Reinforcement of polyurethane/epoxy interpenetrating network nanocomposites with an organically modified palygorskite

An organophilic palygorskite (o‐PGS) prepared by the treatment of natural palygorskite with hexadecyl trimethyl ammonium bromide was incorporated into interpenetrating polymer networks (IPNs) of polyurethane (PU) and epoxy resin (EP), and a series of PU/EP/clay nanocomposites were obtained by a sequential polymeric technique and compression‐molding method. X‐ray diffraction and scanning electron microscopy analysis showed that adding nanosize o‐PGS could promote the compatibility and phase structure of PU/EP IPN matrices. Tensile testing and thermal analysis proved that the mechanical and thermal properties of the PU/EP IPN nanocomposites were superior to those of the pure PU/EP IPN. This was attributed to the special fibrillar structure of palygorskite and the synergistic effect between o‐PGS and the IPN matrices. In addition, the swelling behavior studies indicated that the crosslink density of PU/EP IPN gradually increased with increasing o‐PGS content. The reason may be that o‐PGS made the chains more rigid and dense. As for the flame retardancy, the PU/EP nanocomposites had a higher limiting oxygen index than the pure PU. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal degradation of LC epoxy thermosets

A novel liquid crystalline (LC) epoxy monomer was cured with different types of hardeners. The thermal‐degradation properties of cured thermosets were evaluated by thermogravimetric (TG) analysis. Several widely used kinetic models were reviewed and used to fit the TG data. The experimental results showed that the methods from one constant heating rate are insensitive to the magnitude of reaction order n. The Kissinger and Osawa methods from multiple processes would give more confident kinetic parameters in these observed systems. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1514–1521, 2000     

Thermal degradation mechanism of polycarbonate/organically modified montmorillonite nanocomposites

There were contradictory results about the effect of clay on polycarbonate (PC) thermal stability in previous reported papers. For ascertainment of the actual role of clay, PC nanocomposites were prepared by direct melt‐mixing PC with hexadecyl trimethyl ammonium chloride modified montmorillonite (OMT). The results of X‐ray diffractometry, transmission electron microscopy, and high‐resolution electron microscopy experiments present the formation of uniformly intercalated structure. Thermogravimetric analyses show the onset decomposition temperature of PC/OMT nanocomposites is earlier 65°C than neat PC. The mechanism of PC thermal decomposition effected by OMT was discussed in detail. It reveals that OMT can catalyze thermal degradation of PC macromolecular chains and decrease thermal stability of the nanocomposites. POLYM. COMPOS., 37:2301–2305, 2016. © 2015 Society of Plastics Engineers     

Structure and properties of nanocomposites based on poly(butylene succinate) and organically modified montmorillonite

Poly(butylene succinate) and organically modified montmorillonite nanocomposites with there different compositions were prepared via melt blending in a twin‐screw extruder. The structure of the nanocomposites was studied with X‐ray diffraction and transmission electron microscopy, which revealed the formation of intercalated nanocomposites, regardless of the silicate loading. Dynamic mechanical analysis revealed a substantial increase in the storage modulus of the nanocomposites over the entire temperature range investigated. The tensile property measurements showed a relative increase in the stiffness with a simultaneous decrease in the yield strength in comparison with that of neat poly(butylene succinate). The oxygen gas barrier property of neat poly(butylene succinate) improved after nanocomposite preparation with organically modified montmorillonite. The effect of the layered‐silicate loading on the melt‐state linear viscoelastic behavior of the intercalated nanocomposites was also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 777–785, 2006     

Intercalation of epoxy resin in organically modified montmorillonite

Various methods of preparation of epoxy resin/clay mixtures, before the addition of the crosslinking agent and curing to form epoxy‐based polymer layered silicate (PLS) nanocomposites, have been investigated to determine their effect on the nanostructure. Organically modified montmorillonite clay was used, and the mixtures were prepared by both simple mixing and solvent‐based methods. X‐ray diffraction shows that intercalation of the resin into the clay galleries occurs for all clay loadings up to 25 wt % and for both preparation methods, but the dispersion of the clay in the resin, observed by optical microscopy, is significantly better for the solvent preparation method. Differential scanning calorimetry (DSC) shows that the intercalated resin has the same molecular mobility as the extra‐gallery resin, but suggests that the intercalated resin does not penetrate completely into the galleries. Prolonged storage of the resin/clay mixtures at room temperature leads to changes in the DSC response, as well as in the response to thermogravimetry, which are interpreted as resulting from homopolymerization of the epoxy resin, catalyzed by the onium ion in the modified clay. This confirms and explains the earlier observation of Benson Tolle and Anderson (J Appl Polym Sci 2004, 91, 89) that “conditioning” of the resin/clay mixtures at ambient temperature has a significant effect when the crosslinking agent is subsequently added, and indicates that the preparation method has important consequences for the nanostructure development in the PLS nanocomposites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3751–3763, 2006     

