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Thermal degradation and stability of epoxy nanocomposites: Influence of montmorillonite content and cure temperature

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Abstract

The thermal behaviour and stability of epoxy nanocomposites were studied by thermogravimetric analysis (TGA). The nanocomposites consisted of a trifunctional epoxy resin, a hardener containing reactive primary amine groups and clay nanoparticles (i.e. montmorillonite), previously treated with octadecyl ammonium. Three levels of nanoclay content (0, 5 and 10%) and three temperature levels (120, 150 and 200 °C) were used. The exfoliation of nanoparticles within the material was analyzed by X-ray diffraction (XRD). The cure conversion was determined by Fourier transform infrared (FTIR) spectroscopy by selecting the suitable band for epoxide functional groups. The study demonstrated that the nanoclay greatly accelerates the cure, at the different cure temperatures studied. Finally, the thermal stability of the various nanocomposites was established by calculating various characteristic temperatures from thermograms as well as conversion and conversion derivative at maximum decomposition rate. The collisions between resin molecules, which are trapped within the nanoclay galleries, were less effective because they were protected against thermal degradation by the galleries. However, once the collision was effective, the thermal activation occurred more readily.

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... Wang et al. [15] also conducted similar investigations and concluded that type of amine curing agent and rate of chemical reaction are key factors in the formation of exfoliated microstructure. Surface modifications and processing techniques have also been identified as key factors affecting mobility of nanoclay particles during dispersion, influencing viscosity and cure behavior, including rate of conversion (catalytic), cross-linking, and overall properties of the final composites [16,[18][19][20][21][22][23]. ...
... Figure 3 shows representative curves of viscosity as function of temperature for different MMT loadings and average cure characteristic parameters are presented in Table 2. Changes in viscosity due to interactions between clay particles and epoxy molecules at increasing temperatures affected the process of gelation, vitrification, and formation of final properties compared to unmodified Journal of Nanomaterials Figure 3: Viscosity dependency on dynamic curing temperature at 5 ∘ C/min. system [19,27]. At the onset of each experiment nanoclay swelling, tethering, and formation of clay particle network in the modified systems lead to an increase in viscosity compared to unmodified system. ...
... The swelling can further expose more unreactive nanoclay surfaces, thus increasing chemical interactions with epoxy molecules and resulting in enhanced catalytic behavior of MMT. This behavior has been attributed to quantity of alkyl ammonium ions used in clay surface modification, MMT concentration, and cure temperature [15,19,20]. Varying MMT content disrupted the process of gelation indicated by "A" (Figure 3) in each modified system during curing. ...
Article
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The primary focus of this study was to understand the effects of different amounts of montmorillonite nanoclay (MMT) loading on viscosity, cure behavior, reaction mechanism, and properties of diglycidyl ether of bisphenol A (DGEBA) epoxy composites. Influence of 1–3 wt.% MMT on rheological and subsequent cure behavior of SC-15 epoxy resin was studied using nonisothermal and isothermal rheometry and differential scanning calorimetry (DSC). Rheological properties were influenced by different amounts of MMT at lower shear rates prior to and during curing. Cure reaction mechanism was unaffected by different MMT concentration; however heat and activation energy of reactions increased with increasing MMT loading. Samples with 2 wt.% MMT showed highest reaction rate constant, indicative of catalytic behavior. X-ray diffraction (XRD) and transmission electron microscope (TEM) revealed mainly intercalated microstructure throughout the MMT infused epoxy composite samples irrespective of the percent loading.
... Recently, because of the improved physical and chemical properties provided by ceramic materials to polymers, lamellar silicate polymer nanocomposites have attracted the attention of both industry and the scientific community 1,2 . ...
... Superposition of the X-ray diffractograms of OMMT and epoxy-based powder coatings with different OMMT contents. the clay in the polymer matrix, thus providing evidence of the presence of nanocomposites of predominantly exfoliated phase 1,4,9,10,[18][19][20][21] . ...
Article
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Polymer coatings have been used for the corrosion protection of metal surfaces acting as a physical barrier against several corroding media. In spite of the good efficiency of these coatings their resistance is limited due to the presence of localized defects which give place to localized corrosion. Aiming to improve the barrier properties of these coatings this work has proposed the use of nanocomposites as powder coatings based on a standard formulation of a commercial powder varnish. Nanocomposites with 2 and 4 wt% contents of organophilic montmorillonite (OMMT) were obtained in the molten state through of a co-rotating twin-screw extruder. The application of the nanocomposite coatings was performed by electrostatic pulverization on mild steel panels. The coatings were characterized to determine their structure using X-ray diffraction (XRD). The morphologies of the coatings were assessed using transmission electron microscopy (TEM). Gloss and adhesion measurements and the flexibility and impact resistance of the coatings were included in the physical assessment of the coatings. The corrosion performance was evaluated by the salt spray test and by electrochemical impedance spectroscopy (EIS). The coatings with clays presented predominantly exfoliated structures, with good dispersion of OMMT in the epoxy matrix. The addition of OMMT reduced the impact resistance, flexibility and gloss but increased the barrier properties of the coatings. The best corrosion performance in NaCl solution was achieved for 4 wt% OMMT.
... Francis et al. 5 have studied cure kinetics of hydroxyl terminated poly(ether ether ketone) based on tert-butyl hydroquinone (PEEKTOH) employing isothermal DSC measurements at different temperatures. Carrasco and Pages 6 have employed FTIR spectroscopy to follow cure conversion (by selecting a suitable band for epoxide functional group) of nanocomposites consisting of a trifunctional epoxy resin, a hardener containing reactive primary amine group, and clay nanoparticles previously treated with octadecyl ammonium. In a recent study by Raman and Palmese,7 FTIR spectroscopy in the near-infrared (NIR) region was used to monitor cure kinetics of diglycidyl ether of bisphenol A (DGEBA) epoxy resin and 4,4′-methylenebiscyclohexanamine in the presence of tetrahydrofuran (THF) as a solvent. ...
... where α is the extent of the reaction, obtained by the partial area under a DSC trace versus time, t. k 1 and k 2 are the specific rate constants of the models and are functions of temperature; m and n are the reaction orders and (m + n) is the overall reaction order. Equation 6 represents the experimental observations. The experimental value of the rate of reaction (dα/dt) and conversion (α) for the complete course of the reaction were computed at all cure temperatures and adjusted with the kinetic equation. ...
