Properties of poly(lactic acid) (PLA) are affected by environmental conditions such as temperature, humidity, and chemical exposure. Mass transport of gases, vapors, and organic compounds in PLA is a concern when designing applications since PLA is permeable to them. Even though mass transfer parameters of PLA such as permeability, diffusion, and solubility coefficients have been reported in the literature, the values and units are scattered and inconsistent and most of the analyses only consider PLA as a two-phase structure consisting of a crystalline and an amorphous phase. The recent concept of the three-phase model that separates the amorphous phases into the mobile and rigid amorphous fractions has barely been considered when assessing PLA's mass transfer properties. Besides gases and vapors, PLA may also interact with solvents and aqueous solutions. Literature on PLA properties "after" being contacted with solvents and solutions is scarce. Only a limited number of studies reported properties of PLA "during" immersion (i.e., in-situ). Thus, this dissertation aims to: 1) provide a comprehensive, systematic, and critical review of mass transfer properties of PLA and PLA-based materials such as blends and composites, along with review of migration of chemical compounds from PLA, and 2) evaluate the in-situ changes in thermo-mechanical properties of PLA when in contact with alcohol solutions using a dynamic mechanical analysis technique. The literature review shows that PLA provides moderate barrier to gases, water vapor, and organic vapors and that PLA barrier can be enhanced through modification such as blending with other polymers. The in-situ immersion of PLA in alcohol solutions showed reductions in PLA's glass transition temperatures (Tg) during immersion when compared to the Tg of dry PLA. The Tg reductions became smaller as the number of carbon atoms in aliphatic alcohols C1-C10 increased. Immersion in 50% (v/v) 2-propanol resulted in a Tg that was higher than when PLA was immersed in 100% 2-propanol but lower than when PLA was immersed in water, implying that the concentrations of the solvents affect the changes in PLA's Tg. The chemical isomerism in propanol (i.e., 1- and 2-propanol) did not affect the Tg reduction. The Flory-Huggins interaction parameters and the Hansen solubility parameters were used to explain the reduction in Tg of PLA based on the interactions of PLA with the alcohol solutions. The relationship explained the interactions between PLA and alcohols with small molecules (C1-C8), but bigger alcohols (C9-C10) did not fit the prediction. Overall, the experimental results are not yet sufficient to predict the Tg reduction of PLA in other solvents. Further research on the mass transfer properties of PLA is needed for PLA to reach its full commercial potential.
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