Greatly enhanced porosity of stretched polypropylene/graphene oxide composite membrane achieved by adding pore-forming agent

A small amount of graphene oxide (GO) was incorporated into polypropylene (PP) to prepare a composite membrane, assisted by the pore-forming agent polyoxyethyleneoctylphenyl-10 (OP-10). The composite membrane was obtained through melt-compounding and a subsequent tensile process. The dispersion of GO in the composite, the dynamic mechanical properties and the melting and crystallization behaviors of the melt-compounded samples were investigated to clearly understand the initial microstructures of the samples. Different tensile strains were applied to obtain the stretched PP composite membrane, and then the morphologies of the composite membrane and the porosity were comparatively investigated. The results showed that the dispersion of GO was apparently improved with the aid of OP-10 and many initial pores were simultaneously introduced into the PP/GO/OP-10 composite, which induced a slight decrease in the storage modulus and glass transition temperature of the PP matrix. OP-10 suppressed the crystallization of the PP matrix, while GO compensated for this effect. Both the stretched PP/OP-10 and the composite membranes exhibited larger mean pore sizes compared with the stretched pure PP membrane. Furthermore, compared with the stretched PP, PP/GO and PP/OP-10 membranes, greatly increased porosity was achieved for the stretched PP/GO/OP-10 composite membrane, especially at relatively high tensile strain. In addition, it was suggested that the initial pores, which were introduced by adding OP-10, acted as a stress concentrator, promoting the formation of more pores during the tensile process by inducing lamellar separation and breakage. This work provided a new method for the preparation of PP-based composite membranes and also endowed them with great potential in many fields.