Article
The in-situ cure and cure kinetics of an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) polymerized with an anhydride hardener and its mixtures with a liquid polybutadiene rubber having hydroxyl functionality (HTPB) were studied using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) in an isothermal mode. The cure reaction was monitored in-situ by FTIR spectroscopy by observing variation in intensity of epoxy, anhydride, and ester bands. The cure reaction mechanisms by which the network structure of epoxy was developed were discussed. Isothermal mode DSC measurements were performed at selected temperatures. The reaction followed an autocatalytic mechanism, and kinetic analysis was done by a phenomenological model developed by Kamal. Good fits were obtained between the autocatalytic model and the experimental data up to the vitrification state. Afterward, the reaction became diffusion controlled. The reaction during the later stages of cure was explained by introducing a diffusion factor, which agreed well with the kinetic data. The nature of the developing morphology of modified epoxies was analyzed by optical microscopy (OM) and small angle laser light scattering (SALLS) technique. The ultimate morphology of the cured blends was analyzed using scanning electron microscopy (SEM). The cure kinetics has been correlated with the developed morphology to get insight into the mechanism of reaction-induced microphase separation.
... The arrangement of silicate particles in a polymer matrix can be found as microsized agglomerates, as in the case of common fillers, or as intercalated or exfoliated particles (Aijuan & Liang 2002;Becker & Simon 2005;Carrasco & Pagès 2008). Normally, the three structures could be observed in a single polymer/ silicate nanocomposite. ...
... Epoxy/layered silicate nanocomposites exhibit improved thermal, barrier and mechanical properties (Carrasco & Pagès 2008). Table 1 summarizes the research on thermal stability and kinetics of decomposition of epoxy/ clay nanocomposites reported by several researchers. ...
Article
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This study utilized the incorporation of nanoparticle filler into an epoxy system to study the effect of different nanosized montmorillonite (MMT) fillers on the thermal stability and mechanical properties of epoxy. The sample was prepared using diglycidyl ether of bisphenol A (DGEBA) with different surface treatments of montmorillonite filler by mechanical stirring. The results of thermal stability and mechanical properties of epoxy/clay system obtained from thermal gravimetric analyzer (TGA), universal testing machine (UTM) and scanning electron microscopy (SEM) were discussed. With the same amount of filler introduced into the system, different thermal stability of epoxy composite can be observed. Bentonite, which contained other contaminant components, can downgrade the enhanced properties of the filler. ABSTRAK Kajian ini dijalankan bagi mengaplikasikan pengisi bersaiz nano ke dalam sistem epoksi yang memberi kesan terhadap kestabilan terma dan ciri-ciri mekanikalnya. Sampel yang digunakan adalah daripada epoksi diglicidil eter bisfenol A (DGEBA) dengan pengisi montmorilonit yang berbeza olahan permukaan melalui kaedah pengadukan mekanikal. Hasil kestabilan terma dan ciri-ciri mekanikal sistem epoksi/lempung diperoleh daripada alat analisis gravimetri terma (TGA), mesin ujian universal dan mikroskopi elektron imbasan (SEM) dibincangkan dengan teliti. Dengan jumlah pengisi yang sama, hasil kestabilan terma yang berbeza dapat diperoleh. Bentonit yang mengandungi bendasing dapat menurunkan ciri-ciri penambah kekuatan pengisi tersebut.
... While a decrease of approximately 4% and 5% was observed for 0.1 and 0.2 wt. % GNP nanocomposites respectively, reiterating the impact of inherent properties of MMT along with the comparatively higher loading compared to GNP [44]. ...
... % GNP decomposition temperature decreased from 365 °C (neat) to 321 °C and 319 °C respectively (Fig. 6). Although GNP nanoparticles have shown to enhance various properties of polymer composites, their effects on thermal stability had been dismal [44]. To compensate for this effect MMT nanoparticles addition has proven to useful in achieving an optimized epoxy system, which still has improved mechanical properties but optimum thermal properties [45]. ...
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Multifaceted effects of Graphene Nanoplatelets (GNP) and Montmorillonite Nanoclay (MMT) reinforcement on mechanical and thermal properties of DGEBA epoxy resin nanocomposites were investigated. Multi-step dispersion techniques involving ultrasonication, shear mixing and magnetic stirring were used to disperse nanoparticles. Impact on thermal properties was investigated via Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA), while mechanical properties were studied using Tensile and Three-point flexure tests. Graphene sheets were instrumental in increasing modulus and strength at a very low percentage whereas nanoclay was helpful in preserving thermal stability of the matrix thus creating a synergistic effect to reflect the reinforcing ability of both GNP and MMT in mechanical and thermal aspects respectively. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) studies showed mixed intercalation and exfoliation of nanoparticles with increased inter-planar spacing and decrease in intensity of crystal peaks. SEM micrographs of failed samples revealed failure mechanisms and the aid of GNP to resist failure. To further investigate the effect of binary nano-reinforcement, hybrid Carbon Fiber Reinforced Polymer (CFRP) samples were fabricated and tested for mechanical properties via Tensile and Flexural tests. The mode of failure was analyzed by SEM imaging. It was confirmed that GNP reinforcement helped in increasing the mechanical properties of material.
... nanoparticles on chemico-physical and chemico-rheological properties of the polymer is of significant importance. This leads to the development of customized parameters necessary for processing such combination and ultimate curing of the final composite [11,12]. Generally, enhanced properties of polymers by nanoparticles have been attributed to structural morphologies, degree of dispersion throughout the polymer, and interfacial interaction between nanoparticles and host polymers and degree of cure [12,13]. ...
... On the other hand, MMT nanocomposites performed better than all the other nanocomposite samples due to its inherent fire retardancy property, giving rise to enhanced thermal stability of the system [11,24]. Thermal decomposition behavior of MMT modified samples was identical to that of neat samples, despite enhanced thermal properties of MMT. ...
... Many factors, such as molecular weight, residual monomers, and moisture content after polymerization, the type of catalyst used, crystallinity, etc., affecting the thermal stability of PLA were reported. [6][7][8][9][10][11][12][13] A simple way of increasing the thermal stability of the polymers is to prepare composites by using inorganic structures with high thermal stability values. [13][14][15] The most commonly reported inorganic structure used for this purpose is montmorillonite (MMT). ...
