Nylon 6 induced morphological developments and electrical conductivity improvements of polypropylene/carbon black composites

In this study, a polar conductive filler [carbon black (CB)], a nonpolar polymer [polypropylene (PP)], and a polar polymer [nylon 6 (PA6)] were chosen to fabricate electrically conductive polymer composites by melt blending and compression molding. The morphological developments of these composites were studied. Scanning electron microscopy results showed that in a CB‐filled PP/PA6 (CPA) composite, CB particles were selectively dispersed in PA6 phases and could make the dispersed particles exist as microfiber particles, which could greatly improve the electrical conductivity. The PA6 and CB contents both could affect the morphologies of these composites. The results of electrical resistivity measurements of these composites proved the formation of conductive networks. The resistivity–temperature behaviors of these composites were also studied. For CB‐filled PP (CP) composites, there were apparent positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effects and an unrepeatable resistivity–temperature characteristic. However, for CPA composites, there were no PTC or NTC effects from room temperature to 180°C, and the resistivity–temperature behavior showed a repeatable characteristic; this proved that CB particles were selectively dispersed in the PA6 phase from another point of view. All experimental results indicated that the addition of PA6 to a CP composite could lead to an expected morphological structure and improve the electrical conductivity of the CP composite. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

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     

Influence of morphology on positive temperature coefficient effect for conductive polymer composites with carbon black dispersed at interface

Selective localization of carbon black (CB) at the interface of polymer blends was achieved by the method that EBA‐g‐MAH was first reacted with CB, and then blended with poly(ethylene‐co‐butyl acrylate)/nylon6 (EBA/PA6). In CB‐filled EBA/PA6 blends, EBA and PA6 phases formed cocontinuous morphology and CB was localized in PA6 phase. The percolation threshold was 5 wt%. A single PTC (positive temperature coefficient) effect was observed in this composite. The appearance of PTC effect was originated from the thermal expansion of EBA phase. In the EBA‐g‐MAH filled EBA/PA6 blends, TEM results showed that CB particles were induced by EBA‐g‐MAH to localize at the interface, resulting that the percolation threshold was much lower than that of EBA/PA6/CB. Influence of morphology on PTC effect of EBA/PA6/EBA‐g‐MAH/CB composites was studied. In the composites with sea‐island morphology, the conductive network was fabricated by dispersed phase and CB at the interface. Thermal expansion of matrix interrupted the contact of dispersed phases and conductive network formed by CB particles at the interface, resulting in the double PTC effect. The composites with co‐continuous morphology exhibited single PTC effect due to the fact that conductive network was only fabricated by CB localized at the interface. POLYM. ENG. SCI., 53:2640–2649, 2013. © 2013 Society of Plastics Engineers     

Thermodynamically induced self‐assembled electrically conductive networks in carbon‐black‐filled ternary polymer blends

By calculating the surface tensions of the components, composites with innovative thermodynamically induced self‐assembled electrically conductive networks were designed, prepared and investigated. Carbon black (CB) was added into a ternary blend system comprised of poly(methyl methacrylate) (PMMA), ethylene–acrylic acid copolymer (EAA) and polypropylene (PP). Scanning electron microscopy images show that the PMMA/EAA/PP ternary blend forms a tri‐continuous phase structure like a sandwich, in which PMMA and PP form a co‐continuous phase while EAA spreads at the interface of the PMMA and PP phases as a sheath. The micrographs and resistivity–temperature characteristic curve results indicate that CB fillers are selectively located at the interface of the PMMA and PP phases, namely the EAA phase. The percolation threshold of PMMA/EAA‐CB/PP composites is 0.2 vol%, which is only one‐fifth of that of PP/CB composites. Copyright © 2011 Society of Chemical Industry     

Characterization of carbon black‐filled immiscible polypropylene/polystyrene blends

