Low Carbon Black Content Research Articles

Tunable electromagnetic interference shielding performance of polypropylene/carbon black composites via introducing microcellular structure

The introduction of cell structures in conductive polymer composites (CPCs) has considerable impacts on electromagnetic interference (EMI) shielding performance of the final CPC foams, and thus it is necessary to clarify the effects of cell structures on the shielding effectiveness (SE) and mechanisms of CPC foams with different filler loadings and expansion ratios more systematically. Herein, polypropylene (PP)/carbon black (CB) composite foams were prepared by core-back foam injection molding (FIM), and their cell structures were well-controlled by changing the CB content and expansion ratio. The results showed that, at different CB contents, the surface EM reflection of all PP/CB foams decreased with increasing the expansion ratio, while their SE values exhibited different trends possibly owing to the changes of sample thickness as well as internal multiple EM reflections/scattering, interfacial polarization and conductive loss during EMI shielding. The EMI SE declined with the increase of expansion ratio for the PP/CB foam with low CB content of 10 wt%, but it was improved for the foam with high CB content of 30 wt%. At a middle CB content of 22.5 wt%, however, the EMI SE of the PP/CB foam first decreased and then increased with the increase of expansion ratio. Our study provides an efficient method to tune the EMI-shielding properties of CPC foams without changing the material weight.

Self-Healing Hydrophilic Porous Photothermal Membranes for Durable and Highly Efficient Solar-Driven Interfacial Water Evaporation

Self-Healing Hydrophilic Porous Photothermal Membranes for Durable and Highly Efficient Solar-Driven Interfacial Water Evaporation

Synthesis, thermal and anticorrosion performance of WPU nanocomposites with low carbon-black content by adding amine-modified multiwall carbon nanotube

A novel waterborne polyurethane (WPU) nanocomposite modified by composite fillers consists of amine-modified multiwall carbon nanotube (NH2-MCNT) and carbon black (CB) has been successfully prepared in this study. IR spectra of the nanocomposites indicated that there were interfacial interactions between the hard segments of PU chains and the filler particles. Thermal properties showed that added composite fillers raised the thermal stability of nanocomposites and glass transition temperature of hard segments (Tg-H), which was probably due to the uniformly dispersed filler particles, increased crosslink density of composites and the strong interfacial interactions between the fillers and WPU matrix evidenced by SEM and TEM microphotographs. Furthermore, the other properties of nanocomposite coatings were evaluated by contact angle measuring system and potentiodynamic polarization measurements. The results indicated that the fillers strengthened the hydrophobicity of the nanocomposites coatings and enhanced the resistance to corrosion.

Conductive coatings with low carbon-black content by adding carbon nanofibers

Abstract Conductive coatings based on low carbon-black content by adding carbon nanofibers are obtained in a silica matrix obtained by the sol–gel process. The carbon nanofibers incorporation allows reducing the percolation threshold down to 20 wt.% of carbon black into the silica matrix obtaining good electrical properties. Coatings are deposited by air-spray deposition onto tile substrates and sintered in the temperature range of 300–500 °C in air atmosphere. The coatings achieve resistivities as low as 2 × 10 −3 Ωm due to the percolation between the carbon black nanoparticles and carbon nanofibers which improves the conductive paths. The samples are microstructural characterized by Scanning Electron Microscopy and Confocal Raman Spectroscopy. The electrical properties are measured by impedance spectroscopy. The thermal properties derived of the Joule effect are measured using DC intensity–voltage curves and thermal infrared camera, and it is observed a nearly linear relationship between electric power and temperature increasing in the measured range. Thereby, a wide range of application is opened by means of tailoring the electrical response of the coatings: higher resistivity coatings produce thermal heating above 90 °C, appropriated for electric heaters, and conductive coatings are suitable for electronic devices, electrodes and EMI/RFI shielding.

Effect of the Extrusion Process on the Morphology and Electrical Conductivity of Injection-Moulded Polypropylene/HDPE/Carbon Black Composites

In this work, isotactic polypropylene (iPP)/high density polyethylene (HDPE) composites filled with carbon black (CB) were prepared by the mild compounding method and the common melt-mixing method. The selective distribution of CB particles in the immiscible iPP/PE blends was determined by the interfacial tensions, but the morphologies of the polyblends strongly depended on the compounding method. The mild compounding method strongly affected PE phases to form triple phase morphology in the composites, which inhibited effective conductivity network formation in the low CB content range. A skin-core structure of the iPP/HDPE/CB composite, prepared by the common melt-mixing process, was present when an effective conductivity network was obtained, and a co-continuous structure of the iPP/HDPE matrix is not necessary.

