Compression and tensile strength of low-density straw-protein particleboard

Wheat straw can be used as a raw material for particleboard, and soybean pr otein can be used as an adhesive in particleboard fabrication. The objectiv e of this research was to characterize the mechanical properties of low-den sity wheat straw-soy protein particleboard as affected by protein modificat ion/denaturation, initial straw moisture content, and chemical treatment of the straw. Methylene diphenyl diisocyanate (MDI), considered an environmen tal-friendly resin, was also used as a binder for comparison. The major fac tors that determined the mechanical properties of wheat-straw particleboard were the types of adhesives, straw surface properties, and moisture conten t of straw. Surface treatment of straw with bleach gave better results than treatments with hydroperoxide alone or combined with sodium hydroxide trea tment. Sodium hydroxide, urea, and dodecylbenzene sulfonic acid were used i n the modification of soy protein. Particleboard with sodium hydroxide-modi fied soy protein had the best mechanical properties. The bondability of mod ified soy protein was highly dependent on straw moisture content. About 30- 40% initial straw moisture content was needed to obtain good bonding. Methy lene diphenyl diisocyanate showed better bondability than modified soy prot ein adhesives. Equilibrium moisture content of straw particleboard increase d as the relative humidity increased. The equilibrium moisture contents wer e similar for straw particleboard with sodium hydroxide-modified soy protei n and methylene diphenyl diisocyanate adhesives at 30 or 60% relative humid ity. Although the soy protein-based adhesive resulted in low-density partic leboard with poorer mechanical properties than the methylene diphenyl diiso cyanate adhesive, it is environmental-friendly and could be used in filters or light-weight core material where the requirement for mechanical strengt h is not stringent. (C) 2001 Elsevier Science B.V. All rights reserved.