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。     

Master batch approach for developing PVDF/EVA/CNT nanocomposites with co-continuous morphology and improved electrical conductivity

Conducting polymer composites constituted by co-continuous poly (vinylidene fluoride) (PVDF)/ ethylene- vinyl acetate copolymer (EVA) blends with multiwalled carbon nanotube (CNT) were prepared by melt mixing using different procedures. The effect of the master batch approach on the conductivity, morphology, mechanical, thermal and rheological properties of PVDF/EVA/CNT nanocomposites was compared with that based on one step mixing strategy. The selective extraction experiments revealed that CNT was preferentially localized in the EVA phase in all situations, even when PVDF@CNT master batch was employed. Nanocomposites prepared with EVA@CNT master batch displayed higher conductivity, whose value reached around 10⁻¹ S m⁻¹ with the addition of 0.56 vol% of CNT. The better electrical performance was attributed to the better distribution of the filler, as indicated by transmission electron microscopy and rheological behavior. The electrical and rheological behavior were also investigated as a function of the CNT content.     

Electrical,rheological and electromagnetic interference shielding properties of thermoplastic polyurethane/carbon nanotube composites

Electrically conducting rubbery composites based on thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) were prepared through melt blending using a torque rheometer equipped with a mixing chamber. The electrical conductivity, morphology, rheological properties and electromagnetic interference shielding effectiveness (EMI SE) of the TPU/CNT composites were evaluated and also compared with those of carbon black (CB)‐filled TPU composites prepared under the same processing conditions. For both polymer systems, the insulator–conductor transition was very sharp and the electrical percolation threshold at room temperature was at CNT and CB contents of about 1.0 and 1.7 wt%, respectively. The EMI SE over the X‐band frequency range (8–12 GHz) for TPU/CNT and TPU/CB composites was investigated as a function of filler content. EMI SE and electrical conductivity increased with increasing amount of conductive filler, due to the formation of conductive pathways in the TPU matrix. TPU/CNT composites displayed higher electrical conductivity and EMI SE than TPU/CB composites with similar conductive filler content. EMI SE values found for TPU/CNT and TPU/CB composites containing 10 and 15 wt% conductive fillers, respectively, were in the range ?22 to ?20 dB, indicating that these composites are promising candidates for shielding applications. © 2013 Society of Chemical Industry     

Flexible and low cost lead free composites with high dielectric constant

Highly flexible lead free composite film having random distribution of ceramic filler was synthesized using Barium Titanate (BT) as a filler and inexpensive Thermoplastic Polyurethane (TPU) as a matrix. The results show that the 30 vol% BT-TPU composite has a dielectric constant of ~31 which is comparable to the expensive and difficult to produce PVDF based composites. With a breakdown field of 150 kV/mm, an energy density value of ~3 J/cm³ was estimated. These lead-free TPU based composites provide an alternative to PVDF based composites for energy storage applications.     

0D surface modification and 3D silicon carbide network construction for improving the thermal conductivity of epoxy resins

With rapid advances in electronic device miniaturization and increasing power density, high thermal conductivity polymer composites with excellent properties are becoming increasingly significant for the progress of next-generation electronic apparatuses. In this work, a new type of three-dimensional (3D) network silicon carbide (SiC) frame and core-shell SiC@SiO₂ (SiC@SiO₂) were successfully prepared. The effects of different filler forms (dispersed particle filler and three-dimensional continuous filler network) on the thermal conductivity of the composites were compared. The composites based on the three-dimensional filler network exhibited evidently better thermal conductivity improvement rates, compared to their traditional counterparts. The thermal conductivity of the epoxy/SiC@SiO₂ composite having a total filler content of 17.0 vol% was 0.857 W/m/K, 328.5% higher than that of pure epoxy resin. Similarly, the thermal conductivity of the EP/3D-SiC composite having a total filler content of 13.8 vol% was 1.032 W/m/K, 416.0% higher than that of pure epoxy resin. The abovementioned stats were proven via molecular simulations. We estimated the interfacial thermal resistance (ITR) of the EP/3D-SiC composite to be 5.98 × 10^?8 m² K/W, which was an order of magnitude lower than that of the epoxy composites without a 3D network. Simultaneously, computerized molecular simulation technology was used to verify the feasibility of the experiment, which provided new ideas for the preparation of other highly thermally conductive materials.     

