Structural and thermal behaviour of epoxy coatings on thermoplastic substrates modified with zinc borate

Abstract

This study examined epoxy coatings reinforced with zinc borate (ZnB) applied on thermoplastic substrates derived from mixed household waste. The study aimed to combine experimental characterization with microstructure informed finite element modelling to evaluate the thermal behaviour and predicted mechanical response of mineral-filled epoxy coatings on heterogeneous waste-derived thermoplastics. The novelty of the work lied in integrating formulation optimization, surface characterization and SEM-informed simulation to investigate how mineral additives influence coating morphology, thermal stability and stress distribution in epoxy-coated sustainable thermoplastic systems. A Box-Behnken experimental design was employed to analyse the effects of shellac-allyl starch mixture (SAM), zinc borate and halloysite on coating film thickness. The statistical model demonstrated strong predictive capability with an adjusted R² value of 0.9637. Thermogravimetric analysis indicated that the decomposition temperature increased from 357.68 °C to 369.57 °C corresponding to a 3.3% increase in thermal stability. Contact angle measurements decreased from 55.38° to 39.83°. Finite element simulations were conducted to evaluate the influence of coating morphology on stress distribution and deformation behaviour. Under tensile loading of 2150 N, the predicted maximum displacement decreased from approximately 1.47 mm in reference coating to about 1.42 mm in coating containing ZnB, corresponding to 3-4% reduction in deformation. The combined experimental and simulation-based approach provided insight into the behaviour of mineral-reinforced epoxy coatings designed for sustainable thermoplastic substrates.