Use of wood fibres as reinforcing fillers for polystyrene

The suitability of wood (aspen and spruce) fibers in the form of different pulps (e.g. chemithermomechanical and sawdust as reinforcing fillers for polystyrene PS667) have been investigated. The variation in the mixing and moulding temperatures of the composites as well as the effect of different parameters (e.g. fibre loading (10–40 wt.%), particle size of the fibres (20 and 60 mesh size), concentration of coupling agents (0–20%) and nature of the coupling agents (isocyanates) on the mechanical properties (e.g. tensile modulus (at 0.1% strain), tensile strength at maximum point and corresponding elongation and energy) were evaluated. Maximum improvements in the mechanical properties occur when mixing or moulding temperatures reach 175–190°C. Also, a higher percentage of the coupling agent (2 wt.%) and a smaller particle size (mesh size 60) in the composite provide maximum improvement. The polymeric nature of poly(methylene (polyphenyl isocyanate)) as well as the π electron of the benzene ring which is also common to polystyrene make it the best coupling agent in comparison with other isocyanates. After optimization of mixing and moulding conditions, and selecting the suitable coupling agents, composites with 30 wt.% of wood fibres in polystyrene offered improved mechanical properties.