Evaluation and modeling of the mechanical behavior of carbon nanoparticle/rubber‐modified polyethylene nanocomposites

Recently, the production of polymers loaded with inorganic nanomaterials has been one of the most economical techniques playing a special role in improving the physical and mechanical properties of nanocomposites. Rubbers loaded with different concentrations of carbon nanoparticles (CNPs) were synthesized. The mechanical properties were tested according to standard methods. It was found that the properties of the investigated nanocomposites were improved, depending on the concentration of CNPs in the investigated composite. The optimum concentration was found to be 1.3 vol %. Affine deformation based on the Mooney–Rivilin model was used to visualize the effect of CNPs on the rubber. When polyethylene (PE) was added to rubber/CNPs at the optimum concentration (12.4 vol %), the modulus, tear resistance, and fatigue life were increased, whereas the tensile strength decreased, and the strain at rupture remained almost same. A crosslink model was used to explain the influence of PE on the rubber/CNP nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of nanoclay type on dyeability of polyethylene terephthalate/clay nanocomposites

Polyethylene terephthalate (PET)-based nanocomposites containing three differently modified clays were prepared by melt compounding. The influence of type of clay on disperseability, thermal, and dyeing properties of the resultant nanocomposite was investigated by various analytic techniques, namely, X-ray diffraction, optical microscopy (OPM), differential scanning calorimetry, thermal gravimetric analysis, dynamical mechanical thermal analysis, contact angle measurement (CAM), reflectance spectroscopy, and light fastness. OPM images illustrated formation of large-sized spherulites in pure PET, while only small-sized crystals appeared in PET/clay nanocomposites. Decreased glass transition temperatures for all PET/clay nanocomposites indicate that the amorphous regions of such composites become mobile at lower temperatures than those in pure PET. CAMs on the resultant PET composites demonstrated that the wettability of such composites depends on hydrophilicity of the nanoclay particles. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Superelastic,fatigue resistant and heat insulated carbon nanofiber aerogels for piezoresistive stress sensors

Ultralight flexible carbon aerogels have been applied in many fields but are always hampered due to their weak mechanical stability, large energy dissipation, and complex preparation methods. Here, a novel polyimide-derived carbon nanofiber aerogel with high fatigue resistance and excellent flexibility is prepared by using the designed “fiber gluing” to construct the elastic continuous fibrous network. The as-prepared carbon nanofiber aerogels exhibit ultralow density of 6.6 mg cm⁻³, excellent fire-resistant performance when exposing to alcohol flames (650 °C), and robust elastic resilience even under 55% compressive strain. In particular, the carbon nanofiber aerogels show ultralow plastic deformation (only 1.3%) and low energy dissipation (<0.22) after 1000 cyclic loading-unloading tests at 55% compressive strain. Benefiting from their excellent flexibility and robust mechanical stability, the as-prepared carbon nanofiber aerogel are a promising candidate in the application of wearable devices and piezoresistive stress sensors.     

Graphene/polyethylene nanocomposites: Effect of polyethylene functionalization and blending methods

Since its recent successful isolation, graphene has attracted an enormous amount of scientific interest due to its exceptional physical properties. Graphene incorporation can improve electrical and mechanical properties of polymers including polyethylene (PE). However, the hydrophobic nature and low polarity of PE have made effective dispersion of nano-fillers difficult without compatibilization. Graphene was derived from graphite oxide (GO) via rapid thermal exfoliation and reduction. This thermally reduced graphene oxide (TRG) was blended via melt and solvent blending with linear low density PE (LLDPE) and its functionalized analogs (amine, nitrile and isocyanate) produced using a ring-opening metathesis polymerization (ROMP) strategy. TRG was well exfoliated in functionalized LLDPE while phase separated morphology was observed in the un-modified LLDPE. Transmission electron micrographs showed that solvent based blending more effectively dispersed these exfoliated carbon sheets than did melt compounding. Tensile modulus was higher for composites with functionalized polyethylenes when solvent blending was used. However, at less than 3 wt.% of TRG, electrical conductivity of the un-modified LLDPE was higher than that of the functionalized ones. This may be due to phase segregation between graphene and PE, and electrical percolation within the continuous filler-rich phase.     

