Effect of recycled fiber, compatibilizer and pre-formed fiber handsheet on the performance of wood-polyolefin composites.

摘要

Effects of recycled materials on the properties of hardboards, of compatibilizer on the wettability and interfacial shear strength of wood and plastics, and of handsheet configuration on the properties of wood fiber-polyolefin laminates were studied. Recycled fibers from three sources showed considerably higher holo- and alpha-cellulose contents, lower extractive and lignin contents, and shorter fiber length than virgin southern pine fiber. Replacing virgin fiber with recycled fiber adversely affected mechanical properties, dimensional stability and wettability of fiberboards. Using layered structures while substituting 20% virgin fiber with polyethylene appreciably increased dimensional stability. Internal bond strength of hardboards made from virgin fiber, recycled fiber and polyethylene was affected by both hot press temperature and panel density, whereas bending properties and water absorption were affected only by panel density. Contact angles on birch plywood surfaces increased upon addition of maleated propylene (E-43) and decreased with increasing E-43 concentration. For E-43-treated wood surfaces, contact angles among the four wetting liquids were in the order of phenol resin {dollar}>{dollar} urea resin {dollar}>{dollar} isocyanate {dollar}>{dollar} water. Contact angles on polyolefin polymer surfaces followed the sequences of polypropylene {dollar}>{dollar} linear low-density polyethylene {dollar}>{dollar} low-density polyethylene. Interfacial shear strength was highest in polypropylene and lowest in low density polyethylene. The effect of E-43 was most pronounced in polypropylene, and less so in low-density polyethylene and linear low-density polyethylene. Increasing E-43 concentration beyond a certain extent decreased interfacial shear strength. Laminates made by interleaving Kraft pulp handsheets and polypropylene films exhibited comparable ultimate tensile strength with natural fiber-reinforced plastics. Effects of fiber content and layer (number of plastic films between two consecutive handsheets) were significant on the tensile properties of wood fiber-polypropylene laminates. Laminates made from one layer showed better ultimate tensile strength, but the interaction between fiber content and layer offset one another on the modulus of elasticity. Increasing fiber content and number of layer decreased dimensional stability. With proper control of plastic layer between two handsheets, wood fiber-polypropylene laminates with as high as 70% fiber loading can be fabricated with favorable mechanical properties.