Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE Schematic illustration of thermal mechanism in SGP composites: (I) SGP composite at room temperature, (II) At elevated temperature (T), (III) When temperature exceeds the melting point of shellac.

ABSTRACT
This study investigates the influence of waste glass powder on the electrical, thermal, mechanical, and dielectric properties of shellac-based composites. Shellac is a natural biopolymer with excellent film-forming ability and water repellence; however, its practical applications are limited by poor thermal stability. To overcome this limitation, waste glass powder was incorporated into the shellac matrix in varying proportions. The Shore-A hardness increased significantly from ~67 for pure shellac to ~94 for the composite containing 60 wt.% glass powder, while density increased from 1.10 to 1.61 g/cm3. Tensile testing revealed optimum mechanical performance, with a maximum tensile strength of 3.38 N/mm2 at 30 wt.% glass powder, representing an approximately 6.4-fold enhancement over pristine shellac. The dielectric constant increased from ~3.5 for pure shellac to ~7.8 for the 60 wt.% glass-filled composite and remained functionally stable up to ~130°C. Thermogravimetric and differential scanning calorimetry analyses confirmed improved thermal stability and delayed degradation compared to neat shellac, with the glass transition (softening) temperature increasing from ~49°C to ~61°C. Overall, the results demonstrate that waste glass powder effectively improves the performance of shellac composites. To the best of our knowledge, this is the first systematic study demonstrating waste-glass-reinforced shellac composites.