1. 1
and
Aerospace Engineering
Ashby Building
Stranmillis Road
Belfast
BT9 5AH
Mechanical and Aerospace Engineering
Final Year Project Technical Report
Project 3B
AER3021
Fabrication and Characterization of Novel Boron Nitride/Polymer nanocomposite
Author: Sayed Asif Iqbal [40110295]
Project Supervisor: Dr Dan Sun
Programme: BEng Aerospace Engineering
Date: 18th
March 2016

2. 2
Table of Contents
List of Symbols and Abbreviations ....................................................................................... 3
1.0 Introduction ................................................................................................................... 4
2.0 Literature Review ........................................................................................................... 5
2.1 BN Nanofillers ......................................................................................................................... 5
2.2 BN Nanofillers in contrast with Carbon precursors ................................................................ 6
2.3 Polymer processing Techniques .............................................................................................. 7
2.4 Dispersion of Nanofillers into Polymer matrix ........................................................................ 8
2.5 Post-extrusion stretching ........................................................................................................ 9
3.0 Methodology .......................................................................................................................... 11
3.1 Materials ............................................................................................................................... 11
3.1.1 Polymers and Nanoparticles .............................................................................................. 11
3.2 Pre-Melt-Mixing Processes ................................................................................................... 11
3.3 Melt-mixing Process .............................................................................................................. 12
3.3.1 Twin-screw Configuration .................................................................................................. 12
3.3.2 Twin-screw Extrusion Processing ....................................................................................... 13
3.4 Characterization ........................................................................................................... 14
3.4.1 Mechanical Analysis ........................................................................................................... 14
3.4.1.1 Tensile test in room temperature conditions ................................................................. 14
3.4.1.2 Uniaxial stretching at elevated temperature conditions ................................................ 15
3.4.2 Thermal Analysis ................................................................................................................ 15
3.4.3 Structural Analysis .............................................................................................................. 16
4.0 Results and Discussion ........................................................................................................... 16
4.1 Mechanical Analysis .............................................................................................................. 16
4.2 Thermal Analysis ................................................................................................................... 20
4.3 Structural Analysis ................................................................................................................. 23
5.0 Conclusions ............................................................................................................................. 24
6.0 Recommendation of further work ....................................................................................... 25
7.0 References .............................................................................................................................. 26

3. 3
List of Symbols and Abbreviations
BN Boron Nitride
HDPE High density Polyethylene
eV Electron Volts
h-BN Horizontal Layered Boron Nitrite
BNNs Boron Nitride nanosheets
BNNTs Boron Nitride nanotubes
CNT Carbon nanotubes
SR Stretching Ratio
Wt% Percentage weight
QUB Queen’s University Belfast
CS Crosshead speed
Tm Melting temperature
Tc Crystallization temperature
Xc Crystallinity content
Impr Improvement

4. 4
1.0 Introduction
Polymers, according to Oxford Dictionary, are simply the combinations of small simple molecules
grouped together in a chain-like order to form large and long groups of atoms. The word ‘polymer’
was first coined by a Swedish chemist called ‘Jöns Jacob Berzelius’ in 1832 [1] and later established
by a German chemist named ‘Hermann Staudinger’ in 1905 [2]. The beauty behind the sciences of
such ‘macromolecules’ intrigued the chemists from the very start of 1900s. With later discoveries
in the progression of time, it was quite surprising to find out that polymers existed all around and
within us. Macro molecules are found to be present by far and wide, from the food we eat which
contains starch or proteins, to the very bits of DNA strands inside our infinitesimal body cells [3].
These naturally occurring polymers emerged after pursuits of tremendous studies conducted to
interpret material sciences and biophysics. From the data gathered from these studies to the in-
depth understanding- all these lead to the evolution of synthetic polymers, and now it is nearly
impossible to imagine our world without them. Understanding these useful macro molecules have
enabled us to customize and alter their structures to achieve composite materials with desired
properties relevant to its use. Greatest evidences will include usage of ‘para-aramid’ in bulletproof
and waterproof vests, ‘meta-aramid’ in the hood of fire-fighter’s mask, ‘copolyamid’ in fiber optic
cables and many more [4]. To get the most out of these materials and to make our lives easier, two
or more different materials are blended in an effort to accomplish the best properties of both. Such
nanocomposite materials with at least one component of nanoscopic scale in size (10-9
m) have
remarkable properties like high surface to volume ratio, increased ductility and are scratch
resistant, and so on. [5].
This project is about fabrication and characterization of Boron nitrite/high density polyethylene
nanocomposites. Along with a comprehensive research for the understanding of the structure and
properties of these materials, the project will also reflect and unfold the industrially relevant
polymer processing technique called "extrusion". Different proportions of boron nitrite powders,
ordered from SIGMA-ALDRICH, will be melt-mixed with high density polyethylene pallets under
twin-screw extrusion process. Suitable composite samples will be extracted from the extruded
sheet and appropriate testing methods standards will be identified. Samples will also be stretched
in the uniaxial direction to scrutinize material behavior exposed to different test conditions.
Moreover, these samples will be tested using different engineering equipment and detailed

5. 5
comparisons will be obtained and investigated. Result analysis will later be discussed to provide
better reasoning and understanding of the micro structural behavior.
2.0 Literature Review
2.1 BN Nanofillers
After the evolution of Rubber technology at roughly 1800s, synthetic polymers started being
fabricated and just prior to world war II, this industry started to grow introducing different arrays
of materials referred to as ‘Plastics’. These pallets or powders are produced by mechanical blending
or melt state mixing procedures [6]. Boron nitride nanocomposites, a structural analogue of carbon
precursors, were first fabricated at the late 90s. Instead of carbon atoms linked in chains, boron
and nitrogen atoms are joined up alternatively [7]. With at least one dimension in between the
scale of 1 to 100 nanometers, these extraordinary and flexible forms of nanostructures can be
formed into various structural arrangements e.g. nanotubes, nanosheets, nanohorns, spherical
nanoparticles, etc[ 8].
Fig 2.1: TEM image of BN Nanosheets
The layered nature and planar networks between the BN hexagons allow such flexibility to produce
nanosized BN which is much superior in various properties compared to the traditional microsized
BN fabricated years ago. BN nanostructures are equipped with novel properties intrinsically which

