Toughened thermoplastic composite. I. Cross‐linkable phenol formaldehyde and epoxy resins‐coated cellulosic‐filled polypropylene composites

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Abstract
Composites of polypropylene (PP) or maleic‐anhydride‐modified polypropylene (MAH‐PP) with uncoated or thermosetting resincoated sawdust or explosion pulp (V‐pulp) were prepared by dynamic cross‐linking and their properties were compared to those of unmodified and uncross‐linked composites. The effects of modification and dynamic cross‐linking on the interfacial adhesion between polymer and filler have also been investigated by a solvent extraction study and microscopic analysis. The new method of dynamic cross‐linking in combination with the additional effect of compatibilization suggests a practical route to obtain high‐strength, toughened thermoplastic composites. Dynamically cross‐linked epoxyor phenolic resin‐coated sawdust or V‐pulp that can be grafted or can have affinity to MAH‐PP was found to improve tensile strength as well as elongation at yield point. The tensile toughness of the dynamically cross‐linked‐compatibilized composites is better than that of an uncross‐linked composite of MAH‐PP and sawdust. The improved toughness of the dynamically cured composites appears to be that further chemical bonds form between coated filler and MAH‐PP in addition to grafting of MAH‐PP onto cellulose chain. © 1993 John Wiley & Sons, Inc.