Note: Descriptions are shown in the official language in which they were submitted.
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WOODIPLASTIC COMPOSITES WITH GLASS FIBER REINFORCEMENT
FIELD OF THE INVENTION
This invention relates wood plastic composites and in particular wood
plastic composites that use glass fibre reinforcing.
BACKGROUND OF THE INVENTION
The increasing use of wood is causing erosion of forest resources
which is detrimental to the future outlook of global environment. It is
imperative for
the well being of human race that this trend be stopped by developing
acceptable
wood replacement altemates. Although reconstituted wood products (pressboard,
chipboard, etc.) have been made with thermosetting resins for many years, only
in
the last two decades, has a serious attempt been made to incorporate cellulose
fibers in thermoplastic resins to produce wood plastic composites (WPC) 1. New
compounding techniques and interfacial treatments, utilizing coupling agents,
make
it feasible to disperse high volume fractions of hydrophilic wood fibers in
various
plastics. These compounds can be continuously extruded, thermoformed, pressed,
and injection molded into any shape and size, and thereby offer the potential
to
replace natural wood in many applications14.
The WPC offer many advantages over natural wood. They do not warp,
expand or shrink; they are weather, fungus and termite resistant and require
very little
maintenance. Moreover, not only can they be recycled, but they can also be
made
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entirely from recycled materials. Therefore, the market for these composites
is growing
at a phenomenal rate so that their market share doubled between 2000 and
20055. But
these composites suffer from the disadvantage of being heavier in weight and
lower in
toughness compared to wood, which makes them unsuitable for many applications2-
'.
Both of these properties can be improved by incorporating a foam structure in
these
composites', s. Foamed WPC are tougher, lighter, feel more like real wood, are
more
economical, and also accept screws and nails, more like real wood than do
their un-
foamed counterparts'.
Over the last few years, a number of such foamed WPC have been
commercially made available. However, foaming leads to poor flexural strength
and
creep deformation6, which severely limits the scope of their applications.
Therefore, a
great deal of improvement in properties is required before they can have a
significant
impact on new wood usage. The mechanical properties of plastics can be
significantly
increased by using glass fiber reinforcements in a plastic matrix'. Therefore,
assuming
that this method of increasing the mechanical properties will also be
effective in hybrid
form of glass fibers and WPC, this work was undertaken to demonstrate the
effectiveness of producing WPC with inclusions of glass fiber reinforcements
(GFR)
and thereby improving the mechanical properties. Very few examples of
GFR/natural
fiber hybrid composites were found in literature. Jiang eta18 and Maldas9 etal
studied
PVC based WPC with GF and found improvement in properties. John etal10 studied
resin based WPC and noted improvement in flexural strength when GF
reinforcement
is used. Kitano etal" studied the effects of long and short GF, along with
other fibers,
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on properties of HDPE (high density polyethylene) based composites containing
20
vol% fibers. They found that tensile strength decreased on increasing the
fiber content
when long fibers were used, whereas, the short fibers did not exhibit this
pattem. They
did not use any coupling agent. No literature could be found on foamed WPC
reinforced with GF.
Accordingly it would be advantageous to provide a wood plastic
composite that uses glass fiber reinforcement to increase the strength and
modulus of
the product.
SUMMARY OF THE INVENTION
The invention is a composite material having a foam structure
comprising: olefins as a matrix material; cellulose fibre filler; and glass
fibre filler.
A further aspect of the invention is a composite material comprising:
olefins as a matrix material; cellulose fibre filler; glass fibre filler and a
coupling agent
which bonds the cellulose fibre filler and the glass fibre filler to the
matrix material.
Further features of the invention will be described or will become
apparent in the course of the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described by way of example only, with
reference to the accompanying drawings, in which:
Fig. 1 is a graph that shows the effect on stress at fracture of adding
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glass fibre to wood plastic composite;
Fig. 2 is a graph that shows the effect on elongation at fracture of adding
glass fibre to wood plastic composite;
Fig. 3 is a graph that shows the effect on secant modules of composites
of adding glass fibre to wood plastic composite;
Fig. 4 is graph that shows the effect on density of composites of adding
glass fibre to wood plastic composite;
Fig. 5a is a microstructure of fracture surface of wood plastic composite
specimen container 30 % wood fibre; and
Fig. 5b is a microstructure of fracture surface of wood plastic composite
specimen containing 30% wood fibre and 5% glass fibre.
DETAILED DESCRIPTION OF THE INVENTION
One aspect- of the invention is a method for producing plasticJnatural fiber
composite structures which are reinforced with smaller amounts of glass fibers
(preferably less than 15% by weight) and the formulation includes a coupling
agent
such as one based on maleic anhydride, which acts as a bonding agent for both
the
natural cellulosic fibers and the glass fibers with the olefin matrix. This
material can be
produced by using any of the standard techniques for producing these
composites,
including extrusion, injection molding, compression molding etc.
