Enhanced Mechanical Performance Of Porous Nanofibrous Membranes

Electrospun polymer nanofibrous membranes are regarded as the ideal materials in energy and environment applications owing to interconnected porous structure,large surface area and high flux.Usually in the preparation of composite membrane,the difference between substrate layer and functional layer will induce the peeling and separation at the interface of two layers which will generate adverse effects in next characterization and application of composite membrane.In this experiment,blend polymer and mixed solvent methods were used to enhance the mechanical performance of porous nanofibrous membranes and improve the integrity of the composite membrane.Electrospun polyacrylonitrile(PAN)membrane was set as the study object.The viscosity of the PAN solution for electrospnning was investigated by rheometer.Here,SEM and FTIR were employed to characterize the change of morphology and chemical structure of membrane.The mechanical performance of membranes was examined by universal testing machine.And the surface fibers junctions were investigated by dynamic water contact test.Routine blend was firstly chosen to enhance the nanofibrous membrane.Polyvinylidene fluoride(PVDF)was chosen as the blend polymer.Blend membrane concentration(7wt%,10wt%)was determined by morphology and diameter of nanofibers from 7wt%,10wt%,13wt%PAN/PVDF solutions.With the increase of PVDF content,average fiber diameter of 13wt%PAN/PVDF blend porous membrane firstly decreased from 603nm to 479nm and then increased to 513nm.This decrease was attributed to the decrease of viscosity of solution and the increase was induced by fiber morphology changing from round to flat.And the second decrease(441nm)was owed to the larger diameter distribution.The porosity of the nanofibrous membranes was changed lightly.The mechanical performance of whole membrane was enhanced significantly;break strength reached highest 8.13MPa with PVDF 40wt%in PAN/PVDF solute.The adhesion of membrane surface fibers was strengthened gradually with the increase of PVDF in solute.Diameters of 10wt%PAN/PVDF fibers followed the change law of 13wt%fibers but the fibers morphology was unstable and plenty of beads appeared from the solution with PVDF 60wt%in solute.The mechanical performance was not enhanced notably because of the nonuniform fiber morphology.Except blend,mixed solvent method was also used in this study.DMSO was with high boiling point,189?.Residual DMSO would generate re-dissolvent at fiber contact point because of its slower evaporation.DMSO was 20wt%,30wt%,40wt%and 60wt%in mixed solvents.With the increase of DMSO in mixed solvents,diameter of 7wt%PAN fiber was increased from 153nm to 223nm and the porosity of the membrane was decreased lightly.The whole membrane mechanical performance was enhanced.Break strength was increased from 2.87MPa to 8.98MPa and the tensile modulus was from 66.24MPa to 159.09MPa.Fiber adhesion appeared after mixed 20wt%DMSO in solvent.Mechanical performance of 10wt%PAN membrane was enhanced greatly owing to the effect of DMSO in mixed solvent.The highest break strength and tensile modulus were 8.59MPa and 171.28MPa.The surface fiber integrity was gradually increased with DMSO increase.The surface fiber morphology of 13wt%PAN was hardly impacted by the mixed solvents.But the membrane mechanical performance was enhanced gradually.