Study On Friction Properties And Mechanism Of The Thermoplastic Polyurethane Composites

Thermoplastic polyurethane（TPU）has become a high-performance sole material widely used because of its outstanding excellent abrasion resistance,resilience,fatigue resistance and flex resistance,but its biggest shortcoming is its inefficient slip resistance,especially in wet and icy environments where it is easy to slip.High vinyl soluble styrene-butadiene rubber（HVSSBR）exhibits better wet skid resistance due to its molecular chain with more than60%vinyl that can hinder the movement of macromolecular chains.Therefore,the performance advantages of each polymer component can be comprehensively utilized by rubber-plastic blending modification of TPU and HVSSBR.In addition,the difference of deformation ability of material surface and the change of material surface micromorphology caused by nano-fillers have important effects on its friction performance,and the related friction mechanism is still unclear.Therefore,this paper firstly studied the effects of operating conditions such as speed,load and temperature on the friction properties of TPU materials under different interface conditions.And then the effects of material factors such as the blending ratio of TPU/HVSSBR composites,the phase structure and the dispersion of nano-fillers in the matrix on the friction properties of dry and wet friction surfaces as well as on ice surfaces are explored,and the corresponding friction mechanisms are analyzed.Specifically,the following aspects are covered:（1）The effects of speed,load and temperature on the friction properties of TPU materials under different interface conditions were studied.The results show that:the effect of speed on dry friction is greater than that of wet friction and ice friction,and the effect of high speed（>0.6km/h）on friction coefficient is greater than that of low speed;the effect of load on the friction coefficient of TPU materials under all three interface conditions is that the friction coefficient decreases as the load increases;and the effect of temperature on the friction coefficient of TPU materials under different interface conditions differs,i.e.,the dry friction coefficient decreases with the increase of abrasive disc temperature,the wet friction coefficient increases with the increase of water temperature,and the ice friction coefficient decreases with the increase of ice surface temperature.And according to the typical usage conditions of footwear materials,the testing conditions of friction coefficient of composite materials were determined as follows:constant temperature and surface pressure,and speed of 0.6km/h.（2）The friction properties and mechanisms of TPU/HVSSBR composites with different blending ratios were explored for dry and wet friction surfaces and different ice surface temperatures（-20°C,-10°C,-5°C）at constant surface pressure.The results showed that the dry friction coefficient f _D,wet friction coefficient f _Wand ice surface friction coefficient f _Iof TPU are improved with the increase of HVSSBR phase addition,where TPU:HVSSBR=60:40TPU/HVSSBR composites increased the f _Dby 35%,the f _Wby 13%,and the f _Iat different ice surface temperatures（-20℃,-10℃,-5℃）increased respectively by 59%,89%,116%.The DMA was used to characterize the dynamic viscoelasticity of the material,and further fit studies were conducted on the parameters of f _D,f _W,f _Iand hardness H,loss factor tanδ,etc.And combining with tribological theory to analyze the material friction mechanism under different interface conditions,it was found that the three friction coefficients were linearly and positively correlated with tanδ/H,and the degree of correlation was:wet friction>ice friction>dry friction,indicating that the wet friction and ice friction mechanism is mainly contributed by adhesion friction,while dry friction is contributed by both adhesion friction and hysteresis friction.（3）The dispersion behaviors of two types of nanofillers,silicon dioxide nanoparticles（Si O₂）and tetra-needle zinc oxide whiskers（T-Zn Ow）,in TPU/HVSSBR composites were explored,and the TEM results showed that Si O₂was more selectively dispersed in the HVSSBR rubber phase,while T-Zn Ow had a more uniform dispersion in both phases.On this basis,the friction properties and mechanism of this composite on different surfaces（rough dry,smooth wet and ice surface）with different filler systems were studied.It was found that the dry friction coefficient decreased with the increase of filler amount under the rough dry surface,in which the addition of Si O₂and T-Zn Ow decreased the dry friction coefficient by 13.9%and 20.2%,respectively;The addition of the two fillers improved the friction coefficients of the materials on smooth wet and ice surfaces,with the addition of T-Zn Ow being more effective,and its incorporation had a maximum enhancement of13.8%and 29.9%on the wet and ice friction coefficients,respectively.And the AFM and SEM characterization of the surface roughness and micromorphology of the materials showed that the nano-filler increased the surface microscopic roughness of the material and was more likely to destroy the water film at the interface,thus it had the greatest effect on the friction performance in aqueous media.Combined with the tribological theory analysis,it is concluded that the friction mechanism of the filler-filled composites in different environments is derived from the combined effect of adhesion friction and hysteresis friction.