Melt-intercalation of sodium-montmorillonite with alkylamine and quarternized ammonium salts of sulfonated polystyrene ionomers

Na-Montmorillonite (Na-Mmt) was melt-intercalated with alkylamine and quarternized ammonium salts of sulfonated polystyrene ionomers (SPS) with no other organic modification. Mixtures of SPS and polystyrene (PS) also exhibited similar intercalation, indicating that the ionomer was an effective compatibilizer for a non-polar polymer such as PS. The materials were mixed in a co-rotating, non-intermeshing twin-screw extruder. The intercalation was relatively insensitive to the melt processing conditions. The key variable appeared to be the ratio of charge between the ionomer and the clay. Intercalation was assessed by wide angle X-ray diffraction and transmission electron microscopy.     

Isothermal crystallization of lightly sulfonated syndiotactic polystyrene/montmorillonite clay nanocomposites

Lightly sulfonated syndiotactic polystyrene (sPS) nanocomposites were prepared using a solution intercalation technique, and the effect of montmorillonite clay on the crystallization kinetics of sulfonated sPS ionomer nanocomposites was systematically studied. Wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) were used to evaluate the dispersion of clay platelets within sPS and sulfonated sPS ionomer (SsPS) matrices. Experimental results obtained from WAXD and TEM revealed a predominately exfoliated morphology within the SsPS ionomer containing 5 wt.% of organically-modified clay. The corresponding non-sulfonated sPS control exhibited a mixed morphological structure consisting of intercalated platelets and many platelets that were present as micron-sized agglomerates. Using differential scanning calorimetry (DSC), the Avrami approach was used to elucidate information related to nucleation and growth within the sPS and SsPS systems during the isothermal crystallization process. Pristine and organically-modified clays significantly increased the overall crystallization rate of the SsPS ionomer, while the nanoclays slightly decreased the crystallization rate of the non-ionic sPS. The mechanistic origins of increased crystallization rates within the SsPS ionomer clay nanocomposites were attributed to multiple phenomena including disruption of the ionomer electrostatic network and a nucleating effect due to the presence of well-separated, homogeneously dispersed clay platelets.     

Polymer/layered clay nanocomposites: 2 polyurethane nanocomposites

A kind of novel polyurethane/Na⁺-montmorillonite nanocomposites has been synthesised using modified 4,4′-di-phenymethylate diisocyanate (M-MDI), modified polyether polyol (MPP) and Na⁺-montmorillonite (layered clay). Here, MPP was used as a swelling agent to treat the layered clay. Experimental results indicated that with increasing the amount of layered clay, the strength and strain-at-break increased. The storage modulus below the glass transition temperature of the soft segments in the polyurethane was increased by more than 350%. With increased loading of layered clay, the thermal conductivity decreased slightly rather than increased. This finding will provide valuable information for polyurethane industry.     

Interface-tuned epoxy/clay nanocomposites

Though interface has been known for a critical role in determining the properties of conventional composites, its role in polymer nanocomposites is still fragmented and in its infancy. This study synthesized a series of epoxy/clay nanocomposites with different interface strength by using three types of modifiers: ethanolamine (denoted ETH), Jeffamine^® M2070 (M27) and Jeffamine^® XTJ502 (XTJ). XTJ created a strong interface between clay layers and matrix because it bridged the layers with matrix by a chemical reaction as proved by Fourier transform infrared spectroscopy; M27 produced an intermediate interface strength due to the molecular entanglement between grafted M27 chains and matrix molecules; the interface made by ETH was weak because neither chemical bridging nor molecular entanglement was involved. The studies of mechanical and thermal properties and morphology at a wide range of magnification show that the strong interface promoted the highest level of exfoliation and dispersion of clay layers, and achieved the most increment in Young’s modulus, fracture toughness and glass transition temperature (T_g) of matrix. With ∼1.3 wt% clay, the critical strain energy release rate G_1c of neat epoxy improved from 179.0 to 384.7 J/m, 115% improvement and T_g enhanced from 93.7 to 99.7 °C, 6.4% improvement.     

