Preparation and properties of octadecylamine modified graphene oxide/styrene‐butadiene rubber composites through an improved melt compounding method

Octadecylamine modified graphene oxide/styrene‐butadiene rubber (GO‐ODA/SBR) composites are prepared by a novel and environmental‐friendly method called “Improved melt compounding”. A GO‐ODA/ethanol paste mixture is prepared firstly, and then blended with SBR by melt compounding. GO‐ODA sheets are uniformly dispersed in SBR as confirmed by scanning electron microscope, transmission electron microscopy, and X‐ray diffraction. The interfacial interaction between GO‐ODA and SBR is weaker than that between GO and SBR, which is proved by equilibrium swelling test and dynamic mechanical analysis. GO‐ODA/SBR show more pronounced “Payne effect” than GO/SBR composites, indicating enhanced filler networks resulted from the modification of GO with ODA. GO‐ODA/SBR composite has higher tensile strength and elongation at break than SBR and GO/SBR composite. The tensile strength and elongation at break for the composite with 5 parts GO‐ODA per hundred parts of rubber increase by 208% and 172% versus neat SBR, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42907.     

Elastomeric ethylene copolymers with carbon nanostructures having tailored strain sensor behavior and their interpretation based on the excluded volume theory

Two ethylene/1‐butene thermoplastic elastomer copolymers were melt mixed with either multiwalled carbon nanotubes (CNTs) or thermally reduced graphite oxide (TrGO) resulting in piezoresistive composite materials. The effect of the polymer matrix, carbon nanostructure and filler concentration on the electrical behavior of the sensors was analyzed. The percolation process confirmed the relevance of these parameters as different thresholds were found depending on both the matrix and the filler. For instance, composites based on TrGO presented higher percolation thresholds than those based on CNTs. Regarding the strain sensor behavior of the electrically conductive composites, by using a matrix with a low amount of 1‐butene comonomer, higher resistance sensitivities were observed compared with the other matrix. Noteworthy, composites based on TrGO filler presented strain sensitivities one order of magnitude higher than composites based on CNT filler. These results are explained by the excluded volume theory for percolated systems. Based on these findings, polyethylene piezoresistive sensors can be designed by a proper selection of polymer matrix, filler concentration and carbon nanoparticles. © 2016 Society of Chemical Industry     

A new method to estimate thermal conductivity of polymer composite using characteristics of fillers

In this work, a new method to estimate the thermal conductivity of polymer composite was suggested. For this purpose, polymer composites composed of high‐density polyethylene (HDPE) and boron nitride (BN) were prepared by twin‐screw extruder melt‐mixing, followed by compression molding technique, and their microstructure was investigated by material simulation. Consequently, the C_f parameter of Agari and Uno equation, which represents an ease in forming conductive chains, was quantified by “Structure factor (related with conductive pathway)” and “Interfacial factors (related with thermal resistance)”, ultimately helping us evaluate the thermal conductivity of arbitrary composite system. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Natural rubber filled SiC and B4C ceramic composites as a new NTC thermistors and piezoresistive sensor materials

A novel electrically conductive composite for NTC thermistor and piezoresistive sensor was successfully fabricated by homogeneously dispersing conductive SiC and B₄C in an insulating natural rubber (NR) matrix. The morphology of the composites was investigated by means of scanning electron microscopy, cross linking density (n), volume fraction of rubber (V_r), and interparticle distance among conductive phases (r_p). The influence of the filler concentrations on the mechanical properties such as modulus of elasticity (E); hardness shore A (H), and elongation at break (EB) were studied in details. The dependences of volume resistivity of NR based composites filled with B₄C and SiC as a function of fillers concentration was investigated. Temperature dependencies of volume resistivity were also measured to examine the possible application of the composites to polymer linear negative temperature (NTC) thermistors. Furthermore, the temperature dependencies of dielectric constant of the composites were studied. For practical application, the thermal stability of the composites was examined by means of resistivity temperature and pressure hysteresis cycle. In parallel, the conduction mechanism of conductivity of the composites was interpreted in terms of the computed the activation and hopping energy. The applicability of the composites to piezoresistive sensor was examined too. The good mechanical properties and thermal stability of NR composites behavior can be utilized for fabricating various electronic devices as NTC thermistors and piezoresistive sensor (i.e. transducers in pressure sensors). POLYM. COMPOS., 29:109–118, 2008. © 2007 Society of Plastics Engineers     

