Nanostructure and dynamic mechanical properties of silane-functionalized montmorillonite/epoxy nanocomposites

In this work sodium montmorillonite (Na-MMT) was functionalized with N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane and the corresponding silylated clay was used to modify epoxy matrix cured with triethylenetetramine. The grafting/intercalation of the aminosilane inside the clay galleries were followed by infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and ²⁹Si cross-polarization magic-angle-spinning nuclear magnetic-resonance (CP/MAS NMR) spectroscopy. Epoxy-based nanocomposites were prepared with different amounts of silylated clay or commercial organoclay, Cloisite 30B, whose intercalating agent consists of a methyl, tallow, bis-2-hydroxyethyl quaternary ammonium salt. The degree of intercalation/exfoliation was estimated by X-ray diffraction experiments and confirmed by small angle X-ray scattering. Nanocomposites prepared with silylated clay displayed no peak in both XRD and SAXS curves whereas those prepared with Cloisite 30B exhibited a clear interference peak corresponding to an interlayer spacing d₀₀₁ of 4.1 nm. The former also presented a better dispersion, with a high proportion of tactoids smaller than 2 nm, as estimated by SAXS. From the results of dynamic mechanical analysis it was observed that most of the nanocomposites display higher storage modulus mainly at temperatures above the glass transition temperature. The glass transition temperature is similar or higher than the neat epoxy network for nanocomposites containing 1 wt.% of silylated clay or higher.     

环氧树脂/蒙脱土纳米复合材料的制备及性能

实验采用长链烷基胺对原始蒙脱土进行有机化处理，再利用环氧树脂对有机蒙脱土插层，制得环氧树脂，蒙脱土纳米复合材料。实验表明，改性环氧树脂的冲击强度有所提高。     

环氧树脂/粘土纳米复合材料的研究

采用原位插层聚合法制备环氧树脂／粘土纳米复合材料，用X衍射（XRD），红外光谱（FTIR），差示扫描量热法（DSC），扫描电镜（SEM）对有机化蒙脱土（OMMT）和环氧树脂／粘土纳米复合材料进行测试与表征，结果表明，与纯环氧树脂固化物相比，环氧树脂／粘土纳米复合材料的力学，热学性能有较大的改善和提高。     

Investigation of polymer and nanoclay orientation distribution in nylon 6/montmorillonite nanocomposite

A method to determine the orientation distribution function of montmorillonite clay in nylon 6 nanocomposite films by a combination of infrared (FTIR) trichroic analysis and transmission electron microscopy (TEM) image analysis is described. The structural absorbance of the nanoclay Si-O vibrations was obtained by the sample tilting method described by Schmidt [Schmidt PG. J Polym Sci: Part A 1963;1:1271-1292]. A nonlinear least squares regression was performed to extract the absorbance of individual peaks. The montmorillonite clay orientation in spun cast nylon 6 films can be described by a Gaussian function having a standard deviation of 15° i.e. 95% of the clay platelets are tilted at an angle of within ±30° of the plane of the film. The transition dipole moment angles of the 1018 and 1046 cm⁻¹ clay vibrations are determined to be 18 and 16° relative to the clay surface, respectively. The orientation of nylon 6 in the nanocomposite was also investigated based on the NH stretching mode. The NH bonds are found to be less preferentially oriented along the plane of the film surface compared to pure nylon 6 film.     

Facile hydroxylation of halloysite nanotubes for epoxy nanocomposite applications

Polymer nanocomposites have been extensively investigated over the past two decades, resulting in a wide range of applications because of their excellent performance. Halloysite, a type of naturally occurring aluminosilicate, has attracted increasing interest in polymer nanocomposite applications, especially for the enhancement of mechanical properties owing to its tubular structure. Herein, we report a facile approach to achieve a high level of dispersion of halloysite nanotubes (HNTs) in epoxy by treating HNTs with a low concentration of sodium hydroxide (NaOH). The NaOH treatment resulted in the formation of hydroxyl groups on the surface of HNTs, leading to a much higher level of dispersion of HNTs in water, organic polar solvents, and epoxy matrix. The higher density of external silanol groups (Si–OH) of hydroxylated HNTs (h-HNTs) was confirmed by X-ray photoelectron spectroscopy (XPS) characterization. Such a higher level of dispersion and stronger interface led to simultaneous enhancement in both the stiffness and the toughness of epoxy/h-HNT nanocomposites. Systematic characterizations were performed to investigate the related stiffening and toughening mechanism. The implication of the present findings is discussed.     