Polyethylene-clay hybrid nanocomposites: in situ polymerization using bifunctional organic modifiers

A hybrid polyethylene-clay nanocomposite was prepared using in situ polymerization with bifunctional organic modifiers. Morphological characterization of the product shows that a fraction of the polyethylene chains is chemically linked to the silicate surface. The chemical modification and intercalation of montmorillonite was carried out with alkylaluminum and vinylalcohol. The vinyl groups chemically linked to the silicate surface were copolymerized with ethylene inside the clay galleries using a coordination catalyst. The polymerization leads not only to effective exfoliation of the layered silicate but also to polyethylene chains that are chemically bonded to silicate surface.     

Preparation and characterization of nylon 11/organoclay nanocomposites

Nylon 11/organoclay nanocomposites have been successfully prepared by melt-compounding. X-ray diffraction and transmission electron microscopy indicate the formation of the exfoliated nanocomposites at low clay concentrations (less than 4 wt%) and a mixture of exfoliated and intercalated nanocomposites at higher clay contents. Thermogravimetric and dynamic mechanical analyses as well as tensile tests show that the degree of dispersion of nanoclay within polymer matrix plays a vital role in property improvement. The thermal stability and mechanical properties of the exfoliated nylon 11/clay nanocomposites (containing lower clay concentrations) are superior to those of the intercalated ones (with higher clay contents), due to the finer dispersion of organoclay among the matrix.     

Investigation on polypropylene and polyamide-6 alloys/montmorillonite nanocomposites

Propropylene (PP) and polyamide-6 (PA6) alloys nanocomposites were prepared using melt intercalation technique by blending PP and PA6 while used organophilic montmorillonite (OMT). The melt intercalation of PP and PA6 alloys was carried out in the presence of a compatibilizer such as maleic anhydride-g-polypropylene (MAPP). Their structures were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and High Resolution Electronic Microscope (HREM). It was found different blend sequences have influence on the dispersibility of OMT and self-assembled structures of OMT appeared in PP and PA6 alloys. The crystallization behavior and crystal structure of PP and PA6 alloys/montmorillonite nanocomposites were investigated by X-ray diffraction. It showed that the blend sequences have influence on crystal structure and a higher cooling rate results in increasing of γ-crystalline phase. Flammability properties are characterized by Cone Calorimeter, which show an unusual phenomenon.     

Measuring the extent of exfoliation in polymer/clay nanocomposites using real-time process monitoring methods

Dielectric and optical transmission measurements obtained during processing of polymer/clay composites yielded quantitative information about the extent of clay exfoliation in the polymer matrix. Measurements were made using an instrumented slit die that was situated at the exit of a twin screw extruder. Nylon 6, 11 and 12 resins were compounded with several organo modified montmorillonite clays. Dielectric and optical data were correlated with off-line transmission electron microscopy. Dielectric observations revealed a large Maxwell-Wagner (MW) relaxation whose characteristic frequency reflects an RC time constant associated with the conduction of ions and the polarization of the resin/clay interface. Optical transmission measurements showed that transmission increased with increasing extent of exfoliation because light scattering due to aggregate clay particles is reduced as the particles exfoliate nanosize silicate flakes. Extent of exfoliation models, based on MW relaxation time and its relationship to interfacial polarization, and based on optical transmission measurements, are developed.     

Preparation of exfoliated isotactic polypropylene/alkyl-triphenylphosphonium-modified montmorillonite nanocomposites via in situ intercalative polymerization

Alkyltriphenylphosphonium-modified montmorillonite(PMMT) was used to prepare TiCl₄/MgCl₂/PMMT compound catalyst and exfoliated i-PP/PMMT nanocomposites were prepared by in situ intercalative polymerization of propylene with TiCl₄/MgCl₂/PMMT catalyst. The catalytic efficiency of the above catalyst under optimum polymerization condition could reach as high as 1300 kg/(molTi h) and the combining of PMMT with Z-N catalyst do not change the stereo-regulation catalytic properties of the Z-N catalyst. The synthesized PP possessed high isotacticity, melting point and molecular weight. Wide angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) examinations evidenced the nanocomposites obtained were exfoliated ones.     

