Study of the morphology and temperature-resistivity effect of injection-molded iPP/HDPE/CB composites

The relationship between morphology and temperature-resistivity effect of injection-molded isotactic polypropylene/high density polyethylene/carbon black (iPP/HDPE/CB) composites with special orientation structure is investigated in detail. The morphological variation induced by melting, disorientation, crystallization and movement of CB particles is responsible for the change of electrical conductivity of the iPP/HDPE/CB composites during the heating and cooling. The room temperature volume resistivity of the composites reduces markedly after a round of heating and cooling because the network is improved through morphological changes and movement of particles during annealing. The continuity of HDPE/CB phase and the effective concentration of the CB particles in HDPE simultaneously determine the temperature-resistivity effects of the composites. Samples with iPP/HDPE mass ratio of 50/50 achieve a better balance of the two factors, which results in more stable conductive properties varying with temperature.     

Improvement of melt spinning properties and conductivity of immiscible polypropylene/polystyrene blends containing carbon black by addition of styrene‐ethylene‐butene‐styrene block copolymer

Conducting polymeric materials prepared from immiscible blends, such as polypropylene (PP)/polystyrene (PS), together with carbon black (CB), are known to have a relatively high electrical conductivity, because of a selective distribution of CB (double percolation). Melt spinning of immiscible blends containing CB has, however, not been extensively reported on previously. An immiscible 1:1 blend of PP and PS to which 4 wt% CB was added exhibited a very low melt draw‐down ratio at rupture compared wit PP with the same content of CB. By adding 5 wt% SEBS (styrene‐ethylene‐butene‐styrene block copolymer), the ultimate melt draw‐down ratio increased about 10 times, which made the material more suitable for melt spinning. As‐extruded samples of the immiscible blends (with CB) did not have higher electrical conductivities than PP/CB. A heat treatment increased the conductivity of immiscible PP/PS/CB composites, and longer treatment times and higher temperatures promoted the conductivity. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Morphology,Resistivity, and PTC behavior of EVOH/CB composites prepared by solvent‐casting saponification and precipitation saponification

Poly(ethylene‐co‐vinyl alcohol)/carbon black (EVOH/CB) composites were prepared by a solvent‐casting saponification (‐D) and precipitation saponification (‐P) methods with a poly(ethylene‐co‐vinyl acetate)/CB (EVA/CB) toluene suspension. The effects of the CB content and saponification time on the morphology, electrical resistivity, thermal, and mechanical properties of EVA/CB composites were examined. The volume resistivity (ρ _v) of the EVA/CB‐D and EVA/CB‐P samples decreased significantly with increasing CB content and the percolation threshold of such composites was determined about 10 wt%. At 10 wt% of CB content, the ρ _v of EVA/CB‐D composite decreased significantly with the saponification time, whereas ρ _v of EVA/CB‐P composites did not change. As the saponification time increased, EVA/CB25wt% composites form cavity structure which CB is usually located in oval cavities larger than the particles themselves. This oval cavity structure almost resembles extruded high‐density polyethylene (HDPE)/CB composites. The morphology and PTC behavior of prepared composites were compared with those of HDPE/CB and the mechanism of PTC and NTC effects was discussed. POLYM. COMPOS., 38:1462–1473, 2017. © 2015 Society of Plastics Engineers     

Effect of morphology on the electric conductivity of binary polymer blends filled with carbon black

Several carbon black (CB)‐filled binary polymer blends were prepared in Haake rheometer. Distribution states of CB and effect of morphology on the electric conductivity of different ternary composites were investigated. Under our experimental condition CB particles located preferentially at the interface between polymethyl methacrylate (PMMA) and polypropylene (PP) in PMMA/PP/CB composites, in high‐density polyethylene (HDPE) phase in PP/HDPE/CB composites, and in Nylon6 (PA6) phase in polystyrene (PS)/PA6/CB, PP/PA6/CB, PMMA/PA6/CB, and polyacrylonitrile (PAN)/PA6/CB composites; the ternary composites in which CB particles locate at the interface of two polymer components have the highest electric conductivity when the mass ratio of the two polymers is near to 1 : 1. The ternary composites in which CB particles located preferentially in one polymer have the highest electric conductivity usually when the amount of the polymer component having CB particles is comparatively less than the amount of the polymer component not having CB particles; if the formulations of PS/PA6/CB, PP/PA6/CB, and PMMA/PA6/CB composites equaled and PA6/CB in them is in dispersed phase, PS/PA6/CB composites have the highest electric conductivity and PP/PA6/CB composites have the lowest electric conductivity; suitable amount of PS or PAN in PA6/CB composites increase the electric conductivity due in the formation of a parallel electrocircuit for electrons to transmit. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Carbon black–filled immiscible blends of poly(vinylidene fluoride) and high density polyethylene: The relationship between morphology and positive and negative temperature coefficient effects