Thermal stability and crystallization kinetics of isotactic polypropylene/organomontmorillonite nanocomposites

The thermal stability and crystallization kinetics of isotactic polypropylene (iPP) and iPP/organomontmorillonite (organo‐MMT) nanocomposites were investigated with differential scanning calorimetry and thermogravimetry. The incorporation of organo‐MMT up to a concentration of 4 wt % did not affect the melting temperature of iPP but did increase the peak thermal degradation temperature by 60°C. The isothermal crystallization kinetics showed that the addition of organo‐MMT increased the crystallization rate of iPP but reduced the isothermal Avrami exponent. The crystallization temperature of the nanocomposites measured with nonisothermal crystallization was higher than that of plain iPP, and this indicated an enhanced crystallization rate. The nonisothermal Avrami exponent, like the isothermal exponent, decreased with the addition of organo‐MMT, and this suggested changes in the crystallite growth geometry. Subsequently, the tensile yield strength and the tensile modulus both increased, but the elongation at break and the notched Izod impact strength did not change significantly. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3404–3415, 2003     

Synthesis and characterization of sPS/montmorillonite nanocomposites

The present work analyzed the possibility of obtaining and producing syndiotactic polystyrene (sPS)–based nanocomposites. The work first focused on possible technology to use for intercalation from solution and melt intercalation. Using a blend of sPS with atactic polystyrene (aPS) as the matrix was also considered. Thermal analysis techniques, such as differential scanning calorimetry (DSC) and thermogravimetry (TGA), were used to study the thermal properties and stability of the nanocomposites obtained and to select the most appropriate nanocharges. The effect of the introduction of nanofillers on these properties also was evaluated. X–ray diffraction was used to investigate the degree of clay exfoliation. Finally, mechanical characterization of the nanocomposites obtained was performed and compared to that of the pure material. The tests demonstrated that nanodispersion of phyllosilicate layers improved the mechanical behavior of the polymers analyzed, especially the annealed sPS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4957–4963, 2006     

Thermal–oxidative degradation and accelerated aging behavior of polyamide 6/epoxy resin‐modified montmorillonite nanocomposites

Polyamide 6 (PA6) nanocomposites based on epoxy resin‐modified montmorillonite (EP‐MMT) were prepared by melt processing using a typical twin‐screw extruder. X‐ray diffraction combined with transmission electron microscopy was applied to elucidate the structure and morphology of PA6/EP‐MMT nanocomposites, suggesting a nearly exfoliated structure in the nanocomposite with 2 wt % EP‐MMT (PA6/2EP‐MMT) and a partial exfoliated‐partial intercalated structure in PA6/4 wt %EP‐MMT nanocomposite (PA6/4EP‐MMT). The thermogravimetric analysis under air atmosphere was conducted to characterize the thermal–oxidative degradation behavior of the material, and the result indicated that the presence of EP‐MMT could inhibit the thermal‐oxidative degradation of PA6 effectively. Accelerated heat aging in an air circulating oven at 150°C was applied to assess the thermal–oxidative stability of PA6 nanocomposites through investigation of reduced viscosity, tensile properties, and chemical structure at various time intervals. The results indicated that the incorporation of EP‐MMT effectively enhanced the thermal–oxidative stability of PA6, resulting in the high retention of reduced viscosity and tensile strength, and the low ratio of terminal carboxyl group to amino group. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40825.     

Effect of silane grafting on the microstructure of high‐density polyethylene/organically modified montmorillonite nanocomposites

Organically modified montmorillonite (org‐MMT) and high‐density polyethylene (HDPE) grafted with silane groups (HDPE‐g‐silane) were melt compounded to give HDPE‐g‐silane‐blend‐org‐MMT nanocomposites. X‐ray diffractometry was performed to investigate the intercalation effect. Transmission electron microscopy was applied to observe the dispersion of org‐MMT layers in HDPE matrices. The results indicate that an intercalated structure can be easily obtained in HDPE‐g‐silane‐blend‐org‐MMT nanocomposites. Furthermore, positron annihilation lifetime spectroscopy was used to characterize the microstructure of the composites. It is found that the ortho‐positron (o‐Ps) intensity for HDPE‐g‐silane is decreased by approximately 10% with a narrower lifetime distribution than that for HDPE. With increasing org‐MMT concentration, the o‐Ps intensity I₃ increases for HDPE‐g‐silane‐blend‐org‐MMT nanocomposites; however, for HDPE‐blend‐org‐MMT composites I₃ decreases. It is found that HDPE composites with good dispersion can be obtained following appropriate modification of the HDPE. And silane grafting has an effect on the free volume of the HDPE nanocomposites. Copyright © 2007 Society of Chemical Industry     

