Combined effects of interface modification and micro-filler reinforcements on the thermal and tribological performances of fabric composites

The high specific-strength of glass fibers and exceptional self-lubrication of polytetrafluoroethylene (PTFE) fibers promote the potential application of hybrid PTFE/glass fabric composites in the tribological field, but their weak interfacial adhesion and inferior thermal properties significantly inhibit their tribological performance and reliability. Herein, a hybrid of polydopamine/silicon carbide/polyethyleneimine (PDA/SiC/PEI) functional coating was co-deposited onto the hybrid PTFE/glass fabric surface through a one-step impregnation method, leading to increased surface roughness and abundant amine groups. Tensile and peeling tests showed that this functional coating offered 47.8% enhancement in the fabric/matrix interfacial adhesion without compromising the strength of the pristine fabric. Moreover, the additional incorporation of WS2, and aluminum nitride (AlN) micro-fillers contributed to the development of a high-quality tribofilm and improved the thermal properties of fabric composites. The results of wear tests proved that the hybrid-fabric composites, after the introduction of functional coating and micro-fillers, exhibited outstanding tribological performance, which was attributed to the superior interfacial adhesion as well as the synergistic enhancement effects between WS2 and AlN micro-fillers.


Introduction
Fiber reinforced polymer (FRP) composites have attracted considerable attention in land vehicles, wind turbine blades, and aircraft because of their low-density, high specific strength/stiffness, outstanding fatigue/ corrosion resistance, and excellent designability [1][2][3][4][5][6]. Hybrid-fabric composites are FRP composites with a unique weaving structure that allows them to integrate the unique performance advantages of different fibers to attain preferable and/or innovative properties [7,8].
In particular, because of their well-known lubricating properties, polytetrafluoroethylene (PTFE) fibers, have emerged as excellent candidates to be blended with other high-performance reinforced fibers including glass fibers, carbon fibers, and aramid fibers for constructing self-lubricating liner material. Over the past years, our research group has carried out numerous related research studies on the tribological performance of the hybrid-fabric composite's design and considerable progress has been made [9][10][11]. Nevertheless, the weak interfacial adhesion between the fibers and the matrix, due to the low surface energy characteristics and smooth surfaces of PTFE and reinforced fibers, remains a limiting factor in the improvement of the overall properties of the resulting fabric composites [12][13][14]. In addition, the poor thermal properties of most polymer matrices suggest that they cannot dissipate friction heat efficiently and provide effective carrying capacity at the sliding interfaces, further inhibiting their performance and reliability [15,16].
Generally, in order to improve the interfacial adhesion strength between fibers and the polymer matrix of these composites to obtain satisfactory mechanical properties, most treatment methods aim to increase the fiber surface roughness and/or introduce specific functional groups in that are compatible with the polymer matrix. Based on by this, various surface modification techniques, including chemical vapor deposition (CVD), electrophoretic deposition (EPD), plasma etching, high-energy irradiation, chemical grafting, and polymeric sizing have been reported to change the surface structure and morphology of the fibers [17][18][19][20][21][22][23]. Modifications to the fiber surfaces can significantly improve the mechanical performance of FRP composites; however, maintaining the strength properties of the pristine fibers is still a major challenge. More importantly, these methods are not universally applicable and are largely restricted by the surface properties of the substrates. Therefore, developing an effective and versatile strategy for the surface modification of diverse materials has become a priority. Recently, mussel-inspired surface chemistry has gained attention owing to its versatility, simplicity, and widespread application [24][25][26]. Among these bio-based strategies for surface modification and functionalization, the polydopamine/polyethyleneimine (PDA/PEI) combinations exhibit a higher amine density, surface energy, and stability than combinations of pure polydopamine (PDA) and other non-covalent PDA co-deposited coatings [14, 27,28]. Additionally, considering that the PDA/PEI can be co-deposited onto virtually all types of inorganic and organic materials and build functional coatings on their surfaces, nanomaterials and even micronmaterials can be introduced into the PDA/PEI reaction system and then simultaneously co-deposited with PDA/PEI onto fiber surfaces. The organic-inorganic hybrid functional coatings on fiber surfaces endow fibers with increased surface roughness and active functional groups, which enhance the interfacial adhesion properties of FRP composites. Furthermore, the entire co-deposition process takes place under mild reaction conditions and therefore does not significantly compromise the mechanical strength of the fibers.
