Layer-by-layer stacking, low-temperature welding strategy to effectively recycle biaxially-oriented polypropylene film waste

High-value recycling and reuse of plastic products is very important to solve global plastic pollution in the era of green development and low-carbon economy. Giving that the mainstream of processing plastic waste is still direct mechanical recycling, the unexpected degradation on mechanical properties betrays the intention to recycle plastic waste. Here, based on the temperature sensitivity of interfacial diffusion and orientation retention, we proposed an innovative protocol of recycling biaxially oriented polypropylene (BOPP) film waste in high value and efficient manner. Specially, a lamellar assembly of the biaxially-oriented film wastes was constructed layer by layer and then compressed into a sheet near the melting temperature. The temperature effects on interfacial fusion and orientation retention were investigated comprehensively. When the welding temperature approached the end melting temperature, the low-temperature laminated processing technology not only enabled strong interfacial adhesion, but also retained most of intrinsic orientation structure, conferring the as-prepared sheet with unprecedented combination of strength and toughness, as evidenced by a dramatic increase in ∼200% of mechanical strength and ∼650% of toughness to that of mechanically-recycled convention polypropylene (PP) products without orientation. The enhancement mechanism, in essence, stemmed from high strength endowed with orientation order and the laminar structure with strong ability to inhibit the crack propagation. Finally, supercritical CO2 foaming technology was utilized to transform the high-performance fused PP sample into more valuable lightweight and rigid foam. This simple, scalable, economical and highly effective method without any interfacial additives is easily applied to the other biaxially-oriented films and sets a good example for the recycling application of biaxially-oriented film wastes to achieve the goal of green and low-carbon life.