The Structure-Property Relationships in Drying Polystyrene/Acrylic Latex Films

This investigation initially set out to study the potential use of a number of additives as humidifying agents for the purpose of modifying the drying properties of water-borne paints. A gravimetric study was used to analyse the rate of evaporation during the early stages of film formation. A Styrene/Acrylic latex was used with varying concentrations of Pluronic PE9200, Methylcellulose (MC) and Hydroxypropyl Methylcellulose (HPMC). It was found that the effect that the additives had on the rate of evaporation was small and, in comparison to the impact of humidity, negligible. Despite this, during this investigation it was observed that the cellulose-derived additives appeared to reduce levels of cracking. This phenomenon was investigated further using a number of techniques, in particular AFM, DMA and Optical Microscopy. Using these methods it was possible to observe how, unlike a conventional coalescent solvent such as Texanol™, the cellulose-derived additives appeared not to plasticise the latex, which raised the question as to how the additives were reducing cracking in the film. Having observed the lack of particle coalescence on the surface of the film, it was hypothesised that the cellulose-derived additives created a network that surrounded the latex particles enabling the formation of a crack-free film. In order to investigate this further, Small Angle X-ray Scattering (SAXS) was used to study particle packing within the film. As predicted, increasing concentrations of the cellulose-derived additives gave rise to increased particle spacing. This confirmed the presence of an additive network surrounding the particles, providing an alternative method for stress-relaxation other than cracking. Due to increasing legislative pressure to eliminate VOCs, coupled with heightened environmental and health concerns, the future use of cellulose-derived additives as a replacement for standard coalescent solvents should be the subject of further investigation