Preparation of a Novel Oriented Structure in Carbon Black Filled Isotactic Polypropylene Composites by Microwave Selective Heating

Microwave heating technology has numerous advantages compared with the traditional heating methods and has been widely used to process materials. However, most thermoplastics do not possess a sufficiently high dielectric property to be heated by microwaves. In this study, carbon black (CB) was utilized as the microwave absorber to improve the microwave heatability of isotactic polypropylene (iPP). Effects of CB contents on the microwave heatability of iPP/CB composites were studied. The temperature of iPP/CB composites with relatively low CB content (5% and 10%) increased slowly and tended to remain unchanged after 120 s of microwave exposure. In contrast, iPP/CB composites with relatively high CB content (15% and 20%) presented a much faster heating rate and the temperature of the sample kept increasing with the prolongation of exposure time. On the basis of the fact that iPP/CB composites with different CB contents have different microwave heatability, a novel oriented structure, in which the core layer has relatively high orientation and the surface layer has relatively low orientation, was prepared by selective microwave heating. Two-dimensional wide angle X-ray diffraction (2D-WAXD) analysis indicates that the orientation parameter calculated by the (040) plane of the surface layer (0.45) was lower than that of the core layer (0.83). The novel oriented structure is different from the common skin-core structure formed in the samples of semicrystalline polymers by traditional polymer processing methods, in which orientation of the skin layer is higher than that of the core layer. The novel oriented structure has not been reported before to our knowledge and its formation mechanism is also discussed in this paper.

Characterization of Carbon Black Particles Dispersion in Polymeric Matrix by Indirect Methods

Abstract Polypropylene (PP)/carbon black (CB) films were prepared via a two-step masterbatch (MB) dilution technique, by the aid of dynamic mixer following two single-screw extruders. The films were quantitatively characterized by color difference (CD), blackness and thermogravimetric analysis (TGA) methods. In the paper, the CD was numerically expressed by CD values. Furthermore, the CD values of films follow quasi-normal distribution as tested by the skewness-kurtosis method. The test of significance confirms the CD values of films are ≤1 NBS (U.S. National Bureau of Standards), which demonstrates CB particles were mixed uniformly in their polymeric matrix. The CD values (quantification) and grey card series (GS, qualification) conform to certain mathematical equation: when CD≤3.4,GS=5-CD/1.7; when CD>3.4, GS=5-lg(CD/0.85)/lg2. In addition, in order to evaluate comprehensively the mixing effect, blackness and TGA method were also employed. With the increment of CB content, the blackness of films increases, which infers that the color difference due to mixing effect of CB particles should be indirectly expressed by blackness. TGA method characterizes mixing uniformity by comparing discrepancy of ash content between films. The results indicate that the films with low CB content have a good mixing effect, while high CB content is unfavorable to decreasing the error of the TGA method.

Non-Isothermal Crystallization Behavior of Poly(Ethylene Terephthalate)/Carbon Black Composite

Poly(Ethylene Terephthalate)(PET)/carbon black(CB) composite was prepared by melt blending using a separate feeding technique. The non-isothermal crystallization process of virgin PET and PET/CB composite were investigated by differential scanning calorimetry (DSC) and the different methods such as Jeziorny modified Avrami equation, Ozawa equation and the method developed by Mo were employed to analyze the non-isothermal kinetics of virgin PET and PET/CB composite. The results show that the CB particles dispersed in PET matrix act as heterogeneous nucleating agents, while CB particles hinder the movement of molecular chains of PET, meanwhile, the crystallization activation energy(⊿E) of PET/CB composite is much greater than that of virgin PET according to Kissinger formula, which is opposite to the low CB content condition. This indicates that CB particles reduce the rate of crystal growth. Whereas, the results obtained from the mentioned three methods simultaneously demonstrate the addition of CB greatly increases crystallization temperature and crystallinity and accelerates crystallization rate. Taking the two seemingly contradictory results, crystal growth has little effect on the crystallization rate and crystal nucleation dominate the crystallization process of PET/CB composite with very high CB content. According to Jeziorny method, the constant of crystallization rate (Zc) increases with the increment of cooling rate and Avrami index (n) doesn’t change significantly, but the Zc and n of PET/CB composite are greater than that of PET. Based on Ozawa method, lg[-ln(1-Xt)] and lgR don’t show a good linear relationship. The parameter F(T) increases significantly with the increasing of relative crystallinity and n is almost unchanged. Besides, the F(T) of PET/CB composite is less than that of PET, while a is greater than that of PET. Comparing with Ozawa and Avrami equation, Mo method can better describe the non-isothermal crystallization of PET and PET/CB composite.

