Enhanced dispersion, flame retardancy and mechanical properties of polypropylene/intumescent flame retardant composites via supercritical CO2 foaming followed by defoaming

The broad technological exploitation of polypropylene (PP)/intumescent flame retardants (IFR) composites with outstanding flame retardancy and mechanical properties is stifled by the lack of effective methods to improve the IFR dispersion, since the opposite polarity between PP and IFR would result in poor compatibility and uneven dispersion. In this work, we have demonstrated an industrially viable and efficient approach for the fabrication of PP/IFR composites with more uniform dispersion by combining the advantages of supercritical CO2 (scCO2) plasticization and biaxial bubble stretching through the scCO2 foaming technique followed by defoaming, and the increasing of the foam expansion ratio could lead to the better IFR dispersion of the final defoamed solid PP/IFR composites due to stronger bubble stretching force. Moreover, the improved IFR dispersion could result in the greatly enhanced flame retardancy and mechanical properties in comparison with those of uneven dispersed ones. We believe that the approach here can be used to guide the future design of high-performance materials on inorganic/organic hybrid polymer composites with homogenous dispersion.