In addition, to effectively solve the thermal dissipation problems at the sliding interface and to promote the load-carrying capability of FRP composites, a variety of micro-fillers have been incorporated to construct a heat conductive network in the matrix and to tailor the formation of a robust and uniform tribo-film on the counterface. Routinely, highly intrinsic thermally conductive fillers, such as aluminum nitrides (AlN), boron nitride (BN), carbon nanotubes (CNTs), and graphene oxide (GO), are incorporated into the polymer matrix to address the heat removal issues of composites [29][30][31]. Meanwhile, it has been noted that the introduction of solid lubricants, for example, graphite, graphitic carbon nitride (g-C 3 N 4 ), MoS 2 , and WS 2 , into the polymer matrix contributes to the formation of solid lubricant tribofilms on the counterface owing to their layered structures [32][33][34]. Based on these by the above considerations, it is expected that the combination of thermally conductive fillers and solid lubricants can generate a synergetic effect hence improving the tribological performance of polymer composites.
To the best of our knowledge, there have been few studies investigating the effects of interface modification and microfiller reinforcement on the tribological behaviors of FRP composites. Herein, we develop a facile and scalable technique to improve the interfacial adhesion between hybrid PTFE/glass fabric and a phenolic resin matrix by co-depositing PDA/PEI with silicon carbide (SiC) nanoparticles onto fabric surfaces. Meanwhile, both the AlN and WS 2 micro-fillers were added to the hybrid-fabric composites to enhance the thermal properties and to contribute to the formation of a solid lubricant tribofilm. The surface microstructure and constitution of the SiC-coated hybrid fabric were analyzed. The mechanical and thermal performances of hybrid-fabric composites with SiC nanoparticles interfacial modification and AlN, WS 2 micro-filler reinforcements were also investigated. The tribological characteristics and internal wear mechanism of pristine and modified hybrid-fabric composites are discussed.

Reagents and materials
The hybrid PTFE/glass fabric (satin weave structure, V PTFE :V glass = 3:1, area density of 420 g/m 2 ) was composed of low-friction PTFE fibers (DuPont Plant, USA) and high-strength glass fibers (Nanjing Fiberglass Research & Design Institute). A phenolic resin (resol) adhesive was obtained from Xing-Guang Chemical Reagent Plant. Dopamine hydrochloride (DA) and polyethylenimine (PEI, Mw = 600 Da) were purchased from Sigma-Aldrich and Meryer Chemical Tech. Co. Ltd., respectively. SiC (99.9%, 40 nm) nanoparticles were provided by Meryer Chemical Tech. Co. Ltd. AlN (99.5%, 2.0 μm) and WS 2 (99.9%, 2.0 μm) microfillers were supplied by Aladdin Biochemical Tech. Co. Ltd. The morphologies and spectra of the micro-fillers are shown in Fig. 1. All chemicals and solvents were used as received.

Preparation of SiC-coated hybrid PTFE/glass fabric
Prior to use, the hybrid PTFE/glass fabric was desized using petroleum ether and ethanol sequentially in a Soxhlet extractor and then dried at 50 °C. The surface modification of the hybrid fabric with SiC nanoparticles was performed using a one-step method based on dopamine chemistry, that is, co-deposition of DA, PEI, and SiC nanoparticles onto the hybrid PTFE/glass fabric. Typically, DA hydrochloride, PEI, and SiC nanoparticles were dissolved or dispersed in a Tris buffer solution (pH = 8.5, 20 mM) with a mass ratio of 2 : 2 : X (0.5, 1, 2) by intense ultrasonic treatment for 30 min. The concentrations of DA and PEI were fixed at 2 mg·mL −1 in the solution, whereas the concentration of SiC nanoparticles was set to 0.5, 1, and 2 mg·mL −1 , respectively. The hybrid PTFE/glass fabric was subsequently immersed in the freshly prepared solution and gently stirred for 6 h at the ambient temperature. The resulting fabric sample, denoted as SiC@hybrid-fabric, was rinsed thoroughly with deionized water and dried overnight. Moreover, SiC@hybrid-fabrics with different concentrations of SiC nanoparticles (denoted as SiC@fabric-0.5, SiC@fabric-1, and SiC@fabric-2) were observed, and the optimal concentration conditions were confirmed. In addition, the SiC@hybrid-fabric was termed SiC@fabric-1 in the following text unless otherwise specified.

