The objective of this research is to study the effect of fungal decay on the mechanical and physical characteristics of thermally treated wood flour-plastic composites. First, the wood chips (Fagus orientalis L.) were treated thermally for 30 and 120 minutes at three various temperatures (120, 150, and 180 °C) under saturated vapor in a steaming vessel and they were ground (40 to 60 mesh size) by wily mill machine. Then polypropylene (PP), thermally treated beech wood flour, and MAPP as compatibilizer were used by melt compounding and injection molding process. Decay resistance, modulus of rupture, modulus of elasticity, notched Izod impact strength, moisture sorption, and swelling of thickness after 2 h and 24 h of soaking in distilled water of WPCs were measured prior to and after being infected by wood-degrading fungus (Coriolus versicolor) for 6 weeks. The modulus of rupture and elasticity, and impact strength of WPCs increased and the moisture sorption and thickness swelling decreased at higher treatment time and temperature. The composite samples produced using heat-treated wood at 180 °C for 120 minutes had the least mass loss. The modulus of rupture and elasticity, and impact strength were reduced after incubation with fungus. Moreover, the results showed that the moisture sorption and thickness swelling for all formulations of unrotted specimens were significantly lower than that of white-rotted specimens.
Long-term hygroscopic thickness swelling rate of polypropylene (PP) composites filled with thermally treated wood flour was investigated. The beech wood chips were heat treated at 120 °C, 150 °C or 180 °C for 30 or 120 min using saturated steam in a digester. The composites based on PP, beech wood flour (BF), and coupling agents (PP-g-MA) were made by melt compounding and injection molding. The weight ratio of BF to PP was controlled at 50/47 for all blends. The amount of coupling agent was fixed at 3 wt.% for all formulations. Further study was conducted to model thickness swelling of the composites, a swelling rate parameter (KSR). The thickness swelling of thermally-treated samples at 120 ºC for 30 min and at 150 ºC for 30 min were lower than that of control samples, followed by thermally-treated samples at 180 ºC for 120 min, at 180 ºC for 30 min, at 120 ºC for 120 min, and at 150 ºC for 120 min, respectively. Furthermore, the thickness swelling of the BF/PP composites decreased with increasing time and temperature of the thermal-treatment. In addition, at 120 ºC for 30 min, the composites showed a lower swelling rate than control samples. The KSR of the composites was influenced both by the time and temperature of thermal treatment.
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