Compatibilizing effect of acrylic acid modified polypropylene on the morphology and permeability properties of polypropylene/organoclay nanocomposites

This work dealt with the morphology and permeability properties of polypropylene/organoclay nanocomposites prepared using an acrylic acid grafted polypropylene (PP-g-AA) as compatibilizing agent. Two PP-g-AA containing the same acrylic acid content (6 wt.%) and having different molar masses were tested. The o-MMT content was 0, 1 or 5 wt.% and the PP-g-AA/o–MMT mass ratio was 0/1, 1/1, 2/1 or 5/1. Results of wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM) showed that without the PP-g-AA, the o-MMT was dispersed in the PP/o-MMT in a micrometer scale, similar to a conventional microcomposite. With the PP-g-AA, the o-MMT was much better dispersed and its interlayers were intercalated and partly exfoliated by the polymer chains. CO₂ permeability values decreased for all samples with the incorporation of the organoclay. The compatibilized samples showed a more significant reduction in CO₂ permeability, up to 50% when compared to the neat PP. In general, the PP-g-AA acted satisfactorily in compatibilizing PP/organoclay nanocomposites. Moreover, samples prepared with the compatibilizer/organoclay ratio of 5/1 had better barrier properties.     

Structure and properties of EVOH/organoclay nanocomposites

The nanocomposites of poly(ethylene-co-vinyl alcohol) (EVOH) with organoclay were prepared by a solution-precipitation method. The structures of nanocomposites were examined by X-ray diffraction. The exfoliation of organoclay was more evident in the nanocomposites of the EVOH containing 18 mol% vinyl alcohol (EVOH18), compared to the EVOH containing 5 mol% vinyl alcohol (EVOH5). Some of the bilayer alkylammonium structures at the clay gallery changed to monolayer structures in the nanocomposites. The thermal properties measured by differential scanning calorimetry showed the organoclay enhanced the crystallization of EVOH, however, it retarded crystallization when there was too much. The modulus of EVOH18 showed about a 2-fold increase of pristine polymer when using 7% of reinforcing organoclay.     

Effects of maleination and heat treatment on morphology and dynamic mechanical thermal behavior of polypropylene/organoclay nanocomposites

Effects of maleinated compatibilizer and heat treatment on the internal structure and physical properties of PP/organoclay nanocomposites were investigated by using various measurements, e.g., SAXS, TEM, DSC and DMTA, and rotational rheometer. Experimental results showed that maleination and heat treatment affected the internal structure and dynamic mechanical properties of PP/organoclay nanocomposites. Storage modulus and loss tangent of PP/organoclay nanocomposites were strongly related to the compatibilizer loadings and heat treatment conditions because the interfacial structure between PP molecular chains and organoclay particles had been changed by the addition of compatibilizer to PP/organoclay nanocomposites. DSC and DMTA results of the compatibilized nanocomposites and effects of heat treatment on crystallization and dynamic mechanical thermal properties demonstrated that there is a small change in the glass transition temperature because the chain mobility and free volume in the amorphous region are increased by heat treatment. It was found that heat treatment imposed influence on both amorphous and crystalline regions of PP/organoclay nanocomposites.     

Dispersion and rheology of polypropylene/organoclay nanocomposites: effect of cation exchange capacity and number of alkyl tails