Syntheses and characterizations of in situ blended metallocence polyethylene/clay nanocomposites

In this paper, we report the preparation of in situ blends of metallocence polyethylene (mPE) with montmorillonite (clay). The polymerization activity of polyethylene decreases upon increasing the amount of the clay feed. The mPE nanocomposites still possess their original melting and crystallization temperatures, but the melting and crystallization enthalpies decrease upon increasing the clay content. In addition, the polymer interaction parameter between mPE and exfoliated clay sheets was calculated to be −0.204 based on a modified Kim-Bae equilibrium melting depression equation. All of the isothermal crystallization kinetics data fit well to the Avrami crystallization equation. We found that increasing the clay content results in a faster rate of crystallization, but pure mPE still crystallizes the fastest. Using a small amount of pretreated clay results in a more homogeneous and finer dispersion of the clay in the polymer matrix, as determined by wide-angle X-ray diffraction and transmission electron microscopy analyses. Both the values of T_1ρ^H in the solid-state NMR spectra of the fast and slow components show increment upon increasing the clay content, which indicates that either the mobile phase tends to increase its rigidity in the clay-containing system.     

Effect of clay modifiers on the morphology and physical properties of thermoplastic polyurethane/clay nanocomposites

Thermoplastic polyurethanes (TPUs)/clay nanocomposites were prepared via melt processing using the ester type and the ether type TPUs and three differently modified organoclays (denoted as C30B, C25A and C15A) as well as pristine montmorillonite (PM). XRD and TEM results showed that the addition of C30B with hydroxyl group led to the nearly exfoliated structures in both TPUs. In the case of C25A and C15A clays, partially intercalated nanocomposites were obtained in both TPUs, where C25A showed better dispersion than C15A. Natural clay (PM) was not effectively dispersed in both TPUs. The tensile properties of nanocomposites with C30B were better than ones with the other clays. Higher tensile properties were obtained for ester type TPU than ether type TPU nanocomposites with all clays tested. Although the improvement in tensile properties decreased after the second extrusion of the nanocomposites, properties of the nanocomposite after first melt processing were still good enough for practical applications. Morphological changes induced by the addition of clays were analyzed using FTIR, DSC and rheological test results. Some clays were observed to cause demixing of hard and soft segments in the nanocomposites and location of clays in either soft segment or hard segment domains was also studied.     

Miniemulsion polymerization for synthesis of structured clay/polymer nanocomposites: Short review and recent advances

This review intends to present different aspects concerning clay/polymer nanocomposites produced by heterophase polymerization in aqueous media. This paper highlights the ability of miniemulsion polymerization to produce clay/polymer nanoparticles with tailored nanostructures. Indeed, this polymerization route enables the synthesis of composite nanoparticles with the clay platelets located either on the surface of the polymer particle or embedded inside the polymer particle. A focus is given on the influence of these nanostructures on the properties of the final material through a direct comparison of the composites obtained after water evaporation from these structured nanoparticles. Indeed, the film obtained from the film forming process of these nanoparticles present significantly different nanostructures and exhibit totally different mechanical behaviours and water uptakes. By comparing experimental results and modeling approaches, it is demonstrated that their properties are clearly related to the clay dispersion and contacts. It is also evidenced that the main drawback of miniemulsion from the coating application point of view, is the large water uptake promoted by the surfactant presence whose localization is strongly influenced by nanostructuration. This stresses the need for the further development of surfactant free miniemulsion polymerization using advantageously the clay presence to stabilize the emulsion.     

