Melt Rheological and Bead Foaming Behavior of Recycled Polyethylene Terephthalate/Polybutylene Terephthalate Blends Modified with a Joncryl Chain Extender

This study investigates the melt rheological properties and foamability of recycled polyethylene terephthalate (rPET) and its blends with polybutylene terephthalate (PBT) modified through an epoxy-based Joncryl ADR 4468 chain extender. A twin-screw extruder was used to prepare rPET/PBT blends at various weight ratios (i.e., 100/0, 75/25, 50/50, 25/75, and 0/100) and with varying Joncryl chain extender contents (i.e., 0.25, 0.5, 0.75, and 1.0 wt %). The small-amplitude oscillatory shear rheological experiments were conducted to analyze the melt viscoelastic behavior of the samples. The melt strength and strain-hardening behavior of the compounds were examined by measuring the extensional rheology and Rheotens tests. Crystallization analysis was conducted on the processed samples by using differential scanning calorimetry. The bead foaming behavior of the samples was investigated using a batch-based foaming reactor with supercritical CO₂. Both compounding with PBT and Joncryl chain modification increased the complex viscosity, melt strength, and strain-hardening behavior of the blends, while their synergistic effect revealed a more noticeable enhancement. Although direct modification of rPET with Joncryl and its direct compounding with PBT could not generate a meaningful foam structure, a homogeneous microcellular foam structure could successfully be induced when 25 wt % rPET was incorporated in blends with PBT modified with 1.0 wt % Joncryl.