Nanocomposites of montmorillonite organoclays and polypropylene (PP) were prepared via direct melt intercalation using maleic anhydride functionalized polypropylene (PP-g-MA) as a compatibilizer. Two montmorillonite clays (MMT) with different cation exchange capacities (CEC) were exchanged with alkyl ammonium ions, in which one or two octadecyl chains are attached to the nitrogen atom. The role of alkyl chain numbers and CEC value on the dispersion of clay and rheology of PP nanocomposites under shear and extensional flow was evaluated by X-ray diffraction, scanning electron microscopy, and rheologic techniques. It was found that the low-CEC organoclay with one alkyl chain could only form a conventional composite. However, the low-CEC organoclay with two alkyl chains or high-CEC organoclay with one alkyl chain can disperse finely in the matrix. Nanocomposites containing these two organoclays showed typical shear rheologic properties of intercalated nanocomposites, but only the former showed a mild strain-hardening behavior in uniaxial extensional flow. When using an intercalant with two tails, the high-CEC clay would lead the organoclay to form mixed structures which further resulted in an inferior dispersion quality. It was proposed that the dispersion quality and rheologic properties of nanocomposites were related to the arrangement of modifier molecules in the clay galleries, which was determined by the CEC of clay and the structure of alkyl ammonium ions.     

Mechanical reinforcement in natural rubber/organoclay nanocomposites

Aim of this work is to get an insight into the mechanisms by which nanofillers produce mechanical reinforcement in polymers above their glass transition temperature. To this purpose, the mechanical behaviour of natural rubber/organo-modified montmorillonite vulcanisates produced by melt mixing with various filler contents was investigated. Data of the initial modulus, evaluated from stress–elongation curves obtained in tensile tests carried out at room temperature and a fixed cross-head rate, were analysed as a function of the organoclay content by applying mechanical models proposed in the literature. Such analysis provided an evaluation of the filler percolation threshold. Further, tests performed with varying temperature and rate pointed out appreciable rate and temperature dependence only for samples containing amounts of organoclay higher than the percolation limit, that is in presence of filler networking. Such a typical viscoelastic behaviour associated to the presence of the filler network contributes to support the hypothesis that in filled rubbers the mechanisms of filler networking is based on the formation of confined regions of immobilised polymer that join the filler particles of the network, as recently proposed.     

Microstructures and toughening mechanisms of organoclay/polyethersulphone/epoxy hybrid nanocomposites

Hybrid nanocomposites (HNCs) with high fracture toughness were successfully prepared by incorporating polyethersulphone (PES) and organoclay into epoxy resin. Their microstructures were studied. They were composed of homogeneous PES/epoxy matrices and micron-scale organoclay agglomerates. These agglomerates consisted of smaller tactoid-like regions which were comprised of ordered exfoliated nanolayers. The toughening mechanisms of the two tougheners were also studied and then related to their microstructures. For one thing, the PES which was dissolved in the epoxy resin homogeneously improved the ductility of the epoxy resin and made it easier to deform. For another, the organoclay agglomerates induced crack front bowing, crack bridging, crack deflection, crack bifurcation and plastic deformation of the matrices on the micron-scale, respectively. These toughening processes were achieved by the ordered exfoliated nanolayers with various orientations, which debonded from the matrices, bridged the cracks and induced the plastic deformation of the matrices on the nanoscale.     

Study of rheological properties of polypropylene/organoclay hybrid materials

Polypropylene nanocomposites reinforced with organic modified montmorillonite clay have been fabricated by melt compounding using extrusion. The morphology of the composites is studied with transmission electron microscopy and X-ray diffraction. The melt-state rheological properties of the nanocomposites have been investigated as a function of temperature and organoclay loading. It is found that the organoclays are intercalated and dispersed evenly in the matrix. The storage and loss moduli of the hybrid composites decrease with temperature and increase with organoclay concentration. Both polypropylene and its composites demonstrate a melt-like rheological behavior, indicating the low degree of exfoliation of the organoclay. A shear thinning behavior is found for both polypropylene and its composites, but the onset of shear thinning for organoclay composites occurs at lower shear rates.     

