Some relationships for the orientational drawing of polymers

Abstract

AbstractThe orientational drawing of films from different thermoplastics has been studied. The value of the activation energy of drawing in the regions of forced elasticity (necking), high elasticity, and viscous flow (ΔE1, ΔE2, ΔE3) has been found to vary directly with the activation energy for viscous flow of the melt (ΔEη). Here ΔE1 < ΔE2 < ΔE3 = ΔEη. Thus Δ Eη characterizes the potential of thermoplastics for orientational drawing under different deformation conditions, since it reflects simultaneously both the intermolecular interaction level and chain flexibility. For maximum chain orientation, the calculated values for the change in the entropy are close to that of the entropy change during crystallization (melting) of the same polymer. The deformation of polymer may be described as a deformation of an entanglement network from the standpoint of classic elasticity theory. Some parameters for an entanglement network were calculated from the results of the drawing experiments. The density of the entanglement network (DEN) depend on the polymer composition: For flexible‐chain polymers the DEN is less, for rigid‐chain polymers (with coiled chains) it is higher. The DEN affects the maximum (prebreak) drawing ratio: The greater the DEN, the smaller the ratio to which a film can be drawn. At high orientation, the tensile strength of different polymer films tend to be similar, if drawing is not accompanied by crazing.