Lignocellulose-polymer composites. V

Water hyacinth, with its composite mechanical pulps, was used as lignocellu lose to produce composites with polystyrene or urea-formaldehyde resins. Th e bending strength of the composites increased with increasing concentratio n of the resin. The temperatures needed to treat the water hyacinth to obta in pulps affect the strength and densities of the composites. This may be a ttributed to the behavior of lignin at temperatures higher than 135 degrees C. However, the composites produced using urea-formaldehyde resins showed s light increases in bending strengths compared with those produced using pol ystyrene, which may be attributed to the ability of formaldehyde to make cr osslinks with the free OH groups of cellulose and hemicellulose. The use of ground palm leaves, together with ureaformaldehyde resin, produc ed composite with high density and low bending strength, while the ground w ater hyacinth failed. The pulp from palm leaves, when processed into compos ites using 10% urea-formaldehyde resin, show bending and densities affected by its preparation and by the amount of the composite mixture to be presse d. Hence, the type of the substrate defined the type of the polymers or res in used to obtain composites with proper mechanical properties. The effect of the pressure (2.4, 3.5, 4.7, and 5.9 megapascal, or MPa) used to produce composites from ground palm leaves or their pulp together with polystyrene was investigated. Linear relationships existed between the bending strengt h and the pressure; the increased pressures enhanced the mechanical propert ies of the composites.