Enhancement of Nanoclay Dispersion and Exfoliation in Epoxy Using Aminic Hardener Treated Clay

Exfoliation and dispersion of nanoclays in epoxy matrices plays an important role in achieving better physical and mechanical properties of resultant nanocomposites. In this article, modification of clay with an aminic hardener for the increment of dispersion and exfoliation into the epoxy matrix has been investigated. In the solvent media, a slurry of hydrophilic Na-Montmorrilonite was mixed and treated with isophoronediamine (IPDA). The nanocomposites containing epoxy and IPDA-modified clay were produced through a recently developed “slurry compounding” method. Dispersion and exfoliation of the modified clay and the microstructure of the resultant nanocomposite were studied by optical microscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier-transform infrared (FTIR) spectroscopy. The samples were then compared with the high shear mixed and sonicated nanocomposites containing commonly used quaternary ammonium modified clays. The comparison showed that dispersion and exfoliation of hardener-modified organoclays in epoxy have been improved due to the treatment of clay and the compounding method.     

Synergistic effects and mechanism of multiwalled carbon nanotubes with magnesium hydroxide in halogen-free flame retardant EVA/MH/MWNT nanocomposites

The synergistic effects and mechanism of multiwalled carbon nanotubes (MWNTs) with magnesium hydroxide (MH) in halogen-free flame retardant EVA/MH/MWNT nanocomposites have been studied by cone calorimeter test (CCT), limiting oxygen index (LOI), thermogravimetric analysis (TGA), torque test, morphological evolution experiment, and scanning electron microscopy (SEM). The data obtained from the CCT, LOI, and TGA show that suitable amount of MWNTs has synergistic effects with MH in the EVA/MH/MWNT nanocomposites. The MWNTs can considerably decrease the heat release rates and mass loss rate by about 50-60%, prolongate the combustion time to near two times, and increase the LOI values by 5% when 2 wt% MWNTs substitute for the MH in the EVA/MH/MWNT samples. The TGA data also show that the synergistic effects of MWNTs with MH apparently increase the thermal degradation temperatures and final charred residues of the EVA/MH/MWNT samples. The experimental observations from the torque, morphological evolution tests, and SEM give positive evidences that the synergistic mechanism of MWNTs with MH can be described to: (i) the increase of melt viscosity because of network structure formation of MWNTs in the EVA/MH matrix; (ii) the enhancement of thermo-oxidation stability due to the MWNTs' mechanical strength and integrity of the charred layers in the EVA/MH/MWNT nanocomposites; (iii) the formation of compact charred layers promoted by MWNTs acted as heat barrier and thermal insulation. All the above-mentioned factors efficiently enhance thermal and flame retardant properties and protect the EVA/MH/MWNT nanocomposite materials to be burning.     

Effect of Organoclays on Silicate Layer Structures and Thermal Stabilities of in-situ Polymerized Poly(D-lactide)/Clay Nanocomposites

Six kinds of organoclays were prepared through three kinds of polyols (PTMG, PEA and PCL) to investigate the effects of molecular weight and the chemical structure of organifiers. PTMG based organoclays showed higher ion-exchanged fraction than other organoclays and long chain organifier showed better efficiency in ion-exchanged fraction in the case of PTMG based organifiers. From WAXD and TEM analysis, it was confirmed that PTMG based organoclays formed partially exfoliated or fully exfoliated silicate layer structures. PDLA/clay nanocomposites were prepared by in-situ ring-opening polymerization of D-lactide with PTMG based organoclays as macro-initiators in the presence of equimolar Sn(Oct)₂/PPh₃ complex catalysts. The molecular weight of PDLA/clay nanocomposite decreased as increasing the feeding amount of organoclay because organoclay had hydroxyl terminal groups which can initiate the ring-opening polymerization of D-lactide. From TGA analysis, thermal stabilities of PDLA/clay nanocomposites improved with increasing organoclay content. From WAXD and TEM analysis, organoclay which was prepared by high molecular weight of PTMG based organifier was effective on the exfoliation of silicate layers in the in-situ polymerized PDLA/clay nanocomposite.     

