Advances in Environmental Biology Norazean Shaari,

Advances in Environmental Biology, 8(8) 2014, Pages: 2736-2741
AENSI Journals
Advances in Environmental Biology
Journal home page: http://www.aensiweb.com/AEB/
Design and Fabrication of High Shear Milling Machine for Nanocomposites
1,2Norazean
1
2
Shaari, 1Aidah Jumahat, 1M.A Afiq M. Ikhsan
Faculty of Mechanical Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, MALAYSIA
Faculty of Engineering, Universiti Selangor, Bestari Jaya Campus, Jalan Timur Tambahan, 45600 Bestari Jaya, Selangor, MALAYSIA
ARTICLE INFO
Article history:
Received 28 February 2014
Received in revised form 25 May 2014
Accepted 6 June 2014
Available online 20 June 2014
Keywords:
High shear milling machine
Nanofiller Polymer
Epoxy Nanocomposites
ABSTRACT
Background: Dispersion and distribution of nanofiller in nanocomposites plays a major
role in influencing the mechanical and physical properties of the nocomposites.
Agglomerated nanoparticle in the matrix introduces local stress concentration and a
weak particle-matrix adhesion reduces the capability of load transfer between them. In
order to achieve homogeneous dispersion of nanofiller in nanocomposite, a suitable
mixing technique is required. There are several techniques for mixing polymer with
nanofiller such as sonication, hand mixing, high pressure mixing, magnetic stirring,
high shear mixing and mechanical stirring. In this study, high shear milling is proposed
to be the most suitable and best mixing technique to ensure dispersion of nanofiller in
nanocomposite. Therefore, a high shear milling machine was designed, fabricated and
tested. The high shear milling machine is considered to have certain specifications
during design process such as gap between rollers, different roller speed and roller’s
temperature to obtain homogeneous dispersion. Objective: To design and fabricate high
shear milling machine that is required for fabrication of epoxy nanocomposite to
prevent agglomeration of nanofiller in epoxy resin. Results: CATIA software V5R18 is
used to design parts and the whole system of the milling machine, namely UiTM High
Shear Milling Machine. The machine consists of three (3) systems that are mechanical
system, electrical system and heating system. Selection of materials and fabrication
method were carried out after the design process completed. The fabrication method
involved several machining processes such as turning, milling, boring and drilling
before all components and parts were assembled. In order to evaluate the performance
of the newly designed and fabricated high shear milling machine, samples of 1wt%,
3wt% and 5wt% nanoclay (Nanomer I.30E) in Morcrete BJC-39 epoxy resin were
prepared. The same samples were also prepared using mechanical stirring process and
both results were compared. It was observed that exfoliated nanoclay in epoxy resin
was achieved in all samples prepared using high shear milling technique. However, for
samples prepared by mechanical stirring technique, only 1wt% sample shows an
ordered exfoliated structure. With increasing of clay contents only intercalated structure
was obtained. Besides, nanovoid was also observed in the samples prepared using
mechanical stirring technique. Conclusion: High shear milling machine produced
exfoliated nanoclay without nanovoids. Therefore, the fabrication of the milling
machine was successful and high qualities of samples were produced.
© 2014 AENSI Publisher All rights reserved.
To Cite This Article: Norazean Shaari, Aidah Jumahat, M.A Afiq M. Ikhsan., Design and Fabrication of High Shear Milling Machine for
Nanocomposites. Adv. Environ. Biol., 8(8), 2736-2741, 2014
INTRODUCTION
Polymer composite materials have been used in automotive, marine, aerospace, transportation and
infrastructure applications due to their high strength, high specific stiffness, low weight, low coefficient of
thermal expansion, good fatigue life and corrosions resistances [1,2, 5]. An understanding of the effect of fiber
types, fillers types and fabric constructions on the performance of such composites would therefore provide very
useful information in applications. Like most laminated composite, they suffer in laminated-structure with poor
matrix-dominated properties such as low compressive strength, matrix cracking, interlaminar strength, fracture
toughness and impact resistance [3,11]. Delamination is considered one of the most common failure forms in
this composite [6,9]. Several effort have been devoted to improve these matrix-dominated properties, but then it
often lead to reduced stiffness and thermal stability and vice-versa [6].
