Polymeric Composites with Different Constituents - Introduction to Polymeric Composites with Rice Hulls - page 69

6 Polymeric Composites with Different

Constituents

6.1 What are Wood Plastics Composites?

Wood plastic composites (WPC) are presented because they are an important branch
of polymeric composites and used widely in many countries. The main difference
between wood plastic composites (WPC) and polymeric composites with rice hulls
(PCRH) is that, while the polymer matrices remain virtually identical, the reinforcing
constituents are different in that one uses wood flour whereas the other uses rice
hull flour. Using comparatively new technology, the emergence of PCRH is gaining
popularity and its superior properties and wider range of end applications will no
doubt pave the way as the number-one product as an ideal substitute for natural
wood or lumber.

WPC are composite materials made of wood flour/fibre and thermoplastic polymers
such as low-density polyethylene (LDPE); high-density polyethylene (HDPE);
polypropylene (PP); polyvinyl chloride (PVC); acrylonitrile-butadiene-styrene; and
polystyrene (PS). Polyethylene (PE)-based WPC are by far the most common, and
virgin resins or recycled resins (or a combination of both) can be used. Depending
on the end application targeted, these composites can be made into grooved, hollow
or solid profiles. In addition to wood flour and plastic resins, WPC can also contain
other lingo-cellulosic and/or inorganic filler materials. Many cellulose-based fibres,
such as pulp fibres, peanut hulls, bamboo, and straw as fillers or reinforcement can
also be used.

WPC came on the market in the 1990s but are considered new materials relative
to the long history of natural lumber as a building material. Manufacturers of this
composite lumber claim that it is more environmentally friendly and requires less
maintenance than the alternative: treated solid natural wood. This composite lumber
can be made in any colour and with/without simulated wood grain effects and
aesthetically pleasing finishes.

6.1.1 General Properties of Wood Plastic Composites

WPC with ≤90% wood fibre or wood flour are possible but optimum properties are
achieved with ratios of 40-60% for a given WPC formulation. The proportions of filler