Thermal Degradation of Wood Fillers at the Melt-Processing Temperatures of Wood-Plastic Composites: Effects on Wood Mechanical Properties and Production of Voiatiles

The objective of this research was to clarify the effect of wood thermolysis during melt processing on the properties of wood-plastic composites. Oven-dried sugar pine wood strips were subjected to thermal degradation in a stirred molten metal bath in the temperature range 220°C to 260°C. Exposure times ranged from 4096 to 4 minutes. The bath and wood strips were kept free of oxygen. Degraded wood specimens and undegraded ones (used as controls) were tested for bending modulus and strength, toughness, and weight loss. Toughness was most affected by the degradative treatment, followed by bending strength and then bending modulus. Apparent Arrhenius parameters for the thermal degradation process were determined from rates of property loss, and times required to produce various relative property losses were calculated. Losses in wood mechanical properties during a single composite extrusion probably would not significantly alter composite properties, but multiple melt processing steps could be deleterious. Possibly more important are volatile degradation products which could be sufficient to create problems in air pollution, in the melt processing and mechanical behavior of composites.