Studies on the oxygen barrier and mechanical properties of low density polyethylene/organoclay nanocomposite films in the presence of ethylene vinyl acetate copolymer as a new type of compatibilizer

Nanocomposite films based on low density polyethylene (LDPE), containing of 2, 3, and 4 wt.% organoclay (OC) and ethylene vinyl acetate (EVA) copolymer as a new compatibilizer were prepared and characterized using rheological tests, X-ray diffraction, differential scanning calorimetry, oxygen permeation measurements, and tensile tests. There was no exfoliation or intercalation of the clay layers in the absence of EVA, while an obvious increase in d-spacing was observed when the samples were prepared with EVA present. This issue was reflected in the properties of nanocomposites. The oxygen barrier properties of the LDPE/EVA/OC film were significantly better than those of the LDPE/OC film. The average aspect ratio of clay platelets in nanocomposites was determined from permeability measurements and using Lape–Cussler model. In addition to barrier properties, the LDPE/EVA/OC film also had better elastic modulus than their counterparts without EVA. The modulus reinforcement of nanocomposites was studied using Halpin–Tsai equations, which are universally used for composites reinforced by flake-like or rod-like fillers.     

Morphology,rheology and mechanical properties of polypropylene/ethylene–octene copolymer/clay nanocomposites: Effects of the compatibilizer

The objective of this study was to investigate the effects of two compatibilizers, namely maleated polypropylene (PP-g-MA) and maleic anhydride grafted poly (ethylene-co-octene) (EOC-g-MA), on the morphology and thus properties of ternary nanocomposites of polypropylene (PP)/ethylene–octene copolymer (EOC)/clay nanocomposite. In this regard the nanocomposites and their neat polymer blend counterparts were processed twice using a twin screw extruder. X-ray diffraction, transmission electron microscopy, Energy dispersive X-ray spectroscopy, and scanning electron microscopy were utilized to characterize nanostructure and microstructure besides mechanical and rheological behaviors of the nanocomposites. Clay with intercalated structure was observed in EOC phase of the PP/EOC/clay nanocomposite. Better dispersion state of the intercalated clay in EOC phase was observed by adding EOC-g-MA as a compatibilizer. On the other hand, adding PP-g-MA resulted in migration of the intercalated clay from the EOC to the PP and to the interface regions. It was also demonstrated that the elastomer particles became smaller in size where clay was present. The finest and the most uniform morphology was found in the PP/EOC/clay nanocomposite. In addition, the rheological results illustrated a higher complex viscosity and storage modulus for PP/EOC/PP-g-MA/clay nanocomposite in which clay particles were present in the matrix. Mechanical assessments showed improvements in the toughness of the nanocomposites with respect to their neat blends, without significant change in stiffness and tensile strength values. These results highlight a toughening role of clay in the polymer blend nanocomposites studied.     

Preparation and properties of nitrile rubber/montmorillonite nanocomposites via latex blending

The nitrile rubber (NBR)/unmodified montmorillonite (Na-MMT) clay nanocomposites were prepared by latex blending method followed by melt mixing of compounding ingredients by using two-roll mill. The X-ray diffraction (XRD) studies showed an increase in the basal spacing and broadening of peak corresponding to crystal structure of Na-MMT indicating the formation of intercalated/exfoliated clay layers in the NBR matrix. Increase in clay content of nanocomposite increased the XRD peak height due to the formation of many of clay tactoids at higher loading. The transmission electron microscopy (TEM) strengthened the XRD finding by showing the presence of intercalated/exfoliated morphology of clay platelets having good dispersion. The modulus and tensile properties of the nanocomposites were improved with addition of Na-MMT which is proportional to clay concentration. The retention of tensile properties of aged nanocomposites, with all clay concentration, was superior to either pure NBR and carbon black filled NBR composite. The dynamic mechanical analysis showed proportional increase in storage modulus analogous to Na-MMT loading at all the temperature ranges due to the confinement of polymer chains between the clay layers. Nanocomposites with different proportions of clay showed a decrease in tan δ_max peak height with a shift towards higher temperature indicating the reduction in the segmental mobility of polymer chain. A linear model was proposed to correlate the influence of Na-MMT content on storage modulus of nanocomposites. Differential scanning calorimetry indicated a linear increase in glass transition of nanocomposites which is proportional to clay loading. Thermogravimetric analysis revealed a small improvement in the thermal stability of nitrile rubber/clay nanocomposites.     

