Structure,thermal conductivity,and thermal stability of bromobutyl rubber nanocomposites with ionic liquid modified graphene oxide

In this report, we demonstrate that both the thermal stability and the thermal conductivity of bromobutyl rubber (BIIR) nanocomposites could be improved by incorporating the ionic liquids (ILs) modified graphene oxide (GO-ILs) using a solution compounding method. The structure, thermal stability and thermal conductivity of this newly modified BIIR nanocomposites were systematically analyzed and studied. The X-ray diffraction (XRD) analysis of GO-ILs showed that ILs had been effectively intercalated into the interlayer of GO, which was found to be able to raise the exfoliation degree of GO. The increased exfoliation degree facilitated a good dispersion of GO-ILs in the BIIR matrix, as revealed by the scanning electron microscope (SEM) images. The glass transition temperatures (T_g) of the GO-ILs/BIIR nanocomposites were also raised by the addition of GO-ILs, which indicates the strong interfacial adhesion between GO-ILs and the rubber. Most importantly, the incorporation of GO-ILs in the BIIR matrix could effectively improve the thermal stability of the rubber nanocomposites according to our thermogravimetric analysis (TGA). The activation energy (E_a) of thermal decomposition of GO-ILs/BIIR nanocomposites increases with the addition of GO-ILs. Besides, the thermal conductivity of GO-ILs/BIIR nanocomposite with 4 wt% of GO-ILs had 1.3-fold improvement compared to that of unfilled BIIR.     

Ball milling: An effective technique for the preparation of exfoliated clay filled unsaturated polyester toughened epoxy nanocomposite

This paper investigates the possibility of improving the mechanical and thermal properties of epoxy and unsaturated polyester toughened epoxy resins through the dispersion of octadecyl ammonium ion-exchanged montmorillonite (organoclay) through exfoliated mechanism. The nanocomposites prepared are characterized for their structural change and studied for their crystallite size, mechanical, thermal and water absorption (hydrophilicity) properties. The mechanical data indicates significant improvement in the flexural and tensile properties over the neat epoxy and UP-epoxy matrix according to the percentage content of organoclay. The thermal behavior too shows noticeable enhancement in glass transition temperature T _g and high thermal stability. Hydrophilicity of all the composites decreases irrespective of the concentration of organoclay on the epoxy and UP-epoxy matrices. The homogeneous morphology of epoxy and UP toughened epoxy nanocomposite hybrid systems is ascertained using scanning electron microscope (SEM). X-ray results point out that the cetyl ammonium modified clay filled composites exhibited the exfoliated structure.     

Thermal stability and toughening of epoxy resin with polysulfone resin

The cure behavior, thermal stability, and mechanical properties of diglycidylether of bisphenol A (DGEBA)/polysulfone (PSF) blends initiated by 1 wt % N‐benzylpyrazinium hexafluoroantimonate as a cationic latent catalyst were investigated. The DGEBA/PSF content was varied within 100/0–100/40 wt %. Latent properties were studied through the measurement of the conversion as a function of the curing temperature, and the cure activation energy (E_a) was studied by the Kissinger method with a dynamic differential scanning calorimetry analysis. The thermal stabilities, largely based on the integral procedural decomposition temperature (IPDT) and decomposed activation energy (E_t), were investigated by the measurement of thermogravimetric analysis. For the mechanical properties of the casting specimens, the critical stress intensity factor (K_IC) test was performed, and their fractured surfaces were examined with scanning electron microscopy. E_a, IPDT, E_t, and K_IC increased with PSF increasing in the neat epoxy resin up to 30 wt %. However, there was a marginal decrease in the blend system in both the thermal and mechanical properties due to the phase separation between DGEBA and PSF. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 121–128, 2001     

Investigation of curing kinetics of epoxy resin/novel nanoclay–carbon nanotube hybrids by non-isothermal differential scanning calorimetry