Fabrication of hybrid fabric/phenolic composites
The phenolic resin adhesive was first diluted with the mixed solvent (V acetone : V ethanol : V ethyl acetate = 1:1:1). The pre-calculated amounts of WS 2 (2 wt%), AlN (2 wt%), and mixed WS 2 -AlN (1 wt%-1 wt%) micro-fillers were dispersed evenly in the phenolic resin solution by magnetic stirring and ultrasonic treatment to achieve a good dispersion of the fillers. Afterwards, the SiC@hybrid-fabric was immersed into the abovementioned micro-fillers/phenolic resin adhesive solution. Repetitive immersion and drying of the hybrid PTFE/glass fabrics was performed until the weight fraction of the hybrid-fabrics reached 72% in the composites. The drying process was carried out at 50 °C for 10 min to remove the mixed solvent. Subsequently, the obtained prepregs were affixed onto the AISI-1045 steel disks using phenolic resin as an adhesive and then solidified at 180 °C for 2 h under 0.2 MPa. Moreover, pristine hybrid-fabric and SiC@hybrid-fabric composites were also prepared by a similar procedure in the absence of microfiller reinforcements to perform a control experiment. The typical preparation process of SiC@fabric/WS 2 -AlN composites is illustrated in Fig. 2.

Characterization of SiC@hybrid PTFE/glass fabric
Similar to the commonly known "bio-glue", PDA can deposit onto nearly all types of substrate surfaces, including smooth and chemically inert materials, and shows great potential for surface modification (Fig. S3 in the Electronic Supplementary Material (ESM)). Despite this, individual PDA deposition would generally lead to a rough coating resulting from the non-covalent stacking of large PDA aggregated particles [35]. Therefore, this method is still limited by inhomogeneous roughness, poor stability, inadequate surface wettability, and slow deposition rate. Thus, dopamine-assisted co-deposition strategies have attracted wide attention, because the surface properties of functional coatings can be easily adjusted by altering the molecular structure and content of co-deposited components. Therefore, the incorporation of polyethyleneimine (PEI) can efficiently destroy the non-covalent interactions of the PDA aggregated particles and accelerate the deposition process by Michael addition and Schiff-based reactions [36]. The resulting coating adheres to the substrate by electrostatic attractions, π-π stacking, and hydrogen bonding.
In addition, inorganic nanomaterials can further be incorporated into the PDA/PEI co-deposition solution to design hybrid functional coatings, to combine the merits of inorganic nanomaterials and PDA/PEI copolymer coating as well as to generate synergistic effects between them. In this study, a PDA/SiC/PEI coating was co-deposited onto the hybrid PTFE/glass fabric surfaces to construct an organic-inorganic hybrid functional coating with different amounts of SiC nanoparticles. A recognized reaction mechanism is schematically presented in Fig. 3. The surface morphologies of the pristine and modified glass and PTFE fibers characterized by field emission scanning electron microscopy (FESEM) are shown in Fig. 4. Clearly, it can be seen that the pristine glass and PTFE fiber surfaces are relatively neat and smooth, except for a few shallow striations along the fiber axis (Figs. 4(a) and 4(e)). In contrast, remarkable differences in the surfaces between the modified and pristine glass and PTFE fibers can be observed.    The insets are the corresponding magnified images. SEM and TEM images of SiC (i, j) and SiC-PDA/PEI nanoparticles (l, k). Scale bars: (a-d) 3 μm, (e-h) 6 μm, (i, l) 500 nm, (j, k) 100 nm, and Agreeing strongly with this modification the insets of (a-h) 2μm.