Conductive polymer composites were prepared by melt-mixing of an immiscible blend of poly(vinylidene fluoride) (PVDF), high density polyethylene (HDPE), and carbon black (CB). Three major factors—the carbon black content, the carbon black type, and the composite morphology—were shown to have remarkable effects on the positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effect of the composites. The relationship between the morphology and the PTC and NTC effects of the composites was investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The OM micrographs indicated that CB was selectively located in the HDPE phase and the SEM micrographs showed that there were some gaps between the two phases. The PTC effect of the composites is caused by the thermal expansion as a result of the melting of the HDPE crystallites. The morphology of the composites greatly affects the PTC and NTC behaviors of the composites. When the CB-filled HDPE formed a continuous phase and the PVDF formed a dispersed phase, the PTC and NTC behaviors of the composites were similar to those of CB-filled neat HDPE composite without crosslinking. When the composite exhibited an interlocking structure, a normal PTC effect could also be observed, but the NTC effect was delayed to higher temperatures. A mechanism was proposed to explain this new physical phenomenon, and the mechanism was verified by another CB-filled polymer blend comprising an alternating copolymer of tetrafluoroethylene-ethylene and HDPE.     

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     

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.     

Preparation of conductive polylactic acid/high density polyethylene/carbon black composites with low percolation threshold by locating the carbon black at the Interface of co-continuous blends

In the current study, polylactic acid/high density polyethylene/carbon black (PLA/HDPE/CB) composites are prepared via a two-step method. A double percolation network with co-continuous structure and filler distribution at the interface is constructed to design conductive polymer composites with low percolation threshold. The controllable distribution of CB at the interface is achieved by appropriate processing procedures involved mixing sequence and mixing time by taking advantage of the migration of CB from the unfavorable PLA phase to the favorable HDPE phase. Morphology characterization reveals that when the mixing time of the added HDPE is 3 min, the formation of co-continuous structure of PLA/HDPE (60/40, w/w) is observed, and CB particles migrate to the co-continuous interface. The electrical conductivity measurement shows that such double percolation conductive network reduces the percolation threshold of PLA/HDPE/CB to 2.42 wt%. The rheological property proves the establishment of particle percolation network, and the rheological percolation threshold is determined as 1.20 wt%. The prepared PLA/HDPE/CB composite by the two-step method displays a notably low percolation threshold than that prepared by one-step simultaneous mixing. Moreover, this strategy presents a high potential application in the fabrication of conductive polymer composites involving other miscible multiphase systems.     

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。     

Hybrid electro-conductive composites with improved toughness, filled by carbon black

The influence of both carbon black (CB), and an ethylene-propylene copolymer grafted by maleic anhydride (EP-g-MA), on the static mechanical properties, impact strength, peel and shear strengths as well as on the electrical conductivity of composites based on high-density polyethylene (HDPE) matrix, was investigated in this paper. It was found that CB improves the stress at yield, the stress at break, and Young’s modulus, as well as the shear strength and peel strength, of the HDPE/CB composites. The percolation threshold was found at 4.5 vol.% of CB. The addition of EP-g-MA to the HDPE/CB composites improves their impact strength, the peel and shear strengths, and the electrical conductivity.     

Design of electrical conductive poly(lactic acid)/carbon black composites by induced particle aggregation

The electrical conductivity of ternary composites composed of a biopolymer blend with conductive particles (carbon black [CB]) is induced by the control of particle dispersion in the dispersed phase. If the CB particles have higher chemical affinity for the secondary phase (poly(caprolactone) [PCL]]) than the matrix (poly(lactic acid) [PLA]), especially as the concentration of the PCL phase decreases significantly to 4 wt%, the PCL phase induces the aggregation of CB particles beyond the selective localization, resulting in a shift of the particle percolation threshold to a lower concentration of particles (2.44 wt% CB). Moreover, the mixing ratio between the CB and the PCL phase significantly affects the formation of percolation of particles. When the mixing ratio of CB to PCL is equivalent (1:1), the ternary composite shows high electrical DC conductivity above 1 S/m with 10 wt% CB. The addition of a small amount of PCL induces the formation of particle aggregates with a high aspect ratio, providing more electron transfer pathways due to the multiple points of contact between the particle aggregates (power law scaling exponent of the composites ~2.14). Meanwhile, a binary composite (PLA/CB) never reaches high electrical conductivity of 1 S/m and even requires a greater concentration of CB (13 wt% CB for 10⁻³ S/m) to accomplish electron transfer because of the small aspect ratio of randomly dispersed particle aggregates (power law scaling exponent ~3.20).     

