Wood plastic composite interface characterization

Background and Objective

Wood plastic composites are a high-growth forest and agriculture processing area. As
many manufacturing industries are turning to renewable sources, WPCs are a compelling alternative
with an increasing range of application areas. This growth is also occurring during a time of
significant decline in some traditional wood application areas such as newsprint and mechanical
pulp. WPCs are hybrids of plastic and wood processing, and overcome many of the shortcomings of
solid wood, broadening the application scope for our wood raw material. Biobased composite
materials are poised as one of the most promising successor application areas. However, to date, no
biobased fibre or particle composite material has performed anywhere near its theoretical
properties. It is the interface, and interfacial behaviour, between the plastic and biobased
components which primarily contribute to this shortfall. Improving this interface during processing
has potential to significantly shape and improve the properties of the final interface.

Approach

In a focused 2-year joint evaluation the fundamental
wood/polymer material interfaces and properties which arise from wood plastic composite (WPC)
processing will be examined. We will focus on characterizing the interface between wood particles and the plastic
polymer matrix; initiating at the interface and extending into the surrounding polymer matrix.

Three major processing variables will be studied. The first is characterization of changes in
the wood/plastic interface due to differences between synthetic polypropylene (PP) and bio-based
Polyhydroxyalkanoates (PHAs). The second will determine how two different wood particle
morphologies affect the interface behaviour, while the last will evaluate the interfacial effects of
WPC processing conditions (including hold times, processing shear and temperature).
Advanced characterisation will be performed at complementary facilities in Rotorua/Hamburg across
Years 1 and 2: Thermal analysis (Rotorua) for molecular level polymer properties (e.g. degree of
crystallinity and α-/β-transitions); Solid state NMR (Rotorua) for complementary molecular
neighbourhood level behaviours and conditions; Electron microscopy (Rotorua/Hamburg) for
processed particle sizes/distributions; Atomic force microscopy (Hamburg) for polymer/particle
interface transitions (hardness); X-Ray Diffraction (Hamburg) for complementary crystallinity
determination of all constituents; and physical testing of WPCs (Rotorua/Hamburg) for bulk material
properties.