... [6][7][8][9][10][11][12][13] A simple way of increasing the thermal stability of the polymers is to prepare composites by using inorganic structures with high thermal stability values. [13][14][15] The most commonly reported inorganic structure used for this purpose is montmorillonite (MMT). [15][16][17] One of the alternative inorganic materials can be perlite, which has a very low-thermal conductivity (0.04-0.06 W/m.K @24 C) and high-thermal stability. ...
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PLA is one of the most frequently used biodegradable polymers. In this work, PLA was synthesized by direct condensation polymerization of lactic acid in the presence of microperlite to obtain enhanced thermal stability of PLA polymer. Molecular weights of the synthesized polymers were determined by GPC. Chemical structure analyses was done by FTIR. The degree of crystallinity was evaluated by DSC and XRD. Thermal stability of polymers was investigated by DSC and TGA. It has been observed that the existence of perlite has significantly increased the crystallinity and degradation temperature, therefore, enhanced the thermal stability of the PLA.
... nanoparticles on chemico-physical and chemico-rheological properties of the polymer is of significant importance. This leads to the development of customized parameters necessary for processing such combination and ultimate curing of the final composite [11,12]. Generally, enhanced properties of polymers by nanoparticles have been attributed to structural morphologies, degree of dispersion throughout the polymer, and interfacial interaction between nanoparticles and host polymers and degree of cure [12,13]. ...
... On the other hand, MMT nanocomposites performed better than all the other nanocomposite samples due to its inherent fire retardancy property, giving rise to enhanced thermal stability of the system [11,24]. Thermal decomposition behavior of MMT modified samples was identical to that of neat samples, despite enhanced thermal properties of MMT. ...
... The ever-increasing commercial importance of polymeric materials has aroused continuous interest in their thermal stability. The kinetic modeling of the decomposition process plays a central role in many of these studies, as it is crucial for an accurate prediction of the material behavior under different working conditions [23][24][25][26][27][28][29][30][31]. A precise prediction requires knowledge of the so-called kinetic triplet: the activation energy, pre-exponential factor, and kinetic model. ...
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Poly(lactic acid) (PLA) and biosourced polyamide (PA) bioblends, with a variable PA weight content of 10–50%, were prepared by melt blending in order to overcome the high brittleness of PLA. During processing, the properties of the melt were stabilized and enhanced by the addition of a styrene-acrylic multi-functional-epoxide oligomeric reactive agent (SAmfE). The general analytical equation (GAE) was used to evaluate the kinetic parameters of the thermal degradation of PLA within bioblends. Various empirical and theoretical solid-state mechanisms were tested to find the best kinetic model. In order to study the effect of PA on the PLA matrix, only the first stage of the thermal degradation was taken into consideration in the kinetic analysis (α < 0.4). On the other hand, standardized conversion functions were evaluated. Given that it is not easy to visualize the best accordance between experimental and theoretical values of standardized conversion functions, an index, based on the integral mean error, was evaluated to quantitatively support our findings relative to the best reaction mechanism. It was demonstrated that the most probable mechanism for the thermal degradation of PLA is the random scission of macromolecular chains. Moreover, y(α) master plots, which are independent of activation energy values, were used to confirm that the selected reaction mechanism was the most adequate. Activation energy values were calculated as a function of PA content. Moreover, the onset thermal stability of PLA was also determined.
... They noted that the addition of bentonite increases the thermal stability of the UP resin. Carrasco and Pagès [2] showed that, at low clay contents (up to 5 wt. %) the addition of clay had no effect on the thermal stability of the epoxy matrix, whereas for higher concentration (10 wt. ...
Article
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The thermal properties of epoxy composites filled with boric acid fine powder at different percentage were studied. Epoxy composites were prepared using epoxy resin ED-20, boric acid as flame-retardant filler, hexamethylenediamine as a curing agent. The prepared samples and starting materials were examined using methods of thermal analysis, scanning electron microscopy and infrared spectroscopy. It was found that the incorporation of boric acid fine powder enhances the thermal stability of epoxy composites.
... The nanocomposites containing 5 % nanoclay had a thermal stability equal to that of the epoxy resin in the absence of nanoclay. An increase of the nanoclay content, up to 10 % determined a slight decrease in the thermal stability of the nanocomposites [61]. ...
Chapter
The chapter coalesces literature studies on recent advances concerning the thermal behavior of different thermosetting blends. The introduction debates the general issue concerning polymer blends, that being the occurrence of phase separation phenomena and lists a series of possibilities to overcome these undesired aspects. The introduction section also presents the most common polymers used as crosslinked scaffolds either individual or for different multicomponent polymeric materials. The subchapters that follow are focused on recent studies on the thermal stability and degradation of thermosetting blends, effect of reinforcement and nanofillers on the thermal stability of thermosetting blends and applications and future trends of thermosetting blends, dealing with the latest issues and trying to reveal solutions.
... Clay mineral based polymer nanocomposites have captured the attention of scientific community due to its emerging high performance applications (Carrado, 2007). Recently epoxy resin reinforced with clay minerals has attracted a significant amount of attention (Andreas et al., 2009;Bluma et al., 2013;Carrasco and Pages, 2008;Li et al., 2012;Sancaktar and Jason, 2011). In this context, the most commonly studied clay minerals are modified layered clays, especially montmorillonite (Mt), due to its high cation exchange capacity (CEC), excellent ability to swell, high aspect ratio and ease with which its surface can be modified . ...