EVA/LDPE/CB导电复合材料结构与性能的研究

以炭黑(CB)粒子为导电填料,乙烯-乙酸乙烯共聚物(EVA)和低密度聚乙烯(LDPE)为基体树脂,在HAAKE转矩流变仪中制备了EVA/LDPE/CB导电复合材料,研究了CB粒子的分散形态、共混体系相形态以及其与EVA/LDPE/CB共混体系导电性能的关系。通过DSC、DMA、SEM、溶剂溶解等方法考察了EVA/LDPE两相体系随着EVA含量的变化引起的相转变情况,同时也考察了CB在EVA/LDPE共混体系中的选择性分散情况。     

Comparison study of graphite nanosheets and carbon black as fillers for high density polyethylene

In this work, the properties of high density polyethylene (HDPE)/graphite nanosheets (GN) and HDPE/carbon black (CB) nanocomposites prepared by melt mixing were studied. GN‐filled HDPE nanocomposites exhibited very low percolation threshold (ca. 6 wt%) as compared with that of HDPE/CB (ca. 22 wt%). Moreover, the impact strength and processing properties of HDPE/GN nanocomposites were superior to those of HDPE/CB within a certain content of fillers. The large aspect ratio of GN plays an important role in reducing the percolation threshold of HDPE/GN nanocomposites. Furthermore, the tensile fracture morphology revealed the formation of continuous conducting networks after the content of GN reached the critical percolation threshold. Differential scanning calorimetry (DSC) analysis illustrated a decreasing degree of crystallinity of HDPE/GN nanocomposites, while the crystalline temperature varied slightly. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Effect of nanoclay on positive temperature coefficient to resistivity characteristics of high density polyethylene/silver‐coated glass bead composites

Positive temperature coefficient to resistivity characteristics of high density polyethylene (HDPE)/silver (Ag)‐coated glass bead (45 wt%) composites, without and with nanoclay, has been investigated with reference to HDPE/carbon black (CB) (10 wt%) composites. Plot of resistivity versus temperature of HDPE/CB (10 wt%) composites showed a sudden rise in resistivity (PTC trip) at ≈128°C, close to the melting temperature (T_m) of HDPE. However, for HDPE/Ag coated glass bead (45 wt%) composites, the PTC trip temperature (≈88°C) appeared well below the T_m of HDPE. Addition of 1 phr clay in the composites resulted in an increase in PTC trip temperature of HDPE/Ag‐coated glass bead (45 wt%) composites, whereas no significant effect of clay on PTC trip temperature was evident in HDPE/CB/clay composites. We proposed that the PTC trip temperature in HDPE/Ag‐coated glass bead composites was governed by the difference in coefficient of thermal expansion of HDPE and Ag‐coated glass beads. The room temperature resistivity and PTC trip temperature of HDPE/Ag‐coated glass bead (45 wt%) composites were found to be very stable on thermal cycling. Dynamic mechanical analyzer results showed higher storage modulus of HDPE/Ag‐coated glass bead (45 wt%) composites compared with the HDPE/CB (10 wt%) composites. Thermal stability of HDPE/Ag‐coated glass bead (45 wt%) composites was also improved compared with that of HDPE/CB (10 wt%) composites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Morphology and electrical conductivity of injection-molded polypropylene/carbon black composites with addition of high-density polyethylene

This work attempts to clarify the influence of carbon black (CB) addition on the microstructure of injection-molded high-density polyethylene (HDPE)/polypropylene (PP) blends and effect of shear-induced polymer deformation on the conductive network structure. We observed that HDPE molecules are strongly interacted with carbon surfaces and CB particles are selectively located in HDPE domains. Morphology of the injection-molded specimen consists of three parts, namely, CB-HDPE complex domain, free HDPE domain and PP domain. The volume and microstructure of the free HDPE domain are significantly influenced by HDPE and CB concentration, CB structure, and PP viscosity. We also confirmed that the CB particles are capable of self-assembly to form random conductive networks even under high shear rate within very short time. The morphological changes were finally correlated to the variation of electrical conductivity.     

Effect of carbon black on electrical property of graphite nanoplatelets/epoxy resin composites

Epoxy/graphite nanoplatelets (GNPs)/carbon black (CB) composites were prepared by liquid mixing method. The morphologies and microstructures of the composites were examined by scanning electron microscope and X‐ray diffraction. The results indicated that CB can improve effectively the dispersion of GNPs and form excellent conductive network in the matrix. When the weight ratio of GNPs to CB was 9:1 (total filler content was 1 wt%), the conductivity of the composite was three orders of magnitude higher than that of composites with GNPs alone (1 wt%). The percolation threshold of GNPs_0.9CB_0.1/epoxy resin composites was 0.5 wt. %, which was lower than that of composites with GNPs alone (1 wt%). The mechanism for the effect of CB on electrical property of GNPs/epoxy resin composites was also investigated. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers.     

