Thermal degradation of impact‐modified PMMA in mechanical and chemical recycling

Poly (methyl methacrylate) (PMMA) is a thermoplastic with outstanding tensile strength, UV resistance, and a high level of transparency that has been used widely for optical applications such as glazing in the automobile industry. Mechanical recycling, the most widespread method, degrades the physical properties and prevents reusing PMMA in transparent applications. Thermal depolymerization to recover methyl methacrylate (MMA) monomer is becoming an alternative route for PMMA recycling. In this paper, the thermal depolymerization process of impact-modified PMMA in a micro fluidized bed reactor was investigated. The pyrolysis was conducted over aluminium oxide (Al2O3) and fluid-cracking catalyst (FCC) as catalytic beds; sand and SiC as inert beds at temperatures below 400°C. A mechanical recycling process was also simulated using sequential injection moulding to investigate its impact on the properties of PMMA. After 5 cycles of injection moulding, the impact strength and optical properties of PMMA were severely diminished due to an increase in free volume and partial thermal degradation. Regarding PMMA pyrolysis, Al2O3 demonstrated limited cracking ability with a maximum MMA yield of 46%, as opposed to FCC, which over-cracked both PMMA and MMA into coke and unwanted products. In contrast, non-catalytic beds exhibited higher activity for MMA recovery, with SiC yielding the highest amount of 92% at 380°C.