Ghasem Naderi

Elastomer Nanocomposites Based on NR/EPDM/ Organoclay: Morphology and Properties

Abstract Natural rubber/Ethylene Propylene Diene Monomer (NR/EPDM) blends of five different compositions (0/100), (25/75), (50/50), (75/25) and (100/0) with 1, 3, 5 and 7 phr organo-modified nanoclay (Cloisite 15A) were prepared by two-roll mill. The effect of organo-modified layered nanosilicates and composition on the cure characteristics, microstructure, mechanical, and rheological properties of the nanocomposites were studied. Results suggested the intercalation of polymer chains into the silicate layers which was evidenced by d-spacing results of X-ray diffraction patterns. TEM micrographs also directly confirmed XRD results. Mechanical properties of the nanocomposites depicted a nearly 40% percents increase respectively in the tensile modulus of 75NR/25EPDM containing 7 wt.% nanoclay.

Three-dimensional Finite Element Modeling of Rubber Curing Process

This paper describes the development of a finite element model for the simulation of the rubber curing process in a mold. Thermal conductivity and heat capacity of the rubber are assumed to be dependent on temperature. The cure kinetic behavior of the rubber is also assumed to be described by an empirical model proposed by Kamal and Sourour. The governing equation is solved using the finite element method in a three-dimensional Cartesian coordinate system. The applicability of the model is verified by a comparison between the results of the simulation of the vulcanization of a rubber part in the mold with experimentally measured temperature profile. It has been shown that there is very good agreement between the model predictions and the actual data.

Effect of type and aspect ratio of different carbon nanotubes on cure behavior of epoxy-based nanocomposites

Effect of incorporation of carbon nanotubes (CNTs) into diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin (HY5052/LY5052 system) on cure reaction was investigated via thermal analysis. Keeping their length constant, CNTs of different diameters were chosen. Samples based on epoxy resin and different type and content of CNTs were prepared and characterized. The cure behavior of epoxy matrix in the presence of CNTs was studied in both glassy and rubbery states. The results indicated that the final cure characteristics of epoxy nanocomposites were controlled by the competition of viscosity-increasing effect and heat-sink effect of CNTs. Isothermal analysis showed that accelerating or decelerating effect of CNTs on the cure process depends on CNT content, its aspect ratio and temperature of isothermal cure. The presence of the CNTs physically hindered the mobility of the epoxy and hardener monomers preventing the cure reaction (viscosity-increasing effect). In contrast, inherent high thermal conductivity of CNTs can act as a heat sink to accelerate the heat absorption of the epoxy (heat-sink effect). Below glass–rubber transition temperature (Tg), heat-sink effect of CNTs was dominant due to the restricted mobility of polymer chains in glassy state, whereas at temperatures higher than Tg, viscosity-increasing effect was dominant. CNTs physically hindered the mobility of reactive species despite the inherent tendency of polymer chains for long-range molecular motions.

Morphology and dynamic-mechanical properties of PVC/NBR blends reinforced with two types of nanoparticles

This article relies on the effect of two types of nanoparticle on morphology and dynamic-mechanical properties of polyvinyl chloride (PVC)/acrylonitrile butadiene rubber (NBR) blends. The results of mechanical investigation revealed that tensile strength and modulus of PVC/NBR nanocomposites reinforced with 1 phr of single-walled nanotube (SWNT) are very close to the case of reinforced with 5 phr of nanoclay. The outcomes of dynamic-mechanical properties revealed that the storage modulus increases with the addition of nanoparticles and the intensity of tan δ get reduced, in two cases. Morphological investigation of nanocomposites was determined by scanning and transmission electron microscopy. In the case of PVC/NBR/nanoclay, fracture surface of specimens were much rough while the fracture surface of virgin PVC/NBR was very smooth. In PVC/NBR/SWNT nanocomposites, with introducing of carbon nanotubes to polymer matrix, dispersion and distribution of NBR as minor phase in PVC as matrix got improved.

