Preparation Of Spent Tea Leaves Filled Polyurethane Composites For Sustainable Sound Absorbing Materials.

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UNIVERSITI TEKNIKAL MALAYSIA MELAKA

PREPARATION OF SPENT TEA LEAVES FILLED

POLYURETHANE COMPOSITES FOR SUSTAINABLE SOUND

ABSORBING MATERIALS

This report submitted in accordance with requirement of the Universiti Teknikal Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering

(Engineering Materials) (Hons.)

CHIA POOI CHING B050910119 890803-08-5712

FACULTY OF MANUFACTURING ENGINEERING 2013

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UNIVERSITI TEKNIKAL MALAYSIA MELAKA

BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA

SULIT

TERHAD

TIDAK TERHAD

(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia sebagaimana yang termaktub dalam AKTA RAHSIA RASMI 1972)

(Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan)

Disahkan oleh:

TAJUK: Preparation of Spent Tea Leaves Filled Polyurethane Composites for Sound Absorbing Materials

SESI PENGAJIAN: 2012/13 Semester2 SayaCHIA POOI CHING

Mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut:

1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis. 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan untuk

tujuan pengajian sahaja dengan izin penulis.

3. Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan pertukaran antara institusi pengajian tinggi.

4. **Sila tandakan ( )

Alamat Tetap: 612, Jalan Tembikai, Taman Chemor, 31200, Chemor, Perak.

Tarikh: ________________________

Cop Rasmi:

Tarikh: _______________________

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DECLARATION

I hereby, declared this report entitled “Preparation of Spent Tea Leaves Filled Polyurethane Composites for Sustainable Sound Absorbing Materials” is the results

of my own research except as cited in references.

Signature : ……….

Author’s Name : ………

Date : ……… CHIA POOI CHING

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APPROVAL

This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a partial fulfillment of the requirements for the degree of Bachelor of Manufacturing Engineering (Engineering Materials) (Hons.). The members of the supervisory committee are as follow:

………

(PROF. DR. QUMRUL AHSAN)

………

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ABSTRAK

Daun teh terpakai (STL) dari kilang penghasilan teh dianggap sebagai sumber baru dalam poliuretana matriks komposit sebagai bahan penyerap bunyi kerana daun teh yang kaya dengan polifenol dan hidrofilik kedua-dua bahan yang memberi manfaat kepada penyerapan bunyi dalam komposit. Laporan ini menyimpulkan penyediaan dan pencirian ke atas penyediaan daun teh terpakai (STL) diisi di dalam poliurethene (PU) komposit sebagai bahan penyerap bunyi. Objektif kajian ini adalah untuk mengkaji sifat-sifat fizikal dan kimia serta morfologi pelbagai gred daun teh terpakai, untuk membuat struktur bahan penyerap bunyi menggunakan teknologi hijau yang diperbuat daripada PU/STL komposit dengan gred dan beban daripada STL yang berbeza melalui teknik tuangan terbuka seterusnya untuk mengkaji fizikal dan kelakuan penyerapan bunyi serta morfologi PU/STL komposit. Terdapat tiga gred STL gentian yang digunakan dalam kajian ini, BM-FAE dan SW-BHE dari tangkai manakala FIBER-FAE dari daun pokok teh. PU/STL komposit telah dihasilkan melalui teknik tuangan terbuka dengan komposisi STL gentian yang berbeza yang terdiri daripada 4, 8, 12, and 16 wt%. Komposit yang dihasilkan kemudian tertakluk kepada ujian fizikal dan penyerapan bunyi serta pemerhatian mikroskopik untuk menganalisis taburan pengisi dalam komposit. Daripada kajian ini, keputusan penyerapan bunyi menunjukkan bahawa gred STL gentian yang paling halus (FIBER-FAE) memberikan pekali penyerapan bunyi yang terbaik dan meningkatkan komposis STL dalam PU mempamerkan pekali penyerapan bunyi mengurangkan secara berunsur-unsur.