hybrid PTFE/glass fabric. The surfaces of the SiC@glass and SiC@PTFE fibers with 1 mg·mL −1 SiC nanoparticles exhibited uniform and dense nanoparticle arrangement (as shown in Figs. 4(c) and 4(g)). However, as the concentration of SiC nanoparticles increased to 2 mg·mL −1 , the surface particles of the hybrid PTFE/ glass fabric showed significant aggregation and agglomeration suggesting that the SiC nanoparticles existing in the dopamine/PEI reaction system at this concentration also present the corresponding aggregation (as shown in Figs. 4(d) and 4(h)). The corresponding overall morphologies of the pristine and modified fibers are shown in Fig. S4 in the ESM. Moreover, in order to further examine the morphological features of SiC nanoparticles coated on hybrid PTFE/ glass fabric surfaces, additional SEM and TEM characterization of SiC nanoparticles dispersed in the dopamine/PEI reaction solution without hybrid-fabric under the same conditions are shown in Figs. 4(k) and 4(l). It can be seen that the SiC nanoparticles are enwrapped uniformly by an ultrathin co-deposited coating. These results indicate that an organic-inorganic hybrid functional coating is co-deposited successfully onto the hybrid PTFE/glass fabric surfaces by this one-step method, and the amount of deposition can be regulated by varying the SiC nanoparticle concentration.
The surface chemical structure changes of SiC nanoparticles and hybrid PTFE/glass fabric are characterized by Fourier transform infrared spectroscopy (FTIR) spectra, as illustrated in Figs. 5(a) and 5(b). The virgin SiC nanoparticles have characteristic peaks at 1,085 and 890 cm −1 assigned to the Si-O and Si-C stretching vibrations, respectively. New peaks arising at 3,240 cm −1 and 1,440 cm −1 after the PDA/PEI co-deposition process can be ascribed to the N-H and C-N stretching vibrations in the PDA/PEI coating. Furthermore, the presence of a broad peak at 1,600 cm −1 illustrates the stretching of aromatic rings. In the spectra of the pristine hybrid PTFE/glass fabric, the signals at 1,200, 1,140, and 634 cm −1 are associated with CF 2 stretching and rocking vibrations. In contrast, the SiC@hybrid-fabric exhibits a broader absorption peak at approximately 3,345 cm −1 , assigned to resonance vibration of NH 2 groups derived from PEI. Additionally, the absorption peaks observed at 2,920 and 2,860 cm −1 represent the CH 2 stretching vibrations, and the peak at 890 cm −1 is associated with the stretching vibration  of Si-C. The XRD patterns of the hybrid PTFE/glass fabric before and after the co-deposition of the PDA/SiC/PEI coating are illustrated in Fig. 5(c). The diffraction peak appears at 18.0° assigned to the (100) crystalline plane of the PTFE fibers for the pristine hybrid PTFE/glass fabric. In the case of the SiC@hybridfabric, the new diffraction peaks at 35°, 60°, and 72° are assigned to the (111), (220), and (311) planes, respectively. Furthermore, thermogravimetric analysis was carried out in an oxygen atmosphere to ascertain the specific coating amount of SiC nanoparticles onto the hybrid-fabric surface (as shown in Fig. 5(d)). SiC nanoparticles and glass fibers have a high thermal stability with negligible mass loss up to 800 °C, whereas the PTFE fibers showed almost complete combustion at this temperature. Therefore, the SiC nanoparticle content on the hybrid-fabric surface could be determined from the residual weight at 800 °C. The residual weights for SiC@fabric-0.5, SiC@fabric-1, and SiC@fabric-2 at 800 °C were 17.3%, 19%, and 20.5%, respectively, attributed to the coating amount of SiC nanoparticles being 0.96%, 3.1%, and 5.03%, respectively.
