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Article

Synergistic Enhancement Effect of Polytetrafluoroethylene and WSe2 on the Tribological Performance of Polyetherimide Composites

by
Fulin Tu
,
Bin Wang
,
Simo Zhao
,
Mingrui Liu
,
Jiangye Zheng
,
Zewen Li
,
Chengyang Hu
,
Tao Jiang
and
Qunchao Zhang
*
Key Laboratory for the Green Preparation and Application of Functional Materials, Hubei Key Laboratory of Polymer Materials, School of Materials Science and Engineering, Hubei University, Wuhan 430062, China
*
Author to whom correspondence should be addressed.
Lubricants 2025, 13(2), 44; https://doi.org/10.3390/lubricants13020044
Submission received: 20 December 2024 / Revised: 17 January 2025 / Accepted: 20 January 2025 / Published: 22 January 2025
Browse Figures
Versions Notes

Abstract

:
To address the issue of high wear of polymer composites during friction, WSe2 nanofillers were incorporated into the polymer matrix as a reinforcing phase to enhance heat transfer and improve the composites’ wear resistance. Tannic acid (TA) was grafted onto the surface of WSe2 through high-energy ball milling, which facilitated the exfoliation of the nanofillers and improved their interfacial compatibility with the matrix material. Tribological experiments revealed that adding 5 wt% TA-WSe2 reduced the friction coefficient and volumetric wear rate to 0.0065 and 8.7 × 10−4 μm3/N·m, respectively, representing reductions of 98% and 94% compared to pure PEI. The TA-WSe2 not only served as a reinforcing phase to enhance heat transfer but also facilitated the timely dissipation of heat generated during friction. Additionally, it formed strong interfacial bonds with both PEI and PTFE, allowing the applied load to be efficiently distributed throughout the composite material. This study offers a practical approach for the functionalization of WSe2 and the development of ternary composite materials for tribological applications.

