The study is focused on multifunctional performance of carbon nanotubes (CNT) and Graphene nanoplatelets (GNP) reinforced PEEK composites enabled via fused filament fabrication (FFF) additive manufacturing (AM) utilizing in-house nanoengineered filaments. Thermo-physical, mechanical and wear characteristics of electro-conductive PEEK nanocomposites are reported. The coefficient of thermal expansion (CTE) is found to decrease by 26% and 18% with the incorporation of 5 wt% GNP and 3 wt% CNT into PEEK polymer, respectively. The decrease in CTE provides better dimensional stability to resulting nanocomposite structures. Due to uniform dispersion of CNT and GNP in the PEEK matrix, the crystallization temperature and degree of crystallinity are both increased. The 3D printed PEEK nanocomposites reveal interfacial voids between the beads and intra-bead pores and thus exhibit lower density compared to that of the 3D printed neat PEEK. Young's and storage moduli are found to increase by 20% and 66% for 3 wt% CNT loading and by 23% and 72% for 5 wt% GNP loading respectively. However, the PEEK nanocomposites exhibit similar tensile strength to that of neat PEEK. The coefficient of friction obtained from fretting wear tests is found to decrease by 67% and 56% for 1 wt% CNT and 3 wt% GNP loaded PEEK nanocomposites, respectively and the decrease is attributed to reduced hardness and increased porosity. Multifunctional performance of carbon nanostructures reinforced AM-enabled PEEK composites demonstrated here makes them suitable for a range of applications such as orthopedics, oil and gas, automotive, electronics and space.

Multifunctional performance of carbon nanotubes and graphene nanoplatelets reinforced PEEK composites enabled via FFF additive manufacturing

Due to the extraordinary thermal stability, chemical resistance and processability, carbon fiber (CF) reinforced polyetheretherketone (PEEK) composites are widely applied in aviation, aerospace, medical fields, etc. However, the non-polar nature and low wettability of CFs limited the interfacial bonding between CFs and PEEK and results in unsatisfied mechanical properties for CF/PEEK composites. In order to enhance interactions between fibers and matrix, the interface in CF/PEEK composites was built through coating a mixture of polyetherimide (PEI) and functionalized multi-walled carbon nanotubes (COOH-MWCNTs) on CFs. The combination of hydrogen bonding between COOH-MWCNT and PEI as well as the π-π interaction between PEI and PEEK significantly improved the miscibility and interfacial interlocking. As a result, the flexural strength, modulus and interlaminar shear strength (ILSS) of modified CF/PEEK were remarkably improved by 76% (667.8 MPa), 119% (40.0 GPa), and 85% (90.7 MPa) respectively. The failure mechanism changed from smooth cracking in interface destruction to zigzag cracking and resin breakage, suggesting that the resultant interface became strong enough to ensure efficient stress transfer from PEEK to CF. The synergistic interfacial interactions via hydrogen bonding and pi-pi stacking are believed to supply an effective strategy for building high-performance thermoplastic composites.

Synergistic effect of hydrogen bonding and π-π stacking in interface of CF/PEEK composites

Reducing friction and increasing lubrication are the goals that every tribologist pursues. Accordingly, layered graphene materials have attracted great research interest in tribology due to their anti-friction, anti-wear and excellent self-lubricating properties. However, recent studies have found that other forms of graphene derivatives not only perform better in tribological and lubricating applications, but also solve the problem of graphene being prone to agglomeration. Based on a large number of reports, herein, we review the research progress on graphene derivatives and their nanocomposites in tribology and lubrication. In the introduction, the topic of the article is introduced by highlighting the hazards and economic losses caused by frictional wear and the excellent performance of graphene materials in the field of lubrication. Then, by studying the classification of graphene materials, the research status of their applications in tribology and lubrication is introduced. The second chapter introduces the application of graphene derivatives in improving tribological properties. The main types of graphene are graphene oxide (GO), doped graphene (doped elements such as nitrogen, boron, phosphorus, and fluorine), graphene-based films, and graphene-based fibers. The third chapter summarizes the application of graphene-based nanocomposites in improving friction and anti-wear and lubrication properties. According to the different functional modifiers, they can be divided into three categories: graphene–inorganic nanocomposites (sulfides, metal oxides, nitrides, metal nanoparticles, and carbon-containing inorganic nanoparticles), graphene–organic nanocomposites (alkylation, amine functionalization, ionic liquids, and surface modifiers), and graphene–polymer nanocomposites (carbon chain polymers and heterochain polymers). Graphene not only exhibits an excellent performance in traditional processing and lubrication applications, but the fourth chapter proves that it has a good application prospect in the field of ultra-low friction and superlubricity. In the application part of the fifth chapter, the lubrication mechanism proposed by graphene as a nano-lubricant is introduced first; then, the main application research status is summarized, including micro-tribology applications, bio-tribology applications, and liquid lubrication additive applications. The last part is based on the following contents. Firstly, the advantages of graphene-based nanocomposites as lubricants and their current shortcomings are summarized. The challenges and prospects of the commercial applications of graphene-based nanocomposites in tribology and lubrication are further described.

