Lignocellulose-polymer composites. V

Water hyacinth, with its composite mechanical pulps, was used as lignocellulose to produce composites with polystyrene or urea-formaldehyde resins. The bending strength of the composites increased with increasing concentration of the resin. The temperatures needed to treat the water hyacinth to obtain pulps affect the strength and densities of the composites. This may be attributed to the behavior of lignin at temperatures higher than 135 degreesC. However, the composites produced using urea-formaldehyde resins showed slight increases in bending strengths compared with those produced using polystyrene, which may be attributed to the ability of formaldehyde to make crosslinks with the free OH groups of cellulose and hemicellulose. The use of ground palm leaves, together with ureaformaldehyde resin, produced composite with high density and low bending strength, while the ground water hyacinth failed. The pulp from palm leaves, when processed into composites using 10% urea-formaldehyde resin, show bending and densities affected by its preparation and by the amount of the composite mixture to be pressed. Hence, the type of the substrate defined the type of the polymers or resin 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 strength and the pressure; the increased pressures enhanced the mechanical properties of the composites.