Foam extrusion of PS blown with a mixture of HFC-134a and isopropanol

Use of mixtures of blowing agents in foam extrusion has gained interest in the past few years. Reasons for blending physical foaming agents (PFA) are numerous. The incentives may be economical, environmental or technical. With respect to that latter factor, blending suitable PFAs is often regarded as providing a better control of processing conditions. For example, a specific PFA could be selected for its inflation performance and blended with other co-blowing agents chosen for their stabilizing role. Although considerable amount of work has been done in that area, very little information has been disclosed in open literature. 1,1,1,2-tetrafluoroethane (HFC-134a) has been reported as an interesting candidate for polystyrene (PS) foaming, although low densities cannot be easily obtained and stable processing conditions are difficult to achieve. This work studies the effect of blending HFC-134a with isopropanol as a co-blowing agent for PS. Off-line solubility data, on-line rheology measurements and extrusion foaming performance of this mixture will be discussed. The function of each blowing agent during the process will be analyzed with respect to the plasticization, nucleation, expansion and stabilization phases. Attention will also be paid to interaction involving the two PFA components.