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includes wider bandgap up to 6 eV, anti-oxidation and structural ability, high thermal conductivity
and great mechanical properties [8]. In contrast with the aforementioned attributes which are quite
similar to corresponding carbon materials, boron nitride analogues possess several unique features
that makes them quite significant in modern world. These structures, unlike carbon
nanocomposites, are white or transparent in color due to its wide bandgap so can be dyed
depending on different requirements [8]. Moreover, the carbon precursors are observed to lower
the electrical insulation of polymers, whereas BN nanostructures are dielectric in nature that
strengthen its use as gate layers and remarkable use in electronic packaging. In recent years,
nanosized BN as shown in figure 2.1 are produced with very high aspect ratio, thermal conductivity
up to thousands of Wm-1
K-1
(when used as nanofillers) and tremendous material strength [8].
2.2 BN Nanofillers in contrast with Carbon precursors
BN nanosheets are comprised of one or few layers of hexagonal boron nitride (h-BN). After the rise
of Graphene in the year of 2005, the first pure monolayer h-BN was originated in a mechanically
milled residue[9]. So far, various methods are implemented including ball milling [11], mechanical
cleavage [10], the reaction between boric acid and urea[13-14] and high energy electron beam
irradiation [12]. Ultrathin nanosheets are produced from chemical vapor disposition (CVD) method
[9]. Whereas the ‘chemical blowing’ method is considered to be the simplest of all due to its catalyst
and substrate-free route [9]. Besides, it not only gives the luxury to obtain larger lateral dimensions
of BN nanosheets that aids research to be carried out regarding its electrical and mechanical
behaviors, but also can be used later on to produce strong polymer composites [9]. The CVD
method is widely used to produce both BN nanosheets and nanotubes: one or few layers of BN
sheets rolled up to nanoscale. Figure 2.1 represents a brief tabular comparison between graphene,
BNNSs, CNT and BNNTs [8]:

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Fig 2.2: Comparison between graphene, BNNSs, CNT and BNNTs properties in different fields in a
nutshell [8].
2.3 Polymer processing Techniques
In the plastic processing industry, injection moulding is widely used to process polymer composites
due to its cost-effective way of processing three-dimensional and complex thermoplastics at
greater quantities [16]. However, the parts and equipment like hopper, feed throat, barrel, etc. are
expensive to maintain and it’s costly to operate the machine as well. With series of procedures,
polymers are processed via injection moulding. The plastic pallets are fed to the injection unit
where it is heated by the barrel and melted the by the sheer force of the revolving screw. Later the
melted polymers are pushed into the mould section where the shape of the plastic is altered by
heating and cooling in various different ways. Other moulding techniques like blow and rotational
moulding are also used.
Techniques like extrusion and injection moulding are worth mentioning. Conventional extrusion
processes are material intensive techniques where the polymers are manipulated in molten
state[6]. This is considered as the state of the art technique till date because it is specialized to
produce final product from raw polymers. The mechanism is quite simple where the nanofillers are
dispersed into the polymer matrix by melt mixing [6]. An archetypal extruder can be of two types:
single screw and twin screw extruder. Both extrusion processes have horizontal barrels with
adjustable temperature cores, a hopper to collect the raw materials, extruder and die section. Raw

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materials are taken down and then crushed and melted by the rotating screw(s) in the extruder,
thus dispersing the additives into the polymer matrix [17]. The final products then exit through the
end of the barrel or die section. The screw speed is alterable to maintain smooth mixing and
dispersion into the polymer matrix, even if the melt solution gets too viscous due to more addition
of nanofillers[18].
The screw(s) inside the barrel play(s) crucial role in mixing the raw materials. Single-screw extrusion
process implies the barrel containing one screw rotating only in order to blend the raw polymers in
few different stages. The screw, when analyzed, is seen to have different depths along its length
and can be classified into three sections carrying out different functions in each region. The feed
section screw will simply rotate and take up the raw materials into the compression section which
has lesser screw depth [18]. This change in depth not only allows to apply pressure and compress
the polymers, but also squeezes the air bubble and send them back to the previous section of the
rotating screw. The polymers are sharply and gradually melt mixed and then conveyed to the meter
section where the screw depth is lowest and is constant throughout the section. Temperature in
each section will differ throughout the process to depending on the melt characteristics of the
materials. The metering screw zone will homogenize the melt until fed to the die section which has
constant temperature and pressure conditions [19]. Moreover, the die section will filter and
separate by getting rid of extraneous material and letting the expected product polymer to extrude
out.
For twin-screw extrusion system, two screws are rotated in different syntaxes to serve the purpose.
The two collaborating screws can be positioned into four types of screw systems including co-
rotating/counter-rotating intermeshed and co-rotating/counter rotating non-intermeshed. For
intermeshing screws attached together, flow patterns are not allowed to pass in-between the
screws. But for non-intermeshing arrangements small clearance is observed where the flow
patterns are compared with the figure-of-eight [18]. Operation variables like heat generation and
mixing efficiency are enhanced to get optimized outputs.
2.4 Dispersion of Nanofillers into Polymer matrix
As far as dispersing nanofillers into polymer matrix are concerned, dispersion properties or types
depend directly on the shear forces exerted by the screw(s) system. Two types of dispersion are
listed as dispersive and distributive mixing. Dispersive mixing is concerned with the process where

