Effect of processing parameters on the surface resistivity of ethylene propylene diene terpolymer/multiwalled carbon nanotube nanocomposites

In this study, ethylene propylene diene terpolymer (EPDM) is melt‐mixed with multiwalled carbon nanotube (MWCNT). To realize full‐scale application of MWCNT to the rubber industries, the effect of melt‐processing parameters on the surface resistivity in the rubber/MWCNT nanocomposites should be well understood. The effect of rotor speed, mixing temperature, and annealing time on the surface resistivity of the EPDM/MWCNT nanocomposites has been investigated. The surface resistivity of EPDM/MWCNT nanocomposites with 3 phr MWCNT increases with increasing the rotor speed and decreasing the mixing temperature. Tensile strength and tensile modulus of EPDM/MWCNT (3 phr) nanocomposites are higher than those of EPDM, respectively. For the nanocomposite with 3 phr MWCNT loadings, surface resistivity increases as the annealing time at room temperature increases. This is the first report that surface resistivity of rubber/MWCNT nanocomposites increases significantly on annealing at room temperature. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40129.     

Effect of cooling rate on the surface resistivity of polymer/multi‐walled carbon nanotube nanocomposites

In this study, ethylene‐vinyl acetate copolymer (EVA) and polystyrene (PS) were melt‐mixed with multi‐walled carbon nanotube (CNT) (MWCNT), respectively. The effect of mixing time, rotor speed, and cooling rate on surface resistivity was investigated. EVA/MWCNT and PS/MWCNT nanocomposites with percolation threshold <1 wt% of MWCNT were prepared using conventional melt‐compounding method. When fast cooling was applied for these nanocomposites, a surface resistivity of 10⁶ Ω/square was obtained at around 7 wt% of MWCNT for EVA and 10⁵ Ω/square at around 3.5 wt% of MWCNT for PS. However, when slow cooling was applied, a surface resistivity of 10⁶ Ω/square was obtained at 0.75 wt% of MWCNT for EVA and 10⁵ Ω/square at around 0.5 wt% of MWCNT for PS. To the best of our knowledge, this is the first report which recognizes the importance of cooling rate on the surface resistivity of polymer/MWCNT nanocomposites. This finding may be potential to the commercialization of the CNT‐based polymer nanocomposites. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Effect of the viscosity and processing parameters on the surface resistivity of polypropylene/multiwalled carbon nanotube and ethylene–propylene–diene/multiwalled carbon nanotube nanocomposites

In this study, relatively large amounts of polypropylene (PP) and ethylene–propylene–diene (EPDM) were melt‐mixed with multiwalled carbon nanotubes (MWCNTs). Although the melt‐compounding method has many advantages, the uniform dispersion of carbon nanotubes in the polymer matrix is still the most challenging task. Because the electrical conductivity of composites is strongly influenced by the filler's state of dispersion and the extent of filler breakage during processing, the effects of the viscosity and processing conditions, such as the mixing time, rotor speed, and cooling rate, on the surface resistivity were studied. The PP/MWCNT nanocomposites displayed a high dependence of surface resistivity on the cooling rate, and the EPDM/MWCNT nanocomposites displayed a higher surface resistivity at the same content of MWCNTs and less dependence of surface resistivity on the cooling rate compared with PP/MWCNT nanocomposites. The increased surface resistivity of the EPDM/MWCNT nanocomposites was observed when EPDM with higher viscosity was used to prepare the EPDM/MWCNT nanocomposites. By increasing the rotor speed, lower surface resistivity was obtained in the PP/MWCNT nanocomposites. However, by increasing the rotor speed, a higher surface resistivity was obtained in the EPDM/MWCNT nanocomposites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Ethylene‐vinyl acetate copolymer/multiwalled carbon nanotube/organoclay nanocomposites

Ethylene‐vinyl acetate copolymer (EVA) was melt‐mixed with multiwalled carbon nanotubes (MWCNTs) and organoclays, and the effects of simultaneous use of organoclays and MWCNTs on the surface resistivity and tensile properties of EVA nanocomposites were investigated. The surface resistivity of EVA/MWCNT nanocomposite with 1 phr of MWCNT is out of our measurement range (above 10¹² Ω/square). With increasing content of organoclay from 0 to 3 phr, the surface resistivity of the EVA/MWCNT/organoclay nanocomposites with 1 phr MWCNT remains out of our measurement range. However, the surface resistivity of the nanocomposite decreases to 10⁶ Ω/square with addition of 5 phr organoclay. The tensile properties of EVA/MWCNT/organoclay nanocomposites with 1 phr MWCNT and 5 phr organocaly are similar to those of EVA/MWCNT nanocomposites with 5 phr MWCNT except tensile modulus. POLYM. COMPOS. 2012. © 2012 Society of Plastics Engineers     

