Effect of sodium dodecyl sulfate (SDS) on mechanical performance of polyvinyl-acetate-based emulsion polymer isocyanate

Abstract Aqueous vinyl acetate copolymer latex with addition of sodium dodecyl sulfate (SDS) was crosslinked by polymeric diphenylmethane diisocyanate (pMDI) for preparing the emulsion polymer isocyanate (EPI) as a high-performance wood adhesive. The effect of SDS on the quasi-static tensile response, dynamic mechanical behavior as well as the residual isocyanate group (NCO) in the cured polymer film was thoroughly discussed. Meanwhile, the bonding strength and water resistance of the adhesive were also investigated in detail. The results indicate that the tensile strength, Young's modulus and dynamic storage modulus markedly increased under a dry condition with the increased weight ratio of SDS. Moreover, a suitable loading of SDS would significantly improve the strength and stiffness of cured film at high humidity, resulting in better adhesive properties and water resistance of glue joints. The EPI, modified at 0.25 wt% of SDS, exhibits not only the highest moisture resistance of the cured films, but also the best adhesive properties. Finally, added surfactant is found to efficiently reduce the residual NCO in the polymer film by means of Fourier transform infrared spectroscopy (FTIR). It enhances the EPI in terms of a larger crosslink density, glass transition temperature and relative humidity due to the more effective dispersion and chemical reaction of pMDI in the main component.