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Call number: LD2668 .T4 1951 B43 / Master of Science

Thesis (M.B.A.)--Boston University

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Doctor of Philosophy / Department of Grain Science and Industry / Sajid Alavi / Poly(lactic acid) (PLA) is the most common bio-based & compostable polymer available commercially that is cost competitive and combines a range of desirable properties like melt processability, high strength and modulus. The films made from this aliphatic polyester tend to be brittle which can be overcome by blending PLA with another bio-based polymer with high flexibility poly(butylene adipate-co-terephthalate) (PBAT), but the resultant blend is only biodegradable in composting conditions. The primary focus of this study was incorporation of thermoplastic starch (TPS) in PLA/PBAT blends to increase the rate of biodegradability and decrease the cost. In the first part of this study, as a preliminary step only PLA/PBAT blends were investigated along with nanofiller nanocrystalline cellulose (NCC) as a nanofiller for enhancing mechanical and barrier properties. Melt extrusion was used for preparation of nanocomposites and 200 microns thick films were formed by melt pressing. PBAT enhanced elongation but NCC did not have any positive impact on the mechanical and barrier properties of the nanocomposites as NCC was aggregated in the polymer matrix due to the difference in polarity based on the hydrophilic nature of the nanofiller and hydrophobic nature of the polymer matrix. In the second part of study, up to 40%TPS was blended along with the PLA/PBAT/NCC nanocomposites. Joncryl (0.5%) was used as a compatibilizer. TPS addition decreased the mechanical and barrier properties (Tensile strength (TS) = 15- 30 MPa, Elongation at break (EB) = 6-12%, Water vapor permeability (WVP) = 1.6-8.3 g.mm/kPa.h.m2), although addition of NCC helped in increasing the TS and decreasing the WVP. Dispersion of NCC improved with the addition of hydrophilic TPS. Analytical techniques including transmission electron microscopy, fourier-transform infrared spectroscopy, differential scanning calorimetry were used to study the polymer-polymer and polymer-nanofiller interactions. Optimization study of PLA/PBAT/TPS/NCC nanocomposites was done using mixture response surface methods. Quadratic models with good predicted R2 (between 84.3% and 97.59%) were developed for all the responses. Optimization study was done that could yield films with optimum properties comparable to commercial plastics and maximizing the level of TPS. Films with optimum properties (TS = 29.5 MPa, EB = 12%, WVP = 1.99 g.mm/kPa.h.m2) were predicted at levels of 64.3% PLA, 14.5% PBAT, 18% TPS and 2.6% NCC along with 0.5% Joncryl. The improved mechanical and barrier performance suggested that PLA/PBAT/TPS/NCC nanocomposites have potential use in food packaging applications. In the final phase of study, mathematical modeling was used to understand the influence of nanofiller (NCC) on the mechanical and barrier properties of the nanocomposites. The modified Halpin-Tsai equation was used to model the elastic modulus of the nanocomposites, while the modified Nielsen equation was used to model the WVP as a function of nanofiller content, geometry, strength and interactions with polymer matrix. The experimental results in both cases were close to the theoretical predictions by the models. The models predicted an increase in mechanical and barrier properties with increase in aspect ratio and surface interactions of nanofiller with polymer matrix.

A range of antioxidants (BHT, Irganox 1010, 1076, 1330 and Irgafos 168) were incorporated into polymers (polyethylene, polypropylene, polystyrene and polyvinyl chloride) and subjected to increasing doses of gamma-irradiation (1,5,10,20,25,35 and 50 kGy) from a cobalt-60 source. The amount of extractable antioxidant from the stabilised polymers was determined chromatographically and a gradual diminution in the total extractable levels of each antioxidant was observed as irradiation progressed, the extent depending on the nature of both the antioxidant and the polymer 2,6-Di-t-butyl-1,4-benzoquinone was shown to be an extractable degradation product, arising from the effects of gamma-irradiation on the phenolic antioxidants. The extractable degradation product arising from the phosphite antioxidant, Irgafos 168, was identified as tris(2,4-di-t-butylphenyl)phosphate. It was demonstrated using 14C-labelled Irganox 1076 that degradation products formed during gamma-irradiation are becoming covalently bound to the polymer, as a result of radical coupling processes. There is a pronounced increase in the extent of covalent binding from 0.4% before irradiation to a minimum of 12.4% after an exposure to 50 kGy. Evidence has also been presented of covalent binding of the degradation product of Irgafos 168 to the polypropylene matrix, via polymeric radicals formed during irradiation. Finally, the effects of gamma-irradiation on the extent of migration of antioxidants from polyolefins into food simulants was studied. It was found that irradiation leads to a decrease in the extent to which hindered phenolic antioxidants migrate from polyolefins into fatty media, consistent with the reduction in extractable antioxidant levels and the increase in the extent of antioxidant-polymer binding.

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by Wong Siu Kay. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 172-175). / Chapter PARTI : --- Naphthalene contamination in Milk Drinks / Chapter Chapter 1 --- Introduction --- p.1 / Chapter Chapter 2 : --- Methods of determination of Naphthalene in Milk and Packaging Materials --- p.6 / Chapter Chapter 3 : --- Prediction Method I - Simulation --- p.15 / Chapter Chapter 4 : --- Prediction Method II- Mathematical Modelling --- p.24 / Chapter Chapter 5 : --- Atmospheric Effect I - Naphthalene Vapour in Air --- p.31 / Chapter Chapter 6 : --- Atmospheric Effect II- Aromatic Hydrocarbons in Air --- p.44 / Chapter Chapter 7 : --- Naphthalene Contamination In Solid Foods --- p.58 / Chapter Chapter 8 : --- Migration of Naphthalene in other Types of Polymers --- p.69 / Chapter Chapter 9 : --- Further Studies --- p.76 / Reference --- p.31 / Appendix I --- p.88 / Chapter Part II : --- General Study of Plasticisers Migration into Food / Chapter Chapter 1 : --- Introduction --- p.91 / Chapter Chapter 2 : --- Survey of Plasticisers Level in Food Contact Materials --- p.100 / Chapter Chapter 3 : --- Survey of Plasticisers Level in Foodstuff --- p.119 / Chapter Chapter 4 : --- Mathematical Modelling --- p.139 / Chapter Chapter 5 : --- Effect of Microwave Heating --- p.159 / Reference --- p.172 / Appendix II --- p.176