Improving the mechanical properties of thermoplastic starch/poly(vinyl alcohol)/clay nanocomposites

Thermoplastic starch/poly(vinyl alcohol) (PVOH)/clay nanocomposites, exhibiting the intercalated and exfoliated structures, were prepared via melt extrusion method. The effects of clay cation, water, PVOH and clay contents on clay intercalation and mechanical properties of nanocomposites were investigated. The experiments were carried out according to the Taguchi experimental design method. Montmorillonite (MMT) with three types of cation or modifier (Na⁺, alkyl ammonium ion, and citric acid) was examined. The prepared nanocomposites with modified montmorillonite indicated a mechanical improvement in the properties in comparison with pristine MMT. It was also observed that increases in tensile strength and modulus would be attained for nanocomposite samples with 10%, 5% and 4% (by weight) of water, PVOH and clay loading, respectively. The clay intercalation was examined by X-ray diffraction (XRD) patterns. The chemical structure and morphology of the optimum sample was also probed by FTIR spectroscopy and transmission electron microscopy (TEM).     

Effect of sintering on thermally sprayed carbon nanotube reinforced aluminum nanocomposite

Reconsolidation of thermally spray formed (plasma and high velocity oxyfuel spraying) hypereutectic Al–Si nanocomposites with multiwalled carbon nanotube (MWCNT) reinforcement was carried out by inert atmosphere sintering for prolonged time periods. The sintering treatment resulted in the removal of porosity and residual stress, and increase in size and volume fraction of primary Si particles in the Al–Si matrix. The morphology of multiwalled carbon nanotubes in sintered nanocomposites remained unchanged after sintering. The interfacial ultrathin product layer of silicon carbide between MWCNT reinforcement and Al–Si matrix was unaltered. Microhardness and elastic modulus of the sintered nanocomposites were influenced by combined effect of multiple factors, i.e. reduction in porosity, residual stress removal and MWCNT distribution. Overall improvement of microhardness and elastic modulus of the sintered nanocomposites was observed. The experimentally measured elastic modulus values were compared with theoretically estimated values using micromechanics models.     

Polylactide (PLA)-clay nanocomposites prepared by melt compounding in the presence of a chain extender

Polylactide-layered silicate nanocomposites with and without a chain extender were prepared by melt mixing using a twin-screw extruder. An organo-modified clay, Cloisite® 30B, and a chain extender Joncryl®-ADR 4368F were employed in this study. The effect of the chain extender and processing conditions on the properties of the PLA-clay nanocomposites were investigated for different strategies of mixing. The resulting nanocomposites were characterized by X-ray diffraction (XRD), while their morphology was observed by SEM and TEM. The incorporation of the chain extender could enhance the degree of clay dispersion provided that it is judiciously added to the nanocomposite. The corresponding results revealed that the Joncryl-based nanocomposites, where nanoclay platelets were well-dispersed, exhibited a significantly reduced permeability as compared to others. The mechanical properties of the neat PLA, the PLA and Joncryl-based nanocomposites were also examined. The increased molecular weight in Joncryl-based nanocomposites caused a significant increase in the modulus, drawability and toughness of the samples.     

Modulus–density negative correlation for CNT-reinforced polymer nanocomposites: Modeling and experiments

Mechanical and weight properties of polymer nanocomposites (PNCs) are measured and modeled at the interlaminar region, predicting the density and elastic modulus of individual carbon nanotubes (CNTs). A simple model of the CNTs density and elastic modulus within the PNC, accounting for fundamental material properties, geometry, and interactions, is developed, capable of predicting CNT contributions in the PNCs. Furthermore, the model is validated with experimental results that demonstrate enhancement of the elastic modulus, while reducing density in the presence of aligned CNTs. By establishing an inverse relation of density and elastic modulus (negative correlation), it is demonstrated the potential of increasing mechanical properties while reducing weight. Therefore, by introducing controlled nanoporosity through suitable CNT distributions within the interlayer of multi-lamina structures, it is possible to simultaneously control effective weight reduction and enhanced modulus, toward bio-inspired carbon fiber reinforced polymer composites.     

Influence of constituent properties and microstructural parameters on the tensile modulus of a polymer/clay nanocomposite

A multi-scale model to predict the moduli of polymer–clay nanocomposites (PCNs) is presented. The model uses a locally orthotropic finite element model to develop constitutive equations to describe the stiffness properties of a group of aligned clay flakes with surrounding interphase suspended in a polymer matrix. The model then assembles a number of flake groups with varied orientations to predict the actual moduli seen in PCNs. The model is in good agreement with an experimentally obtained tensile modulus found in the literature. The model was also applied to estimate the relative influence of constituent properties and microstructural parameters on the anisotropic tensile modulus of the PCN.     

