i

2015

UMEÅ UNIVERSITET

Fysiska institutionen

Michael Bradley

2015-11-11

Course: Physics Thesis, 30hp (5FY026)

Project:

Characterization of Ultra High Molecular Weight Polyethylene

Nano Composites with Mg0.15Ni0.15Zn0.70Fe2O3

Student: Asad Muhammad Azam

Email: asmu0009@student.umu.se

asadpu2003@hotmail.com

Personal No.19830509-5492

Supervisor: Dr.Malik Sajjad Mehmood

Assistant Professor (Physics)

Department Of Basic Sciences, University of Engineering and

Technology, 47050, Taxila, Pakistan

Tel.: 0092 51 9047884

Email: malik.mehmood@uettaxila.edu.pk

Examiner: Dr.Ove Andersson

Professor (Physics)

Department of Physics

Umeå University, Sweden

Tel. +46-(0)90-7865034.

Email: ove.andersson@physics.umu.se

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Characterization of Ultra High Molecular Weight Polyethylene

Nano Composites with Mg0.15 Ni0.15 Zn0.70Fe2O3

Asad Muhammad Azam

(19830509-5492)

Master’s Thesis 30 ECTS (5FY026)

Department of Physics, Umeå University, Sweden

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Abstract

Ultra high molecular weight polyethylene has been commonly used as a biomaterial for total

joint replacements. This thesis concerns with the characterization of nano composites of ultra

high molecular weight polyethylene (UHMWPE) with Mg0.15Ni0.15Zn0.70Fe2O3 using various

analytic techniques such as fourier transform-infrared (FTIR) spectroscopy, differential scanning

calorimetry (DSC), and thermo gravimetric analysis (TGA). An accelerating aging of three

different samples, two commercial and one laboratory grade UHMWPE purchased from Sigma

Aldrich was done to study the thermal stability of UHMWPE, and the results were checked with

FTIR spectroscopy. The FTIR data revealed that UHWMPE purchased from Sigma Aldrich had

the highest thermal stability. Therefore, UHMWPE purchased from Sigma Aldrich was used for

further studies and preparation of nano composites with 1wt% and 2wt% Mg0.15Ni0.15Zn0.70Fe2O3

using the ball milling method. FTIR data show significant alterations as far as material

degradation and crosslinking is concerned. The absorbance in the region 1650-1850 cm-1 and

3000-3700 cm-1 significantly increases due to the enhance of CH2 bending to stretching ratio

with the incorporation of Mg0.15Ni0.15Zn0.70Fe2O3. As far as thermal stability is concerned,

composites with 1 % of Mg0.15Ni0.15Zn0.70Fe2O3 contents were less stable compared to pure

UHMWPE and UHMWPE composites with 2wt% of nano scale Mg0.15Ni0.15Zn0.70Fe2O3. The

degree of crystallinity obtained from DSC data was 41%, 40%, and 43% for UHMWPE,

UHMWPE+1% of Mg0.15Ni0.15Zn0.70Fe2O3, and UHMWPE+2% of Mg0.15Ni0.15Zn0.70Fe2O3,

respectively. The results of current study are useful while considering the nano composites of

UHMWPE with Mg0.15Ni0.15Zn0.70Fe2O3 in order to enhance the mechanical strength of

UHWMPE for industrial as well as medical applications such as orthopedic implants and bullet

proof jackets etc.

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Table of Contents

1. Introduction……………………………………………….…………………………………………………………………………….…..……1

1.1. General Properties of UHMWP…………………………………………………………………………………………….2

1.2. History of UHMWPE as Biomaterials....................................................................................…...4

1.3. Aims and Objectives………………………………………………………………………………………….………………....5

1.4. Thesis Outlines………………………………….……………………………….……………………………………………..….6

2. Literature Review……………………………….……………………………………………………………………………………………...6

2.1. CFR- UHMWPE Composite (Poly II)…………………………………………………………………………....…….….8

3. Experimental Details……………………………….……………………………………….………………………………...…………….10

3.1. Introduction………………………………………………………………………………………………………………….…...10

3.2. Material and Methods………………………………………………….…………………………………………………....10

3.2.1. Preparation of UHMWPE Sheet...……………………...................................................................10

3.2.2. Preparation of UHMWPE/Zn-nano ferrite composite……………………………………………………...11

3.3. Characterization…...................................................................................................................12

3.3.1. FT-IR Spectroscopy…………………………………………………………………………………….…….…….……....12

3.3.2. Thermo Gravimetric Analysis …………………………………………………………………………………….…...13

3.3.3. Differential Scanning Calorimeter..................................................................................…...15

4. Results and Discussion……………………………………………………………………………….…….……………………….………16

4.1. FT-IR study of Three Grades of UHMWPE............................................................…................16

4.1.2. FT-IR Study of UHMWPE/Zn- nano ferrites….………….………………….………….….…………….………22

4.2. Thermo Gravimetric Analysis of UHMWPE /Zn- Nano Ferrites…………………………………….……..25

4.3. Differential Scanning Calorimetric Analysis of UHMWPE/Zn-nano ferrite…...........................30

5.Conclusion…………………………………………………………………………………….……………………………………………………33

6. Future Direction………………………………………………………………………………………………………………………………...35

7. References………………………………….………………………………………………………………………………….……….…….....37

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1. Introduction

Ultra high molecular weight polyethylene known as UHMWPE is a versatile polymer which

belongs to the polyethylene family (PE). UHMWPE was introduced as biomaterial for total joint

applications after the failure of Poly-Tetra-Fluoro-Ethylene (PTFE) in 1962 by Sir John

Charnley. It has been used for various industrial applications which include total joint

replacement, bullet proof jackets and goods for the sports, guide rails etc. More than 90% of the

total joints replacement cases, hip cups and knee inserts are made of UHMWPE for immediate

pain relief in aching patients [1][3]. Artificial joint substitution for elderly people is increasing in

accordance with their desire for independent living and the recovery of functional use. In 1979,

The Swedish Hip Arthoplasty Register (SHPR) reported various types of prosthesis factors

concerning the operation and result in the form of complications. In this regard, the Nordic

Arthoplasty Register Association (NARA) was awarded a major grant from Nordic Council of

Ministers in order to harmonize the generic descriptions of the used prosthetics in the region.

