Thesis (M.Eng.)--Chulalongkorn University, 2004

To focus on investigating methods for preparing microcellular PVC foam with an ultimate aim of reducing its import dependence. The so-called microcellular PVC foam was prepared from PVC resin compounded with azodicarbonamide as a chemical blowing agent and other chemical additives. In the continuous foaming process using a twin screw extruder, azodicarbonamide is thermally decomposed at die temperature varied in a range of 160 to 190 ํC, resulting in generation of microbubbles dispersing in the melting polymer. Chemical additives which are nano-calcium carbonate with nominal diameter of 60 nm and diisononylpthalate (DINP) are added into PVC for enhancing the formation of microcellular pores. The prepared PVC foam density drastically decreased from 1.25 to 0.41 g/cc when azodicarbonamide content was varied from 0 to 10 phr. Meanwhile, it is found that sodium bicarbonate is not effective to help decrease foam density due to its lower solubility in PVC. Addition of DINP into the compounded PVC foam leads to a decrease in its tensile strength. For the prepared PVC with relatively low density, its tensile strength becomes worse because uniform and closed-cell structure is hardly achieved.