Article
Clay minerals, especiallymontmorillonite (Mt), have emerged as a subject of enormous scientific interest due to their unique atomic structure, high cation exchange capacity, high aspect ratio and large surface area. Clay polymer nanocomposites have established a unique position among technologically importantmaterials because of their extensive and potential applications. Herein we have fabricated cloisite epoxy nanocomposites (CPNs) from diglycidyl ether of bisphenol A (DGEBA) epoxy and modified nanoclay, cloisite 93A using triethylenetetramine (TETA) as a curing agent. The major objective was to examine the static and dynamic mechanical properties and the performance of these CPNs for barrier resistance and thermal stability. Determination of cross link density (CLD) of CPNs by Flory–Rehner equation and activation energy by Coats–Redfern procedure were also a focus of the present study. The cloisite layer exfoliation in CPNs was monitored by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and further corroborated using transmission electron microscopy (TEM). Static mechanical properties of CPN were characterized in terms of tensile and flexural properties. Moreover, dynamic mechanical and thermal properties were evaluated by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) respectively. XRD and TEM revealed that the cloisite distribution in the epoxy matrix is of the partially exfoliated kind at lower level loadings and intercalated at higher loadings. The enhancement of mechanical properties of CPNswas to the level of 15% increase in tensile strength and 23% in flexural strength at very low cloisite loadings. The interfacial interactions brought about by cloisite 93A also benefited the thermomechanical properties to a large extent in the form of improved glass transition temperature and an impressive enhancement in storagemodulus. Results based on equilibrium swelling experiments revealed that a maximum of 61% increase in barrier performance was achieved by the addition of 5 phr (per hundred gramof resin) cloisite. CLDmeasurements demonstrated an 11% increase in CLDat 1 phr cloisite loading. TGA results revealed that cloisite can impart greater thermal stability to pure epoxy. All the propertieswere correlated with the dispersion state of the cloisite in the epoxy resin matrix
... Another important factor is the interaction between clay particles and different polymer molecules to form strong interfacial bonding based on the processing parameters. Studies have shown these factors to significantly affect the microstructure of the epoxy resin [21e23], its curing kinetics [24,25] and finally the sought out properties. Some processing parameters such as curing time and temperature can all be affected due to the effects of the clay on viscosity [23] and mobility of reacting species to form the network chain that determines the properties of the final composite. ...
Article
The primary focus of this study was to evaluate the effects of different montmorillonite nanoclays (MMT) on the thermal stability and degradation of epoxy composites exposed to UV radiation and elevated temperatures. Diglycidyl ether of bisphenol A (DGEBA) epoxy resin, SC15 was reinforced with three different montmorillonite nanoclays, Nanomer� I.28E, Cloisite� 10A and Cloisite� 30B. Thermal properties of modified DGEBA nanocomposites were characterized. Subsequently, neat and nanocomposites were subjected to 500 h of UV radiation and characterized to determine the effects of various nanoclays on the degradation. Addition of nanoclays increased the thermal properties compared to the unmodified composite and better retention of material properties after exposure to UV radiation. Viscoelastic properties increased with addition of nanoclays in both unexposed and UV radiation exposed samples.
... All cure cycle temperatures must be carefully selected; otherwise, detrimental effects may result, even when similar levels of exfoliation and mechanical properties are achieved. However, Carrasco and Pagès [110] found that the thermal decomposition of cured materials was independent of cure temperature but dependent on the clay content. ...
Chapter
Similar to its mechanical and barrier properties, the homogeneous dispersion of silicate layers in a polymer matrix can also enhance the thermal degradation of PNCs. This chapter highlights the effects of different organically modified clays and their dispersion on polymer thermal stability.
... To determine the influence of clay on degradation, a near-onset temperature at a 5% weight loss in TGA thermograms was chosen to characterize the thermal stability, which can avoid temperature variations at the beginning of thermal decomposition. 71 The E a could be obtained from the slope of log β against 1/T at a fixed 5% conversion but under various heating rates (see Fig. 9 (inset) and 10). Fig. 10 presents plots of log β versus 1/T; surprisingly, not all plots displayed linearity over the entire time-temperature range: two degradation mechanisms dependent on the rate of degradation were clearly observed for both neat EGS polymers and for mechanically shear dispersed samples, whereas sonication dispersion method composites showed one, consistent degradation activation energy process over the time-temperature range. ...
Article
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Epoxy-clay nanocomposites derived from renewable soybean oils and organo modified montmorillonite clay were efficiently prepared. Better efficiency was achieved through new, low viscosity, glycidyl esters of epoxidized fatty acids (EGS) were used as epoxy monomer and 4-methyl-1,2-cyclohexanedicarboxylic anhydride as comonomer. Tensile testing showed that 1 wt.-% of clay improved nanocomposite strength and modulus by 22 % and 13 %, respectively. Tensile modulus was increased 34 % by nanocomposite clay without sacrifice of strength. Three types of dispersion technique, mechanical stirring, high speed shearing, and ultrasonication, were carried out to disperse the clay directly into epoxy or anhydride portion of the thermoset system without added solvent. Dispersion of the clay particles into monomer was assessed by means of solubility parameters, optical and scanning electron microscopies and further confirmed by small angle X-ray scattering and transmission electron microscopy. Sonication dispersion of
... Nanocomposites are relatively a new class of composites with at least one phase having a dimension in the vicinity of 1-1,000 nm, and have some unique outstanding properties compared with the conventional microcomposite counterparts. The development and application of nanocomposites have attracted both academic and industrial interests in the last few decades [5][6][7]. A special interest exists for the incorporation of nano-sized particles and fillers of metal oxides, smectite clays, glass fiber, carbon fiber, boron nitride, CaCO 3 , and carbon nanotube dispersed into polybenzoxazine matrices to improve thermomechanical properties [8][9][10][11]. ...
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The present work is a generic study to examine the effects of the glass-to-rubber transition of resin matrix on the friction and wear characteristics of zirconium oxide (ZrO2) reinforced polybenzoxazine nanocomposites, in relation to the content of ZrO2. The thermal and tribological properties of the nanocomposites were measured by dynamic mechanical thermal analysis (DMA) and friction test, respectively. DMA results revealed that the storage modulus and T g values of the nanocomposites increased with increasing ZrO2 content to 4 wt%, due to the exceptional mechanical strength of ZrO2 particles and the interfacial adhesion between ZrO2 and matrix to restrict the segmental motion of polymer. The friction coefficient (COF) values as a function of applied load (50–750 N) for the nanocomposites under testing temperatures (50, 100, 200, 250, and 300 °C) were measured. Comparable to the pure resin, the nanocomposites possessed relatively higher COF values with the increase of applied pressure under varying temperatures, which resulted from the reinforcement of ZrO2. It is noted that the nanocomposites containing 4 wt% ZrO2 occupied relatively higher modulus and glass transition temperature, resulting in better capability to stabilize the friction coefficient and wear rate under the applied conditions. In addition, the friction mechanism of the nanocomposites were proposed based on the experimental and reference results.
... In polymer science, thermal methods of analysis have been used in important applications, and among them, the determination of the kinetic parameters is crucial. For this purpose, thermogravimetry analysis (TG) [2][3][4][5] is a common technique that is widely applied for studying polymer degradation kinetics. ...