Mild processing and characterization of silica epoxy hybrid nanocomposite

Previous research has shown that the inclusion of the spherical silica (SiO₂) nanoparticles into epoxy resin can achieve simultaneous improvement of fracture toughness and modulus. However, the glass transition temperature of the nanocomposite was significantly decreased when loading the nanosilica was higher than 5 wt.%. This perhaps was caused by utilization of the ultrasonication probe in the processing of these materials. In this paper, milder processing procedures were applied to make spherical silica epoxy nanocomposites while investigating if the homogeneous dispersion and morphology of the individual silica nanoparticle dispersed in the epoxy matrix could still be achieved. The results show that even at high loading of the silica nanoparticle, such as 30 wt.% silica, the perfect morphology of the nanocomposite could still be achieved with these milder processing conditions which indicates that ultrasonication is not needed. With the use of milder processing conditions, the glass transition temperature of the nanocomposite of 5 wt.% silica loading did not change, and the drop in the T_g was minimal for silica loading up to 15%, but some effects of self-polymerization of the epoxy were noted on T_g up to 30 wt.% loading of silica. Thermal analysis and flammability testing of the resulting materials suggest that nanosilica has only an inert filler effect (dilution of fuel) on flammability reduction and char yield increase, not a synergistic decrease in heat release as is often observed for clays and carbon nanotubes/nanofibers. So the mild and easy processing procedure only achieved uniform nanoscale morphology with excellent dispersion in the final nanocomposite, but also the effect on the change in the T_g can be minimized as nanosilica loading was increased.     

纳米有机蒙脱石改性环氧树脂的研究

利用长链的有机阳离子改性天然蒙脱石，制备出有机蒙脱石，用于改性环氧树脂。在有机蒙脱石低含量范围，环氧树脂有机蒙脱石复合物的触变性得到了显著改善；同时将固化产物的热降解温度从380．4℃提高至397．4℃。     

A new approach to polymer/montmorillonite nanocomposites

A novel method for preparation of exfoliated/intercalated nanocomposites is reported based on two steps, i.e. preparation of treated-montmorillonite (MMT) solution and solution blending with polymers. After in situ polymerization of dimethyldichlorosilane between layers and separation of most polydimethylsiloxane (PDMS), the treated-MMT solution shows good storage stability. Although elemental analyzer shows no residue PDMS, NMR proves residue PDMS still exists in the solution. The residue PDMS is believed to graft onto the MMT layer surface via condensation of hydroxyl groups of PDMS and those that existed on MMT surface. Lower relaxation time of end-capped CH₃ of alkyl ammonium grafted onto layer surface via ion exchanging in the solution shows that the layer spacing was increased significantly or even exfoliated. When the solution was blended with some polar polymers, exfoliated nanocomposites were found. When it was blended with some nonpolar polymers, however, intercalated nanocomposites were obtained. The reason was explained in the light of compatibility between polymer matrix and MMT as well as alkyl ammonium and PDMS grafted on the layer surface. For intercalated nanocomposites, different layer spacing corresponds to different chain flexibility and the presence of multi-peaks is caused by the processing of these blends.     

Preparation of epoxy–clay nanocomposite and investigation on its anti-corrosive behavior in epoxy coating

An epoxy–clay nanocomposite was synthesized using a quaternary ammonium-modified montmorillonite clay and diglycidyl ether of bisphenol A (DGEBA) type epoxy resin, in order to produce anti-corrosive epoxy coating. Anti-corrosive properties of the nanocomposite were investigated using salt spray and electrochemical impedance spectroscopy (EIS) methods. The results showed an improvement in the barrier and anti-corrosive characteristics of epoxy-based nanocomposite coating and a decrease in water uptake in comparison with pure epoxy coating. Wide-angle X-ray diffraction (WAXD) patterns and transmission electron microscopy (TEM) analysis showed that the interlayer spacing of clays increased after addition of epoxy resin along with applying shear force and ultrasound sonicator. The best performance of this coating was achieved at 3 and 5 wt.% clay concentration.     

