Poly(ethylene terephthalate) (PET) is widely used as an engineering plastic due to its excellent mechanical properties and reasonable thermal stability. PET waste is commonly degraded into terephthalic acid for disposal. This work aims to employ a simple solvothermal method to chemically convert PET waste into PET-based engineering plastics (PEPGs) with excellent mechanical strength by soil burial degradation. The inherently excellent mechanical properties of PET waste molecular chains could be harnessed to create a new molecular structure composed of PET and poly(vinyl alcohol) (PVA) units through dehydration condensation, transforming PET waste into PEPGs. This macromolecular reaction can be easily performed under solvothermal conditions without the need for high temperatures or catalysts, resulting in PEPGs with enhanced tensile strength of up to 78 MPa. When subjected to tensile forces or impact, the shape of the PEPGs remained largely unchanged, demonstrating their good durability. The activation energies (E a) of PET waste and PEPGs were 206.67 and 155.38 kJmol-1, respectively, as determined using Kissinger kinetics. The addition of the PVA units changed the molecular chain properties of PET waste, effectively reducing the E a and allowing the PEPGs to exhibit degradation properties. This work offers a new approach to converting PET waste into degradable, PET-based engineering plastics with excellent mechanical properties and durability.

Bearing plates made from plastic composites can be used as an alternative to their steel counterparts in rock bolt or soil nail applications. To achieve this goal, an existing recycled highdensity polyethylene bearing plate was investigated and later modified to improve its engineering properties. Laboratory studies were conducted to determine the failure load of the existing and modified plates, and a numerical model was developed for complementary analysis. The results of both efforts clearly showed that the existing bearing plate was not adequate in terms of strength and creep properties, as it quickly yielded with large displacements at relatively low loads. In order to enhance the strength of the plate, both geometric and material modifications are made by our research group to obtain a more efficient plate. Numerical models were used to determine the frame layout, and a series of analyses were performed to evaluate the effects of frame thickness, number and arrangement. Once the design was optimized and finalized, a mold was created to match the new geometry for manufacturing new plates through injection molding. A test setup was also established in the laboratory and numerous compression tests were performed on the manufactured new plates. The measured load-displacement behavior of plates made of polyethylene and polyamide with a variety of additives were discussed separately. It was determined that the new plastic plates reinforced with polyamide through various additives have the potential to reach a strength up to 200-240 kN, which is at least two times higher than the existing one, with distinct economic advantages.