Microcellular Conductive Carbon Black or Graphene/PVDF Composite Foam with 3D Conductive Channel: A Promising Lightweight,Heat-Insulating,and EMI-Shielding Material

In this study, a lightweight microcellular carbon-based filler/poly(vinylidene fluoride) (PVDF) composite foam is fabricated with a 3D conductive network that is thermally insulating, electrically conductive, and fabricated on a large scale. This composite can be used for high-efficiency thermal insulation and electromagnetic interference (EMI) shielding applications. The prepared composite demonstrates low density, high electrical conductivity, and excellent thermal insulation properties. The structure and density of the conductive network and the carbon-based filler content has a significant influence on the electrical conductivity of the prepared composite foam. Although the composite comprises microcellular PVDF beads of the same density, the conductivity of the composite-comprising strip beads is greater than that comprising spherical beads. In the same conductive network structure, as the size of the microcellular PVDF beads decrease, the conductive network becomes denser, which results in a higher conductivity. Furthermore, with an increase in the conductive filler content, the conductivity improves significantly. Excellent EMI shielding materials with optimal filler content and particle shapes, exhibiting EMI shielding effectiveness of up to 40–50 dB, are developed. The prepared composite foam possesses excellent application potential in the fields of ultra-light thermal insulation, conductivity, and EMI shielding.     

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.     

Mechanical properties and morphology of thermoplastic polyurethane elastomer with pol(vinylidene fluoride) blends

A study on blends of thermoplastic polyurethane elastomer (TPU)/poly(vinylidene fluoride) (PVDF) is described. This investigation focused on the effects that PVDF has on the mechanical behaviors and morphological characteristics of the blends. Basic thermodynamic and structural considerations were applied to predict the blend miscibility. It was found that addition of PVDF disrupted the intermolecular chain interactions in TPU, resulting in lowering of mechanical properties in the blends. Our results showed that the 50/50 blend has the lowest mechanical strength. At higher levels of PVDF (<50%), the mechanical strength increased proportionally to PVDF. It was also found that both the breaking strain and the energy at break of these blends decreased with increased PVDF content. The lowering of the mechanical properties in the blends could be attributed to the formation of layered structures caused by the immiscibility of the polymers. It was concluded that TPU/PVDF blends were incompatible at all compositions. © 1996 John Wiley & Sons, Inc.     

Conducting aluminum‐filled nylon 6 composites

This work is concerned with the preparation and characterization of composite materials prepared by compression molding of a mixture of aluminum flakes and nylon 6 powder. The electrical conductivity, density, hardness and morphology of composites were investigated. The electrical conductivity of the composites is < 10⁻¹¹ S/cm unless the metal content reached the percolation threshold, beyond which the conductivity increased markedly by as much as 10¹¹. The volume fraction of conductive filler at the percolation threshold was calculated from experimental data, by fits to functions predicted by the percolation theory. Decreasing the average particle diameter of filler leads to increased percolation threshold (it varies from 23 to 34 vol% for the three different fillers studied) and decreased maximal conductivity of composites. The density of the composites was measured and compared with values calculated assuming different void levels within the samples. Furthermore, it is shown that for certain sizes of particle filler, the hardness decreases initially with the increase of metal concentration, possibly because of poor surface contact with the nylon matrix, but, starting from a certain value, there is a hardness increase. For the smallest particle filler, the hardness of samples is not influenced by the presence of the filler.     

The influence of filler treatment on the properties of TPU/PP blends: I. Thermal properties and stability

Commercially available organosilane (3‐glycidoxypropyltrimethoxysilane (GPTMS)) coupling agent was used to treat talc in order to improve the affinity relative between the filler and the polymer in composites as well as filler and polymer in the thermoplastic polyurethane/polypropylene (TPU/PP) blends (talc content was 5 wt%). The talc particles were first modified with GPTMS and then introduced into TPU, PP as well as TPU/PP blends with different weight ratios of polymers using blending method and subsequently injection molded in a hydraulic press. The aim was to report the effect of silane coupling agent on the thermal and morphological properties of talc filled composites and blends. The results showed that the thermal properties of the TPU, PP composites and TPU/PP blends were improved with the addition of silane treated talc (higher melting (T_m), crystallization (T_c) temperatures and degree of crystallinity (χ_c)). The glass transition temperature (T_g) obtained by dynamic mechanical analysis (DMA) of the TPU soft segments in TPU/PP blends increased with the addition of untreated and silane treated talc due to lower mobility of the soft segments in TPU and better miscibility of TPU and PP. TPU/PP blends with the silane treated talc show better thermal stability than the TPU/PP blends with untreated talc. POLYM. ENG. SCI., 55:1920–1930, 2015. © 2014 Society of Plastics Engineers     