According to SHPR annual report 2013, 16,299 total hip replacement operations were operated

in Sweden which corresponds to 324 per 100,000 inhabitants of age 40 years or older.

International comparisons of the developed countries reveal that Sweden is among the countries

where life expectancy is increasing and the proportion of elderly people is higher [2]. In case of

knee joint substitution, average life of UHMWPE joint is 15-20 years and for older people it

might need revised surgery because the life of an artificial joint depends on the degree of

deterioration of UHMWPE. Similarly, in USA’s current budget of total joint replacements is

more than 5 billion dollars and it is expected to rise steeply in the forth years. In USA Census

Bureau data, Nationwide Inpatient Sample(1990 to 2003) documented an increase to 3.48 million

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for primary total knee replacements while an increase of 572,100 in primary hip replacement is

expected to increase until 2030 [6]. Moreover, 11th annual report from the National Joint

Registry’s for England and Wales in 2014 which states more than 1.6 million cases which are

expected to rise rapidly [7].

Bio-implant materials such as Acetabular Liners and Tibial Inserts which are made of UHMWPE

of its biocompatibility, high wear resistance, low coefficient of friction, suitable stiffness,

abrasion resistance, toughness and relative low cost [4]. The extremely high viscosity of

UHMWPE has made it a challenging task to process reinforced UHMWPE composites. The high

viscosity of UHMWPE makes melt processing extremely difficult or almost impossible. For the

purpose of making UHMWPE composites; researchers are therefore trying to find the most

appropriate processing methods to incorporate fillers [5]. The most recent interest of researchers

concerns morphology, the structural and thermal properties of UHMWPE composites with micro

or nano fillers.

1.1. General Properties of UHMWPE

General properties of UHMWPE are summarized in table 1.1 [8]. UHMWPE is a linear homo-

polymer with a general formula (-CH2-CH2-) n having n degree of polymerization. It is formed

from ethylene gas C2H2 having molecular weight 28 g mol-1 [3]. The molecular weight of

UHMWPE is from 3 to 5 million g mol-1 having approximate degree of polymerization n ~

36000 in accordance with ISO-11542 while on the other hand ASTMD-4020 defines UHMWPE

molecular weight greater than 3.1 million g mol-1 with approximate degree of polymerization n ~

110,000 [2] [3] [9] [10]. The structure of UHMWPE has three phase morphology with highly oriented

and folded 10-50 nm thick and 10-50 µm long crystalline regions and the amorphous regions.

3

Table 1.1: General Properties of UHMWPE.

The amorphous phase is interlinked with crystalline phase through all-trans inter-phase region.

Its melting temperature (Tm) is around 137 0C and glass transition temperature (Tg) is about -150

0C [3]. UHMWPE has an orthorhombic crystal structure [9] and it does not exhibit flow transition

due to high molecular weight. The degree of crystallinity (Xc) is 39-75 % i.e. usually lower than

high density polyethylene (HDPE) which has crystallinity in the range 60-80 % [11].The

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morphological composition (crystalline, amorphous and inter-phase) determines the mechanical

strength and fatigue resistance of UHMWPE.

1.2. History of UHMWPE as a Biomaterial

UHMWPE has become the model standard for hip cups or knee inserts since its introduction as

biomaterial in 1962 due to its mechanical, chemical and structural properties. Many scientists

evaluated it as biomaterial in joints arthoplasty. In 1958, a technique of low friction arthoplasty

was introduced by Charnley while using PTFE as the bearing material implants. However, after

complete failure of PTFE, he adopted the chemically sterilized UHMWPE for low friction

arthoplasty (LFA) in 1962 due to the aforementioned properties of UHMWPE. In 1968-1969

commercial production of gamma sterilized UHMWPE was introduced because of toxic effects

of chemical sterilization. In 1998, clinical introduction of first-generation highly cross linked and

thermally stabilized UHMWPE came on the scene. In 2011-2012, clinical introduction of

polyethylene ether ketone (PEEK) in parallel with vitamin E diffused UHMWPE has been

introduced by various companies in the orthopedic community.

The longevity of the total hip or knee joints depends upon degradation of UHMWPE. UHMWPE

hip cup or knee plateau degradation during implantation is a big issue for the orthopedic

community because of its failure after few years of implantation. Oxidation degradation due to

trapped free radicals (formed mechanically, chemically and/or due to gamma-sterilization) is a

major factor for its failure. It is also experimentally determined that trapped free radicals which

are the result of gamma sterilization and/or cross linking causes material degradation via

oxidative reaction during aging at shelf and in vivo. The oxidation process of UHMWPE is very

complex; studies are still in progress to understand the complete oxidation mechanism of

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implants. Many scientists have tried to explain the oxidation mechanism but a comprehensive

and true picture is missing to the best of our knowledge. However, efforts have been made to

stabilize or eliminate these radicals by different means e.g. post irradiation, thermal treatments

(melting or annealing) and by adding a natural antioxidant such as vitamin E. In addition to this,

UHMWPE has been modified by incorporation of micro/nano particles to enhance the structural

and thermal stability.

1.3. Aims and Objectives

Among the major objectives of the current study are:

1. To determine the structural changes after incorporation Zn- nano ferrites using

mechanical ball milling method.

2. To determine the effect of Mg0.15Ni0.15Zn0.70Fe2O3 fillers on the heat of fusion and degree

of crystallinity of UHMWPE.

3. To determine the thermal stability of UHMWPE/Mg0.15Ni0.15Zn0.70Fe2O3 nano

composites.

