Enhanced Impact Properties of High-Recycled Content Polycarbonate-Polybutylene Terephthalate Blends

Polycarbonate-polybutylene terephthalate (r-PC/PBT) blends with recycled content were prepared by compounding post-industrial recycled (PIR-mechanical) polycarbonate (r-PC) from automotive part production with virgin polybutylene terephthalate (PBT). Impact modifiers, reactive compatibilizer, thermal stabilizers, and processing aid were used to prepare high-performance blends showing tensile strength of > 60 MPa, high elastic modulus (2–2.4 GPa) with recycled (r-PC) with r-PC content up to 70%. The morphology of the blends was investigated by scanning transmission electron microscope (STEM) and elemental mapping of carbon, oxygen, and osmium by energy dispersive x-ray spectroscopy (STEM-EDS). Crystallization and transesterification of PBT were assessed by differential scanning calorimeter (DSC) and by electron diffraction analyses. STEM-EDS analyses of the blend samples revealed a nanoscopic semi-interpenetrating network (SIPN) structure. DSC analyses showed exothermic reactions during the first melting of compounded samples, stemming from transesterification and polymer mixing and progressing to nearly complete amorphization of the blend during successive second heating cycles. Impact modified and amorphized r-PC/PBT blends showed very high Charpy notched impact strength of > 70 kJ/m². Compared to the reference sample, the dynamic mechanical analysis (DMA) of r-PC/PBT blends revealed only a single relaxation peak located between the glass transition temperatures of the PBT and the r-PC indicating improved miscibility and molecular-level interactions between the polymer phases. Retention of the high elastic storage modulus up to the relaxation temperature near +100°C was observed, reaching > 20°C higher temperatures than the reference PC/PBT blends.