Abstract
Chemical or feedstock recycling of poly(methyl methacrylate) (PMMA) by thermal degradation is an important societal challenge to enable polymer circularity. The annual PMMA world production capacity is over 2.4 × 106 tons, but currently only 3.0 × 104 tons are collected and recycled in Europe each year. Despite the rather simple chemical structure of MMA, a debate still exists on the possible PMMA degradation mechanisms and only basic batch and continuous reactor technologies have been developed, without significant knowledge of the decomposition chemistry or the multiphase nature of the reaction mixture. It is demonstrated in this review that it is essential to link PMMA thermochemical recycling with the PMMA synthesis as certain structural defects from the synthesis step are affecting the nature and relevance of the subsequent degradation reaction mechanisms. Here, random fission plays a key role, specifically for PMMA made by anionic polymerization. It is further highlighted that kinetic modeling tools are useful to further unravel the dominant PMMA degradation mechanisms. A novel distinction is made between global conversion or average chain length models, on the one hand, and elementary reaction step-based models on the other hand. It is put forward that only by the dedicated development of the latter models, the temporal evolution of degradation product spectra under specific chemical recycling conditions will become possible, making reactor design no longer an art but a science.
Highlights
Today recycled polymers account for only 6% of the total polymer amount in Europe [1,2].Low prices and uncertainties about market outlets have initially led to prospects of low profitability and depressed investments in new polymer recycling capacity in the last decades, causing the EU polymer recycling sector to suffer [2]
Kashiwagi et al proposed a three-stage thermal degradation mechanism of poly(methyl methacrylate) (PMMA) synthesized via free radical polymerization (FRP) and a one stage thermal degradation mechanism for PMMA obtained via anionic polymerization (AP) [28]
This proposition is based on thermogravimetric analysis (TGA), which allows to measure the mass loss of AP initiators (A−B+ species in Figure 6) are either electron transfer agents or strong anions which transfer an electron to an methyl methacrylate (MMA) molecule
Summary
Today recycled polymers account for only 6% of the total polymer amount in Europe [1,2]. Significant focus has been put breaking, on thermochemical recycling ofsteam vinyl are pyrolysis,cracking gasification, liquid-gas hydrogenation, viscosity reactive extrusion and polymers, such as polyolefins producing a mixture of numerous components, which can be used as or catalytic cracking [6,7,8,9,10]. Significant focus has been put on thermochemical recycling of vinyl fuels Condensation polymers, such as polyethylene and nylon,which can polymers, such as polyolefins producing a mixture of terephthalate numerous components, canbebesubjected used as to chemical recycling to produce oligomers that can be subsequently converted in high-added value fuels. A second distinction is made between depolymerization of PMMA as such and copolymers with as major monomer unit MMA The focus is both on experimental analysis modeling tools, to understand the interplay of chemical reactions. Applications based on the work of the Methacrylate Sector Group [40]
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