Here in this study the characterization of UHMWPE/ Mg0.15Ni0.15Zn0.70Fe2O3 has been

performed using a variety of analytical tools such as FT-IR, TGA and DSC.

.

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1.4. Thesis Outline

The thesis has a major focus on the investigation of structural changes and thermal changes of

UHMWPE on incorporation of Mg0.15Ni0.15Zn0.70Fe2O3. The investigation has been performed

using FT-IR Spectroscopy, thermo gravimetric analysis and differential scanning calorimetric

analysis. The thesis provides a comprehensive literature review, detail of materials, sample

preparations, aging along with the experimental techniques used during the study. Structural

changes and effect of heat on oxygen induced residual radicals in UHMWPE/Zn nano ferrites are

the main results and the focus of the discussion in this thesis. At the end, conclusions along with

purposed future extensions and directions are discussed as well.

2. Literature Review

At nano-scale, UHMWPE is amorphous made of inherently composite material strengthen with

crystalline lamellae. UHMWPE can be customized at micro/nano scale by joining together

micro/nano particles resin with polymer powder before consolidation. UHMWPE fibers are

useful in fabricating composites since sheets or plies can be turned into multi-dimensional

structures with strong directional dependence of the properties. In the manufacture of blocked

cell, open cell as well as armored compound, UHMWPE can be treated as an intermediate or

final step. UHMWPE can be taken as matrix/fiber in multi choice of composite materials by

keeping in view the application. UHMWPE polymer and composite materials play a vital role in

armed forces, industry, and devour applications. Permeable UHMWPE materials have

application in water filters while in lead automotive batteries, mixture of glass fibers with

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UHMWPE composite films function as an insulative barrier. UHMWPE fibers have applications

in armed and personal shield equipment like cut-resistant ornament for kitchen use and body

protection (figure 2.1) [12]. These non-medical applications of UHMWPE fiber and matrix open

up doors for researchers to consider UHMWPE composites as a candidate for biomaterials.

Figure 2.1: Body Shield (A), Gloves (B) natural fiber from UHMWPE fibers. Courtesy of Carina Snijder and

DSM Dyneema.

In 1970, UHMWPE toughened with carbon fibers was tested for orthopedic insertions and

introduced commercially (USA, Indiana, Warsaw, Zimmer, Inc.,). Surgeons realized that

UHMWPE composites may not be suitable for total joint replacement applications due to

catastrophic instant clinical drawback [13] [14].Currently, the development of UHMWPE

composites by irradiation, thermal mechanism techniques and non-medical applications of

UHMWPE is considered as a low cost and beneficial material for biomedical applications. The

interest of the thesis is to discuss the chronological overview briefly concerning CFR-

UHMWPE composites known as poly II used in orthopedic implants and recent advancement in

UHMWPE matrix as well as fiber induced composites for biomedical purposes.

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2.1. CFR- UHMWPE Composite (Poly II)

UHMWPE with carbon is collectively called Poly II which was commercially and clinically first

used in USA, Indiana, Warsaw and Zimmer, Inc. The CFR-UHMWPE was reinforced in a

straight density molded UHMWPE matrix with randomly tilting carbon fibers [15]. During initial

experiment testing, the manufacturer found that CFR-UHMWPE shows improvement of wear

behavior relative to neat UHMWPE [16]. Further studies discovered that the fibers also improve

ductility, decrease fracture resistance and the surface of the UHMWPE fiber matrix [17].Wear

studies revealed consequences of abrasive wear concerning metallic counter face and fiber

disruption at the surface [18]. Poly II was observed to have premature fracture, wear and prevalent

delamination after its clinical introduction [13] [14] [19] [20] [21] and the material was eventually

withdrawn from further use. This clinical failure was not well simulated when materials were

studied by methods of standard testing and investigation. Initially, carbon in powder and fiber

forms armored with UHMWPE provided hopeful results. Numerous studies showed that carbon-

UHMWPE composites have superior tribological and mechanical results than neat UHMWPE

[16] [22] [24].

Wright et al reported that a CFR-UHMWPE composite was 88% harder than normal UHMWPE

and had the ability to withstand 17% additional compressive force. In 1970, biocompatibility

studies of CFR-UHMWPE showed that its response is satisfactory [25]. After clinical implant of

12-15 months it was observed that Poly II remained preserved from any significant foreign body

reactions according to Groth et al [26]. Rae and Rushton found that poly II causes an intra-

articular reaction in Mice similar to that of neat UHMWPE [27]. Research showed that CFR-

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UHMWPE composites for knee and hip joint substitution especially after clinical coverage has

casted uncertainty on the critical capability of CFR-UHMWPE composite. Rostoker and Galante

reported that in 25% graphite powder-filled UHMWPE in which short moment increase of wear

resistance seemed to be vanished [28]. Reinforced composites showed poor result of tensile

strength because of fiber breakage under injection molding, which was observed by Sclippa and

Piekarski [29]. Partial particle fusion and polymer molding problems were reported by others.

According to Wright et al, carbon fibers have been found to play a role in preventing firm

locking of polyethylene particles prepared from a matrix of poly II knee substitution components

when compared to clinical results from retrieved components [13] [14]. According to Connolly et

al, fiber-matrix union of reinforced UHMWPE composites showed approximately eight times

better fatigue crake expansion rate than pure UHMWPE [30].

Scanning electron microscopy is used to illustrate damaged knee cap components of the bearing

surface and shows that UHMWPE matrix has poor adhesion with carbon fibers (figure 2.2).

Figure 2.2: Scanning Electron Microscopy picture by Francisco Medel, PhD-student at Drexel University.

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Partial consolidation and instant clinical drawbacks of Ploy II components in certain cases

occurred due to direct decrease in volume of molded components. McKellop et al studied wear

behavior of Polly II and found that it has 10 times larger wear rate than UHMWPE also by

looking other common counter features of graded stainless steel and alloy of CoCr [30] [31].

