Influence of the odd-even effect of dicarboxylic acids as crosslinker on the physicochemical properties of polyvinyl alcohol

Polyvinyl alcohol (PVA) was crosslinked with a homologous series of four different dicarboxylic acids, HOOC(CH2) n-2COOH (n = 2 to 5) viz. oxalic acid (OA; C2), malonic acid (MA; C3), succinic acid (SA; C4) and glutaric acid (GA; C5) containing odd and even number of carbon atoms. The characterization and assessment of synthesized crosslinked films were done using ATR-FTIR, XRD, SEM, AFM, DSC, rheology, percent swelling and sessile drop contact angle. The odd-even effect of dicarboxylic acids was observed to significantly influence the physicochemical properties of PVA when employed as a crosslinker. PVA films crosslinked using dicarboxylic acids containing an even number of carbon atoms, displayed translucency, roughness, and an irregular matrix. In contrast, films incorporating an odd number of carbon atoms were transparent, homogenous, and densely packed. Furthermore, films containing even acids exhibited relatively lower crystallinity, lower melting temperature (Tm) and displayed an unexpected irregular trend in swelling as crosslinker concentration increased compared to films containing dicarboxylic acids with an odd number of carbon atoms which exhibits a consistent swelling with increasing crosslinker concentration. These results are attributed to the difference in the solubility and crystal structures of the odd-even series of dicarboxylic acids. Polyvinyl Alcohol was crosslinked with four different dicarboxylic acids, viz. oxalic acid, malonic acid, succinic acid and glutaric acid containing odd and even number of carbon atoms. The characterization of synthesized crosslinked films were done using ATR-FTIR, XRD, SEM, AFM, DSC, percent swelling and sessile drop contact angle. image