The electrical and rheological behaviors of carbon black (CB)‐filled immiscible polypropylene (PP)/polystyrene (PS) blends were investigated. The compounding sequence influences the phase morphology of the ternary CB/PP/PS composites and the distribution of CB aggregates. Simultaneous measurements of resistance and dynamic modulus were carried out to monitor the phase coalescence of the ternary composites and CB migration and agglomeration in the PS phase during annealing at temperatures above the melting point of PP. The variation of resistivity is mainly attributed to CB agglomeration in the PS phase and the interfacial region, while the variation of dynamic modulus is regarded as the superimposition of the phase coalescence and CB agglomeration in the PS phase. The ternary composites with the majority of CB particles distributed in the interfacial region show the lowest conductive percolation threshold and the most stable resistivity–temperature performance during heating–cooling cycles. Copyright © 2011 Society of Chemical Industry     

Rheological and electrical properties of carbon black‐based poly(vinylidene fluoride) composites

Carbon black (CB)–filled poly(vinylidene fluoride) composites (PCBp) were prepared by melt compounding. The linear rheology was then studied in detail. The composites show typical solid‐like response in the low‐frequency region, which is attributed to the percolation of CB particles. However, the transient percolated CB network is temperature dependent during the small amplitude oscillatory shear flow. Therefore, the principle of time–temperature superposition is invalid on the dynamic rheological responses of those percolated PCBp. A two‐phase viscoelastic model was then used to further describe the linear responses of PCBp to relate hierarchical structures of CB particles to flow responses of composites. In addition, the electrical and dielectric properties of PCBp were also investigated, aiming at further exploring the percolation behavior of CB. POLYM. ENG. SCI., 53:2541–2548, 2013. © 2013 Society of Plastics Engineers     

Special electrical conductivity of carbon black‐filled two‐phased thermoplastic vulcanizates

The electrical properties of carbon black (CB)‐filled two‐phased thermoplastic vulcanizates (based on ethylene‐propylene‐diene copolymer and polypropylene, TPV) were investigated in this article. The results showed that the composites had a singularity in electrical conductivity compared with CB‐filled polypropylene composites. Both the loading of CB and the concentration of rubber phase in TPV had the remarkable effect on electrical property of composites. The rubber particles in TPV presented unique and competitive effects in constructing CB electrical conducting network, namely exclusion and block effects. The percolation threshold value of composites apparently decreased with rubber phase content. However, percolation behavior of composites was weakened when rubber phase content was very high. The percolation behavior of composites with loading of CB is weakened apparently by rubber particles. When annealing the composites in the melt state, the resistance‐time dependence of composites was strongly affected by the pressure of mold annealing. Although air aging had a negligible effect on the electrical properties, the microstructure of the CB/TPV composites had changed during air aging. CB/TPV composite only exhibited the negative temperature coefficient behavior even though the temperature was in the melting region of polypropylene, which was mainly attributed to the exclusive effect brought by the thermal expansion of rubber particles. The special electrical properties of CB/TPV can find potential application in many fields. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of glass fiber on the electrical resistivities of polyoxymethylene/maleic anhydride‐grafted polyethylene/multiwalled carbon nanotube composites

The effect of glass fiber (GF) on the electrical resistivities of polyoxymethylene (POM)/maleic anhydride‐grafted polyethylene (MAPE)/multiwalled carbon nanotube (MWCNT) composites is investigated. The POM/MAPE/MWCNT composites at a MWCNT loading of 0.75% are nonconductive because most of MWCNTs are isolated in the MAPE islands, and their electrical resistivities decrease significantly after the addition of GF because of the formation of MAPE‐coated GF structure, which facilitates the formation of conductive paths and was confirmed by field emission scanning electron microscopy (FESEM). The formation of MAPE‐coated GF structure is attributed to the interaction between GF and MAPE during melt compounding, as contrasted by the uncoated GF using high‐density polyethylene (HDPE) instead of MAPE. Nonconductive POM/5–20% MAPE/0.75% MWCNT composites become conductive upon the addition of 20% GF. This preparation method for conductive materials can be generalized to POM/5–20% maleic anhydride‐grafted polypropylene (MAPP)/0.75% MWCNT composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41794.     