3. Experimental Details

3.1. Introduction

In this study, composites of UHMWPE with Mg, Zn, Ni and Fe2O3 nano-ferrites (from here on

written as UHMWPE/MgZnNi-Fe2O3 nano ferrite composites) were characterized using Fourier

Transform Infra-red (FTIR) spectroscopy. The thermal stability of these composites will be

assessed with the help of Differential Scanning Calorimetry (DSC) and Thermo Gravimetric

Analysis (TGA). The main focus of this study is to analyze the structural changes at molecular

and atomic levels. Moreover, the effect of these changes on the thermal characteristics will also

be evaluated for its potential industrial applications. After discussing the material and method

used in this research, the basic principle of the experimental techniques along with used

experimental setting, temperature etc. will be discussed briefly in this chapter.

3.2. Material and Methods

3.2.1. Preparation of UHMWPE Sheets

In order to select the suitable and more stable grade of UHMWPE, three different grades i.e.

GUR 1020, i.e. GUR-1050 (commercial), and Sigma Aldrich (laboratory) were tested prior to the

preparation of UHMWPE/Zn-nano ferrite composites.

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The UHMWPE (GUR 1020, GUR-1050, and Sigma Aldrich) was pressed into the sheets of 1mm

thickness using hot press 190 0C at 20MPa with a hold time of 10 minutes. After the compression

treatment, the samples were cooled down to room temperature at 20 MPa. After preparation, the

samples were divided into four groups, one was kept as non-aged sample and other three samples

were put into an oven for one week, two weeks and three weeks of accelerated aging,

respectively. All the samples were aged at 80 0C in air following ASTM standard guide (ASTM

F2003-00) [79]. Note that the UHMWPE which was purchased from Sigma Aldrich is labeled as

“S” in the thesis from here on.

3.2.2. Preparation of UHMWPE/Zn-Nano Ferrite Composites

The appropriate concentrations (1.0% & 2.0 %) of nano-scale Mg0.15Ni0.15Zn0.70Fe2O3 (which is

called as Zn-nano Ferrite from here on throughout the thesis) were dispersed in acetone (100

mL) for approximately 45 to 50 min. The blends of UHMWPE and dispersed Zn-nano ferrite (in

acetone) were prepared by shaking the admixture. The acetone was then evaporated from the

slurry by heating the mixture at 60-70 °C for overnight in an oven. Afterward, ball milling of

samples were performed for 2 hours at 200 rpm using the ball milling facility available at

Pakistan Institute of Engineering and Applied Sciences, 45650, Islamabad Pakistan.

Subsequently, the homogenized UHMWPE/ Zn-nano ferrite composites were pressed by using

hot press (Gibitre Instrument srl or Gibitre Instruments Laboratory Press) and molded into sheets

of micron size.

The compression molding of composites was carried out in three systematic steps given below:

Step-1: The composites in powder form were preheated at 150°C for 5 minutes. It is worth to

mention here that during this preheated period the pressure was kept as low as possible.

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Step-2: The pressure and temperature were gradually raised to 200 bars and 190 °C, and on

achieving the required pressure and temperature samples were further kept at 190 °C for next 15

minutes.

Step-3: After combined heating and pressing treatment, samples were cooled to room

temperature (i.e. 25 °C) under the pressure of 40 MPa.

After the preparation of UHMPWE/Zn-nano ferrite composite sheets, all the samples were

labeled with various codes for their identification as far as concentration of Zn-nano ferrites was

concerned. The samples with codes are given in table 3.2.2.

Table 3.2.2: Sample codes used for identification within the text of this thesis

3.3. Characterization

3.3.1. FT-IR Spectroscopy

The absorption of electromagnetic energy in the infrared (IR) region occurred due to vibrational

modes of atoms in solids and liquids. Chemical species having different molecular formula are

present in semi-crystalline materials such as polymers. FT-IR spectroscopy is an extensively

used experimental technique for investigation of molecular structures and chemical bonds of

polymers. Nicolet-6700 fourier transform infrared spectrophotometer (Thermo Electron

Corporation, Waltham, MA, USA) was used to record infrared spectra in attenuated total

13

reflectance mode and plotted in transmission mode. The spectra were obtained in the range of

4000 cm-1 to 500 cm-1 at a resolution of 6 cm-1 after acquiring 216 scans.

Figure 3.3.1: FTIR Experimental arrangement.

3.3.2. Thermo Gravimetric Analysis

Thermal decomposition is studied using Thermo Gravimetric Analysis (TGA). The sample (~

mg in weight) under examination is immediately brought to the desired temperature non-

isothermally during TGA analysis. The weight loss as a function of temperature is counted at a

14

constant heating rate. The results obtained during TGA tests depend upon sample weight, size,

heating rate, dimensions and nitrogen flow or purge rate etc. In this particular study we have

done the TGA in open air environment.

Importance of these experimental parameters is due to the fact that temperature induced

decomposition rate is not only a function of temperature but also relates with amount and nature

of thermal decomposition process. During TGA experiments, one must be careful when samples

are tested for comparison purposes.

Thermo Gravimetric Analyzer from Mettler Toledo (Model: TGA/STDA 851e, Schwerzenbaclz,

Switzerland) has been used to investigate thermal stabilities of samples in the present study. The

samples (~10 mg) were prepared in an alumina crucible. For all samples, heating process run

from 50 0C to 600 0C at a rate 20 0C/min. Temperature versus % loss in sample mass is plotted.

Figure 3.3.2: TGA Experimental arrangement.