Development of high‐performance epoxy/clay nanocomposites by incorporating novel phosphonium modified montmorillonite

Novel organoclays were synthesized by several kinds of phosphonium cations to improve the dispersibility in matrix resin of composites and accelerate the curing of matrix resin. The possibility of the application for epoxy/clay nanocomposites and the thermal, mechanical, and adhesive properties were investigated. Furthermore, the structures and morphologies of the epoxy/clay nanocomposites were evaluated by transmission electron microscopy. Consequently, the corporation of organoclays with different types of phosphonium cations into the epoxy matrix led to different morphologies of the organoclay particles, and then the distribution changes of silicate layers in the epoxy resin influenced the physical properties of the nanocomposites. When high‐reactive phosphonium cations with epoxy groups were adopted, the clay particles were well exfoliated and dispersed. The epoxy/clay nanocomposite realized the high glass‐transition temperature (T_g) and low coefficient of thermal expansion (CTE) in comparison with those of neat epoxy resin. On the other hand, in the case of low‐reactive phoshonium cations, the dispersion states of clay particles were intercalated but not exfoliated. The intercalated clay did not influence the T_g and CTE of the nanocomposite. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Morphology and mechanical and viscoelastic properties of rubbery epoxy/organoclay montmorillonite nanocomposites

The morphology and mechanical and viscoelastic properties of rubbery epoxy/organoclay montmorillonite (MMT) nanocomposites were investigated with wide‐angle X‐ray scattering (WAXS), transmission electron microscopy (TEM), tensile testing, and dynamic mechanical thermal analysis. An ultrasonicator was used to apply external shearing forces to disperse the silicate clay layers in the epoxy matrix. The first step of the nanocomposite preparation consisted of swelling MMT in a curing agent, that is, an aliphatic diamine based on a polyoxypropylene backbone with a low viscosity for better diffusion into the intragalleries. Then, the epoxy prepolymer was added to the mixture. Better dispersion and intercalation of the nanoclay in the matrix were expected. The organic modification of MMT with octadecylammonium ions led to an increase in the initial d‐spacing (the [d₀₀₁] peak) from 14.4 to 28.5 Å, as determined by WAXS; this indicated the occurrence of an intercalation. The addition of 5 phr MMTC18 (MMT after the modification) to the epoxy matrix resulted in a finer dispersion, as evidenced by the disappearance of the diffraction peak in the WAXS pattern and TEM images. The mechanical and viscoelastic properties were improved for both MMT and MMTC18 nanocomposites, but they were more pronounced for the modified ones. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 103: 3547–3552, 2007     

Orientation of montmorillonite clay in dicyclopentadiene/organically modified clay dispersions and nanocomposites

Highly delaminated dispersions of the organically modified clay I‐28 (Nanocor, Inc.) in liquid dicyclopentadiene (DCPD) were prepared. In situ ring‐opening metathesis polymerization of I‐28/DCPD nanodispersions generated I‐28/poly(DCPD) nanocomposites. When clay/DCPD dispersions were cured under shear, alignment of clay platelets, tactoids, and small particles was captured. This orientation was confirmed by X‐ray diffraction and transmission electron microscopy. The Herman's orientation parameters were calculated for the oriented nanocomposites. Viscosities of these liquid nanodispersions exhibited thixotropic flow behavior, prior to curing. The time‐dependent viscosity effects became more pronounced with an increase in delamination. Initial viscosities increased with progressive clay platelet generation during delamination and nanodispersion within the liquid monomer. Viscosity can be used to follow clay exfoliation/delamination. Etching the surface of a 2 wt % I‐28 clay/poly(DCPD) nanocomposite with oxygen plasma eroded the matrix, exposing clay tactoids protruding from the surface. These surfaces were examined by SEM and energy dispersive X‐ray spectroscopy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2743–2751, 2006     

Novel polyether polyurethane/clay nanocomposites synthesized with organicly modified montmorillonite as chain extenders

