EXTRUSION OF FOAMED PVC: EFFECTS OF A COMBINATION OF TWO CHEMICAL BLOWING AGENTS (ABFA AND SBC) ON RHEOLOGICAL, MECHANICAL AND MORPHOLOGICAL PROPERTIES

Abstract

The present study deals with the behavior of two chemical blowing agents (BA) in a rigid Poly (Vinyl Chloride) (PVC) compound under processing conditions. The first part of the work discusses the effect of the addition of a combination of two chemical BA; AzoBisFormAmide (ABFA) and/or Sodium BiCarbonate (SBC), on the processability of rigid PVC compound, using a Brabender torque rheometer. This apparatus simulates the conditions of temperature and shear that occur during processing. This technique was previously used under conditions bearing no relation to real polymer processing. Our contribution is to overcome this problem and to provide a complimentary comprehension. It was found that addition of BA separately, leads to the appearance of a new peak following that of the fusion (fluxing) one on the Brabender torque rheometer process curve. On the other hand, two distinct peaks were shown when both BA are added together. These peaks correspond to the decomposition of the BA and the expansion of the resulting cells. From this study, the Brabender torque rheometer has proven to be a valuable new technique to follow the stages of decomposition of the BA and the cell expansion within an environmental polymeric resin under real processing conditions. The second part of the work deals with the effect of the addition of a combination of two chemical BA; ABFA and SBC, on the foaming efficiency of rigid PVC compound using a laboratory scale extruder. It was found that foaming efficiency increased with BA loading to an optimum value, which is characterized by a critical concentration (CC) of BA. This CC was noticed to be higher in the case of SBC compared to that of ABFA. On the other hand, the foaming efficiency showed a synergistic effect according to some mixing ratios of two BA (70% ABFA).These mixing ratios were based on the CC of each BA.