SCIENCE AND ENGINEERING

INSTITUTE OF TECHNOLOGY DELHI

MAY 2023

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© Indian Institute of Technology (IITD), New Delhi , 2023

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“PROCESSING AND PERFORMANCE PROPERTIES OF POLYPROPYLENE/SISAL FIBRE COMPOSITES

AND THEIR FOAMS”

by

AJIT BABARAO BHAGAT

DEPARTMENT OF MATERIALS SCIENCE AND ENGINEERING

Submitted

in fulfilment of the requirements of the degree of Doctor of Philosophy

to the

INDIAN INSTITUTE OF TECHNOLOGY DELHI

MAY 2023

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Dedicated to my

Father “Baba V. Bhagat”

&

Mother “Sheela Bhagat”

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Certificate

This is to certify that the thesis entitled “Processing and Properties of Polypropylene/Sisal fibre composites and their foam” being submitted by Mr. Ajit Babarao Bhagat to the Indian Institute of Technology Delhi, for the fulfilment of award of the degree “Doctor of philosophy” is a record of bonafide research work carried by him under our supervision and guidance. This thesis has been prepared in conformity with the rules and regulations of the Indian Institute of Technology Delhi, New Delhi.

We further certify that the thesis has attained a standard required for the Ph.D. degree of the institute. To the best of our knowledge, the research reported and result presented in the thesis have not been submitted in part or full to any other institute or university for the award of any other degree or diploma.

(Anup Kumar Ghosh) (Bhabani Kumar Satapathy)

Emirates Professor Professor

Department of Materials Sci. & Engg. Department of Materials Sci. & Engg.

Indian Institute of Technology Delhi Indian Institute of Technology Delhi New Delhi-110016, India.

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New Delhi-110016, India.

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Acknowledgements

It gives me immense pleasure to express my deep sense of gratitude to all who have helped me along my way through the doctoral studies and a memorable stay at IIT Delhi. First of all, I would like to express my gratitude to my family, who always motivated me to come to this great seat of learning and helping me in every challenging phase of my life.

I express my profound sense of gratitude and veneration to my supervisor, Prof. Anup K.

Ghosh for his guidance and his inspiration to look positively at every situation in life and will always be. I extend my gratitude to my supervisor Prof. Bhabani K. Satapathy for guiding me all the way during my PhD tenure. I appreciate their constant encouragement, way of informal teaching on handling things with patience and maturity. These helped me to tide over the difficult situations. They always boosted me to put in extra efforts and I am indebted to them for what I am today.

I express my deep sense of gratitude to my student research committee members, Prof. Naresh Bhatnagar, Prof. Leena Nebhani, and Prof Sampa Saha who have monitored my work and provided me the valuable suggestions. I am also thankful to Prof. Josemon Jacob, Prof. Rajesh Prasad, Prof. Jayant Jain, Prof. Nitya Nand Gosvami, Prof. Suresh Neelakantan, Prof. Bijay P. Tripathi, Prof. Nirat Ray, Prof. Ankur Goswami, Prof. Lakshmi Narayan Ramasubramanian., Prof. Sangeeta Santra, and Prof. Shib Shankar Banerjee who in spite of their busy schedule have always made themselves available for valuable discussions and support. I would like to extend my thanks to Prof. B. K Behra, Prof. Abhijit Majumdar, and their students for helping and supporting me by giving laboratory facilities whenever needed.

This work would not be possible without the support and encouragement from my friends, seniors and juniors. My special thanks to Dr. Sabapathy Shankar for his extraordinary support and guidance throughout my Ph.D. I would like to convey special thanks to Dr. Anindya Dutta, Dr. Ruchi Pal, Dr. Srijita Purkayastha, Dr. Prajesh Nayak, Dr. Dhiraj Kumar Rana, Mr. Ashok

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Bakshi, Mr. Mayank Prakash, Ms. Aiswarya S., Mr. Pratip Shankar Banarjee, Ms. Subhashree S. Pradhan, Dr. Shivangi Sharma, Dr Agni K Biswal, Dr. Ifra Mirza, Ms. Kalpana Pandey, Ms. Shaifali Dhingra, Ms. Nidhi Gupta, Ms. Aiswarya T.T., Ms. Meenakshi Verma, Ms.

Shubhra Goel, Ms. Shikha, Ms. Shivani Goyal and Ms. Ujjawal Bairagi for their all possible support in my research work as well as creating beautiful memories during my PhD journey.