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the screws exert high shear forces which breaks large clusters into small ones by overcoming
interacting forces and dispersing them throughout the solution. Whereas distributive mixing, on
the other hand, is referred to take place in a low shear exertion system where the weak forces
interacting between the nanofillers, distributing them uniformly through the melt. Screw
geometries are responsible for the amount of shear force exerted to the mixture which, therefore
high shear forces are crucial to achieve dispersive mixing. However, high shear forces are
responsible for breaking the clusters into finer ones, but this type of flow is not enough as we are
required to disperse the nanofillers as well. Applying high shear forces by altering screw geometries
is only half the job done, other main flow type is solely required referred to as elongation plays a
great role in uniform dispersion [20]. Higher extensional elongation can be applied to the
nanoparticles in the polymer melt in the twin screw extrusion process. It is also observed that high
screw speed and longer mixing time is the key to better morphology of the nanocomposites
obtained.
2.5 Post-extrusion stretching
Biaxial and uniaxial stretching takes place in the extrusion process where the nanoparticles and the
polymer while in melt state. Not only that during post processing, a sample cut from the extruded
sheet can be taken and stretched in solid state in one or both direction in the x, y plane. It is
significant to observe that the post-extrusion stretched nanocomposites had different properties
compared to that of un-stretched ones. In a research carried out by the School of Aerospace and
Mechanical Engineering, QUB on biaxial stretching [21] of polymer nanocomposites, novel
enhanced properties were observed. With a temperature between 145-150 degrees being set up,
a 76mm×76mm×1mm compression moulded sheet of PET/clay nanocomposite is biaxially
stretched at 1.5, 2.5, 3 and 3.5 stretching ratios and loaded at the strain rate of 8 and 16s-1. Each
test were repeated twice to get a better approximation of the results. The forces and displacement
at x, y plane were recorded by the help of Labview Data Logging Package. Looking at the results, it
concludes that higher strain rates were driving a higher yield stress of the sample [21]. Moreover,
addition of clay as a filler were contributing to greater entanglement of the molecules. Higher yield
stress at lower temperature was also observed as nanofilled composite materials are more sensitive
to temperature. Under X-ray diffraction (XRD) analysis, it is monitored that the d-spacing in the
PET/clay lattice is noted to reduce at the strain rate of 1.5. Besides, the d-spacing slightly increased
with higher strain rates which was still lower than that of the unstretched sheet. So this overall
decrease took place because of the compression of the clay particles (nanofillers) due to stretching

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[21].
In TEM analysis, the stretched and unstretched samples are compared under ultrahigh
magnification where it is observed that on stretching it is evident that the delamination of
nanofillers were resulting to stack up and align the particles. Differential Scanning Calorimetry (DSC)
were used to examine the crystallinity of the test sample. It was observed that the crystallinity was
increasing with higher strain rates but it also concluded that greater crystallinity doesn’t contribute
to higher mechanical strength [21]. It is also seen that the tensile strength only increases, when the
sample is stretched and the highest strength is achieved at the highest strain rate of 3.5, also giving
rise to the break stress. This is described and associated with the better unity of the polymer due
to temperature application and stress exertion. It is also very important to notice that the effect on
modulus is not observed until the sample was stretched up to SR 2.5. This happens because the
degree of alignment of the molecules are only articulated at this very stage. This rate might differ
from different starting material to form the nanocomposite [21].
Unlike biaxial stretching, uniaxial stretching is similar but the sample is either stretched along the
length or perpendicular to the length. In terms of uniaxial stretching, equipment like two
dimensional wide angle x-ray scattering (2D-WAXS) fit to serve the purpose to characterize the
sample after it is stretched. DSC is also used in biaxial stretching characterization. The process is
quite similar to biaxial stretching as the sample is uniformly heated and but stretched at one
direction only. Hence by the help of all state of the art equipment, like WAXS and DSC, the sample
uniaxial stretched sample is characterized in terms of thermal or mechanical strengths.

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3.0 Methodology
The mechanisms equipped in QUB to produce boron nitride/high density polyethylene
nanocomposite sheets and preparing them for characterization processes are shown in Fig 3.1:
Fig 3.1: Preparation plan for high density polyethylene/boron nitride nanocomposites samples
3.1 Materials
3.1.1 Polymers and Nanoparticles
Non hazardous and odorless High density polyethylene, ordered from Safripol, were used as a
polymer matrix for this project. These pallets were grounded prior to twin-screw melt mixing
process in order to ensure a homogenous mix. Boron Nitride powder, molecular weight of
24.82g/mol, were procured from Sigma-Aldrich in order to be used as filler material to produce
BN/HDPE nanocomposite sheets, of approximately 1mm thickness, through an industrially relevant
processing route called twin-screw extrusion.
3.2 Pre-Melt-Mixing Processes
Five transparent plastic bags were labelled initially with an intent to classify different percentage
of filler composition to be mixed with the polymer matrix. Both materials were weighed manually
using the available laboratory scale equipment in the Material processing hall at QUB. Five
compositions were pre-melt-mixed at 0 wt%, 0.1 wt%, 0.2 wt%, 0.5 wt% and 1 wt% BN powders
with HDPE pallets. Five plastic bags containing the aforementioned composition of BN powder with
HDPE pallets were well shaken up for few minutes. Safety measures like disposable face masks and
HDPE(Polymer)
Pallets
Boron Nitride
Powder
Melt Mixing in
QUB Twin-screw
extruder
Extruded
Sheet
Cut
Samples
Characterization

