Preparation Of High Surface Adhesive UHMWPE Fibers

High strength high modulus polyethylene fibers,which are also known as ultrahigh molecular weight polyethylene(UHMWPE) fibers,have good prospects in the application areas of composite materials and special materials because of their high tensile properties,light weight,corrosion resistant,and excellent chemical and impact resistance.However,the interfacial adhesion between UHMWPE fibers and matrix is poor because of the chemical inertness of fibers.Therefore the range of fibers' applications is limited greatly,it's necessary to improve the surface adhesion of UHMWPE fiber.A variety of techniques are useful for improving UHMWPE fiber's surface adhesion,but there are many shortages for these techniques.In this thesis, many experiments are conducted to find a simple and easy to be industrialized method, which can significantly improve the surface adhesive properties of fibers without damaging the excellent mechanical properties of UHMWPE fibers.There exists loose network structure in UHMWPE gel fibers after phase separation,many nano-sized and micro-sized poles occur in UHMWPE gel fibers after extraction.If the modifiers are dissolved or dispersed in the extraction agent of UHMWPE gel fibers and are used to treat gel fibers,the modifiers could diffuse into gel fibers.Then the modifier molecules are trapped on the fiber surface after subsequent ultra-drawing,which are beneficial to improve the surface adhesion of UHMWPE fibers.In this thesis,different coupling agents and different nano-particles are used as modifiers.UHMWPE fibers are treated with modifiers solution or modifiers suspension during extracting process.The modification mechanism and effects are investigated in details,with measurements on the changes of fibers' structure and properties,especially the changes of fibers' surface adhesion.Firstly,three kinds of coupling agent,γ-aminopropyl triethoxysilane (SCA-KH-550),γ-glycidoxypropyl trimethoxysilane(SCA-KH-560) and isopropyl tri(dioctylpyrophosphate) titanate(TCA-NDZ-201),are used to modify UHMWPE fibers.The surface chemical and morphological structure,the crystallization and orientation structure,surface wetting ability,surface adhesion and mechanical properties of treated UHMWPE fibers are studied and compared with untreated fibers. The results show that coupling agent molecules could diffuse into the surface layer and the inner layer of gel fibers and then are trapped on the fiber surface.The surface wetting ability of modified fibers and the interfacial adhesion between fibers and matrix are tremendously improved.SCA-KH-550 has the best modification effect among three selected modifiers.The interfacial adhesion of UHMWPE fibers increases with increasing coupling agent concentration and gradually reached a plateau value with 105%improvement when the concentration of SCA-KH-550 is 1.0%.As the coupling agent concentration increases,fibers' crystallinity becomes higher and their crystal size becomes smaller,the mechanical properties modified fibers are significant improved,after treatment with 1.5 wt%solution of SCA-KH-550, the tensile strength and modulus of modified fibers are increased by 11%and 37%, respectively.The coupling agent trapped nano-SiO₂ dispersed in xylene is used to modify UHMWPE gel fibers during the extraction stage,and the structure and properties of untreated and treated fibers are investigated and compared with untreated fibers.The results show that the interfacial adhesion between obtained UHMWPE/SiO₂ fibers and matrix are tremendously improved and increase with increasing nano-SiO₂ concentration in the extraction agent.When the concentration of nano-SiO₂ is 1.5%, the interfacial adhesion of treated fibers is an increase of about 149%than that of untreated fibers.The crystallinity and mechanical properties of UHMWPE/SiO₂ fibers reach the maximum values when the concentration of nano-SiO₂ is 0.5%,and the tensile strength and modulus of UHMWPE/SiO₂ fiber are higher than the values for the UHMWPE fiber by approximately 23%and 76%,respectively.Further increasing the nano-SiO₂ concentration resulted in a decrease in the crystallinity,mechanical properties,apparent crystal size,and orientation degree of UHMWPE/SiO₂ fibers. With increasing the extraction time,the interfacial adhesion between UHMWPE/SiO₂ fibers and matrix are unchanged,but the mechanical properties of UHMWPE/SiO₂ fibers are greatly improved and level off in the extraction time of 6 min.The coupling agent trapped attapulgite and original attapulgite are used as modifiers to treat the UHMWPE fibers,and the structure and properties of untreated and treated fibers are investigated and compared with untreated fibers.The results show that the coupling agent trapped attapulgite can is well-dispersed in the surface of UHMWPE fibers,but the original attapulgite is easy to congregate on the surface of UHMWPE fibers.The interfacial shear strength of treated UHMWPE fibers increase by 59%for UHMWPE fiber treated by the coupling agent trapped attapulgite and 82%for UHMWPE fiber treated by original attapulgite compared with that of untreated fibers.The coupling agent trapped attapulgite can diffused into the inner of UHMWPE fibers,and result in the increase of crystallinity and the decrease of apparent crystal size.Compare with those of untreated UHMWPE fibers,the tensile strength and modulus of treated fibers increase by approximately 7%and 24%, respectively,and thermal and thermodynamic properties of treated fibers are greatly improved.Finally,the effects of two types of nanomaterials on modified UHMWPE fibers are compared.The effect of three-dimensional nano-SiO₂ on the mechanical properties is more effective than the two-dimensional attapulgite,and then on the interfacial adhesive propertied is more or less the same with two-dimensional attapulgite.The main innovative points of the dissertation are as follows:several modifiers are found,the surface adhesive properties of the UHMWPE fibers are greatly enhanced,as well as its mechanical properties are improved.