Laser pyrolysis of poly(methyl methacrylate) to high-yield and high-purity methyl methacrylate monomer: A solvent- and catalyst-free strategy for chemical recycling

Laser pyrolysis directly depolymerizes PMMA without solvents or catalysts. • Optimized laser pyrolysis yields a liquid product containing 96.9% MMA. • Laser-specific energy consumption is only 0.0103 kWh/g of liquid product at 40 W. • Recovered MMA repolymerizes to R-PMMA with comparable optical transparency and mechanical performance. • Varied PMMA-based feedstocks afford MMA-rich products by laser pyrolysis. The widespread use of poly(methyl methacrylate) (PMMA) has generated substantial plastic waste, yet its practical recycling efficiency remains critically low. Herein, we report a laser pyrolysis strategy for the highly efficient depolymerization of PMMA back to its monomer methyl methacrylate (MMA). Employing a 915 nm infrared laser as a photothermal source and a small amount of carbon black (<1 wt%) as a photothermal agent, the depolymerization of PMMA proceeds in the absence of pre-modification, solvent, or catalyst, yielding MMA monomer with high recovery. Under optimized parameters (30 W laser power, 0.2 wt% carbon black loading), an MMA recovery of 91.0% was achieved, with the product composition confirmed by FTIR, NMR, and GC–MS. When the laser power was elevated to 40 W, the productivity reached 23.6 g/h (extrapolated from a ∼ 5 min single-batch experiment), accompanied by a laser-specific energy consumption of 0.0103 kWh/g. The recovered MMA was further repolymerized successfully via emulsion polymerization, and the regenerated R-PMMA exhibited comparable chemical structure, molecular weight, optical transparency and mechanical properties relative to pristine virgin PMMA. The applicability of this strategy was further demonstrated across a range of PMMA-based samples, including industrial waste, Fe 2 O 3 -containing PMMA, and PE-containing blends, with MMA recoveries ranging from 71.3% to 90.3%. This work establishes a high-efficiency, solvent- and catalyst-free depolymerization route with promising potential for PMMA monomer recovery and subsequent material regeneration. Download: Download high-res image (372KB) Download: Download full-size image