XPS spectra were used to further examine the composition of the chemical elements and types of chemical bond of the hybrid PTFE/glass fabric and SiC nanoparticles, as shown in Fig. 6. The spectrum for the pristine glass fibers displays four peaks of Si 2p3/2, Si 2s, C 1s, and O 1s, whereas the new N 1s peak appears after the co-deposition of the PDA/ SiC/PEI hybrid coating ( Fig. 6(a)). In addition, the Si 2p3/2 peak in the SiC@glass fibers was resolved into Fig. 6 The survey scan spectra of (a) glass fibers, (d) PTFE fibers, and (g) SiC nanoparticles. The corresponding high-resolution Si 2p3/2 spectra of (b) pristine glass fibers and (c) SiC@glass fibers; the corresponding high-resolution C 1s spectra of (e) pristine PTFE fibers, (f) SiC@PTFE fibers, (h) virgin SiC nanoparticles, and (i) SiC-PDA/PEI nanoparticles. C-Si (100.6 eV) and SiO 2 (101.8 eV), compared to the single SiO 2 bond type in pristine glass fibers. This is consistent with the chemical characteristics of the hybrid functional coating (Figs. 6(b) and 6(c)). For the SiC@PTFE fibers, an additional peak at 400 eV ascribed to N 1s appeared and the C/F ratio increased from 0.85 for pristine PTFE fibers to 1.36 (Fig. 6(d)). Meanwhile, the C 1s peak of pristine PTFE fibers could be divided into five peaks of C-H (283.4 eV), C-C (284.8 eV), C-CF (286.5 eV), C-F (290.9 eV), and CF 3 (293.8 eV), while the new C-Si (282.9 eV), C-N (285.5 eV), and C-O (286.6 eV) bands present in the C 1s peak of SiC@PTFE fibers, suggesting the successful co-deposition of PDA/SiC/PEI functional coating onto the surface of the PTFE fibers (Figs. 6(e) and 6(f)). Moreover, the emerging N element and additional C-N (285.5 eV), and C=O (288 eV) bands in the C 1s peak of SiC-PDA/PEI confirm the presence of the PDA/PEI coating on the surface of SiC nanoparticles (Figs. 6(g-i)).

Mechanical and thermal properties of hybrid PTFE/glass fabric composites
As discussed above, the coated PDA/SiC/PEI layer introduced significant surface roughness and substantial amine functional groups for the hybrid PTFE/glass fabric and thus provided numerous reactive sites for interfacial adhesion. The mechanical properties of the hybrid PTFE/glass fabric and their composites were evaluated by tensile and peeling tests to determine the interfacial properties and tensile strength of the hybrid-fabric, as shown in Fig. 7. In the case of SiC@fabric composites, the bonding strength reaches up to 3.4 N/mm, presenting a 47.8% increment compared to that of pristine fabric composites (2.3 N/mm). This remarkable increase can be attributed to the physical and chemical influences resulting from the PDA/SiC/PEI hybrid functional coating. First, an increase in the surface roughness of the hybrid-fabric will increase the interfacial contact area for resin infiltration and mechanical interlocking [37,38]. On the other hand, the introduction of active functional groups onto the fabric surfaces allows the formation of chemical bonding between the fabric and resin matrix, thus leading to greatly improved interfacial adhesion [39]. Notably, the interfacial adhesion strength gradually decreases with a further increase in the SiC nanoparticle concentration, indicating that the agglomeration of SiC at the interphase degrades the interfacial adhesion of the fabric composites (Fig. S5 in the ESM). Excessive SiC nanoparticles can induce a local stress concentration and decrease the energy dissipation. In addition, the narrow gap between SiC can restrict the afflux of resin to the hybrid-fabric surface and result in poor interfacial adhesion between the fabric and phenolic resin. Comparable bonding strength was observed for the SiC@fabric/WS 2 , SiC@fabric/AlN, and SiC@fabric/WS 2 -AlN composites, suggesting that the introduction of WS 2 , and AlN micro-fillers does not result in any discernible decrease in the interfacial adhesion of the fabric composites. Figure 7(b) shows the tensile strength results of pristine hybrid-fabric and SiC@hybrid-fabric are 400 and 380 N, respectively. It was found that the one-step co-deposition process does not cause serious degradation in the tensile strength of the hybrid PTFE/glass fabric, | https://mc03.manuscriptcentral.com/friction