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MGBEMENA, CHINEDUM OGONNA

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  • Name: EVALUATION OF THE MECHANICAL PROPERTIES OF POLYPROPYLENE/CALCIUM CARBONATE NANOCOMPOSITE AT VARIOUS CREEP CONDITIONS
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  • Length: [92] Pages

 

ABSTRACT

The mechanical properties of Polypropylene and Polypropylene/Calcium
Carbonate nanocomposites were evaluated. Data on the influence of Calcium
Carbonate on the tensile strength, young’s modulus, elongation and creep modulus
were obtained for the nanocomposite by conducting a tensile test for the coated and
uncoated samples and creep test for the coated samples at different Calcium
Carbonate loadings by varying the stresses and temperatures. It was found that the
resistance to creep was high for the nanocomposite as compared to the neat
Polypropylene. The Young’s modulus of the nanocomposite showed some
improvements with the incorporation of the Calcium Carbonate nano-filler while
the tensile strength deteriorated. The Creep modulus decreases with increase in
temperature and time. Above all, the Polypropylene and Polypropylene/Calcium
Carbonate creep responses showed a non-linear response for the properties
evaluated revealing viscoelasticity of the polymer matrix materials.

TABLE OF CONTENTS

Title Page ———————————————————————i
Approval———————————————————————-ii
Dedication——————————————————————–iii
Acknowledgement———————————————————–iv
Abstract————————————————————————v
Table of Contents————————————————————-vi
List of Tables—————————————————– ————ix
List of Figures—————————————————————–xv
Notation————————————————————————xix
Abbreviation——————————————————————xx

CHAPTER ONE
INTRODUCTION 1
1.1 Mineral Filled Polypropylene (PP) 4
1.2 Motivation 6
1.3 Objective of the Study 7

CHAPTER TWO
LITERATURE REVIEW 8
2.1 Introduction to Creep 13

VII

2.2 Creep in Plastics 16
2.2.1 Creep Modulus 18
2.2.2 Crazing Strength 19
2.2.3 Creep Rupture 19

CHAPTER THREE
EXPERIMENTAL WORK 20
3.1 Materials 20
3.2 Method of Preparation 20
3.2.1 Manual Mixing and Compounding 20
3.3 Rule of Mixtures 21
3.4 Tensile testing of the Samples 26
3.5 Creep Testing of the Samples 28
3.5.1 Apparatus Required 28
3.5.2 Description of the Apparatus 28
3.6 Experimental Procedure 30

CHAPTER FOUR
ANALYSIS 32
4.1 Results 32
4.2 Tensile Test Results 32

VIII

4.3 Creep Test Results 36
4.3.1 Creep Response at Ambient Temperature 37
4.3.2 Creep Test Results at a Stress of 13.08 MPa 37
4.3.3 Creep Test Results at a Stress of 19.60MPa 44
4.3.4 Creep Test Results at a Stress of 22.87MPa 50
4.4. Creep Responses at Temperature of 50oC 55
4.5 Creep Responses at Temperature of 70oC 61

CHAPTER FIVE
CONCLUSION AND RECOMMENDATIONS 71
5.1 Conclusion 71
5.2 Recommendations 72
REFERENCES

CHAPTER ONE

INTRODUCTION
Nanocomposites refer to materials consisting of at least two phases with one
dispersed in another that is called matrix and forms a three-dimensional network.
It can be defined as a multi-phase solid materials where one of the phases has one,
two or three dimensions of less than 100 nano metres (nm) or structures having
nano-scale repeat distances between the different phases that make up the
material(Manias,2007).

Nanocomposites differ from conventional composite materials mechanically due
to the exceptional high surface to volume ratio of the reinforcing phase and/or its
exceptional high aspect ratio. The reinforcing material can be made up of particles
(e.g. minerals), sheets (e.g. exfoliated clay sticks) or fibres (e.g. carbon nanotubes
or electro spun fibres). The area of the interface between the matrix and the
reinforcement phase(s) is typically an order of magnitude greater than for
conventional composite materials.

Polypropylene is isotactic, notch sensitive and brittle under severe conditions of
deformation, such as low temperatures or high temperatures. This makes limited
its wider range of usage for manufacturing processes. It is a versatile material
widely used for automotive components, home appliances, and industrial
applications. This is attributed to their high impact strength and toughness when
filler is incorporated.

2
To meet demanding engineering and structural specifications, PP is rarely used in
its original state and is often transformed into composites by the inclusion of
fillers or reinforcements.

Introduction of fillers or reinforcements into PP often alters the crystalline
structure and morphology of PP and consequently results in property changes
(Karger-Kosis, 1995).

Polypropylene is an exceedingly versatile polymer, made from a widely available,
low cost feedstock in a relatively straightforward and inexpensive process.
Polypropylene has good mechanical properties, chemical resistance, accepts fillers
and other selected additives very well, and is easy to fabricate by a variety of
methods. In addition, it is quite easy to incorporate small amounts of other
copolymers, such as ethylene, to yield Polypropylene copolymers with different
and commercially desirable properties. Overall, the combination of low cost, ease
of fabrication, ability to tailor the resin with co-monomers, and its acceptance of
high levels of fillers and other additives make Polypropylene a material of choice
in many cost-sensitive application.

