Extrusion foaming of neat and recycled polyethylene terephthalate (PET) resins are difficult due to their high melting temperature and low melt strength. Chemical crosslinking modification of the PET resins is the most widely used method to solve this problem. However, the modified resins are expensive and difficult to be re-used. In this work, micro-graphite or nanoclay particulates were added to PET to adjust its melt viscosity and strength and to serve as a nucleation agent to facilitate cell growth during extrusion. Micro-graphite is an excellent infrared attenuation agent (IAA) that may provide enhanced thermal insulation to PET foams. Using our small lab extruder, the foamed micro-graphite/PET composite extrudates could reach a low density of 0.21 g/cm~3, close to that achieved by chemical crosslinking modified PET resins, using injected hydrofluorocarbon (HFC) as a blowing agent in extrusion. Properties of the PET foam including density, cell size, and crystallinity depend on particulate type and processing conditions.
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