1. Introduction

Friction and wear are fundamental tribological phenomena that significantly influence the efficiency, reliability, and durability of mechanical systems [1,2]. High friction leads to increased energy loss and heat generation, while excessive wear causes material degradation and reduces the lifespan of components. These challenges are particularly pronounced in demanding environments such as aerospace, automotive, and industrial machinery, where systems often operate under extreme conditions of high temperature, pressure, or load [3,4]. Traditional materials, including metals and polymers, often exhibit insufficient tribological performance in such environments, with issues like poor wear resistance, high friction coefficients, and thermal instability [5]. As a result, improving the tribological properties of materials has become a pressing priority. Recent research has increasingly focused on developing advanced composite materials, which integrate reinforcing fillers into polymer matrices [6]. This approach not only enhances load-bearing capacity and wear resistance but also offers opportunities for tailoring materials to meet specific operational requirements, paving the way for breakthroughs in tribological performance.
Building upon these challenges, polyetherimide (PEI) emerges as a promising material due to its exceptional combination of properties [7,8]. PEI is a high-performance engineering thermoplastic known for its superior mechanical strength, high thermal stability, excellent chemical resistance, and reliable electrical insulation. With its elevated glass transition temperature, PEI is ideal for demanding engineering applications, such as aerospace shuttles, high-speed aircraft, and automotive components, where both strength and temperature resistance are critical [9,10]. Additionally, PEI exhibits remarkable tribological and corrosion-resistant characteristics, making it suitable for components like ship bearings [11], oil lubrication systems [12], and low-temperature friction applications [13]. However, despite its numerous advantages, PEI exhibits limitations in tribological performance, particularly in terms of friction reduction and wear resistance under severe operating conditions.
To further enhance the tribological performance of PEI in harsh environments, incorporating stiff fillers into the PEI matrix presents a straightforward and effective strategy [14]. These fillers include binary or ternary doping materials such as natural fibers (hemp, jute, and flax fibers) [15], metallic fillers (copper, graphite, and aluminum) [16], ceramic fillers (silica, zirconia, and alumina) [17], and organic fillers (polytetrafluoroethylene, carbon black) [18]. Nanofillers, with their high aspect ratio and large surface area, exhibit excellent heat transfer properties in composites [19,20]. They significantly enhance the tribological performance of polymers by improving load-bearing capacity, preventing subsurface cracks, and lubricating sliding interfaces [21,22]. For instance, Zhang et al. reported that adding 10 vol% short carbon fiber (SCF) markedly improved the anti-wear and anti-friction properties of PEI in oil-lubricated environments, enabling the composites to withstand higher PV values due to increased load-bearing capacity [23]. Li et al. further enhanced interfacial adhesion by coating SCF with hydroxylated boron nitride (BNO) and PEI, achieving improvements in bending strength (60.8%), interlaminar shear strength (49.3%), and thermal conductivity (14.5%) [24]. Similarly, Liu et al. demonstrated that decorating reduced graphene oxide with polyethylenimine (PEI-rGO) reduced friction coefficient by 54.6% and wear rate by 45.0%, highlighting the potential of functional nanofillers in improving tribological properties of PEI [25]. However, the fillers help improve its mechanical strength and tribological properties but may not fully address issues like friction reduction or lubrication, which are vital for specific applications.
Currently, research has concentrated more on multicomponent composites, wherein lightweight polymers can augment friction performance while nanofillers serve as reinforcing agents to counterbalance the decrease in strength [26,27]. PTFE is well-known for its self-lubricating properties and low friction coefficient, making it a key material for reducing friction in various systems [28]. However, its limited mechanical strength and wear resistance necessitate the use of reinforcing fillers. Tungsten selenide (WSe2), a transition metal dichalcogenide (TMD), with its unique lamellar structure and exceptional thermal stability, offers significant improvements in wear resistance and load-bearing capacity, especially under extreme conditions [29]. By combining these materials with PEI, which is known for its high thermal stability and mechanical strength, a synergistic effect can be achieved, resulting in a composite that exhibits enhanced frictional and wear properties. The incorporation of PTFE and WSe2 into the PEI matrix offers the potential for overcoming the limitations of individual components, creating a composite with superior tribological performance, which can meet the demands of high-load, high-temperature applications. However, it is a great challenge to prepare the polymers and fillers with a homogeneous distribution and to regulate the exact doping ratio.
In this work, PEI (polyetherimide) composites synergistically modified with polymer and transition metal materials were prepared by grafting tannic acid (TA) onto the surface of WSe2 using high-energy ball milling and ternary blending with PTFE and PEI. The presence of -NH3 groups in PEI enables the formation of hydrogen bonds with the -OH groups in TA, resulting in strong interfacial adhesion between the nanoparticles and the polymer matrix. Subsequently, the effects of adding PTFE and WSe2 on the frictional and mechanical properties of the composite system were investigated, and the wear resistance mechanism of the composite material was analyzed. The results showed that adding 5 wt% TA-WSe2 reduced the friction coefficient and volumetric wear rate to 0.0065 and 8.7 × 10−4 μm3/N·m, respectively, representing reductions of 98% and 94% compared to pure PEI showed low COF, better wear resistance, and higher load carrying capacity.

2. Materials and Method

2.1. Materials

Tannic acid (TA, ACS grade) was purchased from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). WSe2 powder (99.99% metals basis) with an average diameter of 5.886 μm, was provided by Mackling Biochemical Technology Co., Ltd. (Shanghai, China). Polyetherimide (PEI, Grade 1000) was acquired from Sabic Research & Development Co., Ltd., (Shanghai, China). Polytetrafluoroethylene (PTFE, KT-600M) was obtained from Kitamura Co., Ltd. (Aichi, Japan).

2.2. Preparing of Hydroxylation WSe2

WSe2 modified with tannic acid was prepared using the mechanochemical exfoliation method. Generally, 10 WSe2 and 20 gTA were loaded into a 250 mL stainless steel tank with zirconia balls. Then, the mixture was ground in a planetary ball mill (XQM-4, Tiankang Powder Company, Hunan, China) at a fixed speed of 600 rpm for 10 h. Finally, the as-prepared powder was washed several times with deionized water and ethanol to remove free TA and dried in a lyophilizer (ST-10N-60A, SAN TI YI QI Company, Sha dong, China). The synthesis process of the composite materials is shown in Figure 1.

