Wood-polymer composites manufacturing processes

Jackson, S.M. Advanced process technology for manufacturing wood-polymer composites. In Wood-Plastic Conference, Conference Proceedings, Baltimore, MD, December 5-6, 2000 21-28. 

The enthusiasm in this field is explained by the number of potential applications. For example wood-polymer composites (WPC), mostly manufactured through extmsion and injection moulding processes are used in automotive (dashboards or screen-doors of the vehicles) and construction applications (interior floor coverings, profiles for doors and windows, ornamental panels, external shutters, pavements, garage, or entrance doors). Replacement of wood products for building applications such as particleboard and fiberboard materials or injection mouldable wood is another area where natural fibers are generating increased interest. 

Guo, G., Rizvi, G.M., Park, C.B. and Lin, W.S., Critical Processing Temperature in Manufacture of Fine-Celled Plastic/Wood-fiber Composite Foams. J. Appl. Polym. ScL, 91. 621 (2004). 

Many carpet manufacturers, fiber and chemical suppliers, recycling companies, and academic institutions are actively pursuing various methods to recycle fibrous waste. The approaches include chemical processes to depolymerize nylon and other polymers, recovery of plastic resins from carpet fibers, direct extrusion of mixed carpet waste, composites as wood substitutes, fibers for concrete and soil reinforcement, waste-to-energy conversion, and carpet as feedstock for cement kilns. 

The greatest volume of wood adhesives for structural applications are thermosetting phenol-formaldehyde (PF) or urea-formaldehyde (UF) polymers or their derivatives. PFs are the commodity for exterior applications, while UFs are the commodity for interior applications. Because each composite product and the associated process may require a somewhat different resin, many variations of PF and UF resins are available. Isocyanate crosslinking resins are used to a lesser extent than PFs or UFs in manufactured board. Although these resins impart a durable, water resistant bond suitable for exterior application, the cost per pound of adhesive is greater than for PFs or UFs. 

Microwaves can be applied for the nonintrusive inspection of dielectric materials, including polymers, wood, and ceramics [107-117]. The inspection of dielectric polymeric materials is easily performed, because of their relatively high transparency towards microwaves. Of technical importance are methods based on reflection measurements on sheet materials, such as composites made from several layers adhesively bonded together. In this case, microwave techniques can be used to control composite processing and manufacturing. 

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