due to the mild treatment conditions. The change in bonding strength is closely related to the interfacial failure mode of fabric composites. Figure 8 depicts the surface morphology of the resin matrix after debonding from the reinforced fabric in the weft direction. Apparently, for the pristine fabric composites, it can be seen that the cambered surface of the phenolic resin is neat and regular implying that the debonding between the pristine fabric and resin matrix involves adhesive failure due to weak van der Waals forces. This phenomenon indicates that no resin fragments are attached to the fabric surface and the poor interfacial adhesion of pristine fabric composites. In contrast, the fracture surfaces of SiC@hybrid-fabric composites appear to become rough and abundant plastic dimples have emerged, suggesting the shift in the failure mode from adhesive failure involving fabric/matrix interfacial debonding to cohesive failure of the interphase. Meanwhile, the trace on the cambered surfaces of resin matrix from SiC@fabric/WS 2 , SiC@fabric/AlN, and SiC@fabric/ WS 2 -AlN composites are not regular, consistent with the results shown in Fig. 7(a).
Under dry sliding, the temperature of the contact surface increased due to the accumulation of frictional heat, leading to the degradation of mechanical properties of the material resulting in a higher wear rate and friction failure [40,41]. In consideration of the extreme temperature susceptibility of polymeric materials, thermal properties are therefore of great importance for the tribological performance of hybrid-fabric composites. The thermal stability of the pristine and modified hybrid PTFE/glass fabric composites was evaluated by TGA at a heating rate of 10 °C/min in air atmosphere. As seen in Fig. 9(a), all the samples displayed similar thermal degradation profiles within the temperature range, suggesting that the co-deposition of PDA/SiC/PEI functional coating and introduction of WS 2 , and AlN micro-fillers did not significantly alter the degradation mechanism of the fabric composites. The pristine hybrid-fabric composites produced approximately 10 wt% weight residue due to the remaining glass fibers when heated to 600 °C, whereas the modified hybrid-fabric composites exhibited a higher weight residual rate compared to that of the pristine fabric composites resulting from the introduction of SiC and AlN particles. From Table 1, it can be seen that both the T _ onset and T _ max of hybrid-fabric composites, after the introduction of the PDA/SiC/PEI functional coating, WS 2 , and AlN micro-fillers, showed different levels of growth, indicative of the improvement of thermal stability. Specifically, the interface interaction between the SiC@hybrid-fabric and phenolic resin matrix can increase the thermal degradation activation energy of SiC@fabric composites by confining the thermal motion of the resin chains, thus improving the thermal stability of the phenolic resin [42]. Meanwhile, the additional WS 2 and AlN micro-fillers with high aspect ratios and specific surface areas in resin matrices construct a tortuous path for the diffusion of gaseous decomposition products and impedes the permeation rate of oxygen, leading to further improvement in the thermal stability of hybrid-fabric composites [43,44]. Figure 9(c) shows the variations in the thermal conductivity (K) of the hybrid PTFE/glass fabric composites with increasing experimental temperature. Apparently, the K value of pristine hybrid-fabric composites is maintained at approximately 0.30 W/mK that does not present significant alteration within the experimental temperature range. Moreover, a significant improvement in the K value for the hybridfabric composites is observed with the co-deposition of hybrid functional coating and introduction of microfiller reinforcements. For instance, the K values of SiC@fabric, SiC@fabric/WS 2 , SiC@fabric/WS 2 -AlN, and SiC@fabric/AlN composites at 150 °C reached 0.324, 0.359, 0.371, and 0.394 W/mK, respectively, corres- Fig. 9 (a, b) TGA curves, (c) thermal conductivity, and (d) storage modulus of the pristine and modified hybrid PTFE/glass fabric composites.