Evaluation of amine functionalized polypropylenes as compatibilizers for polypropylene nanocomposites

The compatibilization effects provided by amine functionalized polypropylenes versus those of a maleated polypropylene, PP-g-MA, for forming polypropylene-based nanocomposites were compared. Amine functionalized polypropylenes were prepared by reaction of maleated polypropylene, PP-g-MA, with 1,12-diaminododecane in the melt to form PP-g-NH₂ which was subsequently protonated to form PP-g-NH₃⁺. Nanocomposites were prepared by melt processing using a DSM microcompounder (residence time of 10 min) by blending polypropylene and these functionalized materials with sodium montmorillonite, Na-MMT, and with an organoclay. X-ray and transmission electron microscopy plus tensile modulus tests were used to characterize those nanocomposites. Composites based on Na-MMT as the filler showed almost no improvement of tensile modulus compared to the polymer matrix using any of these functionalized polypropylenes, which indicated that almost no exfoliation was achieved. All the compatibilized nanocomposites using an organoclay, based on quaternary ammonium surfactant modified MMT, as the filler had better clay exfoliation compared to the uncompatibilized PP nanocomposites. Binary and ternary nanocomposites using amine functionalized polypropylenes had good clay exfoliation, but no advantage over those using PP-g-MA. The PP-g-MA/organoclay and PP/PP-g-MA/organoclay nanocomposites showed the most substantial improvements in terms of both mechanical properties and clay exfoliation.     

Bacterial cellulose-laponite clay nanocomposites

A novel material comprised of bacterial cellulose (BC) and Laponite clay with different inorganic-organic ratios (m/m) was prepared by the contact of never-dried membranes of BC with a previous dispersion of clay particles in water. Field emission scanning electron microscopy (FE-SEM) data of composite materials revealed an effective adhesion of clay over the surface of BC membrane; inorganic particles also penetrate into the polymer bulk, with a significant change of the surface topography even at 5% of clay loading. As a consequence, the mechanical properties are deeply affected by the presence of clay, increasing the values of the Young modulus and the tensile strength. However the maximum strain is decreased when the clay content is increased in the composite in comparison to pristine BC. The main weight loss step of the composites is shifted towards higher temperatures compared to BC, indicating that the clay particles slightly protect the polymer from thermal and oxidative decomposition.     

Nano-composites derived from melt mixing a thermotropic liquid crystalline polyester and zinc sulfonated polystyrene ionomers

A nano-composite was produced by simply melt mixing a blend of a thermotropic liquid crystalline polyester (LCP) and the zinc salt of a lightly sulfonated polystyrene ionomer at 300 °C. The nano-particles, which were in the form of relatively uniform rectangular prisms of ca. 30 nm×30 nm×200 nm, formed from the LCP phase due to an ester-interchange reaction between the LCP and residual catalytic amounts of zinc acetate that were present from the neutralization step in the preparation of the ionomer. The nano-particles possessed a different crystal pattern and higher melting point than the parent LCP, and they were easily oriented when the blend melt was uniaxially stretched. The nano-particles provided reinforcement of the ionomer comparable to what would be expected of short fibers with a modulus of at least 25 GPa.     

The relationship between thermal degradation behavior of polymer and the fire retardancy of polymer/clay nanocomposites

The change in the degradation pathway of a polymer by incorporation of clay has a significant effect on the fire retardancy of polymer/clay nanocomposites. Since the clay layers act as a barrier to mass transport and lead to superheated conditions in the condensed phase, extensive random scission of the products formed by radical recombination is an additional degradation pathway of polymers in the presence of clay. The polymers that show good fire retardancy upon nanocomposite formation exhibit significant intermolecular reactions, such as inter-chain aminolysis/acidolysis, radical recombination and hydrogen abstraction. In the case of the polymers that degrade through a radical pathway, the relative stability of the radical is the most important factor for the prediction of the effect that nanocomposite formation has on the reduction in the peak heat release rate. The more stable is the radical produced by the polymer, the better is the fire retardancy, as measured by the reduction in the peak heat release rate, of the polymer/clay nanocomposite.     