Effect of the processing parameters on the surface resistivity of acrylonitrile–butadiene rubber/multiwalled carbon nanotube nanocomposites

In this study, acrylonitrile–butadiene rubber (NBR) was melt‐mixed with multiwalled carbon nanotubes (MWCNTs). Because the electrical conductivity and mechanical properties of composites are strongly influenced by the filler's state of dispersion and the extent of filler breakage during processing, the processing conditions are very important parameters. The effects of the mixing time, rotor speed, cooling rate, and sulfur concentration on the surface resistivity were investigated. Increasing the rotor speed from 20 to 60 rpm at mixing times of 15 and 30 min led to an increase in the surface resistivity from around 10⁴ to 10¹¹ Ω/square. However, at a mixing time of 7 min, the surface resistivity slightly decreased with increasing rotor speed. When slow cooling was applied, a surface resistivity of 10⁴ Ω/square was obtained at around 2‐phr MWCNTs. However, when the fast cooling was applied, a surface resistivity of 10⁶ Ω/square was obtained at 5‐phr MWCNTs. The tensile strength and tensile modulus at 300% elongation were improved with the addition of MWCNTs into NBR. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of processing conditions on the structural morphology of PP–EP/EVA/organoclay ternary nanocomposites

The effect of processing conditions on the morphology of heterophasic PP–EP/EVA/organoclay ternary nanocomposites was examined. The nanocomposites were prepared in a co-rotating twin screw extruder with different screw configurations and incorporation methods. Three different sizes of EVA granules were used. The results obtained by X-ray scattering (WAXD) and electronic microscopy (TEM) showed an increase in d spacing value of the clay associated with the polar interactions between the vinyl acetate of EVA and the surface of the nanoclays. In addition, some chains of the non-polar copolymer PP–EP may have become intercalated into the clay galleries as a result of polymer diffusion induced by shear stress during melt mixing. An increase in surface area of EVA granules resulted in a more homogenous clay dispersion and intercalation. The morphologic changes resulted in an increase in heat distortion temperature (HDT) and flexural modulus of the ternary nanocomposites.     

Effect of processing parameters, applied pressure and temperature on the electrical resistivity of rubber-based conductive composites

Carbon black- and short carbon fibre (SCF)-filled conductive composites were prepared from ethylene vinyl acetate (EVA), ethylene propylene diene (EPDM) rubber and their 50:50 blend. The electrical resistivity of carbon black- and SCF-filled composites were measured under different conditions. The electrical conductivity of filled polymer composites is due to the formation of a continuous conductive network in the polymer matrix. These conductive networks involve specific arrangement of conductive elements so that the electrical paths are formed for free movement of electrons. It was found that electrical conductivity of filled conductive composites depends on different processing parameters like mixing time, rotor speed, mixing temperature, vulcanization time and pressure and service conditions like applied pressure and temperature. The results of different experiments have been discussed in light of break down and formation of the continuous conductive network.     

Electrical and mechanical properties of acrylonitrile‐butadiene‐styrene/multiwall carbon nanotube nanocomposites prepared by melt‐blending

The electrical properties in polymer/carbon nanotube (CNT) nanocomposites are governed not only by the degree of dispersion but also to a greater extent on the aspect ratio of the CNTs in the final composites. Melt‐mixing of polymer and CNTs at high shear rate usually breaks the CNTS that lowers the aspect ratio of the nanotubes. Thus, homogeneous dispersion of CNTs while retaining the aspect ratio is a major challenge in melt‐mixing. Here, we demonstrate a novel method that involves melt‐blending of acrylonitrile‐butadiene‐styrene (ABS) and in situ polymerized polystyrene (PS)/multiwalled CNT (MWCNT) nanocomposites, to prepare electrically conducting ABS/MWCNT nanocomposites with very low CNT loading than reported. The rationale behind choosing PS/MWCNT as blending component was that ABS is reported to form miscible blend with the PS. Thus, (80/20 w/w) ABS/(PS/MWCNT) nanocomposites obtained by melt‐blending showed electrical conductivity value ≈1.27 × 10^?6 S cm^?1 at MWCNT loading close to 0.64 wt %, which is quite lower than previously reported value for ABS/MWCNT system prepared via solution blending. Scanning electron microscopy and differential scanning calorimetry analysis indicated the formation of homogenous and miscible blend of ABS and PS. The high temperature (100°C) storage modulus of ABS (1298 MPa) in the nanocomposites was increased to 1696 MPa in presence of 0.64 wt % of the MWCNT. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Nanostructure of EVA/organoclay nanocomposites: Effects of kinds of organoclays and grafting of maleic anhydride onto EVA

