Stretching induces pore formation in the β-nucleated polypropylene/graphene oxide composite

A few amount of graphene oxide (GO) and β-nucleating agent (β-NA) were introduced into polypropylene simultaneously through melt-compounding processing. The microstructures of the compression-molded samples were characterized and the results showed that in the composite, the nucleation efficiency of the β-NA was higher than that of the GO, which resulted in the formation of a large number of β-PP. The compression-molded samples were stretched under different conditions and the pore morphology and the porosity were investigated. The results showed that the presence of GO induced the formation of pores with smaller size in all conditions. Increasing the stretching temperature or tensile speed induced the decrease of the porosity, although the stretched samples exhibited higher mean pore size. Furthermore, the results showed that the pore size and porosity of the composite increased with increasing the tensile strain, but too high tensile strain also resulted in the decrease of the porosity. Further results proved that annealing pretreatment facilitated the formation of regular pores, and the stretched sample exhibited higher porosity. This work provided a new method to prepare the hybrid porous PP sample with great potential in application.