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lab eyewear were equipped at all times to prevent accidental exposure of the materials with human
contact.
3.3 Melt-mixing Process
3.3.1 Twin-screw Configuration
The Collin GmbH twin-screw extruder were set up at a particular customized screw configuration
to enhance mixing of the materials shown below in figure 3.2. The screw profile consists of
kneading blocks(KB), conveying(GL) and mixing elements(ZMI) in both forward(R) and reverse(L)
directional flow effects. The detailed screw configuration indicates the variation of different
mixing inputs at each section of the screw profile which contributes to the enhancement of the
mixing quality and filler dispersion.
Fig 3.2: Schematic of screw profile designed to enhance mixing
For better and in-depth understanding, few screw elements were picked from this configurations
and notations were described in figure 3.3 below:
Overall length (mm)
Conveying direction (R=forward, L=Reverse)
Fig 3.3: Nomenclature for ZK 25 co-rotating twin-screw extruder screw profile
Width of discs (mm) (KB only)
Angular offset of the discs(KB); Pitch (mm)
(GL)
Nominal diameter (mm)

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3.3.2 Twin-screw Extrusion Processing
The melt-mixing process, with an intent to disperse the nanofillers uniformly into the polymer
matrix, were conducted using the Collin GmbH co-rotating intermeshing twin screw extruder. With
the screw diameter of 25mm and barrel length of 750mm, the temperature settings of six different
zones were configured from 170 to 200 degrees Celsius ranging from zone 1 to 6. Six different screw
configurations were used to facilitate mixing as mentioned in the previous section of the report.
The premixed BN powders and HDPE pallets were fed to the hopper using screw speed of 85 rpm.
With a residence time 1.75 min allowed for each mixture composition, six different batched were
subjected to the hopper one after another. The initial plan was to create a master batch of the
extruded composite material of different specifications and palletize them for further compression
molding in the QUB platen press equipment. But due to the lack of enough materials and to save
time the batches were extruded directly into sheets of 1 mm thickness and the width of 100 mm
after exiting through the die using the controllable clearance between two hydraulically closed chill
rolls in three roll up stack configuration depicted in figure 3.4. The following table 3.1 gives detailed
picture of the parameters used in the process:
Table 3.1: Process parameters set for BN/HDPE twin-screw extrusion
Fig 3.4: Chill rolls in three roll up stack configuration (left), Collin ZK 25 twin-screw extruder (right)
BN/HDPE Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Die
Set Temperature(°C) 170 195 200 200 200 200 205
Actual Temperature(°C) 168 195 200 201 201 200 205
Screw Rotation Direction Co-rotating
Screw Speed(rpm) 85
Residence Time(min) 1.75
Feeding rate(kg/h) 3.5
BN Loading(%) 0 0.1 0.2 0.5 1

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3.4 Characterization
3.4.1 Mechanical Analysis
3.4.1.1 Tensile test in room temperature conditions
After the fabrication process were carried out under twin-screw extrusion, the individual extruded
sheet of 1mm thickness and 100mm width were labelled carefully to classify four filler composition
batches with the virgin material batch and stored for testing and characterization phase. Stamping
press at the QUB characterization lab was used to cut five type 1BA dumbbell shaped specimens
from each fabricated sheets of different BN loadings along the extrusion or machine direction(MD)
as shown in figure 3.5.
Instron 5564 universal tester with a gauge length of 55mm were set up at room temperature
conditions, where samples were stretched up to an extension of 10mm at 5mm/min crosshead
speed. At this specific phase the elastic modulus was found from the slope of tensile stress and
strain curve, and the test was repeated four more times. Specimen thicknesses were measured
before every repetition to enhance accuracy of the results. The equipment was also set up to
increase the crosshead speed to 500mm/min once it reached the extension of 10mm, subjecting
the specimen up to its complete deformation or breaking point, to predict the strength and
elongation values at a constant gauge length. Detailed and in-depth characterized parameters and
findings will be discussed on the next section of the technical report (see section 4.1).
Fig 3.5: Schematic of uniaxial machine direction stretching

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3.4.1.2 Uniaxial stretching at elevated temperature conditions
BN/HDPE composite dumbbell shaped specimens of 1mm thickness and 75mm length were also
exposed to higher temperature conditions and uniaxially stretched to detect temperature
responsive variations in material behavior. The temperature conditions were controlled by a box
shaped environmental chamber along with an in-built fan wrapped around the Instron 5564
universal tester crossheads where the maximum elongation was limited to 60mm due to structural
constraints or limitations.
The gauge length was reduced to 25mm to accommodate the samples to be pulled up to the
stretching ratio of 3. Crosshead speed were adjusted according to the strain rate of 4/s. The samples
were loaded and the temperature was raised to 125°C and stretched under aforementioned
parameters and later allowed to cool down back to room temperature normally. Three samples
from each of five total compositions are tested to minimize errors. Figure 3.6 below shows the
environmental chamber equipment and a stretched sample. Strength and elongation values
formulated during the process were extracted for benchmarking and analysis.
Fig 3.6: Environmental chamber (left), Stretched specimen (right)
3.4.2 Thermal Analysis
Percentage of crystallinity of the BN/HDPE nanocomposite samples were investigated by DSC
(Differential Scanning Calorimetry) using a Perkin-Elmer DSC model 6 under inert nitrogen
atmosphere. Uniaxially stretched and unstretched samples were taken and cut into small samples,

