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

宏工程技术公司最近设计了一种新的串联挤出机，用于生产具有定制性能的聚合物泡沫。其应用之一是制造热塑性泡沫片材用于后处理，例如热成型，其将片材成形为最终产品（例如，饮料杯和食品容器）。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，也称为Styrofoam。然而，包括多伦多在内的世界各地的许多地方政府都对聚苯乙烯泡沫塑料用于包装产品和/或食品和饮料容器实施了严格的禁令或罚款。因此，业界正在探索一种新的环保替代品。最有前途的候选者之一是聚乳酸（PLA），其是由可再生资源（例如，玉米和甜菜）通过乳酸的缩聚或丙交酯的开环聚合。然而，PLA的低耐热性和脆性的缺点限制了其通过热成型制造食品和饮料容器的用途。特别是，典型PLA的热变形温度为55 ℃，显著低于聚苯乙烯的105 ℃。这限制了它们在高温应用中的使用。因此，本研究的目的是：（i）设计新的材料配方和加工条件来定制PLA泡沫片材;（ii）表征PLA泡沫片材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PLA泡沫片材中的泡沫形态和结晶度对其热成型性的影响;（iv）研究PLA泡沫片材中的泡沫形态和结晶度对PLA泡沫片材的热成型性的影响。以及（iv）研究热成型PLA泡沫产品在高温下的尺寸稳定性。这项研究将有助于先进材料和制造领域，无论是国内还是全球。这有助以聚乳酸泡绵产品取代发泡胶产品，因为聚乳酸泡绵产品可生物降解，因而在环境方面更具可持续性。这将使工业部门保持创新和竞争力，同时承担更大的环境责任。

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.