Chemical hybrid of nanoclay (NC)/carbon nanotube (CNT) was synthesized via growth of CNTs by chemical vapor deposition. The cure kinetics of epoxy resin in the presence of novel chemical hybrid of NC/CNT (CNC) was studied by non-isothermal differential scanning calorimetry. The effect of the CNC on cure kinetics was compared with conventional nanofillers such as CNTs, NC, and physical mixture of them (PNC). The kinetic parameters of the cure reaction were determined by iso-conversional method. The accelerating effect of CNT, CNC, and PNC in initial stage of cure reaction was related to the high thermal conductivity of CNTs, while the decelerating effect of nanofillers as the cure proceeded can be attributed to the reduction of polymer molecules motion caused by enhanced viscosity. The apparent activation energy (E _α) as the function of conversion (α) was calculated by five methods categorized into two different types: (1) conversion-dependent methods: Kissinger–Akahira–Sunose (KAS), Ozawa–Flynn–Wall (OFW), and Friedman; (2) conversion-independent methods: Kissinger and Augis. The accelerating effect of CNT, PNC, and CNC was observable as the reduced E _α values in low conversion only with KAS and OFW methods. The reverse trend of E _α values was observed with the introduction of these nanofillers at high conversions. The uniqueness of the CNC was more marked in increasing E _α values of epoxy after initial stage due to its special 3D structure of CNC. Calculated data using KAS and OFW methods showed the best agreement with the obtained experimental data.     

Synthesis and properties of Fe0.83V1.17O4

Thermal properties of the organic–inorganic bicontinuous nanocomposites prepared via in situ two-stage polymerization of various silanes, epoxy, and amine monomers are investigated, and the impact of filler content and its organic compatibility on thermal stability of these nanocomposites is studied. Two series of epoxy–silica nanocomposites, namely, EpSi-A and EpSi-B containing 0–20 wt% silica, are synthesized. An epoxy–silane coupling agent is employed to improve the organic compatibility of silica in EpSi–B nanocomposites. The composites synthesized via two-stage polymerization are characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric (TG) analysis. DSC and TG/differential thermogravimetric results reveal substantially high glass transition (T _g) and excellent thermal stability of the bicontinuous nanocomposites as compared with pristine epoxy polymer. Both T _g and thermal properties, however, considerably vary depending on the organic compatibility of the nanocomposites. Significantly higher decomposition temperatures are recorded in case of EpSi-B nanocomposites owing to the chemical links between the epoxy and silica phases. Kinetic studies also show relatively higher activation energies of pyrolysis for EpSi-B nanocomposites.     

Thermal degradation mechanism of highly filled nano-SiO2 and polybenzoxazine

Effects of high nano-SiO₂ loading (up to 30 mass%) on polybenzoxazine (PBA-a) thermal degradation kinetics have been investigated using nonisothermal thermogravimetric analysis (TG). The DTG curves revealed three stages of thermal decomposition process in the neat PBA-a, while the first peak at low temperature was absent in its nanocomposites. As a consequence, the maximum degradation temperature of the nanocomposites shifted significantly to higher temperature as a function of the nano-SiO₂ contents. Moreover, the degradation rate for every degradation stage was found to decrease with the increasing amount of the nano-SiO₂. From the kinetics analysis, dependence of activation energy (E _a) of the nanocomposites on conversion (α) suggests a complex reaction with the participation of at least two different mechanisms. From Coats–Redfern and integral master plot methods, the average E _a and pre-exponential factor (A) of the nanocomposites showed systematically higher value than that of the PBA-a, likely from the shielding effect of the nanoparticles. The main degradation mechanism of the PBA-a was determined to be a random nucleation type with one nucleus on the individual particle (F1 model), while that of the PBA-a nanocomposite was the best described by diffusion-controlled reaction (D3 model).     

