The Tribological Mechanism of Poly(Vinylidene Fluoride) Composites Reinforced with Carbon Fibers

The current study examines the tribological performance of poly(vinylidene fluoride) (PVDF) and carbon fiber-reinforced poly(vinylidene fluoride) (CF/PVDF) under dry sliding condition. Different contents of carbon fibers were employed as reinforcement. All filled and unfilled polyimide composites were tested against CGr15 ball and representative testing was performed. The effects of carbon fiber content on tribological properties of the composites were investigated. The worn surface morphologies of neat PVDF and its composites were examined by scanning electron microscopy (SEM) and the wear mechanisms were discussed. Moreover, all filled PVDFs have superior tribological characteristics to unfilled PVDFs. The optimum wear reduction was obtained when the content of carbon fiber is 20 vol%.     

The effect of carbon fiber content on the friction and wear properties of carbon fiber reinforced polyimide composites

The current study examines the tribological performance of polyimide and carbon fiber reinforced polyimide (CF/PI) under dry sliding condition. Different contents of carbon fibers were employed as reinforcement. All filled and unfilled polyimide composites were tested against CGr15 ball and representative testing was performed. The effects of carbon fiber content on tribological properties of the composites were investigated. The worn surface morphologies of neat PI and its composites were examined by scanning electron microscopy and the wear mechanisms were discussed. Moreover, all filled polyimides have superior tribological characteristics to unfilled polyimides. The optimum wear reduction was obtained when the content of carbon fiber is 20 vol %. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Electrical characteristics of fluorinated carbon black‐filled poly(vinylidene fluoride) composites

Dispersion and electrical properties of fluorinated carbon black‐filled poly(vinylidene fluoride) (PVDF) composites were studied as a function of the fluorine content. It was found that with increasing the fluorine content carbon particles tend to stick together to form large aggregates. The percolation concentration increases to a high concentration, whereas the percolation process becomes gradual. The temperature dependence of resistivity measurements show that the fluorinated carbon black‐filled PVDF composites exhibit a high PTC intensity and a low NTC effect. These phenomena were discussed in terms of thermodynamic interactions between fluorinated carbon and the PVDF matrix. The dielectric behavior was also investigated in this study. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1063–1070, 2001     

Poly(vinylidene fluoride)/thermoplastic polyurethane flexible and 3D printable conductive composites

This work focus on the development of polymeric blends to produce multifunctional materials for 3D printing with enhanced electrical and mechanical properties. In this context, flexible and highly conductive materials comprising poly(vinylidene fluoride)/thermoplastic polyurethane (PVDF/TPU) filled with carbon black-polypyrrole (CB-PPy) were prepared by compression molding, filament extrusion and fused filament fabrication. In order to achieve an optimal compromise between electrical conductivity, mechanical properties and printability, blends composition was optimized and different CB-PPy content were added. Overall, the electrical conductivities of PVDF/TPU 50/50 vol% co-continuous blend were higher than those found for PVDF/TPU 50/50 wt% (i.e., 38/62 vol%) composites at same filler content. PVDF/TPU/CB-PPy 3D printed samples with 6.77 vol% filler fraction presented electrical conductivity of 4.14 S m⁻¹ and elastic modulus, elongation at break and maximum tensile stress of 0.43 GPa, 10.3% and 10.0 MPa, respectively. These results highlight that PVDF/TPU/CB-PPy composites are promising materials for technological applications.     

Properties of carbon fiber reinforced poly(vinylidene fluoride)‐based friction materials of ultrasonic motors

