Effects of Blending of Branched and Linear Polypropylene Materials on the Foamability

摘要

The foaming behaviours of blends of linear and branched propylene polymers are presented in this paper. The effects of increasing the amount of branched propylene polymer materials on the expansion ratio and cell density of extruded foam were examined. In foam processing of linear polypropylene resins, the quick loss of blowing agent from the foam, promoted by cell coalescence, causes foam contraction, and results in low expansion. On the other hand, the branched propylene polymer resins are well known to retard cell coalescence, to increase the expansion ratio, and to increase the processing window. Due to the high cost of branched resin and in order to design foam properties, the use of blends of linear and branched propylene polymers has been of interest to the foam industry. This paper presents the changes in the processibility and foam qualities as a function of the amount of the branched resin. The foam morphologies of propylene polymer blends at various processing temperatures were investigated using a tandem foam extrusion system, and their volume expansion and cell nucleation behaviours were compared. As expected, increasing the percentage of branched resin in the blends promoted the volume expansion and cell density that resulted in an increase in the processing window for the maximum achievable volume expansion, and a finer cell structure.