I would like to thank Dr. Sucharita Sethy, Dr. Deepika Sharma, Dr. Debarghya Saha, Dr. Saroj K. Samantaray, Mr. Harshal Peshne, Mr. Vikramsingh Thakur, Ms. Krishnpriyadarshni Das, Ms. Tina Joshi, Ms. Aanchal Jaisingh, Mr. Lukkuman Hakkim N., Mr. Amit Kumar, Dr.

Sumbul, Dr. Smrutirekha Misra, Mr. Biswajit Misra, Ms. Shraddha Shahane, Ms. Jyoti Kumari, and Ms. Supriya Maiti. I would like to acknowledge my roommates Mr. K. Dinesh, Mr. Kashish Jain, Mr. Dinesh Kumar, Mr. Shubham Vashishth, Mr. Sagar Dhanushkar, Mr.

Vaibhav Thul, Mr. Makarand Belsare, Mr. Pramod Pawar, Mr. Pramod Gurave, Mr. Abhishek Vhanbatte, and Dr. Umesh Marathe, Ms. Shruti Sunil Raut, Mrs. Monika Ramteke Meshram, Mr. Ashish Ghogare and Mr. Brijesh Nagdeote who were with me during my all ups and downs.

I owe thanks to the laboratory and office staffs Mr. Ashok Kapoor, Mr. Surender Sharma, Mr.

Ehteshamul Islam, Mr. Gajraj Singh, Mr. Jitendra Rathore, Mr. Ashish Sharma, Mr.

Gyanendra K. Yadav, Mr. Subhash Chand, Ms. Shalini Arora, Mr. Narender Kumar, Mr. Amit Kumar, Mr. Sudhir K. Pandey, Mr. Pramod Kale, Ms. Sunita Rani, Mr. Kuldeep Sharma, Mr.

Mahesh Soni and Ms. Aastha Sharma for their all-possible support and suggestions.

I wish to acknowledge, Ministry of Human resource development (MHRD), Government of India for providing me financial assistance to carry out my research work smoothly.

The acknowledgement will sound empty if it does not include my family, without which I stand nowhere. I take the opportunity to express my deepest gratitude to my father Mr. Baba V.

Bhagat, and my mother Mrs. Sheela Bhagat for always believing in me and supporting me with love, strength and confidence. I extend my gratitude to my elder Brother Dr. Sujit B. Bhagat

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and my sister in low Dr. Jyoti Thul and my elder sister Mrs. Jaya Wawre and my brother in low Mr. Lalit Wawre, my niece Dr. Manasi Bhagat for always being my shield so that I can accomplish my dream.

It is not possible to list all those who contributed directly or indirectly for successful completion of the thesis. This is a mere note of some of them, however I thank all of them, who are missed in this acknowledgement, for their kind support and encouragement.

New Delhi Ajit Babarao Bhagat

Date:

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Department of Materials Science and Engineering IIT Delhi, New Delhi, India

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Abstract

This work explores the processability and foamability of Polypropylene/sisal fibre (PP/SF) composites having near critical fibre length and short fibres. The addition of near critical fibre length is expected to cause the rheological percolation which is not possible in short fibre composites. Sisal fibres were treated with sodium bicarbonate (NaHCO3) for different time intervals and the optimization of the treatment time was done by analysing fibre roughness, crystallinity and tenacity. Specifically, the effect of fibre treatment, fibre length, and addition of compatibilizer (polypropylene grafted maleic anhydride) on the performance properties of the composites were studied. The critical fibre length for the PP/SF composite system was found to be 8 mm. PP/SF composites were prepared using an internal mixer by varying fibre concentration (10, 20, 30, 40 wt.%), and the average fibre length (~17 mm) in the composites confirms the presence of near-critical fibre length. The investigation of the performance of PP/SF composites having near-critical fibre length was carried out using physicomechanical, thermal, rheological, and dynamic mechanical parameters. With increase in fibre concentration, significant improvements in mechanical and thermal properties were observed.

The results show that sisal fibre has an undeniable impact on the dynamic mechanical properties of the prepared composites as the storage modulus and loss modulus increase with increase in sisal fibre concentration. The improvement in modulus results from the physical interaction between PP and sisal fibre; however, the load transfers from fibre to matrix restrict the segmental mobility of the PP chains. Shear rheology analysis confirms strong shear thinning behaviour as the power-law exponent decreases with increased fibre concertation.

However, marginal improvement in the mechanical properties were observed in case of PP/SF composites with short fibres. The marginal improvement in the properties might be due to the short length of fibres, which is unable to transfer load from fibre to matrix.

