Plasticization Effects of Propane-1,3-Diol (PDO) on the Physical Properties of Polyvinyl Alcohol (PVA) and Percolation-Based TiCN-PVA Composites

Water ingress in engineering structures is potentially dangerous, and its detection before related damage appears is crucial. Percolation sensors, based on poly(vinyl alcohol) (PVA) filled with titanium carbonitride particles (TiCN), show promise for detecting water ingress. However, implementing this sensor in industry is challenging due to the brittleness of PVA, exacerbated by TiCN. While glycerol, the established benchmark plasticizer, can reduce brittleness, its high viscosity poses processing challenges compared with low-viscosity propane-1,3-diol (PDO), which remains untested for plasticizing PVA. Therefore, this experimental-modeling study explores the plasticization effects of PDO on the physical properties of PVA and TiCN-PVA composites. Subsequently, PDO enhances the processability of PVA by linearly lowering its melting temperature (Tm) upon increasing the PDO concentration up to 40 wt %. Moreover, the glass transition temperature (Tg) dropped from 62.9 ± 3.5 (0 wt % PDO) to 8.9 ± 3.0 °C (40 wt % PDO), and from 58.3 ± 3.6 (0 wt % PDO) to −17.0 ± 0.8 °C (25 wt % PDO) for PVA and the TiCN-PVA composite, respectively. This important decrease in Tg means that PDO significantly reduces brittleness. Among the Fox, Gordon–Taylor, Venditti–Gillham, and Kwei models, the latter best describes the plasticization effects on the Tg, as it accounts for intermolecular interactions (hydrogen bonding). Finally, a nonlinear relationship between Tg and Tm was identified in PVA plasticized with PDO. This nonlinearity was successfully described by adjusting a thermodynamic model (Boyer) on the sole condition that the mixing energy density was non-negligible (B ≠ 0). This finding is logical since PDO strongly interacts with PVA through hydrogen bonding (B ≠ 0), and is therefore in excellent agreement with the conclusions drawn from the Kwei model. Finally, the study demonstrates that PDO simultaneously enhances the processability and reduces the brittleness of PVA comparably to glycerol, making PDO a promising alternative plasticizer.