An extensive work had been done by researcher to improve the properties of epoxy matrix by incorporating
nanofillers such as nanoclay, nanosilica, nanoalumina and carbon nanotubes [4]. The incorporating of nanofiller
is reported can significantly improve the properties of the epoxy matrix such as tensile strength, elastic modulus,
Corresponding Author: Norazean Shaari Faculty of Mechanical Engineering, Universiti Teknologi MARA, 40450 Shah
Alam, Selangor, MALAYSIA.
Tel: +60 3 55435135; E-mail: [email protected] (Aidah Jumahat)
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Advances in Environmental Biology, 8(8) 2014, Pages: 2736-2741
fracture toughness, damage resistance and tolerance. However, uniform dispersion of nanofillers is a general
prerequisite for achieving desired mechanical and physical properties [11].
In this case, the dispersion of nanofiller in epoxy can be categories according to gallery spacing or the gap
between two adjacent platelets (d-spacing) which are tactoid, intercalated and exfoliated. In tactoid, the clay
platelets are still aggregated together, and no polymer molecule moves into the galleries of the adjacent
platelets. The d-spacing in tactoid structure ranges from only 2.30-2.37 nm. An intercalated type nanocomposite
has gallery spacing of 2.37-8 nm in which polymer chains diffuse into the galleries between the clay platelets
and increase the d-spacing [12]. Whereas, exfoliated structure is the best dispersion wherein the d-spacing is
more than 8 nm. The degree of exfoliation depends on the type of clay and its surface treatment, type of epoxy
and hardener (including viscosity of the resins), resin-clay interaction, clay content and processing method. To
date, a processing technique that produces complete dispersion and exfoliation of nanofiller in the polymer
matrix is still a technical challenge.
There are several techniques for mixing polymer with nanofiller such as sonication, hand mixing, high
pressure mixing, magnetic stirring, high shear mixing and mechanical stirring [11,10]. Shokrieh et al. [11]
dispersed nanoclay by using sonication technique in epoxy resin and obtained a d-spacing of 4.2 nm while Qi et
al. [8] dispersed four different nanoclays namely pristine montmorillonite (MMT-Na+), Cloisite 30B (MMT30B), Nanomer I.30E (MMT-I.30E) and MMT-cetylpyridinium chloride (MMT-CPC) using a mechanical
stirrer in Bisphenol-A epoxy. According to transmission electon microscope (TEM) results at 5 wt% of
nanoclays, MMT-Na+ shows tactoid structure, MMT-30B and MMT-CPC show intercalated structure while
MMT-I.30E shows an exfoliated structure. A study by Prolongo et al. (2008) showed that a combination of
magnetic stirrer, sonicator and shear mechanical mixer produced the best dispersion result compared to another
two mixing methods namely magnetic stirring and magnetic stirring with sonication. Yasmin et al. (2003) and
1
Jumahat et al. [4] reported that high shear milling machine is the best method to disperse nanofiller in polymer
matrix compared to mechanical stirring. This method will increase the d-spacing up to the exfoliated structure.
Therefore the purpose of this study is to design and fabricate high shear milling machine so as to produce an
exfoliated structure of nanocomposite.
Experimentation:
Design and Fabrication of High Shear Milling Machine:
In order to obtain a good dispersion of nanofiller in nanocomposite, a high shear milling machine was
designed and fabricated. The high shear milling machine was designed using CAD software, namely Computer
Aided Three Dimensional Interactive Application (CATIA) Software V5R18. The machine consists of three (3)
systems that are mechanical system, electrical system and heating system. Mechanical system consists of 0.55
kW alternating current (AC) motor and 1.5 kW inverter drive. AC motor was chosen because it requires less
maintenance as it is brushless and the voltage can be easily stepped up and down to control motor speed.
Controlled speed is needed to control roller’s rotation. Roller’s rotation need to be controlled as different epoxy
will have different viscosity.
Electrical system includes push button switches, emergency stop pushbutton, thermostat and magnetic
contactor. This milling machine use water as heating source. The heating system consists of water pump,
heating element and piping system. Water pump is used to pump the hot water to circulate into the rollers.