2.3. Preparation of PEI Composites

Table 1 shows the composite materials and their ratios prepared in this study. PEI (grade 1000), PTFE (KT-600M), and TA-WSe2 were blended into the mixer according to the proportion in the table. The processing was carried out at 360°, with a speed of 60 rpm and a mixing time of 8 to 10 min. Close observation of torque changes was highly required during the processing. Then, the mixture was prepared into sheets.

2.4. Characterizations

2.4.1. Structural Characterization

The morphology of WSe2 and TA-WSe2 was observed by ultra-high resolution field emission scanning electron microscopy (SEM, Thermo Fisher Verios 5 UC, Waltham, MA, USA) and high-resolution field emission transmission electron microscopy (TEM, JEOL JEM-F200, Tokyo, Japan). The surface elements were recorded using energy dispersive X-ray spectroscopy (EDX, JXA-IHP200F, Tokyo, Japan) and X-ray photoelectron spectroscopy (XPS, Thermo Fisher Escalab Xi+, Waltham, MA, USA). High-resolution X-ray diffraction (XRD, Bruker, Karlsruhe, Germany) was performed using Cu Kα scanning from 2° to 60° to obtain the crystal structure of nanosheets. A laser particle size analyzer (LPSA, BT-9300S, Liaoning, China) was selected to characterize the size of WSe2 and TA-WSe2 nanosheets. Laser Raman spectroscopy analyzer (Raman, LabRAM Soleil, Kyoto, Japan), adopting 532 nm laser, provided the structure of WSe2, TA-WSe2.

2.4.2. Thermal and Mechanical Performance Characterization

The crystallization and melting behaviors of the PEI composites were measured by a diffraction scanning calorimeter (DSC, Netzsch DSC-204, Selby, Germany) from 0 °C to 300 °C, with a ramping rate of 10 °C/min. The thermal stability of WSe2, TA-WSe2, PEI, PTFE was characterized by thermogravimetric analysis (TG, Discovery TGA 55, New Catle, DE, USA), with a heating rate of 10 °C/min from 25 °C to 850 °C in nitrogen atmosphere. The dynamical mechanical properties of the composites were tested on a dynamical mechanical analyzer (DMA, Netzsch DMA-214, Selby, Germany). The tensile properties of the PEI composites were assessed using an Instron 5566 universal testing machine (Boston, MA, USA) at a constant crosshead speed of 50 mm/min, with rectangular specimens measuring 3 mm × 1 mm × 30 mm.

2.5. Tribological Behavior Test

The tribological characterization was carried out using a Rtec rotary friction testing machine (MFT-5000, Rtec, San Jose, CA, USA). Based on the ball-on-disk model (Figure 2), reciprocating experiments were conducted at room temperature. Low-carbon bearing steel balls (Gcr15, diameter = 10 mm) were used under dry friction conditions, with a sliding frequency of 5 Hz for 20 min. A white light interferometer (Contour GT-X, Bruker, Karlsruhe, Germany) was chosen to analyze the wear amount of the wear trajectory after friction testing. Before the trial, all samples were polished with waterproof grinding paper to obtain Ra ≤ 0.1 μm.