In situ synthesis of polyoxadiazoles (POD) and carbon black (CB) as an approach to POD/CB nanocomposites

Pristine carbon black was oxidized with poly(phosphoric acid) to produce carboxyl groups. The carboxyl groups were consecutively treated with hydrazine sulfate to introduce arylcarbonyl and CONHNH2 groups. The groups on the CB surface were reacted with dicarboxylic acid to anchor the growing of polyoxadiazole chains. The properties of the bulk POD/CB composites were characterized by elemental analysis (EA), Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA). The final composites were processed in films using a solution method aided by the use of a mini-calendar for final high shear mixing. Transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic mechanical thermal analysis (DMTA) and tensile tests were used to systemically characterize the high performance composite films. The POD composites with high molecular weight (in the order of magnitude of 105g/mol) were soluble in polar aprotic solvents and stable at temperatures as high as 465°C. The incorporation of the CB enhanced the overall mechanical properties of the composites at low CB content due to the presence of strong interfacial interaction between the polymer matrix and the filler.

Synergy effect of hybrid fillers on the positive temperature coefficient behavior of polypropylene/ultra‐high molecular weight polyethylene composites

AbstractHybrid nanocomposites of polypropylene/ultra‐high molecular weight polyethylene (PP/UHMWPE, 70/30) with various amounts of carbon black (CB) and carboxylated multiwalled carbon nanotubes (c‐MWNTs) were prepared by the solution mixing and melt blending techniques. The effects of the mixture of CB and c‐MWNTs on the positive‐temperature‐coefficient (PTC) behavior and the negative‐temperature‐coefficient (NTC) behavior, as well as the room temperature resistivity, were studied. The transmission electron microscopy (TEM) images showed that the CB particles were aggregated at the interface, between PP and UHMWPE. This selective localization of the CB particles at the interface along with the formation of continuous conducting media leads to the formation of additional conducting networks, resulting in a percolation threshold at a low CB content. A synergy effect of the hybrid conducting fillers of CB and c‐MWNTs on the PTC behavior of the hybrid blends was also observed. The room temperature resistivity was reduced significantly by the incorporation of the c‐MWNTs into the PP/UHMWPE/CB composite. The intensity and repeatability of the PTC effect in the nanocomposites were improved and the NTC effect weakened by incorporating a small amount (0.5 wt %) of c‐MWNTs. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Ethylene–acrylic acid copolymer induced electrical conductivity improvements and dynamic rheological behavior changes of polypropylene/carbon black composites

AbstractThe experimental data reveal that the addition of ethylene–acrylic acid copolymer (EAA) into carbon black (CB)/polypropylene (PP) composites can improve the electrical conductivity of CB/PP composites by two to six orders of magnitude at a comparatively low CB content (φ), and when φ = 2.5 vol %, 60/40 of PP/EAA is an optimum for electrical conductivity improvement. The dynamic rheological data show that with increasing φ there are apparent rheological percolations for CB/PP composites. A modified Kerner–Nielson equation can be used to describe the correlation between electrical percolation and dynamic viscoelastic percolation. The addition of EAA into CB/PP composites leads to apparent changes in dynamic rheological behaviors. When φ = 2.5 vol %, a rheological percolation appears in CB/PP/EAA (CPE) composites with increasing EAA content. The similar rheological behaviors correspond to the similar morphological structures for CPE composites with φ = 5.0 vol %. The appearance of bumps in the van‐Gurp–Palmen plots corresponds to the formation of network structure in CB/PP and CPE composites, and the more perfect the networks, the higher the amplitude of the bumps. All data indicate that the van‐Gurp–Palmen plot is sensitive to the formation of filler particle networks or cocontinuous phase which spans the whole composite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1762–1771, 2009

Effect of Processing Method on Conductivity and Mechanical Properties of Glass Fibre Reinforced Carbon Black Filled Polyethylene

The conductivity and mechanical properties of carbon black (CB) filled polyethylene (PE) composites depend on the conductive filler, molecular structure of polymer matrix, and the processing methods which are applied. CB filled high density polyethylene without and with glass fibre (GF) composites have been manufactured using single and twin screws extruder. The composite made from the single screw extruder showed a much higher conductivity than that made from twin screws extruder for CB/PE composites with and without glass fibre. The conductive paths are formed at very low CB content (1wt% CB for GF/CB/PE) when using single screw extruder to manufacture. The microstructure of these composites were analysed using SEM.