Electrical behavior and positive temperature coefficient effect of graphene/polyvinylidene fluoride composites containing silver nanowires

Polyvinylidene fluoride (PVDF) composites filled with in situ thermally reduced graphene oxide (TRG) and silver nanowire (AgNW) were prepared using solution mixing followed by coagulation and thermal hot pressing. Binary TRG/PVDF nanocomposites exhibited small percolation threshold of 0.12 vol % and low electrical conductivity of approximately 10^-7 S/cm. Hybridization of TRGs with AgNWs led to a significant improvement in electrical conductivity due to their synergistic effect in conductivity. The bulk conductivity of hybrids was higher than a combined total conductivity of TRG/PVDF and AgNW/PVDF composites at the same filler loading. Furthermore, the resistivity of hybrid composites increased with increasing temperature, giving rise to a positive temperature coefficient (PTC) effect at the melting temperature of PVDF. The 0.04 vol % TRG/1 vol % AgNW/PVDF hybrid exhibited pronounced PTC behavior, rendering this composite an attractive material for making current limiting devices and temperature sensors.     

Vermicular Ni@RL-CS: Preparation,characterization and its applications in electromagnetic shielding

One-dimensional conductive materials are of great significance to the construction of conductive network in the polymer matrix due to their large aspect ratio. In this work, a nickel-plated rod-like calcium silicate composite (Ni@RL-CS) with unique vermicular structure was successfully fabricated by an electroless plating method. The structure and property of as-prepared Ni@RL-CS were characterized, and its electromagnetic shielding ability was evaluated through mixing with thermoplastic polyurethane (TPU). Results indicate that the Ni@RL-CS shows good electrical conductivity, magnetic property and strong dielectric loss ability. The Ni@RL-CS with a one-dimensional vermicular structure is easier to construct a continuous conductive network in TPU matrix, which greatly improves the electromagnetic shielding effectiveness of the TPU resin. TPU/Ni@RL-CS binary composite with 20 vol% Ni@RL-CS achieves ultrahigh specific EMI SE/thickness of 92.6 dB/mm in the frequency of X-band. By further hybridizing Ni@RL-CS with GNPs, the TPU/Ni@RL-CS/GNPs trinary composite exhibits excellent electromagnetic shielding performance. When the contents of Ni@RL-CS and GNPs are 10 vol% and 1.5 vol%, respectively, the specific EMI SE/thickness of the corresponding trinary composite reaches 74.6 dB/mm in the X-band owe to the dense conductive network, which is 56.5% higher than that of the binary TPU/Ni@RL-CS composite with the same content of 10 vol% Ni@RL-CS.. The synergistic effects of dielectric loss, magnetic loss, and the interfacial polarization loss are the main shielding mechanism. This work provides a strategy to prepare a functional filler based on an insulating inorganic material for electromagnetic shielding. The as-prepared Ni@RL-CS with the unique vermicular structure and outstanding electromagnetic shielding performance can serves as a functional filler to modify polymers for electromagnetic shielding applications.     

Effect of mechanical stretching on electrical conductivity and positive temperature coefficient characteristics of poly(vinylidene fluoride)/carbon nanofiber composites prepared by non-solvent precipitation

Poly(vinylidene fluoride) (PVDF)/carbon nanofiber (CNF) composites with filler content ranging from 0.047 to 4.7 vol.% were prepared with non-solvent precipitation followed by melt compression. The morphology and electrical conductivity of the composites before and after mechanical stretching were examined. The results showed that CNFs were dispersed homogeneously in the PVDF matrix and a low electrical percolation threshold of 0.90 vol.% CNFs was obtained. Mechanical stretching led to a sharp decrease in the electrical conductivity of a composite containing 0.94 vol.% CNF. This was caused by the destruction of a conducting network structure when the fillers aligned along the stretching direction. This did not happen when the filler content was increased to 1.88 vol.%. The percolating composites displayed a positive temperature coefficient (PTC) effect with the effect being larger in stretched composites. This can be attributed to the presence of PVDF β-phase in stretched composites as revealed by X-ray diffraction and Fourier transform infrared spectroscopy.     