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vi Further, the foamability of PP and the prepared composites (having both NCFL and short fibre) were carried out with batch foaming setup using supercritical CO2 (sc-CO2) as a physical blowing agent. Foam processing was performed at different temperatures (145, 155, and 165^oC); however, the optimized foaming temperature was found to be 145^oC. PP/SF short fibres composites were foamed at the optimized temperature. The incorporation of sisal fibre into the PP matrix helps in cell nucleation; hence, cell density increases and cell size decreases, as analysed from SEM. Effect of fibre length on the foamability of PP/SF composites were observed using SEM and the results revel that the microcellular structure being present in NCFL based PP/SF composites. The prepared rigid microcellular foams offer properties that can be potentially used to produce high strength-to-weight ratio structural components, which could be employed in applications related to sound absorption.

The continuous foam processability of polypropylene/Sisal fibre composites were determined using extrusion foaming. CO2 gas was used as a physical blowing agent. Foaming was carried out at 60 Bar pressure, screw speed of 40 rpm, and at different temperatures (160^oC and 200^oC).

The lowest density and highest volume expansion ratio were found in foams prepared at a temperature of 160ôC. Further, scanning electron microscopy analysis supports the physical property results, and the smallest cell size and more significant cell density were found in the foams prepared at 160ôC. Though cell size increased with fibre concentration (0-10 wt.% of sisal fibre), the microcellular foam structure was found in foams prepared at 160ôC. Thus, it can be concluded that 160ôC was the optimized temperature for foam processing. The addition of sisal fibres in the PP matrix apparently decreases the impact absorb energy, but the foam prepared at 160ôC shows enhanced energy absorption than that of the sample prepared at 200ôC. The prepared rigid foam composites might find the potential application in automobiles (e-vehicles) and packaging.

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vii

सार

यह काम पॉलीप्रोपाइलीन / सििल फाइबर (पीपी / एिएफ) कंपोजिट की प्रक्रियात्मकता और फोमबबसलटी की पड़ताल करता है, जििमें महत्वपूर्ण फाइबर लंबाई और छोटे फाइबर होते हैं।

लगभग महत्वपूर्ण फाइबर लंबाई के अलावा ररयोलॉजिकल परकोलेशन का कारर् बनने की

उम्मीद है िो छोटे फाइबर कंपोजिट में िंभव नहीं है। अलग-अलग िमय अंतराल के सलए सििल फाइबर को िोडियम बाइकाबोनेट (NaHCO₃) के िाथ इलाि क्रकया गया था और फाइबर

खुरदरापन, क्रिस्टलीयता और दृढ़ता का ववश्लेषर् करके उपचार िमय का अनुकूलन क्रकया गया

था। ववशेष रूप िे, कंपोजिट के प्रदशणन गुर्ों पर फाइबर उपचार, फाइबर लंबाई, और कॉजम्पटटबबलाइज़र (पॉलीप्रोपाइलीन ग्राफ्टेि मेननक एनहाइड्राइि) के प्रभाव का अध्ययन क्रकया

गया। PP/SF िमग्र प्रर्ाली के सलए महत्वपूर्ण फाइबर की लंबाई 8 सममी पाई गई। पीपी/एिएफ कंपोजिट्ि को अलग-अलग फाइबर कंिंट्रेशन (10, 20, 30, 40 विन%) द्वारा एक आंतररक समक्िर का उपयोग करके तैयार क्रकया गया था, और कंपोजिट में औित फाइबर लंबाई (~ 17 सममी) ननकट-महत्वपूर्ण फाइबर लंबाई की उपजस्थनत की पुजटट करती है। ननकट-महत्वपूर्ण फाइबर लंबाई वाले पीपी/एिएफ कंपोजिट के प्रदशणन की िांच क्रफजियोमेकेननकल, थमणल, ररयोलॉजिकल और िायनेसमक मैकेननकल पैरामीटर का उपयोग करके की गई थी। फाइबर एकाग्रता में वृद्धि के िाथ, यांबिक और तापीय गुर्ों में महत्वपूर्ण िुिार देखा गया। पररर्ाम बताते हैं क्रक सििल फाइबर का तैयार कंपोजिट के गनतशील यांबिक गुर्ों पर एक ननववणवाद

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viii प्रभाव पड़ता है क्योंक्रक भंिारर् मापांक और हानन मापांक में वृद्धि के िाथ सििल फाइबर एकाग्रता में वृद्धि होती है। पीपी और सििल फाइबर के बीच भौनतक िंपकण िे मापांक में

