| In recent years, polyurethane (PU) is widely used in the construction; mining, medical, aerospace and other fields because of its unique soft and hard segment alternate structure, good wear resistance, high resistance to tear and strong resistance to chemical. But the thermal stability and flame retardant performance of PU is poor, which has a potential danger in the high temperature environment. In this paper, we modify PU by using high strength & high modulus PVA fiber modified and unmodified, and explore the relations of the performance and structure of PVA fiber/PU composites.Two kinds of silane coupling agent KH550 and KH560, three kinds of isocyanate TDI, MDI and IPDI were used to modify high strength & high modulus PVA fiber by the method of hydrolysis and suspension graft polymerization. The result shows that the adding amount was 15% of the theoretical value of modifying agent KH550, KH560, TDI and MDI, the grafting rate reached maximum.With increasing of adding amount of surface modifier, the grafting rate decreased. The mount of IPDI has a little influence on grafting rate of PVA fiber. For the surface modifier KH55O and KH560, the optimum reaction temperature is 75 ℃, and for TDI, MDI and IPDI, the optimum reaction temperature is 85℃. Stannous octoate can effectively improve PVA fiber grafting rate for isocyanate modification. The structure and properties of modified or unmodified PVA fiber were invesgated by FTIR, TG, SEM, XRD, DSC and contact angle Analyzer. The result showed that five kinds of modifier successfully grafted to the surface of PVA fiber, Its thermal decomposition temperature was influenced by the surface properties of modified PVA fiber, the modified PVA fiber surface became more rough than pure PVA fiber, and its hydrophobic improved significantly. The melting temperature and Tg of PVA fiber was improved. From XRD pattern, we found that the crystal diffraction peak of samples became weak, crystallinity decreased.The PVA fiber/PU composites were prepared. The mechanical and thermal properties of PU/PVA fiber composites were studied systematically. The results showed that the mechanical properties of modified PVA fiber/PU is better than unmodified PVA fiber/PU, with the increase of unmodified PVA fiber content, the mechanical properties of composites decreased. After the PVA fiber were modified with KH550, KH560, TDI, MDI and IPDI, the performance of PVA fiber/PU composites significantly improved. When the fiber length is 6mm, addition is 0.10%, the tensile strength of PU can reach maximum and adhesive strength increased obviously. Especially, the PVA fiber modified by MDI, the tensile strength, adhesive strength and impact strength of composites reached 54.47MPa,7.97MPa and 18.48KJ/m2 respectively. Modified PVA fiber can improve the thermal stability of composites. When the PVA fiber was modified by KH560 and the mass loss is 30%, the thermal decomposition temperature of the PVA fiber/PU increased by 22℃. PVA fiber can improve the thermal mechanical properties of PU. When the PVA fiber modified by MDI, the Tg of PVA fiber/PU composite reached 69.4℃, which is higher 14.8℃ than pure PU. The thermal aging properties of PVA fiber/PU composites can be improved. When the PVA fiber modified by MDI and its addition amount is 0.10%, after ageing test (120℃,24 hour), the tensile strength and impact strength of PVA fiber/PU composite remained 92.16% and 87.41%, which increased 21.65% and 25.75% than pure PU. From SEM, we found the surface of modified PVA fiber was rougher, which provided proof that mechanical properties and aging properties of composites were improved,... |
PDF Full Text Request