Electroreduction of oxygen on Pt nanoparticle/carbon nanotube nanocomposites in acid and alkaline solutions

The kinetics of O₂ reduction on novel electrocatalyst materials deposited on carbon substrates were studied in 0.5 M H₂SO₄ and in 0.1 M NaOH solutions using the rotating disk electrode (RDE) technique. Pt nanoparticles (PtNP) supported on single-walled (PtNP/SWCNT) and multi-walled carbon nanotubes (PtNP/MWCNT) were prepared using two different synthetic routes. Before use, the CNTs were cleaned to minimize the presence of metal impurities coming from the catalyst used in the synthesis of this material, which can interfere in the electrochemical response of the supported Pt nanoparticles. The composite catalyst samples were characterised by transmission electron microscopy (TEM) showing a good dispersion of the particles at the surface of the carbon support and an average Pt particle size of 2.4 ± 0.7 nm in the case of Pt/CNTs prepared in the presence of citrate and of 3.8 ± 1.1 nm for Pt/CNTs prepared in microemulsion. The values of specific activity (SA) and other kinetic parameters were determined from the Tafel plots taking into account the real electroactive area of each electrode. The electrodes exhibited a relatively high electrocatalytic activity for the four-electron oxygen reduction reaction to water.     

Effect of heat treatment of carbon nanofibers on the electromagnetic shielding effectiveness of linear low density polyethylene nanocomposites

The electrical properties and electromagnetic shielding effectiveness (EM SE) of nanocomposites consisting of heat‐treated carbon nanofibers (Pyrograf® III PR‐19, CNF) in a linear low density polyethylene (LLDPE) matrix were assessed. Heat treatment (HT) of carbon nanofibers at 2500°C significantly improved their graphitic crystallinity and intrinsic transport properties, thereby increasing the EM SE of the nanocomposites. Nanocomposites containing 11 vol% (20 wt%) PR‐19 HT displayed a DC electrical conductivity of about 1.0 ± 0.1 × 10¹ S/m (n = 4), about 10 orders of magnitude better than that of as‐received PR‐19 CNF nanocomposites. Over a frequency range of 30 MHz to 1.5 GHz, nanocomposites (2.5 mm thick) containing PR‐19 HT displayed EM SE average values of about 14 ± 2 dB (n = 4). Absorption was determined to be the main EM SE mechanism for the heat‐treated CNF nanocomposites. The nanocomposites possessed a modulus of 632 ± 36 MPa (n = 6) (nominally twice that of pure LLDPE) and a strain‐to‐failure of 180 ± 98% (n = 6), indicating that a significant ductility is retained in the nanocomposites. Such nanocomposites display potential as absorptive electromagnetic interference shielding materials for thin films and micromolding. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Dependence of electrical properties of polyethylene nanocomposites on aspect ratio of carbon nanotubes

Low density polyethylene nanocomposites filled with carbon nanotubes (CNT) having three different aspect ratios have been prepared by melt mixing technique. The effects of CNT loading, its aspect ratio, and frequency of electric field on electrical and dielectric properties of the nanocomposites have been investigated. DC and AC electrical resistivity are found to decrease with the increase in CNT loading in the composites, while the dielectric constant and loss increase with the increase in CNT loading in the composites. AC electrical resistivity, dielectric constant, and dielectric loss decrease with the increase in frequency. Furthermore, the electrical resistivity decreases with the increase in aspect ratio of CNT, whereas the dielectric constant and loss increase with the increase in aspect ratio of CNT. While probable mechanisms for electrical conduction have been proposed, dielectric results have been explained by considering CNT as nanocapacitors. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Effect of tetragonal zirconia nanoparticle content on enamel strength

The fracture failure of enamel is caused by hole-type flaws and cracks generally present in enamel. In this study, the effect of tetragonal zirconia nanoparticles (nano-t-ZrO₂) on enamel strength was investigated. The addition of nano-t-ZrO₂ improved the surface morphology and reduced the porosity of the enamel as determined by morphological and porosity distribution analyses. The strain on the enamel surface was recorded using a strain gauge attached to the enamel surface. The crack initiation force and strain were measured using the strain gauge, and the crack propagation diagrams at various stages of the tensile process were recorded. The relationship between the crack initiation energy and nano-t-ZrO₂ content was found to be non-linear. Nano-t-ZrO₂ affected the strength of the enamel. Moreover, the tensile force required for the appearance of cracks first increased and then decreased with an increase in the nano-t-ZrO₂ content. The addition of nano-t-ZrO₂ to the enamel matrix suppressed the formation of stress concentration regions and decreased the brittleness of the enamel. At a nano-t-ZrO₂ content of more than 5 wt%, the ZrO₂ particles agglomerated.     

