Packaging Materials account for 31% of the world’s municipal solid waste. Agencies like the Environmental Protection Agency (EPA) and the Agency for Toxic Substances and Disease Registry (ATSDR) are pushing for the increased use of recycled thermoplastic materials. Polyethylene terephthalate (PET) is a commonly recycled thermoplastic which is used to package ready-to-eat fruits and vegetables. Most recycled polyethylene terephthalate (RPET) packaging materials contain heavy metal catalysts, the most common being antimony. The recent increased use of recycled plastic materials has been suspected as the source of increased human heavy metal exposure. In this study, cadmium, chromium, nickel, lead and antimony were quantified in post-consumer RPET rigid containers and films using inductively coupled plasma-atomic emission spectrometry (ICP-AES). Two hundred samples were tested of which 29 were found to be contaminated with heavy metals in the parts-per-million (ppm) range. Chromium was found in all the contaminated sample replicates at an average level of 8.18 ppm. Cadmium was found in all the contaminated samples as well. Lead was found in 90.4% of the contaminated samples and concentrations ranged from a low of 0.02 ppm to a high of 0.36 ppm. Nickel was found in 96.4% of the contaminated samples while antimony was found in 97.6% of the samples. Due to limited sample material, 22 of the 29 contaminated RPET rigid containers and films were tested for heavy metal migration into a 5% citric acid:water solution (w/v) or deionized water. Samples were subjected to prolonged storage at 7.2 or 22.2°C for 1, 7 or 14 days, or were exposed for 5 minutes to microwaves from a 1700-watt microwave oven set to 70% power before analysis. Leachate values were at ppb levels but were often below the ICP-AES Limits of Detection which were at also the ppb level, whether calculated for deionized water or 5% citric acid in water. No measureable levels of heavy metal were detected for any sample exposed to water, regardless of treatment. For samples exposed to 5% citrate and stored or microwaved, only chromium and nickel leached at measurable levels, and the number of RPET’s releasing measurable chromium and nickel increased with microwaving compared to the same plastics stored at 22.2 or 7.2°C. Since leaching was calculated as µg/L of heavy metal lost from the entire inner surface (1021 cm2) of a retail salad bag, actual exposure to heavy metal would be much less than measured in this study as retail fruit and vegetable packages and microwaveable pouches usually contain very little liquid in order to increase food safety. The results therefore suggest the potential for little migration of heavy metal from recycled PET to whole or fresh-cut fruits and vegetables when held at ambient or refrigerated temperatures, or when microwaved.

The feasibility of using oriented polymer technology in the design and manufacture of mechanical power transmission belts has been investigated. Working from an initial selection of polymers a die-drawing technique for orienting the polymers was devised, and the static and dynamic mechanical properties of the oriented polymers were investigated. These results indicated that PP, PBT, PPS and PEEK were suitable for further research. Of these 4 materials PBT was selected as the most appropriate material for belt manufacture based on cost, processability (drawing temperature, natural draw ratio) and limitations of laboratory equipment. A technique based on free-tensile drawing combined with simultaneous rotational motion was designed and used to manufacture oriented PBT flat belts from cylindrical injection moulded preforms. The technique used a tensile machine with two pulley-clamps, a fitted heated chamber and an electric motor to provide rotational motion to the belt during drawing. Two types of oriented PBT flat belts with different cross sections were produced successfully, termed 'thick' and 'thin'. These belts were tested on a purpose-built rig comprising two equal diameter pulleys, one driven by an electric motor and the other connected to a generator to provide load. The belt life and power transmission performance was investigated at various conditions of speed, transmitted torque and tension, and the results indicated that despite their smaller cross section 'thin' flat belts demonstrated up to 3 times longer life. However life was only 100 hours, which was very low compared with conventional flat belts that last for many thousands of hours at higher speeds and much greater power transmission capacity. Synchronous belts were then produced through the same manufacturing method used for flat belts. This aspect of the research concentrated on the initial pitch design and size, i. e. the timing. Initially a rectangular tooth profile was selected for its simplicity in terms of manufacture. The produced belts exhibited high pitch length variation as well as deformed teeth and were not usable for synchronous power transmission. An extra timing feature was included to control orientation; reducing the pitch length variation enabling consistent tooth production. It was observed that the areas between the extra timing feature and the tooth edges did not orient completely with some regions remaining undrawn. Finite Element Analysis (FEA) was used to predict the drawing behaviour of different shapes and dimensions of the timing features. The results suggested that a 4mm wide and 7mm long slot provided the highest possible extension and the minimum non-oriented regions on the groove. Whilst, the thickness and width of the drawn belt timing features showed differences to the FEA predictions, manufactured synchronous belts based on that design had much better controlled dimensions and the lowest achieved pitch length variation ( ±1%), compared to initial attempts. It is concluded that oriented polymers have the potential to be used in power transmission belts since they offer higher stiffness, tensile strength and creep resistance compared with isotropic polymers that are currently used in commercially available belts such as thermoplastic polyurethane (TPU) and polyvinyl chloride (PVC). The main disadvantages were the lack of dimensional stability and number of cycle to failure. / Polymer IRC; The University of Bradford; The Gates Corporation