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3.3.3. Differential Scanning Calorimeter

Differential scanning calorimeter (DSC) is a largely used characterization technique in thermal

analysis of polymeric materials. It has the ability of estimating the degree of crystallinity (Xc),

peak melting temperature and re-crystallization temperature. The peak melting temperature and

width of the endothermic peak give detail about size distribution and crystal perfection. The

degree of crystallinity measured with the help of DSC curve can be used to estimate the

oxidation within the polymeric material. The decrease in Xc and the oxidation shoulder in the

DSC curve are due to main long chain folding on scission in smaller and less perfect crystals.

Moreover, DSC has also been used to determine gel contents and lamellar thickness [32].

DSC experimental analysis reported here are taken from TA Instruments (DSC Q100) in an inert

atmosphere.

Figure 3.3.3: DSC Experimental arrangement.

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The non-isothermal experiments were performed in an inert atmosphere with the rate of 20

0C/min of heating from 25 0C to 180 0C. Firstly, all the samples were heated then cooled to 50

0C. The percentage degree of crystallinity was calculated by using equation

Xc (%) = ∆H0m/∆Hm × 100......................................................................................................... (1)

Here, ∆H0m and ∆Hm represent the enthalpy of sample and enthalpy of melting of perfect

crystalline polyethylene (290 Jg-1) respectively. Heat of fusion was calculated from endothermic

peaks.

4. Results and Discussion

4.1. FT-IR Study of Three Grades of UHMWPE

In order to begin this work, the choice of the most suitable grade of UHMWPE (as far as its

thermal stability and service life is concerned) was essential. Therefore, as a first step, a

comparative study was carried out on two commercially available UHMWPE i.e. GUR 1020,

GUR 1050 and one laboratory grade UHMWPE purchased from Sigma Aldrich. These samples

were subjected to accelerated aging for three weeks following the standard protocol as defined

by ASTM standards [32]. The structural changes and oxidation degradation of these samples were

monitored by ATR-FTIR spectra taken after each week.

The most effective way to accelerate ageing of UHMWPE, which is currently in practice, is oven

aging and researchers are using this method of accelerating aging for estimating the service life

of UHMWPE and its composites [33] [34]. Un-aged and aged samples are tested using FTIR

spectrometer with the recommended setting as mentioned above. The IR absorption bands of

particular interest to evaluate the degradation of these commercial and laboratory graded

UHMWPE are listed in the table 4.1.

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Table 4.1: UHMWPE IR Absorption Bands of our interest.

Description IR absorption band (cm-1)

Alcohol & hydro-peroxide 3,450-3,350 [37] [38]

Carboxylic acid, Aldehydes, ketones &

Carbonyl species

1,710-1,740 [37] [38]

Ethers and other -C-O-C groups 1,100-1,400 [37] [38]

Trans-vinylene groups, C=C Unsaturated

bonds

800-1000 [37] [38]

Figure 4.1: FTIR Spectra of GUR-1020 grade of UHMWPE after 0-3 weeks of aging.

Figure 4.1 shows the FT-IR spectra of sheets of UHMWPE prepared from GUR-1020 which is a

commercially available grade of UHMWPE. In the figure, one can see that each spectrum is

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labeled as 1020-0K-xW, where variable ‘x’ represent the time of oven aging i.e. it is 0 for control

samples, 1 for one week of aging, and so on up to three weeks. It can be seen from the figure that

the spectra of GUR-1020 shows significant increase in absorption in the following bands after

aging.

From 3000 cm-1 to 3750 cm-1 which corresponds to typical end products of polyethylene

(PE) oxidation i.e. hydrogen bonded and non-bonded hydro-peroxide.

From 1650 cm-1 to 1850 cm-1 which is due to absorption of carbonyl species i.e. C=O.

From 1460 cm-1 to 1480 cm-1 and 2880 cm-1 to 3000 cm-1 which is associated with PE

crosslinking.

From 1100 cm-1 to 1400 cm-1 which is associated with –C-O-C– vibrations.

From 800 cm-1 to 1100 cm-1 which is related with the absorption due to C=C un-saturation.

It is evident from the figure that in addition to increase in absorption due to material degradation,

there is significant increase in absorption from 800 cm-1 to 1400 cm-1 which is mainly associated

with –C-O-C– vibrations and C=C unsaturation. Furthermore, there is an abrupt increase in the

absorption of functional groups associated with these bands for three week aged samples. When

all chemical groups are investigated, a similar trend has been observed for all grades i.e. hydro-

peroxides, carbonyl and vinylene species have represented considerably higher content for longer

aging time.

Figure 4.2 and 4.3 show FTIR spectra of samples prepared from GUR-1050 and Sigma Aldrich

grades of UHMWPE. The major changes are similar as those mentioned above for GUR-1020.

However, one can see from figure 4.2 and figure 4.3 that except from the typical oxidation

products and carbonyl species, the absorption due to –C-O-C– vibrations and C=C unsaturation

is considerable lower. This fact suggests that GUR-1050 and Sigma Aldrich UHMWPE have

19

higher stability than GUR-1020 when subjected to accelerated aging. The lower molecular

weight and shorter chains of GUR-1020 might be responsible for this fact. However, further

studies are in progress for detailed investigation of this difference as far as stability of various

UHMWPE grades is concerned.

To quantify UHMWPE degradations due to accelerating aging, the oxidation index (OI) of each

sample was calculated following the standard protocol as defined in literature [36] [37]. Basically,

“OI” is the ratio of the peak height due to C=O stretching (ᶹC=0) components of ketone present

at 1718 cm-1 to the absorption band at 2020 cm-1 which belongs to CH2 bending vibrations

(internal standard, ᵟCH2, “twist” bend) i.e.

Oxidation Index (OI) = I1718

I2020

The values of “OI” are shown in table-4.2 below:

Figure 4.2: FTIR Spectra of GUR-1050 grade of UHMWPE after 0-3 weeks of aging.

20

Figure 4.3: FTIR Spectra of UHMWPE samples purchased from Sigma Aldrich after 0-3 weeks of aging.

Table 4.2: Oxidation Index (OI) of UHMWPE grades under investigation.