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ABSTRACT

Spent tea leaves (STL) from tea producing factories are considered as new resources for sound absorbing polyurethane matrix composite materials because tea leaves are rich in polyphenols and hydrophilicity of both materials which is beneficial to the sound absorption properties of the composites. This report deduces the preparation and characterization of spent tea leaves filled polyurethane (PU/STL) composites for sustainable sound absorbing materials. The objectives of this study were to study physical and chemical properties as well as morphology of various grades of spent tea leaves, to fabricate a green sound absorption structure made of PU/STL composites with different grades and loadings of the STL through open molding technique, and to investigate physical and sound absorption behavior as well as morphology of PU/STL composite. There were three grades of STL fiber used in this study, which were BM-FAE and SW-BHE from the stalk while FIBER-FAE from the leaves of the tea plant. The PU/STL composites were fabricated through open molding method by varying fiber loading ranging from 4, 8, 12, and 16 wt%. The fabricated composites were then subjected to physical and sound absorption testing as well as microscopic observations to analyze the distribution of filler in composite. From this study, the sound absorption results shown that the finest grade (FIBER-FAE) spent tea leaves provide the best sound absorption coefficient and increasing the loading of the STL to the PU foam exhibits gradual decreasing of sound absorption coefficient of the PU composite.

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DEDICATION

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ACKNOWLEDGEMENT

First and foremost, I would like to express my utmost gratitude to my supervisor, Prof Qumrul Ahsan for his guidance, advice, concern, understanding and patience throughout the research period. His supervision has helped a lot in the progression of this final year project. I am indeed very grateful to be under his supervision. Besides, I would like to express my appreciation to my co-supervisor, Miss Chang Siang Yee, who has assisted me in ensuring a successful flow throughout the completion of this final year project. In addition, I would also like to express my appreciation to Dr. Azma Putra and his master student, En. Sajidin, as they had guided me in conducting the impedance tube measurement for my final year project.

Not to forget, thanks to the lab technicians involved from both Faculty of Manufacturing Engineering and Faculty of Mechanical Engineering for sharing their experiences, skills, opinions, advices and guidance in handling the equipments throughout the study.

Special thanks to my friends, Siti Aisyah Safuan and Chong Meng Mun for their help in periods of uncertainties and difficulties. Other than that, sincere appreciation is dedicated to my parents and my siblings for their love, encouragement and continuous support particularly when I am facing difficulties.

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TABLE OF CONTENT

Abstrak i

Abstract ii

Dedication iii

Acknowledgement iv

Table of Content v

List of Table viii

List of Figures ix

List of Abbreviations, Symbols and Nomenclatures xiii

CHAPTER 1: INTRODUCTION 1

1.1 Background Study 1

1.2 Problem Statement 3

1.3 Objectives 4

1.4 Scopes 4

CHAPTER 2: LITERATURE REVIEW 5

2.1 Acoustic Materials 5

2.1.1 Sound Absorbing Materials 7

2.1.1.1 Porous Sound Absorbing Materials 9

2.2 Synthetic Acoustic Materials 10

2.2.1 Cellular Porous Sound Absorbing Materials 10

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2.3 Natural Acoustic Materials 15

2.3.1 Fibrous Porous Sound Absorbing Materials 15

2.3.1.1 Tea Leaves (TL) 16

2.4 Sustainable Acoustic Materials 20

2.4.1 Natural Fiber Composites 21

2.4.1.1 Tea-Leaf Fibers Filled Polyurethane Composites 22

CHAPTER 3: METHODOLOGY 24

3.1 Introduction 24

3.2 Raw Materials 24

3.2.1 Polyurethane (PU) Foam 25

3.2.2 Spent Tea Leaves (STL) 26

3.3 Raw Materials Characterization 27

3.3.1 Dimensional Measurement 28

3.3.2 Particle Size Analyser (PSA) 29

3.3.3 Density Measurement 29

3.3.4 Fourier Transform Infrared Spectroscopy (FTIR) 29

3.3.5 Scanning Electron Microscopy (SEM) 30

3.4 Sample Fabrication 31

3.4.1 Preparation of Spent Tea Leaves (STL) 31

3.4.2 Preparation of Spent Tea Leaves Filled Composite 33

3.4.3 Sample Preparation 34

3.5 Sample Conditioning Test 35

3.6 Samples Characterization 35

3.6.1 Density Measurement 35

3.6.2 Scanning Electron Microscopy (SEM) 36

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3.8 Flow Chart Methodology 41