Synergistic effect of hybrid graphene and boron nitride on the cure kinetics and thermal conductivity of epoxy adhesives

In the present study, the synergistic effect of hybrid boron nitride (BN) with graphene on the thermal conductivity of epoxy adhesives has been reported. Graphene was prepared by chemical reduction of graphite oxide (GO) in a mixture of concentrated H₂SO₄/H₃PO₄ acid. The particle size distribution of GO was found to be ~10 μm and a low contact angle of 54° with water indicated a hydrophilic surface. The structure of prepared graphene was characterized by Fourier transform infrared (FTIR), X‐ray diffraction (XRD), Raman spectroscopy and atomic force microscopy (AFM). The thermal conductivity of adhesives was measured using guarded hot plate technique. Test results indicated an improvement in the thermal conductivity up to 1.65 W/mK, which was about ninefold increase over pristine epoxy. Mechanical properties of different epoxy formulations were also measured employing lap shear test. The surface characterization of different epoxy adhesive systems was characterized through XRD, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies. Fourier transform infrared also served to determine the nature of interactions between filler particles and epoxy resin. Non‐isothermal differential scanning calorimetric (DSC) technique was used to investigate the effects of graphene and BN particles on the cure kinetics and cross‐linking reaction of epoxy cured with amine curing agent. The Kissinger equation, the model‐free isoconversional Flynn–Wall–Ozawa method and the Ozawa model were used to analyze the kinetic parameter. Copyright © 2017 John Wiley & Sons, Ltd.     

Morphology and thermal properties of polyhedral oligomeric silsesquioxane/polybutadiene nanocomposites prepared by anionic polymerization

The morphology and thermal properties of Allylisobutyl Polyhedral Oligomeric Silsesquioxane (POSS)/Polybutadiene (PB) nanocomposites prepared through anionic polymerization technique were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results of XRD, SEM and TEM showed that the aggregation of POSS in PB matrix occurred obviously, forming crystalline domains and the size of POSS particles increased with increasing POSS content. The DSC and TGA results indicated that the glass transition temperature (T _g) of the nanocomposites was significantly increased and the maximum degradation temperature (T _dmax) of nanocomposites was slightly increased compared with pure PB, implying an increase in thermal stability.     

Thermal Degradation Kinetics and Modeling Study of Ultra High Molecular Weight Polyethylene (UHMWP)/Graphene Nanocomposite

The incorporation of nanofillers such as graphene into polymers has shown significant improvements in mechanical characteristics, thermal stability, and conductivity of resulting polymeric nanocomposites. To this aim, the influence of incorporation of graphene nanosheets into ultra-high molecular weight polyethylene (UHMWPE) on the thermal behavior and degradation kinetics of UHMWPE/graphene nanocomposites was investigated. Scanning electron microscopy (SEM) analysis revealed that graphene nanosheets were uniformly spread throughout the UHMWPE’s molecular chains. X-Ray Diffraction (XRD) data posited that the morphology of dispersed graphene sheets in UHMWPE was exfoliated. Non-isothermal differential scanning calorimetry (DSC) studies identified a more pronounced increase in melting temperatures and latent heat of fusions in nanocomposites compared to UHMWPE at lower concentrations of graphene. Thermogravimetric analysis (TGA) and derivative thermogravimetric (DTG) revealed that UHMWPE’s thermal stability has been improved via incorporating graphene nanosheets. Further, degradation kinetics of neat polymer and nanocomposites have been modeled using equations such as Friedman, Ozawa–Flynn–Wall (OFW), Kissinger, and Augis and Bennett’s. The "Model-Fitting Method” showed that the auto-catalytic nth-order mechanism provided a highly consistent and appropriate fit to describe the degradation mechanism of UHMWPE and its graphene nanocomposites. In addition, the calculated activation energy (E_a) of thermal degradation was enhanced by an increase in graphene concentration up to 2.1 wt.%, followed by a decrease in higher graphene content.     

Studies on epoxy resins cured by cationic latent thermal catalysts: The effect of the catalysts on the thermal,rheological, and mechanical properties

