Long-Term Hygroscopic Thickness Swelling Rate of Hydrothermally Treated Beech Wood / Polypropylene Composites

Abstract

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 degrees C, 150 degrees C or 180 degrees 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 (K-SR). The thickness swelling of thermally-treated samples at 120 degrees C for 30 min and at 150 degrees C for 30 min were lower than that of control samples, followed by thermally-treated samples at 180 degrees C for 120 min, at 180 degrees C for 30 min, at 120 degrees C for 120 min, and at 150 degrees C 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 degrees C for 30 min, the composites showed a lower swelling rate than control samples. The K-SR of the composites was influenced both by the time and temperature of thermal treatment.