Nanostructure of poly(ethylene‐co‐vinyl acetate)/organically modified montmorillonite (MMT; EVA/organoclay) nanocomposites prepared by melt intercalation process was investigated using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Three kinds of organoclays were used to see their influences on the nanostructure of the EVA hybrids. The effects of the polar interactions between the polymer and the silicate layers of organoclays were also investigated by grafting maleic anhydride onto EVA. It was found that the strong polar interactions between the polymer and the silicate layers of organoclays are critical to the formation of polymer‐layered silicate nanocomposites. The results also showed that increasing the mixing temperature was unfavorable to improve the dispersion of organoclays in the EVA matrix. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1901–1909, 2003     

Aspects of producing hydrogenated nitrile butadiene rubber (HNBR) nanocomposites by melt compounding processing

Industry is constantly demanding for materials with differential properties that explores nanoscale fillers functionality. Unfortunately, most of the papers present processing methods that are hard to scale up. Effects in addition different amounts of multiwall carbon nanotubes (MWCNT) and few-layer graphene (FLG) on cure behaviour, viscoelastic, mechanical and electrical properties of a hydrogenated nitrile butadiene rubber (HNBR) are investigated and compared with those composites having carbon black (CB) as filler. Looking for scale up the produced nanocomposites, rubber composites were produced in a closed mixing chamber by melt mixing with unmodified fillers. Addition of nanotubes reduces curing time. Microstructural analyses indicate that FLG cannot be easily dispersed by this methodology. Significant improvement in mechanical properties is observed with MWCNT addition, with 940% modulus increment regarding to the pure polymer and also, in lower intensity, in HNBR/FLG composites. Moreover, HNBR/MWCNT composites presented a sharp reduction in electrical resistivity at low loading level.     

Poly(lactic acid) and layered silicate nanocomposites prepared by melt mixing: Thermomechanical and morphological properties

Poly(lactic acid) (PLA) nanocomposites were prepared by melt mixing technique in a Haake batch mixer. The clay dispersion within the PLA matrix during melt mixing was well explained through the morphological characterization. Morphological characterizations were studied by X‐ray diffraction and transmission electron microscopy. The exfoliation/intercalation of the clay particles within the polymer matrix during melt mixing depends on the mixing torque generated during the preparation of nanocomposites. The significance of processing temperature and the mixing time in melt mixing were studied for PLA/C93A and PLA/C30B nanocomposites. The structure and properties of the nanocomposites were also characterized by differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, and mechanical properties by standard tensile testing. The incorporation of nanoclays into the PLA matrix enhanced the mechanical properties and thermal stability of the PLA nanocomposites. This may be due to the reinforcing effect of nanoclays within the polymer matrix. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Effect of organoclay content on the mechanical properties of ethylene‐vinyl acetate copolymer/ multi‐walled carbon nanotube/organoclay foams

The main objective of this study is to obtain ethylene‐vinyl acetate copolymer (EVA)/multi‐walled carbon nanotube (MWCNT)/organoclay foams with improved mechanical properties without increase of their density, compared with EVA/MWCNT foams. MWCNT content was fixed at 5 phr in this study. To achieve the objective, EVA was melt‐mixed with MWCNTs and organoclays in a bench kneader. And the obtained EVA/MWCNT/organoclay mixtures were mixed with chemical blowing agent and cross‐linking agent in a two roll‐mill. After being mixed in a two roll‐mill, the mixtures were put in a mold and the foams were obtained by compression‐molding. The effect of organoclay content on the mechanical properties and surface resistivity of EVA/MWCNT (5 phr)/organoclay foams was investigated. The addition of 1 phr organoclays to the EVA/MWCNT (5 phr) foams resulted in the improvement of tensile strength, 100% tensile modulus, tear strength, and compression set without increase of the density. However, further increase in content of organoclay (3 phr) leaded to a deterioration of mechanical properties. Therefore, determining the optimal content of organoclay was very important in order to achieve the main objective of this study. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Optimizing mechanical and morphological properties of biodegradable thermoplastic elastomer based on epoxidized natural rubber and poly(butylene succinate) blends