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Friction 9(5): 1110-1126 (2021) | https://mc03.manuscriptcentral.com/friction ponding to 8%, 19.6%, 23.6%, and 31.3% increment, respectively, in comparison to pristine hybrid-fabric composites. For the SiC@fabric composites, it is suggested that the interfacial thermal resistance between the hybrid-fabric and resin matrix is reduced by the co-deposition of the PDA/SiC/PEI functional coating that contributes to increasing the thermal conductivity. In addition, the introduction of WS 2 and AlN microfillers into hybrid-fabric composites further enhances the K values that may be ascribed to the formation of additional thermally conductive pathways by bridging micro-fillers inside the resin matrix [45][46][47]. Meanwhile, the SiC@fabric/AlN composites present the highest K value, resulting mainly from the improvement of interfacial adhesion and high intrinsic thermal conductivity of the AlN micro-fillers.
For examining the effects of the interfacial modification and WS 2 -AlN micro-filler reinforcements on the storage modulus of the hybrid-fabric composites, the dynamic mechanical properties of the hybrid PTFE/glass fabric composites were measured by dynamic mechanical analysis (DMA), as shown in Fig. 9(d). It can be seen that the storage modulus of all hybrid-fabric composites decreases with increasing temperature. As the temperature increases, the components of the hybrid-fabric composites become much more mobile and start to move away from each other. Thus the stress transfer between the hybridfabric and resin matrix is heavily inhibited, resulting in a sharp decline in the storage modulus. Moreover, the storage modulus of the hybrid PTFE/glass fabric composites increased with the co-deposition of functional coating and introduction of micro-filler reinforcements. Specifically, the storage modulus at 30 °C was significantly enhanced from 600 MPa for the pristine fabric composites to 1,115 MPa for the SiC@fabric composites. This dramatic increase in the storage modulus indicates that the interfacial interactions between the SiC@hybrid-fabric and resin matrix are strong enough to ensure an effective load transfer to the hybrid-fabric, resulting in high mechanical strengths [48,49]. Moreover, the WS 2 -AlN micro-filler reinforcements within the resin matrix serve as the network centers to dissipate the local stress evenly and restrict the movements of the polymer chains, allowing a further increase in the stiffness of the hybrid PTFE/glass fabric composites.

Tribological properties of hybrid PTFE/glass fabric composites
The variations in the specific wear rates (K o ) and average friction coefficients (μ) of the pristine and modified fabric composites subjected to different loading conditions are shown in Fig. 10. Clearly, the K o and μ of all hybrid-fabric composites increase markedly with increasing applied loads from 50 to 65 MPa, suggesting changes in the dominant wear mechanisms. The increase in friction force is normally undesirable for polymeric materials that not only accelerates the abrasion of the materials but also leads to a high contact temperature resulting from the friction heat, and thus a heat-inducible mechanical failure of the material. Under low loading conditions, the abrasion process of the hybrid PTFE/glass fabric generally undergoes fiber thinning, fiber fracture, and removal of broken pieces sequentially. However, as the load increases, the breakage of the phenolic matrix occurs, especially at the fiber/matrix interfacial region; therefore, fiber bundles are cut off and pulled out more easily because of the lack of local support of the resin matrix. The resulting large fiber debris, especially the glass fiber debris, can further lower the abrasion resistance of the hybrid-fabric composites due to a third-body abrasive wear effect, resulting in the progressive increase of K o and μ. Nevertheless, it can be seen that a satisfactory improvement in the tribological properties is achieved after the interfacial modification and introduction of WS 2 -AlN micro-filler reinforcements under various applied loads. In the following sections, the wear mechanisms of hybridfabric composites are further investigated based on microscopic observations. In particular, the mechanisms for the positive effects of interfacial adhesion and micro-filler reinforcements on the tribological behaviors of hybrid-fabric composites are discussed in more detail. Figure 11 compares the worn surfaces of the pristine and modified hybrid-fabric