Preparation of highly exfoliated epoxy/clay nanocomposites by "slurry compounding": process and mechanisms

Epoxy/clay nanocomposites with a high degree of exfoliation were achieved using a so-called "slurry-compounding" process with which the dispersed state of clay in water can be successfully transferred to an epoxy matrix. In this process sodium montmorillonite was first exfoliated and suspended in water. This suspension was further treated with acetone to form a clay-acetone slurry followed by chemical modification using silane. The modified slurry was then mixed extensively with epoxy to form epoxy/nanoclay composites. It has been shown that the morphologies of clay before and after curing are quite similar and the exfoliation process is termed "slurry compounding". Furthermore, the amount of organic modifier used is only 5 wt % of clay, in contrast to conventional organoclays which normally contain at least 25-45 wt % of organic surfactant. The resulting epoxy/nanoclay composites exhibit a high degree of clay exfoliation and a better thermal mechanical property.     

Influence of gamma irradiation on high density polyethylene/ethylene‐vinyl acetate/clay nanocomposites

The study of high density polyethylene (HDPE)/ethylene‐vinyl acetate (EVA)/and organically‐modified montmorillonite (OMT) nanocomposites prepared by melt intercalation followed by exposure to gamma‐rays have been carried out. The morphology and properties of the nanocomposites were studied using X‐ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and cone calorimetry. The purpose of the study focuses on the influence of gamma irradiation on the morphology, thermal stability and flammability properties of the nanocomposites. XRD studies and TEM images verified that the ordered intercalated nanomorphology of the nanocomposites was not disturbed by gamma irradiation. TGA data showed that the nano‐dispersion of clay throughout the polymer inhibited the irradiation degradation of HDPE/EVA blend, which led to the nanocomposites exhibiting superior irradiation‐resistant properties than that of the pure blend. Cone calorimetry results indicated that the improvement in heat release rate (HRR) for irradiated HDPE/EVA blend was suppressed efficiently when clay was present. Increasing clay loading from 2 to 10% was beneficial by improving the flammability properties of the nanocomposites, but promoted a rapid increase in the sub‐peak HRR at high irradiation dose level. Copyright © 2004 John Wiley & Sons, Ltd.     

Effect of the type of alkylammonium ion clay modifier on the structure and thermal/mechanical properties of glassy and rubbery epoxy-clay nanocomposites

Glassy and rubbery epoxy-clay nanocomposites were synthesized by using various montmorillonite organoclays in order to investigate and compare the effect of the type of alkylammonium ion clay modifier on the structure and properties of the nanocomposites. The organoclays studied were the Nanomer I.28E and I.30E and the Cloisite C10A, C15A and C20A. The functionality (acidity), size and shape of backbone chain, hydrophobicity and polarity were the varying parameters of the organic modifiers that were correlated to the ability of the organoclays to form highly intercalated or exfoliated nanocomposites and to the changes observed in the mechanical (tensile measurements), thermo-mechanical (DMA) and thermal (TGA) properties of the epoxy nanocomposites. The primary alkylammonium ion modifiers with reactive/acidic hydrogen atoms, compared to the quaternary octadecyl, dihydrogenated tallow and benzyl-substituted hydrogenated tallow ammonium ions, were the most effective for the formation of exfoliated clay glassy and rubbery epoxy nanocomposites which exhibited improved properties compared to the pristine epoxy polymers.     

Degradation of poly(ethylene terephthalate)/clay nanocomposites during melt extrusion: Effect of clay catalysis and chain extension

Organoclays with various contents of hydroxyl groups and absorbed ammonium were prepared and compounded with poly(ethylene terephthalate) (PET), forming PET/clay nanocomposites via melt extrusion. Dilute solution viscosity techniques were used to evaluate the level of molecular weight of PET/clay nanocomposites. Actually, a significant reduction in PET molecular weight was observed. The level of degradation depended on both the clay structure and surfactant chemistry in organoclays. The composites, based on clay with larger amount of hydroxyl groups on the edge of clay platelets, experienced much more degradation, because the hydroxyl groups acted as Brønsted acidic sites to accelerate polymer degradation. Furthermore, organoclays with different amounts of absorbed ammonium led to different extents of polymer degradation, depending upon the acidic sites produced by the Hofmann elimination reaction of ammonium. In addition, the composite with better clay dispersion state, which was considered as an increasing amount of clay surface and ammonium exposed to the PET matrix, experienced polymer degradation more seriously. To compensate for polymer degradation during melt extrusion, pyromellitic dianhydride (PMDA) was used as chain extender to increase the intrinsic viscosity of polymer matrix; more importantly, the addition of PMDA had little influence on the clay exfoliation state in PET/clay nanocomposites.     