Biodegradable thermoplastic elastomer (BTPE) blends of epoxidized natural rubber (ENR) and poly(butylene succinate) (PBS) were prepared by the melt mixing process. Influences of the processing parameters mixing temperature, rotor speed, and mixing time on mechanical and morphological properties of BTPE were investigated. Taguchi method was applied to improve the mechanical and morphological properties by optimizing the processing parameters. That is, the experimental design adopted the L9 Taguchi orthogonal array with three manipulated factors (i.e., mixing temperature, rotor speed, and mixing time). Analysis of mean and analysis of variance were also exploited and the mixing temperature was found to be the most significant processing parameter regarding mechanical properties. The mixing temperature showed large contributions to Young's modulus, 100% modulus, tensile strength, and elongation at break, namely 45.33, 40.38, 49.31, and 36.04%, respectively. Furthermore, the optimum conditions found for mixing temperature, rotor speed, and mixing time were 140 °C, 100 rpm and 10 min, respectively. The result was confirmed by atomic force microscopy and scanning electron microscopy micrographs showing fine‐grained co‐continuous phase morphology of the ENR/PBS blends. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46541.     

Natural rubber/poly(ethylene‐co‐vinyl acetate)‐blend‐based nanocomposites

Natural rubber (NR)/poly(ethylene‐co‐vinyl acetate) (EVA) blend–clay nanocomposites were prepared and characterized. The blend nanocomposites were prepared through the melt mixing of NR/EVA in a ratio of 40/60 with various amounts of organoclay with an internal mixer followed by compression molding. X‐ray diffraction patterns revealed that the nanocomposites formed were intercalated. The formation of the intercalated nanocomposites was also indicated by transmission electron microscopy. Scanning electron microscopy, used to study the fractured surface morphology, showed that the distribution of the organoclay in the polymer matrix was homogeneous. The tensile modulus of the nanocomposites increased with an increase in the organoclay content. However, an increase in the organoclay content up to 5 phr did not affect the tensile strength, but the organoclay reduced this property when it was increased further. This study also indicated that a low silicate content dispersed in the blend matrix was capable of increasing the storage modulus of the material. The addition of the organoclay also increased the decomposition temperature of the NR/EVA blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 353–362, 2006     

Thermal and electrical conductivity of melt mixed polycarbonate hybrid composites co‐filled with multi‐walled carbon nanotubes and graphene nanoplatelets

In this work, we present thermoplastic nanocomposites of polycarbonate (PC) matrix with hybrid nanofillers system formed by a melt‐mixing approach. Various concentrations of multi‐walled carbon nanotubes (MWCNT) and graphene nanoplatelets (GnP) were mixed in to PC and the melt was homogenized. The nanocomposites were compression molded and characterized by different techniques. Torque dependence on the nanofiller composition increased with the presence of carbon nanotubes. The synergy of carbon nanotubes and GnP showed exponential increase of thermal conductivity, which was compared to logarithmic increase for nanocomposite with no MWCNT. Decrease of Shore A hardness at elevated loads present for all investigated nanocomposites was correlated with the expected low homogeneity caused by a low shear during melt‐mixing. Mathematical model was used to calculate elastic modulus from Shore A tests results. Vicat softening temperature (VST) showed opposite pattern for hybrid nanocomposites and for PC‐MWCNT increasing in the latter case. Electrical conductivity boost was explained by the collective effect of high nanofiller loads and synergy of MWCNT and GnP. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42536.     

