| In the competitive market of fiber industry, polyacrylonitrile (PAN) fibers have a recession indemand in the clothing field, but PAN fibers can be found their special application in someindustrial fields due to their unique structure and properties. In order to explore their potentialapplication in industrial areas, the structure and properties of PAN fibers prepared from differentspinning technology processes were compared systematically. On this basis, the changes ofstructure and properties of PAN fibers during the application environment in asphalt and cementwere investigated.Firstly, the chemical structure of PAN fibers prepared from different processes wascharacterized by FT-IR,1H-NMR, elemental analysis as well as molecular weight test. Thesupramolecular structure of the PAN fibers was studied by synchrotron wide-angle X-rayscattering (WAXS). According to the results, the differences between the structure and propertiesof these fibers were pointed out.Having analyzed the basic structure and properties of the fibers, three different kinds of PANfibers were chosen to investigate their structure and properties changes during the heat treatment.The samples were prepared by wet spinning technology using dimethyl sulfoxide (DMSO) assolvent (Wet-DMSO), dry spinning technology using N, N-dimethylformamide (DMF) as solvent(Dry-DMF) and wet spinning technology using N, N-dimethylacetamide (DMAc) as solvent(Wet-DMAc). The Wet-DMSO fibers had higher strength and modulus than the other two fibers atroom temperature. However, the most severe thermal oxygen degradation of Wet-DMSO fibersoccurred at150°C compared with that of Dry-DMF and Wet-DMAc fibers, leading to the loweststrength retention. In addition, with the increase of heat treatment temperature, the crystallinityand the crystal sizes of all the samples increased first and then decreased, the crystallineorientation of the Wet-DMSO fibers dropped dramatically compared with Dry-DMF andWet-DMAc fibers. Dynamic creep test at different temperatures illustrated that Wet-DMSO fibers had better creep resistance to Dry-DMF and Wet-DMAc fibers at the temperature between30-100°C, but when the temperature rose to200°C its creep resistance became the lowest. Thethermal mechanical analysis (TMA) showed that the Wet-DMSO fibers had the largest internalshrinkage stress in the heating processing, resulting in the poorest dimension stability of the threefibers. This indicated that although the stress and modulus of Wet-DMSO fibers were closer to therequirements of fiber reinforced asphalt, however, it was not suitable for using as asphaltreinforcement material due to it thermal oxidation degradation.Besides, considering the alkaline conditions in the application process of using as cementreinforcement fibers, the structure and properties changes of PAN fibers were studied in thealkaline treatment process referring to GB (GBT21120-2007). The results showed that all thesamples treated in alkaline solution were hydrolyzed to some extent and the crystallinity, crystalsizes as well as crystalline orientation have a certain decrease, which were relative with thecomposition of copolymer and compactness of the fibers. It is analyzed that the presence of estercomonomer in the molecular chains induced the chains arrange loosely, which make the cyanogroup vulnerable offensive by the OH-in the alkaline solution. Additionally, the alkaline solutionwas not easy to enter and corrode the structure in the fiber core when the fiber had highcrystallinity and crystalline orientation. In the alkaline treatment experiment, the strength retentionof Wet-DMSO fibers was obviously higher than that of Dry-DMF and Wet-DMAc fibers, showingbetter alkaline resistant. Meanwhile, the Wet-DMSO fibers had less irreversible deformation andbetter creep recovery capability after alkaline treatment. In conclusion, it was believed thatWet-DMSO fibers had the potential to be used as reinforcement material in cement. |
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