A kind of novel polyether polyurethane (PU)/clay nanocomposite was synthesized using poly(tetramethylene glycol), 4,4′‐diphenylmethane diisocyanate (MDI), 1,6‐hexamethylenediamine, and modified Na⁺‐montmorillonite (MMT). Here, organicly modified MMT (O‐MMT) was formed by applying 1,6‐hexamethylenediamine as a swelling agent to treat the Na⁺‐MMT. The X‐ray analysis showed that exfoliation occurred for the higher O‐MMT content (40 wt %) in the polymer matrix. The mechanical analysis indicated that, when the O‐MMT was used as a chain extender to replace a part of the 1,2‐diaminopropane to form PU/clay nanocomposites, the strength and strain at break of the polymer was enhanced when increasing the content of O‐MMT in the matrix. When the O‐MMT content reached about 5%, the tensile strength and elongation at break were over 2 times that of the pure PU. The thermal stability and the glass transition of the O‐MMT/PU nanocomposites also increased with increasing O‐MMT content. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 6–13, 2006     

High‐performance epoxy hybrid nanocomposites containing organophilic layered silicates and compatibilized liquid rubber

A mixture of two epoxy resins, tetraglycidyl 4,4′‐diaminodiphenyl methane and bisphenol‐A diglycidylether, cured with 4,4′‐diaminodiphenyl sulfone, was used as matrix material for high‐performance epoxy hybrid nanocomposites containing organophilicly modified synthetic fluorohectorite and compatibilized liquid six‐arm star poly(propylene oxide‐block‐ethylene oxide) (abbreviated as PPO). The hydroxy end groups of the poly(propylene oxide‐block‐ethylene oxide) were modified, yielding a six‐arm star PPO with an average of two pendant stearate chains, two phenol groups, and two hydroxy end groups. The alkyl chains of the stearate end groups played an important role in tailoring the polarity of the polymer. Its phenol end groups ensured covalent bonding between liquid polymer and epoxy resin. Two different organophilic fluorohectorites were used in combination with the functionalized PPO. The morphology of the materials was examined by transmission electron microscopy. The hybrid nanocomposites were composed of intercalated clay particles as well as separated PPO spheres in the epoxy matrix. As determined by dynamic mechanical analysis, the prepared composites possessed glass‐transition temperatures around 220°C. Although the tensile moduli remain unaltered, the tensile strengths of the hybrid materials were significantly improved. The relatively high fracture toughness of the neat resin, though, was not preserved for the hybrid resins. Scanning electron microscopy of the fracture surfaces revealed extensive matrix shear yielding for the neat resin, whereas the predominant fracture mode of the hybrid nanocomposites was crack bifurcation and branching. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3088–3096, 2004     

Thermal degradation kinetics of polyimide nanocomposites from different carbon nanofillers: Applicability of different theoretical models

In this study, the nanocomposites of polyimide (PI) with the nanofillers multiwalled carbon nanotube (MWCNT) and carbon nanofiber (CNF) were prepared by in situ polymerization technique. The thermal stability of the nanocomposites were investigated and discussed with respect to nanofillers type, concentration, and their functionality within the PI matrix. It is observed that there are 16 and 18 °C increment in thermal degradation temperature with the addition of 3 wt % MWCNT and CNF within the PI matrix, respectively. The thermal degradation kinetics of the nanocomposites were studied by Kissinger–Akahira–Sunose method, Flynn–Wall–Ozawa method, and Kim–Park method. The results show that these models are well fitted with the experimental data. It is found that the calculated activation energy increases with the increase in nanofillers loading and PI/CNF nanocomposites exhibit higher activation energy compared to PI/MWCNT composites at their similar loading. Moreover, the effect of nanofillers type and loading on the glass transition temperature of nanocomposites were also investigated in details. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45862.     

Thermal stability and kinetics analysis of rubber‐modified epoxy resin by high‐resolution thermogravimetric analysis

A dynamic heating rate mode of high‐resolution thermogravimetric analysis was used to study the thermal and thermal‐oxidative stability, as well as kinetics analyses, of a model liquid rubber‐modified epoxy resin, Ep/CTBN, made up of bisphenol A diglycidyl ether‐based epoxy and carboxyl‐terminated butadiene acrylonitrile rubber (CTBN). Results show that the thermal degradation of Ep/CTBN resin in nitrogen and air consists of two and three independent steps, respectively. Moreover, Ep/CTBN has a higher initial degradation temperature and higher activation energy than those of pure epoxy resin in both gases, indicating that the addition of CTBN to epoxy can improve the thermal and thermal‐oxidative stability of pristine epoxy resin. Kinetic parameters such as activation energy, reaction order, and preexponential factor of each degradation step of both Ep/CTBN and pure epoxy resins in air and nitrogen were calculated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3594–3600, 2003     