Article
The decomposition kinetics of glycerol diglycidyl ether (GDE)/3,3-dimethylglutaric anhydride/nanoalumina composite have been investigated by thermogravimetry analysis under nonisothermal mode. The activation energy, E a, of the solid-state decomposition process was evaluated using the advanced isoconversional method. From the experimental data, the dependence of conversion on temperature and activation energy was constructed allowing calculating the master plots. Our results showed that the decomposition mechanism at temperatures below 400 °C could be fitted by R2 kinetic model with E a = 143 kJ mol−1. The information about the kinetic parameters based only on thermal degradation data has been used for quick lifetime estimation at different temperatures. The Vyazovkin method was also employed to predict the times to reach α = 0.5 at isothermal mode using the activation energy calculated by the advanced isoconversional approaches. Scanning electron microscopy (SEM) analysis was carried out to investigate the fracture surface morphology. It was revealed from the SEM images that the presence of nanoalumina results in reinforcement of GDE matrix.
... Indeed the composite with 7 % of clays shows the temperature peak 7°lower than the pristine resin. These results demonstrate and confirm that the surface modifier of the nanoclay accelerates the cure process, as previously reported [33,34]. It was demonstrated that acidic onium ions (i.e. ...
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Three different organo-modified clays have been incorporated by sonication into a high performance epoxy resin before the cross-linking reaction. The X-ray analysis indicated that, depending on the organoclay type, partially exfoliated and partially intercalated composites have been obtained. As shown by the DSC analysis, the clay addition seems to interact with the cross-linking reaction. The incorporation of organoclay into epoxy increased free volume and micro-voids in the samples. Sorption of water in the composite samples resulted higher than that of the pristine resin, whereas the diffusion coefficient is significantly lower. The lower value of diffusion makes the permeability at ambient conditions lower than the pristine resin. The elastic modulus of the composite sample results higher than that of the pristine resin, especially in the temperature region around the glass transition. The presence of organoclay in epoxy matrix decreased the glass transition temperature, whether the nanocomposites were in a dry or wet condition.
... The protection against corrosion is directly related to the barrier properties of the coating. Although several studies related to the preparation and characterization of polymer/MMT nanocomposites are reported in the literature, few studies have demonstrated improvements in the resistance to corrosion [1,[9][10][11][12][13][14][15][16][17][18], these being mostly related to epoxy-based coatings. ...
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In nanotechnology and nanoscience the development of hybrid (organic–inorganic) nanocompounds has attracted particular attention due to the significant improvement in the properties and the wide diversity of applications compared to conventional composites. In this study, formulations of commercial powder coatings were investigated with 2 and 4% (w/w) of montmorillonite (MMT) in the polyester resin matrix. The coatings were applied by electrostatic spraying on AISI 1008 carbon steel panels. The samples were characterized by TGA, DSC, XRD and TEM. The corrosion performance was evaluated using the salt spray test. Transmission electron microscopy revealed the presence of MMT in the coatings in the exfoliated form. The formulations with MMT presented better performance in terms of the corrosion protection properties.
... TGA is a classic and effective method used to find out the reaction mechanisms and also to estimate the kinetic parameters, such as the activation energy and the pre-exponential factor, for the thermal degradation of polymers (Carrasco and Pages, 2008;Carrasco et al., 2010b). In addition, due to the poor thermal stability of polymers, the effects of additives (nano-fillers, flame retardants) on the thermal decomposition characteristics of polymers have also been widely studied (Bourbigot et al., 2004;Chrissafis et al., 2007;Chatterjee, 2010;Orhan et al., 2011;Zou and Yoshida, 2010). ...
Article
With the development of ultra-fine powder technology, micron polymer materials are widely used, but the thermal decomposition hazard of micron polymers have rarely been studied. In this study, the thermal decomposition of micron Poly (methyl methacrylate) (PMMA) and Polystyrene (PS) with different sizes were studied by thermogravimetry (DTG) technique under nitrogen. Various degradation models including the Friedman method, Kissinger-Akahira-Sunose method and Coats-Redfern method were employed to determine the thermal decomposition mechanisms and kinetics of these polymers. The results showed that the thermal decompositions of micron PMMA and PS under nitrogen atmosphere follow the first-order reaction mechanism. The mean activation energy values of the micron PMMA with sizes of 5 μm, 10 μm and 15 μm were 157 kJ/mol, 170 kJ/mol and 174 kJ/mol, respectively, while values of the micron PS with sizes of 5 μm, 10 μm and 20 μm were 188 kJ/mol, 196 kJ/mol and 206 kJ/mol, respectively. The results indicated that the thermal decomposition stability of the polymer increases with increasing particle size. This work can increase the knowledge of the thermal decomposition of polymers, in particular to understand the influence of particle size on the thermal decomposition characteristics of micron polymers.
... Thermal Gravimetric analysis(TGA) of epoxy nanocomposites in the presence of silane-modified clay nanoparticles was investigated in nitrogen condition. The results showed that modifying the surface of clay nanoparticles increases thermal stability [8]. Thermal stability study of epoxy nanocomposite sample in the presence of carboxyl group modified multiwalled carbon nanotubes showed that surface modification has no effect on thermal stability [9]. ...
Poster
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In this study, the thermal stability and maximum degradation temperature of pure epoxy resin and the effect of 0.5, 1 and 1.5% elastomeric nanoparticles on epoxy resin by thermal gravimetric analysis at different heating rates of 10, 15 and 20 o c/min have been investigated. Evaluation of thermal degradation behavior of epoxy resins and nanocomposites showed that thermal degradation is single-stage. 0.5% nanocomposite increases thermal stability by increasing the heating rate and also reduces the rate of thermal degradation. with increasing heating rate, T50 for epoxy resin and 1% nanocomposite increased, and also for 0.5 and 1.5% nanocomposites initially increased, and then decreased. By adding elastomeric nanoparticles to the epoxy resin matrix, the amount of Tm nanocomposites increased.
... The nanocomposites containing 5 % nanoclay had a thermal stability equal to that of the epoxy resin in the absence of nanoclay. An increase of the nanoclay content, up to 10 % determined a slight decrease in the thermal stability of the nanocomposites [61]. ...