Dynamically vulcanized polypropylene/ethylene‐propylene diene monomer/organoclay nanocomposites: Effect of mixing sequence on structural,rheological, and mechanical properties

Dynamically vulcanized thermoplastic elastomer (TPE) nanocomposites based on polypropylene (PP), ethylene‐propylene diene monomer (EPDM) and cloisite 15A were prepared via direct melt mixing in a co‐rotating twin‐screw extruder. The mixing process was carried out with optimized processing parameters (barrel temperature = 180°C; screw speed = 150 rpm; and feeding rate = 0.2 kg/hr). The formulation used to prepare the nanocomposites was fixed to 75/20/5 (PP/EPDM/Cloisite^©15A), expressed in mass fraction. Effect of mixing sequence on the properties of vulcanized and unvulcanized (TPE) nanocomposites prepared under similar conditions was investigated using X‐ray diffraction (XRD) and a tensile testing machine. Results showed that the sequence of mixing does affect the properties of final TPE nanocomposites. Accordingly, nanocomposite samples prepared through mixing the preblended PP/clay masterbatch with EPDM phase, show better clay dispersion within the polymer matrix. J. VINYL ADDIT. TECHNOL., 22:320–325, 2016. © 2014 Society of Plastics Engineers     

Multiwall‐carbon‐nanotube‐reinforced poly(ethylene terephthalate) nanocomposites by melt compounding

Poly(ethylene terephthalate) (PET) nanocomposites reinforced with multiwall carbon nanotubes (MWCNTs) were prepared through melt compounding in a twin‐screw extruder. The presence of MWCNTs, which acted as good nucleating agents, enhanced the crystallization of PET through heterogeneous nucleation. The incorporation of a small quantity of MWCNTs improved the thermal stability of the PET/MWCNT nanocomposites. The mechanical properties of the PET/MWCNT nanocomposites increased with even a small quantity of MWCNTs. There was a significant dependence of the rheological properties of the PET/MWCNT nanocomposites on the MWCNT content. The MWCNT loading increased the shear‐thinning nature of the polymer‐nanocomposite melt. The storage modulus and loss modulus of the PET/MWCNT nanocomposites increased with increasing frequency, and this increment effect was more pronounced at lower frequencies. At higher MWCNT contents, the dominant nanotube–nanotube interactions led to the formation of interconnected or networklike structures of MWCNTs in the PET/MWCNT nanocomposites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1450–1457, 2007     

Tuning the nano/micro‐structure and properties of melt‐processed ternary composites of polypropylene/ethylene vinyl acetate blend and nanoclay: The influence of kinetic and thermodynamic parameters

The present study reports the dependence of the nano/micro‐structure and properties of polypropylene (PP)/ethylene vinyl acetate (EVA)/nanoclay ternary composites on the kinetics and thermodynamics of the melt‐mixing process. The size of dispersed EVA particles in the blends increased in the presence of the nanoclay particles, whereas in the ternary blend composites the size of the EVA dispersions decreased with increasing processing time. Intercalation and exfoliation were achieved more efficiently in ternary composites prepared with a longer EVA processing time. Moreover, the incorporation of the nanoclay particles within the EVA phase and interphase, as well as a long processing time stabilized the morphology. The degree of crystallinity, melting behavior, and crystallization temperature of PP in the ternary composites were not influenced by the presence of the nanoclay particles or by the duration of the melt‐mixing process. The thermal stability of the ternary composites improved with increasing melt‐mixing time. The rheological and thermomechanical properties were found to be dependent on the processing time and on the resulting structure. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45585.     

Reduction of percolation threshold of multiwall carbon nanotube (MWCNT) in polystyrene (PS)/low‐density polyethylene (LDPE)/MWCNT nanocomposites: An eco‐friendly approach

In this article, we introduce an eco‐friendly approach to achieve electrical conductivity at sufficiently lower loading of MWCNT in the PS/LDPE/MWCNT nanocomposites through judicious control of temperature during melt blending. The percolation threshold was achieved at 0.21 wt% of MWCNT following this method, which is lower, compared to the result obtained from direct mixing as well as the previously reported data. The morphological analysis revealed a co‐continuous structure of the (70/30, PS/LDPE)/MWCNT nanocomposites in such a high asymmetric composition of blend constituents, which facilitates in the lowering of percolation threshold through selective dispersion of MWCNT in the minor LDPE phase. The electron conduction in the nanocomposites has well been explained in terms of tunneling mechanism, supporting thin coating of polymer over individual CNTs. The morphological, electric and dielectric properties have been well explained in this article. POLYM. COMPOS., 36:1574–1583, 2015. © 2014 Society of Plastics Engineers