Polyethylene Wax Upcycled From Waste Polyethylene by Laser‐Induced Flash Pyrolysis and Its Plasticizing Performance

High‐density polyethylene (HDPE), a dominant plastic with 55 million metric tons of global consumption in 2023, poses significant recycling challenges. This study introduces a laser‐induced flash pyrolysis (LFP) method for upcycling waste HDPE into high‐purity polyethylene wax (PE‐wax) with yields up to 65 wt%. Leveraging millisecond‐scale infrared laser heating, the process enables controlled depolymerization to produce linear PE‐wax with low molecular weight ( M n = 704) and < 5 μm particle size, featuring exceptional structural purity and selectivity. Due to its molecular similarity to PE matrices, the wax acts as an efficient processing plasticizer. When incorporated into HDPE, it enhances melt flow index by 166% compared to virgin resin, while reducing apparent viscosity in ultra‐high molecular weight polyethylene (UHMWPE) to improve processability. Mechanical evaluations show that both HDPE and UHMWPE retain > 79% tensile strength while achieving significant gains in elongation at break, demonstrating balanced property retention and processability improvement. This catalyst‐free, energy‐efficient LFP technology offers a sustainable pathway to convert waste HDPE into high‐value additives, addressing plastic waste management challenges while enabling advanced processing of high‐performance polyolefins.