Surface wetting kinetics of water soluble organic film

Abstract

The wetting kinetics of poly(vinyl alcohol) (PVA)-based films by water was investigated using contact angle (CA) goniometry, Fourier-transform infrared spectroscopy, and atomic force microscopy. We show that CA evolution is determined by four main factors: film composition, preparation method, presence of plasticiser in the matrix, and relative humidity (RH) conditions during aging. All formulations prepared from partially hydrolysed polymer were less susceptible to dissolution compared to fully hydrolysed counterparts, with the CA evolution character shifting from exponential to linear for respective formulations. This behaviour is likely attributed to the intrinsic properties of PVA matrices, i.e. changes in free volume, tortuosity, as well as size and distribution of crystalline regions. Incorporation of glycerol as a plasticiser results in overall faster CA evolution, with surface spreading playing more significant role compared to non-plasticised samples. Furthermore, aging of PVA-based films does not lead to profound changes in any environment except 100% RH. For these conditions, the initial stages of PVA dissolution due to water absorption were observed, with the changes in the matrix continuity dependent on PVA degree of hydrolysis. These results expand on the understanding of initial stages of polymer dissolution in consumer goods products and can pave the way to enhanced performance and prolonged shelf life of the products.