UHMWPE

Grade

Control 1-Week Aging 2-Week Aging 3-Week Aging

GUR-1020 0.02 0.10 0.13 0.18

GUR-1050 0 0.05 0.13 0.14

Sigma Aldrich 0.01 0.04 0.08 0.09

From table 4.2 one can see that, the value of “OI” index is almost zero for control samples and

that it increases with increase in aging time. As expected, all three grades i.e. GUR-1020, GUR-

1050, and Sigma Aldrich show maximum values after 3rd week of aging. However, GUR-1020

is found to suffer more after three weeks of aging with an “OI” index of 18 % whereas

21

UHMWPE which was purchased from Sigma Aldrich shows a value of 0.09 which is found less

than 10 %. These quantitative results further confirms that UHMWPE which was purchased from

Sigma Aldrich (also commonly used for research work), is more stable when subjected to

accelerated aging as compared to GUR-1020 and GUR-1050. From these results one can

conclude that UHMWPE, which was purchased from Sigma Aldrich and frequently used by

researchers in laboratory work, is more thermally stable and may have longer service life as

compared to GUR-1020 and GUR-1050. On the basis of these results, further experimental work

reported in this thesis was carried out using UHMWPE which was purchased from Sigma

Aldrich.

22

4.1.2. FTIR study of UHMWPE/Zn- Nano Ferrites

Figure 4.1.2 (a, b): FTIR Spectra of Mg0.15Ni0.15 Zn0.70 Fe2O3 (a) and 1wt % and 2 wt % of UHMWPE/Zn-nano

ferrite composites (b).

(b)

(a)

23

Figure 4.1.2 (a) shows FTIR spectra of Mg0.15Ni0.15Zn0.70 Fe2O3 from 400 cm-1to 4000 cm-1 along

with the zoomed in segments from 400 cm-1 to 2000 cm-1and 400 cm-1 to 650 cm-1, respectively.

The synthesization controlled by thermal annealing at 500 °C sample explains typical

absorptions of ferrite phase at around 600 cm-1 and weak absorption in the range 410-450 cm-1

[39]. This difference in the band location is expected because of the difference in the Mg+-O2-

distance for octahedral as well as tetrahedral compounds. Waldron [40] considered viberational

spectrum of ferrites and assigned the sharp absorption band in the region of 600 cm-1 to the

intrinsic vibrations of the tetrahedral groups and the other band to the octahedral groups.

There is strong absorption in the region of 1600 cm-1 which suggests the existence of a small

quantity of residual carbon contents in the samples. The absorptions in the current case are

extremely strong which indicates that residual carbon remained after the synthesis process. The

wave numbers belonging to these absorptions indicate that residual carbon contents exist in the

form of complex carbonates. Annealing of this synthesized sample at 500 °C for 24 hour results

in decrease of this absorption [41] [46].The absorption bands at 3150 and 3450 cm−1, a broad

absorption feature to hydrogen-bonded OH groups is observed. The most interesting range of the

IR spectra, with respect to Ni–Zn ferrites, is the 650– 400 cm−1 range [42] [45] which is shown in

the inset of the figure 4.1.2 (a). This range is assigned to the vibrations of ions in the crystal

lattice. In this range, ferrites give rise to two prominent absorption envelopes. Between 800 and

500 cm−1, the v 1 band is found, which is assigned to FeIII–O and Zn II–O. The reported results

here are in good agreement with the already published literature [39] [42].

Figure 4.1.2 (b) shows FTIR spectra of UHMWPE nano composites with 1% and 2%

Mg0.15Ni0.15Zn0.70 Fe2O3 added in the UHMWPE matrix using ball milling, whereas the IR active

bands of particular interest are presented in table 4.1.2.

24

Table: 4.1.2: Characteristic FTIR absorption in the range investigated in this study.

IR Frequency (cm-1) Specifications/Functional Groups

963 Trans-vinyelene, (−CH=CH−)

910 Vinyl (-CH=CH2)

888 Vinyledene

1718 Ketone and/or ester (C=O vibration)

3420, 3550 Hydrogen and Non-Hydrogen Bonded

Peroxide

3605 Alcohols

1630 Carboxylic acid (R-COOH) group

1450-1480 CH2 bending vibration area

2880-2950 CH2 stretching vibration area

All hybrids exhibited the characteristic bands of the –CH stretching vibration of the CH2 group at

2924 cm-1 and 2849 cm-1, -CH2 bending vibration at 1470 cm-1 and 1460 cm-1 and the rocking

deformation of the long chain – CH2- groups at 730 cm-1 and 717 cm-1, respectively.

In the figure 4.1.2 (b) one can easily see that addition of Mg0.15Ni0.15Zn0.70Fe2O3 does induced

significant changes on the aforementioned functional groups. A slight increase in the region of

C=C unsaturation is observed in the 1wt% Mg0.15Ni0.15Zn0.70Fe2O3UHMWPE composite.

However, increasing the concentration of Mg0.15Ni0.15Zn0.70Fe2O3 from 1 % to 2 % had negligible

further effect on the concentrations of C=C unsaturation within the polyethylene (PE) matrix. A

significant increase in the absorbance from 1650-1850 cm-1 and 3000-3750 cm-1 shows that

25

addition of Mg0.15Ni0.15Zn0.70Fe2O3 followed by hot pressing the material at 200 °C induces

chain breaking and oxidation degradation via free radicals chain reaction mechanism. These free

radicals further react with the diffused oxygen of ferrites and results in enhancing the oxidation

degradation of nano composites of UHMWPE [43] [44]. The increase in absorbance from 1460-

1470 cm-1 indicates that the crosslinking density increased within the UHMWPE matrix [47] [48].

As far as Mg0.15Ni0.15Zn0.70Fe2O3 absorbance peaks are concerned, one can clearly see the

increase in absorbance in the 400– 650 cm−1 range which is due to Ni-Zn ferrites absorbance.

