Tribological evaluation of thermoplastic polyurethane-based bearing materials under water lubrication:Effect of load,sliding speed,and temperature

Polymers are widely used in bearing applications.In the case of water-lubricated stern tube bearings,thermoplastic polyurethane(TPU)-based composites are used due to their excellent wear resistance,corrosion resistance,and tunable mechanical properties.Their tribological performance,however,depends on operating conditions.In this work,TPU was blended with carbon fiber,graphene platelet,and ultra-high molecular weight polyethylene(UHMWPE).Friction tests of TPU based-composites against copper countersurface were carried out in water to mimic the actual operating conditions of the bearing.Most of the resulting contacts were in the boundary lubrication regime,in which friction was attributed to both contact mechanics of asperities as well as water lubrication.Our results show that the viscoelasticity of TPU has a considerable impact on its tribological performance.Water lubrication at 50°C promotes the softening of polymer surface material during sliding,resulting in higher fluctuation in the coefficient of friction and wear loss.This is attributed to the reduced thermomechanical properties.In addition,Schallamach waviness is observed on worn surface.The tribological properties of TPU are significantly improved by the inclusion of carbon fiber,graphene platelet,and UHMWPE.The formation of graphene transfer-layers and UHMWPE transfer film reduces friction and wear loss,while the inclusion of carbon fiber enhances wear resistance due to improved mechanical properties and load bearing capacity.

Polyurethane-polysiloxane Copolymer Compatibilized SiR/TPU TPV with Comfortable Human Touch Toward Wearable Devices

Because of its softness,wear resistance,biocompatibility,extremely comfortable human touch,thermoplastic vulcanizate(TPV)comprised of silicone rubber(SiR)and thermoplastic polyurethane(TPU)(SiR/TPU TPV)is especially suitable for wearable intelligent devices.Nevertheless,developing good compatibilizer is still required to prepare high performance SiR/TPU TPV.In this study,three kinds of polyurethane-polysiloxane copolymer(PU-co-PSi)with different contents of polysiloxane segment were selected,and their compatibilization effect on SiR/TPU blends was studied using nanomechanical mapping technique of AFM.The results show that using PU-co-PSi with the highest content of polysiloxane segment(PU-co-HPSi),the interface thickness largely increases,and the average size of SiR dispersed phase largely decreases,indicating its good compatibilization effect.By using PU-co-HPSi as compatibilizer,SiR/TPU TPV with a fine SiR dispersed phase and good mechanical performance were successfully prepared.The mechanism on the compatibilization effect of these PU-co-PSi on SiR/TPU TPVs was revealed.

Preparation and 3D printing of high-thermal-conductivity continuous mesophase-pitch-based carbon fiber/epoxy composites

To meet the requirements of spacecraft for the thermal conductivity of resins and solve the problem of low thermal conduction efficiency when 3D printing complex parts,we propose a new type of continuous mesophase-pitch-based carbon fiber/thermoplastic polyurethane/epoxy(CMPCF/TPU/epoxy)composite filament and its preparation process in this study.The composite filament is based on the high thermal conductivity of CMPCF,the high elasticity of TPU,and the high-temperature resistance of epoxy.The tensile strength and thermal conductivity of the CMPCF/TPU/epoxy composite filament were tested.The CMPCF/TPU/epoxy composites are formed by 3D printing technology,and the composite filament is laid according to the direction of heat conduction so that the printed part can meet the needs of directional heat conduction.The experimental results show that the thermal conductivity of the printed sample is 40.549 W/(m·K),which is 160 times that of pure epoxy resin(0.254 W/(m·K)).It is also approximately 13 times better than that of polyacrylonitrile carbon fiber/epoxy(PAN-CF/epoxy)composites.This study breaks through the technical bottleneck of poor printability of CMPCF.It provides a new method for achieving directional thermal conductivity printing,which is important for the development of complex high-performance thermal conductivity products.