The effect of chemical treatment of wood and polymer characteristics on the properties of wood–polymer composites

The physical-mechanical properties and the microscopic structure of caixeta (Chrysophyllum viride) and slash pine (Pinus elliottii) impregnated with polystyrene (PS) were investigated. The influences of a pretreatment with hydrogen peroxide (H₂O₂) solutions utilized in the production of the wood–polymer composites (WPC) and the characteristics of polystyrene formed in situ on the properties of WPC were analyzed. The incorporation of polystyrene improved the compression and static bending properties of slash pine and caixeta. The micrographies confirmed that there were distinct but continuous phases of polymer and wood cell wall which granted the composites a better physical-mechanical behavior. The sensibilizing treatment with dilute hydrogen peroxide solution led to an increase in the viscosity average molecular weight (M_v) of polystyrene, and to the graft polymerization of the monomer, which, in turn, enhanced the stress properties of caixeta–polystyrene composites. Concentrated H₂O₂ solutions degraded caixeta wood, decreasing its tensile properties. Lower initiator concentration favoured higher molecular weight of polystyrene formed in pine wood. A fivefold increase in M_v of PS, however, had little effect on the compression properties of pine–polystyrene composites.