Study of crystal texture in pvc gels by x‐ray diffraction and infrared dichroism

Abstract

An enquiry is presented into the nature and origin of thermoreversible gelation of poly(vinyl chloride) (PVC). In line with a previous paper it is demonstrated by direct x‐ray diffraction evidence that the origin of the gelation is crystallization, and that this crystallinity can be conspicuously apparent even for the usual technological polymer. In addition some unusual diffraction effects become apparent such as do not obviously follow from existing notions of the PVC structure. Combined infrared dichroism and x‐ray studies revealed that these new effects are attributable to a two‐component nature of the crystallinity where the components are distinguished by their orientation behavior, lateral extension, and possibly morphology of the crystallites. Some of the crystals orient with their a axes (type A crystals) and some with their c axes (type B crystals) along the stretch direction. Other more complex orientability differences are also manifest during film formation. Crystals B are smaller, and are believed to correspond to the network forming junctions, hence to fringed micellar crystals. Crystals A have a less evident connection with the network and are hypothesized to be of lamellar character, the behavior of which is closely simulated by lamellar crystal additives (stabilizer crystals). High‐temperature x‐ray work revealed no melting of crystals even in the temperature range where endotherms appear in the thermograms.

Structural studies on gels from isotactic polystyrene

“…The interpretation of the morphological origin of perpendicular textures in oriented gels follows the lines laid out in our previous gel studies on other systems [1,13]. It was envisaged that the orthogonal texture corresponds to platelet type crystals which are either unconnected or only loosely (i. e. not in a load bearing fashion) connected to the network.…”

“…This is being mentioned because such a situation has indeed arisen with drawn gels of PVC [13]. In the present case there can be no ambiguity: we have both the traditional 31 helix structure in two mutually perpendicular orientations and the new gel structure in its expected fibre alignment in the stretch direction.…”

Study of the physical structure of PVC by infrared techniques: A short review

“…It has been observed that for PVC/polycaprolactone (PCL) blends, the atactic fraction of PVC is less oriented than the syndiotactic fraction. Guerrero, et al, have shown from dichroism measurements that PVC gelled from solution consists of two crystal populations (23,24). A crystal, well developed and melted at high temperature (around 24OoC), are lamellar type crystallites.…”

Effect of mechanochemical degradation on gelation and mechanical properties of PVC

“…[7][8][9][10] The effect of vibromilling or jet milling on influence of heat and shearing force. 2,3 The meltgelation and mechanical properties was studied ing enthalpy of PVC crystallites recrystallized in hopes of gaining an innovative route to raise during cooling from processing temperature to the G value of PVC. room temperature is DH A .…”