Article
Remaining waste disposal after leather tanning has become a cause of worldwide major concern since conventional disposal methods are not practicable when it comes to tanned leather wastes, such as Cr3+ conversion to Cr6+, hydrogen cyanide, nitrogen oxide and ammonia emissions. In order to bring knew knowledge and know–how into the replacing of the hazardous Cr tanned leather (wet–blue) with the eco–friendly Ti–Al tanned leather (wet–white), one must first comprehend the photodecomposition mechanism of the differently tanned leathers under environmental accelerated aging conditions. It is theferore that this paper deals with comparing the influence of tanning agents on the artificial accelerated aging of the two tanned leathers. Structural changes during UV exposure were monitored by color modification measurements, fourier transform infrared spectroscopy, differential scanning calorimetry, scanning electron microscope equipped with a EDX for elemental analysis and dynamic water vapour sorption measurements. The different crosslinking patterns with tanning agents and irradiation wavelengths generated differences in photodecomposition behavior, occuring predominantly through collagen triple helix denaturation, at 365 nm, and/or cleavage of intermolecular hydrogen bonds and polypeptide chains, at 254 nm. The proteic structures photochemically decomposed through a photo–oxidative mechanism, assisted by the oxygen from air, with the formation of hydroperoxide entities. The wet–white leather was found to be less stable than the wet–blue leather in the UVA region, because of higher tendencies of polypeptide bonds cleavage occuring together with collagen triple helix denaturation. This aspect was also demonstrated by the more intense color modification registered for wet–white leather. These differences in photodegradation patterns may also further help in finding suitable photostabilizers.
... One of the ways to enhance the thermal stability of epoxy polymers is introduction of the special additives into epoxy resins. Various inorganic particles have been used to improve the properties of epoxy resins [6][7][8][9][10][11][12][13]. ...
Article
The particles of natural zeolite in combination with boric acid were incorporated into the epoxy resin ED-20 in order to improve the thermal stability of epoxy polymer. Epoxy resin was cured using polyethylenepolyamine. Characterization of the epoxy composites was carried out by using Fourier transform infrared spectrometry, thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) under flow of air and argon. The thermal behavior of the zeolite/boric acid-based epoxy composites (total percentage 15 mass%) were compared with that of 15 mass% boric acid-based epoxy system and the neat epoxy resin. TG and DSC results revealed that the combination of 5 mass% zeolite and 10 mass% boric acid significantly increased the mid-point temperature and residue, and decreased the maximum decomposition rate of the epoxy composites at the heating.
... In other words, organoclay E þ NC nanocomposites represent higher thermal stability compared to E þ NC-00 composites. Similar results were reported by Isik et al. [50] Improvement in performance of organoclay E þ NC nanocomposite can be attributed to the possible accelerated curing influenced by catalytic effect of nanoclay [51] and thus increased in bulk cross-linking density due to cross-linking among the polymer chains. This behavior was authenticated by researchers. ...
Article
Effect of organoclays on formation of intercalated/exfoliated structure in epoxy–clay nanocomposites at 2 wt% filler loading was carried by spectral analysis. Organoclays were dispersed in epoxy matrix by ultrasonication method. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were carried to characterize function group, morphology of structure, surface and glass transition temperature of the nanocomposite, respectively. FTIR study reveals the presence of epoxy in the galleries of organoclays was confirmed and proves the existence of chemical bonds between the organoclays and the epoxy matrix. XRD analysis indicated that, the interlayer spacing between the clay platelets was increased significantly, thus, the polymer is able to intercalate between the clay layers. As a result, the fully exfoliated structure was found in the E + NC-III nanocomposite while the intercalated structure was obtained in the E + NC-I, E + NC-II, E + NC-IV and E + NC-V nanocomposites. The glass transition temperature measured by TGA was increased with the addition of organoclay in epoxy matrix but decreased for unmodified nanoclay and neat composite. SEM imaging showed good filler dispersion and distribution in E + NC-III nanocomposite, highlighting the very smooth surface due to absence of clay aggregates and no voids.
... Among all these, nanoclay is the most versatile nano filler due to its low cost and ease of dispersion in the resin systems. Many researchers have reported significant improvements in stiffness and strength of pure polymeric matrices with the addition of a small amount of nanoclay particles [9][10][11][12][13][14][15][16]. This is due to the high aspect ratio (200-1000) and modulus (170 GPa) of nanoclay and its ability to offer high amount of surface area (750 m 2 /g) as a filler which restricts the mobility of polymer chains under stress. ...
Article
Full-text available
The mechanical, thermal and ablation properties of carbon phenolic (C-Ph) composites (Type-I) reinforced with different weight percentages of organo-modified montmorillonite (o-MMT) nanoclay have been studied experimentally. Ball milling was used to disperse different weight (wt) percentages (0, 1,2,4,6 wt.%) of nanoclay into phenolic resin. Viscosity changes to resin due to nanoclay was studied. On the other hand, nanoclay added phenolic matrix composites (Type-II) were prepared to study the dispersion of nanoclay in phenolic matrix by small angle X-ray scattering and thermal stability changes to the matrix by thermo gravimetric analyser (TGA). This data was used to understand the mechanical, thermal and ablation properties of Type-I composites. Inter laminar shear strength (ILSS), flexural strength and flexural modulus of Type I composites increased by about 29%, 12% and 7% respectively at 2 wt.% addition of nanoclay beyond which these properties decreased. This was attributed to reduced fiber volume fraction (%Vf) of Type-I composites due to nanoclay addition at such high loadings. Mass ablation rate of Type-I composites was evaluated using oxy acetylene torch test at low heat flux (125 W/cm²) and high heat flux levels (500 W/cm²). Mass ablation rates have increased at both flux levels marginally upto 2 wt.% addition of nanoclay beyond which it has increased significantly. This is in contrast to increased thermal stability observed for Type-I and Type-II composites upto 2 wt.% addition of nanoclay. Increased ablation rates due to nanoclay addition was attributed to higher insulation efficiency of nanolcay, which accumulates more heat energy in limited area behind the ablation front and self-propagating ablation mechanisms triggered by thermal decomposition of organic part of nanoclay.
... Contudo, a concentração destas nanocargas aos polímeros é um fator determinante nas propriedades finais do nanocompósito. Estudos mostraram que a adição de nanocargas em baixa concentração (inferior a 10% em massa) proporciona uma melhora nas propriedades da matriz tais como, propriedades mecânicas, de barreira e principalmente impermeabilidade e inflamabilidade, dentre outras [8,[10][11][12]. ...
