Materials Engineering Department
BS in Materials Engineering
This project has two parts:  a migration and diffusivity model for candidate plastics used in containers, and  a product cost model for Westridge Laboratories (Santa Ana, CA).
Diffusion modeling is a useful tool to predict migration of polymer constituents into exposed liquids. Polyvinyl chloride (PVC), polyethylene terephthalate (PET) and polylactic acid (PLA) were studied to estimate production costs, and component migration into water-based liquids from plastic containers. Bis (2-ethylhexyl) phthalate (DEHP), antimony trioxide, and stannous octoate, are components of concern in the three candidate polymers, respectively. Normal detection limits for these constituents are about 1 - 10 ppb, so they are often difficult to measure at ultra trace levels after migration (< 1 pptr). This study uses modified Fick’s First and Second Laws, and a modified Arrhenius equation, to develop a working migration model. PLA is the only biodegradable candidate polymer. With properties similar to PET (e.g., optical clarity and inertness), PLA could be a preferred PET alternative. According to this model PVC has higher migration rates at higher temperatures for chosen analytes, than either PET or PLA. However at lower temperatures PET has the highest migration rate. Since PLA is somewhat new, there is a paucity of study data. Reasonable range assumptions were made for PLA diffusion coefficients. PET and PLA show similar migration curves.