16. 16
typical mass of only 7-10mg, followed by sealing them inside small aluminum pans and lids by
crimping them in the press. The inner and outer lids of the DSC furnace were removed to place the
sealed sample on the left sample pan. The furnace lids were replaced back and the equipment were
set up to raise the temperature of the furnace from 30°C to 200°C at a pace 10°C/min for both
stretched and unstretched samples. Furthermore, the unstretched samples were held at 200°C for
3 minutes and cooled down to 30°C at the same rate of 10°C/min and heated back to 200°C again
using the same gradient trend mentioned above to check the bulk properties have changed
fundamentally or not. Stretched samples were not checked for bulk property changes because they
were already heated again while stretching under elevated temperature conditions. The apparent
percentage crystallinity of the content is measured using the formula below:
% 𝑐𝑟𝑦𝑠𝑡𝑎𝑙𝑙𝑖𝑛𝑖𝑡𝑦 =
𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 ∆𝐻
100% 𝑐𝑟𝑦𝑠𝑡𝑎𝑙 ∆𝐻
×100
∆𝐻 = 𝐻𝑒𝑎𝑡 𝑜𝑓 𝑓𝑢𝑠𝑖𝑜𝑛
100% 𝑐𝑟𝑦𝑠𝑡𝑎𝑙 ∆𝐻 = 293 J/g [22]
3.4.3 Structural Analysis
The structure of the samples and the degree of dispersion of the BN fillers into the HDPE matrix
were investigated using Scanning Electron Microscopy (SEM). Reactive ion etching system were
used to plasma etch the samples. This high speed plasma glow discharge is shot at the samples for
60 s and at the power of 100w and then gold coated or sputtered prior to imaging. Joel 6500 Field
Emission Scanning Electron Microscopy were used with operating voltages of 3 and 5 kV to
examine the samples.
4.0 Results and Discussion
4.1 Mechanical Analysis
Dog bone-shaped samples were stretched as mention previously and tensile tests were carried out
at room temperature conditions. Five samples were tested till breaking stress were applied and
average young’s modulus and yield stress values were extracted from the Instron data logging
package. Figure 4.1 provides the variation of tensile modulus and yield stress values with different
composition of boron nitride fillers used during fabrication process.

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Fig 4.1: Variation of Young’s Modulus and Yield Stress observed in Tensile test at room
temperature
The elastic modulus of pure HDPE samples was measured to be 100.17 MPa and according to the
graphical representation, these values were observed to increase with increasing wt% of filler
boron nitride upto 0.1 wt% BN, but decrease dramatically with higher filler compositions. The
moduli values were seen to increase 2.4% for 0.1 wt% BN, 1.1% for 0.2 wt% BN, decrease afterwards
to 5.5% for 0.5 wt% BN and 3.3% for 1 wt% BN with respect to unfilled pure HDPE samples. All these
values are the result of the 85rpm rotation speed used during twin-screw extrusion fabrication
process. The elastic modulus would have been different if different screw speeds were used during
the fabrication process due to different degree of filler distribution into the polymer matrix. Higher
screw speeds would add up to higher shear forces at increasing mixing energy input that would
have triggered the modulus values. However, there is a significant increase of 2.4% in tensile
modulus at 0.1 wt% BN and the highest value achieved was 1024.56 MPa from these samples. The
increase in modulus is indicative of good particle dispersion at the loading level of 0.1 wt% BN that
resulted higher stiffness. Moreover, the significant elastic modulus drop at higher BN loadings is
suspected to result due to the increase in particle agglomeration. This kind of behavior is suspected
because the materials were melt-mixed and extruded straight to sheets of 1mm thickness rather
than extruding them into pallets and preparing the samples after compression molding.
Besides, the yield stress values were seeming to drop as well with increasing filler composition of
BN. The stress values are observed to drop by 1.2% at 0.1 wt% BN, 1.19% at 0.2 wt% BN, 4.7% at
0.5 wt% BN and 6.1% at 1 wt% BN with respect to neat unfilled HDPE samples. This indicates that,

18. 18
the stress level at which the filled polymers ceased to behave elastically decreased with higher filler
composition, probably due to creation of microvoids resulting from phase separation of BN/HDPE
interface [23]. This can also result from lesser restriction on molecular mobility or decreased
entanglement of molecules.
By increasing the crosshead speed to 500mm/min the samples were also examined to detect
mechanical behavior in complete deformation process. The breaking stress is discovered to
increase till 0.1 and 0.2 wt% BN with contrasting value drops at other two higher BN compositions.
This might be attributed to the structural orientation of the molecules and non-uniform filler
dispersion on higher BN loadings. On the other hand, strain to failure percentage data on different
filler composition is scrutinized to show very low fluctuations except 0.1 wt% BN. The bar charts
below depict the breaking stress and strain fluctuations:
Fig 4.2: Effect of addition of BN fillers on breaking stress and strain values
Its is very vital to note that all these aforementioned tensile tests were carried out under normal
room temperature conditions. On the other hand, samples were also subjected to elevated
temperature condition of 125°C by stretching them up to the ratio of three and strain rate of 4/s.
With respect to the tensile test carried out at room temperature, both Young’s modulus and yield
stresses are observed to decrease in high magnitudes with high temperature conditions. Both the
filler and polymer matrix materials are observed to be highly responsive to temperature and strain
rates while stretched and the parameters used in both scenarios are very different from each other
that generated such significant variation in the extracted values presented at figure 4.3 below:

19. 19
Fig 4.3: Variation of Young’s Modulus and Yield Stress observed in Tensile test at 125°C
Young’s Modulus(MPa)
At rtp, cs 5mm/m At 125°C, sr=3 Drop(%)
100 HDPE 1000.17 28.75 97.12
0.1 wt% BN 1024.56 24.73 97.58
0.2 wt% BN 1010.83 23.88 97.63
0.5 wt% BN 944.72 24.45 97.41
1 wt% BN 966.70 26.56 97.25
Yield Stress(MPa)
100 HDPE 26.10 2.77 89.38
0.1 wt% BN 25.77 1.91 92.59
0.2 wt% BN 25.79 2.39 90.73
0.5 wt% BN 24.88 2.47 90.07
1 wt% BN 24.52 2.46 89.96
Table 4.1: Effect of temperature and strain rate on tensile properties
It is observed that both young’s modulus and yield stress dropped remarkably with increasing
temperature and strain rate conditions up to 97.63% and 90.73% respectively. It is also discovered
that under elevated temperature conditions that filled HDPE samples were characterized to have
lower elastic modulus with respect to the unfilled samples. It is believed that the drop in both of
these mechanical parameters is related to the fall in strain hardening rate of the materials. It is
expected that the temperature applied were close to the glass transition temperature of HDPE
where molecular segmental motions were activated and less force was required for deformation
as elastic modulus is basically a measure of stiffness or hardness. HDPE is a semi crystalline polymer
where the main crystalline regions break down close to the melting temperatures. It is indicative of
the partial polymer chain rotations that resulted such a high drop in the elastic modulus. It is also
detected that at high temperature the variation or standard deviation between the moduli values
are also decreased substantially with a similar pattern in the stress at yielding stage.

