what is WPC?

Wood-plastic composites (WPC) are composite materials made of wood fiber/wood flour and thermoplastic(s) (includes PE, PP, PVC etc.).

Chemical additives seem practically "invisible" (except mineral fillers and pigments, if added) in the composite structure. 

They provide for integration of polymer and wood flour (powder) while facilitating optimal processing conditions.

In addition to wood fiber and plastic, WPC can also contain other ligno-cellulosic and/or inorganic filler materials. 

WPC are a subset of a larger category of materials called natural fiber plastic composites (NFPCs), which may contain no cellulose-based fiber fillers such as pulp fibers, peanut hulls, bamboo, straw, digestate, etc.