Abstract
This study investigates the effect of using a multifunctional epoxide chain extender (Joncryl® ADR 4468) on the thermal stabilization and rheological properties of recycled polyethylene terephthalate (R-PET) and its blends with polybutylene terephthalate (PBT). The R-PET samples were prepared without and with chain extender (CE) contents of 0.4 wt% and 0.8 wt%. R-PET/PBT blends with weight ratios of 75w/25w, 50w/50w and 25w/75w were also prepared without and with a given CE content of 0.2 wt%. The thermal stability of the melt blended samples was analyzed through small amplitude oscillatory shear (SAOS) rheological experiments. The structure of the samples was evaluated using a Fourier transform infrared (FTIR) spectrometer. While the dynamic rheological properties of R-PET were improved with the addition of Joncryl and by blending with PBT, during the SAOS rheological experiments, the complex viscosity of R-PET further increased due to the concurrent polycondensation of R-PET and the resumption of Joncryl reaction with R-PET molecules. These reactions during the rheological experiments were further expedited with increasing the testing temperature. On the other hand, in R-PET/PBT blends, the reactivity of Joncryl was more noticeable in blends with higher R-PET contents due to the higher available internal reactive sites of much shorter R-PET molecules. It was observed that the addition of only 0.2 wt% Joncryl to the blends of R-PET/PBT (75w/25w) dramatically improves the thermal stability and dynamic rheological properties of R-PET and most likely its processability.
Highlights
Polyethylene terephthalate (PET) is a semi-aromatic thermoplastic polyester, which is widely used in many commodity and engineering applications [1,2,3]
This study investigates the effect of using a multifunctional epoxide chain extender (Joncryl® ADR 4468) on the thermal stabilization and rheological properties of recycled polyethylene terephthalate (R-PET) and its blends with polybutylene terephthalate (PBT)
The complex viscosity of PBT decreased around 40 % after 20 min at 285 oC. Such different thermal stability behaviors in R-PET and PBT samples could indicate that while polycondensation and thermal degradation could concurrently exist in both polyterephthalates, the polycondensation reaction is more pronounced among the short molecules of R-PET than their thermal degradation
Summary
Polyethylene terephthalate (PET) is a semi-aromatic thermoplastic polyester, which is widely used in many commodity and engineering applications [1,2,3]. Melt reprocessing of PET could cause chemical, mechanical, thermal, and oxidative degradations These result in reduced molecular weight and viscosity of PET, which eventually suppress its processability. Due to its good processability, fast crystallization, and similar molecular structure, polybutylene terephthalate (PBT) is recognized as one of the most promising thermoplastics to be melt blended with R-PET This is to resolve the suppressed mechanical, thermal, and rheological properties of R-PET. In this context, the enhanced melt properties and increased crystallization rate of RPET/PBT blends could improve the poor processability of R-PET [43,44,45,46,47,48,49]. Fourier-transform infrared (FTIR) spectroscopy is used to better understand the structure of the melt processed samples
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