Thermoplastic Elastomer Nanocomposites Based on PA6/NBR

Abstract Thermoplastic elastomer nanocomposites (TPE nanocomposites) based on PA6/ NBR/Cloisite 30B were prepared through a direct melt mixing process in an internal mixer. The effects of NBR content (10, 30 and 50 wt.%) and nanoclay loading (3, 5 and 7 wt.%) on morphology and mechanical properties of the nanocomposites have been studied and compared with unfilled PA6/NBR blends as well. The TPE nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential scanning calorimeter (DSC) and mechanical properties. XRD results suggested that the nanoclay is exfoliated into the TPE nanocomposite matrix. TEM image of the PA6/NBR/nanoclay composite showed partial exfoliated structure of silicate layers dispersed through the both NBR and PA6 phases. The SEM photomicrograph of PA6/NBR nanocomposite showed an increasing of the rubber particles size in comparison with unfilled PA6/NBR TPE. By presence of nanoclay, improved modulus of the prepared TPE nanocomposites was achieved. DSC studies showed that loading of the nanoclay reduced the degree of crystallinity of the nanocomposite samples.

Effect of single-walled carbon nanotubes on morphology and mechanical properties of NBR/PVC blends

Dynamically vulcanized thermoplastic elastomer based on Nitrile butadiene-rubber (NBR)/PVC with functionalized single-walled carbon nanotubes (f-SWNTs) and non-functionalized single-walled carbon nanotubes (SWNTs) were prepared using a brabender internal mixer. Effects of two types of SWNTs (functionalized and non-functionalized) on morphology and mechanical properties of NBR/PVC blends were studied. Results showed that the mechanical properties of NBR/PVC/SWNTs nanocomposites improved with the increasing of SWNTs content and in particular with the increase of f-SWNTs content. Moreover, the enhancement of mechanical properties of NBR/PVC blends reinforced with functionalized SWNT was higher than that of NBR/PVC blends with non-functionalized SWNT. Dispersion of SWNTs and morphology of NBR/PVC/SWNT nanocomposites were determined by scanning electron microscopy and transmission electron microscopy (TEM) techniques. TEM images illustrated that f-SWNTs were dispersed uniformly in NBR/PVC matrix while non-functionalized SWNTs showed much aggregation. Dynamic mechanical thermal analysis of NBR/PVC/SWNTs nanocomposites was also studied. The outcomes indicated that in the case of f-SWNTs, the intensity of tan δ peak was lower than that in the case of non-functionalized SWNTs. Meanwhile, the intensity of tan δ peak reduced when the content of f-SWNTs was increased.

Investigation of curing kinetics of epoxy resin/novel nanoclay–carbon nanotube hybrids by non-isothermal differential scanning calorimetry

Chemical hybrid of nanoclay (NC)/carbon nanotube (CNT) was synthesized via growth of CNTs by chemical vapor deposition. The cure kinetics of epoxy resin in the presence of novel chemical hybrid of NC/CNT (CNC) was studied by non-isothermal differential scanning calorimetry. The effect of the CNC on cure kinetics was compared with conventional nanofillers such as CNTs, NC, and physical mixture of them (PNC). The kinetic parameters of the cure reaction were determined by iso-conversional method. The accelerating effect of CNT, CNC, and PNC in initial stage of cure reaction was related to the high thermal conductivity of CNTs, while the decelerating effect of nanofillers as the cure proceeded can be attributed to the reduction of polymer molecules motion caused by enhanced viscosity. The apparent activation energy (Eα) as the function of conversion (α) was calculated by five methods categorized into two different types: (1) conversion-dependent methods: Kissinger–Akahira–Sunose (KAS), Ozawa–Flynn–Wall (OFW), and Friedman; (2) conversion-independent methods: Kissinger and Augis. The accelerating effect of CNT, PNC, and CNC was observable as the reduced Eα values in low conversion only with KAS and OFW methods. The reverse trend of Eα values was observed with the introduction of these nanofillers at high conversions. The uniqueness of the CNC was more marked in increasing Eα values of epoxy after initial stage due to its special 3D structure of CNC. Calculated data using KAS and OFW methods showed the best agreement with the obtained experimental data.

