Dimensional stability of oriented, rigid poly(vinyl chloride)

Abstract

ABSTRACT:Oriented PVC has enhanced properties, but on heating it begins to shrink and eventually reverts to its original dimensions. Thermomechanical analysis was used to study the effects of orientation variables and subsequent annealing or aging on the shrinkage of rigid PVC. The thermal history of the oriented PVC affected its crystallinity and the free volume in the oriented structure. These changes modified the temperature at which the oriented samples began to shrink (i.e., their dimensional stability.) Higher draw and annealing temperatures can be used to improve dimensional stability; however, their effective use is limited because PVC has a peak elongation at 90°C. Increased annealing time also increases dimensional stability. Aging greatly improves the dimensional stability of the material; this process can be accelerated at temperatures up to 60°C. The shrinkage onset temperature can be increased without compromising the enhancement of mechanical properties achieved by orientation.

Principles of Thermal Degradation

“…The second curve mostly reflects HCl loss but also formation of some aromatic content. 163 Figure 4.16 shows plasticizer loss at relatively low temperatures during 2 hours of exposure of PVC containing dioctyl phthalate and benzyl butyl phthalate (PVC:plasticizer=2:1). 161 Two phases can be distinguished: until about 350 o C the concentration of carbon increases because of gradual loss of chlorine; above 350 o C also, carbon concentration decreases because degraded polymer becomes oxidized and volatile products are produced from carbon.…”

Mechanical and thermal properties of poly(vinyl chloride)/α‐methyl‐styrene‐acrylonitrile blends prepared by melt extrusion

“…Poly(vinyl chloride) (PVC) is known as a versatile thermoplastic with good mechanical properties and also possesses excellent flame retardant properties among general purpose commercial plastics. [1][2][3][4] However, its thermal stability is not always satisfactory because of its low glass transition temperature (T g ). A formulation that performs well at room temperature application may become miserable even for 80 C environments.…”

Variation of thermal stress and dimension of rubber solids upon heating

“…However, these stretched chains tend to shrink at elevated temperatures because of entropic considerations. The stretched chains are in a low entropy state because of their high order [5]. If heat is applied to a stretched specimen, the rubber chains return to a high entropy state.…”

“…The crosslinking in rubber materials introduces structural elements that hold the molecular chains in fixed relations to each other and suppress the plasticity. When rubber chains are straightened out by an applied force and released, they retract to their original dimensions as their thermal motion allows [3][4][5]. Rubber products stretched or drawn during processing are deformed or shrink upon heating, since the extended chains tend towards a coiled conformation because of entropic considerations [6a,6b].…”