An Effective Strategy to Achieve Ultralow Electrical Percolation Threshold with CNTs Anchoring at the Interface of PVDF/PS Bi‐Continuous Structures to Form an Interfacial Conductive Layer

Conductive composites based on polymers and conductive nanofillers are widely studied as a promising material. The rational design of 3D conductive networks in composites is crucial to improve their electrical conductivity and reduce the dosage of nanofillers. Herein, poly(vinylidene fluoride) (PVDF) and polystyrene (PS) bi‐continuous structures with modified carbon nanotubes (CNTs) tailored to anchor at the interface are designed to achieve an ultralow electrical percolation threshold because of the formation of a thin interfacial conductive layer. In this work, the modification of CNTs with poly(methyl methacrylate) (PMMA), which contributes to the improvement of the compatibility between PVDF and CNTs, is effective to control the distribution of CNTs in composites. It promotes the migration of CNTs from the PS phase to the interface of PVDF and PS. Consequently, the interfacial conductive layer is formed at a low CNT content, and the electrical percolation threshold of PVDF/PS/CNTs‐PMMA nanocomposites is only 0.07 vol%, having a great decrease of about 50% compared with that of PVDF/PS/CNTs nanocomposites. Thus, it is demonstrated that the distribution of CNTs can be tailored to anchor at the interface by proper chemical modification to form an interfacial conductive layer and a decrease of percolation threshold can also be achieved.     

Mechanical,electrical, and dielectric properties of polyvinylidene fluoride/short carbon fiber composites with low‐electrical percolation threshold

In this investigation, polyvinylidene fluoride (PVDF)/short carbon fiber (SCF) composites have been prepared by solution casting technique to enhance electrical and dielectric properties with very low‐electrical percolation threshold (0.5 phr SCF). The effect of SCF content on mechanical, thermal and morphological properties of the composites have also been investigated. The mechanical properties of the composites are found to reduce compared to neat PVDF due to poor polymer–filler interaction which can be concluded from FESEM micrographs showing poor bonding between PVDF and SCF. The PVDF/SCF composites exhibit either positive temperature coefficient effect of resistivity or negative temperature coefficient effect of resistivity depending on the loading of SCF in the polymer matrix. The change in conductivity during heating–cooling cycle for these composites shows electrical hysteresis along with electrical set. The melting point of the composites marginally increases with the increase in fiber loading in PVDF matrix as evidenced from DSC thermograms. X‐ray diffraction analysis reveals the crystallinity of PVDF decreases with the increase in SCF loading in matrix polymer. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39866.     

Lightweight and thermally conductive thermoplastic polyurethane/hollow glass bead/boron nitride composites with flame retardancy

Polymeric composites with low density and high thermal conductivity (TC) are greatly demanded in some specific applications such as aeronautics, astronautics, and deep-sea exploration. It is a great challenge to obtain lightweight and thermally conductive polymer composites because the heat fillers have high density (>2 g/cm³) Herein, lightweight and thermally conductive thermoplastic polyurethane/hollow glass bead/boron nitride composites (TPU/HGB/BN) were prepared with the construction of a 3D BN network under the assistance of ultralightweight HGB by a solution-mixing and hot-pressing method. A 3D BN heat network has been constructed in the TPU matrix due to the alignment of the BN platelets along with the HGB microspheres during hot-pressing, which leads to a higher TC (5.34 W/mK) of the TPU/HGB/BN composites with a low density of 1.23 g/cm³, which is close to the density of pure TPU (1.20 g/cm³). In addition, the TPU/HGB/BN composites show good thermal stability with TC losses of 4.24% and 2.22%, respectively, even after treated for 50 hot-cold cycles and heated at 80 °C for 50 h. Moreover, the limiting oxygen index (LOI) of the TPU/HGB/BN composites is 51%, and they can extinguish in 8 s after ignition and exhibit enhanced flame retardancy. This work presents a simple method to design and prepare lightweight, flame retardant and thermally conductive composite materials, which can be used as lightweight thermal management materials.     

Economical conductive graphite-filled polymer composites via adjustable segregated structures: Construction,low percolation threshold,and positive temperature coefficient effect

The economical graphite-filled thermoplastic urethane/ultra-high molecular weight polyethylene (TPU/UHMWPE) composites with the segregated structure were constructed by the combination of mechanical crushing and melt blending method. The low percolation threshold of 1.89 wt% graphite in the adjustable segregated composites was obtained and high electrical conductivity was about 10⁻¹ S m⁻¹ at 10 wt% graphite loadings owing to the formation of three-dimensional conductive networks. Moreover, when the graphite loadings were over the percolation threshold, the remarkable positive temperature coefficient (PTC) effect of electrical resistivity for TPU/UHMWPE-Graphite composites were achieved, originating from the combined thermal motion of TPU and UHMWPE. Meanwhile, the outstanding repeatability of PTC effects was obtained after 5-time cycles. Therefore, economical conductive polymer composites were still the promising field in the practical application of PTC materials.     

