Influence of Graphite Concentration on Content-Dependent Crystallinity, Thermal Stability, and Energy Band-Gap of PCL/PVC Composite Films

Graphite-reinforced solvent-cast poly(ε-caprolactone)/poly(vinyl chloride) (PCL/PVC) blend films (0–40 wt% graphite) were prepared and characterized by XRD, ATR-FTIR, DSC, TGA/DTG and UV–Vis spectroscopy. XRD and DSC reveal a progressive reduction in crystallinity (27% to 15% at 40 wt%) and a modest PCL melting-point depression (58.4 to 55.0°C), consistent with partial disruption of PCL crystalline domains. ATR-FTIR shows no new chemical bands, indicating physical dispersion rather than chemical modification. TGA/DTG indicate enhanced thermal resistance: major degradation events, including the PVC dehydrochlorination region, shift to higher temperatures and char yield increases with graphite content. UV–Vis measurements show increased absorbance and marked optical band-gap narrowing with filler loading, reaching 2.1 eV at 40 wt% (from >4 eV for the neat blend, model dependent). These findings demonstrate that graphite effectively tunes microstructure, thermal stability, and optical properties of PCL/PVC blends for thermal-management and optoelectronic applications.