Phase separation of polystyrene/poly(vinylmethylether)/organoclay nanocomposites

The effect of addition of organically modified montmorillonite (OMMT) on the phase separation of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blend was examined. Using two types of OMMT modified with two different kinds of surfactants, the effect of organic modification on nanocomposites was investigated by focusing on three major aspects: phase transition, morphological study, and melt rheological behavior both below and above the critical transition temperature. X-ray diffraction (XRD) patterns revealed the formation of intercalated nanocomposites and transmission electron micrographic (TEM) observations showed that the ordering of silicate layers in blend matrix is well matched with the XRD patterns. The addition of clay was found to affect both the mechanism of phase separation and the final morphology. Such effects resulted in uncommon rheological behavior of the blend both below and above the critical transition temperature. Surface phase separation of thin films for virgin blend and nanocomposites was also examined by atomic force microscopy (AFM). Morphology resulting after phase separation was found to be dependent on the nature and the amount of OMMT added to the polymer blend.     

Fracture behavior of polypropylene/clay nanocomposites

Polypropylene (PP)/clay nanocomposites have been prepared via a reactive compounding approach with an epoxy based masterbatch. Compared with PP and common PP/organoclay nanocomposites, the PP/clay nanocomposites based on epoxy/clay masterbatch have higher impact strength. The phenomenon can be attributed to the epoxy phase dispersed uniformly in the PP matrix, which may act as impact energy absorber and helps to form a large damage zone, thus a higher impact strength value is achieved.     

Millable polyurethane/organoclay nanocomposites: preparation, characterization, and properties

Novel millable polyurethane (PU)/organoclay nanocomposites have been successfully prepared by conventional transformation techniques. One natural (C6A) and two organically modified (C15A and C30B) montmorillonites have been used as clays for preparing PU nanocomposites. The optimum dispersion of nanofiller at a nanometer scale in PU matrix was confirmed by X-ray diffraction patterns and transmission electron microscopy. A substantial improvement of the PU properties by addition of only a small amount of organoclay was observed. It is worthy to note that the organoclays show a different interfacial interaction with the PU matrix, which was reflected in different macroscopic properties. Thus, C30B organoclay seems to react with PU chains to form covalent bonds, while C15A only interacts physically with PU chains. Mechanical and barrier properties are analyzed.     

Properties of silane grafted polypropylene/montmorillonite nanocomposites

Polypropylene/montmorillonite nanocomposites were prepared by melt compounding using organosilane modified polypropylene (PP-g-VTES) as compatibilizing agent. The materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), tensile modulus, and Izod impact strength. Addition of PP-g-VTES improved clay dispersion, as shown by the distribution of platelets per particle, and improve the interaction between clay and polymer matrix. Crystallization peak temperature (T_p) was increased in 10 °C using PP-g-VTES as compatibilizing agent. However the crystallization process and its rate were unmodified. The tensile modulus of compatibilized nanocomposite is 1.5 times higher compared to pure PP.     

Mechanical,thermal and microstructural characteristics of cellulose fibre reinforced epoxy/organoclay nanocomposites

Epoxy nanocomposites reinforced with recycled cellulose fibres (RCFs) and organoclay platelets (30B) have been fabricated and investigated in terms of WAXS, TEM, mechanical properties and TGA. Results indicated that mechanical properties generally increased as a result of the addition of nanoclay into the epoxy matrix. The presence of RCF significantly enhanced flexural strength, fracture toughness, impact strength and impact toughness of the composites. However, the inclusion of 1 wt.% clay into RCF/epoxy composites considerably increased the impact strength and toughness. The presence of either nanoclay or RCF accelerated the thermal degradation of neat epoxy, but at high temperature, thermal stability was enhanced with increased char residue over neat resin. The failure micromechanisms and energy dissipative processes in these nanocomposites were discussed in terms of microstructural observations.     

Morphologies and properties of polyurethane/epoxy resin interpenetrating network nanocomposites modified with organoclay

Polyurethane/epoxy resin interpenetrating network nanocomposites containing various contents of organophilic montmorillonite (oM-PU/EP nanocomposites) were prepared by a sequential polymeric technique and an in situ intercalation method. Transmission electronic microscopy and scanning electronic microscopy analysis showed that the interpenetrating process of PU and EP increases the exfoliation degree of organophilic montmorillonite (oMMT), and that oMMT improves the compatibility and phase structure of polyurethane/epoxy resin interpenetrating polymer networks (PU/EP IPNs). Tensile test, differential scanning calorimetry and thermal gravity analysis proved that the mechanical and thermal properties of the oM-PU/EP nanocomposites are superior to those of the pure PU and PU/EP IPNs.     