3. Results and Discussion

3.1. Characterization of WSe2, TA-WSe2

Figure 3a shows the morphology of WSe2, with a smooth surface exhibiting typical TMDs material structure. After grafting TA and ball milling, it was clearly observed that the surface in Figure 3c had become coarse. Due to the high surface polarity, it brought about small nanoparticles aggregation and accumulation. TEM and EDX Mapping further provided the microstructure and element distribution, where W and Se elements could be observed to be almost uniformly distributed throughout the entire region. The presence of the O element proved, from another perspective, that TA was grafted onto the surface. X-ray photoelectron spectroscopy (XPS) for WSe2 and TA-WSe2 performed component analysis. Comparing the full spectrum (Figure 3i), the O 1s orbital peak appeared at 533 eV, as derived from TA. In the Se 3d orbital map, 3d3/2 and 3d5/2 were fitted at 55.14 eV and 56.02 eV [30], while in Figure 3l. There were two prominent peaks at 32.8 eV and 35.1 eV, belonging to the 4f5/2 and 4f7/2 orbitals of WSe2 [31,32]. The above results confirm that TA-WSe2 was successfully prepared.
The Raman spectrum of WSe2 and TA-WSe2 nanopowder is shown in Figure 4a. The main peak of WSe2 can be observed at 245 cm−1, which is consistent with literature [33]. However, after ball milling, peeling, and surface modification, new peaks appeared at 715 cm−1 and 807 cm−1, which undoubtedly belonged to -OH in tannic acid [34]. It was also found that the main peak position of TA-WSe2 had shifted. That is because WSe2 nanopowder is a layered material. After being stripped by high-energy ball milling, the distance between the layers increased. Under the irradiation of a raman laser, the peak position shifted due to the change in crystal structure (defects or voids). Meanwhile, due to TA grafting on the surface of WSe2, the surface stress and band structure of the crystal surface were altered. Therefore, under the synergistic effect of peeling and grafting, the raman spectrum underwent a shift [35,36]. It can be seen from Figure 4b that the size of the nano powder after ball milling exhibited a minor sign (WSe2 D50 = 5.886 μm, TA-WSe2 D50 = 0.782 μm). Based on the reduction in grain size, according to the Debye–Scheler formula (D = Kλ/βCOSθ), it is known that the diffraction peak undergoes broadening, which can be verified from the XRD pattern (Figure 4c) [37]. When the temperature was raised from room temperature under N2 atmosphere, thethermal performance of WSe2 and TA-WSe2 was observed. Pure WSe2 begins to decompose at 200 °C, which includes the disintegration of crystals and surface groups. From the TGA curves (Figure 4d), it can be seen that the char residues at 800 °C of WSe2, TA-WSe2, and TA are 88 wt%, 95 wt%, and 1 wt%, respectively.