Effects of different kinds of clay and different vinyl acetate content on the morphology and properties of EVA/clay nanocomposites

A series of EVA/clay nanocomposites and microcomposites have been prepared via melt-blending. Using four kinds of EVA with different vinyl acetate (VA) contents: 28, 40, 50 and 80 wt%, and four kinds of clay: three are organophilic clay (OMMT) and one unfunctionalized clay (Na-MMT), the effects of different VA content of EVA and the kinds of the clay on the morphology and properties of EVA/clay nanocomposites were systematically investigated. In previous studies, there are only two distinct nanostructures to distinguish polymer/clay nanocomposites: the intercalated and the exfoliated. But in this paper, we proposed a new nanostructure—‘the wedged’ to describe the dispersion degree of clay in nanocomposites, it means the sheets of clay were partly wedged by the chains of polymer. The wedged, the intercalated and the partially exfoliated structures of EVA/clay nanocomposites were characterized by X-ray diffraction (XRD) and by high-resolution transmission electron microscopy (HRTEM). The enhanced storage modulus of EVA/clay nanocomposites was characterized by dynamic mechanical thermal analysis (DMTA). The enhanced degree in the storage modulus of the OMMT on EVA/clay nanocomposites with the partially exfoliated and intercalated structure is much higher than that with wedged structure, and that with the higher VA content is higher than that with the lower. The thermal stabilities of EVA/clay nanocomposites were also studied by thermal gravimetric analysis (TGA).     

Microstructural evolution of electrically activated polypropylene/layered silicate nanocomposites investigated by in situ synchrotron wide-angle X-ray scattering and dielectric relaxation analysis

Electric field was found to facilitate the destruction of layer stacking and separation of silicate layers in polypropylene (PP)/layered silicate nanocomposites, resulting in the penetration of polymer chains into silicate galleries. In this study, we describe the real-time microstructural evolution of PP/clay nanocomposites under electric field investigated by in situ synchrotron wide-angle X-ray scattering (WAXS) analysis. We were able to identify two distinctive mechanisms for the formation of nanocomposites depending on the type of electric field. We observed that the exfoliation process prevails in the AC field, while the alignment of silicates parallel to the electric field predominates in the DC field. Dielectric relaxation analysis showed that the different mechanisms originate from different charge distributions of bound ions attached to the clay surfaces due to the applied electric field.     

Intercalated polyaniline/Na-montmorillonite nanocomposites via oxidative polymerization

This work focuses on the preparation, characterization and electrical conductive properties of intercalated polyaniline/Na-montmorillonite nanocomposites. These materials consisting of polyaniline and Na-montmorillonite were prepared by oxidative polymerization with benzoyl peroxide as oxidizing agent. The synthesized nanocomposites were investigated by a series of characterization techniques; including Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and thermal analysis. X-ray diffraction and scanning electron microscopy images showed that the polyaniline was inserted into the clay layers. The modest increase in layer spacing was as much as 0.53 nm. The thermogravimetric analysis and differential thermal analysis demonstrated the improved thermal stability of the intercalated nanocomposites relative to the pure polyaniline due to the incorporated Na-montmorillonite. The room temperature electrical conductivity of nanocomposites varied from 1.0 × 10⁻⁷ to 5.8 × 10⁻⁵ Scm⁻¹.     

A rheological method to compare the degree of exfoliation of nanocomposites

A method to quantify the shear thinning effect for polymer-clay nanocomposites has been developed. It relies on the shear thinning exponent n. The method allows to compare the extent of delamination of platelet stacks based on a routine polymer characterization experiment. Since technical properties of nanocomposites are closely linked to delamination or exfoliation, the method helps to predict the level of properties of a nanocomposite. The method is expected to become a highly useful analytical tool in the development of nanocomposites from thermoplastic polymers and virtually all kinds of platy, fibrous, or dendritic filler materials with high aspect ratio.