Reduced graphene oxide (RGO)-induced compatibilization and reinforcement of poly(vinylidene fluoride) (PVDF)–thermoplastic polyurethane (TPU) binary polymer blend

Compatible blends of nonreactive thermoplastic fluoropolymer, poly(vinylidene fluoride) (PVDF) and thermoplastic polyurethane (TPU) at 70/30 weight ratio, were prepared by utilizing the unique structural feature of reduced graphene oxide (RGO). Here, RGO acts as a compatibilizer as well as a reinforcing filler. RGO interacts with both polymers and reduces the interfacial tension between them, leading to compatibilization. RGO content in the blends was varied from 0 to 0.5 wt %, and the best result was found at 0.3 wt % loading. Excellent compatibilization between PVDF and TPU was established by mechanical, morphological, and thermal property studies. Chemical interaction between the RGO/TPU and RGO/PVDF was proved by FTIR–ATR study. With the incorporation of 0.3 wt % RGO, tensile strength, Izod impact strength, and elongation at break of the blend were increased by 42%, 83%, and 43%, respectively. FESEM and AFM images of blends without loading of filler after etching out of TPU phase show nonuniformly distributed hole morphology. RGO-containing blend has shown much finer and uniformly distributed holes that confirm improved compatibility between the two incompatible polymers. RGO also improves the thermal stability of the compatible blends considerably. At 0.3 wt % loading, the onset of thermal degradation increased by about 10 °C. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47010.     

Conductive poly(vinylidene fluoride)/polyethylene/graphene blend‐nanocomposites: Relationship between rheology,morphology, and electrical conductivity

Relationship between rheology, morphology, and electrical conductivity of the poly(vinylidene fluoride)/polyethylene/graphene nano‐platelets ternary system (PVDF/PE/GnP) were investigated. All the blend nanocomposites were prepared via a two‐step melt mixing method. GnP (0.75 and 1.5 wt %) was first compounded with PVDF and then the resulted premixtuers were melt mixed with PE to achieve the desired compositions. The corresponding reference nanocomposites and filler‐less blends were also prepared. Effect of an interfacial agent (PEMA; maleic anhydride grafted polyethylene) was also studied in this work. The results of rheological analysis in conjunction with the Raman spectroscopy experiments revealed that GnP had higher affinity to PVDF than PE, which in turn led to creation of conductive networks of GnP (1.5 wt %) in PVDF matrix exhibiting the electrical conductivity of about 10^?2 (S/cm). Double percolated micro‐structure was predicted for the PE/PVDF 40/60 (wt/wt) blend containing low GnP content (0.9 wt %) and confirmed via direct electron microscopy and conductivity analysis. Using 5 wt % of the PEMA reduced the conductivity to 10^?5 (S/cm) and further increase in PEMA content to 10 wt % led to non‐conductive characteristics. The latter was attributed to the migration of GnP from the PVDF phase to PE/PEMA phase and hence disturbance of double percolated micro‐structure. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46333.     

Effects of glass fiber on the properties of polyoxymethylene/thermoplastic polyurethane/multiwalled carbon nanotube composites

The effects of epoxy‐functionalized glass fiber (GF) on the electrical conductivity, crystallization behavior, thermal stability, and dynamic mechanical properties of polyoxymethylene (POM)/thermoplastic polyurethane (TPU)/multiwalled carbon nanotube (MWCNT) composites are investigated. The electrical resistivities of POM/5%−20% TPU/1% MWCNT composites are significantly reduced by nine orders of magnitude after the addition of 20% GF because of the formation of TPU‐coated GF structure facilitating the construction of conductive networks. GF has no obvious influence on the crystallization temperature, melting temperature, and degree of crystallinity of POM in POM/TPU/MWCNT composites because of their relatively bigger size compared with POM chains and MWCNTs. The storage moduli of POM/TPU/MWCNT composites are improved by the addition of GF, indicating that POM/TPU/MWCNT/GF composites are promising materials with good electrical and mechanical properties. POLYM. COMPOS., 38:1319–1326, 2017. © 2015 Society of Plastics Engineers