Thermal degradation kinetic studies of polypropylene (PP)/titanium dioxide (TiO₂) composites

Abstract

The degradation kinetics of polypropylene (PP) composites reinforced with titanium dioxide (TiO_₂) microparticles were investigated using various kinetic models. The composites were prepared through a twin-screw extrusion process by varying the filler loading up to 30 wt%. The thermal degradation studies were conducted by using a thermogravimetric analyzer (TGA) at four different heating rates. The activation energies of the degradation of the composites were calculated using different model equations such as Friedman, Kissinger-Akahira-Sunnose (KAS), Ozawa-Flynn, Wall (OFW), and Starink. The Horowitz and Metzger method revealed an increasing trend in activation energy with higher filler loadings, attributed to enhanced barrier properties, improved dispersion, increased thermal stability, and the formation of protective layers. The Coats-Redfern method indicated a transition in the thermal degradation mechanism from the contracting sphere model to the contracting cylinder model with the incorporation of TiO₂. The Criado model highlighted a shift from the Avrami-Erofeev equation (A₂ mechanism) to the power law-contracting cylinder mechanism (R₂) in PP/TiO₂ composites, driven by improved nucleation and growth, filler-matrix interactions, and barrier effects. These findings demonstrate that the incorporation of TiO₂ particles significantly enhances the thermal stability and alters the degradation mechanisms of PP composites, providing valuable insights for the development of advanced composite materials with improved thermal properties.

Keywords

Polypropylene / Titanium dioxide / Composites / Thermal degradation kinetics / Iso-conversional methods / Kinetic models

Declaration of Competing Interest

The authors declare that they have no known financial interests or personal relationships that could have appeared to influence the work reported in this paper.

CRediT authorship contribution statement

Krishna Prasad Rajan: Writing - review & editing, Writing - original draft, Visualization, Validation, Supervision, Software, Resources, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Mohammed Rafic: Validation, Supervision, Software, Resources, Methodology, Investigation. Selvin P. Thomas: Writing - review & editing, Writing - original draft, Validation, Supervision, Resources, Methodology, Investigation, Conceptualization.

Supplementary materials

Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.chphma.2025.09.003.

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