Effect of addition of oligobetapinene on morphology, thermal and gas permeation properties in blends with HDPE

Abstract

Binary blends of high density polyethylene (HDPE) and oligobetapinene (OBP) were prepared by melt mixing. The morphology, thermal and permeability properties of compression molded and slow cooled films are reported. Applying the first-derivative procedure on differential scanning calorimetry (DSC) traces, we have detected the temperature of glass transition (T g ) of HDPE as a large peak centered from Ϫ125 to Ϫ100°C. In the blends, we observed that the OBP molecules were able to resolve the transition into two components. The lower one was ascribed to the ␥-transition of HDPE, and the upper one was attributed to its T g . The OBP molecules also formed another transition at a higher temperature. The blends were composed at least of three distinct phases, likely composed of amorphous HDPE with some amount of OBP molecules, amorphous OBP with some polyolefin and crystalline HDPE. The scanning electron microscopy (SEM) investigations revealed segregation of the components. The permeation to CO 2 of plain HDPE and 90/10 blends was similar, but at higher concentrations of oligomer, the value was slightly higher than that of neat HDPE. The decrease of overall crystallinity was counterbalanced by the presence of an OBP rich phase in the blend and could explain the slight increase in permeability of the film blends.