On the conformational behavior and solid‐state extrudability of crystalline polymers

Abstract

Extrusion experiments on thirteen polymers in our laboratory and extrusion and forging studies on nine polymers in other laboratories reveal that solid‐state extrusion and malleability occur in semi‐crystalline polymers that have a crystalline relaxation, αc at the temperature Tαc, and do not occur in semicrystalline polymers devoid of αc. The solid‐state extrusion takes place in the temperature range of Tαc ≤ T < Tm with Tm being the melting point. In this temperature, range, the polymeric crystals show a measure of disorder, observed by several techniques and by small heats and entropies of fusion. A survey of the literature indicates that, in general, polymers which have a αc and are solid‐state extrudable have shallow and broad bottoms to the energy‐wells describing their most stable crystalline conformations, and polymers showing no αc have steep‐walled energy‐wells for the same conformations.

Polymer ultradrawability: the crucial role of α-relaxation chain mobility in the crystallites

“…We would like to mention that NMR, by unequivocally demonstrating the occurrence of helical jumps or similar large-amplitude motions, disproves the suggestion by Aharoni and Sibilia [49] that small-angle torsional motions were responsible for the a c -relaxation. A shallow mini-mum in the intra-molecular energy, as implicated by Aharoni and Sibilia, may be necessary to allow for the distortions occurring in the traveling defect that rotates the chain, but cases like iPS show that the barrier height in the intermolecular energies is similarly important [88].…”

“…This work extends an empirical correlation of polymer extrudability and the crystalline a -relaxation by Aharoni and Sibilia [49,50]. On the basis of Aharoni's work, Bigg [51] and Gedde [52] have also stated that the a c -relaxation is important for ultradeformation in general, however without detailed justification or a critical discussion of alternative models.…”

“…For these systems, it is not clear whether translational motion occurs. However, since good extrudability and workability is observed in the a c -relaxation region [49], it seems likely that translational chain motions in the crystallites are also facile (see below).…”

Solid state extrusion of vinylidene fluoride (VF2)/vinylidene trifluoride (VF3) copolymers. I: Dynamics of solid state extrusion

“…Literature on the solid state extrusion is rather limited compared to other polymer processes. Aharoni and Sibilia ( 12) reviewed the literature of solid state extrudability of semicrystalline polymers up to 1979. In solid state extrusion, the polymer ( 13) is placed in the reservoir of a ram extruder and compacted at a temperature just below the polymer melting point.…”

“…Solid state extrusion of homopolymers is possible at temperatures between the crystalline relaxation temperature and melting temperature (12). This is a result of abrupt increase in thermal expansion coeffi-*To whom correspondence should be addressed which causes a reduction in intra-crystallGe forces within the crystalline regions thus enabling them to be extruded in the solid state.…”