Morphology and thermal properties of PAN copolymer based electrospun nanofibers

Ultra-thin fibers are obtained from polyacrilonitrile co-polymer (PAN-CP)/N,N-dimethylformamide (DMF) solution by electro-spinning technique. The different wt. content of PAN-CP solution is electrospun with varying processing parameters to get nanofibers. The morphology of nanofibers is studied by scanning electron microscopy (SEM) and thermal properties are primarily investigated by DSC and TGA. The polymer nanofibers are stabilized and carbonized to get carbon nanofibers, after stabilization and carbonization nanofibers are characterized by FTIR, XRD, SEM and SPM. It is found that the diameter of nanofibers varies from 150 to 1300 nm, that increases with increasing polymer concentration and decreases with increasing the tip to collector distance and collector speed. The DSC studies show that the exothermic peak occurs at two different temperatures 275 and 320 °C in case of nanofibers. While in case of micron fiber single exothermic peak occurs at ∼275 °C. This might be due to the alignment of polymeric chain along the fiber direction. This is due to the stretching and whipping that occurs during the electrospinning process. As a consequence, increase in thermal stability and decrease in weight of nanofibers is confirmed by TGA. However, in the nanofibers of diameter >1000 nm, weight loss pattern is found to be similar as that of micron fibers. This could be due to the entrapping of solvent between polymeric chains. On stabilization and carbonization there is a decrease in fiber diameter in all the cases. The extent of decrease is higher in case of 10 wt.% electrospun fibers, from 350–400 nm to 100 nm. The SPM investigations reveal that the surface area and roughness changes due to the transverse shrinkage of nanofibers.