20. 20
4.2 Thermal Analysis
For DSC examination, the stretched and unstretched samples were taken up and tested to measure
percentage crystallinity of five different BN loadings for unstretched and three BN composition for
stretched samples. Melting and crystallization behavior for these samples were extracted and
presented in figure 4.4. The thermograms of the unstretched samples are compared within
different phases that refers to the first heating cycle, cooling down in the same rate and heating
again for second time to delete thermal history and to check if the bulk polymer may have changed
fundamentally or not.
It is clearly visible on figure 4.4 that the crystallization endotherms have changed its shape with
increasing BN filler addition as the crystallization peaks get wider due to the change in crystal type
and perfection. This can happen because less perfect crystallites melt partially at low temperatures
making the average crystal shape larger [24]. And at higher temperatures the molecular chains are
more mobile producing more crystallites and making the average crystal size smaller. These
recrystallized crystallites are also detected to have higher melting peaks corresponding to higher
BN loadings due to the formation of more perfect crystals with greater dimensions and lesser
deformity.
Fig 4.4: Crystallization exotherms of unstretched samples
The addition of BN have contributed to slight improvement in percentage crystallinity with respect
to the unfilled neat HDPE. Highest improvement in crystallinity for unstretched samples are found
to be 67.05% for 0.2 wt% BN loading which enhanced the unfilled HDPE up to 9.58%. At higher filler

21. 21
composition the enhancements are found to be a bit upsetting as higher loadings of 0.5 and 1 wt%
BN did improve the crystallinity with respect to neat HDPE but reduced with respect to unstretched
0.2 wt% BN samples. This explains that at higher BN loadings, it is relatively difficult to disperse the
fillers into the polymer matrix during melt-mixing. Higher screw speeds might have been required
to enhance mixing and enhance the availability of nucleating sites for HDPE crystallization [25].
Fig 4.5: Comparison of melting endotherms with first and second stage heating
Other set of stretched samples are only tested for first heating cycle as they have already been
subjected to higher temperature during uniaxial stretching. The generated endotherms are found
to be potent and narrower, implying that the uniaxial stretching has contributed to more ordered
and synchronized crystallite patterns. Addition of BN and stretching barely affected the melting
temperature. It is also important to note that, the highest enhancement in percentage crystallinity
is found in stretched 1wt% BN samples where it is calculated out to be 15.94% higher than the
unfilled stretched sample (see Table 4.2 and Figure 4.6). Moreover, a contrasting behavior can be
pointed out if compared to the unstretched material of same BN loading of 1wt%. Moreover, the
crystallinity content increased by 18.6% higher due to stretching at higher temperature condition
that helped the molecular chains to align in a better orientation with the fillers. Percentage
crystallization Xc of unfilled HDPE were measured to be about 61.2% that raised to 63.9% with an
addition of 1wt% BN, which further increased to 74.8% after being stretched uniaxially at 125°C.
This undoubtedly indicates that both BN nucleated and strain induced HDPE crystallization has
contributed to the higher crystallization content achieved.

22. 22
Fig 4.6: Melting Endotherms of Stretched samples at high temperatures
Table 4.2: Effect of wt% MWCNT and the uniaxial stretching on the Thermal properties of unfilled
HDPE and BN/HDPE composites.
First Heating Cycle Cooling stage Second Heating Cycle
Tm
(°C)
Impr
(%)
∆H
(J/g)
Xc
(%)
Impr
(%)
Tc
(°C)
Impr
(%)
∆H
(J/g)
Tm
(°C)
∆H
(J/g)
Xc
(%)
Impr
(%)
Unstretched Samples
Unfilled
HDPE
133.85 199.48 68.10 113.27 194.93 135.07 179.30 61.19
0.1
wt% BN
132.69 -0.87 205.49 70.13 2.90 114.27 0.88 186.58 134.69 187.26 63.91 4.45
0.2
wt% BN
133.02 -0.62 205.79 70.23 3.12 114.31 0.91 193.89 134.78 196.45 67.05 9.58
0.5
wt% BN
133.02 -0.62 194.29 66.31 -2.63 113.69 0.37 194.08 134.91 189.84 64.79 5.89
1 wt%
BN
133.07 -0.58 181.47 61.93 -9.05 114.11 0.74 192.18 136.00 184.75 63.05 3.03
Stretched Samples*
Unfilled
HDPE
136.16 189.01 64.51 * Stretched samples at 125°C
0.2
wt% BN
136.62 0.33 188.01 64.16 -0.54
1 wt%
BN
136.15 -0.01 219.13 74.79 15.94

23. 23
4.3 Structural Analysis
Typical SEM micrographs were obtained from the plasma etched samples to conduct structural and
morphological study effected from the addition of BN fillers. The pure HDPE micrographs gives a
vivid identity of semi-crystalline structure of HDPE chains with the mixture of both semi-crystalline
and amorphous regions. Furthermore, SEM image of a filled 0.5wt% BN samples were clicked at
higher magnifications to understand the degree of dispersion of BN fillers in the HDPE polymer
matrix. It is seen and discovered that the filler distribution is not that uniform and lot of
agglomeration regions are pointed out that can be the reason why higher BN loadings did not
achieve remarkable enhancement in crystallinity content. Besides, microscopic voids were detected
in the image of the same BN loading sample that might have resulted from phase separation
BN/HDPE interface which, in turn, have decreased the yield stresses with increasing BN additions.
With even higher magnifications the stretched samples at 1wt%BN at high temperature were
scrutinized to detect the shear and stretching direction. These micrographs are the evidence that
stretching and high temperature exposure of these samples contributed to better alignment of the
BN fillers and molecular mobility that enhanced the crystallinity content.
Fig 4.7: Unfilled HDPE (upper left); unstretched 0.5 wt%BN (upper right); stretched
1wt%BN(lower)