... The ever increasing commercial importance of polymeric materials has entailed a continuous interest in their thermal stability. The kinetic modeling of the decomposition process plays a central role in many of those studies, being crucial for an accurate prediction of the materials behavior under different working conditions [18][19][20][21][22][23][24][25][26][27][28][29][30][31]. A precise pre- diction requires knowledge of the so called kinetic triplet, namely, the activation energy, the pre-exponential factor and the kinetic model, f (α). ...
Article
A reactive extrusion-calendering process (REX) was used in order to manufacture square plates with a nominal thickness of 3 mm of poly(lactic acid) (PLA) and its bioblend with acrylonitrile-butadiene-styrene (ABS). During processing, the properties of the melt were stabilized and enhanced by the addition of a styrene-acrylic multi-functional-epoxide oligomeric reactive agent (SAmfE). The general analytical equation has been used in order to evaluate the kinetic parameters of the thermal degradation of PLA-REX, ABS and its bioblend with a weight content of 70/30. Various empirical and theoretical solid-state mechanisms have been tested to elucidate the best kinetic model. In order to reach this goal, activation energy values were calculated by means of the Kissinger-Akahira-Sunose method. On the other hand, the standardized conversion functions have been constructed. Given that it is not always easy to visualize the best accordance between experimental and theoretical values of standardized conversion functions, a recently proposed index has been determined to quantitatively support our findings relative to the best reaction mechanisms. It has been demonstrated that the best mechanism for the thermal degradation of PLA-REX and ABS was the random scission of macromolecular chains. The bioblend thermal degradation occurred in two steps: the first step (α < 60%) took place through an R2 mechanism whereas the second step (α > 75%) did it according an F3 mechanism. Moreover, y(α) master plots have also been used in order to confirm that the selected reaction mechanisms were adequate.
... The nanocomposites containing 5 % nanoclay had a thermal stability equal to that of the epoxy resin in the absence of nanoclay. An increase of the nanoclay content, up to 10 % determined a slight decrease in the thermal stability of the nanocomposites [61]. ...
Chapter
In the recent decades, bio-based polymers have gained increasing interest, especially for composite materials. These polymers and their respective monomers are derived from renewable resources, being thermoplastics or thermosetting resins which are biodegradable or non-biodegradable. Thermosettings are strong, rigid polymer materials and cannot be easily processed by melting after their hardening. At present, thermosetting resins are obtained using highly toxic and volatile petrochemicals, which require human and environmental safety monitoring. Considering the wide range of diverse renewable monomers available, vegetable oils (VOs) are especially well-suited when it comes to the synthesis of thermosetting resins due to their carbon-carbon double bonds, highly desirable for this type of application as these unsaturated bonds can be chemically modified in order to increase reactivity toward further polymerization. Thus, epoxidation, which consists of introducing a single oxygen atom to each non-saturated bond to yield in an epoxidic cycle, is a simple, effective method to modify these VOs. The resulted thermosetting resins exhibit improved toughness and environmental-friendly behavior. VOs, especially soybean oil which is abundant and cheap, are typically mixtures of unsaturated fatty acids with numerous bonds that can be easily converted into the more reactive oxirane rings through the reaction with peracids or peroxides. The present chapter focuses on composites obtained from epoxidized vegetable oils (EVOs) and epoxy resins and their properties in correlation with their envisaged applications.
... Recent researches found that the use of clay concentrations up to 10% [12,15,16] produces significant improvements in the thermal, mechanical and chemical properties of powder coatings [13,[15][16][17][18][19] . Thus, the objective of this work is to produce, apply and characterize a hybrid powder coating by separately adding mica muscovite and MMT 30B at concentrations of 2, 4 and 6 phr, evaluating the thermal, mechanical, chemical and morphological properties resulting from the addition of these clay minerals. ...
Article
Full-text available
Abstract Powder coatings have been used for coating metal substrates in industrial applications. The incorporation of nanofillers as muscovite mica and montmorillonite (MMT) can improve the properties of the coatings. The objective of this study is to develop, apply and characterize a hybrid powder coating (30% epoxy/70% polyester) adding nanofillers in concentrations of 2, 4 and 6 phr separately in a twin screw extruder. The characterization of the coatings was performed by thermal, mechanical and chemical analysis. The incorporation of clay into the polymer increased the surface roughness resulting in a diffuse reflection of incident light and on a gloss reduction. The muscovite mica presented a lamellar structure, constituted by a set of overlapping parallel plates. The morphology analysis showed that the MMT presented irregular agglomerates resulting in inferior mechanical properties to coatings with muscovite mica. In the salt spray test, all samples showed high corrosion protection, around 850 hours.
Article
Full-text available
An enhanced general analytical equation has been developed in order to evaluate the kinetic parameters of the thermal degradation of poly(lactic acid) (PLA) at various linear heating rates and at constant rate conditions. This improvement consisted of replacing the n-order conversion function by a modified form of the Sestak-Berggren equation f(α) = c(1−α)nαm, which led to better adjustment of experimental data, and also adequately represented the conventional mechanisms for solid-state processes. The kinetic parameters so obtained have been compared to those determined by conventional differential and isoconversional methods. Given that the thermal degradation of PLA has been argued to be caused by random chain scission reactions of ester groups, the conversion function (α) = 2(α1/2−α), corresponding to a random scission mechanism, has been tested.
Article
Full-text available
The study of degradation kinetics of epoxy nanocomposites is very important because it can determine the temperature range and life of the system. Degradation kinetics modeling has become widely used as an essential tool for engineers to predict the thermal durability of materials before they are used in industry, leading to reduced costs and product development, manufacturing costs, time and quality of the designed product. Dispersion and distribution of clay nanoparticles in epoxy resin matrix are two important factors in the physical and mechanical properties of epoxy nanocomposites .Also, the inhibitory properties of clay nanoparticles or layered silicates against hydrogen and oxygen, as well as the type of structure can cause thermal stability of epoxy resin. Modification of the surface of clay nanoparticles can delay the degradation reaction of epoxy nanocomposites. The percentage of addition of clay nanoparticles to the epoxy resin matrix and the type of production process are two important factors in investigating the degradation kinetics of epoxy resin in the presence of clay nanoparticles. In this study, the effect of clay nanoparticles and modified clay nanoparticles on the degradation kinetics of epoxy resin and investigation of different models of degradation kinetics, activation energy, thermogravimetric analysis and weight loss percentage, and the effect of different types of clay nanoparticles on the degradation kinetics of epoxy resin have been reported.