Thermal stability and flammability properties of heterophasic PP-EP/EVA/organoclay nanocomposites

A study on the thermal behavior and flammability properties of the heterophasic polypropylene-(ethylene-propylene) copolymer (PP-EP)/poly(ethylene vinyl acetate) (EVA)/montmorillonite nanocomposite is presented. Nanoclay nanocomposites were prepared using a twin screw extruder. Both the fluidity of the EVA phase and compatibility conditions between PP-EP and EVA were used in order to obtain the required nanocomposites. Therefore, no additional compatibilizer was required to achieve the clay dispersion. Products exhibited the partially exfoliated/intercalated nanoclay dispersion. Thermogravimetric analyses indicated that nanoclays retard thermal degradation depending on nanoclay concentration. The retarding process was assigned to the exfoliation and dispersion of the silicate layers which impeded heat diffusion to the macromolecules. Thermal studies, under non-isothermal crystallization, indicated the lack of influence of nanoclay on the thermal behavior. Flammability characteristics were however affected by the nanoclay layers which overall generated flame retardation both in the EVA host and in the complex nanocomposites.     

Photopolymerization behavior in nanocomposites formed with thiol–acrylate and polymerizable organoclays

Because of the inherent characteristics of the thiol–ene step growth mechanism in preparation of thiol–ene photopolymer clay nanocomposites, the ratio between thiol and ene functional groups at and near the organoclay surfaces may have a significant effect on the polymerization behavior. This study investigates the influence of monomer composition and the type of polymerizable organoclay on thiol–acrylate photopolymerization behavior in preparation of photocurable clay nanocomposite systems. To this end, two types of polymerizable organoclays with acrylate or thiol functional group on the clay surfaces were compared in monomer compositions with different polarity and functionality. Real‐time infrared spectroscopy was used to characterize polymerization behavior in conjunction with photo‐DSC. The degree of clay exfoliation was evaluated using small angle X‐ray scattering and correlated with photopolymerization behavior. Higher chemical compatibility of components induced enhanced clay exfoliation resulting in increase in photopolymerization rate. By affecting the stoichiometric ratio of functional groups in the clay gallery, thiolated organoclays enhance thiol–ene reaction, whereas acrylated organoclays encourage acrylate homopolymerization. In addition, inducing more propagating thiyl radicals on the organoclay surfaces by increasing functionality of thiol monomer also facilitates thiol–ene copolymerization, whereas the increase of acrylate functionality reduces final thiol conversion. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Glycerol: a promising agent for nanodispersion and compatibility of EVA/organomodified montmorillonite nanocomposites

Ethylene‐vinyl acetate (EVA) nanocomposites were extruded with two types of organomodified montmorillonite (OMMT) and 1 wt% glycerol. The characterization of the nanocomposites was performed by transmission electron microscopy, X‐ray diffraction, differential scanning calorimetry, and dynamic mechanical analysis. The experimental results revealed that glycerol improved the Cloisite 30B clay exfoliation and promoted a rise in aspect ratio of the Cloisite 20A clay. In the rubbery region, the EVA/G showed a higher storage modulus than the EVA, as a result of the network of hydrogen bonds. The entanglements of long chains were more effective in the restrictions of large‐scale movements than the chemical interactions. The addition of glycerol promoted greater reinforcement and an increase in the tenacity of the nanocomposites in the glassy region. The use of glycerol for the production of EVA/OMMT nanocomposites was found to be promising. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of the Organoclay Structure on Morphology and Rheological Response of PBT Nanocomposites

In this paper the effect of different organoclays on the structure and the rheological properties of poly(butyleneterephtalate)–clay nanocomposites produced by melt compounding was investigated. The study was carried out using as nanometric fillers four commercial montmorillonites, treated with different organic modifiers and having similar interlayer spacing and organo-modifier concentration. Each organoclay was melt compounded with PBT (at 3%, 6% and 9% by weight of clay) using a twin screw extruder. Using the same processing conditions, hybrid samples containing the unmodified silicate were also prepared for comparison purposes. All the obtained nanocomposite samples were submitted to physico-chemical (XRD, TEM and FT-IR), and rheological measurements in order to evidence the role of polymer-clay affinity on the morphology and on the viscoelastic response of the materials. The results have pointed out that, with the used processing conditions, all nanocomposites exhibit a mixed intercalated/exfoliated structure; nevertheless, the clay dispersion homogeneity and the exfoliation level reached in the samples are higher for Nanofil 919 and Dellite 43B fillers, the organic modifiers of which may favorably interact with PBT matrix.     