िुिार; हालााँक्रक, लोि फाइबर िे मैटट्रक्ि में स्थानांतररत होता है, पीपी श्ृंखलाओं की खंिीय गनतशीलता को प्रनतबंधित करता है। कतरनी ररयोलॉिी ववश्लेषर् मिबूत कतरनी पतले व्यवहार की पुजटट करता है क्योंक्रक शजक्त-कानून प्रनतपादक बढ़े हुए फाइबर िंघनन के िाथ घटता है।

हालांक्रक, छोटे फाइबर वाले पीपी/एिएफ कंपोजिट के मामले में यांबिक गुर्ों में मामूली िुिार देखा गया। गुर्ों में मामूली िुिार फाइबर की कम लंबाई के कारर् हो िकता है, िो फाइबर

िे मैटट्रक्ि में भार स्थानांतररत करने में अिमथण है।

इिके अलावा, भौनतक ब्लोइंग एिेंट के रूप में िुपरक्रिटटकल िीओ2 (एििी-िीओ2) का उपयोग करके बैच फोसमंग िेटअप के िाथ पीपी और तैयार कंपोजिट (एनिीएफएल और शॉटण फाइबर दोनों) की फोमबबसलटी की गई। फोम प्रिंस्करर् ववसभन्न तापमानों (145, 155, और 165^oC) पर क्रकया गया था; हालााँक्रक, अनुकूसलत फोसमंग तापमान 145^oC पाया गया। पीपी/एिएफ शॉटण फाइबर कंपोजिट को अनुकूसलत तापमान पर फोम क्रकया गया। पीपी मैटट्रक्ि में सििल फाइबर का िमावेश िेल न्यूजक्लएशन में मदद करता है; इिसलए, िेल घनत्व बढ़ता है और िेल का

आकार घटता है, िैिा क्रक एिईएम िे ववश्लेषर् क्रकया गया है। PP/SF िजम्मश् की झाग क्षमता

पर फाइबर की लंबाई का प्रभाव SEM का उपयोग करके देखा गया और पररर्ाम बताते हैं क्रक NCFL आिाररत PP/SF िजम्मश् में माइिोिेलुलर िंरचना मौिूद है। तैयार कठोर माइिोिेलुलर

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फोम गुर् प्रदान करते हैं जिनका िंभाववत रूप िे उच्च शजक्त-िे-विन अनुपात िंरचनात्मक घटकों का उत्पादन करने के सलए उपयोग क्रकया िा िकता है, जिन्हें ध्वनन अवशोषर् िे

िंबंधित अनुप्रयोगों में ननयोजित क्रकया िा िकता है।

एक्िट्रूज़न फोसमंग का उपयोग करके पॉलीप्रोपाइलीन / सििल फाइबर कंपोजिट की ननरंतर फोम प्रक्रियाशीलता ननिाणररत की गई थी। CO₂ गैि का उपयोग भौनतक ब्लोइंग एिेंट के रूप में क्रकया िाता था। फोसमंग 60 बार दबाव, 40 आरपीएम की पेंच गनत और ववसभन्न तापमानों

(160ôC और 200ôC) पर क्रकया गया था। 160ôC के तापमान पर तैयार फोम में िबिे कम

घनत्व और उच्चतम आयतन ववस्तार अनुपात पाया गया। इिके अलावा, स्कैननंग इलेक्ट्रॉन माइिोस्कोपी ववश्लेषर् भौनतक िंपवि के पररर्ामों का िमथणन करता है, और िबिे छोटा िेल

आकार और अधिक महत्वपूर्ण िेल घनत्व 160^oC पर तैयार फोम में पाया गया। यद्यवप कोसशका का आकार फाइबर िांद्रता (0-10 सििल फाइबर का विन%) के िाथ बढ़ गया, 160^oC पर तैयार फोम में माइिोिेलुलर फोम िंरचना पाई गई। इि प्रकार, यह ननटकषण ननकाला

िा िकता है क्रक फोम प्रिंस्करर् के सलए 160ôC इटटतम तापमान था। पीपी मैटट्रक्ि में सििल फाइबर के अलावा प्रभाव अवशोवषत ऊिाण को स्पटट रूप िे कम कर देता है, लेक्रकन 160ôC पर तैयार फोम 200ôC पर तैयार क्रकए गए नमूने की तुलना में ऊिाण अवशोषर् को बढ़ाता है।