Effect of carbon nanoparticle type,content, and stress on piezoresistive polyethylene nanocomposites

This study examines the piezoresistive behavior of polyethylene (PE) composites containing different types of carbon nanoparticle fillers. The fillers investigated are single‐wall carbon nanotube (SWCNT), multi‐wall carbon nanotube (MWCNT), and graphene nanoplatelets (GNP), which were dispersed in PE through melt blending in concentrations ranging between 0.5 and 10 wt%. The dispersion and nanocomposite morphology were investigated using scanning electron microscopy and X‐ray diffraction with strong evidence found for shear‐induced orientation of GNP nanoparticles during the compression molding process. The conductivity and permittivity of the composite materials was investigated using impedance spectroscopy and the lowest percolation threshold and highest electrical conductivity was observed for SWCNT composites, followed by MWCNT and GNP. The compressive piezoresistance of the nanocomposites was measured and the initial, elastic, and plastic deformation regions were all identifiable by the resistance measurements. The main finding of this study is that the piezoresistance of MWCNT nanocomposites is more sensitive to the effects of varying stress and composition than SWCNT nanocomposites. This indicates an evolving filler network in the case for MWCNT, while a static network for SWCNT, which is explained by the higher aspect ratio and surface area of the latter. POLYM. ENG. SCI., 55:1643–1651, 2015. © 2014 Society of Plastics Engineers     

Influence of rigid segment content on the piezoresistive behavior of multiwall carbon nanotube/segmented polyurethane composites

Tensile piezoresistive properties of multiwall carbon nanotube (MWCNT)/segmented polyurethane (SPU) composites comprising 15, 30, and 50 wt % rigid segment (RS) contents and 2, 4, and 6 wt % MWCNT contents are investigated. The physicochemical properties of such composites are used to better understand their mechanical and piezoresistive behavior. Infrared spectra shows that for 15 and 30 wt % RS composites the addition of MWCNTs promotes a more structured RS domain which increases the phase separation, while for 50 wt % RS composites the MWCNTs disrupt the RS domains of the polymer with a high phase separation. Overall, MWCNT content has less effect on the phase separation than RS content. The composites with 6 wt % MWCNT content reached electrical conductivities of the order of ～10^?1 S/m using 15 and 50 wt % RS polymers. Upon deformation, composites with 15 wt % RS and 4 wt % MWCNT achieved changes in electrical resistance of the order of 5000 times their unstrained value, which are outstanding values that can be exploited for applications such as human motion detection. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44448.     

Electrical,mechanical, and piezoresistive properties of carbon nanotube–polyaniline hybrid filled polydimethylsiloxane composites

The electrical, mechanical, and piezoresistive properties of ternary composites based on elastomeric polydimethylsiloxane (PDMS), carbon nanotubes (CNTs), and polyaniline (PANI) were studied and compared with those of binary PDMS–CNT composites. The presence of PANI affected the percolating network of the CNTs. At lower PANI concentrations (2.5 and 5%), the conductive network of the CNTs was constructively modified; this led to an enhancement in the conductivity in the sample containing 2% CNTs. A higher PANI content (7.5%) hindered the flow of main charge carriers through the composite. The piezoresistive response of the binary and ternary composites was studied by cyclic experiments under compression loads. In all of the samples, the electrical resistance increased monotonically up to a 10% strain. The reproducibility of the piezoresistive behavior in the binary and ternary composites provided evidence that the fillers could reversibly recover their initial position together with the PDMS chains without a significant displacement with respect to their original positions. The reduction of the piezoresistive sensibility by PANI addition was attributed to the displacement restrictions of the CNTs within the composite under pressure because of the volume exclusion of PANI particles; this maintained the probability of CNT contact and increased the possibility of the formation of new CNT conductive channels. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44780.     