To investigate the effect of catalysts on the thermal, rheological, and mechanical properties of an epoxy system, a resin based on diglycidyl ether of bisphenol‐A (DGEBA) was cured by two cationic latent thermal catalysts, N‐benzylpyrazinium hexafluoroantimonate (BPH) and N‐benzylquinoxalinium hexafluoroantimonate (BQH). Differential scanning calorimetry was used for the thermal characterization of the epoxy systems. Near‐infrared spectroscopy was employed to examine the cure reaction between the DGEBA and the latent thermal catalysts used. The rheological properties of the blend systems were investigated under an isothermal condition with a rheometer. To characterize the mechanical properties of the systems, flexure, fracture toughness (K_IC), and impact tests were performed. The phase morphology was studied with scanning electron microscopy of the fractured surfaces of mechanical test samples. The conversion and cure activation energy of the DGEBA/BQH system were higher than those of the DGEBA/BPH system. The crosslinking activation energy showed a result similar to that obtained from the cure kinetics of the blend systems. The flexure strength, K_IC, and impact properties of the DGEBA/BQH system were also superior to those of the DGEBA/BPH system. This was a result of the substituted benzene group of the BQH catalyst, which increased the crosslink density and structural stability of the epoxy system studied. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 187–195, 2001     

A comprehensive assessment on degradation of multi-walled carbon nanotube-reinforced EMA nanocomposites

Thermal degradation kinetics of MWNT-reinforced EMA-based nanocomposites having different methyl acrylate (MA) contents (by % mass) ranging from 9 to 30% have been monitored. Kissinger and Flynn?CWall?COzawa methods for evaluating non-isothermal degradation of polymers have been examined. Overall, the thermal stabilities of the nanocomposites are the function of amount of MWNTs loading and their state of dispersion that depends on the MA content of respective EMAs. Composite samples exhibit higher activation energy (E _a) than the neat EMAs but the E _as of the composites diminish with increased MA contents of the matrices. TG-Mass spectrometry has been used to identify the volatile products resulting from thermal degradation of composites, and a promising mechanism has been proposed over different range of temperatures of degradation. It is proposed that the side-group scission of methoxycarbonyl group initiates thermal decomposition following combination of chain end and random chain scission reactions, ensuing pseudo second-order kinetics.     

Evaluating a four-directional benzene-centered aliphatic polyamine curing agent for epoxy resins

A four-directional benzene-centered aliphatic polyamine, MXBDP, with high functionality and low volatility, is used to cure epoxy resin (DGEBA). Herein we originally report the isothermal cure kinetics and dynamic mechanical properties of DGEBA/MXBDP. Differential scanning calorimetry confirms that MXDBP is more reactive than commercial linear metaxylenediamine and branched Jeffamine T-403 and the isothermal curing reaction is autocatalytic. The Kamal model is found to be able to well describe the curing rate up to the onset of diffusion control, and the excellent match over the whole conversion range is achieved using the extended Kamal model. Interestingly, the isoconversional kinetic analysis indicates that the effective reaction activation energy (E _α ) changes substantially with conversion, and ultimately decreases to a very small value (<10 kJ mol^?1) because of the diffusion-controlled reaction kinetics. Then, dynamic mechanical analysis reveals that DGEBA/MXBDP exhibits the higher α- and β-relaxation temperatures and the much higher crosslink density than DGEBA/metaxylenediamine. Our experiment results support that MXBDP has the high reactivity and improved thermal resistance in combination with the advantages of the high functionality, low volatility and decreased CO₂ absorption. Therefore, MXBDP may be especially suitable for room temperature-cure epoxy coatings and adhesives.     

Isothermal cure kinetics of epoxy/phenol‐novolac resin blend system initiated by cationic latent thermal catalyst

The investigation of the cure kinetics of a diglycidyl ether of bisphenol A (DGEBA)/phenol‐novolac blend system with different phenolic contents initiated by a cationic latent thermal catalyst [N‐benzylpyrazinium hexafluoroantimonate (BPH)] was performed by means of the analysis of isothermal experiments using a differential scanning calorimetry (DSC). Latent properties were investigated by measuring the conversion as a function of curing temperature using a dynamic DSC method. The results indicated that the BPH in this system for cure is a significant thermal latent initiator and has good latent thermal properties. The cure reaction of the blend system using BPH as a curing agent was strongly dependent on the cure temperature and proceeded through an autocatalytic kinetic mechanism that was accelerated by the hydroxyl group produced through the reaction between DGEBA and BPH. At a specific conversion region, once vitrification took place, the cure reaction of the epoxy/phenol‐novolac/BPH blend system was controlled by a diffusion‐control cure reaction rather than by an autocatalytic reaction. The kinetic constants k₁ and k₂ and the cure activation energies E₁ and E₂ obtained by the Arrhenius temperature dependence equation of the epoxy/phenol‐novolac/BPH blend system were mainly discussed as increasing the content of the phenol‐novolac resin to the epoxy neat resin. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2945–2956, 2000     