तैयार कठोर फोम कंपोजिट ऑटोमोबाइल (ई-वाहन) और पैकेजिंग में िंभाववत अनुप्रयोग पा

िकते हैं।

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List of Figures

Figure 1.1: Reaction mechanism of sodium bicarbonate and sisal fibre ... 7

Figure 1.2: Reaction mechanism of PP-g-MA and sisal fibre ... 7

Figure 1.3: Composites based on orientation a) Particulates randomly oriented b) randomly oriented fibres c) discontinuous unidirectional oriented fibres d) unidirectional continuous fibres ... 11

Figure 1.4: Classification of composite materials... 12

Figure 1.5: Foaming mechanism of polymers using sc-CO2 ... 22

Figure 1.6: Schematic of extrusion foam processing ... 24

Figure 1.7: Foam processing mechanism of PP/SF composites having a) short fibres and b) Near critical fibre length sisal fibres. ... 25

Figure 1.8: Plan of work ... 28

Figure 2.1: Chemical structure of Polypropylene (PP) ... 46

Figure 2.2: FTIR Spectra of PP... 48

Figure 2.3: DSC Second heating curve of PP ... 49

Figure 2.4: DSC First cooling curve of PP ... 49

Figure 2.5: TGA scan of PP ... 50

Figure 2.6: DTG scan of PP ... 51

Figure 2.7: XRD spectra of PP ... 51

Figure 2.8: Chemical structure of PP-g-MA ... 52

Figure 2.9: DSC Second heating scan of PP-g-MA ... 53

Figure 2.10: DSC First cooling scan of PP-g-MA ... 53

Figure 2.11: TGA scan of PP-g-MA ... 54

Figure 2.12: DTG scan of PP-g-MA ... 55

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xix Figure 2.13: Raw Sisal fibre a) Image taken by camera b) Optical micrograph c) SEM image

... 56

Figure 2.14: FTIR Spectra of Raw Sisal Fibre ... 57

Figure 2.15: TGA scan of Raw Sisal Fibre ... 59

Figure 2.16: DTG scan of Raw Sisal Fibre ... 59

Figure 2.17: XRD Spectrum of sisal fibre ... 60

Figure 2.18: Chemical structure of Sodium Bicarbonate... 60

Figure 2.19: Image of PP/SF composites after batch mixing (Haake rheomix) ... 63

Figure 2.20: sc-CO2 assisted batch foaming setup ... 64

Figure 2.21: Twin screw extruder (OMega 20, STEER Engineering Pvt. Ltd., India) ... 66

Figure 2.22: CO2 assisted extrusion Foaming setup: a) Haake Rheodrive b) feeder c) CO2 gas injection port d) static mixer e) sheet die f) chill roll g) chill roll driving unit h) CO2 pressure gauge and inside image showing zoomed view of extruded foamed PP sheet ... 67

Figure 2.23: Image of Foamed PP and their composites at 160^oC a) EF PP b) EF PP/SF02 c) EF PP/SF05 d) EF PP/SF10 ... 67

Figure 2.24: FTIR instrument, Thermo Scientific, Nicolet iS50 spectrometer ... 68

Figure 2.25: Scanning electron microscope (ZEISS EVO 50) ... 69

Figure 2.26: TGA instrument, Perkin–Elmer Pyris 6 system ... 69

Figure 2.27: a) Instron 3365 tensile testing instrument b) enlarged view of the tensile grip of the instrument... 71

Figure 2.28: Rigaku Ultima IV WAXD equipment ... 72

Figure 2.29: Internal mixer (Thermo scientific Haake polylab OS, Germany) ... 73

Figure 2.30: Compression molding machine (Labtech engineering)... 74

Figure 2.31: Tensile testing machine (Zwick Z/010) ... 75

Figure 2.32: Notched impact tester (Tinius Olsen) ... 76

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Figure 2.33: Differential scanning calorimetry (TA instruments [DSC Q200]) ... 77

Figure 2.34: Micro compounder (Thermo Scientific, Haake MiniLab II, Germany) ... 78

Figure 2.35: Parallel plate rheometer (Bohlin C-VOR instrument) ... 78

Figure 2.36: Melt flow index equipment (by Flexitest) ... 79

Figure 2.37: Dynamic mechanical analyzer (TA instruments [DMA Q800]) ... 80

Figure 2.38: HDT testing equipment (by JJ test) ... 80

Figure 3.1: FTIR spectra of raw sisal fibre and sisal fibres with different treatment times. ... 86

Figure 3.2: SEM analysis a) RSF b) SF 2h c) SF 4h d) SF 8h. ... 87

Figure 3.3: TGA analysis of raw sisal fibre and fibres treated at different treatment time. .... 88