Effects of crosslinking reaction and extension strain on the electrical properties of silicone rubber/carbon nanofiller composites

Stretchable conductive silicone rubber (SR) composites are important in wearable electronic devices and the crosslinking of SR composites is necessary for their applications. But the effect of the crosslinking reaction on the electrical conductivity of SR composites is rarely reported. In this article, the effect of crosslinking reaction on the electrical conductivity of SR composites filled with conductive carbon black, carbon nanotubes, and graphene are studied. The crosslink density of SR composites increases with increasing curing time, but the electrical conductivity decreases sharply at the early stage of crosslinking, especially for SR/conductive carbon black composite, which is ascribed to the reaggregation of conductive nanofillers in SR during the crosslinking process. The elastic modulus of the three SR composites gradually increases while the elongation at break decreases with increasing curing time, and the SR/carbon black composite shows ultra-high elongation at break (1578%). In addition, SR/graphene composite is more sensitive to the extension strain than SR/carbon black and SR/carbon nanotubes composites, and its gauge factor is 414 at the strain ranges of 3–25%. This research work brings a new method to optimize the crosslinking structure of conductive SR composites.     

Effect of composite preparation techniques on electrical and mechanical properties and morphology of nylon 6 based conductive polymer composites

Nylon 6/carbon black conductive composites were prepared using two different methods, masterbatch dilution and melt mixing. Their effect on the size and distribution of carbon black agglomerates in the matrix was studied in terms of electrical and mechanical properties and morphology. The electrical resistivity of composites prepared by both methods decreased with increasing filler composition. The electrical resistivity of the diluted masterbatch composites and the melt mixed composites was reduced from the resistivity of pure nylon 6, 10¹⁵ “ohm, cm”, to 10⁷ “ohm, cm” at 1 and 6 wt % of carbon black, respectively. As the filler content increased, elongation at break and impact strength decreased, but tensile modulus increased. Masterbatch dilution method provided smaller carbon black clusters in composites compared to melt mixing method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2520–2526, 2006     

Relationship between electromechanical response and percolation threshold in carbon nanotube/poly(vinylidene fluoride) composites

This paper reports on the piezoresistive response of carbon nanotube/poly(vinylidene fluoride), CNT/PVDF, composites prepared with different CNT types with and without functionalization, via in situ-generated diazonium compounds. The results show that for a CNT concentration close to the percolation threshold, tunneling is the main mechanism responsible for the electrical response, leading also to a significant increase of the piezoresistance of the composites. Interestingly, this fact is independent of the CNT type or functionalization, as well as of the percolation threshold concentration. In this way, a close relationship between the percolation threshold and the piezoresistive response was demonstrated. The electromechanical response, as characterized by the gauge factor, reach values up to 3.9, being among the largest obtained for thermoplastic composites and demonstrating the suitability of these materials for sensor applications.     

Fabrication of Cellulose Nanofiber/Reduced Graphene Oxide/Nitrile Rubber Flexible Films Using Pickering Emulsion Technology for Electromagnetic Interference Shielding and Piezoresistive Sensor

With the rapid development of flexible electronics, the demand for flexible electromagnetic interference (EMI) shielding materials is increasing. This study develops a new green and effective strategy, consisting of graphene oxide (GO) and cellulose nanofibrils (CNF) co-stabilized Pickering emulsion combined with hot-pressing technology, to prepare flexible and conductive nitrile rubber (NBR) composite films. The composite films consist of a 3D network conductive skeleton structure of reduced GO (RGO) and an isolated NBR structure. This specific design results in a maximum high conductivity of 99 S m⁻¹, which is higher by an order of magnitude compared with that of the composites obtained using the traditional solution blending method, and a stable EMI shielding effectiveness of 25.81 dB in the X band. The introduction of the flexible NBR results in the excellent flexibility and structural strength of the composite film, and exhibits a decrease of 2.51% in the EMI shielding efficacy after 5000 cycles. As a piezoresistive sensor for wearable devices, the CNF-RGO/NBR flexible film can hold precise current signals and respond to finger motion. The findings of this study can provide new insights for the design of conductive and flexible composites as wearable and portable medical equipment and electronic devices.     