Crystallization behavior of carbon nanofiber/linear low density polyethylene nanocomposites

Crystallization behavior of LLDPE nanocomposites is reported in the presence of three types of carbon nanofibers (CNFs) (MJ, PR‐19, and PR‐24). During nonisothermal crystallization studies, all three crystalline melting peaks for LLDPE matrix were observed in the presence of PR‐19 nanofibers (up to 15 wt % content), but only the high‐ and low‐temperature peaks were observed in the presence MJ nanofibers. The broad melting peak at low‐temperature became bigger, suggesting an increase in the relative content of thinner lamellae in the presence of MJ nanofibers. TEM results of nanocomposites revealed transcrystallinity of LLDPE on the surface of CNFs, and a slightly broader distribution of lamellar thickness. STEM studies revealed a rougher surface morphology of the MJ nanofibers relative to that of PR nanofibers. Also, BET studies confirmed a larger specific surface area of MJ nanofibers relative to that of PR nanofibers, suggesting that the larger and the rougher surface of MJ nanofibers contributes toward the different crystallization behavior of MJ/LLDPE nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of fiber content and type,compatibilizer, and heating rate on thermogravimetric properties of natural fiber high density polyethylene composites

Natural fiber polyethylene composites containing kenaf fibers, wood flour, newsprint, and rice hulls at 25 and 50% (by weight) fiber content were sampled and studied using thermogravimetric analysis (TGA). The effects of fiber type and content, compatibilizer and heating rate on the thermal stability and degradation of the composites were evaluated. Among different natural fibers, kenef fibers were found to be the least thermally stable ones whereas newsprint fibers proved to be the most stable fibers in composite formulations. Composites containing higher amounts of natural fiber degraded at a higher rate and exhibited higher weight loss. The presence of the compatibilizer resulted in composites with slower thermal degradation. Heating rate increased both temperature and rate of main degradation peaks. FTIR and DSC results are also presented to discuss phenomena leading to thermal degradation. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers.     

Facile fabrication of polyethylene/silver nanoparticle nanocomposites with silver nanoparticles traps and holds early antibacterial effect

Antibacterial polyethylene (PE)/silver nanoparticle (AgNP) nanocomposites containing AgNPs at concentrations of 5 × 10^?5, 5 × 10^?4, and 5 × 10^?3 wt % were fabricated and tested. Transmission electron microscopy revealed an even dispersion of surface AgNPs in the PE/AgNP nanocomposites. No AgNP agglomeration was observed. The tensile strength, elongation at break, and Young's modulus of these PE/AgNP nanocomposites were similar to those of neat PE. Differential scanning calorimetry demonstrated that the PE/AgNP nanocomposites and neat PE had similar melting and crystallization temperatures of 126 ± 0.5 and 109 ± 0.6°C, respectively. The heats of fusion of the PE/AgNP nanocomposites containing AgNPs at concentrations of 5 × 10^?5 and 5 × 10^?4 and of 5 × 10^?3 wt % were lower than those of neat PE by 5 and 7%, respectively. These PE/AgNP nanocomposites were immersed in shaking liquid cultures of the potential pathogenic bacteria Escherichia coli, Bacillus subtilis, and Salmonella typhimurium in the lag phase. The results show that the growth rates of all of the tested bacteria were restricted effectively after 1.5, 3, and 6 h of cultivation, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43331.     

Effect of carbon black on properties of rubber nanocomposites

Polymer based nanocomposites were prepared using brominated poly(isobutylene‐co‐paramethylstyrene) (BIMS) rubber and octadecyl amine modified montmorillonite nanoclay. The effect of nature and loading of carbon black on these nanocomposites and the control BIMS was investigated thoroughly using X‐ray diffraction technique (XRD), Fourier transform infrared spectroscopy (FTIR), and mechanical properties. The addition of 4 parts of the modified nanoclay to 20 phr N550 carbon black filled samples increased the tensile strength by 53%. Out of the three different grades of carbon black (N330, N550, and N660), N550 showed the best effect of nanoclay. Optimum results were obtained with the 20 phr filler loading. For comparison, china clay and silica at the same loading were used. Fifty‐six and 46% improvements in tensile strength were achieved with 4 parts of nanoclay added to the silica and the china clay filled samples, respectively. N330 carbon black (20 parts) filled styrene butadiene rubber (SBR) based nanocomposite registered 20% higher tensile strength with 4 parts of the modified nanoclay. In all the above carbon black filled nanocomposites, the modulus was improved in the range of 30 to 125%. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 443–451, 2005     

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.     