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.     

Electromagnetic absorption efficiency of polypropylene/montmorillonite/polypyrrole nanocomposites

Electrical conductivity and dielectric properties have been studied for two types of polypropylene composites containing conducting phase. One type comprised conducting polymer–polypyrrole while the second employed montmorillonite particles coated with conducting polymer–polypyrrole. Composites’ shielding properties were estimated based on their previously determined electromagnetic characteristics. Unlike a basic binary polypropylene/polypyrrole composite, the ternary sample with multicomponent montmorillonite particles exhibits higher dielectric losses and consequently a significant rise in shielding efficiency in the radio-frequency range of 0.1–1.5 GHz. This stems from the presence of highly polarizable multicomponent montmorillonite anisotropic lamellar particles with polypyrrole conducting layer, which considerably increases the complex permittivity of the composite.     

Highly ordered hierarchical poly(ethylene oxide)-b-polystyrene/organoclay nanocomposites

A lamellar forming poly(ethylene oxide)-b-polystyrene (PEO-b-PS)/organoclay nanocomposite with a unique hierarchical structure has been fabricated, by casting solution blends of the block copolymer and organoclay, with subsequent annealing at 180 °C for 8 h under uniaxial constraint. PEO-b-PS provided the nanocomposite lamellar structure with a slightly increased long period. Lamellar layers of the nanocomposite block copolymer were oriented parallel to the film plane. Fully exfoliated clay platelets were localized mostly in the aligned PEO layers, and all platelets were found to be parallel to the interface between PEO and PS layers. PEO crystals in the nanocomposite were oriented with the c-axis perpendicular to the phase-separated layers. The orientation function degree of the PEO crystals within the nanocomposite was lower than that of the crystals within the neat block copolymer.     

Morphological and structural characterization of PHBV/organoclay nanocomposites by small angle X-ray scattering

In this work, the morphological and structural behaviors of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) nanocomposites were investigated using small angle X-ray scattering (SAXS), wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). The nanocomposites with 1, 3 and 5 wt.% of organically modified montmorillonite Cloisite® 30B (OMMT) were prepared by melt processing in a twin screw extruder using two different processing conditions (low and high shear intensity). The lamellar long period of the polymer was lower for the nanocomposites, with high polydispersity values. However, the crystalline thickness increased with the clay content and was independent of the processing conditions. This behavior resulted in a high linear crystallinity of the nanocomposites with 3 and 5 wt.% OMMT. The disruption factor (β) was in agreement with the WAXD and TEM findings, indicating a good dispersion of the nanoparticles in the PHBV matrix with 3 wt.% of OMMT during the high shear intensity of melt processing.     

Creep behaviour of injection moulded polyamide 6/organoclay nanocomposites by nanoindentation and cantilever-bending

The creep behaviour of injection moulded PA 6/organoclay nanocomposites was studied by depth-sensing nanoindentation and DMA cantilever-bending. The glass transitions of PA 6 and its nanocomposites were decreased below room temperature upon saturation with water so that the materials could be tested in the rubbery regime. For nanoindentation creep on the skin and core regions of injection moulded samples, whilst organoclay improves the creep resistance of PA 6, the enhancement is due to the decrease of the initial compliance at zero time but the time-dependent creep is actually increased. In contrast, for cantilever-bending creep, organoclay reduces the creep compliance and the time-dependent creep in PA 6. It is suggested that the organoclay imparts a constraint effect on the PA 6 molecular chains, restricting their mobility in the bulk compared to the surface and hence improving their resistance to creep. A modified Halpin-Tsai equation was used to model their creep behaviour under these two loading configurations and compared to experimental data.