24. 24
5.0 Conclusions
• Young’s Modulus for tensile testing at room temperature have increased highest up to 2.4%
at 0.1wt%BN resulted from good particle dispersion, and decreased up to 5.5% at
0.5wt%BN loading levels suspected due to higher particle agglomeration. Yield stresses
were measured to drop at all higher BN loading levels with the highest of 6.1% at 1wt%BN.
Breaking stresses at higher crosshead speed showed similar patterns with young’s modulus
whereas percentage strain at break got barely affected with different BN loading levels.
• Both BN and HDPE were observed to be highly responsive to temperature and strain rates
as both young’s modulus and yield stress values dropped significantly attributed to the
decreasing strain hardening rate of the materials while subjected to 125°C. At such
conditions the standard deviations of the moduli values were very low compared to that of
lower room temperature settings.
• For unstretched samples, addition of BN fillers have triggered a slight improvement in the
crystallinity contents. Highest Xc was measured to be 67.05% at 0.2wt%BN. Moreover, with
higher BN loadings than 0.2wt% the crystallinity content were measured to drop indicating
the difficulty to disperse the filler material in the polymer matrix in melt-mixing.
• For uniaxially stretched at high temperature samples, highest Xc among all other
crystallinity content were measured to be 74.8% at 1wt% BN. This is attributed to the better
ordering of the crystallites pattern that enabled better alignment of the fillers with the
HDPE molecular chains. BN addition and high temperature stretching had both collectively
contributed to the improvement in crystallization content.

25. 25
6.0 Recommendation of further work
• The samples selected for this project includes small percentage (0.1, 0.2, 0.5, and 1) of BN
loadings to be added with HDPE that implies the difficulty to compare characterized
parameters. With such small composition of fillers, little interference might add up to
higher margin of error that makes difficult to draw conclusions. Higher BN loadings
composite materials like 5wt%, 10wt% and 20wt% can be processed by twin screw
extrusion process.
• Regardless of the fact that we are dealing with lower or higher compositions, different
screw speeds can be applied while melt mixing to detect the effect of screw speed in
mechanical and thermal properties of the fabricated composite material.
• The samples can also be stretched biaxially and tested later by DSC to see the change of
crystallinity content, melting and crystallization peaks with respect to uniaxially stretched
samples.
• The uniaxially stretched samples which were tested in DSC can be later tested again at
Instron till breaking or totally deforming the sample at room temperature to measure the
difference in young’s modulus, yield stress and other vital elongation values with respect
to the unstretched samples.

26. 26
6.0 References
1. Berzelius, J.J. and Svanberg, “Jahres-Bericht über die Fortschritte der Chemie”, Vol. 11-13,
p-64, 1832.
2. Mülhaupt, R., “Hermann Staudinger and the Origin of Macromolecular Chemistry”,
Angewandte Chemie International Edition, 43: 1054–1063. doi:10.1002/anie.200330070,
2004.
3. John, M.J. and Thomas, S., “Natural Polymers: Composites”, Royal Society of Chemistry,
2012.
4. Peacock, A.J. and Calhoun, A.R., “Polymer Chemistry: Properties and Application”, Hanser
Gardner Publications, 2006.
5. Twardowski, T.D., “Introduction to Nanocomposite Materials: Properties, Processing,
Characterization”, DEStech Publications, pp. 2-3, 2007.
6. Strutt, J.V.a.D., Polymer Processing. Materials Science and Technology, 2003. 19(9): p.
1161-1169.
7. Chopra, N.G., Luyken, R.J., Cherrey, K., Crespi, V.H., Cohen, M.L., Louie, S.G., Zettl, A., Boron
nitride nanotubes. Science, 1995. 269(5226): p. 2
8. Wenjun Meng, Y.H., Yuqiao Fu, Zifeng Wanga and Chunyi Zhi, Polymer composites of boron
nitride nanotubes and nanosheets Journal of Material Chemistry C, 2014(2): p. 13.
9. Xuebin Wang, C.Z., Qunhong Weng, Yoshio Bando and Dmitri Golberg, Boron Nitride
Nanosheets: novel Syntheses and Applications in polymeric Composites Journal of physics,
2013(471): p. 10.
10. Novoselov KS, Jiang D, Schedin F, J Booth T, Khotkevich VV, Morozov SV and Geim AK 2005
Proc. Natl. Acad. Sci. USA 102, 10451
11. Pacile D, Meyer JC, Girit CO and Zettl A 2008 Appl. Phys. Lett. 92, 133107
12. Li LH, Chen Y, Behan G, Zhang HZ, Petravic M and Glushenkov AM 2011 J. Mater. Chem. 21,
11862
13. Jin C, Lin F, Suenaga K and Iijima S 2009 Phys. Rev. Lett. 102, 195505
14. Nag A, Raidongia K, Hembram KPSS, Datta R, Waghmare UV and Rao CNR 2010 ACS Nano
4, 1539
15. Raidongia K, Nag A, Hembram KPSS, Waghmare UV, Datta R and Rao CNR 2010 Chem. Eur.
J. 16, 149