Effect of Organoclay Mixture on the Rheological Properties of ABS-Clay Nanocomposites

Summary: In this work, poly(acrylonitrile-butadiene-styrene) (ABS) and different organically modified montmorillonite clay nanocomposites were prepared by melt intercalation in a co-rotating twin screw extruder. The influence of the screw torque during processing and of the mixture of the modified organoclays in the intercalation/exfoliation of the clay in the polymeric matrix was evaluated through low angle X-ray diffraction range and capillary and parallel plate-plate rheometry.     

混合条件对环氧有机土纳米复合材料插层剥离行为及性能的影响

采用X 射线衍射仪、透射电镜 (TEM )研究了混合条件 ,即混合温度和时间 ,对环氧 /16 烷基胺有机蒙脱土体系在固化前的混合物以及加入固化剂、促进剂固化后有机土的插层与剥离行为的影响 .同时采用拉伸试验机、冲击试验机和热机械分析仪测定了插层与剥离型纳米复合材料的物理力学性能 .从X 射线衍射看出 ,有机土很容易在混合过程被环氧所插层 .混合物经固化后可以形成插层型或剥离型纳米复合材料 .存在一个混合温度 时间 插层剥离转变的 3 T图 .只有在一定的混合条件的区域内才能形成剥离型纳米复合材料 .剥离型比插层型纳米复合材料具有较高的力学性能     

Thermal properties and microhardness of HDPE/clay nanocomposites compatibilized by different functionalized polyethylenes

The calorimetric characteristics, the flammability, the thermal stability and the microhardness of polyethylene high density/clay nanocomposites (HDPE/clay) have been studied by differential scanning calorimetry, thermogravimetry, determination of limiting oxygen index and microhardness tests. The nanocomposites have been compatibilized by ethylene–acrylic acid copolymer (EAA), acrylic acid grafted HDPE (HDAA) and maleic anhydride grafted HDPE (HDMA). The clay was montmorillonite Cloisite 15A. The influence of the presence and the type of the compatibilizers on the properties of the nanocomposites has been evaluated. The results have shown that the thermal stability, the reduction of the flammability and the microhardness of HDPE/clay nanocomposites, compatibilized by HDAA and HDMA are higher than those for nanocomposite compatibilized by EAA. Moreover, the presence and the type of compatibilizer have negligible effect on the characteristics of the HDPE phase transitions. These results have been interpreted by the better clay dispersion and higher level of clay exfoliation in the presence of compatibilizers HDAA and HDMA, than those in the presence of EAA compatibilizer.     

外力辅助分散作用下环氧树脂粘土纳米复合材料中粘土的微观结构与解离机理研究

采用不同分散方法(机械搅拌、高速均质搅拌和球磨分散)制备环氧树脂粘土纳米复合材料,研究了分散方法对不同有机粘土解离结构和纳米复合材料力学性能的影响,并在此基础上探讨了粘土的解离机理.结果表明,普通机械搅拌只能使小粒径粘土或大粒径粘土团聚体的外部片层解离;施加一定的外力(如高速均质搅拌)促进粘土团聚体分散,有利于粘土片层的解离;利用剪切摩擦作用较强的球磨法分散粘土,不同处理剂改性粘土的内外片层都可以充分解离,而有机改性剂中酸性质子的催化作用对粘土片层解离的影响不大,只要粒径足够小,片层解离的驱动力(基体弹性力、反应性等)能够克服其所受阻力(片层引力、层外基体粘性阻力、层内粘性引力等),粘土内外各片层将会同时向外迁移而解离.纳米复合材料的力学性能大大改善,冲击强度和弯曲强度分别提高近50%和8%;     

Effect of the urethane group on treated clay surfaces for high-performance poly(butylene succinate)/montmorillonite nanocomposites

We successfully modified organic clays containing the urethane group by introducing a covalent bond between the silanol group on the clay side and the hydroxyl group of organic modifier in the silicate layer using 1,6-diisocyanatohexane (HDI), namely surface-treated montmorillonite (30BM), to increase both basal spacing and the favorable interaction between clay and polymer. The effect of the surface urethane modification of clay on poly (butylene succinate) (PBS)/30BM nanocomposites was studied. The results of transmission electron microscopy micrographs at a 10-nm resolution and X-ray diffraction measurements allowed us to examine the degree of the high exfoliation and the effect of surface urethane modification on clay dispersibility. As results of high exfoliation, PBS/30BM nanocomposites not only exhibited the high thermal properties, but also showed a remarkable increase in physical properties (e.g., tensile strength, Young's modulus, elongation at break) due to enhanced affinity between the clay and PBS matrix. Over all, the results suggest that wide gallery spacing and the predominant affinity between PBS and clay must be considered simultaneously to increase the degree of exfoliation and physical properties as key factors.     