Processing and characterization of solid and microcellular poly(lactic acid)/polyhydroxybutyrate-valerate (PLA/PHBV) blends and PLA/PHBV/Clay nanocomposites

The morphology, microstructure, tensile properties, and dynamic mechanical properties of solid and microcellular poly(lactic acid) (PLA)/polyhydroxybutyrate-valerate (PHBV) blends, as well as PLA/PHBV/clay nanocomposites, together with the thermal and rheological properties of solid PLA/PHBV blends and PLA/PHBV/clay nanocomposites, were investigated. Conventional and microcellular injection-molding processes were used to produce solid and microcellular specimens in the form of ASTM tensile test bars. Nitrogen in the supercritical state was used as the physical blowing agent in the microcellular injection molding experiments. In terms of rheology, the PLA/PHBV blends exhibited a Newtonian fluid behavior, and their nanocomposite counterparts showed a strong shear-thinning behavior, over the full frequency range. An obvious pseudo-solid-like behavior over a wide range of frequencies in the PLA/PHBV/clay nanocomposites suggested a strong interaction between the PLA/PHBV blend and the nanoclay that restricted the relaxation of the polymer chains. PLA/PHBV/clay nanocomposites possess a higher modulus and greater melt strength than PLA/PHBV blends. The addition of nanoclay also decreased the average cell size and increased the cell density of microcellular PLA/PHBV specimens. As a crystalline nucleating agent, nanoclay significantly improved the crystallinity of PHBV in the blend, thus leading to a relatively high modulus for both solid and microcellular specimens. However, the addition of nanoclay had less of an effect on the tensile strength and strain-at-break.     

Effect of organic modification of sepiolite for PA 6 polymer/organoclay nanocomposites

Polyamide 6 nanocomposites based on sepiolite needle-like clay were prepared via melt extrusion. Sepiolite was organomodified with trimethyl hydrogenated tallow quaternary ammonium (3MTH) by using different amounts of modifier respect to the sepiolite. The effect of modifier/sepiolite ratio on the final nanocomposite properties and the catalytic effect of the sepiolite on the polymeric matrix were evaluated. The presence of organomodified sepiolite on the polymer matrix favoured the crystallinity of the PA 6. The catalytic effect of the sepiolite was reduced as the modifier amount increased. The elastic modulus and Heat Deflection Temperature (HDT) in PA 6/organosepiolite nanocomposites increased ∼2.5 times respect to the neat PA 6 matrix. The higher the modification grade the better the dispersion and orientation of needle-like sepiolite clay were attained. This effect supported the reinforcement efficiency of organosepiolites with high modifier content.     

Mechanical and thermal behavior of nanoclay based polymer nanocomposites using statistical homogenization approach

In the present study, the effects of nanoclay additives on the effective mechanical and thermal properties of polymer/nanoclay composites have been investigated using experimental and simulation analyzes. In this research, we propose the use of strong contrast statistical continuum theory to predict the effective elastic and thermal properties. To validate our modeling approach, we conducted experimental measurements of these properties for polyamide/nanoclay nanocomposites with concentrations of 1, 3 and 5 wt.% of nanoclay particles. Three-dimensional isotropic nanocomposite samples with randomly oriented monolayer nanoclays were computer generated and used to calculate the statistical correlation functions of the realized model. These correlation functions have been exploited to calculate effective thermal and elastic properties of the nanocomposite. The simulation results have shown that effective stiffness can be increased significantly with small amounts of particle concentration for the exfoliated clay monolayers. The predicted effective conductivity and elastic modulus have been compared to our experimental results. Effective thermal conductivity shows satisfactory agreement with experimental data. However, the predicted results for the elastic modulus overestimate the experimental data, which might be due to the increasing intercalated structure for high concentration of nanofiller and to anisotropic properties of the nanoclay.     

