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Degradation of polyethylene terephthalate (PET) plastic waste via hydrolysis for bitumen modifier: response surface methodology optimisation and characterisation
Summary
Scientists found an efficient way to break down PET plastic (the kind used in water bottles) using a chemical process, turning it into a material that could be mixed into asphalt for road construction. This matters because it offers a practical way to reuse plastic waste that normally sits in landfills for centuries, potentially reducing the amount of plastic that breaks down into microplastics in our environment, water, and food supply.
Polyethylene terephthalate (PET) waste accumulates yearly due to its resistance to natural degradation. The situation has led to the recognition of chemical hydrolysis as part of the most effective methods of degrading PET waste, but the efficiency is strongly affected by several parameters. Therefore, this study aims to optimise the PET hydrolysis process and investigate the physicochemical changes of the hydrolysed product as a fundamental basis for potential application as a bitumen modification material. The optimisation process was conducted using response surface methodology (RSM) with central composite design (CCD) through the adoption of three independent variables including NaOH solution concentration (30–50%) (X1), reaction time (105–120 min) (X2), and PET waste particle size classified as PETA (passing sieve No. 4 and retained on sieve No. 8) and PETB (passing sieve No. 8) (X3). The experimental design and statistical analysis were performed using Minitab® software with the percentage conversion of PET into disodium terephthalate (Na2-TP) selected as the response variable (Y). Moreover, PET and Na2-TP were characterised using SEM–EDX, FTIR, XRD, and DSC. The results showed that the hydrolysis process of PET plastic waste could be optimised using RSM–CCD with optimal conditions of 82.31% (verification of prediction results) at a NaOH solution concentration of 30%, a reaction time of 94 min, and through the PETB plastic waste size. Furthermore, the characterisation results confirmed significant structural degradation of PET after hydrolysis. The hydrolysed material could be used as a bitumen modifier in road pavements.