Tensile,fatigue and thermomechanical properties of poly(ethylene-co-vinyl acetate) nanocomposites incorporating low and high loadings of pre-swelled organically modified montmorillonite

The production of exfoliated polymer/clay based nanocomposites is crucial to obtain an actual benefit of nanoscale reinforcement in the polymer matrix. In this project, the production of exfoliated polymer/clay nanocomposite was aimed through the use of poly(ethylene-co-vinyl acetate) (EVA) copolymer as matrix and organically modified montmorillonite (O-MMT) as nanofiller. The research work involved the use of pre-swelled technique through magnetic stirring and ultra-sonication to obtain more readily exfoliated and dispersed O-MMT nanofiller for EVA nanocomposite production. The aims were to allow the improvement in O-MMT exfoliation and dispersion when the nanofiller was incorporated in high loading (greater than 3 wt%) into the copolymer. The original and pre-swelled O-MMTs were employed to produce the EVA/O-MMT nanocomposites with 1, 3, 5, 7 and 9 wt% nanofiller by melt compounding technique. The results of TEM, tensile and fatigue tests, XRD, FTIR and DMA proved that the pre-swelling technique applied on the O-MMT before melt compounding with the EVA copolymer can bring positive impact to the performance of the nanocomposite. As opposed to the original O-MMT, the pre-swelled O-MMT has the ability to improve the tensile toughness, cyclic stability and storage modulus of the EVA copolymer even when high O-MMT loading (7 wt %) was employed. Improvement in the EVA - O-MMT interactions in the nanocomposite system was postulated to be the main reason for such observations.     

Polymer Nanocomposites from Organoclays: Structure and Properties

Summary: Polymer nanocomposites formed from organically modified montmorillonite offer the promise of greatly improved properties over those of the matrix polymer, provided the organoclay can be dispersed, or exfoliated, into the polymer matrix to generate high aspect ratio particles. The exfoliation of organoclays in two series of ethylene-based polymers, ethylene-vinyl acetate copolymers and sodium ionomers of ethylene-methyacrylic acid copolymers, is described along with the properties of these nanocomposites.     

Study on intercalation and exfoliation behavior of organoclays in epoxy resin

Intercalation and exfoliation behavior of organoclays in epoxy resin has been studied through XRD and DSC. It was found that the organoclays were easily intercalated by epoxy oligomer to form a stable epoxy/clay intercalated hybrid. Under appropriate conditions the clays were able to be further exfoliated as the epoxy resin was cured; thus, a nanocomposite was obtained. It was also found that the exfoliating ability of the organoclays was basically determined by the nature of the clays and the curing agent used. The exfoliation mechanism is discussed in this paper. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 115–120, 2001     

Effect of process variables on mechanical properties of polyurethane/clay nanocomposites

This paper addresses the effects of operating variables on mechanical properties of polyurethane/clay nanocomposites including tensile strength, abrasion resistance, and hardness. The variables were prepolymer type, clay cation, clay content, and prepolymer–clay mixing time. The experiments were carried out based on the design of experiments using Taguchi methods. The nanocomposites were synthesized via in situ polymerization starting from two different types of prepolymers (polyether‐ and polyester‐types of polyol reacted with toluene diisocyanate), and methylene‐bis‐ortho‐chloroanilline (MOCA) as a chain extender/hardener. Montmorillonite with three types of cation (Na⁺, alkyl ammonium ion, and MOCA) were examined. Among the parameters studied, prepolymer type and clay cation have the most significant effects on mechanical properties. Polyester nanocomposites showed larger improvements in mechanical properties compared to polyether materials due to higher shear forces exerted by polymer matrix on clay aggregates during polymer–clay mixing. The original MMT with Na⁺ cation results in weak improvements in mechanical properties compared to organoclays. It is observed that the stress and elongation at break, and abrasion resistance of the nanocomposite samples can be optimized with 1.5% of clay loading. The morphology and chemical structure of the optimum sample were examined by X‐ray diffraction and FT‐IR spectroscopy, respectively. Copyright © 2009 John Wiley & Sons, Ltd.