Electrical conductivity and electromagnetic interference shielding effectiveness of carbon black/sisal fiber/polyamide/polypropylene composites

The effects of hybrid fillers on the electrical conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) of polyamide 6 (PA6)/polypropylene (PP) immiscible polymer blends were investigated. Carbon black (CB) and steam exploded sisal fiber (SF) were used as fillers. CB was coated on the surface of SF, and this was exploded by water steam to form carbon black modified sisal fiber (CBMSF). CB/SF/PA6/PP composites were prepared by melt compounding, and its electromagnetic SE was tested in low‐frequency and high‐frequency ranges. We observed that SF greatly contributed to the effective decrease in the percolation threshold of CB in the PA6/PP matrix and adsorbed carbon particles to form a conductive network. Furthermore, an appropriate CB/SF ratio was important for achieving the best shielding performance. The results indicate that CBMSF was suitable for use as electronic conductive fillers and the CB/SF/PA6/PP composites could be used for the purpose of EMI shielding. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42801.     

Electrical properties and morphology of carbon black‐filled HDPE/EVA composites

The sensitive effect of weight ratio of the high‐density polyethylene (HDPE)/ethylene‐vinylacetate copolymer (EVA) on the electrical properties of HDPE/EVA/carbon black (CB) composites was investigated. With the EVA content increasing from 0 wt % to 100 wt %, an obvious change of positive temperature coefficient (PTC) curve was observed, and a U‐shaped insulator‐conductor‐insulator transition in HDPE/EVA/CB composites with a CB concentration nearby the percolation threshold was found. The selective location of CB particles in HDPE/EVA blend was analyzed by means of theoretical method and scanning electron micrograph (SEM) in order to explain the U‐shaped insulator‐conductor‐insulator transition, a phenomenon different from double percolation in this composite. The first significant change of the resistivity, an insulator‐conductor transition, occurred when the conductive networks diffused into the whole matrix due to the forming of the conductive networks and the continuous EVA phase. The second time significant change of the resistivity, a conductor‐insulator transition, appeared when the amorphous phase is too large for CB particles to form the conductive networks throughout the whole matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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     

Thermoplastic polyurethane–carbon black compounds: Structure,electrical conductivity and sensing of liquids

Thermoplastic polyurethane (TPU) copolymers are interesting host matrices for the incorporation of conductive carbon black (CB) particles. The two‐phase character of the TPU systems provides an opportunity for the CB particles to distribute nonuniformly within the phases, owing to their different characteristics. Thus, in spite of its highly polar nature, the TPU/CB system percolates at a relatively low CB content. The CB presence affects the TPU two‐phase structure, resulting in a large change of its low temperature loss modulus. CB‐containing extruded filaments produced by a capillary rheometer at various shear rates were studied as sensing materials for different alcohols. All filaments displayed an increase in resistance upon exposure to various alcohols. Filaments exposed to methanol exhibited the highest sensitivity. This behavior was related to the sorption kinetics by the TPU/CB compound, which is affected by the different characteristics of the solvents. The resistance of filaments exposed to ethanol or methanol tended to reversibility during the drying cycle, returning to the initial values. The relatively rapid recovery to the filaments' initial resistance values (for methanol and ethanol) suggests that the structural changes due to solvent sorption mainly occur in the outer skin regions of the extruded filaments, whereas the core region remains essentially intact.     

Mechanical,thermal, and dynamic mechanical properties of long glass fiber‐reinforced thermoplastic polyurethane/polyoxymethylene composites

Long glass fiber (LGF)‐reinforced thermoplastic polyurethane (TPU) elastomers and polyoxymethylene (POM) (LGF/TPU/POM) composites were prepared by using self‐designed impregnation device. Dynamic mechanical properties of the LGF/TPU/POM composites have been investigated by using dynamic mechanical thermal analysis. The results indicated that the storage modulus and glass transition temperature of the composites increase with increasing the glass fibers content and scanning frequencies. In addition, the Arrhenius relationship has been used to calculate the activation energy of α‐transition of the LGF/TPU/POM composites. The thermal stability of the LGF/TPU/POM composites was investigated by thermogravimetric analysis. The consequence demonstrated that the thermal stability increase with augmenting the content of glass fibers. The mechanical properties of the composites are investigated by a universal testing machine and a ZBC‐4 Impact Pendulum. The results demonstrated the mechanical properties of the composites aggrandize with augmenting the glass fibers content. The good dispersion of the LGFs in the matrix resins is obtained from scanning electron micrographs. POLYM. COMPOS., 35:2067–2073, 2014. © 2014 Society of Plastics Engineers     

