Investigation of the Interfacial Compatibility of PEG and Thermally Modified Wood Flour/Polypropylene Composites Using the Stress Relaxation Approach

Stress relaxation has been proven to be a good measure for studying the interaction between the constituents in wood flour/polymer composites by evaluating the internal bonding quantitatively. In order to investigate the combination effect of polyethylene glycol (PEG) impregnation and heat treatment on the interfacial compatibility of wood flour/polypropylene composites, the stress relaxation of PEG and/or thermally modified wood flour/polypropylene composites was determined at three temperatures (26, 40, and 60 °C). The apparent activation energy (ΔE) was also calculated according to Eyring’s absolute rate reaction theory. The results showed that PEG treatment accelerated the stress relaxation rate of the composites and decreased the ΔE. However, heat treatment resulted in an alleviation of the increasing rate of stress relaxation caused by PEG modification and an increase in the ΔE of the composites. These results suggested that PEG treatment had a negative effect on the interfacial compatibility between wood flour and polypropylene in the composites, and heat treatment could compensate for this effect to a certain extent.