Preparation of ultraviolet‐cured bisphenol A epoxy diacrylate/montmorillonite nanocomposites with a bifunctional,reactive, organically modified montmorillonite as the only initiator via in situ polymerization

A bifunctional reactive surfactant containing a polymerizable methacrylate group and a benzophenone group, [2‐(methacryloyloxy)ethyl](4‐benzoylbenzyl)dimethylammonium bromide (MDAB), was synthesized to modify montmorillonite (MMT) for the preparation of nanocomposites via photoinduced polymerization. Fourier transform infrared, thermogravimetric analysis, and X‐ray diffraction results indicated that MDAB‐modified MMT was obtained and had intercalated structures. The morphology of the ultraviolet‐cured bisphenol A epoxy diacrylate/MMT nanocomposites prepared from the organically modified MMTs was studied with X‐ray diffraction and transmission electron microscopy, and the results showed an intercalated structure with partial exfoliation for all the samples. Experimental results from thermogravimetric analysis, differential scanning calorimetry, and mechanical property testing also indicated that the thermal and mechanical properties of the ultraviolet‐cured nanocomposites were significantly enhanced by the presence of this bifunctional, reactive, organically modified MMT. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Isothermal and nonisothermal cure kinetics of an epoxy/poly(oxypropylene)diamine/octadecylammonium modified montmorillonite system

The effect of an octadecylammonium‐exchanged montmorillonite on the curing kinetics of a thermoset system based on a bisphenol A epoxy resin and a poly(oxypropylene)diamine curing agent were studied with differential scanning calorimetry (DSC) in isothermal and dynamic (constant‐heating‐rate) conditions. Montmorillonite and the prepared composites were characterized by X‐ray diffraction analysis and simultaneous DSC and thermogravimetric analysis. The analysis of the DSC data indicated that the intercalated octadecylammonium cations catalyzed the epoxy–amine polymerization. A kinetic model, arising from an autocatalyzed reaction mechanism, was applied to the DSC data. Fairly good agreement between the experimental data and the modeling data was obtained. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1765–1771, 2006     

Flammability and thermal degradation behaviors of phosphorus‐containing copolyester/BaSO4 nanocomposites

A novel phosphorus‐containing copolyester (PET‐co‐DDP)/barium sulfate (BaSO₄) nanocomposite was synthesized by in situ polymerization. The oxygen index values of the resulting nanocomposites decreased with increasing the content of BaSO₄ nanoparticles, but their antidripping behaviors were improved obviously through the UL‐94 test. The flammability tests based on the cone calorimetry showed that the introduction of nano‐BaSO₄ to the copolyester decreased remarkably the heat release rate and effective heat of combustion. The thermal oxidative decomposition behaviors of PET‐co‐DDP/BaSO₄ nanocomposites were studied by a conventional dynamic thermogravimetric analysis in a flowing air atmosphere with a heating rate of 20°C/min. The activation energies determined from Kissinger method, Flynn‐Wall‐Ozawa method, and Friedman method had a same variation trend. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 564–570, 2006     

Studies on epoxy/calcium carbonate nanocomposites

The article describes the preparation of epoxy‐calcium carbonate nanocomposites using diaminodiphenyl sulfone (DDS) as a curing agent. The curing behavior of diglycidyl ether of bisphenol‐A (DGEBA) (1 mol) in the presence of varying amounts of nanocalcium carbonate was investigated by differential scanning calorimetry (DSC) using stoichiometric amounts of diaminodiphenyl sulphone (0.5 mol) as curing agent. The amount of calcium carbonate (～ 44 nm) was varied from 2% to 10% (w/w). In the DSC scans of these samples, a broad exothermic transition due to curing was observed in the temperature range of 110–335°C. As expected, heat of curing decreased with increasing amount of nanocalcium carbonate; however it did not affect the curing characteristics, thereby indicating that the filler did not hinder the curing reaction. Thermal stability of DGEBA in the presence of varying amounts of nano‐CaCO₃ after isothermal curing [(i.e., by heating in an air oven at 80°C (1 h), 100°C (1 h), 120°C (1.5 h), and 180°C (4 h)] was evaluated by thermogravimetry. All the samples were stable upto 350°C, and char yield at 800°C increased with increasing amount of nanocalcium carbonate. Rectangular bars were prepared by mixing DGEBA, DDS, and varying amounts of CaCO₃ using silicone mold. The nanocomposites were characterized by X‐ray, scanning electron microscopy (morphological characterization), and dynamic mechanical analysis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009