Effect of crystallinity on PVC physical properties

Abstract

Crystallinity in PVC contributes significantly to the strength and resiliency of the polymer. Two types of crystallites have been described: a primary crystallite in the virgin powder state pictured as a platelet or flat needle‐like lamellar crystallite, and a secondary, fringed micellar crystallite from melts or solutions. Both crystallites create loose, crosslinking networks. The secondary crystallite forms when plastisol melts are cooled or solutions are gelled. Crystallites exert a major effect on rheological properties. The thermal destruction of the primary crystallite networks in the melt phase results in a decrease in elastic modulus. Cooling from the fused state creates secondary crystallites that affect tensile and elongation.

Influence of crystallinity in the curing mechanism of PVC plastisols

“…With regard to the second temperature interval (160 -180°C), some authors have indicated that PVC is not a completely amorphous-glassy material. 1,7,23 This affirmation has been based on electronic microscopy and measurements. The proposal of a secondary crystallinity could justify the observation of a second stage in the gelation process due to the breaking of the primary crystalline structure.…”

“…With regard to the second temperature interval (160–180°C), some authors have indicated that PVC is not a completely amorphous–glassy material 1, 7, 23. This affirmation has been based on electronic microscopy and measurements.…”

“…The same authors indicated that the crystallinity of a dried gel is very low and does not represent any variation in some properties, such as elasticity, but in the case of a wet gel, crystallinity varies significantly, inducing some changes in elasticity and the glass‐transition temperature ( T g ) 6. It proposed that two types of microcrystals were present in the gel structure: primary microcrystals in the virgin powder and secondary and fringed micellar microcrystals from melts or solutions 7. The secondary structure forms when the plastisol melts are cooled or the solutions are gelled.…”

“…6 It proposed that two types of microcrystals were present in the gel structure: primary microcrystals in the virgin powder and secondary and fringed micellar microcrystals from melts or solutions. 7 The secondary structure forms when the plastisol melts are cooled or the solutions are gelled. Those two structures exert a major effect on the rheological and mechanical properties.…”

Equations of State and Free‐Volume Content

“…Detection of this temperature is contingent on the polymer achieving sufficient crystalline content. For example, poly(vinyl chloride), usually treated as an amorphous polymer, shows T m = 444 to 452 K when the crystalline content of the syndiotactic isomer is about 2 wt% [Marshall, 1994].…”