A novel method to chemically convert waste PET plastic into high–value monolithic materials with excellent flame retardancy, mechanical strength and hydrophobicity

Pyrolysis or dissolution of waste PET plastics (WPP) by specific solvents, which is inevitable in the resource’s secondary utilization, will lead to chemical bond fracture thus resulting in loss of mechanical strength. This greatly restricts the secondary utilization of WPP. We proposed a simple and economical new chemical method to transform WPP into a high–value monolithic material, which not only solves the problem of environmental pollution, but also provides a new idea for the disposal of WPP. The new high temperature resistant chemical structure Al–O–P–O–Al was successfully generated through the reaction of high temperature resistant adhesive Al(H 2 PO 4 ) 3 (AHP) with the monomer or polymer from dissolved WPP. New chemical bonds such as –OH, C = O, C–Cl, P = O were also formed in the transformed monolithic material structure, and they were the principal reason for the increase in mechanical strength of monolithic material. The original hydrophilic group on the surface of the monolithic material was replaced by the hydrophobic group –CH 3 after the treatment by triethoxyoctylsilane (TS). Ultimately, the resulting monolithic material exhibited good comprehensive properties of high flame retardancy, flame retardancy (~ 1300 °C), mechanical strength (maximum compressive strength of 29.1 MPa), and hydrophobicity (water contact angle: 110°). This work has important implications for solving the serious problem of a sharp decline in mechanical strength and inflammability in the reuse of WPP.