Another aspect of the invention is a method for producing plastic/natural
fiber composite with a cellular structure which is reinforced with smaller
amounts of
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glass fibers and the formulation includes a coupling agent such as one based
on
maleic anhydride, which acts as a bonding agent for both the natural
cellulosic fibers
and the glass fibers with the olefin matrix. This material can be produced by
using any
of the standard techniques for producing these composites in extnision or
injection
molding. The preferred method of producing these composites in extrusion is
described in US Patent # 6,936,200.
The invention herein is a wood plastic composite that includes glass fibre
as filler. The glass fibre is preferably less than 15 % by weight. Preferably
the plastic
is a thermoplastic composite and more specifically preferably the plastic is
chosen from
the group of olefin plastics.
The invention herein is described below by way of example only. The
plastic material used in this study was HDPE (2710, MI=17, Nova Chemical), and
the
WF used was standard softwood (pine) grade 12020, supplied by American Wood
Fibers. The coupling agent used for improving the adhesion between the
hydrophobic
HDPE and the hydrophilic WF was the maleic anhydride-g-HDPE (MAH-g-PE,
Fusabond MB-100D, 0.8-1.1 wt% of MAH, MI 2.0 g/10min, DuPont Canada) and in
all
compositions it was 3 wt% of mixed HDPE and WF. The glass-fiber (GF) used was
Owens Coming Milled Fiber, 737-BD, 1/32" in length and 16 micron diameter. The
coupling agent used also improved adhesion between plastic and GF.
Experimental
Preparation of Samples: HDPE, WF and the coupling agent were mixed
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in a kinetic mixer from Werner & Pfleiderer till the temperature rose to 180 C
and
allowed to cool down. It was then granulated using a C.W. Brabender granulator
into
small pellets, which were then oven dried, ovemight, under a vacuum using an
Advantec-Vacuum drying oven at a temperature of 80 C. The mixture was then
extruded in C.W. Brabender extrusion system and pelletized in a C.W. Brabender
pelletizer. In the case of HDPE-WF/GF composite, the milled GF were added and
mixed with the oven-dried mixture before being extruded and pelletized.
Compression Molding: The pellets were then compression-molded into
sheets using a Carver Hydraulic press. The mold was compressed at 160 C under
4.5
metric tons for one minute. After forming, the sheets where cooled, under
pressure, to
ambient temperature and cut into dog-bone shaped sample conforming to ASTM
D638
type -V specifications.
Mechanical Property Testing: The dog-bone shaped samples cut from
the compression-molded sheets were tested on a LLOYD Instruments LSIOO
Universal
Testing Machine, till fracture, according to ASTM D638, but with the cross-
head speed
of 1 mm/min, and the results were obtained using NEXYGEN MT software. For each
composition 10 samples were tested and the average values were used for
interpreting
the results.
Density: The densities of the samples were determined using ASTM
D792-00.
Scanning Electron Microscope (SEM) Characterization of fracture
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surface: The samples were cut near the fracture surface and SEM micrographs of
fracture surfaces were taken. For this, each sample was first gold-coated,
using a
sputter coater (E 50000C PS3), and the microstructure was examined using a
Hitachi
510 SEM.
Results and Discussion
Effect of GF on stress at fracture: One advantage of using the maleic
anhydride as a coupling agent is that it promotes adhesion between plastic and
both
WF and GF so that only one coupling agent can be used for both materials.
Figure 1
shows the result of adding 5% GFR in WPC. As expected the fracture strength of
WPC
increased from 16 to 31% for different compositions of WPC, due to the
addition of
GFR. The strong GF did contribute to increasing the load bearing ability of
the WPC.
This also indicates that maleic-anhydride coupling agent successfully promoted
adhesion between GF and the plastic matrix.
Effect of WF content on stress at fracture: Figure 1 also shows the
effect of WF content on the stress level at which fracture occurs in WPC and
WPC +
5% GFR samples. The WPC did not exhibit any remarkable change in fracture
stress
levels with varying WF contents. However, when 5% GF was added, not only did
the
fracture stress level increased in general, but it also increased with
increasing WF
content, increasing from 16% compared to WPC when WF content was 10%, to 31 %
compared to WPC when the WF content was 30%.. This result is somewhat
surprising.
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In all compositions, the coupling agent constituted 3 parts per 100 parts
of mixture by weight. Therefore, one possible explanation for the observed
behavior is
that with increasing WF content, the concentration of coupling agent in the
plastic
matrix increased, as it would not be dissolved in the solid wood particles.