However, the levels of fillers and other additives that must be incorporated to
achieve the desired properties are difficult or even impossible to incorporate “in
line” either in the polymerization process or in the fabrication step.

3
These fillers generally target specific property improvement, such as stiffness and
elastomeric properties, as shown in figure 1, or to meet service requirements such
as flame retardant specifications.
The common materials compounded into Polypropylene are mineral fillers (e.g.
calcium carbonate, talc or barium sulphate), glass fibre, elastomers such as
polyolefin elastomers or Ethylene-Propylene-Diene Rubber, and high levels of
colourants or other additives.

The incorporation of fillers and additives by compounding serves to extend the
performance envelope of Polypropylene to compete with engineering plastics or
against thermoset or thermoplastic elastomers.

For the purpose of this thesis, a composite is defined as a mixture of
Polypropylene and ingredient(s) in specific proportion to give a defined result or
product. The production of Polypropylene materials containing high levels of
additives, most notably fillers, is considered as compounding.The resultant
composite formed using nano filler is called a nanocomposite.

4
Stiffness/ HDT
Toughness
Glass filled coupled PP
Glass filled PP
Mineral filled PP
Homo PP
Co PP

Figure 1: Polypropylene properties.
source:www.nexant.com/products/csresports/index.asp?
Recently, many nanometer-sized types of filler have been commercially produced
and they represent a new class of alternative fillers for polymers. Among the
promising nano fillers that have stirred much interest among researchers include
organo clay, nano silica, carbon nano tube and nano calcium carbonate.
Studies have shown that the large surface area possessed by these nano fillers
promotes better interfacial interactions with the polymer matrix compared to
conventional micrometer sized particles, leading to better property enhancement
(Goa, 2004).

1.1 Mineral Filled Polypropylene (PP)
There are a number of inorganic mineral fillers used in Polypropylene. The most
common of these fillers are talc, calcium carbonate and barium sulphate; other
mineral fillers used are wollastonite and mica.

5
Mineral fillers are generally much less expensive than Polypropylene resin itself.
Mineral fillers reduce the costs of the compound formed with Polypropylene and
also increase the stiffness. Mineral fillers also provide reinforcement to the
polymer matrix as well. Some mineral fillers are surface treated to improve their
handling and performance characteristics. Sudhin and David (1998) Silanes,
glycols, and stearates are used commercially to improve dispersion, processing,
and also to react with impurities.

For the purpose of this thesis, the mineral filler used is calcium carbonate.
Calcium Carbonate (CaCO3) can be classified as:-
Mineral ground or Natural
Precipitated or Synthetic
Naturally occurring CaCO3 is found as chalk, limestone, marble and is the
preferred variety for filler incorporation into PP.
A typical composition of filler grade CaCO3 is shown below:
CaCO3 : 98.5 – 99.5%
MgCO3 : up to 0.5%
Fe2O3 : up to 0.2%
Source: Material safety data sheet
Other impurities include Silica, Alumina and Aluminum Silicate, depending on
location and source of the ore.

6
Loadings of CaCO3 in PP typically run from 10 to 50%, although concentration as
high as 80% has been produced Karger-Kosis (1995).
CaCO3 is usually selected as filler when a moderate increase in stiffness is desired.
It also increases the density of the PP compound; reduces shrinkage, which can be
helpful in terms of part distortion and the ability to mould in tools designed for
other polymers. At typical levels of 10 to 50%, the CaCO3 does not significantly
affect the viscosity of the compound. The main secondary additive employed in
CaCO3 is a stearate. The stearic acid acts as a processing aid. It helps to disperse
the finer-particle size CaCO3. It also helps to prevent the absorption of stabilizers
into the filler. Finally, as an added benefit, it acts to cushion the system, resulting
in improved impact. The dispersion qualities of CaCO3 particles play a crucial role
in its toughening efficiency.

1.2 Motivation
Nanocomposites have attracted attention in recent years because of improved
mechanical, thermal, rheological, solvent resistant and fire retardant properties
compared to the pure or conventional composite materials. Therefore, much work
has focused on developing PP/CaCO3 nanocomposites with tailored mechanical
and morphological properties.This has received much attention from academia and
industry globally.
Engineers and polymer scientists are working hard to produce lightweight
materials as suitable replacement for metals.

7
1.3 Objectives of the Study
The present work aims to:
 Evaluate the Tensile properties of coated and uncoated calcium carbonate
nano-filler with Polypropylene as the host polymer for different volume
fractions.
 Evaluate creep behavior of the coated nanocomposite, for each volume
fraction of the fillers.
 Examine the effects of the fillers on the mechanical behavior of the
nanocomposite. This examination can be utilized for processability and in
developing optimum morphology to maximize products performance.
 This work is an attempt at nano structure fabrication and to get into the
main stream of composite technology of the 21st century.

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