In order to improve output properties and anti‐irradiation capability of ultrasonic motors (USMs), which are driven by friction forces of friction material between the stator and rotor, a type of friction material is fabricated by composite materials consist of carbon fiber (CF) and polyvinylidene fluoride (PVDF). The effects of different contents of CF on the mechanical and tribological properties of PVDF‐based friction materials are studied, and the mechanical features of the relative USMs are measured. Further, the worn surface morphology of PVDF composites is observed by means of scanning electron microscope and the wear mechanisms are also discussed. In addition, the anti‐irradiation capability of the type of friction materials is measured by the γ‐ray irradiation at room temperature environment with the total radiation dose of 4.0X rad (Si). The experimental results show that the incorporation of CF into PVDF can effectively improve the friction and wear properties of the friction materials, and the mechanical properties of TRUM‐60 used by relative PVDF composites are also increased with the increase of CF. For TRUM‐60, both the no‐load speed and holding torque of the USMs were high, and the wear of friction material was lowest, when the CF content is 15 wt%. The experiment results also show that this PVDF‐based friction material has a good anti‐irradiation property. Therefore, the composite materials consist of CF and PVDF are beneficial for the applications in USMs, especially for some radiation environment. POLYM. COMPOS., 37:547–552, 2016. © 2014 Society of Plastics Engineers     

Carbon black–filled immiscible blends of poly(vinylidene fluoride) and high density polyethylene: Electrical properties and morphology

The electrical conductivity, current-voltage characteristics and morphology of carbon black–filled immiscible blends of poly(vinylidene fluoride)(PVDF) and high density polyethylene (HDPF) were investigated. Carbon black (CB) had stronger affinity to HDPE than to PVDF, resulting in its selective localization in the HDPE phase. The CB content and PVDF/HDPE volume ratio were the two main factors influencing the electrical conductivity, current-voltage characteristics, and morphology. At a fixed PVDF/HDPE volume ratio of 1/1, a percolation threshold of 0.037 volume fraction of CB was observed, and that value was much lower than that for conventional CB-filled polymer composites. At a fixed CB content (10 wt% CB), a maximum electrical conductivity was observed at a PVDF/HDPE volume ratio of 2.75. An increase in CB content in the composites with a fixed PVDF/HDPE volume ratio (1/1) and an increase in PVDF content in composites with a fixed CB content (10 wt%) greatly decreased the domain size of the PVDF phase. A positive-temperature-coefficient effect was used to determine the location of CB in the blends.     

Tribological behaviors of carbon series additions reinforced CF/PTFE composites at high speed

The tribological, mechanical, and thermal properties of carbon series additions reinforced CF/PTFE composites at high speed were investigated. In this work, carbon fiber (CF) filled polytetrafluoroethylene (PTFE) composites, which have excellent tribological properties under normal sliding speed (1.4 m/s), were filled with some carbon materials [graphene (GE), carbon nanotubes (CNTs) and graphite (Gr)] respectively to investigate the tribological properties of CF/PTFE composites at high sliding speed (2.1 and 2.5 m/s). The results reveal that the carbon series additions can improve the friction and anti‐wear performances of CF/PTFE, and GE is the most effective filler. The wear rate of 0.8 wt % GE/CF/PTFE was decreased by 50 ? 55%, 55 ? 60%, 40 ? 45% at 1.4, 2.1, and 2.5 m/s compared with CF/PTFE. SEM study shows GE could be helpful to form smooth and continuous transfer film on the surface of counterparts. Meanwhile, GE can improve its tensile strength and elastic modulus obviously. Thin layer structure of GE could enhance the thermal conductivity, which can be helpful to dissipate heat of CF/PTFE composites wear surface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43236.     

Enhanced tribological performance of hybrid polytetrafluoroethylene/Kevlar fabric composite filled with milled pitch‐based carbon fibers

As self‐lubricating bearing liner materials, tribological properties of milled pitch‐based carbon fibers (CFs) modified polytetrafluoroethylene (PTFE)/Kevlar fabric composites were investigated, and the microscopic morphology of worn surface was studied. The results show that the appropriate incorporation of CFs can obviously reduce the wear rate of the fabric composite with almost unchanging friction coefficient. The wear rates of 5 wt % CF‐filled PTFE/Kevlar fabric composites are decreased by 30% and 48% for two kinds of composites made with fibers from different producers compared with unfilled fabric composites. Scanning electron microscopy observations show that the appropriate incorporation of CFs obviously improves the interfacial bonding and reduces pull‐out and fracture of Kevlar fiber. Meanwhile, the introduction of CFs at proper fraction is helpful to form smooth and continuous transfer film on the surface of metal counterpart. The improving mechanism of the CF is attributed to increasing mechanical strength, thermal conductivity and self‐lubricating effects. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46269.     

