Studying On The Modification Of UHMWPE Fiber With MWNTs

Ultrahigh molecular weight polyethylene(UHMWPE)fibers have been widely used in fiber-reinforced composite materials owning to their high strength,high modulus,light weight,excellent chemical resistance,corrosion and impact resistance and other outstanding properties.However,the interfacial adhesion between UHMWPE fiber and matrix is poor due to fiber's smooth surface and the absence of polar groups in UHMWPE molecular chains.In addition,the heat and creep resistance of UHMWPE fibers are poor,which greatly restrict their application in the fields of composite materials.Therefore,the surface modification of UHMWPE fiber is extremely important.There are many methods to modify UHMWPE fiber but there are some deficiencies for all these modification methods.In this thesis,many experiments are conducted to find a simple and easy to be industrialized method,which can significantly improve the surface adhesion fiber without damaging the excellent mechanical properties of UHMWPE fibers.Meanwhile,the heat and creep resistance of fibers have also been improved to some extent.In this thesis,several kinds of multi-wall carbon nanotubes(MWNTs)are used to modify UHMWPE fibers with the methods of spinning modification and extracting modification.The spinning modification is firstly dispersing MWNTs in UHMWPE solution and then the modified UHMWPE fibers are made by directly gel spinning with the composite solution.The extracting modification is firstly dispersing MWNTs in the extracting agent of UHMWPE gel fibers,and then the modified UHMWPE fibers are made by extracting the UHMWPE gel fibers with the composite extracting agent.The DXLL-20000 tensile tester,scanning electron microscopy(SEM)and infrared spectrometer(FTIR)are used to study the mechanical and morphological properties of the fibers.Differential scanning calorimeter(DSC)and thermal gravimetric analyzer(TGA)are used to characterize the thermal properties and heat resistance of fibers.One and two dimensional Wide angle X-ray diffraction(WAXD or 2D-WAXD)are used to measure the crystallinity and crystal orientation of the fibers before and after modification.Contact angle and interfacial shear strength(IFSS)between UHMWPE fibers and epoxy resin are measured to characterize the surface adhesion properties of the different fibers.Firstly,MWNTs and MWNTs-COOH are used to modify UHMWPE fiber with both modification methods,the changes in the structure and properties of modified fibers are investigated.The results show that monodisperse MWNTs could diffuse into the surface layer of UHMWPE gel fiber during extracting process and then are trapped on the fiber surface.The spinning modified MWNTs/UHMWPE fibers have poor drawing properties,while the drawing and mechanical properties of extracting modified MWNTs/UHMWPE fibers are basically the same with those of unmodified ones.After modified with MWNTs-COOH by two methods,the MWNTs-COOH are well dispersed in UHMWPE fibers,the mechanical properties of both modified fibers are slightly higher than those of unmodified ones.The melting temperature and crystallinity of fibers are both slightly increased after modification,while the crystal sizes are somewhat reduced.The heat resistance of the modified fibers is improved greatly,the fiber's decomposing temperature at 5%weight loss is increased by 21? after extracting modified with MWNTs-COOH.In addition,the creep resistance and surface adhesion properties of modified fibers are also improved after introduction of MWNTs.Compared with spinning modification,extracting modification contributes more to the surface adhesion of fibers,the IFSS between UHMWPE fibers and epoxy resin is increased by 33.9%after extracting modified with MWNTs-COOH.Then,silane coupling agent KH550 is used to functionally treat MWNTs and the obtained MWNTs-KH550 is used to modify UHMWPE fibers with both modification methods.The structure and properties of modified fibers are investigated.The results show that the mechanical properties of fibers have been further improved after modification,the fibers' modulus has been greatly improved by 60%after extracting modification.The melting temperature and DSC crystallinity are both increased after modified with MWNTs-KH550.The fiber's decomposing temperature at 5%weight loss increased by 19? and 20 ? after spinning and extracting modification,respectively.The creep resistance of modified fibers is also improved after introduction of MWNTs.Raman analysis shows that the MWNTs are better orientated in UHMWPE fibers after pre-treated with KH550.The crystallinity and fibers' crystal orientation are increased with increasing the draw ratio,and they increase rapidly during the early drawing stage while the increasing trend becomes slow during the late drawing stage.The surface wetting and surface adhesion properties are greatly increased after extracting modification,the modification effect of MWNTs-KH550 is better than that of MWNTs-COOH,the increase in 41.1%is got for extracting modified MWNTs-KH550/UHMWPE fibers.