Dissertation (Ph.D.)--University of Toledo, 2007. / Typescript. "Submitted as partial fulfillment of the requirements for The Doctor of Philosophy Degree in Engineering." Bibliography: leaves 200-205.

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Poly(ethylene terephthalate) (PETE) packaging is becoming an increasingly popular choice of packaging material for milk, but has the disadvantage of releasing odorous acetaldehyde into food matrices. Sensory detection group thresholds for acetaldehyde in whole, low fat and nonfat unflavored milks were 3939, 4020, and 4040 ppb respectively with no significant difference due to fat level. Chocolate flavored milk and spring water showed detection thresholds levels for acetaldehyde of 10048 and 167 ppb respectively. This information assisted in determining if acetaldehyde migration from the package to the product would influence the flavor of the product. Whole milk was packaged in glass, high density polyethylene (HDPE), amber PETE, clear PETE, and clear PETE with UV light block and was exposed to fluorescent light of 1100-1300 lux (100-120 FC) at 4oC for 18 days. Sensory and chemical analysis and was done on milk from all containers over a period of 18 days. Emphasis was on oxidation, acetaldehyde and lacks freshness off-flavors and byproducts. All volatile flavor compounds studied (acetaldehyde, pentanal, dimethyl disulfide, and hexanal) were increased in light-exposed milk samples. Amber PETE showed the least amount of oxidation off-flavor, while clear PETE with UV block showed significantly less oxidation off-flavor than glass, clear PETE or HDPE on day 7 and 18. Acetaldehyde was not detected by sensory analysis in either light-exposed or light-protected samples. Chemical analysis showed relative acetaldehyde levels in glass (2220 ppb), HDPE (1265 ppb), amber PETE (3397 ppb), clear PETE (2930 ppb), and clear PETE with UV light block (1754 ppb) were all below concentrations found for human flavor threshold. / Master of Science

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published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

The effect of antiplasticization on barrier properties of poly(ethylene terephthalate) (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. Our oxygen and carbon dioxide transport results were well described by a combination of the free volume based interpretation and interaction energy estimation. Transport characterization and DSC techniques verified that there exists a third element, a de-densified 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 an 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. A thorough molecular level study using dynamic mechanical analysis 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. 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.

The effect of various inorganic and organic additives as possible nucleating agents on the crystallisation behaviour of P. E. T. and the suosequent influence on the morphological and mechanical properties has been examined. Various methods of mixing(: the polymer and additive were investigated and a method involving the screw-Extrusion of the polymer and the additive was ultimately adopted. Crystallisation studies were carried out using differential scanning calorimetry under dynamic and isothermal modes. The results produced under conditions of isothermal crystallisation were analysed by means of a computer. Despite differences between batches of polymer all the additives with the exception of indigo produced a nucleating effect in the polymer as indicated by an increase in the rate of crystallisation compared with that of the base polymer. Two organo-metallic substances (sodium benzoate and sodium stearate) proved to be the most effective in this respect by decreasing the degree of supercooling of the polymer by 20 [degrees]. Morphological studies were carried out on isothermally crystallised samples, after etching and replication using a transmission electron microscope. A nodular structure whose dimensions were sensitive to both the nucleating agent and the temperature of crystallisation was observed. Mechanical testing of samples direct from the D. S. C. was carried out using a compression method. The breaking loads were found to vary with both the type of nucleating agent used and the crystallisation temperature chosen. A separate study involving the exanination of the resulting fracture surfaces by scanning electron microscopy revealed that a, high breaking load was associated with a fine discontinuous structure whereas lower breaking loads were characterised by a more continuous linear appearance. This implies a higher energy of fracture due to the increased surface area of the fracture surface of the former.

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