3.2. Thermo and Mechanical Properties of PEI Composites

The effect of the inclusion of the hybrid on the thermal behavior of nanocomposites was detected by DSC, as shown in Figure 5. By comparing the glass transition temperature, it can be seen that the Tg of nanocomposites gradually transitions towards higher temperature. The thermal conductivity of WSe2 is much higher than that of PEI. Thus, the introduction of PTFE and TA–WSe2 hybrid can bear partial heat dissipation to improve the thermal stability of composite materials, which helps to prevent molecular chain movement in nanocomposites during friction and maintain the stability of the matrix [38].
Figure 6a,b show the TGA and DTG curves of PEI composites with different nanofiller contents. From the graph, it can be seen that, compared to the temperature at 5% decomposition, the composite material with 5% addition increased from 527.8 °C to 530.3 °C compared to pure PEI. In addition, with the increase in PTFE and TA–WSe2 hybrid material content, the carbon residue at 700 °C shows a trend of first increasing and then stabilizing. This is because PTFE and TA-WSe2 mixtures are very stable throughout the entire temperature range and can serve as insulation layers for composite materials to delay polymer thermal decomposition [39]. When the addition amount exceeds 7%, the thermal insulation effect of the nanofiller reaches saturation under high temperature.
Dynamic mechanical analysis (DMA) testing was conducted on PEIPEI/PTFE-WSe2 composite materials in the temperature range of 25–300 °C. During the dynamic stress oscillation process at a frequency of 1 Hz, the storage modulus (E′) and loss factor (tanδ) were measured, and results are shown in Figure 7. From Figure 7a, it can be seen that as the temperature increased, while the storage modulus of all samples shows a decreasing trend. Comparing samples 1# and 2#, it was found that there was a slight decreased after the addition of 10% PTFE. Obviously, -F and vinyl groups forming PTFE molecular branches could move more flexibly at high temperatures, unlike PEI with the benzene ring. Therefore, the molecular structure became slightly softer, resulting in a decrease in storage modulus. Then, after adding the rigid nanofiller WSe2, the storage modulus of PEI/PTFE-WSe2 composite materials increased, which can be attributed to the reinforcement effect of the filler [40]. Among them, samples 3# and 7# showed higher enhancement effects and later reached saturation. Figure 7b presents the tan δ of all samples, revealing a pronounced peak between 200 °C and 250 °C. Samples 3# and 7# exhibited higher peak values, correlating with their elevated storage modulus. As shown in Figure 7b, all samples exhibited high loss factors, which can be attributed to the rigid benzene ring structure of PEI. This structure facilitates energy dissipation through internal friction rather than effective deformation under cyclic loading. The incorporation of rigid WSe2 nanofillers enhances the hardness of the matrix material, thereby restricting segment relaxation at elevated temperatures. However, the TA grafted onto the surface of WSe2 melts at high temperatures, enabling the formation of hydrogen bonds between the melted TA and the PEI/PTFE matrix. This interaction significantly improves interfacial adhesion between WSe2 and the PEI/PTFE matrix, thereby markedly enhancing the mechanical properties of the composite materials [41].
The tensile properties of PEI/PTFE-WSe2 composites are presented in Figure 7c,d. Among the tested samples, 1# exhibited the highest tensile strength (85.06 MPa) and elongation at break (11.73%), suggesting superior toughness. As the WSe2 content increased, a gradual enhancement in the tensile properties of the composites was observed, with 4# achieving the highest tensile strength (59.67 MPa). This improvement can be attributed to the increased content of TA polymer chains, which facilitated stronger interfacial interactions between the filler and the matrix [42]. The typical tensile stress versus strain curves in Figure 7d corroborated the tensile strength data presented in Figure 7c. All samples displayed a characteristic brittle fracture behavior. As a rigid engineering plastic, pure PEI exhibited approximately 30% higher tensile strength compared to the modified composites. This disparity can be attributed to crystallinity alterations in the composites induced by the incorporation of fillers [43]. However, the reinforcing effect of WSe2 was insufficient to compensate for the inherent mechanical differences between PEI and PTFE, resulting in the observed brittle fracture behavior in all samples.

