CHEMICAL UPCYCLING TO MONOMERS (CUCMS) OF ESTER-BASED PLASTICS VIA AMINOLYSIS

Lin Shao

doi:10.7273/000006498

In this research, a method of chemical upcycling to monomers (CUCMs) for ester-based plastics was demonstrated. Polylactic acid (PLA) with linear structure was decomposed into monomer, N-lactoyl ethanolamine (N-LEA), at mild conditions (100 °C, 1 h, at atmosphere) through aminolysis. N-LEA was further derivatized by reacting with methacrylic anhydride to yield a cross-linkable dimethacrylate monomer. When combined with a comonomer and initiator, this leads to the production of a photocurable resin. This resin is compatible with various commercially available photocuring 3D printers. The resulting 3D printed parts, derived from PLA waste materials, demonstrate impressive properties including a tensile strength of 58.6 MPa, a Young's modulus of 2.8 GPa, and a glass transition temperature of 180 °C.Additionally, one-pot synthesis was employed to produce high-performance photo-curable 3D printing resin. In this effort, an excess amount of methacrylic anhydride was purposely employed to react with N-LEA in the preparation of the dimethacrylate. The residual methacrylic anhydride and methacrylic acid formed in the reaction mixture acted as solvent for the dimethacrylate product. The resulting solution is a photocurable resin ready for 3D printing without any other treatment. The 3D printed parts display a set of unparalleled properties compared to some of the strongest photocurable 3D printing resin on the market. The tensile strength of 132.8 MPa, glass transition temperature of ~190 °C, and heat deflection temperature ~163 °C. Furthermore, aminolysis kinetics of polylactic acid (PLA) in 2-aminoethanol (EA) under normal atmospheric pressure was investigated, utilizing a gravimetric analysis method. Results indicated that diffusion had minimal impact on the overall degradation process and could be largely discounted. The surface area of PLA emerged as a critical factor influencing the kinetics of aminolysis. Various kinetic models, including first- and second-order equations, were employed to evaluate PLA’s aminolysis kinetics. Among these models, the first-order kinetic model demonstrated the most accurate depiction of PLA’s degradation behavior, with a high regression coefficient (R2 > 0.98) observed within the temperature range of 60-90 °C. By applying the Arrhenius equation, the activation energy of the aminolysis reaction was determined to be 70.06 kJ/mol, with a pre-exponential factor of 2.058×107. This study not only highlights the importance of reaction conditions such as temperature and surface area in PLA aminolysis but also offers a quantitative insight into the reaction kinetics, facilitating optimization for industrial applications. At last, anhydride cured diglycidyl ether of bisphenol epoxy that contains ester linkage in the crosslinked network structure can be also decomposed into monomers with 2-aminoethanol by aminolysis without using any catalyst. The epoxy resin underwent complete decomposition at 160°C within 4 hours, yielding two distinct high-purity monomers, namely amidodiol from the anhydride component (HHPA-OH) and bisphenol A epoxy component (BPA-OH). Subsequently, BPA-OH was employed in the synthesis of a polyurethane coating, exhibiting exceptional properties including a high glass transition temperature (88.9°C), scratch hardness (8H), gouge hardness (6H), adhesive strength (5B), and robust solvent resistance. HHPA-OH, possessing two hydroxyl groups, was further reacted with methacrylic anhydride to produce a dimethacrylate monomer. This monomer served as an effective crosslinker to produce photo-curable 3D printing thermosetting polymers, achieving impressive tensile strength of up to 64 MPa and impact strength of 4.86 kJ/m2. This upcycling method allows for a more efficient utilization of degradation products, upcycling ester-based plastics wastes into high-performance materials.

CHEMICAL UPCYCLING TO MONOMERS (CUCMS) OF ESTER-BASED PLASTICS VIA AMINOLYSIS

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