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Application of graphene derivatives and their nanocomposites in tribology and lubrication: a review

The effective role of Lithium Titanate (Li4Ti5O12) filled in Poly (vinylidene fluoride)/Poly (n-vinyl carbazole) (PVDF/PVK) (80/20 wt/wt%) blend matrix was demonstrated. PVDF/PVK/Li4Ti5O12 nanocomposite films with ratios 0.2, 0.5, 1.5, and 2.0 wt% of Li4Ti5O12 NPs have been successfully synthesized via casting technique. Structural, optical, and electrical properties of the prepared PVDF/PVK/Li4Ti5O12 films have been evaluated via several techniques such as; XRD, FTIR-ATR, UV–vis and A.C. conductivity. The XRD and FTIR-ATR results confirmed the interaction between the PVDF/PVK blend and Li4Ti5O12 NPs. Also, the increasing of ratios of lithium titanate NPs decreased the degree of crystallinity of PVDF/PVK blend. UV–vis data obtain that there are two new peaks at 348 nm and 380 nm and their intensities increase with increasing lithium titanate NPs. The behavior of dielectric constant and dielectric loss are progressively decreased as the frequency increased. The values of AC conductivity are increased as the ratios of Li4Ti5O12 NPs in the PVDF/PVK blend matrix increased. AC conductivity results of PVDF/PVK/Li4Ti5O12 blend confirm the ability of this nanocomposite in Rechargeable Batteries Applications.

The role of Li4Ti5O12 nanoparticles on enhancement the performance of PVDF/PVK blend for lithium-ion batteries

Polymer nanocomposites with enhanced performances are becoming a trend in the current research field, overcoming the limitations of bulk polymer and meeting the demands of market and society in tribological applications. Polytetrafluoroethylene, poly(ether ether ketone) and ultrahigh molecular weight polyethylene are the most popular polymers in recent research on tribology. Current work comprehensively reviews recent advancements of polymer nanocomposites in tribology. The influence of different types of nanofiller, such as carbon-based nanofiller, silicon-based nanofiller, metal oxide nanofiller and hybrid nanofiller, on the tribological performance of thermoplastic and thermoset nanocomposites is discussed. Since the tribological properties of polymer nanocomposites are not intrinsic but are dependent on sliding conditions, direct comparison between different types of nanofiller or the same nanofiller of different morphologies and structures is not feasible. Friction and wear rate are normalized to indicate relative improvement by different fillers. Emphasis is given to the effect of nanofiller content and surface modification of nanofillers on friction, wear resistance, wear mechanism and transfer film formation of its nanocomposites. Limitations from the previous works are addressed and future research on tribology of polymer nanocomposites is proposed.

Effect of Nanofillers on Tribological Properties of Polymer Nanocomposites: A Review on Recent Development.

http://digital.csic.es/bitstream/10261/171257/1/2019%20Carbon%20Postprint.pdf

Tribological and mechanical properties of graphene nanoplatelet/PEEK composites

PEEK has been implemented in various orthopaedic applications due to its many beneficial mechanical, tribological, and radiolucent properties. These properties can be further tailored by introducing fillers into the PEEK matrix. In this work, graphene has been incorporated due to its high mechanical resistance, intrinsic stiffness, and lubricating properties [2].

M. Castro

Papers

Tribological and mechanical properties of graphene nanoplatelet/PEEK composites

Tribological Behavior and Mechanical Properties of Graphene/PEEK Composites