3.3. Tribological Properties of PEI Composites

Figure 8 presents the tribological properties of PEI/PTFE-WSe2 composites under dry friction conditions at a load of 15 N for 20 min. Sample 1# exhibited significantly higher coefficient of friction (COF, 0.31) and wear rate (1.58 × 10−3 μm3/N·m) compared to the other samples. Comparing samples with the same content (3#, 4# and 8#, 9#), it was found that the composite material COF and wear rate were lower after TA modification, which is consistent with the results observed in SEM earlier. Smaller-sized fillers can be uniformly dispersed in the matrix material, and the polymer long chains grafted on its surface can generate stronger interfacial adhesion, thus exhibiting superior tribological properties after TA modification [44]. The COF and wear rate of the composites decreased progressively with the increasing PTFE and WSe2 content, indicating enhanced lubrication performance. The incorporation of WSe2 contributed to improved load-bearing capacity, reducing frictional stress at the interface. However, further increase in the filler content led to a deterioration in tribological performance due to the agglomeration of fillers within the matrix [45]. Non-uniform stress distribution caused by agglomeration resulted in localized wear and increased debris generation, leading to surface damage [46]. Notably, sample 5#, containing 5 wt% TA-WSe2, exhibited the lowest COF (0.0065) and volume wear rate (8.7 × 10−4 μm3/N·m), representing 98% and 94% reductions, respectively, compared to pure PEI. This indicates that 5 wt% TA-WSe2 can significantly improve lubrication performance.
The surface morphology of the composite material was examined after friction testing using scanning electron microscopy, focusing on four distinct samples to evaluate various wear mechanisms (samples 1#, 2#, 5#, and 9#). Figure 9a–h illustrate the morphology of the worn surfaces of the composite material and the corresponding steel balls. As shown in Figure 9a, significant wear scars are evident on the sliding surface of pure PEI. Large aggregates of debris and numerous wrinkles were observed on the surface of the steel ball (Figure 9b). This phenomenon is attributed to the adhesive forces between PEI and the steel ball, which induce surface deformation. Under reciprocating motion, debris is continuously generated and accumulates, progressively eroding the surface. At this stage, the predominant wear mode for PEI is adhesive wear. The addition of 10% PTFE improved the surface wear of the composite material (Figure 9c), however, it still exhibited typical polymer wear characteristics, with wrinkles remaining on the surface of the steel ball (Figure 9d–1), indicating ongoing adhesive wear. The incorporation of nanofillers led to smoother worn surfaces and lighter wear marks, accompanied by minimal debris (Figure 9e,g), indicating the presence of abrasive wear. Comparative analysis of the wear patterns on the steel balls reveals that the more uniform dispersion of 5 wt% TA-WSe2 within the PEI/PTFE matrix results in a smoother wear surface, with no observable wrinkles or grooves. The EDX elemental mapping image of the wear surface (Figure 9i) further confirms the uniform distribution of N, O, F, and Se on the surface, substantiating the formation of a transfer film containing these elements, which significantly enhances the friction performance of the composite material. Conversely, grooves were observed on the steel ball with 2 wt% WSe2. This can be attributed to the inadequate ball milling of WSe2, which prevents its uniform distribution within the PEI/PTFE matrix and leads to poor dispersibility, resulting in restacking within the composite material. Additionally, the interfacial adhesion between WSe2 and the PEI/PTFE matrix is weak, hindering effective load transfer and resulting in stress concentration.
The surface morphology of wear marks on PEI composite materials is presented in Figure 10a–d (pure PEI, PEI/PTFE, PEI/PTFE/5 wt% TA-WSe2, PEI/PTFE/WSe2, respectively). Under the load of 15N, pure PEI exhibits the greatest wear depth, with significant accumulation of debris at both ends of the wear track. The surface roughness (Sa = 1181.09 nm) is relatively high, contributing to the most severe wear. The incorporation of 5 wt% TA-WSe2 reduces the surface roughness to 284.9 μm, leading to uniform wear marks and preventing debris accumulation on the surface. This improvement is attributed to the reinforcing effect of nanofillers, which enhances the hardness and mechanical properties of the PEI/PTFE composites. Consequently, the wear volume and depth of the material are reduced to some extent. However, increasing the filler content may lead to deeper wear, as excessive filler tends to aggregate within the matrix, reducing the crystallinity and toughness of the material, ultimately making it more susceptible to wear under heavy loads [47].
Therefore, as shown in Figure 11, the potential wear mechanisms of these four different materials can be summarized as follows. (1) Polymer composites composed solely of PEI and PTFE are susceptible to surface deformation under load, generating significant amounts of debris. As this accumulated debris progressively erodes the surface, the wear mechanisms may include abrasive wear, adhesive wear, and fatigue wear. (2) The addition of WSe2 enhances the rigidity of the composite material; however, the defects associated with nanofillers impede effective load transfer, resulting in the primary wear modes being abrasive wear and adhesive wear. (3) Following high-energy ball milling and surface modification of TA, WSe2 demonstrates good dispersibility within the PEI/PTFE matrix, allowing for uniform stress distribution across the composite surface and stronger interfacial bonding between the filler and matrix. This results in superior tribological properties, with abrasive wear being the predominant wear mechanism.