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16. Kennedy, P. (1995). Flow Analysis of Injection Molds. Cincinatti, Hanser/Gardner
Publications.
17. Crawford, R. J., (1998), “Plastics Engineering”, 3rd edition, BH., Oxford.
18. Mark, J.E., (2007), “Physical properties of polymers handbook”, 2nd edition, Springer, New
York.
19. Kroschwitz, J.I., Mark H.F., (2003), “Encyclopedia of polymer science and technology”, 3rd
Edition, Wiley Interscience.
20. Giles H.F., Wagner J. R., Mount, E.M. (2004) Extrusion: The definitive processing guide and
handbook. William Andrew Inc., 11, 97-101; 12, 115-120; 13, 133-136.
21. Abu-Zurayk, R, Harkin-Jones, E., McNally, T., Menary, G., Martin, P., Armstrong, C. Biaxial
deformation behavior and mechanical properties of a polypropylene/clay nanocomposite,
Composites Science and Technology 69 (2009) 1644–1652.
22. Wunderlich, B., Macromolecular Physics, Crystal structure, Morphology, Defects, Vol. 1,
Academic press, 1973.
23. Astarita G., Nicolais L., Polymer Processing and Properties, Springer Science and Business
Media, 2012.
24. Tzavalas, S., Mouzakis, D.E., Drakonakis, V., Gregoriou, V.G. (2008) ‘Polyethylene
terephthalate-multiwall nanotubes nanocomposites: Effect of nanotubes on the
conformations, crystallinity and crystallization behavior of PET’, J. Polym. Sci., Part B:
Polym. Phys, 46, 668-676.
25. G. Gamon, Ph. Evon and L. Rigal, Industrial Crops and Products, 2013, 46, 173.

28. 28
Appendix A Project Management
Project Title Fabrication and Characterization of Novel BN/HDPE nanocomposites
Supervisor Dr Dan Sun Student Sayed Asif Iqbal
Date And Time 16/11/2015 Location Ashby(06.035)
Review of actions from previous meeting
Progression of reading more papers about the topic. Lab induction attended along with gaining
lab access. BN powders ordered from Sigma Alrich.
Discussions, Decisions, Assignments
Few aspects of the confusions arised from the research papers are clarified. Guidance about
progress report is provided. Contents to be written are suggested.
Agreed actions and completion dates
Progress report is to be completed and submitted by 20th
of November
Date and time of
next meeting
23/11/15
Project Title Fabrication and Characterization of Novel BN/HDPE nanocomposites
Supervisor Dr Dan Sun Student Sayed Asif Iqbal
Date And Time 23/11/2015 Location Ashby(06.035)
Review of actions from previous meeting
Progress report handed in.
Discussions, Decisions, Assignments
Sample preparation using single/twin screw extrusion method using different percentage of BN
powders. Multiples samples are to be prepared for stretching and distinguished. Get 5 samples
each for different tests.
Agreed actions and completion dates
Get the sample size dimensions used in a previous study of such kind
Date and time of
next meeting
30/11/15

29. 29
Project Title Fabrication and Characterization of Novel BN/HDPE nanocomposites
Supervisor Dr Dan Sun Student Sayed Asif Iqbal
Date And Time 1/12/2015 Location Ashby(06.035)
Discussions, Decisions, Assignments
Quantities of samples to be formed (six for each). Use SEM to analyze morphology of the
stretched and unstretched samples.
Agreed actions and completion dates
Contact Physics building to Book SEM
Complete sample cutting before next meeting
Date and time of
next meeting
8/12/15
Project Title Fabrication and Characterization of Novel BN/HDPE nanocomposites
Supervisor Dr Dan Sun Student Sayed Asif Iqbal
Date And Time 14/12/2015 Location Ashby(06.035)
Discussions, Decisions, Assignments
Cut more dumb-bell-shaped samples for tensile testing along the machine direction. Try
different strain rates at higher temperature condition.
Agreed actions and completion dates
Meet Dr. Beatriz to discuss about characterization
Book Instron and DSC
Date and time of
next meeting
25/01/2016
Project Title Fabrication and Characterization of Novel BN/HDPE nanocomposites
Supervisor Dr Dan Sun Student Sayed Asif Iqbal
Date And Time 25/01/2016 Location Ashby(06.035)
Review of actions from previous meeting
Additional tensile test samples were cut.
Discussions, Decisions, Assignments
Availability of the test equipments. Biaxial samples to be cut.
Agreed actions and completion dates
Contract Dr. Richao to see how tensile tests are done
Understand DSC procedures
Date and time of
next meeting
02/02/2016
Project Title Fabrication and Characterization of Novel BN/HDPE nanocomposites
Supervisor Dr Dan Sun Student Sayed Asif Iqbal
Date And Time 02/02/2016 Location Ashby(06.035)
Review of actions from previous meeting
Instron booked for 9th
February
Discussions, Decisions, Assignments
Biaxial stretching procedures. DSC procedures
Agreed actions and completion dates
Contract Dr. Richao to see how tensile tests are done
Understand DSC procedures
Date and time of
next meeting
16/02/2016

30. 30
Project Title Fabrication and Characterization of Novel BN/HDPE nanocomposites
Supervisor Dr Dan Sun Student Sayed Asif Iqbal
Date And Time 16/02/2016 Location Ashby(06.035)
Review of actions from previous meeting
Tensile tests carried out. More samples are cut for biaxial stretching
Discussions, Decisions, Assignments
Choice of protocol for DSC procedures
Agreed actions and completion dates
Finish biaxial stretching as soon as possible
Date and time of
next meeting
01/03/2016
Project Title Fabrication and Characterization of Novel BN/HDPE nanocomposites
Supervisor Dr Dan Sun Student Sayed Asif Iqbal
Date And Time 01/03/2016 Location Ashby(06.035)
Review of actions from previous meeting
Biaxial stretching were attempted several times, but couldn’t be carried out due to technical
difficulties. DSC done for 8 samples in total
Discussions, Decisions, Assignments
Comparison of stretched and unstretched samples. Mechanical, thermal and structural analysis
suggestions were given out by the supervisor. Conclusion and future recommendations are to
be included in the final year technical report.
Agreed actions and completion dates
Write up final technical report within 18th
march 2016
Date and time of
next meeting
Appendix B Turnitin Originality Check