Natural rubber latex modification by sodium polyphosphate: a SPM study on the improved latex adhesion to glass sheet

Addition of sodium polyphosphate (NaPP) to natural rubber latex at 0.4 weight ratio improves the adhesion of cast latex dry films to flat glass surfaces. Rubber–polyphosphate dispersions were analyzed by turbidimetric titration, PCS and ultramicroscopy, and the results indicate the formation of two domains within the latex–polyphosphate dispersions: one domain has higher rubber particle content than the other. Thick rubber films were examined by AFM, scanning electric potential and modulated force microscopy. The images show that rubber film morphology is completely altered by NaPP addition. Two types of domains are observed in the dry latex film: one type carries excess positive charges and is harder than the other, negative domains. Both domains are compatible, as shown by the extensive interfaces observed in all images observed. In the latex–glass joints, the positive domains concentrate in the vicinity of the negative glass surface, thus making an electrostatic contribution to glass–latex adhesion.