Fracture resistance of hybrid PP/elastomer/wood composites

PP was modified with elastomer and wood to prepare materials with large stiffness and impact resistance. Three wood fibers with different particle characteristics were used, and elastomer as well as wood content changed in a wide range. Interfacial adhesion was modified through the use of maelated polypropylene (MAPP) coupling agent. The structure of ternary PP/elastomer/wood composites was manipulated by the use of functionalized polymers and processing conditions. Considerable embedding of the wood into the elastomer was achieved in some cases depending on the variables. Wood increases impact resistance slightly, elastomer drastically in two-component composites and blends, but fracture toughness remains small in three-component hybrid systems irrespectively of structure. Depending on particle size and interfacial adhesion fiber fracture and debonding occur in wood reinforced composites, mainly plastic deformation takes place in blends. This latter process is suppressed by cavitation promoted further by the presence of wood fibers which increase local stresses. The usual concept of three-component materials does not work in wood composites, micromechanical deformations must be controlled to diminish or completely eliminate cavitation and to increase the plastic deformation of the matrix polymer.