| Poly(ethylene terephthalate) has been widely used in the packaging industry due to its ease in processability, excellent transparency, and good barrier properties. Although PET is an excellent, broadly accepted barrier material for current generation applications, expansion to new markets such as oxygen sensitive juices, flavored water, and energy drinks requires improved CO 2 and O2 barrier properties. Combination of antiplasticization and crystallization can be one of the most effective approaches to achieve highly improved barrier properties for the next generation packaging industry.;The effect of antiplasticization on barrier properties of PET has been investigated through transport measurements and some supplementary characterization techniques including dynamic mechanical measurements and solid state 13C cross polarization/magic angle spinning (CP/MAS) NMR. This systematic study on antiplasticization of PET was initiated after the sample preparation procedure using a heat press was optimized. This aspect of the work was quite challenging. Transport measurements demonstrated that the incorporation of low molecular weight diluents (LMWDs) such as phenacetin and acetanilide at low concentration levels (~2wt%) into PET leads to barrier improvement by antiplasticization. Based on the combined results from carbon dioxide permeation and sorption measurements, further barrier improvement was found to be due to the further reduction in the diffusion coefficient. Transport results were well described by a combination of the free volume based interpretation and interaction energy estimation. Combination of transport measurements and supplementary techniques including DMA and solid state 13C NMR allows improved understanding of barrier properties of PET with a more molecular perspective.;Transport characterization and DSC techniques verified that there exists a third element, a dedensified amorphous fraction in crystallized PET. Both oxygen and carbon dioxide permeabilities at 1 atm at 35ºC in PET with different crystallinities were well described by the Nielsen model due to the presence of adjustable parameter, Ar, even though it is based on a two phase model. The comparison of the barrier improvement factor (BIF) values for samples annealed at 100ºC demonstrated that a combination of antiplasticization and crystallization allows for very efficient chain packing, which significantly improves the barrier properties of PET. It is due to the fact that dedensified amorphous regions created by crystallization in PET were filled with LMWDs. A thorough molecular level study using dynamic mechanical analysis also supported the synergistic effect of antiplasticization and crystallization on the molecular motion in PET.;Lastly, a vapor/gas permeation system with a new concept of a flexible humidity and methanol vapor partial pressure clamp was designed and constructed. A new cell design for transport characterization was designed and constructed as well. Even though its permeation results are not available at this point, its operational feasibility was well verified by pre-calculations and physical explanations. This system may be used for future studies to evaluate barrier properties of PET or modified PET samples. |
