The Effects Of New-style Spinneret On Spinning Process And Properties Of PAN-based Carbon Fiber Precusor

Carbon fibers,the fibrous materials with more than 90%of carbon content,are new-style materials which have high tenacity,high modulus, heat-resistance,corrosion resistance,and a series of excellent performances.As a kind of reinforcing fiber of advanced materials,it is used widely in all kinds of fields.Carbon fibers can be made by carbonization in high temperature from organic fibers of rayon,PAN and pitch.With the rapid development of technology,PAN-based carbon fibers play the main role in the carbon fiber industry.Currently, researchers home and aboard show no differences that the quality of PAN precursor fiber is critical for high-quality PAN-based carbon fiber.To yield the high-quality PAN-based carbon fiber,the PAN precursor fiber must have some performances of high tenacity,high purity,high compactness and the uniform structure,etc.Firstly,the new type of spinneret materials and the application of this new-style spinneret in the spinning process of PAN-based carbon fiber precursor were mainly investigated in this paper.For the purpose of avoiding die swell as well meeting the basic requirements of spinneret materials and the manufacture techniques of these materials,we made the contact angle experiments to test the surface tension between different materials and PAN/DMSO spinning solution and finally developed the new type of materials for the spinneret in the experiments.It was found that the surface tension between the Si₃N₄ ceramic material and PAN/DMSO spinning solution was relatively larger.In addition,the Si₃N₄ ceramic materials have an advanced"incising comes before sintering"manufacture technique,so it can be made for the spinneret with satisfied ratio of length to diameter(L/D),which can decrease the die swell effect in the spinning process effectively and avoid the spreading phenomenon of spinning solution on the spinneret surface.Therefore,the Si₃N₄ ceramic materials are chosen for the new-style spinneret material.Then in the fixed conditions,we used the Si₃N₄ ceramic spinneret and the traditional 1Cr18Ni9Ti stainless steel spinneret for spinning.Through comparing the cross-section shape and diameter of PAN as-spun fiber,the swellability,the crystallinity,the preferred orientation,and the tenacity of PAN precursor fiber,we get the conclusion that the new-style ceramic spinneret can replace the traditional metal spinneret in the industry of fibers.Secondly,the effects of ratio of length to diameter(L/D) of new-style spinneret on properties of PAN precursor fiber were investigated in this article.Using wet spinning,dry-jet wet spinning and gel spinning in experiments,we analyzed the effects of ratio of length to diameter(L/D) on die swell phenomenon in the spinning process,and on the swellability,the crystallinity,the preferred orientation and the mechanics performance of PAN precursor fiber comprehensively.The results show that with the increase of ratio of length to diameter(L/D), die swell effect in the spinning process decreases and the spreading phenomenon of spinning solution on the spinneret surface can be avoided effectively.So the stability of spinning and the performance of PAN precursor fiber can be improved.But when the L/D value reaches a certain one,the effects will diminish gradually.Lastly,the spinnability(V_1m) of PAN spinning solution using DMSO as the solvent was investigated for wet spinning and dry-jet wet spinning of PAN precursor fiber in this paper.It is expressed by the intuitionistic parameter V_1m-the maximal rotational speed of the first winding roller after the coagulating bath.Among many variables responsible for spinnability,the coagulating conditions,the air gap length,the nonsolvent(NSA) content in spinning solution,the spinning temperature and the spinning solution concentration have been viewed as the key factors.We investigated these factors in the dry-jet wet spinning of PAN precursor fiber,and compared them to the wet spinning.For the dry-jet wet spinning,the results show that the coagulation bath conditions exert little influence on spinnability(V_1m).It depends on many spinning variables,including the spinning temperature and the spinning solution concentration,the spinneret hole size and shape,the air gap length,etc.