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

宏控工程技术公司最近设计了一种新的串列挤出机，用于生产具有定制性能的聚合物泡沫。它的应用之一是制造热塑性泡沫塑料板材，用于热成型等后处理，将板材成型为最终产品(例如，饮料杯和餐饮容器)。用于制造这些热成型产品的常规材料是闭孔聚苯乙烯泡沫塑料，也称为聚苯乙烯泡沫塑料。然而，包括多伦多在内的世界各地的许多地方政府都对使用聚苯乙烯泡沫塑料包装产品和/或食品和饮料容器实施了严格的禁令或罚款。因此，该行业正在探索一种新的环保替代品。聚乳酸是最有前景的候选材料之一，它是一种以可再生资源(如玉米和甜菜)为原料，通过乳酸缩聚或丙交酯开环聚合而成的生物基可生物降解聚合物。然而，聚乳酸的耐热性低和脆性的缺点限制了其在热成型制造食品和饮料容器方面的应用。特别是，典型的聚乳酸的热变形温度为55摄氏度，大大低于聚苯乙烯的105摄氏度，这限制了它们在高温应用中的使用。因此，本研究旨在：i)设计新的材料配方和工艺条件以定制聚乳酸泡沫片；(Ii)表征聚乳酸泡沫片的泡沫形态和结晶度，并将其与材料配方和加工条件相关联；(Iii)研究聚乳酸泡沫片中的泡沫形态和结晶度对其热成形性能的影响；以及(Iv)研究热成型聚乳酸泡沫塑料制品在高温下的尺寸稳定性。这项研究将为国内和全球的先进材料和制造领域做出贡献。这将有助于用聚乳酸泡沫塑料产品取代聚乳酸泡沫塑料产品，因为聚乳酸泡沫塑料产品是可生物降解的，因此在环境上更可持续。这将使工业部门在承担更大的环境责任的同时，保持创新和竞争力。

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.