COEFFICIENTS OF DYNAMIC FRICTION AND THE MECHANICAL MELTING MECHANISMFOR VINYLIDENE-CHLORIDE COPOLYMERS

Previous research and this research indicate that the mechanical melti ng for poly(vinylidene chloride) copolymers (PVDC) is complex. Mechani cal melting is defined as the melting (or devitrification) of a polyme r when a significant portion of the thermal energy originates from a m echanical energy dissipative process. PVDC mechanically melted on a mo ving metal surface at temperatures of the test instrument that were co nsiderably lower than the differential scanning calorimetry (DSC) onse t melting temperature. PVDC formulated with low levels of high density polyethylene (HDPE), however, melted at metal temperatures near the D SC onset melting temperature. Two different mechanical melting mechani sms are proposed to explain the data, and the frictional data are disc ussed with respect to solids conveying in a single-screw, plasticating extruder.