Visualization of structural rearrangements during annealing of solvent-crazed isotactic polypropylene

Abstract

Structural rearrangements taking place upon the annealing of solvent crazed isotactic PP are studied by the direct microscopic method. Independently of the type of its crystalline structure, solvent crazed PP undergoes shrinkage in a wide temperature interval, starting even from room temperature and up to its melting temperature. This shrinkage is a result of the structural processes in crazes and proceeds via shutting down of the walls of individual crazes. This low temperature shrinkage of solvent crazed PP is assumed to have an entropy nature. This process involves the contraction of extended polymer chains and their transition into thermodynamically favorable conformations. This contraction is allowed because, upon annealing, the entropy contracting force increases. As a result, the crystalline framework of oriented PP melts down (amorphization), extended chains appear contracted, stored stresses relax, and subsequent recrystalli zation in the unstressed state takes place.

Evolution of the Nanoporous Structure of High-Density Polyethylene during Drawing in Supercritical Carbon Dioxide

“…The mechanism of such high reversible deformations has remained unclear so far. It has been suggested 56 that the driving force of the shrinkage is the entropic elasticity, mainly the excessive surface free energy and high specific surface area of the crazes.…”

Strain-induced softening of glassy and crystalline polymers

“…26). 111 The entirely crystalline product has to exhibit a negative equilibrium force coefficient. Samples of PP subjected to crazing in AAM were studied.…”

“…SEM images of commercially available membranes based on hard-elastic PP (a) and HDPE (b) 111. Curves of isothermal annealing of samples of PP strained in AAM according to mechanisms of delocalized (1) and classical (2) solvent crazing.…”

Plastic deformation of polyethylene terephthalate films during rolling

“…was described in [29][30][31][32]. This technique consists of applying a nanometer metallic coating to the surface of a polymer.…”

“…With the use of this method, the shrinkage during subsequent heating of amorphous polycarbonate pre rolled at room temperature was investigated [31]. The deformation of polycarbonate during rolling was found to proceed heterogeneously, and there were areas with different directions of polymer orientation.…”