The reinforcement with nanofillers greatly improves desirable properties
of thermoplastics. The ability to develop and process nanocomposite materials
into various products will be of critical importance in the development of
polymer products in this era of life to meet the ever increasing demands.
The need to promote organophilicity in place of the natural hydrophilic
character in inorganic nanomaterials is a crucial prerequisite for the good
performance of polymer-clay nanocomposites. When properly dispersed in
polymer matrix, nanofiller can provide excellent reinforcement, even when
present in very low filler loadings. Short fibre reinforced composites are
finding ever increasing applications in engineering and consumer products.
Short fibres are used in order to improve or modify certain thermomechanical properties of polymeric materials so as to meet specific
application requirements or to reduce cost of the fabricated article. Short
fibres can be directly incorporated into thermoplastics during processing
along with other additives and the resulting composites are amenable to the
standard processing steps and various type of moulding operations. But in
most of the cases fibre reinforced composites require fairly high fibre
loading to get the desired property. Higher fibre loading causes processing
difficulty which increases the chance for the voids during manufacturing
processes. This causes reduction in properties of short fibre reinforced
composites. Hence a composite with low filler loading is always the
optimum choice. Addition of small volumes of nanofillers into fibre
composites can effectively improve the properties. This type of hybrid
nanocomposites based thermoplastics are expected to possess attractive
performance even at low filler loading. The main objective of the present
study is to develop cost effective and highly versatile hybrid composite
based on Polypropylene (PP)/High Density Polyethylene (HDPE) blends.
To make the composite cost effective, surface modified kaolinite clay is
used as the nanofiller while the proven glass fibre as the microfiller. The
resultant nano and hybrid composites were characterized by analyzing
thermal, mechanical, rheological and morphological behaviour. While
many studies on nanocomposites focus on the importance of chemical
surface modification and the use of compatibilizers, the role and
importance of processing conditions are not extensively studied. Hence the
optimization of processing conditions and filler loading is carried out using
Box-Behnken method of Design of Experiments (DoE) and Minitab IV
software. Further if the mechanical properties are not described by
appropriate models, the application spectrum of the hybrid composite will
be seriously restricted. Hence micromechanical modelling is performed in
the last section to analyze the structure-property relationship and behaviour
of the composites under applied load.
The thesis is divided into nine chapters as follows.
Chapter 1: Introduction
A review of earlier studies conducted on mechanical, thermal,
rheological and morphological properties of nanoclay composites, short
glass fibre composites and hybrid composites along with a review on
design of experiments and micromechanical modelling is given in this
chapter. The scope and objectives of the present work are also discussed.
Chapter 2: Experimental
A brief description of the materials and experimental procedures
adopted for the preparation, analytical techniques and characterization
methods used for the study of both nano and hybrid composites of
PP/HDPE blend, nanokaolinite clay and E-glass fibre are presented in this
chapter
Chapter 3: Preliminary experiments for selection of materials and
range of experimentation
In this section the material system best suited to produce high
performance nanocomposites and hybrid composites is selected and the
range of melt compounding temperature is fixed by changing one factor at
a time method. The results are organized in 4 sections.
In section 3.3.A, the effect of surface modification of nanoclay in
improving the dispersion characteristics in polymer matrix is described.
Five different commercially available surface modified nanoclays are
added to the PP/HDPE blend and the mechanical, thermal and
morphological properties are analyzed. Based on the results, amino silane
modified nanoclay and unmodified nanoclay are selected to upgrade
PP/HDPE blend.
Optimization of blend composition of PP/HDPE/nanokaolinite clay
composites in the case of both unmodified and amino silane modified
nanoclay is described in section 3.3.B. The mechanical properties are
analyzed and 80 PP/20 HDPE blend is selected as the base polymer matrix.
Selecting the range of melt compounding temperature and glass fibre
content suitable for the preparation of nano and hybrid composites are
depicted in sections 3.3.C and 3.3.D respectively.
Effect of compatibilizers on the mechanical properties of PP/HDPE/
unmodified clay nanocomposites is illustrated in section 3.3.E.
Chapter 4: Mechanical properties of PP/HDPE/nanokaolinite clay
composites.
In this part, the effect of modified and unmodified nanoclay on the
mechanical properties of PP/HDPE matrix is described. Experiments are
carried out according to the Box-Behnken design table and the contour and
surface plots are drawn, which give a clear picture of response variation.
Model equations are developed to calculate the value of response at any
combination of process variable within the experimental domain. The main
effects plots are drawn to study the individual effect of each variable on the
mechanical properties. The p (probability of occurrence) and ANOVA
(Analysis of Variance) tests are carried out to investigate the relative effect
of each process variable. Statistical evaluation is also carried out to check
the adequacy of the model and the effect of process variables on the
responses. The tensile strength, tensile modulus, flexural strength and
flexural modulus increase on the addition of nanoclay where as the impact
strength decreases.
Chapter 5: Characterization of PP/HDPE/nanokaolinte clay composites
The PP/HDPE/naokaolinite clay composites are characterized using
thermogravimetric analysis(TGA), differential scanning calorimetry(DSC),
dynamic mechanical analysis(DMA), dynamic rheological analysis(DRA),
X-Ray diffraction(XRD), scanning electron microscopy(SEM) and
transmission electron microscopy(TEM) in this section.
Chapter 6: Mechanical properties of PP/HDPE/nanokaolinite clay/E-glass
fibre hybrid composites.
The mechanical properties of PP/HDPE/nanokaolinite clay/E-glass
fibre hybrid composites are analysed in this section according to BoxBehnken experimental design. The synergistic effect of surface modified
nano-micro filler suggests that organomodifed clay can act as a molecular
bridge between the hydrophilic glass fibre and organophilic polymer matrix
improving filler matrix adhesion and filler dispersion. This improves all the
mechanical properties including impact strength. The model equations are
developed, response surface, contour and main effects plots are drawn and
statistical evaluation is carried out.
Chapter 7: Characterization of PP/HDPE/nanokaolinte clay/E-glass
fibre hybrid composites.
The PP/HDPE/naokaolinite clay/E-glass fibre hybrid composites are
characterized using TGA, DSC, DMA, DRA, XRD, SEM and TEM in this
section.
Chapter 8: Micromechanical modelling of PP/HDPE/nanokaolinite
clay composites and PP/HDPE/nanokaolinite clay/E glass
fibre hybrid composites
Micromechanical modelling of both nano and hybrid composites is
carried out to obtain a better understanding of the behaviour of composite
under load bearing conditions. The experimental data on tensile modulus is
compared with conventional composite theories & models like Halpin-Tsai
model, Modified Halpin-Tsai model, Takayanagi model, Voigt rule of
mixtures, Reuss inverse rule of mixtures and Ji’s three phase model.
Chapter 9: Summary Conclusions
The summary and conclusions of the study are given in this section