Effects of carbonate salts on crystallization kinetics and properties of recycled poly(ethylene terephthalate)

In this study, thermal and microscopic analyses were used to evaluate a variety of carbonate and bicarbonate salts (alkali, alkaline-earth, and other metals), having different thermal stability within the range of poly(ethylene terephthalate) (PET) processing temperatures, as nucleating agents for recycled bottle PET. In addition, the effects of the salts on the melt viscosity and MW of the resin after melt processing were investigated in attempts to determine their overall relative performance as potential nucleating agents during injection molding. It was found that among the additives tried sodium salts are the most effective nucleating agents for recycled PET crystallization with a concomitant relatively small reduction in molecular weight. All other salts were less effective nucleating agents and, in some cases, caused also significant resin degradation. Mechanisms explaining the behavior of the different salts are proposed. With regard to processability of recycled PET in injection molding, it was found that for certain additives temperatures below 100°C could be effectively used, resulting in short cycles that produced crystalline products with satisfactory mechanical properties.