Sustainable utilization of disposed photovoltaic backsheet to microcellular thermal-insulation foam through two-steps supercritical CO2 foaming

Abstract

Upcycling of disposed photovoltaic backsheets plays important role in sustainable development of the photovoltaic industrial chain. However, the melt strength of the main component (rPET) decreased dramatically after long-term outside exposure, it is still challenging to develop a rPET-based microcellular thermal-insulation foam. Herein, we utilize a crystalline-amorphous network (CAN) strategy to enhance rPET melt strength and develop microcellular thermal-insulation material via supercritical CO₂ (scCO₂) foaming technology. The tunable CAN fractions can be achieved by manipulation of crystallinity and rigid amorphous fraction (RAF) via annealing processes. The crystallinity was increased to 31.9 % for the sample annealed at the temperature of 115 °C, while the RAF value rose to 44.6 %. Consequently, the zero-shear complex viscosity (${\eta }_0^{*}$) of rPET samples increased from 164.2 Pa·s to 1826.6 Pa·s with increased CAN fractions up to 76.5 %, demonstrating a typical shear-thinning behavior. Combined with the scCO₂ foaming technology, the void fraction can be tuned from 31.6 % to 83.5 %. The cell density was optimized, reaching a high value of 1.12 × 10⁹ cells/cm³ with the CAN fraction of 21.5 %. Furthermore, the thermal conductivity decreased from 254 mW•m⁻¹K⁻¹ for a solid rPET sample to 47.3 mW•m⁻¹K⁻¹ for thermal-insulation rPET foam. As a proof of concept, this work provides a novel route for resource utilization of disposed photovoltaic backsheet.