World Journal of Engineering
MANUFACTURING BIOCOMPOSITE PARTS USING LRTM
J. Raghavan1, B. O’Connor1, G. Kime2, B. Klimack3, J.A. Milne3, and P. Zanetel4
1
Composite Materials and Structures Research Group & Mechanical and Manufacturing
Engineering Department, University of Manitoba, Winnipeg, MB R3T 5V6, Canada
2
Stemergy Renewable Fiber Technologies, Delaware, ON, Canada
3
Carlson Engineered Composites Inc, 4New Flyer Industries. Winnipeg, MB, Canada
was in the range of 500 – 1300 g/m2.
Unsaturated polyester (Stypol 8086 from Cook
Composites and Polymers, Kansas, MO, USA)
and Luperox 224 initiator from Sigma Aldrich
(Oakville, Ontario, Canada) were used to
manufacture natural fiber – unsaturated polyester
composite. 1.25 % (w/w) of Luperox 224 was
used. Existing LRTM molds, designed for glass
fiber composites, were used to eliminate any
additional cost of adopting the natural fiber.
LRTM uses a semi-flexible composite skin in
lieu of vacuum bag used in VARTM and uses a
lower resin injection pressure than RTM.
Introduction
Natural fibers, such as hemp and flax, are
emerging as an alternative to glass fibers in
polymer composites, due to their natural
abundance, specific properties comparable to
glass fibers and their biodegradability.
Thermoplastic composites with discontinuous
natural fibers are already in use in automotive
and building product industries [1-3]. These
composite parts are relatively small and are
mainly manufactured by injection / compression
molding. However, natural fibers are yet to find
application in medium to large size parts, such as
those used in buses. These parts are currently
manufactured by liquid injection molding
(LRTM, VARTM) using thermoset resins and
non-woven glass fiber mats. Current application
of thermoset biocomposites in semi-structural /
structural applications is virtually non-existent
due to lack of market pull, lack of commercial
availability of natural fiber mat, and large scatter
in properties of natural fibers and biocomposites.
This study discusses various issues related to
manufacturing of thermoset biocomposite parts
using Light Resin Transfer Molding (LRTM).
Results and Discussion
The diameter of the decorticated hemp fibers
exhibited a distribution in the range of 50 – 800
m with a mean of 200 m, which is almost 20
times the diameter of the glass fiber. Hence, for a
given aerial weight, the hemp fiber mats were
thicker than glass fiber mats. This impacted
manufacturing in a number of ways. Firstly, it
affected mold closure and creation of a good
vacuum seal, specifically when the mat thickness
was close to the thickness of the elastomeric
seals. Secondly, the flexibility of the mat to
conform to the complex shape of a mold was
impaired by the thickness of the hemp mats.
Thirdly, it influenced the mass of the
biocomposite part. In order for the mass of the
biocomposite part to be equal to or less than that
of the glass fiber part, its thickness should be,
(1)
where GSM, t and  are mat aerial weight (grams
per square meter), thickness, and density
respectively. The subscripts c, h, g, m correspond
to composite, hemp fiber, glass fiber and matrix
respectively. For a given GSM, either the
Experimental Details
Hemp fibers were supplied by Stemergy
Renewable Fiber Technology. Non- woven mats
were manufactured using the facilities at Nonwovens Cooperative Research Centre of North
Carolina State University. Hemp mats were
manufactured by air-laying the fibers to form a
web and needle punching the web to bind the
fibers together. Hemp mats were manufactured
using a needle punch density in the range of 2.6150 Punch/cm2 and a needle punch depth in the
range of 2-15 mm. The areal weight of the mats
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World Journal of Engineering
thickness of the mat ≤ tc,h or the compaction of
the mat, during manufacturing, is sufficient to
yield desired tc,h. This compaction is influenced
by mat properties (GSM, t) and mold design. For
example, a glass fiber bus part, which was
replaced with a hemp fiber part in this study,
had a weight, average thickness, and density of
6630 g, 4.16 mm, and 1.4973 g/cc respectively.
According to eqn (1), a biocomposite part with
equivalent mass should have a thickness and
density of 4.98 mm and 1.251 g/cc, when 1283
GSM -150 punch density mat is used. However,
the manufactured biocomposite part had a
weight, average thickness, and density of 7785 g,
5.715 mm, and 1.089 g/cc respectively. This is
due to resin rich regions and inadequate
compaction caused by non-optimal interaction
between the thick hemp mat (6.12 mm) and mold
(designed for thinner (5.1mm) glass mat). A 500
GSM-150 punch mat yielded a biocomposite part
(Fig. 1) lighter than glass fiber part with a
weight, density, and average thickness of 6310 g,
1.303 g/cc, and 4.782 mm (despite a mat
thickness of 2.898 mm), respectively. The mold
did not compress the mat resulting in a resin rich
layer. A proper mold design may yield optimal
values (3808 g, 2.898 mm, 1.234 g/cc).
these factors. The modulus of the decorticated
fibers exhibited a distribution in the range of 335 GPa (due to distribution in diameter) with a
mean of 9.2 GPa. Despite this, some mats
yielded a modulus comparable to that of glass
fiber composite.
10
Modulus (GPa)
8
2.6P-8
7P-8
30P-8
70P-8
150P-8
7P-2
No Punch
Glass Fiber
30P-2
30P-15
30P-500
GSM
6
4
2
0
0
10
20
30
40
50
60
Fiber Volume Fraction (%)
Fig. 2 Modulus of biocomposites using mats
with various punch density, depth, and GSM
Conclusions
Various issues related to manufacturing of
biocomposite parts using hemp mat have been
highlighted. Successful replacement of glass
fiber with hemp fiber requires good control over
the level of fiber refining (i.e. diameter), hemp
mat manufacturing parameters, and mold design.
References
1. Joshia SV, Drzal LT, Mohanty AK, Arorac S. Are
natural fiber composites environmentally superior
to glass fiber reinforced composites? Composites
A, 35 (2004) 371–376.
2. Clemons C. Wood fiber-plastic composites in the
United States: History and current and future
markets. In: Proceeding of 3rd International Wood
and Natural Fiber Composites Symposium;
Kassel, Germany; 2000; 1-7.
3. Bledzki AK, Faruk O, Sperber VE. Cars from bio
fibers.
Macromolecular
Materials
and
Engineering, 291 (2006) 449-457.
Fig. 2 Hemp biocomposite bus part
Finally, it influenced the properties of the
biocomposite. Hemp fiber volume fraction in the
part can be determined using eqn. (2).
(2)
where mf is the mass of fibers in the part and A
is the area of the part. This depends on the initial
fiber volume fraction in the mat and the level of
compaction during manufacturing. Both are
dependent on GSM, initial mat thickness, punch
density and depth. Fig. 2 highlights the
variability in modulus of the composite due to
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