Furthermore, the strong absorbance peak at 1600 cm-1 is due to residual carbon which vanishes

completely after the molding process. High temperatures during the compression molding

process of UHMWPE nano composites might be the reason for elimination of this absorbance. It

has previously been reported that heat treatment of ferrites at and around 250 °C results in total

disappearance of this peak indicating the complete removal of residual carbon from sample [39]

[40].

4.2. Thermo Gravimetric Analysis of UHMWPE /Zn- Nano Ferrites

Figure 4.2 (a) shows the thermo-grams of Mg0.15Ni0.15Zn0.70Fe2O3 and involves only two

transitions physical and chemical during decomposition. Usually decomposition starts to occur at

about 100 0C with loss of water of crystallization, combustion, reduction of metal oxides and

physical transition like vaporization, evaporation and sublimation etc. Ferrites usually have

higher melt temperature round 900 0C [49] [50]. Figure 4.2 (b-d) shows the thermo-grams of P-0,

PF1-0, and PF2-0, respectively with the values of temperature corresponding to the beginning of

degradation and mass loss labeled in the figure. All the samples display single step mass loss

corresponding to the degradation of polyethylene backbone. Depending on the amount of mass

26

loss with temperature, the trend for each hybrid is divided into four steps: a slight increase in the

PE mass loss with maximum value at temperature TA=313-3250C ; an abrupt linear mass loss

started at temperature TB=400 0C; a sudden mass gain with maximum value at temperature

TC=455-465 0C and the complete volatilization of UHMWPE with onset temperature at TD=530-

537 0C .The observed changes in the thermo grams of the hybrids might be explained on the

basis of the different processes involved in the decomposition and volatilization of UHMWPE

which are: oxygen uptake, oxidation cycle as well as pure thermal degradation. The initial

increase in the mass loss of the hybrids is due to the uptake of diffuse oxygen in the amorphous

phase of UHMWPE. It can be seen from figure 4.2(b-d) that the temperature corresponding to

the start of thermal degradation (Temperature onset ) of pure UHMWPE is 400 °C, which is 5 °C

higher in PF1-0 and 5 °C lower for PF2-0 sample. The higher thermal stability of the composites

as compared with the pure one is attributed to the formation of a cross-linked network upon

chain scission and improved compactness of the PE [51] [53]. On the other hand, the influence is

found to decrease at 2% of ferrites. The decreased value of crosslink density and increased value

of oxidation degradation might be the reason for this because it has been reported that saturation

in crosslink density results in improved thermal stability of UHMWPE [52] [54]. Finally, the

incorporation of Mg0.15Ni0.15Zn0.70Fe2O3 appears to have no significant effect on the volatilization

stage of UHMWPE.

27

Figure 4.2 (a): TGA plot of powder (F) of Mg0.15Ni0.15Zn0.70Fe2O3.

28

Figure 4.2 (b): TGA plot of pure UHMWPE (P-0).

29

Figure 4.2 (c): TGA plot of I wt% Mg0.15Ni0.15Zn0.70Fe2O3 UHMWPE nano composite (PF1-0).

30

Figure 4.2(d): TGA plot of 2 wt% Mg0.15Ni0.15Zn0.70Fe2O3 UHMWPE nano composite (PF2-0).

4.3. Differential Scanning Calorimetric Analysis of UHMWPE/Zn-Nano

Ferrites

For further investigation of the thermal characteristics of UHMWPE/Zn- Nano Ferrites,

DSC has been performed and the results of the first heating run are shown in figure 4.3

(a).

31

Figure 4.3 (a): DSC curves of pure UHMWPE and UHMWPE + 1% and 2 % of Mg0.15Ni0.15Zn0.70Fe2O3.

All samples show a characteristic endothermic melting peak with melting temperatures at 138.20

°C, 140.56°C, and 143.56 °C, respectively. These values are comparable to already reported

values in the literature i.e. 137-140 °C for UHMWPE. The values of % crystallinity are 41.80 %,

40.82 % and 43.39 %, respectively. The peak melting temperature (Tm), heat of fusion (∆H0m),

and degree of crystallinity are listed in table 4.3 below.

32

Table 4.3: Peak Melting Temperature (Tm), Heat of Fusion (∆H0m) and (%) Crystallinity

of UHMWPE/Zn-Nano Ferrites.

Sample code Tm (°C) ∆H0m (J/g) Crystallinity (%)

P-0 138.20 121.24 41.80%

PF1-0 140.56 118.37 40.82 %

PF2-0 143.11 125.83 43.39%

A slight decrease in the heat of fusion (which is calculated while using the area under the

endothermic peak) with the incorporation of 1 % Mg0.15Ni0.15Zn0.70Fe2O3 is found while the

results for 2 % of Mg0.15Ni0.15Zn0.70Fe2O3 are comparable with the control one i.e. P-0. The

possible explanation for this behavior is the chain scissions close to crystalline lamella on

incorporation of 1% Mg0.15Ni0.15Zn0.70Fe2O3 is higher as compared to 2 % Mg0.15Ni0.15

Zn0.70Fe2O3. Further studies are in progress to have in-depth investigation, however, these initial

results reveals that adding lower contents of Mg0.15Ni0.15 Zn0.70Fe2O3 causes structural alterations

within the UHMWPE matrix. The decrease of heat of fusion for 1 % Mg0.15Ni0.15Zn0.70Fe2O3 also

reveals that degree of crystallinity of UHMWPE also decreased for this particular sample.

Furthermore, Mg0.15Ni0.15Zn0.70Fe2O3 has no melting peak within the range of our interest i.e.

from 25-180 °C (see figure 4.3(b)).

33

Figure 4.3 (b): DSC curve of Mg0.15Ni0.15 Zn0.70Fe2O3 (F).