Crystallization and melting behavior of multi‐walled carbon nanotube‐reinforced nylon‐6 composites

The crystallization and melting behavior of neat nylon‐6 (PA6) and multi‐walled carbon nanotubes (MWNTs)/PA6 composites prepared by simple melt‐compounding was comparatively studied. Differential scanning calorimetry (DSC) results show two crystallization exotherms (T_{CC, 1} and T_{CC, 2}) for PA6/MWNTs composites instead of a single exotherm (T_{CC, 1}) for the neat matrix. The formation of the higher‐temperature exotherm T_{CC, 2} is closely related to the addition of MWNTs. X‐ray diffraction (XRD) results indicate that only the α‐phase crystalline structure is formed upon incorporating MWNTs into PA6 matrix, independently of the cooling rate and annealing conditions. These observations are significantly different from those for PA6 matrix, where the increase in cooling rate or decrease in annealing temperature results in the crystal transformation from α‐phase to γ‐phase. The crystallization behavior of PA6/MWNTs composites is also significantly different from those reported in PA6/nanoclay systems, probably due to the difference in nanofiller geometry between one‐dimensional MWNTs and two‐dimensional nanoclay platelets. The nucleation sites provided by carbon nanotubes seem to be favorable to the formation of thermodynamically stable α‐phase crystals of PA6. The dominant α‐phase crystals in PA6/MWNTs composites may play an important role in the remarkable enhancement of mechanical properties. Copyright © 2005 Society of Chemical Industry     

Production of electrically conductive networks in immiscible polymer blends by chaotic mixing

A minor polymer was deformed into lamellar and fibrillar morphological forms in a chaotic mixer, which rendered the resultant immiscible blend electrically conductive along the flow direction. This was demonstrated using a blend consisting of 10 wt% polypropylene (PP), polyamide 6 (PA6), and 1 wt% conductive carbon black (CB) particles. It was found that PP‐phase containing CB particles deformed into lamellar and fibrillar morphological forms produced continuous networks in the flow direction, and provided conductivity by double percolation. Breakup of PP fibrils into droplets destroyed the continuous conductive networks, although conductivity was sustained purportedly due to migration of CB particles from the bulk to the surface of closely spaced PP droplets. This was augmented by the formation of much smaller PP droplets in the presence of CB particles. On continued mixing, the blend eventually turned into insulator as CB particles migrated from the polymer–polymer interfaces to PA6 phase. POLYM. ENG. SCI., 46:19–28, 2006. © 2005 Society of Plastics Engineers     

Effect of Mixing Process and Morphologies on the Electrical Conductivity of PA6/EVA/CB Composites

Nylon6 (PA6)/Ethylene-(vinyl acetate) (EVA)/carbon black (CB) composites with different electrical conductivity were prepared in an internal mixer. The factors influencing the electrical conductivity of the ternary composites were investigated, including mixing mode, mixing time and mass ratio of PA6 and EVA, and so on. Among three kinds of PA6/EVA/CB composites, including ones prepared by directly mixing (composites A), EVA and CB were mixed prior to melt-compounding with PA6 (composites B) and PA6 and CB were mixed prior to melt-compounding with EVA (composites C), the mixing time only significantly influenced the electrical conductivity of composites A. Good conductivity of the composites could be realized because the distance between CB particles became closer with the increasing of mixing time. However, the mixing time has no effect on the electrical properties of the composites B and the composites C, due to there were no CB particles migrated phenomenon happened. Scanning electron microscopy (SEM) was used to assess the fracture surface morphologies and the dispersion of the CB particles. The results showed that the dispersion of the CB particles significantly affects the electrical conductivity of the composites. Based on the study of the influence of various mass ratios of EVA and PA6 on the morphologies and electrical properties of PA6/EVA composites filled with 10 phr (parts per hundred resins) CB particles, we suggested that the mass ratio of EVA and PA6 affected the volume resistivity of the ternary composites significantly. In addition, the composites were almost insulation when the mass ratios of EVA and PA6 were 80/20 and 70/30, while the composites became conductivity with the mass ratio of EVA and PA6 higher than 60/40. The PA6/EVA/CB composites which CB particles locate at the interface of EVA and PA6 have the lowest volume resistivity when the mass ratio of two components was 60/40.     

