Dispersion-controlled thermal degradation kinetics of PMMA/NiFe₂O₄ nanocomposites prepared with different mixing times

Abstract

The thermal degradation behavior of polymer nanocomposites is strongly governed by nanoparticle dispersion; however, the relationship between dispersion homogeneity and degradation kinetics remains unclear. In this study, PMMA/NiFe₂O₄ nanocomposites were prepared using controlled melt mixing with different mixing times in order to systematically investigate the role of dispersion state on thermal degradation kinetics. Structural and morphological characterization was carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM), while non-isothermal differential thermal analysis (DTA) was employed at multiple heating rates to evaluate degradation behavior. XRD results confirmed that the incorporation of NiFe₂O₄ nanoparticles did not alter the amorphous structure of the PMMA matrix. SEM analysis revealed that prolonged mixing significantly improved nanoparticle dispersion, whereas shorter mixing resulted in partial agglomeration. Despite comparable degradation peak temperatures for all samples, pronounced differences were observed in degradation kinetics. Activation energies calculated using Kissinger, Ozawa, and Augis–Bennett methods demonstrated that the PMMA-6 nanocomposite exhibited the highest activation energy (~270 kJ/mol), representing an increase of approximately 30% compared to neat PMMA and ~25% compared to the more homogeneously dispersed PMMA-12 sample. These results indicate that maximum nanoparticle dispersion does not necessarily correspond to maximum thermal resistance. Instead, an optimum dispersion state characterized by partial agglomeration and enhanced interfacial constraint governs the thermal degradation kinetics of PMMA/NiFe₂O₄ nanocomposites. This study highlights the critical role of processing-controlled dispersion in tailoring the thermal performance of polymer nanocomposites without inducing structural changes.