Thermoforming of Bio-based Thermoplastics - Polylactic Acid (PLA) Sheet Foams

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Macro Engineering and Technology Inc. has recently designed a new tandem extruder for producing polymer foams with tailored properties. One of its applications is to manufacture thermoplastic foam sheets for post-processing such as thermoforming, which shapes the sheets into final products (e.g., beverage cups and food service containers). The conventional material being used to make these thermoformed products is closed cell polystyrene foam, also known as Styrofoam. However, many local governments around the world, including Toronto, have implemented strict bans or fines on the uses of Styrofoam for packaging products and/or food and beverage containers. Therefore, the industry is exploring a new eco-friendly substitute. One of the most promising candidates is polylactic acid (PLA), which is a bio-based and biodegradable polymer made from renewable resources (e.g., corn and sugar beets) through condensation polymerization of lactic acid or ring-opening polymerization of lactide. Nevertheless, the drawbacks of PLA's low heat resistance and brittleness have limited its uses to manufacture food and beverage containers through thermoforming. In particular, the heat distortion temperature of typical PLA is 55 degree C, which is significantly lower than polystyrene's 105 degree C. This has limited their uses in high temperature applications. Thus, this research aims to: i) design new material formulations and processing conditions to tailor PLA foam sheets; (ii) characterize the foam morphology and crystallinity of PLA foam sheets and correlate them to material formulations and processing conditions; (iii) investigate the effects of foam morphology and crystallinity in PLA foam sheets on their thermoformability; and (iv) study the dimensional stability of thermoformed PLA foam products at elevated temperature. This research will contribute to the areas of advanced materials and manufacturing, both nationally and globally. It would facilitate the replacement of Styrofoam products by PLA foam products, which are biodegradable and thereby more environmentally sustainable. This would permit the industrial sectors to remain innovative and competitive, while taking greater environmental responsibility.