Preparation of conductive polyphenylene sulfide/polyamide 6/multiwalled carbon nanotube composites using the slow migration rate of multiwalled carbon nanotubes from polyphenylene sulfide to polyamide 6

Conductive polyphenylene sulfide (PPS)/polyamide 6 (PA6)/multiwalled carbon nanotube (MWCNT) composites having 10–30 wt % PA6 and 1 wt % MWCNTs are prepared by melt mixing at 300°C for 8 min using a high concentration PPS/MWCNT masterbatch approach, and the migration kinetics of MWCNTs from thermodynamically unfavored PPS to favored PA6 was investigated. The morphology of the composites was investigated by field emission scanning electron microscopy and transmission electron microscopy, showing the localization of most MWCNTs in the PPS phase and at the interface, being different from the case of direct melt mixing where non‐conductive materials were obtained with most MWCNTs found in the PA6 phase and at the interface. The electrical resistivity and morphology of the materials as a function of time were investigated, showing that the conductive materials can be prepared within a mixing time of 4–16 min because of the slow migration rate of MWCNTs from PPS toward PA6, and MWCNTs can eventually migrate into the PA6 phase after a long mixing time of 30 min. The slow migration rate of MWCNTs was attributed to the high viscosity ratio of the two phases. This article shows a good example where the migration of MWCNTs was slow enough to control and can be used to prepare conductive polymer blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42353.     

Electrical conductivity and rheological behavior of multiphase polymer composites containing conducting carbon black

Multiphase polymer composites of carbon black (CB), polypropylene (PP) and low density polyethylene (LDPE) were prepared by melt‐mixing method to reduce the amount of CB in the conductive composites. SEM images showed that CB preferably located in LDPE phase and formed electrically conductive path. The measurement of conductive properties showed that the ternary materials possessed lower percolation than binary composites of CB/PP or CB/LDPE, the former was ～6 wt% and the latter was 9–10 wt%. Positive temperature coefficient (PTC) effects of the binary and ternary composites were investigated, indicating that the latter exhibited a relatively high PTC intensity. A rheological percolation estimated by a power law function is 2.66 wt% of CB loading, suggesting an onset of solid‐like behavior at low frequencies. This difference between the electrical and rheological percolation thresholds may be understood in terms of the smaller CB–CB distance required for electrical conductivity as compared with that required to impede polymer mobility. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Interfacial reaction and its influence on phase morphology and impact properties of modified‐polyacetal/thermoplastic polyurethane blends

The cationic polymerization of 1,3,5‐trioxane, 1,3‐dioxolane and a small amount of 2‐hydroxyacetic acid (HAA) was carried out, and the resulting modified‐polyacetal (POM) was blended with thermoplastic polyurethane (TPU) in melt. The results of ¹H NMR analysis indicated that HAA was almost incorporated in the modified‐POM, and that the resulting carboxyl end‐group and hydroxyl end‐group in the modified‐POM reacted with TPU during the melt blending. There were many boundary layers between the cavities and matrix in the modified‐POM/TPU (82/18 by weight) blend that was etched with tetrahydrofuran (THF), and the diameter of the cavities became ～0.3–1 μm long when the blending time reached 10 min. The results of scanning electron microscopic (SEM) observation and dynamic mechanical analysis (DMA) indicated that the modified‐POM/TPU blend had a good compatibility because of the interfacial reaction between the modified‐POM and TPU phase in the blend. The modified‐POM/TPU blend exhibited higher Charpy impact strength when compared with a normal‐POM/TPU blend; the toughness of the modified‐POM/TPU blend attributed to the good compatibility between the two phases. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4375–4382, 2006