CHAPTER 4: RESULTS & DISCUSSION 42

4.1 Raw Materials Characterization 42

4.1.1 Dimensional Measurement 43

4.1.2 Particle Size Analyser (PSA) 44

4.1.3 Density Measurement 46

4.1.4 Fourier Transform Infrared Spectroscopy (FTIR) 47 4.1.5 Scanning Electron Microscopy (SEM) 54 4.2 Samples Characterization 57

4.2.1 Density Measurement 58

4.2.2 Scanning Electron Microscopy (SEM) 62

4.3 Impedance Tube Measurement 66

CHAPTER 5: CONCLUSIONS & FUTURE WORK 74

5.1 Conclusions 74

5.2 Future Work 76

REFERENCES 77

APPENDICES

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LIST OF TABLES

2.1 A Brief Summary of Flexible and Rigid Polyurethane Foams 13

3.1 Properties of Polyol and Isocyanate Components 26 3.2 Characteristics of Flexible Polyurethane (PU) Foam 26 3.3 Comparison of Polyurethane (PU) Composites and their Relative Codes 33

4.1 Minimum, Maximum, and Average Length Values of Three Different 43 Grades of Spent Tea-Leaf Fibers

4.2 Minimum, Maximum, and Average Diameter Values of Three Different 43 Grades of Spent Tea-Leaf Fibers

4.3 Minimum, Maximum, and Average Particle Sizes Values of Three Different 45 Grades of Spent Tea-Leaf Fibers

4.4 Average Densities Values of Three Different Grades of Spent tea-Leaf Fibers 46 4.5 FTIR Adsorption Bands of Typical Celluign Materials 52 4.6 Density Measurement of Composites 59 4.7 Average Values of Maximum Absorption Coefficients of Polyurethane 67 Matrix Composites

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LIST OF FIGURES

2.1 Acoustic Materials. 6 2.2 Description of Function of Sound Absorbing Materials. 7 2.3 Typical Variation of Sound Absorbing Coefficient for Different Absorbers. 8 2.4 Three main types of Porous Sound Absorbing Materials. 9 2.5 (a) Reactants Used for Polyurethane (PU) and (b) Polyurethane (PU) 11 2.6 Scanning Electron Micrographs of (a) Closed Porous Cells of Rigid 12

Polyurethane Foams and (b) Open Porous Cells of Flexible Polyurethane Foams.

2.7 Influences of Open Porosities of FPF on the Acoustic Absorption 14 Coefficients: C6–16.0 % Open Porosity, C7–25.0 % Open Porosity,

C8–83.0 % Open Porosity, and C9–88.6 % Open Porosity

2.8 Two Leaves and a Bud of Tea Plant Camellia Sinensis 16 2.9 Composition of Fresh Tea Flush (% dry weight) 17 2.10 Cellulose, Hemicelluloses, and Lignin Exist in Lignocellulosic Fiber 18 2.11 Sound Absorption of Three Different Layers of TLF Waste Materials 20 2.12 Sound Absorption Coefficient Values of Polyurethane and Tea-Leaf 23

Fibers Reinforced Polyurethane Composites with the Composition of 8%, 16%, and 24%

3.1 Polyurethane (PU) Foam 25

3.2 Different Grades of Spent Tea Leaves: (a) BM-BHE, (b) BM-FAE, 27 (c) SW-BHE, (d) SW-FAE, and (e) FIBRE-FAE.

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3.3 Vacuum Drying Oven 28

3.4 Vertical Optical Comparutor 28

3.4 Fourier Transform Infrared Spectroscopy (FTIR) 30

3.6 Scanning Electron Microscopic 31

3.7 Drying Oven 32

3.8 Pulverizor Machine 32

3.8 Test Sample for Impedance Tube Measurement 34

3.9 Electronic Densimeter 36

3.10 (a) Impedance Tube Kit Brüel&Kjael Type 4206, 38 (b) 40AE Prepolarized Free Field Microphones,

