Morphology of PA6 nanocomposites prepared by pressurized insertion of aqueous nanoparticle dispersions

Aqueous nanoparticle dispersions were introduced in extrusion processing using high enough pressure to build up a blend consisting of aqueous dispersion and polymer melt. Two mechanisms occurring during this process were investigated experimentally utilizing three different nanoparticles (TiO2, BaSO4, SiO2) dispersed in water. The results were compared to a simplified theoretical model, describing the particle diffusion from the dispersing agent into the polymer melt and the competition of reduction of droplet size by shear forces of the mixing element and the build-up of bigger droplets by surface tension of polymer melt and dispersing agent. The smallest droplet size, occurring in the latter process, could be determined. The size was determined by the ratio of the viscosity of polymer melt and dispersing agent, their relative surface tensions and the shear stresses in the extruder. Such calculated smallest agglomerate size was not smaller than 100 nm in the pursued range. Furthermore, very dense agglomerates were formed. The SiO2 nanoparticles did not undergo a diffusion mechanism ending up in big remaining agglomerates. As remarkably small nanoparticle agglomerates ( < 100 nm for TiO2) and primary particles (BaSO4) could be found, it could be assumed that the diffusion mechanism also occurred. Thus, the pressurized injection of aqueous nanoparticle dispersions represents an adequate processing method for nanocomposites with BaSO4 and TiO2 fillers.