Composite Materials Journal of Thermoplastic - LSU School of ...

210 S.-Y. LEE ET AL.
INTRODUCTION
THE USE OF lignocellulosic materials and polymers from renewable
resources has recently attracted increasing attention, predominantly due
to environmental concerns and the depletion of petroleum resources [1–3].
In general, polymers from renewable resources can be categorized into
natural polymers such as starch [4–6], protein and cellulose [7–9], and
synthetic polymers [10–12]. The development of synthetic polymers using
monomers from natural resources provides a new direction for the
development of biodegradable polymers.
The most common biodegradable synthetic polymers are aliphatic
polyesters such as polylactic acid (PLA), polyglycolic acids (PGA),
polycaprolactone (PCL), and polyhydroxybutyrate (PHB). Among these
biopolymers, PLA as biodegradable aliphatic polyester is of increasing
commercial interest, because of its desired mechanical strength, thermal
plasticity, and biocompatibility [13,14]. PLA has been used for many
applications including grocery and composting bags, automobile panels,
textiles, and bio-absorbable medical materials [15,16]. PLA is generally more
expensive than many petroleum-derived commodity polyolefins such as
polypropylene (PP) and polyethylene (PE). However, its price has been
falling recently as more biopolymer production comes on-line [17].
The compounding of fillers obtained from various sources into polymer
matrices has been a well-accepted process to enhance mechanical and thermal
properties of materials [1,2,18]. Wood flour (WF) and talc are two commonly
used fillers for wood plastic composites (WPCs) [19,20]. The use of WF can
reduce material costs and provide specific properties such as low density, high
specific stiffness, and biodegradability [21–24]. In particular, WPCs with
50 wt% or less plastic by weight, have been accepted by the construction
industry and homeowners, largely for decking, fencing, roofing, window
profile, and automotives [21]. Talc (up to 30% by weight) can have a positive
influence on modulus, strength, processing efficiency, creep and elastic recovery
performance of WPCs [25]. A combination of organic (e.g., wood) and
inorganic (e.g., talc) fillers in PLA may lead to interesting composite properties.
In the intricate structure and morphology of polymer reinforced by
organic and/or inorganic fillers, there is a problem related to the character
and extent of interaction at the polymer-filler interfaces [21]. The established
procedure for improving the interfacial adhesion of polymer and wood fiber
is the use of coupling agent, resulting in a good chemical and/or physical
bonding between polymer matrix and particle surfaces [26]. For example,
various types of silanes have been developed to promote the interfacial
adhesion. Organo-functional silanes are used to couple organic polymers
with inorganic materials such as talc, silica, and mica [27].
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