(d) LDS Photon+, and (e) G. R. A. S. Sound Calibrator Type 42AB

3.11 Flow Chart of Methodology 41

4.1 Particle Size Results for Spent Tea-Leaf Fibers with BM-FAE, SW-BHE, 45 FIBER-FAE Grades

4.2 FTIR Spectrum of Spent Tea-Lead Fibers with BM-FAE Grade 48 4.3 FTIR Spectrum of Spent Tea-Lead Fibers with SW-BHE Grade 49 4.4 FTIR Spectrum of Spent Tea-Lead Fibers with FIBER-FAE Grade 50 4.5 FTIR Spectrum of Spent Tea-Lead Fibers with BM-FAE, SW-BHE, and 51

FIBER-FAE Grades

4.6 Morphology of (a) BM-FAE, (b) SW-BHE, and (c) FIBER-FAE Grade 55 of Spent Tea-Leaf Fiber under Objective Lens Magnification x100

4.7 Morphology of (a) BM-FAE, (b) SW-BHE, and (c) FIBER-FAE Grade 56 of Spent Tea-Leaf Fiber under Objective Lens Magnification x300

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In the As-Received Form such as BM-FAE, SW-BHE, and FIBER-FAE with the Composition of 4% Mixed Polyurethane Composites

4.9 Measured and Theoretical Densities Values of Spent Tea-Leaf Fibers 61 In the Granulated Form such as BM-FAE, SW-BHE, and FIBER-FAE

with the Composition of 4%, 8%, 12%, and 16% Mixed Polyurethane Composites

4.10 Morphology of Polyurethane (PU) Cell Structure under Objective Lens 62 Magnification x50

4.11 Morphology of Cell Structure of (a) 4% As-Received, (b) 4% Granulated, 63 and (c) 16% Granulated BM-FAE Grade of Spent Tea-Leaf Fiber Mixed

Polyurethane Composite under Objective Lens Magnification x50

4.12 Micrograph of Cross-sectional SEM Images of Polyurethane Foam with 64 Spent tea-Leaf Fibers Additives under Objective Lens Magnification

(a) x200 and (b) x250

4.13 Micrograph of Cells Size Measurement of Polyurethane Foam for 65 PU/G BM-FAE4 Cell Structure under Objective Lens Magnification x200

4.14 Sound Absorption Coefficient Graph of (a) 4% As-received and (b) 4% 66 Granulated BM-FAE Grade of Spent Tea-Leaf Fiber Mixed Polyurethane

Composite

4.15 Average Values of Maximum Absorption Coefficients of Polyurethane 68 and Spent tea-Leaf Fibers in the As-Received Form such as BM-FAE,

SW-BHE, and FIBER-FAE with the Composition of 4% Mixed Polyurethane Composites

4.16 Average Values of Maximum Absorption Coefficients of Spent tea-Leaf 68 Fibers in the Granulated Form such as BM-FAE with the Composition

of 4%, 8%, 12%, and 16% Mixed polyurethane Composites

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Fibers in the Granulated Form such as SW-BHE with the Composition of 4%, 8%, 12%, and 16% Mixed polyurethane Composites

4.18 Average Values of Maximum Absorption Coefficients of Spent tea-Leaf 69 Fibers in the Granulated Form such as FIBER-FAE with the Composition of 4%, 8%, 12%, and 16% Mixed polyurethane Composites

4.19 Average Values of Maximum Absorption Coefficients of Spent tea-Leaf 71 Fibers in the As-Received and Granulated Form such as BM-FAE, SW-BHE, and FIBER-FAE with the Composition of 4% Mixed Polyurethane Composites 4.20 Average Values of Maximum Absorption Coefficients of Spent tea-Leaf 72

Fibers in the Granulated Form such as BM-FAE, SW-BHE, and FIBER-FAE with the Composition of 4%, 8%, 12%, and 16% Mixed Polyurethane Composites

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LIST OF ABBREVIATIONS, SYMBOLS AND

NOMENCLATURE

ASTM - American Society for Testing and Materials

BM - Broken mat

EHT - Extra High tension

FPF - Flexible Polyurethane Foams

FTIR - Fourier Transform Infrared Spectrocospy

–OH - Hydroxyl Ion

LaB6 - Lanthanum hexaboride

MP - Mechanical Pulp

mg KOH/g - Milligram of potassium hydroxide per gram

PMCs - Polymer Matrix Composites

PP - Polypropylene

PSA - Particle Size Analyser

PU - Polyurethane

KBr - Potassium Bromide

RPF - Rigid Polyurethane Foams

SEM - Scanning Electron Microscopy

STL - Spent Tea leaves

SW - Sweeping

TLF - Tea-Leaf-Fibre

USM - Universiti Sains Malaysia

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CHAPTER 1 INTRODUCTION

This chapter describes the background of studies, the problem statements, the objectives and as the scopes of the studies.