5. Conclusion

The first step in this thesis work was the choice of a suitable grade of UHMWPE (as far as its

thermal stability and service life is concerned). For this purpose, three different grades (two

commerical GUR-1020 and GUR-1050 and one labortary grade purchased from Sigma Aldrich)

were subjected to accelerated aging during three consective weeks and tested after each week

using ATR-FTIR spectrometer. The results obtained revealed that GUR-1020 suffer more as

compared to other two grades i.e. GUR-1050 and Sigma Aldrich. The quantitative analysis show

that GUR-1020 degraded 18%, GUR-1050 degraded 14 %, and Sigma Aldrich UHMWPE

degraded less than 10 % , after three weeks of aging. These results showed that UHMWPE

34

which was purchased from Sigma Aldrich, and frequently used by researchers in labortory work,

is more stable when subjected to thermal/accelerating aging.

In the next step, composites of UHMWPE with nano scale Mg0.15Ni0.15Zn0.70Fe2O3 were prepared

and characterized using FTIR, TGA, and DSC for observing the alteration in structural and

thermal properties of UHMWPE. Mg0.15Ni0.15Zn0.70Fe2O3 is used in 1 % and 2 % concentration

by weight for composites preparation. Ball milling at 200 rpm for 2 hours has been performed to

obtain a homogeneous distribution of nano ferrites within the polymer matrix. FTIR data show

significant alterations as far as material degradation and crosslinking is concerned. The

absorbance in the region 1650-1850 cm-1 and 3000-3700 cm-1 increased significantly along with

the enhancement of CH2 bending to stretching ratio with the incorporation of

Mg0.15Ni0.15Zn0.70Fe2O3. As far as thermal stability is concerned, a composite with 1 % of

Mg0.15Ni0.15Zn0.70Fe2O3 contents showed lower stability than pure UHMWPE and UHMWPE

composite with 2 % contents of nano scale Mg0.15Ni0.15Zn0.70Fe2O3. The values for the degree of

crystallinity obtained from DSC data were 41.80 %, 40.82 % and 43.39 % for UHMWPE,

UHMWPE+1% Mg0.15Ni0.15Zn0.70Fe2O3, and UHMWPE+2% Mg0.15Ni0.15Zn0.70Fe2O3,

respectively. Therefore, on the basis of aforementioned results, one can conclude that

incorporating Mg0.15Ni0.15Zn0.70Fe2O3 in ≤1 % is not beneficial in order to achieve further

improvement in UHMWPE properties.

35

6. Future direction

On the basis of investigations presented in this study following future directions are

recommended:

The effect of incorporating the Mg0.15Ni0.15Zn0.70Fe2O3 nano particles on the optical

activation and sub band gap energies can be investigated for utilization of this material in

application such as optical sensors, solar cells etc.

The effect of high energy radiations in order to further improve structural and thermal

properties can be investigated.

The combined effects of different natural and synthetic antioxidant and

Mg0.15Ni0.15Zn0.70Fe2O3 can be investigated to improve results at lower contents.

In addition to FTIR measurement and/or by using any other non-destructive techniques,

such material’s optical properties, polarization properties, fluorescence properties, and

elastic light scattering properties can be used to study the variation within the material.

The techniques based on the above mentioned optical properties particularly polarization

properties such as Mueller matrix polarimetery and optical coherence tomography can

also be used for the estimation of Mg0.15Ni0.15Zn0.70Fe2O3 concentration with more

quantitative accuracy than FT-IR spectroscopy.

36

Acknowledgment

First and the foremost, I would like to say '' All praises to Allah'' who gave me the strength and

good health to complete this thesis.

Dr.Malik Sajjad Mehmood, Supervisor: I am grateful to you who has been served as an

excellent supervisor for the duration of my M.Sc. Physics thesis. Your door has always been

open to me for which I am grateful to you. You are truly an inspiring person with your

knowledge, passion, curiosity, dedication and struggle for Science and Technology. I am grateful

to you for all the opportunities and circumstances given to me. I will always be in debt to you. I

appreciate your kind and valuable guidance, advices, insightful comments on my work. You

have been always helping me to bring my thesis up to the necessary standards for its completion.

I owe my deepest gratitude to all the people who have been a part of this thesis in one or in

another way. All the authors particularly Dr Malik Sajjad Mehmood would like to thank Dr

Muhmmmad Shah Jahan, University of Memphis, Memphis, TN, USA and Ticona Inc. for

providing some samples/grades of UHMWPE for this research.

Dr.Rogger Halling, Study Advisor: I am grateful to you for all your kind help, guidance and

discussions about the M.Sc. Physics Thesis .You helped and stood by me in the toughest period

of my life. I really appreciate your guidance and affection to me during my whole study program

of Masters in Physics.

Dr.Jens Zamanian, Current Study Advisor: Sir, you are a kind, helpful, generous person who

always encouraged and motivated me to the accomplishment of my M.Sc. Physics thesis. I am

sure that every master student has excellent regards for you in the forest of curricular, extra-

curricular and administrative tasks. I am thankful to you for kind supports in the achievement of

37

one of the greatest goals of my life that is M.Sc. Physics thesis. I will always be in debt to you

for your educational and administrative help extended to me.

Dr. Sune Petersson, Professor:I am grateful to you for helping me in studies. Your attitude

towards me has always been very kind and inspiring.

Andreas Sandström, PhD Student of Professor Ludvig Edman: I appreciate your valuable

help and guidance in the laboratory work especially during my project of Advanced Materials

Course. I gained much knowledge from you in writing Laboratory Reports.

Nasir Mehmood, Testing and Evaluation Engineer. I am grateful to you (my brother) for

helping me in my studies.

Abdul Rehman Ahmed: I want to dedicate my thesis work to you who always inspired me to

struggle to do more to secure and make my future better. Finally, I acknowledge the constant

help, support and encouragement of my family members especially my mother Aziz Akhtar and

father the great Subedar Ch. Muhammad Khan.

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