Chemical and physical properties of self-crosslinked poly(vinyl chloride)/nitrile rubber nanocomposites prepared by melt-mixing process

Abstract In this article, poly(vinyl chloride) (PVC)/acrylonitrile butadiene rubber (NBR)/clay nanocomposites were melt-mixed using the computerized Brabender plasticorder. During preparation of the nanocomposites self-crosslinking (crosslinking without aid of any crosslinking agent) occurs and affects all properties of a sample. The extent of crosslinking reaction depends on the processing temperature, rotor speed and mixing temperature and it increased with increasing each of mixing parameters. The mechanism of the self-crosslinking reaction was examined by the Fourier transform infrared spectroscopy test. The morphology of the materials was characterized using X-ray diffraction and scanning electron microscope. The swelling test and tensile test were applied to distinguish the effects of self-crosslinking phenomena on physical properties of NBR/PVC nanocomposites. Dynamic mechanical thermal analysis tests of nanocomposites were also performed to study the physical properties, such as glass transition temperature (T g). The results showed that the crosslinking reaction made a material more strong with high modulus and tensile strength. Thus, it can be deduced that crosslinks convert the NBR/PVC nanocomposites to stiffer materials that are less penetrable by the solvent. The results drawn from the loss tangent (tan δ) curves of nanocomposite samples can be used as further evidence for the above conclusions.

Finite element analysis of flow of thermoplastic elastomer melt through axisymmetric die with slip boundary condition

Abstract A finite element model for the flow of thermoplastic elastomers in extrusion dies has been developed. The rheological behaviour of the polymer melt is assumed to be described by the generalised Newtonian models and as a special case, the well known, power law equation was selected. Owing to the very low variation of the temperature field, the flow regime was considered to be isothermal. The set of governing equations are solved using the finite element method in a cylindrical (r, z) coordinate system. Slip–stick of the polymer melt on the solid wall, encountered in the flow of highly viscous fluids, is incorporated into the model by the use of Naviers slip condition. A new method based on a technique developed previously is described for the inclusion of this condition in the working equations. The applicability of the model was verified by a comparison between the results of the simulation of a polypropylene–nitrile/butadiene rubber thermoplastic elastomer with experimentally measured data. These comparisons show that there are very good agreements between the model predictions and actual data, provided that the slip of the polymer melt during the flow in extrusion die has been taken into consideration.

Effect of Organo-clay on Properties and Mechanical Behavior of Fluorosilicone Rubber

High performance Fluorosilicone rubber (FS)/organoclay (OC) nanocomposites have been prepared by a melt compounding process. The results of mechanical investigation revealed that Young’s modulus and hardness of FS rubber are improved with introduction of OCs while an inverse trend was observed for elongation at break and tensile strength. Eight constitutive models, Yeoh, Arruda-Boyce, Mooney-Rivilen, Neo-Hookean, Marlow, polynomial, Van der Waals, and Odgen were studied to investigate the stress-strain behavior of FS/OC nanocomposites. It was concluded that the ability of these models to predict the true behavior of the FS/OC samples directly depends on the amount of OC. Two modified Halpin-Tsai and inverse rule of mixtures theories were applied to evaluate the dependence of Young modulus of nanocomposites on volume fraction of OCs. The experimental data were employed for determining modified models parameters as well as for validating models. It was shown that, OCs can also play a fundamental role in controlling volume shrinkage of FS after cure. FS was proved that still retain its specific properties as well as the fuel and thermal resistance after introduction of OCs. Combination of these results verifies that incorporation of OCs can provide tailored mechanical properties without sacrificing fuel and thermal resistance of FS elastomers.