Yuanshi Xin

Modified Graphene/Polyimide Nanocomposites: Reinforcing and Tribological Effects

By taking advantage of design and construction of strong graphene-matrix interfaces, we have prepared modified graphene/polyimide (MG/PI) nanocomposites via a two-stage process consisting of (a) surface modification of graphene and (b) in situ polymerization. The 2 wt % MG/PI nanocomposites exhibited a 20-fold increase in wear resistance and a 12% reduction in friction coefficient, constituting a potential breakthrough for future tribological application. Simultaneously, MG also enhanced thermal stability, electrical conductivity, and mechanical properties, including tensile strength, Youngs modulus, storage modulus, and microhardness. Excellent thermal stability and compatibility of interface, strong covalent adhesion interaction and mechanical interlocking at the interface, as well as homogeneous and oriented dispersion of MG were achieved here, contributing to the enhanced properties observed here. The superior wear resistance is ascribed to (a) tribological effect of MG, including suppression effect of MG in the generation of wear debris and protective effect of MG against the friction force, and (b) the increase in mechanical properties. In light of the relatively low cost and the unique properties of graphene, the results of this study highlight a pathway to expand the engineering applications of graphene and solve wear-related mechanical failures of polymer parts.

Preparation and utility of a self-lubricating & anti-wear graphene oxide/nano-polytetrafluoroethylene hybrid

We design a feasible approach to prepare a self-lubricating and anti-wear graphene oxide/nano-polytetrafluoroethylene (GO/nano-PTFE, abbreviated GNF) hybrid additive by chemical compounding as a novel nano-solid lubricant. This proposal is to overcome the high friction coefficient of GO/polymer specimens for further increase in wear resistance. To explore the utility of GNF, it was incorporated into polyimide (PI) and epoxy (EP) matrices to yield GNF/PI and GNF/EP composites. The tribological properties and mechanism of GNF/polymer composites were investigated in detail. A nearly 60% reduction in friction coefficient and more than two orders of magnitude reduction in wear rate were obtained in both GNF/PI and GNF/EP composites with only 1 wt% GNF addition. Compared with unfilled polymers or polymers with individual fillers, the major increase in tribological properties of the GNF/polymer composites shows the synergy effect between nano-PTFE and GO. The increased tribological properties can be ascribed to four aspects: homogeneous GNF dispersion and strong interface, the increased mechanical properties, transfer film and tribological effect (protective effect and suppression effect) of GNF. It is demonstrated that this approach provides a novel self-lubricating and anti-wear nano-solid lubricant that greatly reduces wear and material loss.

Preparation and tribological properties of graphene oxide/nano-MoS2 hybrid as multidimensional assembly used in the polyimide nanocomposites

A three-step strategy was employed to prepare a self-lubricating and anti-wear graphene oxide/nano-MoS2 (GO/nano-MoS2, abbreviated GMS) hybrid by chemical compounding as a novel multidimensional assembly. This development aims to overcome the high friction coefficient of GO/polymer composites and to explore the variations in the tribological properties stemming from the different nanoparticles immobilized on the GO surface. The as-prepared GMS was incorporated into a polyimide (PI) matrix to yield GMS/PI composites by in situ polymerization. The mechanical, thermodynamic, surface, and tribological properties of the GMS/PI composites were investigated, and the synergistic effects of the abovementioned properties between nano-MoS2 and GO were discussed in detail. A homogeneous dispersion of GMS, a suppressive and protective effect of graphene sheets, a rolling friction effect of the detached nano-MoS2 particles, and a transfer film composed of MoS2 were achieved herein, contributing to the enhanced tribological properties. The differences in the enhancement effects of nanohybrids can be mainly attributed to two aspects: the intrinsic characteristics of the assembled nanoparticles and the combinational structure of the multidimensional assemblies.

Study on the Tribological Properties of Carbon Fabric/Polyimide Composites Filled with SiC Nanoparticles

ABSTRACT Carbon fabric reinforced thermoplastic polyimide composites have significant applications in the field of tribology. However, there are relatively few studies that have been focused on the investigation of these materials. In the present study, carbon fabric/polyimide (CF/PI) composites, reinforced further with SiC nanoparticles, were prepared by dip-coating and hot press molding methods. Rockwell hardness and flexural testing of the composites were conducted. The friction and wear behavior of the resulting carbon fabric composites were evaluated in a ring-on-block contact mode under dry sliding condition. The results showed that the SiC nanoparticles significantly improved the hardness and flexural strength when compared to the CF/PI composites without the SiC additions. The CF/PI composites reinforced with 5 vol% SiC nanoparticles demonstrated the most beneficial mechanical and tribological properties compared to the composites with greater and lesser SiC nanoparticles. Scanning electron microscopy (SEM) and optical microscopy (OM) were employed in order to study the mechanism of tribological behavior. A continuous and thin transfer film formed during the friction test of the composites led to a significant improvement of the tribological properties.

Fabrication and multifunctional properties of polyimide based hierarchical composites with in situ grown carbon nanotubes

Polyimide (PI) based hierarchical composites reinforced with carbon nanotubes (CNTs) directly grown on the surface of carbon fabric were prepared. The growth morphology and other characteristics of the CNTs were analyzed by detailed techniques, which proved the growth of CNTs on the surface of carbon fiber (CF). The CNT–CF/PI composites with a growth time of 40 min showed an increase of 33% in flexural strength, 42% in flexural modulus, 17 °C in the temperature at 5 wt% of weight loss, 27 °C in glass transition temperature and five orders of magnitude in through-thickness electrical conductivity as compared to those of conventional carbon fabric reinforced polyimide composites. The significant improvement of the comprehensive properties of the hierarchical composites can be attributed to the stiffer CNTs-reinforced matrix, the enhanced fiber–matrix interfacial adhesion and/or the strong synergetic effect between the nano and micro-scale fillers. The enhancement mechanism of the hierarchical composites on various different scales was also discussed in detail. It is believed that the present study can provide broad application potential in polyimide-based polymer composites and other types of high performance thermoplastic systems.

Multidimensional structure and enhancement performance of modified graphene/carbon nanotube assemblies in tribological properties of polyimide nanocomposites

Modified graphene/carbon nanotube (abbreviated GCNT) assemblies were prepared by chemical compounding from amino-functionalized graphene (abbreviated MG) and carboxyl-functionalized multi-walled carbon nanotube (abbreviated MCNT). Diverse hybrid structures, such as graphene-shelled CNT microspheres, graphene/CNT interlayers and CNT-coated graphene nanosheets, have been obtained by adjusting the reaction ratio of the two precursor particles. The as-prepared GCNTs were incorporated into polyimide (PI) matrix to yield GCNT/PI composites by in situ polymerization. The mechanical, thermo-mechanical and tribological properties of GCNT/PI composites were investigated and synergistic effects in terms of lubrication and wear resistance have been acquired. The friction coefficient and wear rate decreased by 29.3% and 75.8%, respectively, with only 0.5 wt% addition of GCNT14 (WMG/WMCNT = 1 : 4), compared to virgin PI. The results indicate that combinational structure of multidimensional assemblies has a great influence on the enhancement performance and tribological mechanism of nanocomposites.