1.1 Background Study

In 1987, the World Commision on Environment and Development developed a definition of sustainability which became widely known as the Brundtland Report. It stated that

“Sustainable development meets the needs of the present without compromising the ability of future generations to meet their own needs.” From this point of view, a product can be considered sustainable if its production enables the resources from which it is made to continue to be available for future generations and has the lowest possible impact on human health as well as on the environment (Asdrubali, 2006).

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At present, green technology is widely used to produce materials from agriculture products as a substitute to synthetic fibers and wood-based materials (Mohd Nor et al., 2004). Organic natural fibers from agriculture are increasingly being investigated for various usages in many structural and non-structural applications such as automotive lining components and acoustic absorption barrier. For instance, coir fibers are the natural fibers used to replace synthetic fibers and wood-based materials for absorbing sound (Zulkifli et al., 2008). The introduction of the natural fibers as an alternative for glass-or mineral-fiber materials used as commercially available sound absorption materials in the building construction industry is due to the geometry and properties of the fibers. The plant-based fibers have a hollow and cellular nature and thus perform well as acoustic and thermal insulators (Zulkifi et al., 2008 and Chand and Fahim, 2008). Besides, these fibers are inexpensive, renewable and available in abundance, non-abrasive, does not give rise to health and safety issues during processing and handling, as well as light weight (Mohd Nor et al., 2004 and Chand and Fahim, 2008).

Though so, composite materials are the most advanced and adapted engineering materials because the matrix gives a composite its shape, surface appearance, environmental tolerance and overall durability while the fibrous reinforcement carries most of the structural loads, thus giving macroscopic stiffness and strength (Sreekum and Thomas, 2008). Therefore, natural-fiber reinforced composites have been developed through the incorporation of natural fibers into a matrix material such as thermosetting plastics, thermoplastics, or biopolymers. Natural fibers can be embedded in the polymeric matrices to reinforce and achieve desired properties such as sound damping, impart strength, stiffness, low density, and texture together with eco-friendly characteristics in the composites (Huda et al., 2008). It is evidenced in work done by Lopez et al. (2012) that the incorporation of mechanical pulp (MP), which is known as stone ground fiber, into polypropylene (PP), improvement of mechanical properties such as tensile strength and stiffness as well as sound absorption coefficient was found.

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1.2 Problem Statement

Various researches had been done on the natural-fiber reinforced composites from the past as the sound absorption purpose. However, some disadvantages of using these natural fibers in the composites had been indicated such as enormous variability, poor moisture resistance, poor fire resistance, lower durability, and lack of fiber-matrix adhesion (Joseph et al., 2005). Hence, in this study, spent tea leaves (STL) from tea producing factories are considered as new resources for sound absorbing composite materials because tea leaves are rich in polyphenols which are also referred as to tannins (Shu et al., 2006). The plentiful phenolic extractive of tea leaves possess high durability (Yalinkilic et al., 1998), high resistance to fungal and termites (Shu et al., 2006), and high resistance to fire (Dittenber and GangaRao, 2012). Meanwhile, in this research, STL filled polyurethane (PU) composites may attribute excellent adhesion properties between the STL fibers and the PU matrix due to hydrophilicity of both materials (Zhao et al., 2011) and this is beneficial to the sound absorption properties of the composites.

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1.3 Objectives

The aims of this research include:

1. To characterize physical and chemical properties as well as morphology of various grades of spent tea leaves.

2. To fabricate a green sound absorption structure made of spent tea leaves filled polyurethane composite with different grades and loadings of the spent tea leaves through open molding technique.

3. To investigate physical and sound absorption behavior as well as morphology of spent tea leaves reinforced polyurethane composite as sound absorbing material.