Tensile behavior of polyolefin composites: the effect of matrix parameters

Polyolefin composites were prepared from 14 PE matrices and three different mineral fillers (montmorillonite, palygorskite and glass microspheres) via melt compounding in an extruder. Mechanical properties of the obtained systems were analyzed with emphasis on elongation at break and conditions for ductile/brittle failure were determined. When filler content is raised beyond a certain “critical” value, tensile properties are dramatically altered and transition occurs from ductile behavior to brittle fracture. This transition is displayed by a well‐defined “step” on the plot of strain at break versus concentration of particles. The value of “critical filler content” was found to depend mainly on level of crystallinity of a matrix while other parameters (chemical nature of filler particles, their size, shape and surface treatment) are less significant. “Critical filler content” will decrease with growth of crystallinity of a polymer and with highly crystalline HDPEs it is as low as 2–8 vol %. Otherwise, with noncrystallizing and low‐crystalline polymers elongation at break decreases gradually with concentration of mineral particles and ductile type deformation is maintained at fairly large filler fractions. The results presented here will be useful for a proper selection of a matrix polymer in composites with mineral fillers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43819.     

Effect of shape and size of nickel‐coated particles fillers on conductivity of silicone rubber‐based composites

Electrically conductive polymer composites have been widely used in recent years. The resistivity of the composites is influenced by several factors. The conductive silicone rubbers (CSRs) were prepared by adding the nickel‐coated graphite (Ni‐G) and/or nickel‐coated carbon fiber (Ni‐CF) into liquid silicon rubbers which were then subjected to the vulcanization. The effect of particle shape and size on the electrical conductivity of CSR was investigated; the results indicate that Ni‐CF filled CSR have lower percolation threshold than Ni‐G filled CSR. Compared to the filled particles with larger size, a higher amount of smaller particles are needed to form the same conductive pathway in CSR. Thus, there are more contact points in conductive pathway, which increase the total contact resistance. The volume resistivity of CSR can be significantly reduced by the doping of Ni‐CF particles, while the effect begins to wear off under high doping content. The fiber‐like Ni‐CF has a good “bridging” function for the formation of conductive pathway in CSR, which is greatly enhanced by increasing the length to diameter (l/d) ratio of Ni‐CF particles. Therefore, doping of the particles that have low percolation threshold can reduce the resistivity of the composites. POLYM. COMPOS., 36:1371–1377, 2015. © 2014 Society of Plastics Engineers     

Composites based on CB/CF/Ag filled EPDM/NBR rubber blends with high conductivity

For many applications of conductive rubbers, it is desirable to endow the conductive rubber with high conductivity at low conductive filler loading. In this work, composites based on ethylene‐propylene‐diene monomer (EPDM) rubber and nitrile‐butadiene rubber (NBR) were prepared using carbon blacks, carbon fibers, and silver powders as fillers. As the weight fraction of silver powder increased, the hardness of composites increased gradually while the tensile strength and elongation at break decreased. SEM revealed that the EPDM/NBR blends exhibited a relatively co‐continuous morphology. The differential scanning calorimetry (DSC) curves reported the EPDM/NBR rubber blends were incompatibility. The thermogravimetry (TG) studies showed that adding a small amount of silver powder could improve the thermal stability of composites. These conductive composites exhibited good electrical property. At room temperature, when the total volume fraction of fillers was 15.20%, the volume resistivity of EPDM/NBR blend was only 0.0058 Ω cm. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41357.     

Electrically Conductive Fibre Composites Prepared from Polypyrrole‐Engineered Pulp Fibres

In this research work, electrically conductive paper composites were prepared from polypyrrole‐engineered pulp fibres by two methods: (a) exclusively from such engineered fibres; and (b) from a mixture of the modified fibres and unmodified ones. Both composites were investigated for their conductivity and strength properties as a function of monomer dosage or percentage of treated fibres in the mixture. It was found that, for the “mixture” method (i.e., by adding treated fibres as conductive fillers), less monomer (i.e., conductive polymer) was needed to achieve the same conductivity while a higher tensile strength in the paper was attained when comparing with paper obtained exclusively from treated fibres. The percolation model was adopted to describe such paper—conducting polymer composites, and the much lower percolation threshold achieved through the “mixture” method can be explained by a multiple‐percolation theory. The long‐term environmental aging stability of these composites was also monitored, and attempts were made to interpret the observed conductivity decay through existing kinetic models.     