Effect of functionalized polyethylenes on clay dispersion in high density polyethylene nanocomposites

The compatibilization effects provided by maleic anhydride (MA), itaconic acid (IAc), itaconic anhydride (IA), and 2-[2-(dimethylamine)-ethoxy]ethanol (DMAE) functionalized polyethylenes for forming high density polyethylene (HDPE)-based nanocomposites were studied and compared. IAc and IA were grafted into HDPE by melt mixing to obtain functionalized polyethylenes (HDPEgIAc and HDPEgIA) and amino alcohol functionalized polyethylene was prepared by reaction of commercial HDPEgMA with DMAE in the melt to form polyethylene-grafted dimethyl-amine-ethoxy-ethanol (PEgDMAE). Nanocomposites were prepared by melt processing using a twin screw extruder by blending polyethylene and these compatibilizers with a quaternary ammonium surfactant-modified montmorillonite clay (Nanomer I28E). FTIR characterization confirmed the formation of these compatibilizers and confirmed the reaction between HDPEgMA and the amino alcohol. All the compatibilized nanocomposites had better clay exfoliation compared to the uncompatibilized HDPE nanocomposites. Barrier properties, X-ray diffraction and transmission electron microscopy results showed the following order of their performance as a compatibilizer: PEgDMAE > HDPEgAI > HDPEgAcI > HDPEgMA. This behavior was attributed to the specific interactions between the anionic surface of the clay and the functionality of the compatibilizer. Samples with higher clay content showed poorer clay dispersion or intercalation which was attributed to possible clay saturation when the van der Waals attractive interactions between the clay layers become dominant when the distance between them was small enough at a certain concentration of clay. A noticeable reduction in the degree of crystallinity with the incorporation of nanoclay was observed by thermal analysis whereas the melting temperature did not change noticeably.     

Effect of polyethylene glycol on the properties of styrene‐butadiene rubber/organoclay nanocomposites filled with silica and carbon black

Polyethyene glycol (PEG) is widely used as a dispersing agent and can also be used to prevent the adsorption of ingredients on the surface of silica. From the XRD results, PEG that was used as the dispersing agent on the SBR/organoclay compound filled with silica and carbon black (CB) was intercalated between the organoclay layer. Additionally, the interactions with the PEG differed depending on whether 3‐aminopropyltriethoxysilane (APTES) or N,N‐dimethyldodecylamine (DDA) were used as clay modifiers. When PEG was added, the T_g of the SBR/silica/APTES‐MMT compound increased through the formation of hydrogen bonds between the ether linkages of PEG and the hydroxyl groups of APTES. For the SBR/silica/DDA‐MMT compound with PEG, slippage occurred between the silicate, and DDA because of the alkyl chain of DDA. The SBR/silica/APTES‐MMT/CB compound with PEG exhibited the highest T_g value and the highest bound rubber content, with high modulus values at 100 and 300%. The SBR/silica/DDA‐MMT/CB compound had the best properties in terms of the wet skid resistance and the rolling resistance. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Separating stress and time dependent effects in the temperature dependent creep of polyethylene nanocomposites

The nonlinear time dependent creep of linear‐low density polyethylene (LLDPE) reinforced with montmorillonite layered silicate was investigated. A previous study related the time/stress dependence of creep compliance of the material at room temperature using the Burger and Kohlrausch‐Williams‐Watts models. Using both the creep and recovery compliance curves, we employ the Schapery formulation to study the relationship between deformation, time, stress, and temperature of LLDPE nanocomposites. Smooth mastercurves are constructed using time–temperature–stress superposition principles. The stress and temperature‐related creep constants and shift factors were determined for the material using the Schapery nonlinear viscoelastic equation. The prediction results confirm the enhanced creep resistance of nanofillers even at extended time scales and low temperatures. POLYM. ENG. SCI., 50:1646–1657, 2010. © 2010 Society of Plastics Engineers     

Linear low-density polyethylene/high-density polyethylene blends: Effect of high-density polyethylene content on die swell and flow instability

This work aimed to evaluate the effect of high-density polyethylene (HDPE) content and of shear rate on the die swell and flow instability of linear low-density polyethylene (LLDPE)/HDPE blends. The results showed that the die swell of the LLDPE/HDPE blends increased with the increase in the shear rate. At high shear rates, the increase in the HDPE content led to an increase in the die swell of LLDPE/HDPE blends. The surface morphology analysis of the extrudates by optical and scanning electron microscopy revealed the presence of sharkskin and stick–slip flow instabilities in LLDPE and LLDPE/HDPE blends at the shear rates investigated. These instabilities were attenuated with the addition of HDPE and almost disappeared in the LLDPE/HDPE blend containing 50 wt% of HDPE.     

