Surface modification of polyvinyl alcohol films by functionalized soybean oil triglycerides

Abstract

In this study, maleinized (SOMAP) and isocyanated (SONCO) soybean oil triglycerides have been successfully grafted onto the surface of polyvinyl alcohol (PVA) films. The surface grafting occured through the reaction of succinic anhydride or isocyanate functionalities of soybean oil and available hydroxyl groups of PVA films in toluene using DMAP as a catalyst. After grafting, the films were rinsed with toluene to remove ungrafted triglycerides from the surface. The reaction on the surface was confirmed by ATR-IR and 1H NMR spectroscopic techniques. A series of films were prepared by different concentrations of SOMAP or SONCO in toluene. The increase in hydrophobicity with an increase in SOMAP or SONCO concentrations was observed by contact angle measurements and the contact angles reach their maximum value of 88o and 94o for 26 and 2.5 per cent SOMAP and SONCO concentrations in toluene, respectively. Surface morphology and roughness of PVA-g-SOMAP film was investigated by AFM while optical microscopy was used for characterization of PVA-g-SONCO films. The homogeneity of the grafted surfaces was examined by optical microscopy after the colour reaction which gives a blue colour complex with pure PVA films. PVA-g-SONCO films were not dyed meaning that nearly all the surface was completely grafted successfully while there were unreacted regions on the PVA-g-SOMAP films. Quantitative determination of the extent of grafting per surface area (cm2) was done by titration of the free acid groups produced in esterification reaction. Grafting density was found to be 1.56x10-4 mole triglyceride per cm2 of the PVA film. The grafted films were further characterized by DSC. SOMAP or SONCO grafted PVA films have lower Tg values than pure PVA film which proves the surface grafting. However, the difference between Tg values of the grafted films and pure PVA film is very low due to the fact that grafting occurs only on the top of surface while the rest of the sample remains pure PVA.