Gas check prevention during calendering of poly(vinyl chloride) films using poly(caprolactone)-based additives

Abstract

Gas checks on poly(vinyl chloride) (PVC) calendered films are a common but not well understood surface quality defect that causes delays and resource wastage during the manufacturing of plastic sheets and films. Three modified poly(caprolactone) (PCL)-based additives of differing molecular weights were used as a secondary plasticizer in PVC with the goal of preventing the formation of gas checks without modifying the calendering process conditions. To better understand gas check prevention processes, the effects of the PCL-based additives on the thermal, mechanical, rheological, and chemical properties of PVC blends were assessed. A high molecular weight (2000 g/mol) PCL-based additive was unable to prevent gas checks in PVC blends, unlike the lower molecular weight (540 g/mol and 900 g/mol) additives. Chemical and physicochemical properties affect the prevention or reduction of gas checks showing that the acid values and molecular weights of the PCL-based additives are related to the number of gas checks. In contrast, physical properties, including rheological ones like complex viscosity or the storage and loss moduli that were previously hypothesized to be important factors in preventing gas check formation, were not significantly impacted by the addition of the secondary plasticizer. Furthermore, the acid value was observed to be related to the reduction in gas checks, likely due to the interaction of the dispersed functional acid groups with the entrapped air. Consequently, the effectiveness of the additive in eliminating gas checks declines as the acid value decreases.

Highlights

• Low concentrations of PCL-based additives prevent gas checks on PVC films.
• They do not significantly affect the physical/mechanical properties of films.
• Higher molecular weight additives are beneficial, but only below 2000 g/mol.
• The effectiveness of PCL-based additives increases with acid value.