Figure 3.4: DTGA analysis of raw sisal fibre and fibres treated at different treatment times. 89 Figure 3.5: XRD analysis of raw and fibre treated at different treatment times. ... 91

Figure 3.6: Fibre length distribution for short sisal fibres a) Initial b) Final ... 93

Figure 3.7: Fibre length distribution for near critical fibre length sisal fibres a) Initial b) Final ... 93

Figure 3.8: Interfacial shear strength and critical fibre length of PP/SF system ... 95

Figure 3.9: Pictorial view of rheological percolation threshold. a) PP/SF short fibre composite b) PP/SF composite having NCLF ... 96

Figure 3.10: a) Storage modulus and b) loss modulus vs. frequency graph of PP/SF composites having short sisal fibres ... 97

Figure 3.11: Storage modulus and loss modulus vs. frequency graph of PP/SF composites having near critical fibre length ... 98

Figure 4.1: SEM micrograph of impact fractured composites. (a) PP/SF10 (b) PP/SF20 (c) PP/SF30 (d) PP/SF40 ... 105

Figure 4.2: a) Stress vs. strain curve of tensile samples of composites b) Elongation at break c) Tensile strength d) Tensile modulus ... 106

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xxi Figure 4.3: a) Stress vs. strain curve of the flexural test b) Flexural strength c) Flexural modulus

d) Strain at max force ... 107

Figure 4.4: Effect of fibre addition on the impact properties of composites ... 108

Figure 4.5: Relative rheological measurements for PP and its composites with different weight % of sisal fibre. ... 110

Figure 4.6: Modulus vs. angular frequency of PP and their composites ... 111

Figure 4.7: Complex viscosity vs. frequency of PP and its composites ... 112

Figure 4.8: a) Storage modulus vs. fibre concentration at two different angular frequencies (0.1 rad/s and 1 rad/s) b) fitting to the power law relation [log G’ vs. log(W-Wr)] ... 113

Figure 4.9: Cole-Cole analysis of neat PP and PP/SF composites ... 114

Figure 4.10: a) Hardness vs. fibre concentration and b) storage modulus vs. hardness graph ... 116

Figure 4.11: Dynamic mechanical properties: a) Storage modulus b) Loss modulus c) Tan delta of PP/SF composites having NCLF d) Storage modulus vs. fibre concentration at different temperature ... 119

Figure 4.12: Effect of fibre concentration on normalized storage modulus (E') of composites ... 120

Figure 4.13: Melting temperature thermogram of PP/SF composites having near critical length fibres. ... 121

Figure 4.14: Crystallization temperature thermogram of PP/SF composites having near critical length fibres. ... 122

Figure 4.15: TGA graph of PP/SF composites having NCLF. ... 123

Figure 4.16: DTG graph of PP/SF composites having NCLF ... 124

Figure 4.17: XRD spectra of PP/SF composites with NCLF... 125

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xxii Figure 4.18: Experimental and theoretical density of composites with increasing concentration

of fibres ... 127

Figure 4.19: Graph of Experimental and Theoretical Elastic modulus of composites with increasing concentration of fibres ... 129

Figure 4.20: Graph of Experimental and Theoretical Tensile strength of composites with increasing concentration of fibres ... 129

Figure 4.21: Variation of (a) density and (b) volume expansion ratio (VER) of PP and its foamed composites with foaming temperature at 100 Bar pressure and 15 min saturation time ... 137

Figure 4.22: Morphology of foamed PP at 100 Bar, 15 min saturation time, and a) 145ôC, b) 155ôC, c) 165ôC ... 139

Figure 4.23: Morphology of foamed PP and their composites, foamed at 145^oC, 100 Bar, and 15 min saturation time: (a)FPP, (b)FPP/SF10, (c) FPP/SF20, (d) FPP/SF30 and, (e) FPP/SF40 ... 140

Figure 4.24: Influence of fibre concentration on cell size, cell density ... 141

Figure 4.25: Influence of fibre concentration on nucleation ratio ... 141

Figure 4.26: WAXD analysis of FPP and its foamed composites ... 142

Figure 4.27: Compressive properties: a) Modulus and b) Fmax of FPP and their composite foams ... 144

Figure 4.28: Dynamic mechanical analysis of foamed PP and foamed PP/SF composites: a) Storage modulus (E’), b) Loss modulus (E”) and, c) damping factor (Tanδ) ... 147