This
increased concentration of coupling agent in the plastic matrix resulted in
improvement
in adhesion between the GF and the plastic matrix resulting in higher
mechanical
properties.
Effect of WF and GF content on elongation at fracture: Figure 2
shows these effects clearly. Addition of GF decreases the elongation at
fracture due to
the increased stiffness provided by these fibers. Increasing the WF content
also
reduces the elongation at failure due to reduction in the amount of ductile
plastic matrix
in the composite.
Effect of WF and GF content on modulus: Figure 3 shows the secant
modulus of WPC and GFR-WPC. The modulus increases with increasing WF contents
for all composites. However, the inclusion of GF resulted in the very
significant
increase of about 50% in the value of the modulus. This is directly due to the
high
value of the reinforcing material's modulus.
Effect of WF and GF content on density: Figure 4 shows the density of
the composites. Addition of GF increased the density of the composite by about
2 to
3%. Increasing the WF composition by 10% also resulted in similar amount of
density
increases.
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Microstructure of the fracture surfaces: Figures 5 show the SEM
micrographs of xx% WPC and WPC + 5% GF. In the WPC with GF, the glass fiber
can be seen clearly and apparently the coupling agent has not fully acted on
the glass
surface as adhesion is not observed. Whereas, the WF are not distinguishable
indicating that the amount of coupling agent used is sufficient for fully
compatibilizing
the WF but not the GF. Additional work is needed to clarify the amount of
coupling
agent required for full compatibilization of GF.
Conclusion
The inclusion of 5% GF reinforcement resulted in substantial
improvements in both strength and modulus of WPC. However, inspection of SEM
micrographs indicates that perhaps the GF have not achieved full adhesion with
the
plastic matrix and there may be room for further improvement in properties.
In this study, tensile tests of WPC specimen with and without GFR were
carried out for varying amounts of WF content. Density and surface
characteristics of
the fractured specimen were also studied. Significant improvements in
properties were
observed.
A common problem in production of natural fiber composites is the
control of volatiles emitted by the cellulosic fibers at the elevated
processing
temperatures. In normal composites, the volatile emissions can cause unwanted
voids
which can severely hamper the mechanical properties of the composites. In
foamed
composites, these volatiles can deteriorate the cell structure of the obtained
foams,
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leading to poor mechanical properties. One way of alleviating this problem is
to pre-dry
the cellulosic natural fibers by using one of the standard drying techniques
and limiting
the duration and temperature of the process to a low value as taught by the US
Patent
6,936,200 issued August 30, 2005 to Park et al.
The invention herein is related to the use of glass fibre filler with wood
plastic composite foams. As well the invention herein has determined that the
use of a
coupling agent that is compatible with both the wood filler and glass fibre
filler improves
the properties of the wood plastic composite.
As used herein, the terms "comprises" and "comprising" are to construed
as being inclusive and opened rather than exclusive. Specifically, when used
in this
specification including the claims, the terms "comprises" and "comprising" and
variations thereof mean that the specified features, steps or components are
included.
The terms are not to be interpreted to exclude the presence of other features,
steps or
components.
It will be appreciated that the above description related to the invention by
way of example only. Many variations on the invention will be obvious to those
skilled
in the art and such obvious variations are within the scope of the invention
as
described herein whether or not expressly described.
References
I J.H. Schut, Plastic Technology, March (1999).
2 C. Clemons, Forest Products J, 54, 6, 10 (2002).
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3 R.G. Raj, BV Kokta, JD Nizio, J Appl Polym Sci, 45, 91, (1992).
4 R.G. Raj, B.V. Kokta, G. Groleau, and C. Daneault, Plast. Rubber Proc.
Appl.,
11, 215 (1989).
http=//www princiaiaconsultinq com/publishing/news cfm?article=56
5 6 F.A. Shutov, in Handbook of Polymeric Foams and Foam Technoloov, D.
Klempner and K. C. Frisch, eds., Hanser, New York (1991)
7 N.P. Cheremisinoff, P.N. Cheremisinoff, Fiberglass Reinforced Plastics,
1995 Noyes
8 H. Jiang, D.P. Kamden, B. Bezubic and P. Ruede, J Vinyl & Add Technol, 9, 3,
138-145 (2003)
9 D. Maldas and B.V. Kokta, lntern. J Polymeric Mater. 17, 205-214 (1992).
10 K. John and S.V. Naidu, J Reinf. Plastics and Comp., 23, 15, 1601 (2004).
11 T. Kitano, E. Haghani, T Tanegashima and P. Saha, Polym Comp, 21, 4, 493-
505(2000)
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