VGCF填充PVDF/PMMA复合材料导电性能的研究

以气相生长碳纤维（VGCF）为导电填料，聚偏氟乙烯（PVDF）、聚甲基丙烯酸甲酯（PMMA）为基体制备复合型导电高分子材料。考察了填料用量、基体种类、配比以及PVDF结晶行为对复合材料导电性能的影响。结果表明，VGCF填充PMMA、PVDF、PVDF／PMMA（50／50）体系的渗滤阔值分别为5、4、3phr的填料用量。VGCF的加入会导致PVDF／PMMA体系发生微观相分离，而且VGCF会选择性富集在PVDF的非晶相中，所以PVDF／PMMA／VGCF体系的导电性呈现双重渗滤现象，该体系的体积电阻率不仅取决于富集相中VGCF的含量，而且还与PVDF相的连续性及其结晶行为密切相关。     

Crystallization and thermal conductivity of poly (vinylidene fluoride)/boron nitride nanosheets composites

ABSTRACT

In this work, boron nitride (BN) and exfoliated boron nitride nanosheets (BNNs) were employed as thermal conductive fillers to improve the thermal conductivity of poly(vinylidene fluoride) (PVDF) composites. Results suggested that the thermal conductivity of PVDF increases significantly with an increase in loading content of functional fillers. When the mass ratio of fillers was more than 30 wt%, the heat conduction network was formed. BNNs were capable of forming denser heat conduction network as per the SEM observations. In this scenario, PVDF/BNNs composites demonstrated excellent thermal conductivity. For example, the thermal conductivity of PVDF/BNNs (60/40) was 0.82 W/mK, which was 2.4 times and 17% higher than that of neat PVDF and PVDF/BN (60/40) counterpart, respectively. The non-isothermal crystallization of corresponding composite was studied by Mo method. Combining with XRD results, both BN and BNNs acted as the nucleation agents but had no effect on crystal forms.     

Tribological properties of SiO2 nanoparticle filled–phthalazine ether sulfone/phthalazine ether ketone (50/50 mol %) copolymer composites

SiO₂ nanoparticle filled–poly(phthalazine ether sulfone ketone) (PPESK) composites with various filler volume fractions were made by heating compression molding. The tribological behavior of the PPESK composites was investigated using a block‐on‐ring test rig by sliding PPESK‐based composite blocks against a mild carbon steel ring. The morphologies of the worn composite surfaces, wear debris, and the transferred films formed on the counterpart steel surface were examined with a scanning electron microscope, whereas the chemical state of the Fe element in the transfer film was analyzed with X‐ray photoelectron spectroscopy. In addition, IR spectra were taken to characterize the structure of wear debris and PPESK composites. It was found that SiO₂ nanoparticle filled–PPESK composites exhibit good wear resistance and friction‐reduction behavior. The friction and wear behavior of the composites was improved at a volume fraction between 4.2 and 14.5 vol % of the filler SiO₂. The results based on combined SEM, XPS, and IR techniques indicate that SiO₂ nanoparticle filled–PPESK composite is characterized by slight scuffing in dry sliding against steel and polishing action between composite surface and that of the countpart ring, whereas unfilled PPESK is characterized by severe plastic deformation and adhesion wear. In the former case a thin, but not complete, transfer film was formed on the surface of the counterpart steel, whereas in the latter case, a thick and lumpy transfer film was formed on the counterpart steel surface. This accounts for the different friction and wear behavior of unfilled PPESK and SiO₂ nanoparticle filled–PPESK composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2136–2144, 2002     

A study of the mechanical and electrical properties of a polymer/carbon black binder system used in battery electrodes

