RECYCLING OF TLCP REINFORCED POLYPROPYLENE
Maharshi M. Chauhan, Robert T. Young, and Dr. Donald G. Baird
National Science Foundation Science and Technology Center:
High Performance Polymeric Adhesives and Composites, and
Department of Chemical Engineering
Virginia Polytechnic Institute and State University
Blacksburg, Virginia
ABSTRACT
A mixture consisting of 75 wt% polypropylene (PP) and 25 wt% thermotropic liquid crystalline polymer (TLCP) was blended with an extrusion process in order to pregenerate the optimal TLCP reinforcement. This blend was then reprocessed five times by succe sive granulation and injection molding at temperatures below the melting point of the TLCP. The machine direction tensile modulus declines linearly with each reprocessing in a manner similar to glass reinforced composites. Differential scanning calorim try (DSC), scanning electron micrographs (SEMs) and rheological tests were performed in order to help to determine the cause for the decline in mechanical properties. DSC scans indicated that there was no appreciable degradation of the polypropylene an this was supported by tests performed on pure propylene that had undergone a similar processing history. SEMs showed that as the material is processed repeatedly, the TLCP fibrils become twisted and broken which reduces the effective aspect ratio of th reinforcement. The decline in effective aspect ratio was verified experimentally by studying the transient rheological behavior of the PP/TLCP blends. The possibility of regenerating the TLCP fibrils in situ was considered by injection molding the ble d at a temperatures greater than the melting point of the TLCP.