Preparation Of PAN Fibers By Plasticized Melting Spinning And Drawing Extraction Process

Due to a strong polar cyano group(-CN),polyacrylonitrile(PAN)has a very high melting temperature which is even higher than its decomposition temperature,that is to say,when heated,PAN will decompose before reaching its melting point.And for this reason,melting spinning seems to be impossible to be used to produce PAN fibers,which are prepared by solution spinning methods generally,including dry spinning,wet spinning and dry-jet wet-spinning.During those production process,using a large amount of chemical solvents which are toxic or corrosive is prevalent,it is not only contaminate the environment but also enhance the production cost of PAN fibers dramatically.In addition,the spinning efficiency of solution spinning is too low,compared to melt spinning.Actually,these shortcomings will be solved perfectly if PAN fibers could be prepared by melt spinning.At present,polyacryonitrile-based carbon fiber with the highest yield and the most varieties is growing the fastest and has the most mature technology within all of carbon fiber kinds.High quality polyacrylonitrile fibers is a prerequisite for the preparation of high performance carbon fiber,there exists many problems related to domestic PAN precursor production,which seriously inhibit the development of high-performance carbon fibers and its composites.It's time to solve the key problems during the preparation of PAN fibers and put forward innovative technology in order to change the carbon fibers backwardness situation of China.In the thesis,adding appropriate plasticizer into PAN,the melt spinning of PAN on a conventional melt-spinning equipment was realized successfully.Then,through the drawing and extraction process of as spun filaments,high performance PAN fibers were obtained which could meet the requirements of carbon fiber precursor.The rheological properties of PAN/plasticizer melt and the effects of plasticizer on the glass transition temperature of PAN were studied.The results showed that the suitable melt-spinning temperature for plasticized PAN melts was 180 ?,at which PAN was thermally stable.The effects of winding speed,drawing methods,drawing temperatures,drawing ratios and its distribution in the first stage and second stage,and extraction methods of plasticizer on the properties of drawn PAN fibers was investigated.The results showed that the suitable first stage draw ratio was 1.6 and the optimum drawing temperature in the first stage was 60?.The winding speed had important effects on the drawability of as spun filaments and the performance of drawn fibers,although there was no significant difference among the preorientation degree of as spun filaments with different winding speed.When the winding speed was 200 m/min,the total draw ratio reached 7.0.But the drawability of as spun filaments and the total draw ratio decreased with the increase of winding speed.The tenacity of drawn yarns could achieve more than 7.0 CN/dtex via drawing.The PAN fibers prepared by plasticized melt spinning possess many excellent characteristices:circular cross section,smooth surface,compact structure,no obvious core-skin structure and high tenacity.It is proved that melting spinning PAN fibers is suitable for carbon fibers precursor.Via melting spinning to prepare carbon fiber precursor can greatly save the cost of carbon fiber and bring us to an era of low cost of carbon fibers.