Figure 5.1: SEM micrograph of impact fractured composites. a) PP/SF10(short) b) PP/SF20(short) c) PP/SF30(short) d) PP/SF40(short) ... 156

Figure 5.2: Density of PP/SF short fibre composites ... 157

Figure 5.3: DSC melting endotherm of short fibre PP/SF composites ... 158

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xxiii

Figure 5.4: DSC crystallization exotherm of short fibre PP/SF composites... 159

Figure 5.5: TGA thermogram of short fibre PP/SF composites ... 160

Figure 5.6: DTG thermogram of short fibre PP/SF composites ... 161

Figure 5.7: Modulus vs. angular frequency of short fibre PP/SF composites ... 163

Figure 5.8: Complex viscosity vs. angular frequency of PP/SF(short) ... 163

Figure 5.9: XRD spectra of short fibre PP/SF composites ... 164

Figure 5.10: Melt flow rate of short fibre PP/SF composites ... 165

Figure 5.11: a) Stress vs. strain curve of tensile samples of short fibre PP/SF composites b) Tensile strength c) Tensile modulus ... 166

Figure 5.12: a) Stress vs. strain curve of flexural samples of short fibre PP/SF composites b) Flexural strength c) Flexural modulus ... 167

Figure 5.13: Effect of fibre addition on the impact properties of short fibre PP/SF composites ... 168

Figure 5.14: Graph of experimental and predicted tensile strength of PP/SF composites .... 171

Figure 5.15: Effective fibre volume fraction vs. fibre concentration of PP/SF composites .. 172

Figure 5.16: Different models for predicting the tensile modulus od the PP/SF composites 173 Figure 5.17: Modified ROM for tensile strength of composites for different value of η0 .... 173

Figure 5.18: Modified ROM for tensile modulus of composites for η0 = 0.375 and ηL = 0.87 ... 174

Figure 5.19: Comparison of Tensile strength of NCFL and short fibre composites... 175

Figure 5.20: Comparison of Tensile modulus of NCFL and short fibre composites ... 176

Figure 5.21:Comparison of Impact strength of NCFL and short fibre composites ... 176

Figure 5.22: a) Density b) VER of PP/SF(short) ... 181

Figure 5.23: Morphology of PP/SF composites having short sisal fibres a) PP/SF10(short) b) PP/SF20(short) c) PP/SF30(short) d) PP/SF40(short) ... 182

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xxiv

Figure 5.24: Influence of fibre concentration on cell size, cell density ... 183

Figure 5.25: XRD spectra of PP/SF composites having short sisal fibres ... 184

Figure 5.26: Compressive properties of PP/SF composites having short sisal fibre a) compressive modulus b) Fmax at 10% deformation ... 186

Figure 5.27: SEM image of a) PP/SF40 b) PP/SF40(short) ... 187

Figure 5.28: Comparison of cell diameter of NCFL and short fibre composite foams ... 187

Figure 5.29: Comparison of compression modulus of NCFL and short fibre composite foams ... 188

Figure 6.1: Density of neat and extrusion foamed composites ... 195

Figure 6.2: Volume expansion ratio of foamed composites ... 196

Figure 6.3: SEM micrograph of a) EF PP b) EF PP/SF02 c) EF PP/SF05 d) EF PP/SF10 at 60 Bar and 200^oC ... 197

Figure 6.4: SEM micrograph of a) EF PP b) EF PP/SF02 c) EF PP/SF05 d) EF PP/SF10 at 60 Bar and 160^oC ... 198

Figure 6.5: SEM analysis of PP and their composites at 200^oC and 60 Bar... 198

Figure 6.6: SEM analysis of PP and their composites at 160^oC and 60 Bar ... 199

Figure 6.7: Nucleation Ratio at different temperatures ... 199

Figure 6.8: Mechanism of extrusion foaming of EF PP and EF PP/SF10 ... 200

Figure 6.9: XRD spectra of PP and their composites films ... 201

Figure 6.10: XRD spectra of foamed PP and their composites at 160^oC ... 201

Figure 6.11: XRD spectra of foamed PP and their composites at 200^oC ... 202

Figure 6.12: Melting endotherm of EF PP and its composites at 160^oC ... 203

Figure 6.13: Crystallization exotherm of EF PP and its composites at 160^oC (DSC analysis) ... 204

