Date of Award
Doctor of Philosophy in Chemical Engineering - (Ph.D.)
Chemical Engineering, Chemistry and Environmental Science
David S. Kristol
George Y. Lei
James M. Grow
In order to reduce waste generation, and comply with state and federal laws, plastic beverage bottles are usually undergoing recycling. Poly(ethylene terephthalate) [PET], which is the main component the bottles are made of, cannot be used for manufacturing new food containers, and has to be used for manufacturing other end consumer products. The recycled PET is a cheap material, but its use is problematic due to the low crystallization rates of PET. The present study investigates ways of accelerating PET crystallization by using inorganic carbonate salts as nucleating agents. This study also explores the possibility of forming polymer blends based on recycled PET.
Crystallization kinetics of recycled PET were studied in the presence of Na2CO3, NaHCO3, K2CO3, Li2CO3, MgCO3, CaCO3, SrCO3, BaCO3, ZnCO3, CdCO3, and PbCO3 as nucleating agents. Based on results from Differential Scanning Calorimetry, Optical Microscopy, and thermal stability studies, it has been concluded that among the additives tried, Na2CO3 and NaHCO3 are the most effective nucleating agents for recycled PET crystallization. From the results obtained during this study, and from published data on virgin PET crystallization, it has been concluded that the effectiveness of an additive as a nucleating agent for PET can be predicted based on the following general criteria: the additive must have a good solubility in both water and alcohol and the resulting solution must be basic; the additive should be easily dispersed in the molten PET.
Processability of recycled PET in injection molding has been also investigated in the present study. It has been found that temperatures below 100°C can be effectively used with low cycle times. More specifically, it has been found that a mold temperature of 40°C can be used to produce amorphous specimens while at 90°C, and in the presence of either Na2CO3 or NaHCO3, crystalline products with good properties can be formed.
Recycled PET has been also used for producing blends with polyester elastomers and low density polyethylene (LDPE). With polyester elastomers the blends resulted in products having a high degree of crystallinity, a good appearance, but relatively poor mechanical properties. With LDPE, blends of very good properties were produced but only in the presence of various ionomers which acted as compatibilizers.
Hsu, Peming Peter, "Crystallization kinetics and polyblends of poly(ethylene terephthalate) recycled from post-consumer beverage bottles" (1991). Dissertations. 1140.