4. Conclusions

In this study, WSe2 nanofillers were exfoliated using high-energy ball milling, and TA was grafted onto their surfaces to obtain functionalized TA-WSe2. SEM results indicated that the surface of the TA-WSe2 nanofillers became rougher after modification. XPS elemental analysis revealed the presence of O elements. Moreover, the Raman spectra exhibited peaks at 715 cm−1 and 807 cm−1, corresponding to the -OH groups in TA, indicating the successful grafting of TA onto WSe2. Analysis of thermal performance revealed that increasing the content of TA-WSe2 enhanced both the thermal conductivity and heat resistance of the composite material. Dynamic mechanical analysis (DMA) and tensile tests indicate that TA-WSe2 effectively matches the rigid polyetherimide (PEI) structure, resulting in stronger interfacial bonding and improved toughness of the composite material. Tribological testing demonstrated that the addition of 10 wt% PTFE to the PEI composite resulted in a COF of 0.063 and a volume wear rate of 2.3 × 10−4 μm3/N·m, representing reductions of 80% and 85% compared to pure PEI, respectively. Based on these results, the addition of 5 wt% TA-WSe2 resulted in the lowest COF of 0.0065 and volume wear rate of 8.7 × 10−4 μm3/N·m, corresponding to reductions of 98% and 94%, respectively. Finally, white light and SEM were utilized to simulate and survey 3D wear surfaces, enabling the analysis of potential wear mechanisms across different composite materials. This work offers a viable approach to functionalizing WSe2 and utilizing ternary composite materials for tribological applications.

Author Contributions

Methodology, F.T.; Software, B.W. and J.Z.; Formal analysis, F.T.; Investigation, S.Z., M.L., J.Z., Z.L. and C.H.; Resources, Q.Z.; Data curation, F.T., B.W. and M.L.; Writing—original draft, F.T.; Writing—review & editing, F.T.; Supervision, T.J. and Q.Z.; Funding acquisition, Q.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Science and Technology Department of Hubei Province (202311301203007).

Data Availability Statement

The data will be made available on request from the author.

Conflicts of Interest

The author declares no conflicts of interest.

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Figure 1. Preparation route of the PEI composite materials.
Figure 1. Preparation route of the PEI composite materials.
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Figure 2. Ball-on-disk model.
Figure 2. Ball-on-disk model.
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Figure 3. SEM images of (a,b) WSe2; (c,d) TA-WSe2; (e) TEM images of (e) TA-WSe2; (f–h) EDX mapping images of TA-WSe2. (i) Wide scan survey XPS spectra of WSe2 and TA-WSe2; (j–l) O 1s, W 4f, and Se 3d of TA-WSe2.
Figure 3. SEM images of (a,b) WSe2; (c,d) TA-WSe2; (e) TEM images of (e) TA-WSe2; (f–h) EDX mapping images of TA-WSe2. (i) Wide scan survey XPS spectra of WSe2 and TA-WSe2; (j–l) O 1s, W 4f, and Se 3d of TA-WSe2.
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Figure 4. (a) Raman spectra of WSe2 and TA-WSe2; (b) particle size distribution of WSe2 and TA-WSe2; (c) XRD patterns of WSe2 and TA-WSe2; (d) TG curves of WSe2 and TA-WSe2.
Figure 4. (a) Raman spectra of WSe2 and TA-WSe2; (b) particle size distribution of WSe2 and TA-WSe2; (c) XRD patterns of WSe2 and TA-WSe2; (d) TG curves of WSe2 and TA-WSe2.
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Figure 5. DSC melting curve for PEI composites.
Figure 5. DSC melting curve for PEI composites.
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Figure 6. (a) TGA (b) DTG curves for PEI composites.
Figure 6. (a) TGA (b) DTG curves for PEI composites.
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Figure 7. Dynamic mechanical analysis (DMA) of pristine PEI and the PEI/PTFE-WSe2 composite materials: (a) storage modulus and (b) loss factor. (c,d) Tensile properties of PEI and PEI/PTFE-WSe2 composite materials.
Figure 7. Dynamic mechanical analysis (DMA) of pristine PEI and the PEI/PTFE-WSe2 composite materials: (a) storage modulus and (b) loss factor. (c,d) Tensile properties of PEI and PEI/PTFE-WSe2 composite materials.
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Figure 8. (a) Dynamic friction coefficient curves and (b) tribological properties of PEI/PTFE-WSe2 composites materials.
Figure 8. (a) Dynamic friction coefficient curves and (b) tribological properties of PEI/PTFE-WSe2 composites materials.
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Figure 9. SEM images of topology of worn surfaces of composites and steel balls; (a,b) pure PEI, (c,d) PEI/PTFE, (e,f) PEI/PTFE/5 wt% TA-WSe2, and (g,h) PEI/PTFE/2 wt% WSe2; (i) EDX mapping images of the worn surfaces of PEI/PTFE/5 wt% TA-WSe2.
Figure 9. SEM images of topology of worn surfaces of composites and steel balls; (a,b) pure PEI, (c,d) PEI/PTFE, (e,f) PEI/PTFE/5 wt% TA-WSe2, and (g,h) PEI/PTFE/2 wt% WSe2; (i) EDX mapping images of the worn surfaces of PEI/PTFE/5 wt% TA-WSe2.
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Figure 10. (a) 3D morphologies of the worn surface and the corresponding 2D height profile curves of (a,a1) pure PEI, (b,b1) PEI/PTFE, (c,c1) PEI/PTFE/5 wt% TA-WSe2, and (d,d1) PEI/PTFE/WSe2.
Figure 10. (a) 3D morphologies of the worn surface and the corresponding 2D height profile curves of (a,a1) pure PEI, (b,b1) PEI/PTFE, (c,c1) PEI/PTFE/5 wt% TA-WSe2, and (d,d1) PEI/PTFE/WSe2.
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Figure 11. Schematic diagram of lubrication mechanism of PEI composite materials of (a) PEI/PTFE, (b) PEI/PTFE/2 wt% WSe2, and (c) PEI/PTFE/5 wt% TA-WSe2.
Figure 11. Schematic diagram of lubrication mechanism of PEI composite materials of (a) PEI/PTFE, (b) PEI/PTFE/2 wt% WSe2, and (c) PEI/PTFE/5 wt% TA-WSe2.
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Table 1. The composition of composite materials.
Table 1. The composition of composite materials.
SamplesCodePEI (g)PTFE (g)Pristine WSe2 (g)TA-WSe2 (g)
1#PEI50------
2#PEI + 10%PTFE455----
3#PEI + 10%PTFE + 1%TA-WSe244.55--0.5
4#PEI + 10%PTFE + 3%TA-WSe243.55--1.5
5#PEI + 10%PTFE + 5%TA-WSe242.55--2.5
6#PEI + 10%PTFE + 7%TA-WSe241.55--3.5
7#PEI + 10%PTFE + 10%TA-WSe2405--5
8#PEI + 10%PTFE + 1%WSe244.550.5--
9#PEI + 10%PTFE + 3%WSe243.551.5--
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MDPI and ACS Style

