SiO 2 ‐covered graphene oxide nanohybrids for in situ preparation of UHMWPE/GO(SiO 2 ) nanocomposites with superior mechanical and tribological properties

Effects of Silicon Dioxide/Graphene Oxide Hybrid Modification on Curing Kinetics of Epoxy Resin

In this study, SiO₂-grafted graphene oxide (GO-SiO₂) was prepared using the oxygen-containing group on the GO surface as the active site of the reaction. The chemical structure, morphology, and particle size of GO and GO-SiO₂ were carefully investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, thermogravimetry, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy, and the results proved that the grafting modification was successful. Furthermore, epoxy (EP)/GO composites were prepared, and the effects of unmodified GO and GO-SiO₂ on the curing kinetics of EP were comparatively studied by differential scanning calorimetry (DSC). The results showed that, compared with neat EP and EP/GO, GO-SiO₂ significantly reduces the curing temperature of the composites, indicating that GO-SiO₂ has a more significant catalytic effect on the curing process of EP. The calculation results of the Kissinger method showed that the curing activation energy of EP/GO-SiO₂ is obviously lower than that of EP/GO and neat EP. Results of the Ozawa method showed that the introduction of GO-SiO₂ reduces the curing activation energy during the whole curing process, and in the middle and late stages of curing (α = 0.5-1) can significantly reduce the curing activation energy. The related mechanism has been proposed.

Crystallization and Melting Behavior of UHMWPE Composites Filled by Different Carbon Materials

In order to understand the effect of different carbon materials on the crystallization and melting behavior of ultrahigh molecular weight polyethylene (UHMWPE), UHMWPE composites were prepared by different carbon materials through solution mixing in this paper. UHMWPE was oxidized to improve the interfacial interaction between UHMWPE and carbon materials. The UHMWPE composites and oxidized UHMWPE composites were prepared using granular graphite particle (GP), graphite nanoplatelets (GNP), and flaky graphene oxide (GO) as fillers. The effect of the type and the content of carbon materials and the oxidization of UHMWPE on crystallization and melting temperatures, crystallinity, and crystal form of UHMWPE and oxidized UHMWPE composites was investigated by differential scanning calorimetry, X-ray diffraction, scanning electron microscope, X-ray photoelectron spectrum, and Fourier transform infrared spectroscopy. The results indicated that there are coexistence of the heterogeneous nucleation and the hindering effect of crystal growth by carbon materials for UHMWPE crystallization. The different influence of carbon materials on the crystallization and melting behavior of UHMWPE was discussed by the heterogeneous nucleation of carbon materials and the restriction of the macromolecular chain motion of UHMWPE by carbon materials.

Amino-Functionalized MXene Nanosheets Doped with Ce(III) as Potent Nanocontainers toward Self-Healing Epoxy Nanocomposite Coating for Corrosion Protection of Mild Steel

MXene sheets, as new 2D nanomaterials, have been used in many advanced applications due to their superior thin-layered architecture, as well as their capability to be employed as novel nanocontainers for advanced applications. In this research, intercalated Ti₃C₂ MXene sheets were synthesized through an etching method, and then they were modified with 3-aminopropyltriethoxysilane (APTES). Cerium cations (Ce³⁺) as an eco-friendly corrosion inhibitor were encapsulated within Ti₃C₂ MXene sheets to fabricate novel self-healing epoxy nanocomposite coatings. The corrosion protection performance (CPP) of Ce³⁺-doped Ti₃C₂ MXene nanosheets (Ti₃C₂ MXene-Ce³⁺) in a 3.5 wt % sodium chloride (NaCl) solution was studied on bare mild steel substrates using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. The self-healing CPP of epoxy coatings loaded with 1 wt % undoped and doped Ti₃C₂ MXene was evaluated using EIS, salt spray, and field emission scanning electron microscopy (FE-SEM) techniques. The introduction of Ti₃C₂ MXene-Ce³⁺ into the corrosive solution and artificially scribed epoxy coating enhanced the total impedance from 717 to 6596 Ω cm² and 8876 to 32092 Ω cm², respectively, after 24 h of immersion compared to the control samples.

Thermal Degradation Kinetics and Modeling Study of Ultra High Molecular Weight Polyethylene (UHMWP)/Graphene Nanocomposite

The incorporation of nanofillers such as graphene into polymers has shown significant improvements in mechanical characteristics, thermal stability, and conductivity of resulting polymeric nanocomposites. To this aim, the influence of incorporation of graphene nanosheets into ultra-high molecular weight polyethylene (UHMWPE) on the thermal behavior and degradation kinetics of UHMWPE/graphene nanocomposites was investigated. Scanning electron microscopy (SEM) analysis revealed that graphene nanosheets were uniformly spread throughout the UHMWPE’s molecular chains. X-Ray Diffraction (XRD) data posited that the morphology of dispersed graphene sheets in UHMWPE was exfoliated. Non-isothermal differential scanning calorimetry (DSC) studies identified a more pronounced increase in melting temperatures and latent heat of fusions in nanocomposites compared to UHMWPE at lower concentrations of graphene. Thermogravimetric analysis (TGA) and derivative thermogravimetric (DTG) revealed that UHMWPE’s thermal stability has been improved via incorporating graphene nanosheets. Further, degradation kinetics of neat polymer and nanocomposites have been modeled using equations such as Friedman, Ozawa–Flynn–Wall (OFW), Kissinger, and Augis and Bennett’s. The "Model-Fitting Method” showed that the auto-catalytic nth-order mechanism provided a highly consistent and appropriate fit to describe the degradation mechanism of UHMWPE and its graphene nanocomposites. In addition, the calculated activation energy (E_a) of thermal degradation was enhanced by an increase in graphene concentration up to 2.1 wt.%, followed by a decrease in higher graphene content.

Influence of processing conditions on microstructural, mechanical and tribological properties of graphene nanoplatelet reinforced UHMWPE

Ultra-high molecular weight polyethylene (UHMWPE) is a relevant thermoplastic in industry and a well-proven standard biomaterial in joint replacements. To enhance its tribological properties while preserving its bulk ones, composite coatings on a UHMWPE substrate were prepared using non-functionalised graphene nanoplatelet (GNP) at reinforcement concentration of 0.1-5 wt% and two mechanical mixing techniques (ball mill or blade mixer) with different consolidation temperatures of 175-240 °C. Changes in morphology and size of the UHMWPE particles before hot-pressing were observed in function of the mechanical mixing techniques applied. Wear rate was affected by graphene content, reaching a minimum at 0.5 wt% GNP, with a reduction of 20 and 15%, for ball milling and blade mixer, respectively. However, blade mixer increased the wear rate by around twice respect the ball milling results, for all the studied materials. The coefficient of friction decreased notably, by ~25%, below 3 wt% GNP content, and hardness increased by 24%, regardless of the mechanical mixing process used. Finally, consolidation temperature had a positive influence on wear rate at temperatures of around 195 °C, which could be related to the free radical scavenger effect of the GNP.