Polymer Foams Made of Immiscible Polymer Blends Compatibilized by Janus Particles-Effect of Compatibilization on Foam Morphology

Polymer blends have the potential to be homogenously foamed, since the interface area between their phases can be used as bubble nucleating agents during the foaming process. Immiscible polymer blends of poly(2,6‐dimethyl‐1,4‐phenylene ether) PPE and poly(styrene‐co‐acrylonitrile) SAN with a weight ratio of 60/40 are compatibilized by different amounts (1–10 wt%) of Janus nanoparticles (JPs). Here, we report on the nucleation effect of JPs and the dispersed PPE phase on the foaming behavior of PPE/SAN blends. The plasticization of CO2 and its solubility and diffusion behavior in the PPE/SAN blend are analyzed and correlated to blend morphologies. It is shown that partial coverage of the raspberry structure results in stress concentration at the blend interface during the saturation step. This formation of new surfaces by cleavage (and maybe microcrazes) results in a higher sorption of the blowing agent, which affects the foaming behavior. Through temperature‐induced batch foaming with CO2, the blends are foamed to find the optimum foaming conditions and relationships between the morphology of the compact and foamed blends (cellular structure) and the density are established. Finally, it was concluded that by using Janus particles, homogenous foams with small cell sizes, and relatively high densities are produced. Highly active Janus particles result in much finer morphologies in the compact blend materials after compatibilization. Their effect on the foam morphologies is even more significant due to the larger surface area available for nucleation, which result in a very fine cellular structure. Strong JP bonds at the interface also result in partially open cell structures in the foam.