1.4 Scopes

The scope of study is mainly focusing on the sound absorption behavior of thermosetting plastics composites of polyurethane reinforced with three various grades of spent tea leaves like BM-FAE, SW-BHE, and FIBER-FAE as filler respectively with four different weight ratio of the fraction of composition in the composite; 96:4, 92:8, 88:12, 84:16, and 100:0 as a control specimen. It includes the determination of physical property through density measurement and sound absorption property under impedance tube measurement. The microscopic observation on the microstructural morphology of the composites is also included in this study to evaluate the distribution of filler in composite which is related to the sound absorption properties of the composites.

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CHAPTER 2 LITERATURE REVIEW

A literature review on previous research work in various areas which is relevant to this research is presented in this chapter.

2.1 Acoustic Materials

Noise pollution has becomes a common major problem to various developing nations (Mahzan et al., 2010). The noise pollution generally refers to unwanted sound produced by human activities unwanted in that it interferes with communication, work, rest, recreation, or sleep (Yuhazri et al., 2011). According to Ahmad and Wahid (2011), noise can cause, or be a factor in causing hearing difficulties, work-related stress, an increased risk of workplace accidents, the effects of noise on performance, interference with speech communication, sleep disturbance, cardiovascular and physiological effects, mental health effects, and effects of noise on residential behavior and annoyance. Here lies the importance of noise control, which tries to reduce the direct contact of noise to human. Various techniques have been implemented to reduce noise pollution, example wearing

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hearing protection, installation of sound barrier and implementing sound absorption panel (Mahzan et al., 2010).

Efforts to control noise and vibration in a wide range of mechanisms and devices inevitably require the use of passive acoustical materials, as shown in Figure 2.1. Conventionally speaking, acoustic materials are those materials designed and used for the purpose of absorbing sound that might otherwise be reflected. The acoustic materials work by two processes: absorption of sound energy, which dissipates sound as heat energy, and reflection, which reflects noise away from a location where silence is desired (Ahmad and Wahid, 2011). In the science of acoustical control, two classes of acoustical treatments are used to address airborne noise – noise is propagated through the air, namely barriers and absorbers. Likewise, two classes of acoustical treatments are used to address structure-borne noise – noise is propagated through the air after being radiated by a structure, namely isolators and dampers (Parikh et al., 2006). In general, effective noise control incorporates the use of both barriers and absorbers for airborne noise and both isolation and damping for structure borne noise (Ahmad and Wahid, 2011).

Figure 2.1: Acoustic Materials.

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Currently, commercially available sound absorption materials for acoustic treatment used in the building construction industry consisted of mineral fiber materials (Zulkifil et al., 2008). The European building insulation market of a value of approximately 3.3 billion Euros has been estimated to: mineral wool (glass): 27%, mineral wool (stone): 30%, foam plastics: 40%, and other materials: 3% (Asdrubali, 2006).

2.1.1 Sound Absorbing Materials

Arenas and Crocker (2010) claimed that sound-absorbing materials undergo their function by absorbing most of the sound energy striking them and reflecting very little, making them very useful for the control of noise, as shown in Figure 2.2.

Figure 2.2: Description of Function of Sound Absorbing Materials.

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1.2 Problem Statement

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1.3 Objectives

The aims of this research include:

1. To characterize physical and chemical properties as well as morphology of various grades of spent tea leaves.

2. To fabricate a green sound absorption structure made of spent tea leaves filled polyurethane composite with different grades and loadings of the spent tea leaves through open molding technique.

3. To investigate physical and sound absorption behavior as well as morphology of spent tea leaves reinforced polyurethane composite as sound absorbing material.

1.4 Scopes

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CHAPTER 2

LITERATURE REVIEW

A literature review on previous research work in various areas which is relevant to this research is presented in this chapter.

2.1 Acoustic Materials

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hearing protection, installation of sound barrier and implementing sound absorption panel (Mahzan et al., 2010).

Figure 2.1: Acoustic Materials.

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2.1.1 Sound Absorbing Materials

Figure 2.2: Description of Function of Sound Absorbing Materials.

Preparation Of Spent Tea Leaves Filled Polyurethane Composites For Sustainable Sound Absorbing Materials.

UNIVERSITI TEKNIKAL MALAYSIA MELAKA