聚丙烯/尼龙/玻璃纤维/炭黑四元双逾渗复合体系的压阻行为

研究了聚丙烯（PP）/尼龙（PA）/玻璃纤维（GF）/炭黑（CB）四元复合体系的逾渗现象与压阻行为。通过SEM分析得出PA/CB体系的逾渗作用及其包裹GF对PP逾渗作用形成的导电网络是四元体系导电的根源,而且电阻的变化与GF的含量密切相关。GF低含量下出现微弱的NPC现象,在高含量下随应力的增大先出现的NPC现象,后出现PPC现象,本文对两种现象出现的原因进行了理论阐述。经多次应力循环,体系电阻的稳定性得到很大改善。     

Processing and mechanical properties of bio‐derived vinyl ester resin‐based composites

A “green” vinyl ester resin (GVER) is investigated for use in structural applications. The GVER was formulated using a monodisperse vinyl ester created via a novel synthetic route capable of using bio‐waste material from paper and biodiesel industries. The GVER was used either as a neat resin or as blended with a commercial vinyl ester resin. The processing viscosity and gel times are investigated. The GVER reaches a similar viscosity as the commercial resin with only half the styrene monomer content, thereby reducing the volatile organic compounds associated with manufacturing. Composites of the GVER matrix reinforced by carbon fabric were tested for their tensile and flexural properties. The mechanical performance of the GVER compares favorably with commercial resin and provide a route for composites manufacturing from sustainably sourced vinyl ester matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44642.     

填充型NBR/EPDM导电复合材料的研究

研究了石墨/炭黑填充的NBR/EPDM导电复合材料力学性能、动态力学性能和压阻、温阻特性。结果表明,随NBR用量的减少,复合材料拉伸强度、撕裂强度和拉断伸长率均降低;与纯胶相比,填料在NBR/EPDM中分散性变差,复合材料Payne效应和损耗因子都增大。电阻率测试结果表明,NBR/EPDM并用胶电阻率明显低于纯胶;恒温下其电阻率随压力的增大先减小后增大;恒压下其电阻率随温度的升高而减小;NBR/EPDM并用比不同时,复合材料电阻率随压力、温度的变化趋势不尽相同。     

镀银镍粉/硅橡胶高导电复合材料的制备及性能研究

研究镀银镍粉体积分数对镀银镍粉/硅橡胶高导电复合材料性能的影响。结果表明:随着镀银镍粉体积分数增大,复合材料的邵尔A型硬度增大,拉断伸长率快速减小,体积电阻率减小并出现明显逾渗现象;当镀银镍粉体积分数为0.44时,复合材料具有良好的导电稳定性和优异的电磁屏蔽效能,但耐电化学腐蚀性能较差。     

Effect of nanostructures of modified clay–carbon black on physico‐mechanical,electrical, and acoustic properties of elastomer‐based composites

Elastomeric composites based on nitrile rubber (NBR), carbon black (CB), and organically modified nanoclay (NC) were prepared using a laboratory two‐roll mixing mill. Influences of the hybrid filler system (CB+NC) on various properties of NBR compound were analyzed. It was found that the addition of hybrid filler (CB+NC) over only carbon black enhances various properties. It was also found that the addition of nanoclay to the rubber matrix effectively improved key properties. Acoustics and electrical properties were modified with reduced water absorption because of layered clay platelets. The lower volume resistivity of NBR composites reflected better electrical conductivity attributed to the presence of nanoclay leading to effective filler connectivity. X‐ray diffraction and transmission electron microscopy measurements revealed that nanoclays were mostly intercalated and were uniformly dispersed. Use of calcium stearate facilitated dispersion of nanoclay in the rubber matrix which was observed through the formation of nanostructures including “nano” and “halo” units. Time temperature superposition in dynamic mechanical analysis test of the composites indicated lower mechanical loss in the frequency range of interest. The advantages accruing due to overall property enhancement, including lower water absorption, and better electrical and excellent acoustic properties of NBR composites make it suitable as underwater acoustic transparent materials for transducer encapsulation application. POLYM. COMPOS., 37:1786–1796, 2016. © 2014 Society of Plastics Engineers