Study Of Swelling And Dissolution Process Of Ultrahigh Molecular Weight Polyacrylonitrile In NaSCN Aqueous Solution

Due to high performance of ultrahigh molecular weight polyacrylonitrile fiber (UHMWPAN, generally M_W> 40×l0~4) via dry-jet wet-spinning or gel spinning, the fiber became a kind of perfect material for making high performance carbon fiber and could be used in many industrial areas. Many papers about the spinning of high performance polyacrylonitrile fiber have been published. Compared with the preparing of the homogeneous solution of ordinary polyacrylonitrile or copolymer (M_W= 7×l0~4), the homogeneous solution of UHMWPAN could not be obtained by the same way as ordinary polymer did. Due to ultrahigh molecular weight of polymer, the preparing of homogeneous solution of the UHMWPAN was very difficult and became a key process to make high performance fiber. However, many researchers focused their attention on how to spin and there were few research achievements on swelling and dissolution process of polyacrylonitrile (PAN), especially ultrahigh molecular weight polyacrylontirle. None of research achievements on the swelling and dissolution process of UHMWPAN- sodium thiocyanate (NaSCN) aqueous solution has been seen. Therefore, it was necessary to study the swelling and dissolution process of UHMWPAN in NaSCN aqueous solution in detail.As to UHMWPAN-NaSCN aqueous solution system, the key factors that affect the swelling and dissolution process of UHMWPAN were studied via the measurement of the swelling value based on orthogonal design. The swelling and dissolution process of UHMWPAN was studied by the stirring torque measurement of the mixture of UHMWPAN-solvent or swelling agent via a device specially developed by our group, then the key parameters of preparing homogeneous solution could be obtained easily. Furthermore, the relation between the stirring torque peak and the destruction of various textural units of UHMWPAN was also discussed in the paper. Besides these works above, ultrahigh molecular weight polyacrylonitrile (M_η= 80×l0~4) was prepared via bulk polymerization using fluoro-containing radical as initiator since UHMWPAN was necessary for making high performance PAN fiber. At last, the swelling and dissolution processes of poly(vinyl alcohol) (PVA) and ultrahigh molecular weight polyethylene (UHMWPE) were also studied by the stirring torque measurement. The major conclusions were listed as follows:1.UHMWPAN could be prepared via bulk polymerization using fluoro-containing radical as initiator, the reaction act on the general rule of free radical polymerization, the best reaction conditions were also obtained. The polymerization method possessed the character of low reaction temperature, less chain transfer reaction and side reaction.2. The rate of polymerization, conversion and molecular weight could increased to some extent by adding water and solvent in reaction system; the molecular weight and conversion could also be raised by after-treatment of reaction production;3. The results of orthogonal design experiments showed that the influence of the concentration of NaSCN aqueous solution on the swelling process of UHMWPAN was most significant, the influence of the swelling time was not significant, the influences of the swelling temperature and polymer content were significant.4. The slight amount of water content in UHMWPAN particles will hinder the swelling process and lead to a higher swelling temperature needed for the swelling process.5. Based on the experimental results of stirring torque measurement, observation by optical microscope and environmental scanning electrical microscope, and the measurement of polymer particles diameter, it was proven that in technological views 41% NaSCN aqueous solution was a perfect swelling agent of UHMWPAN, the various textural units were destroyed step by step during the swelling process, and the swelling process should go on progressively in order to destroyed all the units thoroughly. The optimal swelling conditions should be that during the progressive swelling process, the swelling system should be kept at 33, 41, 52°C for 1 —2hr respectively, at 65°C...