The effects of carbon black content and crosslinking on the mechanical and electrical properties of a fluorinated elastomer, FC2178 (Dyneon Corp., Oakdale, MN), poly(vinylidene fluoride‐co‐hexafluoropropylene), were investigated and compared to those of poly(vinylidene fluoride) (PVDF). Attention was given to changes in mechanical and electrical properties of the polymers when under cyclic deformation. To describe the mechanical properties of the carbon‐filled polymers in a way that is independent of the chemical details, two mechanical models were used to fit cyclic stress–strain experiments. The linear model was used to determine the effect of crosslinking on the mechanical properties of crosslinked FC2178 films. However, when carbon black was added to the polymer films, the linear model no longer fit the data well. In particular, the cyclic stress–strain curves for carbon‐filled polymers showed non‐linear regions and displayed the characteristic of ‘memory.’ A non‐linear element was added in parallel with the existing elements of the linear model to successfully describe the effects of the added carbon black. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1891–1899, 2003     

Core@double-shell structured fillers for increasing dielectric constant and suppressing dielectric loss of PVDF-based composite films

High dielectric constant polymer dielectrics have attracted a great deal of attention in flexible electronics. However, it appears to be a paradox for polymer dielectrics that the enhancement of their dielectric constant often comes along with the increase of dielectric loss. Hence, we reported core@double shell structured filler/poly(vinylidene fluoride) (PVDF) composites to overcome this paradox. The hybrid filler with BaTiO₃ (BT) as the core, conductive carbon as the inner shell, and insulating polydopamine (PDA) as the outer shell was synthesized. As a result, the BT@C@PDA/PVDF composites at the filler content of 11 vol% exhibit an outstanding dielectric performance with a dielectric constant of 45 and a dielectric loss of 0.053 at 10³ Hz. This phenomenon can be attributed to the increased interfacial polarization induced by the inner carbon shell and the conductive paths blockade caused by the outside PDA shell inside the BT@C@PDA/PVDF composites. This work reveals that rational design of core@double shell structured hybrid fillers maybe a promising way to optimize the overall dielectric performance of the PVDF-based composites.     

高压气体压缩机阀片用材料的研究

根据气体压缩机阀片的要求，制备了碳纤维(CF)和二硫化钼(MoS2)填充热塑性聚酰亚胺(PI)复合材料；研究了不同组成材料的力学性能、摩擦性能，考察了载荷对材料摩擦性能的影响，观察了材料磨损面形貌，并对磨损面进行了元素分析。结果表明：通过填充碳纤维，可以有效增强聚酰亚胺材料的强度；填充MoS2后，材料的力学性能有所下降，但可有效提高材料的极限PV值；随载荷增加，材料的磨损率及摩擦系数都不断减小；该材料适于作高压气体压缩机构件。     

酸性溶液中PTW增强PTFE复合材料的耐蚀性和摩擦磨损性能

分别研究了不同含量钛酸钾晶须(PTW)、碳纤(CF)填充聚四氟乙烯(PTFE)复合材料在硫酸溶液中和干摩擦条件下摩擦学性能以及酸中的耐蚀性能,借助SEM等分析探讨了相关机理。结果表明,酸中纯PTFE耐磨性较干摩擦条件下提高了2个数量级,摩擦系数也只有干摩擦的15.3%。与CF/PTFE相比,PTW/PTFE复合材料在酸中显示更好的耐蚀和耐磨性能。PTW可以进一步提高PTFE酸中耐磨性能、降低摩擦系数。含15%（质量）PTW时复合材料具有最低的磨损率,此时比纯PTFE酸中耐磨性提高13.8倍,是相同含量CF/PTFE耐磨性的3.2倍。由于酸溶液的冷却和润滑作用,复合材料的摩擦系数与干条件相比明显降低。然而,酸溶液阻止了转移膜的形成。不管是干摩擦还是在酸性溶液中,当填料含量超过15%（质量）时,犁削和磨粒磨损是PTFE复合材料的主要磨损机理。     

Melt processing of composites of PVDF and carbon black modified with conducting polymers

