the temperature of composite fibers can increase from room temperature to higher than hundreds of degree celsius measured by an infra red ir microscope the joule heating effect can also be estimated according to one dimensional steady state heat transfer equation which reveals the temperature can be high enough to stabilize or carbonize the fibers in the experimental embodiment polyacrylonitrile pan molecular weight 10 5 g mol with 6 7 methyl acrylate as a copolymer obtained from japan exlan co was dried under vacuum at 80 u00b0 c before being used carbon nanotubes multi wall carbon nanotubes were obtained from iljin nanotech co of korea the pan powder was dissolved in dimethylformamide dmf obtained from sigma aldrich co using an impeller at 90 u00b0 c and the cnt powder was dispersed in dmf using a bath sonicator branson 3510 mt the cnt dmf dispersion was subsequently mixed with the pan solution for fiber spinning and the pan cnt composite fibers were fabricated using a dry jet wet spinning unit obtained from the bradford university research uk with a spinneret of 250 u03bcm diameter and two coagulation dmf water baths the fibers were subsequently drawn in boiling water and dried in an oven at 50 u00b0 c for 7 days the joule heating effect was induced by applying electrical current using a source meter unit keithley 2400 sourcemeter the fiber structure was measured by real time wide angle x ray equipment during joule heating process wide angle x ray diffraction waxd.