Graphene Modified with Curcumin: A Novel Approach to Tailoring the Glass Transition of PVC

The glass transition temperature (T_g) is a critical parameter that defines the thermal and mechanical functional limits of poly(vinyl chloride) (PVC) and its nanocomposites. The influence of graphene (GN) and curcumin noncovalent-modified graphene (GN@CU), on the glass transition behavior and molecular dynamics of unplasticized PVC was investigated. A comprehensive set of thermal, mechanical, dielectric, and spectroscopic techniques, including differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), dielectric loss measurements, and solid-state ¹H nuclear magnetic resonance (NMR) spectroscopy, was applied to investigate both local and segmental chain mobility in PVC-based nanocomposites. Spin-lattice relaxation times (T₁), obtained from NMR measurements, provided molecular-level insights into chain dynamics associated with the glass transition. The results demonstrate that both GN and GN@CU restrict the mobility of the PVC chain, resulting in an increased T_g and composite stiffness. Especially, curcumin modification occurring according to the π-π interaction mechanism enhances filler dispersion and polymer-filler interfacial interactions, thereby further amplifying these effects. This work highlights the importance of integrating thermal, mechanical, dielectric, and NMR techniques to elucidate polymer-nanofiller interactions at the molecular level, which is crucial for designing PVC-based nanocomposites with improved thermal stability and mechanical properties suitable for demanding industrial applications.