Piping system is important as it conveys water from water tank into the rollers.
Milling machine is separated into two (2) main components; top component and lower component. This is
to ease the machine and component design processes as separate components reduced the work scope. The top
component of the machine consists of rollers, sliding component, end cap, spur gear, threaded shaft and turning
knob. Roller with dimension of 80 mm diameter and 200 mm length was designed. Gearing system is attached
to the longer shaft and roller consists of a through end-to-end hole with a diameter of 12 mm. This hole is for
water circulation as heating element for the roller. In order to achieve different speed of each roller, gearing
system is needed to obtain specific ratio of each roller. The ratio used is 9:3:1 for front roller, middle roller and
back roller respectively. Spur gear is the best gear type to be used because of parallel roller position. Fig. 1
shows the arrangement of spur gears for the machine. Front, middle and back roller are represented by left shaft,
middle roller and right shaft respectively.
Lower component of this machine includes body-work which are a frame of the lower component, water
container, electrical box and machine cover. The design of the machine is shown in Fig. 2(a) while Fig. 2(b)
shows the machine top component.
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Advances in Environmental Biology, 8(8) 2014, Pages: 2736-2741
100 RPM
33.3 RPM
11.1 RPM
Fig. 1: Spur gear arrangement.
Fig. 2: (a) Design of high shear milling machine, i. Top component, ii. Lower component;
(b) Design of rolling system, i. Front roller, ii. Middle roller, iii. Back roller.
There are several types of materials used to fabricate the high shear milling machine. Stainless steel was
used to fabricate rollers as it needs material with high tensile strength to ensure the crushing forces between
rollers are adequate. Stainless steel also used to fabricate water container due to its corrosion resistance
properties. For the fabrication of framework and sliding mechanism part, aluminum was chosen because of its
durability, lightweight, ease of machining and corrosion resistance. Two different materials were used for spur
gear, acetal for small spur gear and stainless steel for large spur gear. Movement of spur gear is based on direct
contact of each spur gear, thus if both small and large spur gear use the same material, it will create noise due to
friction. Mild steel was used as the body-frame as it can sustain both transverse and axial forces.
Manufacturing processes involved before the assembly process are turning, milling, drilling and boring
processes. Fabrication of nanofiller filled epoxy nanocomposites start after assembly of high shear milling
machine completed. Fig. 3 shows the fabricated UiTM High Shear Milling Machine.
Fabrication and Characterization of Nanofiller filled Epoxy Nanocomposite:
Samples of 1 wt%, 3 wt% and 5 wt% nanoclay (Nanomer I.30E) in Morcrete BJC-39 epoxy resin were
prepared in order to test the performance. of machine in which the mixtures of nanoclay and epoxy were poured
into the milling machine. The machine was set at a temperature of 60 oC with rotation speed of 10 rpm. The gap
of in front adjacent roller was set at 0.5 µm while for back adjacent roller was at 1.5 µm. The process was
repeated for five times in order to get homogenous dispersion of nanoclay. Dispersion of nanoclay was attained
by shear forces generated between the adjacent rollers. The mixtures were then degassed in vacuum desiccators
for 1 hour to remove the entrapped air, followed by pouring into trapezium shape release-coated silicone mould
before cured at room temperature for 24 hours.
The same samples were also prepared using mechanical stirring technique in order to compare the
dispersion results. The specific amounts of nanoclay were mixed with the epoxy resin using a mechanical stirrer
at 400 rpm in a heated oil bath of 80 oC for 1 hour. This was followed by degassing in a vacuum oven for 1 hour
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at 85oC to remove any entrapped air in the mixture. The mixture was then poured into a preheated silicon mould
(pre-treated with mould-release agent) with various shape cavities. It was returned into the vacuum oven for
another 1 hour. After degassing, it was covered with a PTFE bleed out fabric and a glass plate (wrapped with
PTFE release film) to produce a flat and near net shape specimens and cured at room temperature for 24 hours.
All samples were then cut using a Leica EM UC7 Ultra-microtome machine to get a thickness of 85-90 nm.
