Study On The Non-coagulation Bath Spinning Of Polyacrylonitrile Fiber

At present,the most commonly used spinning method of PAN based carbon fiber precursor is wet spinning and dry jet wet spinning.Coagulation bath is used in these two kinds of spinning method,its role is to enable the spinning trickle solidified into nascent fiber as soon as possible without adhesion mutually.Double diffusion occurs rapidly between spinning trickle of solvent and coagulant in contact with the coagulation bath,leading to the surface and in the interior of the as spun fiber has many pores and skin-core structure defects.From the as spun fiber to Fiber precursor although with multi-step tension and densification steps to maximize the elimination of these holes,the surface of the precursor will be more or less defective finally.These defects will eventually be "inherited" to the carbon fiber,and it will affect the performance of carbon fiber.90% of the defect of PAN fiber is the surface defect,which is the main defect of the tensile strength of the carbon fiber.Therefore,avoiding and reducing the surface defects is an effective way to obtain high performance carbon fiber.This paper is based on years of work in our laboratory,adding a layer of oil layer in the method of non-coagulation bath,the surface of the filament which is sprayed from the spray head is wrapped to prevent sticking.Using conventional molecular weight and high molecular weight PAN mixed solution to prepare high viscosity PAN spinning solution,and using self-made spinning equipment to carry out spinning.The morphology of the surface and section of the primary fiber was observed by SEM,determination of crystallinity of fiber by X-ray diffraction,determination of mechanical strength and modulus of fibers by electronic single fiber strength tester.The influence factors of spinning process parameters such as spinning height,spinning speed,spinning temperature and spinning parameters on fiber diameter,surface morphology,crystallinity and mechanical properties were studied.The results show that the use of the oil layer can effectively avoid the formation of sticky silk.The spinning height is 7.0cm,the spinning speed is 25.0m/min,the tensile strength and modulus of the primary fiber are as high as 2.41 cN/dtex and 90.60 cN/dtex respectively.In addition,we have tried to add a layer of oil layer in the traditional dry-spray-wet spinning method,which is the spinning method of "air layer-oil layer-coagulation bath".Adding oil layer,which is not only increased the stretching distance before fiber into the coagulation bath layer(air layer + oil layer height),and what is more important is that,before entering into coagulation bath layer,the surface of the fiber with a layer of oil,in the coagulation bath solvent double diffusion can be to better control,so it has fewer defects on the surface of the fiber.SEM preliminary observation results show that the fiber surface is smooth and the mechanical strength is higher than other method.