composites under drysliding conditions. Pristine fabric composites have been recognized for their severely worn surfaces, including resin peel-off, fiber breakage, debonding, and pull-out (Figs. 11(a) and 11(e)). These phenomena show that the internal reinforcing fibers are directly involved in the friction process without effective protection from the phenolic resin matrix, which can be ascribed to the resin adhesive on the fabric surface peeled off easily due to poor interfacial adhesion and resin degradation. As a result, a large amount of wear debris exists in the sliding interface and is distributed on the steel surface, as evidenced by the counterface morphology (Figs. 12(a) and 12(e)), generating a thirdbody abrasive wear effect accelerating the abrasion of pristine fabric composites consistent with the higher K o and μ values, as shown in Fig. 10. In contrast, the debonding and pull-out wear mechanism of the reinforced fibers were significantly alleviated for the SiC@fabric composites. Although resin exfoliation and some broken PTFE fibers still occur on the abrasion surface, the interior glass fibers are wrapped tightly by the phenolic resin and the dominant wear mechanism changes from fiber pull-out to fiber thinning. The improved fiber/matrix interfacial adhesion facilitates | https://mc03.manuscriptcentral.com/friction the absorption of rupture energy and realizes an effective stress transfer between the reinforced fabric and resin matrix. Thus the breakage of the matrix at the interfacial regions is much more limited, and the hybrid PTFE/glass fabric is always removed gradually accounting for the improved load-carrying capacity and reduced K o [50]. Further addition of low-loading micro-WS 2 into fabric composites leads to a much smoother worn surface and exerts an important influence on the transfer film structure (Table S1 in the ESM). In comparison to the patch-like tribofilm of SiC@fabric composites, a uniform, thin and continuous tribofilm is formed on the counterface surface after rubbing with SiC@fabric/WS 2 composites, implying that the beneficial role of micro-WS 2 in developing a high-quality tribofilm is responsible for the wear resistance of the fabric composites (Figs. 12(c) and 12(g)). Meanwhile, the incorporation of micro-AlN can effectively enhance the stiffness and creep resistance as well as the thermal conductivity of fabric composites that reduces the temperature increment in the contact area by dissipating the friction heat in a timely manner. As a result, the enhanced temperature resistance and cohesive strength of fabric composites resulted in improvements in wear resistance [51]. Compared to the addition of WS 2 , and AlN micro-fillers, the addition of combined AlN-WS 2 reinforcements leads to an even smoother worn surface, where no serious fiber breakage and pull-out wear mechanism are characterized except for little phenolic resin exfoliation. Therefore, the lamellar micro-WS 2 contributes to producing a tough tribofilm withstanding severe rubbing conditions, while micro-AlN enhances the stiffness and cohesive strength of the resin matrix. Thus the synergistic effect between WS 2 and AlN leads to improved tribological properties of the fabric composites (Fig. S6 in the ESM). Based on the above results, a mechanism for the wear behavior of the hybrid PTFE/glass fabric composites as well as the synergistic effects between the PDA/SiC/PEI functional coating and WS 2 , and AlN micro-fillers is shown in Fig. 13. Therefore, it is concluded that the combined interface

Conclusions
In summary, a uniform and dense hybrid PDA/SiC/ PEI layer was successfully coated onto the surface of a hybrid PTFE/glass fabric surface using a facile one-step co-deposition technique. The attachment of PDA/SiC/PEI was clearly verified to bring about increased surface roughness and more active functional groups for the hybrid-fabric that contributed to the improvement in interfacial adhesion through mechanical interlocking and chemical reaction. The improved fiber/ matrix interfacial adhesion facilitates the absorption of rupture energy and leads to an effective stress transfer between the reinforced fabric and resin matrix during the sliding process. Meanwhile, the inclusion of the lamellar micro-WS 2 produces a tough tribofilm withstanding severe rubbing conditions, whereas micro-AlN enhances the stiffness and cohesive strength of the resin matrix. As a result, the SiC@fabric/ WS 2 -AlN composites exhibited optimal tribological performance under various applied loads.