Dielectric properties of montmorillonite clay filled poly(vinyl alcohol)/poly(ethylene oxide) blend nanocomposites

Organic–inorganic nanocomposites of poly(vinyl alcohol) (PVA)–poly(ethylene oxide) (PEO) blend filled with montmorillonite (MMT) nanoclay up to 10 wt.% concentration were synthesized by aqueous solution-cast technique. The complex dielectric function, electrical conductivity, electric modulus and impedance spectra of the nanocomposites were measured in the frequency range 20 Hz–1 MHz at ambient temperature. A direct correlation was observed between the real part of dielectric function and the mean relaxation time of the polymer chain segmental dynamics, with the exfoliated and intercalated MMT clay structures, and the extent of miscibility between PVA and PEO due to hydrogen bonded bridging through exfoliated MMT clay nanosheets. The large increase of dielectric relaxation time revealed that the dispersed exfoliated nanoscale MMT clay in the polymers blend matrix produces a large hindrance to the polymer chain dynamics. Results confirm that the real part of dielectric function of the nanocomposites can be tailored by varying amount of MMT clay filler for their use as nanodielectric materials in the microelectronic technology.     

Preparation and properties of reduced graphene oxide/polyacrylonitrile nanocomposites using polyvinyl phenol

Nanocomposites of polyacrylonitrile (PAN) with reduced graphene oxide (rGO) were prepared using a solution mixing technique employing polyvinyl phenol (PVP) as a compatibilizer. The PVP can facilitate composite formation by interacting with both rGO and PAN via π-π and H-bonding respectively. Various amounts of rGO were used to prepare PAN nanocomposites. The cross-sectional morphology of the composite films shows a uniform dispersion of rGO sheets in the PAN matrix. The Fourier transform infrared (FT-IR) studies revealed that good interaction of the rGO/PVP hybrid with PAN. The wide angle x-ray diffraction (WAXS) study confirms that the rGO sheets were uniformely dispersed as individual sheets in the PAN matrix. Thermogravimetric analysis shows enhanced thermal stability of the composite compared to pure PAN. The tensile strength and elastic modulus of the nanocomposites increased with increasing rGO content. A 102% enhancement in tensile strength and a 62.9% enhancement in elastic modulus were observed in the nanocomposite with 5% rGO.     

Biaxial deformation behavior and mechanical properties of a polypropylene/clay nanocomposite

Polymer nanocomposites offer the potential of enhanced properties such as increased modulus and barrier properties to the end user. Much work has been carried out on the effects of extrusion conditions on melt processed nanocomposites but very little research has been conducted on the use of polymer nanocomposites in semi-solid forming processes such as thermoforming and injection blow molding. These processes are used to make much of today’s packaging, and any improvements in performance such as possible lightweighting due to increased modulus would bring significant benefits both economically and environmentally. The work described here looks at the biaxial deformation of polypropylene–clay nanocomposites under industrial forming conditions in order to determine if the presence of clay affects processability, structure and mechanical properties of the stretched material. Melt compounded polypropylene/clay composites in sheet form were biaxially stretched at a variety of processing conditions to examine the effect of high temperature, high strain and high strain rate processing on sheet structure and properties.     

PHBV nanocomposites based on organomodified montmorillonite and halloysite: The effect of clay type on the morphology and thermal and mechanical properties

The aim of this study was to evaluate the effect of the addition of two types of nanoparticles, organomodified montmorillonite Cloisite® 30B (C-30B), and a tubular like clay, halloysite (HNT), on the morphology and thermal and mechanical properties of poly(hydroxybutyrate-co-hydroxyvalerate) – PHBV nanocomposites. TEM and WAXD results showed a combination of a few tactoids and a partially exfoliated structure for PHBV/C-30B nanocomposites and a good dispersion of HNT in the PHBV matrix. DSC analysis indicated a lower nucleation density with the addition of nanoparticles. Furthermore, the presence of C-30B led to the formation of double melting peaks, related to different crystalline phases. However, a higher melting temperature was obtained for PHBV/HNT nanocomposites. A general increase in the Young’s modulus was observed. However, for PHBV/C-30B nanocomposites, this enhancement was at the expense of the strain at break and impact strength, probably due to the degradation of the polymer during processing.     

Effect of organoclay platelets on morphology and properties of LLDPE/EMA blends

Blends of linear low density polyethylene (LLDPE) and ethylene-co-methyl acrylate (EMA) and their nanocomposites with two types of modified montmorillonite (organoclay) were explored in order to achieve an improved balance between stiffness and toughness. The nanocomposites were prepared in a HAAKE RHEOMIX at three different mixing sequences. The compression molded nanocomposites were utilized to evaluate the morphology and the properties like mechanical, dynamic mechanical and thermal. The results reveal that the morphology and the properties of the nanocomposites are dependent on the blending sequence as well as the type of nanoclay used. The addition of organoclay slightly increases the tensile modulus for all the nanocomposites. On the other hand, a drastic improvement of the impact strength was observed when the organoclay located at the dispersed EMA phase. The effects of clay concentration on the properties of the nanocomposites were also studied. The optimum dispersion as well as property was found for the nanocomposite at 5 wt% of the nano clay.     

