Influence of hydrophobically modified inulin (INUTEC NRA) on the stability of vulcanized natural rubber latex

The effect of a graft copolymer of inulin (linear polyfructose with degree of polymerization greater than 23) on which several C12 alkyl chains are grafted (INUTEC NRA surfactant) on the stability of vulcanized natural rubber was investigated. This surfactant showed a high adsorption affinity to latex surface, and the adsorption isotherms could be fitted to Langmuir equation. The plateau adsorption is approximately 3.4 mol m−2, corresponding to an area per INUTEC molecule of 4.9 nm2. The polymeric surfactant adsorbed layer thickness was determined using zeta potential and dynamic light scattering (PCS techniques). This gave an electrokinetic layer thickness at the plateau adsorption of 3.5 nm and a hydrodynamic thickness of 3.1 nm. These values indicate that the surfactant can increase the colloidal stability of rubber latex particles, by steric repulsion. The stability of the rubber particles with the surfactant was determined by measuring the critical coagulation concentration (CCC) of calcium nitrate. The adsorption of the surfactant causes a large increase in particle stability; and it was found that the CCC of rubber particles containing the copolymer surfactant increased with the increase in surfactant concentration. Three stability regions were distinguished, namely the coagulation region, the weak flocculation region and the stable dispersion region. The weakly flocculated region may allow the formation of a more uniform layer of latex, which is a very important objective in the industry of glove manufacturing. Thin films of latex have been prepared by a dipping method, and the results clearly demonstrate that smoother films are obtained as a result of a weak flocculation behaviour induced by the presence of surfactant. The results described in this paper may allow the formation of more homogeneous thin films of latex.