Direct conversion of PMMA to MAA in twin-screw extruder

Polymethyl methacrylate (PMMA) is a multi-functional polymer with excellent tensile and flexural strength, UV resistance, and transparency. Industry produces 2.2 million tons of PMMA per year as a resin for coatings, automotive, electronics, boat hulls, and wind turbine blades. Plastic recycling reduces energy, consumption of fresh raw materials, and water and air pollution (from landfilling and/or incineration). Chemical recycling is a promising route to produce monomer since PMMA thermally depolymerizes into its monomer(MMA) at its decomposition temperature. However, additives or fillers in waste PMMA lower the yield and purity of the produced methyl methacrylate (MMA) and restrain the continued operation of PMMA depolymerization due to the formation of coke or nondegradable residues. In this study, we propose to produce a pure stream of methacrylic acid (MAA) by combining PMMA thermal depolymerization and in-situ MMA hydrolysis in the presence of free radical generators (e.g. H2O2) and hydrolysis catalysts. Free radical generators speed up PMMA depolymerization, while hydrolysis catalysts convert MMA to MAA. A Brabender batch mixer with two parallel screws blends PMMA and catalysts (e.g. ZSM-5, Al2O3, and persalts) at 280-320 ℃ and a syringe pump injects H2O2 solution or water into the batch mixer. A condensation vacuum system collects and cools valuable volatile compounds. To evaluate the feasibility of this reaction in an extruder, we simulate the mixing and degradation behavior of PMMA based on an intermeshing twin-screw model in ANSYS.