Conductive composites from poly(vinylidene fluoride) (PVDF) and a novel thermally stable conductive additive made via in situ deposition of polyaniline or polypyrrole on carbon black particles were produced by a melting process. Electrical conductivity in the order of 10^?2 S/cm could be achieved with low contents of the conductive filler. Thermogravimetric analysis (TGA) showed that there is no appreciable degradation of the composites at temperatures as high as 300°C. Moreover, the addition of the conducting polymer‐modified carbon black additive is advantageous to the melt processing of the composites, reducing the melt viscosity in comparison to the addition of pure carbon black. Composites containing the β‐phase of PVDF could be obtained via quenching from the melt, as indicated by X‐Ray diffraction analysis. The type and amount of the additive and the quenching rate influence the formation of β‐phase in the PVDF composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 553–557, 2004     

Dielectric properties of Ag@C/PVDF composites

The core–shell Ag@C nanoparticles were prepared by hydrothermal method. The silver cores with diameters from 100 to 120 nm are each covered with a carbon shell about 60–80‐nm thick. Ag@C/poly(vinylidene fluoride) (PVDF) composites were prepared by the solution cast method. Transmission electron microscopy showed that the Ag@C core–shell nanoparticles were dispersed homogenously in the PVDF matrix with little agglomeration. The crystallization behavior and dielectric properties of the Ag@C/PVDF composites as a function of frequency and temperature were studied. The differential scanning calorimeter measurements showed that the crystallinity of the Ag@C/PVDF composites decreased with the increasing content of the Ag@C nanoparticles. The dielectric tests showed that the permittivity of the Ag@C/PVDF composites increased obviously over that of the pure PVDF with increasing content of Ag@C particles because of the enhanced interfacial polarization. The tan δ of the composites remained at a low level (～0.08 at 1000 Hz). Furthermore, the permittivity and the tan δ of the composites increased with increasing temperature. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The Effect of Carbon Fiber Content on the Mechanical and Tribological Properties of Carbon Fiber-Reinforced PTFE Composites

Blending polytetrafluorothylene (PTFE) to carbon fiber at different compositions was produced in a corotating twin screw extruder where PTFE acts as the polymer matrix and carbon fiber as the dispersed phase. The effects of carbon fiber content on mechanical and tribological properties of the composites were investigated. The worn surface morphologies of neat PTFE and its composites were examined by scanning electron microscopy (SEM) and the wear mechanisms were discussed. The presence of carbon fiber dispersed in the PTFE continuous phase exhibited superior tribological characteristics to unfilled PTFE. The optimum wear reduction was obtained when the content of carbon fiber is 30 vol%.     

A new approach for conductive network formation in electrospun poly(vinylidene fluoride) nanofibers

Conductive nanofibers of poly(vinylidene fluoride) (PVDF) filled with polyaniline (PANi)‐coated multi‐wall carbon nanotubes (MWCNTs) were fabricated using the electrospinning technique. PANi is an intrinsically conductive polymer. The addition of PANi‐coated MWCNTs to PVDF created short conductive strands on the surface of the nanofibers, facilitating the formation of a conductive network in the transverse direction of the nanofibers. Piezoelectricity along with electric conductivity makes these PVDF nanofibers promising for applications such as sensors and actuators. Electrospun PVDF nanofiber mats had higher piezoelectricity than melt‐processed samples produced using traditional polymer processing techniques, such as compression molding. Spectroscopic imaging techniques were employed to study the effects of the filler and processing conditions on the nanofiber structure. X‐ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry results indicated a large increase in the β‐phase crystals of the PVDF nanofibers. This higher content of β‐phase crystals enhanced the piezoelectricity of the nanofibers. © 2015 Society of Chemical Industry     

Melt processible fluoropolymer composites

A series of melt-processible fluoropolymer compounds including ethylene-tetrafluoroethylene (ETFE), poly(vinylidene fluoride) (PVF₂), ethylene-chlorotrifluoroethylene copolymer (ECTFE), perfluoroalkoxy modified tetrafluoroethylene (PFA), and fluorinated ethylene-propylene copolymer (FEP) containing reinforcing glass fiber, milled glass fiber, carbon fiber, minerals, poly(tetrafluoroethylene) (PTFE) lubricant powder, graphite powder and MoS₂ were prepared and characterized. The mechanical, physical, thermal, and tribiological properties of these composites were compared and ranked for suitability in various applications. These composites represent the first comprehensive evaluation of reinforced and filled meltprocessible fluoropolymer composites.