Film formation and redispersion of waterborne latex coatings

Poly(vinyl acetate-co-ethylene) latex dispersions are prepared and their fi lms investigated with a focus on the effect of composition upon redispersio n. Films of dispersions containing sufficient amounts of poly(vinyl alcohol ) (PVA) can be redispersed in water. This property is lost in the presence of surfactant, a fact which suggests a procedure to control film formation. It is demonstrated that redispersion is due to a PVA-membrane which separa tes the particles. Loss of redispersibility in the presence of surfactant p roceeds with the breakup of the membranes and a corresponding change of fil m properties. Experimental data is provided by light microscopy, mechanical testing, and TEM in conjunction with a staining method new to the field. T he hypothesis is developed that interaction with surfactant leads to imperf ect PVA-membranes that are no longer able to prevent latex polymer interdif fusion. Fluorescence correlation spectroscopy demonstrates the formation of surfactant micelles, as well as the simultaneous adsorption and aggregatio n of PVA onto the micelles. It is concluded that the competing surface of t he surfactant micelles traps enough PVA to cause thinning and fragmentation of the membranes surrounding the particles, which enables interdiffusion o f latex polymer This effect can be used to convert the system from one form ing a redispersible coating to one forming a nonredispersible (permanent) f ilm. (C) 2000 Academic Press.