Effect of low‐content carbon nanotubes on the dielectric and microwave absorption properties of graphite/polymer nanocomposites

Honeycomb cores (HCs) coated with graphite and multiwalled carbon nanotubes (MWCNTs) filled in a thermoplastic resin are proposed as microwave absorbers. The MWCNT contents varied from 0.2 to 0.6 wt % in a graphite‐filled (15 wt %) thermoplastic resin. The HCs were coated with three different types of coating materials for the sake of comparison: graphite, MWCNTs, and graphite plus MWCNTs. The dielectric properties [the real and imaginary parts of complex permittivity (ε′ and ε″, respectively)] and reflection loss (RL) of all of the coated HCs were measured and compared. We observed that the permittivities and RL increased significantly with increased weight percentage of the MWCNTs in the graphite‐filled thermoplastic resin. The RL measurements showed a maximum loss of ?20 dB around 7 GHz and a bandwidth of 2.7 GHz at ?10 dB in the HCs coated with the 0.4 wt % MWCNT plus graphite. There was also a shift in the RL peak position from the x band to the c band after the increase of MWCNT content. We also observed from the measurements that a combination of graphite and MWCNTs resulted in a broadband microwave absorber; a bandwidth of 13 GHz was observed for 80% RL when the MWCNT content increased to 0.6 wt % in the graphite‐incorporated resin. The possible mechanism that increased RL with the incorporation of MWCNTs in the graphite‐mixed thermoplastic resin is discussed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40891.     

Effect of SiC nanoparticle content and milling time on the microstructural characteristics and properties of Mg-SiC nanocomposites synthesized with powder metallurgy incorporating high-energy ball milling

The fabrication of magnesium nanocomposites with a homogeneous dispersion of nanoparticles has recently become an important issue. In the current study, micro-sized magnesium powders reinforced with 10, 20, and 30 wt% SiC nanoparticles were synthesized through high-energy ball milling using milling times ranging from 1 to 20 h to overcome the segregation and agglomeration of nanoparticles within the magnesium matrix. The milled nanocomposite powders were then consolidated using uniaxial cold pressing and sintering processes. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction were employed to investigate the effects of different milling times and contents of SiC nanoparticles on the evolution of the morphology of Mg–SiC milled powders and the microstructural characteristics of Mg–SiC sintered samples. In addition, once the consolidation process was complete, the relative densities and hardness values of the Mg–SiC nanocomposites were examined. The results indicated that as the content of SiC nanoparticles and the milling time increased, finer and equiaxed nanocomposite powders were obtained, and the average crystallite size of the milled magnesium powder significantly decreased. A homogeneous distribution of the SiC nanoparticles, including up to 30% of weight fraction, in the magnesium matrix was confirmed after 20 h of milling by elemental mapping generated by EDS. Additionally, the XRD analysis revealed that the diffraction peaks of the magnesium broadened while their maximum intensities decreased with increasing the milling time and SiC content. No undesirable phases were formed by interfacial reactions between magnesium and SiC nanoparticles in the milled nanocomposite powder during mechanical alloying. Furthermore, the results showed that both the relative density and hardness value of the Mg–SiC sintered sample improved as the milling time increased. However, the relative density of the Mg–SiC nanocomposite drastically decreased while the hardness significantly improved, as a result of increasing the content of SiC nanoparticles.     

Shape memory composites based on a thermoplastic elastomer polyethylene with carbon nanostructures stimulated by heat and solar radiation having piezoresistive behavior

A thermoplastic elastomer polyethylene (TEPE) based on an ethylene/1‐butene copolymer having shape memory effect (SME) without any chemical modification is presented and the effect of adding either carbon nanotubes or thermally reduced graphite oxide is analyzed. For electrical percolated samples, the development of a polymer sensor that changes its electrical conductivity under solar radiation triggered by SME is further presented. Our results showed that programmed samples recovered their permanent shape showing SME under a direct heating stimulus at 60 °C. The addition of carbon nanostructures increased the times needed to reach 100% recovery as compared with pure TEPE. Noteworthy, the SME was also stimulated remotely by solar radiation increasing the sample temperature. Composites presented a faster SME under this remote radiation process as compared with pure TEPE due to their higher radiation absorption. Percolated TEPE/carbon nanotube composites displayed further a decrease in the electrical resistivity during SME under this solar radiation. Finally, our results showed that the glass transition also triggered the SME in these samples allowing the development of triple shape memory polyethylenes without any chemical crosslinking process. Based on these findings, a simple route was developed to produce double, or even triple, shape memory piezoresistive polyethylenes that can be activated remotely by solar radiation. © 2018 Society of Chemical Industry