Prevention of surface defects in calendered poly(vinyl chloride) sheets using a succinate-capped poly(caprolactone) additive

Surface defects known as “gas checks” often mar the surfaces of poly(vinyl chloride) (PVC) calendered films. These defects are typically prevented through changes in the calender operating parameters, a costly exercise which also limits the sheet thickness and the production rate. Adding a low concentration of poly(caprolactone) (PCL)-based star-shaped compound can eliminate gas check defects in PVC calendering. The effects of a triheptylsuccinate-terminated PCL with a PCL triol core and number average molecular weight of 540 g/mol (i.e., PCL₅₄₀-[(succ)-C₇]₃) has been investigated on the material, thermal, and processing properties of PVC blends containing diisononyl phthalate (DINP) as a primary plasticizer and PCL₅₄₀-[(succ)-C₇]₃ in low quantities (i.e., 0, 5, or 10 parts per hundred rubber (phr)) as a secondary plasticizer and processing aid. The most significant differences between PVC blends containing PCL₅₄₀-[(succ)-C₇]₃ and those without are in the rheological properties of the PVC blends at higher temperatures and lower angular frequencies. Under these conditions, PVC blends containing 10 phr of PCL₅₄₀-[(succ)-C₇]₃ have a complex viscosity nearly three times higher than those containing only DINP. PVC/PCL₅₄₀-[(succ)-C₇]₃ blends had comparable tensile properties to those containing only DINP, with no significant change in maximum elongation and a small but significant increase of 28% in maximum stress. The addition of PCL₅₄₀-[(succ)-C₇]₃ made it possible to produce calendered films without gas checks that were twice as thick as those produced in its absence. In addition to reduced wastage of marred films, the increased calender operating range for PVC films containing PCL₅₄₀-[(succ)-C₇]₃ has the potential to significantly reduce energy costs for the calendering of thick PVC films.