On the overall elastic moduli of polymer-clay nanocomposite materials using a self-consistent approach. Part II: Experimental verification

Polyamide-6 (PA6) based nanocomposites were prepared using a modified montmorillonite (MMT) Cloisite 20A as nanofillers. The silicate weight fraction of the prepared nanocomposites, determined by burning off the PA6 matrix, was ranged from 0.2 wt% up to 7.5 wt%. The thermomechanical properties of both the neat PA6 and the PA6 filled with MMT nanoclay were measured by means of uniaxial tension tests and dynamic mechanical thermoanalysis, their crystallinity analyzed by differential scanning calorimetry and their morphology observed by transmission electron microscopy. The elastic stiffness of PA6-clay nanocomposites was examined under two moisture levels and was analyzed with the theory formulated in the Part I of this work. Predicted results are found in good agreement with our experiments. The model capabilities are also critically discussed by comparisons with both experiments issued from the literature and the Mori-Tanaka approach widely used in recent literature. It is demonstrated that the proposed micromechanical model is more efficient than the Mori-Tanaka approach. Moreover, the obtained results support the idea that the elastic stiffness of polymer-clay nanocomposites is governed by the same mechanisms as microcomposites, the effects of particle dimension or constrained region being of a second order.     

Porous nanocomposites prepared from layered clay and PMMA [poly(methyl methacrylate)]

The aim of the present work is the preparation of PMMA based porous nanocomposites that contain clay (montmorillonite, MMT) platelets as reinforcements within the cell walls of the porous structure. To render the clay layers organophilic, MMT was surface treated by an ion exchange reaction between interlayer cations of the clay and ammonium ions of a surfactant. Clay/PMMA based porous nanocomposites were prepared by polymerization of water-in-oil emulsions with and without clay addition. The microstructure and compressive mechanical behavior of the nanocomposites were investigated. The results of mechanical tests showed that the porous systems with the addition of 1 wt.% of organoclay (OMMT) exhibited a 90% and 50% increase of collapse stress and elastic modulus values, respectively, as compared to neat porous PMMA.     

Ultrasound assisted synthesis of PMMA/clay nanocomposites: Study of oxygen permeation and flame retardant properties

PMMA/clay nanocomposites were synthesized by ultrasound assisted emulsifier-free emulsion polymerization technique. Ultrasound waves of different power and frequencies were applied to enhance the dispersion of the clay layers with polymer matrix. The structural information of the synthesized materials was studied by X-ray diffraction (XRD) and it was revealed that the interlayer spacing increased with clay loading. The magnitude of dispersion of the clay in the polymer matrix was detected by transmission electron microscopy (TEM). The Young’s modulus, breaking stress, elongation at break, toughness, yield stress and yield strain of the nanocomposites as a function of different clay concentrations and ultrasonic power were measured. Particle diameter of the nanocomposites was measured by laser diffraction technique. Oxygen permeability of the samples was studied and it was found that the oxygen flow rate was reduced by the combined effect of clay loading and ultrasound. The flame retardant property of the nanocomposites due to clay dispersion was investigated by measurement of limiting oxygen index (LOI).     

Clay exfoliation and organic modification on wear of nylon 6 nanocomposites processed by different routes

The role of nanoclay on the wear characteristics of nylon 6 nanocomposites processed via different routes is examined in this paper. Pristine clay and organoclay were used in melt-extrusion with the matrix resulting in a largely aggregated and a highly exfoliated morphology, respectively. High exfoliation of pristine clay was also achieved by a water-assist process in melt compounding. Nylon 6/pristine clay composite had the worst wear resistance due to the large aggregated clay particles. For the two nylon 6/exfoliated clay nanocomposites, the one with the organically modified clay outperformed that with the pristine clay exfoliated by water. Detailed study on the wear track and subsurface below of the nylon 6/clay composites using both transmission and scanning electron microscopy provided new insight into the differences in their deformation and damage mechanisms. It was revealed that the interfacial adhesion of clay to matrix, and not the exfoliated morphology of clay, played a critical role in wear. However, exfoliated clay morphology is preferred to aggregate morphology. Hence, the superior wear-performance of nylon 6/organoclay nanocomposite is brought about by a combined effect of fine dispersion of clay platelets in nylon 6, high interfacial interaction between nylon 6 and clay layers, and effective constraint on surrounding nylon 6 material exerted by the clay platelets.