Tu, F.; Wang, B.; Zhao, S.; Liu, M.; Zheng, J.; Li, Z.; Hu, C.; Jiang, T.; Zhang, Q. Synergistic Enhancement Effect of Polytetrafluoroethylene and WSe2 on the Tribological Performance of Polyetherimide Composites. Lubricants 2025, 13, 44. https://doi.org/10.3390/lubricants13020044

AMA Style

Tu F, Wang B, Zhao S, Liu M, Zheng J, Li Z, Hu C, Jiang T, Zhang Q. Synergistic Enhancement Effect of Polytetrafluoroethylene and WSe2 on the Tribological Performance of Polyetherimide Composites. Lubricants. 2025; 13(2):44. https://doi.org/10.3390/lubricants13020044

Chicago/Turabian Style

Tu, Fulin, Bin Wang, Simo Zhao, Mingrui Liu, Jiangye Zheng, Zewen Li, Chengyang Hu, Tao Jiang, and Qunchao Zhang. 2025. "Synergistic Enhancement Effect of Polytetrafluoroethylene and WSe2 on the Tribological Performance of Polyetherimide Composites" Lubricants 13, no. 2: 44. https://doi.org/10.3390/lubricants13020044

APA Style

Tu, F., Wang, B., Zhao, S., Liu, M., Zheng, J., Li, Z., Hu, C., Jiang, T., & Zhang, Q. (2025). Synergistic Enhancement Effect of Polytetrafluoroethylene and WSe2 on the Tribological Performance of Polyetherimide Composites. Lubricants, 13(2), 44. https://doi.org/10.3390/lubricants13020044

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