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The dissertation describes and assembles the building blocks for sound and accurate models for solid-state polymerization process systems of condensation polymers, particularly poly(ethylene terephthalate) and nylon-6. The work centers on an approach for modeling commercial-scale, as opposed to laboratory-scale, systems. The focus is not solely on coupled polymerization and diffusion, but extends to crystallization, physical properties, and phase equilibrium, which all enhance the robustness of the complete model. There are three applications demonstrating the utility of the model for a variety of real, industrial plant operations. One of the validated simulation models is for commercial production of three different grades of solid-state PET. There are also validated simulation models for the industrial leaching and solid-state polymerization of nylon-6 covering a range of operating conditions. The results of these studies justify our mixing-cell modeling approach as well as the inclusion of all relevant fundamental concepts. The first several chapters discuss in detail the engineering fundamentals that we must consider for modeling these polymerization process systems. These include physical properties, phase equilibrium, crystallization, diffusion, polymerization, and additional modeling considerations. The last two chapters cover the modeling applications. / Ph. D.

Supercritical carbon dioxide (scCO2) was used as a processing aid to improve the level of exfoliation achievable in a PET-layered silicate nanocomposite produced from melt compounding. Layered silicate and scCO2 were allowed to mix for a period of time before being released into the second stage of a single screw extruder. The rapid expansion forced silicate particles into a modified hopper containing neat PET pellets. The mixture of layered silicate and PET was immediately melt mixed in a single screw extruder, cooled in a water bath and pelletized. Two sets of samples each containing layered silicate with different surface chemistries were produced with this method at 1, 3 and 5 wt% silicate. For comparison, samples of the same weight fraction and type of silicate were produced from a traditional melt compounding method. Wide angle x-ray diffraction (WAXD), mechanical testing and rheological analysis were used in order to characterize the silicate morphology, the composite mechanical properties and the relative amount of degradation between the various samples. Results show that scCO2 processed samples contain a higher degree of layered silicate exfoliation than samples produced with traditional melt compounding. Mechanical property improvements are shown to be dependent on the type of silicate surface modification employed. Finally, degradation of the PET matrix appears to be far less extensive in the scCO2 processed samples as shown from rheological data. / Master of Science

Yes / Active packaging consisting of polyethylene terephthalate (PET) trays coated with a Citrus extract, without and with plasma pre-treatment, can reduce lipid oxidation in cooked meat. The mechanism of action of the packaging was investigated by quantifying the extent of transfer of antioxidant components from the active packaging into cooked turkey meat. Kinetic studies revealed the affinity for water of phenolic compounds and carboxylic acids in the Citrus extract, suggesting their diffusion into the water phase of the meat facilitated their antioxidant effect. Analysis by high-performance liquid chromatography permitted the identification of carboxylic acids and flavanones as major components of the extract. Their quantification in meat after contact with the trays revealed a release of 100% of the total coated amount for citric acid, 30% for salicylic acid, 75% for naringin and 58% for neohesperidin, supporting the release of these components into cooked meat as a mechanism of action of the antioxidant active packaging.