Effect of microfiber reinforcement on the morphology,electrical, and mechanical properties of the polyethylene/poly(ethylene terephthalate)/carbon nanotube composites

In situ microfiber reinforced conductive polymer composites consisting of high‐density polyethylene (HDPE), poly(ethylene terephthalate) (PET), and multiwalled carbon nanotube (CNT) were prepared in a twin screw extruder followed by hot stretching of PET/CNT phase in HDPE matrix. For comparison purposes, the HDPE/PET blends and HDPE/PET/CNT composites were also produced without hot stretching. Extrusion process parameters, hot‐stretching speed, and CNT amount in the composites were kept constant during the experiments. Effects of PET content and molding temperature on the morphology, electrical, and mechanical properties of the composites were investigated. Morphological observations showed that PET/CNT microfibers were successfully formed in HDPE phase. Electrical conductivities of the microfibrillar composites were in semi‐conductor range at 0.5 wt% CNT content. Microfiber reinforcement improved the tensile strength of the microfibrillar HDPE/PET/CNT composites in comparison to that of HDPE/PET blends and HDPE/PET/CNT composites prepared without hot stretching. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

PA1 01 O/CB、PE/CB体系的PTC效应研究

研究了炭黑(CB)含量对LDPE、HDPE、PA1010电阻率的影响,以及LDPE/CB、HDPE/CB、PA101/CB复合体系的电阻-温度特性,发现PA101/CB体系的正温度系数(PTC)转变温度较高,但与HDP/CB体系相比,其PTC强度却很低,不适于制备PTC材料.HDPE/CB体系在160℃附近具有较高的PTC效应,且辐射交联可消除其负温度系数(NTC)效应,容易加工成型,是制备低温区PTC材料的较好体系.     

Conductive Materials for Proton Exchange Membrane Fuel Cell Bipolar Plates Made from PVDF,PET and Co‐continuous PVDF/PET Filled with Carbon Additives

The aim of this work was to develop and characterise electrically conductive materials for proton exchange membrane fuel cells and bipolar plates (BPPs). These BPPs were made from highly conductive blends of polyethylene terephthalate (PET) and polyvinylidene fluoride (PVDF), as matrix phase. The conductive materials were developed from carefully formulated blends composed of conductive carbon black (CB) powder and, in some cases, graphite synthetic flakes mixed with pure PET, PVDF or with PVDF/PET systems. They were first developed by twin‐screw extrusion process then compression‐molded to give BPP final shape. As the developed blends have to meet properties suitable for BPP applications, they were characterised for their rheological properties, electrical through‐plane resistivity (the inverse of conductivity), oxygen permeability, flexural and impact properties. Results showed that lower resistivity was obtained with PVDF/CB blends due to the higher interfacial energy between the PVDF matrix and CB and also the higher density and crystallinity of PVDF, compared to those of PET. It was also observed that the lowest resistivity values were obtained with mixing PVDF and PET at controlled compositions to ensure PVDF/PET co‐continuous morphology. Also, slow cooling rates helped to attain the lowest values of through‐plane resistivity for all studied blends. This behaviour was related to the higher crystallinity obtained with low cooling rates leading to smaller amorphous regions in which carbon particles are much more concentrated.     

Blends of polypropylene and ethylene octene comonomer with conducting fillers: Influence of state of dispersion of conducting fillers on electrical conductivity

Blends of polypropylene/ethylene octene comonomer (PP/EOC) with conducting fillers viz., carbon black (CB) and multiwall carbon nanotubes (MWNT) were prepared using melt mixing technique with varying filler concentration and blend compositions. Thermo gravimetric analysis studies indicated that presence of filler enhanced the thermal stability of PP/EOC blends. Morphological analysis revealed the formation of matrix‐dispersed droplet and co‐continuous type of morphology depending on the blend compositions. Significant reduction in droplet size and finer ligament thickness in co‐continuous structure were observed in the blends with filler due to compatibilization action. Fillers were found to be aggregated in the EOC phase irrespective of blends compositions and could be related to the affinity of the fillers toward EOC phase. The electrical conductivity of PP/EOC blends with CB and MWNT was found to be highest for 80/20 composition and decreased as EOC content increased. The percolation threshold of CB was between 10 and 15 wt% for the 80/20 and 70/30 blends whereas it was 15–20 wt% for blends with EOC content higher than 30 wt%. The percolation threshold was 2–3 wt% MWNT for PP/EOC blends. This was attributed to the aggregated filler network preferentially in the EOC phase. The melt‐rheological behavior of PP/EOC blends was significantly influenced in presence of both the fillers. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers