Subcritical CO2-Based Microcellular Extrusion of Environmentally Benign Plastics

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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.