Soft PVC foams: Study of the gelation, fusion, and foaming processes. I. Phthalate ester plasticizers

Compression behavior of soft PVC foams obtained by cardanol-derived plasticizer

This work is aimed to study the application of a bio-based plasticizer, obtained by acetylation and epoxydation of cardanol, for the production of soft PVC foams. The use of epoxidized cardanol acetate allowed obtaining a more efficient foaming of soft PVC compared to phthalate plasticizer bis(2-ethylhexyl) phthalate (DEHP), mainly due to the lower viscosity attained in the decomposition range of azodicarbonamide (AZDC). As a consequence, the foams produced by epoxidized cardanol acetate showed a lower density compared to those produced with DEHP. The lower density yielded lower values of compressive modulus. However, the modulus was shown to be not only dependent on the density, but also showed a direct dependence on the type of plasticizer used, in addition to processing temperature and AZDC content. As a consequence, the specific compressive modulus also showed a direct dependence on the type of plasticizer, processing temperature and AZDC content. Such dependence was explained by considering different cellular morphologies developed during foaming under different processing conditions, including type of plasticizer. In particular, it was shown that the lower viscosity attained by epoxidized cardanol acetate plasticized PVC involved an increase of the average pore size of the foam, which was shown to be the main cause of the variation of the specific compressive modulus.

Study of the rheology and foaming processes of poly(vinyl chloride) plastisols with different foaming agents

Poly(vinyl chloride) (PVC) plastisols are widely used in the production of flexible PVC foams. In this study, we investigated the evolution of the complex viscosity of PVC plastisol by dynamic oscillatory tests, the storage modulus of the PVC compound by dynamic mechanical analysis, and the thermal behavior including the decomposition of three chemical blowing agents (CBAs), namely, azodicarbonamide, 4,4′-oxybis(benzenesulfonyl hydrazide), and sodium bicarbonate, by differential scanning calorimetry. Furthermore, the morphology and quality of the foams obtained from the corresponding plastisols were characterized by scanning electron microscopy. The results indicated that the onset decomposition temperature T2(5%) of a CBA in plastisol is the most critical indicator of the foam quality. The temperature difference corresponding to [T2(5%) – Tηmax] was also proved to be another important parameter. When T2(5%) is within the optimum temperature range of a PVC plastisol, the bigger the [T2(5%) – Tηmax] difference, the better the quality of the foams.

Effect of the particulate morphology of resin on the gelation process of PVC plastisols

The gelation process of poly(vinyl chloride) (PVC) plastisol is very important to ensure the quality of the product and is affected by the type of resins, plasticizers, and other additives. In this study, the gelation process of the as-prepared PVC plastisol was characterized by measuring the evolution of vibrational viscosity with temperature or time using a vibrational viscometer. Furthermore, the effect of some commercial resins with different particulate morphologies on the gelation process was investigated by synchronously combining scanning election microscopy and laser particle size analyses. The results of this study proved that the particle size distribution and the aggregation degree of the secondary particles of a resin are the key factors affecting the gelation process. For the resin with bimodal particle size distribution, the closer the aggregation of the secondary particles, the slower the gel speed; however, an opposite behavior was observed for the resins with unimodal particle size distribution.