Re-Use of Polycarbonate from Compact Discs to Enhance the Thermal Stability of Polylactic Acid Blends

This study investigates enhancing polylactic acid (PLA) by incorporating recycled polycarbonate (r-PC) to address PLA's inherent brittleness and limited thermal stability. Blends with varying PLA/r-PC ratios (100:0 to 0:100) were prepared using an internal mixer, with r-PC sourced from discarded compact discs. The thermogravimetric analysis (-A) demonstrated significant improvements in the thermal stability. The degradation onset temperature (T5 wt%) increased from approximately 315 °C for pure PLA to about 400 °C in the blends, with a maximum decomposition temperature (Tmax) of 520 °C observed for pure r-PC. The char residue also increased markedly, from 1.35% in pure PLA to 24.42% in r-PC, indicating enhanced thermal resistance. Differential scanning calorimetry (DSC) revealed a considerable reduction in PLA crystallinity, declining from 68.17% in pure PLA to 10.32% in the 10PLA90r-PC blend, indicative of the disruption of PLA's crystalline structure. The X-ray diffraction (XRD) analysis supported these findings, showing a transition to a predominantly amorphous structure at higher r-PC contents. Tensile testing highlighted the mechanical improvements achieved through blending. While pure PLA exhibited brittle failure, the 30PLA70r-PC blend displayed plastic deformation, signifying improved toughness. The stress-strain analysis revealed that the 30PLA70r-PC blend achieved a peak toughness of 8725 kJ/m3, nearly ten times higher than the 924 kJ/m3 recorded for pure PLA. However, excessive r-PC content introduced brittleness, diminishing toughness. The dynamic mechanical thermal analysis (DMTA) demonstrated a broadening of the glass transition range, with the Tg shifting from 61 °C for pure PLA to 141 °C in r-PC-dominant blends, reflecting improved phase interactions between the two polymers. Scanning electron microscopy (SEM) revealed significant morphological changes; at high r-PC contents, phase separation and voids were observed, leading to reduced mechanical performance. These results highlight the synergistic potential of blending PLA's biodegradability with r-PC's superior thermal and mechanical properties.