Synthesis and rheological properties of oligoimide/montmorillonite nanocomposites

We report a facile strategy for preparing polyimides (PI)/montmorillonite (MMT) nanocomposites at moderate temperatures that avoids thermal degradation of organically-modified MMT (organo-MMT) that is commonly observed during conventional melt-blending of organo-MMT with commercial high molecular weight PI at elevated temperatures. Novel polyimides of low molecular weight (oligoimides) based on 1,3-bis(3′,4,-dicarboxyphenoxy)benzene and 4,4′ bis(4″-aminophenoxy)diphenylsulfone were synthesized and subsequently melt-blended at temperatures ranging from 150 to 250 °C with special organically-modified montmorillonite clay nanoparticles to form new polyimide/organo-MMT nanocomposites with special combination of physical and chemical properties for diverse applications such as microelectronic components where chemical inertness, high temperature stability, low dielectric constant, mechanical toughness and processability are primary requirements. It was found that application of a strong shearing flow near the glass transition temperature of the oligoimide to the oligoimide/organo-MMT nanocomposite melt blend containing 6±2 vol% of the organo-MMT resulted in three orders of magnitude increase in the viscosity. Partial exfoliation of the organo-MMT together with constrained deformation of the polymer between the rigid nanoparticle layers (as evidenced by formation of the network structure or fractal gel) are thought to be responsible for this observed viscosity behavior. The viscosity behavior is typical for model xylene/MMT system where the MMT particles were dispersed in xylene solvent homogeneously via ultrasonic mixing. This study suggests that the rheological methods used here may provide a valuable analytical tool to accelerate efforts to develop useful polyimide nanocomposites from synthetic oligoimides containing ceramic nanoparticles having different shapes and sizes. Further, because of their facile synthesis and desirable characteristics these polyimide/MMT clay nanocomposites are expected to be excellent model systems for exploring feasibility of new routes for driving organic polymers to self-assemble into useful nanocomposites.     

硅烷偶联剂对蒙脱土/NR纳米复合材料气体阻隔性能的影响

试验研究硅烷偶联剂对蒙脱土（MMT）／NR纳米复合材料性能的影响。结果表明，在MMT／NR复合材料中加入硅烷偶联剂，可提高复合材料的物理性能、耐热空气老化性能、气体阻隔性能和热稳定性。硅烷偶联剂KH-560的改性效果最好，其最佳用量为3份。     

Intercalation and exfoliation relationships in melt-processed poly(styrene-co-acrylonitrile)/montmorillonite nanocomposites

The effects of surfactant structure on the morphology and mechanical properties of melt processed mixtures of poly(styrene-co-acrylonitrile) (SAN) with montmorillonite (MMT) organoclays were examined. The composite which exhibited the greatest change in gallery height, the highest modulus, and greatest aspect ratio (∼50) was produced from an organoclay with the lowest molecular weight surfactant, dimethyl hydrogenated tallow ammonium. For ammonium ion surfactants with ∼18 carbon hydrophobic tail(s), stack swelling, as measured by wide angle X-ray scattering (WAXS), was more strongly related to the reduced surfactant molecular weight than polarity or aromaticity of the head group substituents. A surfactant with a shorter tail length (∼12 vs. 18 carbon tail length) resulted in unswollen stacks in the composite.The swelling of the organoclay galleries seems to be explained by a balance of some favorable interactions of SAN with the montmorillonite platelet surface, versus repulsive mixing of aliphatic surfactant substituents with polar SAN. The repulsive nature of the latter increases as molecular weight of the head group substituents increases. A third factor is the platelet-platelet attraction that seems to explain the lack of swelling in the case of the shorter tail surfactant.Mechanical properties are also reported; and the composite moduli were found to compare to theoretical predictions using the Halpin-Tsai theory based on aspect ratios determined by transmission electron microscopy (TEM). The experimental aspect ratios do not seem to correlate with the WAXS gallery shifts. This and other evidence suggest that exfoliation in melt-processed SAN/MMT composites is not explained by intercalation behavior.     

Flame retardant epoxy complex produced by addition of montmorillonite and carbon nanotube

Flame retardant additives of montmorillonite (MMT) and multi-walled carbon nanotube (MWCNT) were embedded in epoxy resin to improve the resin's resistance to oxidation. The MWCNTs reduced the degradation rate of the epoxy complex and increased the char yield, and also increased the limiting oxygen index in a first order relationship with char yield. MMT acted as an energy storage medium to hinder thermal transfer within the epoxy complex. The thermal activation energy increased upon addition of MMT/MWCNT. Addition of MMT and MWCNT significantly improved the flame retardant and anti-oxidation properties of the epoxy complex.     

