Subcritical CO2-Based Microcellular Extrusion of Environmentally Benign Plastics

这个国家科学基金会资助的项目旨在开发一种亚临界二氧化碳基微孔挤出工艺，用于环保塑料。设想的工艺将使用低压CO2作为发泡剂，为目前用于制造聚合物泡沫的有害化学发泡剂和挥发性气体提供替代品。该研究将重点关注两种环保塑料：再生聚对苯二甲酸乙二醇酯（PET）和天然衍生聚乳酸（PLA）。选择这两种聚合物体系是因为它们对社会的直接影响。再生PET是在许多住房、工业建筑和包装应用中取代PVC的候选材料。聚乳酸是可生物降解的，由每年可再生的资源生产。这项研究基于一种新颖的想法，即用二氧化碳预饱和聚合物颗粒，作为向挤出过程中输送发泡剂的一种手段。这个想法有两个显著的好处：首先，它允许在挤压过程中的低气体饱和压力，这样就可以使用传统的挤压设备；其次，它激活了饱和步骤中的成核位点，因此气泡成核和气泡生长可以解耦，以便于过程控制。这项研究跨越了许多学科，如机械工程、材料科学、化学工程和聚合物物理学。它将为研究生和本科生提供良好的培训机会，以获得跨学科的知识。这项研究产生的新技术将从源头上消除污染，为可持续发展的环境保护资源，并创造新的就业机会，这将使整个社会受益。

This NSF funded project is aimed at developing a sub-critical CO2 based microcellular extrusion process for environmentally benign plastics. The envisioned process will use low pressure CO2 as a blowing agent, providing a substitute for harmful chemical blowing agents and volatile gases now in use in manufacture of polymer foams. The research will focus on two environmentally benign plastics: recycled polyethylene terepthalate (PET) and naturally derived Polylactic Acid (PLA). These two polymer systems are chosen for their immediate impact on the society. Recycled PET is a candidate to replace PVC in many housing, industrial construction, and packaging applications. PLA is biodegradable and produced from annually renewable resources. The research is based on a novel idea of pre-saturating polymer pellets with CO2 as a means to deliver foaming agents to the extrusion process. This idea has two significant benefits: First, it allows low gas saturation pressure in the extrusion process such that conventional extrusion equipment can be used; second, it activates nucleating sites in the saturation step and thus the bubble nucleation and bubble growth can be decoupled for easier process control. The research cuts across many disciplines such as mechanical engineering, material science, chemical engineering, and polymer physics. It will provide excellent training opportunities for both graduate and undergraduate students to gain interdisciplinary knowledge. The new technology resulted from this research will eliminate pollution at the source, preserve resources for a sustainable environment, and create new job opportunities that will benefit the society at large.