Figure 6.14: TGA graph of EF PP and its composites at 160^oC ... 205

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xxv

Figure 6.15: DTG graph of EF PP and its composites at 160^oC ... 205

Figure 6.16: Drop tower impact tester (CEAST, Model: Fractovis Plus) ... 212

Figure 6.17: Principle of Sound wave transformation ... 214

Figure 6.18: Image of PP and their composites (30 mm diameter) a) PP b) PP/SF10 c) PP/SF20 d) PP/SF30 e) PP/SF40 ... 215

Figure 6.19: Image of PP/SF composite foams (30 mm diameter) a) FPP b) FPP/SF10 c) FPP/SF20 d) FPP/SF30 e) FPP/SF40 ... 215

Figure 6.20: Sound absorption testing setup ... 216

Figure 6.21: Total impact absorb energy of foamed PP and their foamed composites at different temperatures ... 217

Figure 6.22: Mechanism of sound absorption in composites and their foams... 220

Figure 6.23: Absorption coefficient vs. frequency of PP and its composites ... 221

Figure 6.24: NRC of PP and its composites ... 221

Figure 6.25: Absorption coefficient vs. frequency of foamed PP and its foamed composites ... 222

Figure 6.26: NRC of foamed PP and their foamed composites ... 222

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xxvi

List of Tables

Table 1.1: Composition of sisal fibres ... 6

Table 1.2: General properties of Polypropylene ... 9

Table 1.3: Influence of fibre length on processability ... 14

Table 2.1: Properties of PP ... 47

Table 2.2: Important peaks in FTIR Spectra of PP ... 47

Table 2.3: DSC data of PP ... 48

Table 2.4: TGA data of PP ... 50

Table 2.5: Properties of PP-g-MA ... 54

Table 2.6: Properties of Sisal fibres ... 56

Table 2.7: Important peaks in FTIR Spectra of Sisal fibre ... 58

Table 2.8: TGA properties of Raw Sisal Fibres ... 58

Table 2.9: Temperature profile of twin-screw extruder (^oC) ... 66

Table 2.10: Composite of PP/SF/PP-g-MA used in experimentation so far... 66

Table 2.11: Processing conditions of compression molding ... 70

Table 3.1: Onset degradation temperature (^oC) of all samples ... 89

Table 3.2: Crystallinity (%) of all samples ... 90

Table 3.3: Tenacity of raw and treated sisal fibres ... 91

Table 3.4: PP/SF composites formulations ... 94

Table 4.1: Mechanical properties of composites having NCFL ... 108

Table 4.2: Rheological parameters, shear viscosity, and torque values ... 110

Table 4.3: Crossover frequency and complex viscosity of PP/SF composites having NCLF ... 115

Table 4.4: Modulus retention variation with an increase in fibre concentration ... 120

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xxvii

Table 4.5: Thermal analysis of PP/SF composites having NCLF and short fibres... 124

Table 4.6: Physical, Morphological and mechanical properties of PP and its composite foams ... 144

Table 5.1: Thermal analysis of PP/SF composites having short fibres... 158

Table 5.2: Crossover frequency and relaxation time of short fibre PP/SF composites ... 162

Table 5.3: Overall mechanical properties of short fibre PP/SF composites ... 169

Table 5.4: Physical, Morphological and mechanical properties of PP and its composite foams ... 183

Table 6.1: Crystallinity % of PP and their composites and their foams ... 202

Table 6.2: Thermal analysis of EF PP and their composites foamed at 160^oC ... 206

Table 6.3: Cell size and impact absorb energy of EF PP and their composite foams ... 218

Processing and performance properties of polypropylene sisal fibre composites and their foams

“PROCESSING AND PERFORMANCE PROPERTIES OF POLYPROPYLENE/SISAL FIBRE COMPOSITES

AND THEIR FOAMS”

AJIT BABARAO BHAGAT

DEPARTMENT OF MATERIALS SCIENCE AND ENGINEERING

INSTITUTE OF TECHNOLOGY DELHI

MAY 2023

© Indian Institute of Technology (IITD), New Delhi , 2023

“PROCESSING AND PERFORMANCE PROPERTIES OF POLYPROPYLENE/SISAL FIBRE COMPOSITES

AND THEIR FOAMS”

by

AJIT BABARAO BHAGAT

DEPARTMENT OF MATERIALS SCIENCE AND ENGINEERING

Submitted

in fulfilment of the requirements of the degree of Doctor of Philosophy

to the

INDIAN INSTITUTE OF TECHNOLOGY DELHI

MAY 2023

Dedicated to my

Father “Baba V. Bhagat”

&

Mother “Sheela Bhagat”

Certificate

Acknowledgements

Abstract

सार

TABLE OF CONTENTS

List of Figures

List of Tables