Preparation of PANI/epoxy/Zn nanocomposite using Zn nanoparticles and epoxy resin as additives and investigation of its corrosion protection behavior on iron

Conducting polyaniline, zinc and epoxy resin solely have anticorrosive properties by different mechanisms on metallic substrates. In this work the triple hybrid of PANI/epoxy/Zn nanocomposite was prepared as a thin layer coating (70 ± 5 μm) on iron coupons and its anticorrosion performance was investigated in HCl (0.1 M) as corrosive solution. Epoxy resin and zinc nanoparticles were applied as additives in the PANI matrix to improve the mechanical properties of PANI coating and investigate their synergetic effects on the anticorrosion performance of PANI coating. At first PANI/Zn nanocomposite coatings with different Zn contents were prepared and the zinc content optimized so that the coating achieve the best anticorrosion performance. Accordingly the iron coupons coated by PANI/Zn coating having 4 wt% Zn content showed more noble open circuit potential and lower corrosion current values. Then epoxy resin was applied as additive to the optimized formulation of PANI/Zn coating in different weight percents (0–20 wt%) and the anticorrosion performance of the related PANI/epoxy/Zn triple hybrid nanocomposite coatings was evaluated. Results showed that the addition of epoxy resin causes to the decreasing of corrosion current of iron samples coated by PANI/epoxy/Zn nanocomposite. An optimum range of 3–7 wt% was obtained for the epoxy content in the composition of PANI/epoxy/Zn nanocomposite in which the coating exhibits the best anticorrosion performance. Iron metal coupon was elementally analyzed and the PANI/Zn and PANI/epoxy/Zn nanocomposites were characterized using Fourier Transform Infrared spectroscopy, X-ray diffraction patterns and Scanning Electron Microscopy techniques.     

Enhanced thermal properties of PS nanocomposites formed from montmorillonite treated with a surfactant/cyclodextrin inclusion complex

We have prepared polystyrene/clay nanocomposites using an emulsion polymerization technique. The nanocomposites were exfoliated at 3 wt% content of pristine clay relative to the amount of polystyrene (PS). We employed two surfactants for the montmorillonite: cetylpyridinium chloride (CPC) and the CPC/α-CD inclusion complex. Prior to polymerization, each surfactant intercalates into the layers of the pristine clay dispersed in water. The inclusion complex was characterized by X-ray diffraction, ¹³C CP/MAS NMR spectra, and ¹H NMR spectroscopy, and TGA. X-ray powder patterns of the CPC/α-CD complex indicate that the α-CDs units form channels. The ¹³C CP/MAS NMR spectrum of the complex suggests that a CPC chain is included in the channel formed by the α-CDs. The ¹H NMR spectra of the complexes indicate that the stoichiometry of the complexes is 1:2 (i.e. one CPC molecule and two α-CD units). The TGA reveals that the inclusion complex has higher thermal stability relative to the virgin CPC. We employed both X-ray diffraction (XRD) and transmission electron microscopy (TEM) to characterize the structures of the nanocomposites. The value of T_g of the PS component in the nanocomposite is 6 °C higher than that of the virgin PS and its thermal decomposition temperature is 33 °C higher. The CPC/α-CD-treated clay is more effective than is virgin CPC-treated clay at enhancing the thermal stability of polystyrene.     

Interactions of BTESPT silane and maleic anhydride grafted polypropylene with epoxy and application to improve adhesive durability between epoxy and aluminium sheet

For improvement of adhesive strength and durability of adhesion between epoxy and aluminium sheet bis-(triethoxysilylpropyl)tetrasulfide (BTESPT) silane and maleic anhydride grafted polypropylene (PP-g-MAH) are chosen for surface pretreatment of the aluminium sheet respectively. Fourier transform infrared (FTIR) spectroscopy was used for characterization of the structure and the interactions in the systems. It is shown that BTESPT silane and the anhydride on PP-g-MAH take part in the curing reactions of the epoxy/polyamide system. The adhesive shear strength of the samples, prepared under different curing temperatures, and after immersion in boiling water and 3.5% NaCl water solution respectively, was tested. The features of the shear fractured surfaces were examined by scanning electron microscope (SEM). For the aluminium sheet pretreated by BTESPT silane, the maximum adhesive shear strength is 22.2 MPa, which is higher than that of 17.5 MPa for aluminium sheet without pretreatment by the silane. After immersion in boiling water for 80 h and in NaCl water solution at 50 °C for 180 h the adhesive shear strengths are 13.39 MPa and 18.4 MPa respectively, which are higher than these (below 6 MPa) for aluminium sheet without pretreatment by the silane. As for the aluminium sheet pretreated by PP-g-MAH, the maximum adhesive shear strength is 13.17 MPa. After immersion in boiling water for 80 h and in NaCl water solution at 50 °C for 180 h the adhesive shear strengths decline to 10.67 MPa and 8.1 MPa respectively.     