Nanoparticle induced network self-assembly in polymer–carbon black composites

A novel percolation phenomenon with inorganic nanoparticle loading in polyamide 6-carbon based nanoparticle hybrids was identified. Percolation threshold substantially shifts to lower carbon black (CB) volume fractions in the presence of optimum concentration of chemically modified montmorillonite (organoclay) while the effective organoclay concentration can be optimized to lower the slope of percolation curve maintaining electrical conductivity within static dissipative 10−6–10−9Scm−1 range. Organoclay/CB ‘nano-unit’ morphology was found in polyamide 6 ternary hybrids. It is composed of stacked organo-montmorillonite platelets that deform to wrap partially around one or two primary CB aggregates. This elementary nano-unit structure induces CB network self-assembly within polyamide 6 matrices. The structure was found to be prevalent throughout the polymer matrix. This morphology remains robust under wide range of thermal-deformation histories due to the strong preferred organoclay/polyamide 6/CB interactions that partially blocks the electron conduction and hopping mechanisms with clay ‘walls’ thereby reducing the slope of the percolation curve. Organoclay can be used as a dispersion control agent in these polymer–carbon systems to induce self-assembly of CB network at low CB content, simultaneously, partial blocking the electron hopping pathways to level the slope of percolation curves. High order exfoliation and nano-scale dispersion of organoclay is essential to induce this advanced percolation phenomenon.

The role of the surface microstructure of the microfibrils in an electrically conductive microfibrillar carbon black/poly(ethylene terephthalate)/polyethylene composite

Carbon black (CB) loading greatly affects the in-situ fibrillation of CB/poly (ethylene terephthalate) (PET) compound in a polyethylene (PE) matrix during melt mixing, slit die extrusion and hot stretching. CB/PET/PE composites with lower CB loadings display well-defined CB/PET microfibrils in which all the CB particles are localized. The surface microstructure (mainly amount and distribution of CB particles) of in-situ CB/PET microfibrils is a key factor determining the electrical conductivity of the microfibrillar composite, and is dominated by the CB content in the in-situ CB/PET microfibrils. With low CB content, there are hardly any CB particles on the surface of the CB/PET microfibril. The volume resistivity of in-situ microfibrillar composite remains high. With higher CB loading, the number of CB particles on the surfaces of the microfibrils increases significantly. Above a critical value (maximum packing fraction), the microfibril network was connected by electrically conductive contact points and thus was able to sustain electron transmission in the whole system. As a result, the volume resistivity of in-situ microfibrillar CB/PET/PE composite dropped sharply and percolation occurred.

PTC behavior of polymer composites containing ionomers upon electron beam irradiation

We have prepared polymer composites of low-density polyethylene (LDPE) and ionomers (Surlyn 8940) containing polar segments and metal ions by melt blending with carbon black (CB) as a conductive filler. The resistivity and positive temperature coefficient (PTC) of the ionomer/LDPE/CB composites were investigated with respect to the CB content. The ionomer content has an effect on the resistivity and percolation threshold of the polymer composites; the percolation curve exhibits a plateau at low CB content. The PTC intensity of the crosslinked ionomer/LDPE/CB composite decreased slightly at low ionomer content, and increased significantly above a critical concentration of the ionomer. Irradiation-induced crosslinking could increase the PTC intensity and decrease the NTC effect of the polymer composites. The minimum switching current (Itrip) of the polymer composites decreased with temperature; the ratio ofItrip for the ionomer/LDPE/CB composite decreased to a greater extent than that of the LDPE/CB composite. The average temperature coefficient of resistance (αT) for the polymer composites increased in the low-temperature region.

Electric Properties of Conducting Composite from Poly(ethylene oxide) and Poly(ethylene oxide)-Grafted Carbon Black in Solvent Vapor

A conducting composite from high molecular weight poly(ethylene oxide)(PEO) and low molecular weight PEO-grafted carbon black(CB) was prepared. The electric resistance of the composite in dry air and chloroform vapor was examined. The effects of many factors, such as CB content, CB type and its dispersion in composite, and thickness of the composite film, on the ratio of electric resistance of the composite in dry air (R0) and in chloroform vapor (R), defined as responsiveness (R/R0) of the conducting composite, were investigated. For both CB (Porousblack and Asahi 60H black) used in this study, at CB content of 20—50 wt%, the responsiveness is high over 104 time. In the case of low CB content, the responsiveness is lower than 0.1. To explain the responsiveness of the composite for high and low CB content, two conduction mechanisms were proposed. To clarify the relationship between responsiveness and amount of vapor absorption, a method to simultaneously determine the resistance and vapor absorption amount of the composite was developed.