Study On The Preparation Of Halloysite Nanotube/PTFE Nanocomposite And Its Friction Properties

Polytetrafluoroethylene(PTFE)is a kind of polymer with high crystallinity,stable chemical properties and excellent self-lubrication property.It can be used in machinery,chemical equipment,electronic,biomedical and other fields.As a friction material,it can offer a very low coefficient of friction.But the weak vander Waals forces between the molecules and the low cohesive energy led to the poor friction properties.Fill modification is an effective method to improve the friction and wear properties of PTFE.One-dimensional and two-dimensional nano-fillers can preferentially support loads in composites,increase the rigidity of the composites and optimize the stress transmission.The halloysite nanotubes(HNTs)are a kind of inexpensive,abundant one-dimensional nanomaterials.There is no report about HNTs in the field of composites friction,especially in PTFE.So the preparation and the study of its frictional properties are a scientific problem which needs to be solved.HNTs/PTFE nanocomposites were prepared by cold pressing sintering and researched by means ofXRD,FTIR,contact Angle,SEM,TEM and TG.The frnction properties and mechanical properties of composite materials were tested by universal friction wear tester and universal material testing machine.The effects of the HNTs filling content,the preparation process and modification of the composite materials on the mechanical and friction properties of HNTs/PTFE nanocomposites were investigated.When the content of HNTs were 2 wt.%,the tensile strength was 29 MPa which was slightly higher than the pure PTFE(28 MPa).With the increase of the HNTs content,the tensile strength of the composite decreased.With the increase of HNTs filling amount,the antiwear properties of the composite rises gradually.When the filling amount of HNTs was 2 wt.%,the volume loss is decreased to 45%of pure PTFE.When the filler content is 10 wt.%,the volume loss is 0.00163 cm3/h,which is only 1/362 of the pure PTFE.In the case of low wear rate is accompanied by the improvement of the coefficient of friction.We adopt the method of solvent mixture to the preparation of hybrid HNTs and PTFE powder,from the point of preparation of composite materials.In the same conditions,the tensile strength of the composites with 2 wt.%HNTs increased 3 to 5 MPa than the composites made by dry methods.The volume loss is 1/5 of the composites made by the dry mixture method.We have grafted PMMA on HNTs,change the surface into the carboxylation and use surfactant(SDS)to modification the HNTs.And we prepared composite materials with a filling content of 2%functional HNTs.The volume loss of the modified composite material is 5%to 8.3%of pure PTFE.In this paper,chloroacetyl chloride was introduced by using the characteristics of hydroxyl on HNTs surface,and then the surface polarity of HNTs was modified by grafting hydrophilic diethanolamine and pro-oil molecule dodecylamine.On the other hand,acrylamide(AM)were adsorbed to the surface of HNTs,through the method of inverse emulsion polymerization to coat on HNTs.From the test we found that the composite material of HNTs/PTFE modified by dodecylamine was the best.The tensile strength increased by 9MPa compared with that of pure PTFE,and the elongation of fracture increased by 30%.In the aspect of friction and wear performance,the friction coefficient of three kinds of modification is slightly higher than that of pure PTFE.The volume loss of composite materials modified by diethanolamine was about 3.9%of pure PTFE.The volume wear of the composite material modified by dodecylamine is about 1.7%of pure PTFE.The volume wear of acrylamide modified composites was about 2.7%of pure PTFE.Based on these results,it can be concluded that the dispersibility and compatibility of HNTs in the PTFE matrix determine the frictional properties of the composites.HNTs modified by hydrophilic and lipophilic methods have similar dispersibility.But lipophilically modified HNTs have better dispersibility and compatibility in the PTFE.Because of this,its friction properties is the best.