Study on the PMMA/GO nanocomposites with good thermal stability prepared by in situ Pickering emulsion polymerization

Graphene oxide (GO) is used as a stabilizer in the Pickering emulsion polymerization of methyl methacrylate (MMA) to prepare PMMA/GO nanocomposites. Transmission electron microscope studies of the emulsion polymerization products showed that the average diameter of nanocomposite particles was about 150 nm, the transparent GO flakes covered the surface of the particles, and were well dispersed in polymer matrix. The influence of GO on the thermal stability of PMMA was investigated by thermogravimetry analysis and differential scanning calorimetry. The results showed that the thermal stability and the glass transition temperature (T _g) of PMMA/GO nanocomposites were improved obviously compared with PMMA. The apparent activation energy (E _a) for the degradation process of PMMA/GO nanocomposites was evaluated by Kissinger method, which indicated that their E _a s were much higher than those of PMMA both in nitrogen and air atmosphere.     

Effect of nanosilica on thermal oxidative degradation of SBR

The effect of silica content on thermal oxidative stability of styrene–butadiene rubber (SBR)/silica composites has been studied. Morphologies of silica in SBR with different contents are investigated by scanning electron microscopy, which indicates that silica can well disperse in SBR matrix below the content of 40 %, otherwise aggregates or agglomerates will generate. Composites with around 40 % silica content show excellent mechanical properties and retention ratios after aging at 85 °C for 6 days. The values of activation energy (E _a) of pure SBR and its composites are calculated by Kissinger and Flynn–Wall–Ozawa methods based on thermogravimetric (TG) results, which suggests that composite with about 20 % silica has minimum E _a, and composite with 30–40 % silica has maximum E _a. According to TG curves, it is found that silica can suppress the formation of char leading to decline in stability to some extent. On the other side, silica also has positive effect on improving thermal stability of the matrix as filler. Thus, the SBR/silica composites with silica content of 30–40 % can possess both excellent resistance to thermal oxidative degradation and superior mechanical properties.     

Synthesis, structural, electrical and thermal properties of Ti-doped Bi2Sn2O7 pyrochlore

Polycrystalline ceramic samples of Bi₂Sn_2?xTi_xO₇ (x?=?0.0, 0.2, 0.4, 0.6, 0.8) have been synthesized by conventional solid-state reaction method. The effect of homovalent cation (titanium) substitution on the Sn-site on the structural, morphological, electrical and thermal properties of the pure Bi₂Sn₂O₇ ceramics have been studied by X-ray diffraction (XRD) followed by scanning electron microscopic techniques, dc conductivity and modulated differential scanning calorimetry. The XRD analysis carried out by performing the Rietveld refinement using the space group Fd3m indicates that the increase of titanium contents do not lead to any secondary phase. The grain size distributions of all the samples were investigated by SEM. It was found that the grain sizes are strongly influenced by the addition of titanium to the system. The frequency and temperature dependent dielectric studies have been carried out. The dc conductivity measurement was carried out for all the compounds and the activation energies were calculated using the relation ???=???0 exp(?E _a/kT). The modulated differential scanning calorimetry has been used to investigate the effect of substitution on the specific heat, heat flow and other thermal parameters of the compounds. The results are discussed in detail.     

Effects of organo-montmorillonite dispersion on thermal stability of epoxy resin nanocomposites

Montmorillonite (MMT) was modified with the acidified cocamidopropyl betaine (CAB) and the resulting organo-montmorillonite (O-MMT) was dispersed in an epoxy/methyl tetrahydrophthalic anhydride system to form epoxy nanocomposites. The dispersion state of the MMT in the matrix was investigated by X-ray diffraction and scanning electronic microscopy. The thermal stability of the epoxy nanocomposites was examined by TGA. Thermal stability of the epoxy nanocomposite is dependent upon the dispersion state of the OMMT in the epoxy matrix although all the epoxy nanocomposites had enhanced thermal stability compared with the neat epoxy resin. The thermal stability of the epoxy resin nanocomposites was correlated with the dispersion state of the MMT in the epoxy resin matrix.     

