Preparation of Low-Density Microcellular Foams from Recycled PET Modified by Solid State Polymerization and Chain Extension
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Recycled polyethylene-terephthalate (RPET) bottle regrinds were physically foamed after two types of industrially feasible molecular weight increasing processes. Intrinsic viscosity (IV) of initial waste (0.71 dL/g) increased both after reactive extrusion carried out using a multifunctional epoxy-based chain extender (0.74 dL/g) and after solid state polycondensation (SSP) (0.78 dL/g), while capillary rheometry revealed higher degree of branching in the chain extended PET material. Despite the relatively low IV values (below 0.80 dL/g), physical foaming, a mild and cost-efficient way, was successful in both cases, uniform microcellular foam structures with void fractions ranging between 75 and 83% were achieved. During the experiments morphology change in the materials was tracked by differential scanning calorimetry (DSC) besides recording IV values. The IV drop during foaming was between 0.03 and 0.10 depending on the pre-processing technology. Structure of foams produced from the two different modified RPET materials was compared with each other based on scanning electron microscopic imaging of cryogenic fracture surfaces. The average cell diameters were measured to be 213 and 360 µm in the case of chain extended and SSP-modified materials, respectively.
KeywordsRecycling PET Physical foaming Chain extension, solid state polycondensation
This research was realized in the framework of TÁMOP 4.2.4. A/1-11-1-2012-0001 “National Excellence Program - Elaborating and operating an inland student and researcher personal support system”. The project was subsidized by the European Union and co-financed by the European Social Fund. The research was financially supported by the Hungarian Scientific Research Fund (OTKA K112644, PD121171 and FK 128352) and by the ÚNKP-18-4-BME-138 New National Excellence Program of the Ministry of Human Capacities. The project was funded by the National Research, Development and Innovation Fund of Hungary in the frame of NVKP 16-1-2016-0012, GINOP-2.2.1-15-2016-00015 and FIEK_16-1-2016-0007 projects. Support of grant BME FIKP-VÍZ by EMMI is kindly acknowledged. K. Bocz is thankful for the János Bolyai Research Scholarship of the Hungarian Academy of Sciences.
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