Preparation of ABS/montmorillonite nanocomposite using a solvent/non-solvent method

Polymer layered silicate nanocomposites have been studied for many years and due to their distinguished properties and applications, it is still the subject of many research programs. There are different methods of preparation, with the melt intercalation method as the mostly used method. Due to the thermal destructive effects of melt mixing on the polymer chains there are currently efforts to develop some new methods of preparation. A solvent/non-solvent method has been developed in this study for the preparation of ABS/clay nanocomposites. ABS nanocomposite is precipitated after addition of ethanol (non-solvent) containing organic modified montmorillonite from a THF solution while it is stirring. A kind of mixing system known as homogenizer has been used in this work. The final product has been determined having an intercalated structure with a uniform interlayer spacing of the silicate layers. The ABS nanocomposites prepared in this work has been studied by X-ray diffraction, FTIR, transmission electron microscope and thermogravimetric analysis. The effect of using homogenizer on the characteristics of the nanocomposites also has been investigated and discussed in several parts of the present work.     

Nanocomposites based on a combination of epoxy resin, hyperbranched epoxy and a layered silicate

Epoxy/clay nanocomposites have been prepared using an diglycidyl ether of bisphenol A (DGEBA) epoxy and its blend with an epoxy functionalized hyperbranched polymer (HBP). The formation of nanocomposites was confirmed by a wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) analysis. The mechanical and dynamic mechanical properties of the nanocomposites were evaluated and compared with the corresponding matrix. The improvement in impact properties in blend and nanocomposites was explained in terms of fracture surface analysis by scanning electron microscopy (SEM).     

Synthesis of allyl ether and benzyl methacrylate functionalized silane monomers for application in acrylate/montmorillonite nanocomposite emulsion

Abstract

Allyl trimethylsiloxybutyl ether (ATE) and 3-(trimethylsiloxy) benzylmethacrylate (TBM), tow novel silane involving monomers were successfully synthesized. Then, by in situ intercalative emulsion polymerization of styrene (St), butyl acrylate (BA), ATE and TBM, poly (silane-co-styrene-co-butylacrylate)/montmorillonite, P (Si-co-St-co-BA)/OMMT nanocomposite emulsions were prepared. The structures of monomers were clarified by the FT-IR, ¹H-NMR, and ¹³?C-NMR spectroscopic techniques and nanocomposites by FT-IR. The results indicated that addition of OMMT improved the thermal and morphological properties of emulsions and among the samples tested, the modified nanocomposites which were prepared by intercalating 1?wt% OMMT showed the most desirable effect. It was also demonstrated by TEM that OMMT addition causes some clusters or agglomerated particles into the polymer matrix and the most OMMT layers are dispersed homogeneously.     

Properties of novel epoxy/clay nanocomposites prepared with a reactive phosphorus-containing organoclay

In this study, a reactive phosphorus-containing organoclay (RPC) was successfully prepared through the cationic exchange reaction of sodium montomorillonite clay with hexyltriphenylphosphonium bromide and surface modification by grafting it with glycidyloxypropyltrimethoxy silane. It is characterized using X-ray diffraction (XRD) and Fourier transform IR (FTIR) measurements. A series of novel epoxy/clay nanocomposites (ERPC) was then prepared with a selected epoxy resin and varying amounts of RPC. The results of XRD and TEM of the nanocomposites showed that the RPC particles were well dispersed in the epoxy matrix with a highly exfoliated structure due to the presence of the reactive epoxide group of RPC. The as-prepared epoxy/RPC nanocomposites (ERPC) were thermally stable up to 388 °C. Thermal stability was increased by increasing the RPC content as indicated by the corresponding activation energies (E_a) and the integral procedural decomposition temperatures (IPDT). Furthermore, the storage modulus in the glass state of the nanocomposites was dramatically increased with the increase in RPC content. In addition, the large increment of limiting oxygen index (LOI) which was 11 units higher than that of the neat epoxy indicates that an extraordinary enhancement of flame retardancy was obtained from the nanocomposite containing 5 wt% of RPC.