Enhancement of tensile,electrical and thermal properties of epoxy nanocomposites through chemical hybridization of polypyrrole and graphene oxide

This paper presents the properties of epoxy nanocomposites, prepared using a synthesized hybrid Polypyrrole-Graphene Oxide (PPy-GO) filler, via in-situ chemical polymerization, at various filler loadings (i.e., 0.5–2 w. t %). The microstructures and properties of the PPy-GO hybrids and epoxy nanocomposites were studied via Fourier transform infrared (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), mechanical (Tensile Properties), electrical, Dynamic mechanical thermal analysis (DMTA) and thermogravimetric analyses (TGA). Morphological study demonstrated that varying the nanofiller nature (PPy-GOs, PPy or GO) lead to different states of dispersion. Mechanical, electrical and thermal analysis demonstrated that the hybrid concentration and its architecture (PPy:GO ratio) are interesting factors significantly affected the properties of the epoxy based nanocomposites. On the other hand, the mechanical performance of the cured nanocomposites outperformed the PPy-GO, with enhancements of 78% and 51% of Young's modulus and strength, respectively. Here it has been established that the embedding of PPy-GO hybrids into pristine epoxy endows optimum dispersion of PPy and GO as well as better interfacial adhesion between the fillers and matrix, which results in a significant improvement in load transfer effectiveness. Electrical conductivity measurements showed that conductivity of epoxy filled nanocomposites increased up 10⁻⁴ S/cm for Epoxy/PPy-GO nanocomposites. DMTA test indicated that incorporation of PPy-GO resulted in a significantly increase in Tg of the resultant nanocomposites, which is attributed to the highly exfoliation structure and the stronger interfacial interaction. The PPy-GO particles enhanced electrical, thermal and mechanical properties of nanocomposites, confirming the synergistic effect of PPy-GO as multifunctional filler.     

A novel phosphorus-containing copolyester/montmorillonite nanocomposites with improved flame retardancy

A novel phosphorus-containing flame-retardant copolyester/montmorillonite nanocomposite (PET-co-HPPPA/O-MMT) was synthesized by the in situ intercalation polycondensation of terephthalic acid, ethylene glycol, and 2-carboxyethyl(phenylphosphinic) acid (HPPPA) with montmorillonite (O-MMT). The morphology was characterized by wide-angle X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The effects of organoclay on the thermal properties and melting behaviors of the nanocomposites were investigated by thermogravimetric analysis and differential scanning calorimetry. The flammability of the nanocomposites was characterized by the limiting oxygen index test and the UL-94 vertical test. The results showed that a small amount of organoclay was able to improve the thermal stabilities and the flame retardancy of PET-co-HPPPA copolyesters, and however there was no significant increase in the melting points of nanocomposites when the content of diethylene glycol was controlled as a certain value. The overall crystallization rate of the nanocomposites is greater than that of neat copolyester. The nanocomposites have better flame retardancy than PET-co-HPPPA.     

The investigation of methyl phenyl silicone resin/epoxy resin using epoxy-polysiloxane as compatibilizer

Styrene–butadiene rubber was subjected to long-term thermal aging treatment at 80 °C with aging period up to 180 days. The degradation kinetics of the aged sample was analyzed by thermogravimetric analysis. Multiple heating rate experiments were carried out in nonisothermal conditions and three isoconversional model-free methods (Friedman; Kissinger–Akahira–Sunose; Li and Tang methods) were employed. The results showed that the temperature for 5 % mass loss increased, whereas the maximum mass loss temperature decreased after aging. Activation energies (E _a) derived from the three methods were found to be dependent on conversion degree (α). E _a increased with increasing α in the whole range of conversion for samples aged for 0, 60, and 120 days, while the aged samples displayed higher E _a values. However, samples aged for 180 days showed declining E _a versus α. The changes on the degradation kinetics were associated with the modification on the chemical structure after thermal aging.