After cutting, sections were collected on 200-mesh copper grids and viewed under FEI TECHNAI G2 20S
TWIN TEM to observe the dispersion of the nanoclay.
Fig. 3: UiTM High Shear Milling Machine.
RESULTS AND DISCUSSION
Transmission Electron Microscopy (TEM) Micrograph Observation:
TEM micrographs observation show the dispersion of I.30E nanoclay in epoxy resin prepared using high
shear milling and mechanical stirring techniques. Fig. 4 below shows the TEM micrographs observation for
nanocomposite samples prepared using mechanical stirring technique. The morphology of nanoclay was
observed as predominantly intercalated with some exfoliated regions. TEM image in Fig. 4(a) shows that at low
clay content of 1 wt%, ordered exfoliated structure can be observed with infrequently presence of randomly
oriented nanoclay. However, the d-spacing reduced with increased of clay content. At higher clay content (3
wt% and 5 wt% ), TEM images show intercalated structure of nanocomposites. The d-spacing measured for
both clay contents is about 5-6 nm (Fig. 4(b) and 4(c)).
Fig. 4: TEM micrographs showing (a) an ordered exfoliated structure of 1 wt%, (b) an intercalated structure of 3
wt% and (c) an intercalated structure of 5 wt% nanoclay prepared using mechanical stirring technique.
Fig. 5 shows the exfoliated I.30E nanoclay in epoxy resin prepared by high shear milling technique. High
magnification TEM images showed that the distance between nanoclay is more than 8 nm. These indicate that
high shear milling technique successfully produced exfoliated type nanocomposite. At low clay content (1 wt%)
a fully exfoliated structure with randomly dispersed nanoclay were observed with an occasional presence of
ordered exfoliated structure (Fig. 5(a)). However, at clay content of 3 wt% and 5 wt%, the TEM images show an
ordered exfoliated structure with d-spacing of 9-15 nm (Fig. 5(b) and 5(c)). This is significantly high
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comparedto the d-spacing obtained using the mechanical stirring technique at similar clay content. Exfoliated
dispersion indicates that nanoclay layers are completely delaminated and are uniformly dispersed in the epoxy
resin.
Fig. 5: TEM micrographs showing (a) a random exfoliated structure of 1 wt%, (b) an ordered exfoliated
structure of 3 wt% and (c) an ordered exfoliated structure of 5 wt% nanoclay prepared using high shear
milling technique.
Besides that, TEM micrographs observation also show that the quality of nanocomposite samples prepared
by mechanical stirring technique were poor compared to those prepared by high shear milling technique.
Entrapped air (nanovoids) observed in the sample of nanocomposite as in Fig. 6(a) and 6(b). Similar result was
reported by 2Jumahat et al. [4] when preparing sample using mechanical stirring technique.
Fig. 6: TEM micrographs showing of nanovoids observed in (a) 1 wt% (b) 5 wt% nanoclay in Morcrete BJC-39
prepared using mechanical stirring technique.
Conclusion:
There are several techniques available for mixing epoxy polymer with nanofillers. However some of the
techniques have high tendency for nanofillers to agglomerate. In this study, a new high shear milling machine,
namely UiTM High Shear Milling Machine was fabricated. Experimental results showed that exfoliated
structure were obtained in all 1 wt%, 3 wt% and 5 wt% samples of nanocomposites prepared using high shear
milling technique. Whereas, for samples prepared using mechanical stirring technique, only sample contains 1
wt% nanoclay shows an ordered exfoliated structure while samples with higher clay contents showed
intercalated structure. Observation also shows that nanovoids exist in the samples prepared using mechanical
stirring technique. Thus, the high shear milling machine was successfully designed and fabricated in order to
obtain homogeneous dispersion.
ACKNOWLEDGEMENT
The authors would like to thank Research Management Institute (RMI) UiTM and Ministry of Higher
Education Malaysia for the financial supports. This research work is conducted at the Faculty of Mechanical
Engineering, Universiti Teknologi MARA (UiTM), Malaysia under the support of Principal Investigator
Support Initiative (PSI) no: 600-RMI/DANA 5/3/PSI (119/2013).
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