Use of acetone in determining poly(vinyl chloride) processing morphology and product morphology

Acetone swells PVC very rapidly but reaches a limit in swelling. This limit suggests a crosslinked network. Acetone apparently enters only the amorphous PVC and does not destroy the crystallites which act as crosslinks. For this reason acetone-swelled then sheared specimens were used to assess the structure of PVC. After melting at 162°C, PVC shows very little interaction of primary particles (1 μm) as judged by their ease of separation in acetone. At 177°C melt temperature the primary particles are not destroyed but show excellent interaction or fusion as judged by the presence of fibrils when swelled and sheared in acetone. Apparently melting of some crystallites allows strong interaction between primary particles; however, not all the crystallites are melted, therefore maintaining the residual primary particle structure. At 215°C, the residual primary particle structure disappears apparently by complete melting of crystallites. Surface roughness, toughness, and toughness retention upon weathering are also explained by the PVC morphology. The technique of acetone swelling/shearing is simple enough to be used by most companies processing PVC such as those making pipe, windows, profiles, siding, and wire insulation. This technique correlates well with the morphology revealed by fracturing at low temperature then examining in the scanning electron microscope. The technique is useful even without the microscope.