Effects of Hydrophobic Wood Flour on Mixing Properties of Compound-Type Wood Plastic Composites
Masako SEKI, Hiroyuki SUGIMOTO, Tsunehisa MIKI, Kozo KANAYAMA and Yuzo FURUTA
Abstract:In a production of compound-type wood plastic composite (WPC), hydrophobic treatments of wood elements were expected to improve interfacial adhesion between hydrophilic woods and hydrophobic plastics. However, some of results obtained by such process did not show improvements on mechanical properties of resultant products. This difference in an effectiveness of hydrophobic treatments of wood seemed to be caused by the mixing and compounding conditions for treated woods and plastics used in previous studies. There were a few studies focused on the mixing condition in WPC productions for treated wood elements. From these points of view, WPC was prepared from hydrophobized wood flour by acetylation (A-WF) and commercialized polypropylene (PP) to investigate the mixing properties as well as the mechanical properties. A blend of wood flour with PP in same weight was compounded in a closed mixing blender under the condition that mixing time was varied from 5 to 30 min at a constant temperature of 180 with a constant blender revolution of 30 rpm. The mixing properties were evaluated by measuring the torque change during the mixing and the dispersion state of the untreated/treated wood flour in the PP compounded in each mixing time. As evaluation of the mechanical properties, the static bending modulus and the impact strength were measured. Results were summarized as follows; 1) It was found from microscopic observations that A-WF has poor dispersiveness than that of the untreated wood flour. 2) By increasing mixing time, the flexural modulus of the WPC tended to be slightly decreased, although the impact strength was obviously improved. 3) By the SEM examination, the A-WF improved interfacial wetting between the wood flour and the PP and increased mutual contact surface by deformation due to softening in the mixing temperature. From the results, it appeared that dispersiveness was changed by hydrophobization of wood and the mechanical properties were consequently affected by this change. Key Words:Compound-type wood plastic composite, Mixing property, Hydrophobic treatment, Acetylation, Interfacial adhesion, Aggregation