Article
In this work, unsaturated polyester/bentonite nanocomposites were obtained and characterized. The bentonite used was unmodified and with different chemical treatments. The effects of these different chemical modifications (cation exchange reactions with quaternary ammonium and phosphonium salts) of this clay as well as the effect of clay content on the thermal, barrier (water absorption), mechanical (flexural) and dynamic-mechanical properties of unsaturated polyester matrix were analyzed. The results clearly show that the chemical modifications of the clay cause a desired effect on its final properties improving the performance of the nanocomposites. The enhancements could be directly related to the dispersion of the clay inside the matrix, as shown by transmission electron microscopy.
Article
Using dynamic finite simulations, we investigate how the friction coefficient of ZrO2/polymer nanocomposite depends on the sliding speed. The load-dependent model we developed corresponds to common friction systems, where the friction couples are sliding under fixed load for various speeds. Here, we study the effect of the sliding speed on the contact distance between two contacting bodies. In accordance with experimental observations and theoretical arguments, we find the contact distance increased with the sliding speed. We show that the dependence of the reaction force on sliding speed can be rationalized by assuming that the frequency dependence of the polymer chains relaxation times is affected by the damping effects of contact stress. By investigating the energy dissipation, we show how the friction coefficient is affected by the sliding speed. The deformation volume and relaxation times decreased with the increasing sliding speed, which result in the decreasing of energy dissipation. Then, the work in pushing the top cylinder across the bottom plateau decreases, results in a reduction of the mean horizontal reaction force and friction coefficient.
Conference Paper
Effects of UV radiation and associated elevated temperature on properties of polymeric composites have been well documented, limiting the scope of their usage in outdoor applications. In order to improve on this limitation, current study focused on incorporating nanoparticles in polymers to delay the deleterious effects of UV radiation. Samples were fabricated and cured to 80% conversion (partially cured) based on isothermal cure study. Influence of 1, 2 and 3 wt. % loading of montmorillonite nanoclay on the cure behavior and development of physical properties of these composites were evaluated. Results of the study revealed that for optimization of modified epoxy composite properties a different curing cycle was necessary due to interaction of different amounts of nanoclay and epoxy molecules. Fabricated samples infused with 1, 2 and 3 wt. % montmorillonite nanoclay were exposed to 1500 hours of continuous UV radiation, where effects of UV radiation on thermal and thermo-mechanical properties were studied and compared to identical set of fabricated samples using manufacturers' recommended cycle (MF-fully cured). Addition of nanoclay increased the viscoelastic properties, and at the end of the study, storage modulus and activation energy of decomposition of partially cured samples evolved over exposure time, while fully cured samples degraded over the same period. Samples cured to 80% showed delayed UV radiation degradation effects.
Article
Fly ash, inexpensive and not eco-friendly material, is the residue from the coal burning in thermal power stations. If ways can be found to use it, it will facilitate applications for the ash materials and simultaneously reduce the pollution. In this study, silane-grafted ultrafine fly ash (S-UFA) was used as a reinforcing filler in poly(lactic acid) (PLA) to prepare a series of PLA/S-UFA composites. The tensile strength of PLA/S-UFA composites increases with the increase of S-UFA content when less than 20 wt %; after a loading fraction greater than 30 wt %, the tensile strength of the composites decreases with the increasing S-UFA weight fraction. The morphology of PLA/S-UFA composites was observed by scanning electron microscope (SEM). X-ray diffraction (XRD) analysis was applied to investigate the crystal structure of S-UFA and the composites. The thermal properties of these composites were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The TGA results showed that the thermal stability of PLA/S-UFA composites slightly decreased with the increasing S-UFA loading fraction.
Article
One-step reactive extrusion-calendering process (REX-calendering) has been used in order to obtain sheets of 1 mm from poly(lactic acid) modified with a styrene-acrylic multifunctional oligomeric agent. In a preliminary internal mixer study, torque versus time has been monitored in order to ascertain chain extender ratios and reaction time. Once all the parameters were optimized, reactive extrusion experiments have been performed. An enhanced general analytical equation has been developed in order to evaluate the kinetic parameters of the thermal degradation of PLA sheets manufactured by reactive extrusion. This improvement has consisted of replacing the n-order conversion function by a modified form of the SestakeBerggren equation f(a) ¼ c (1 � a)nam that led to a better adjustment of experimental data and also adequately represented the conventional mechanisms for solid-state processes. The kinetic parameters so obtained have been compared to those determined by conventional differential methods and n-order reaction kinetics. Given that the thermal degradation of PLA has been argued to be caused by random chain scission reactions of ester groups, the conversion function f(a) ¼ 2 (a1/2 � a), corresponding to a random scission mechanism for L ¼ 2 (as well as other functions for L values up to 8), has been tested. Once optimized the kinetic model, the thermal degradation kinetics of sheets obtained by REX-calendering process was compared to that of conventional sheets and polymer matrix.
Article
The present work reports the influence of the MMT content in the dispersing and exfoliating method of the nanofillers on non-isothermal cure behavior, morphology and solid viscoelastic properties of the epoxy resin/MMT systems were determined. The curing kinetics of the polymer systems are controlled by random and diffusion mechanisms. The amount of MMT content does not change the type of mechanism, but it has influence on the reaction enthalpy values and peak. The nanocomposite morphology indicated that the increase in mixing time caused an improvement in the level of dispersion of the clay. The use of ultrasonication decreases the dispersion of MMT in the epoxy matrix. The amount of MMT influences the delamination and uniformity of the matrix and consequently, the systems with 5 wt.% of MMT exhibited greater homogeneity than those containing 3 wt.%. The nanocomposites prepared without ultrasonication showed two peaks in tan δ, which might be related to the consequent formation of regions with different levels of clay distribution and heterogeneities. The storage modulus of the obtained nanocomposites decreased compared to the epoxy matrix. This may be related to the contribution of the interphase region, side reactions, and plasticizing effects of the organic modifier of the clay.
Chapter
Increased use of fiber reinforced polymeric composites in an outdoor environment has led to questions concerning their environmental durability, particularly as related to ultraviolet (UV) radiation, moisture, and temperature exposure. This chapter describes the effects of UV and UV radiation + condensation (UC) on the static and dynamic compressive properties of unidirectional glass/epoxy composites. The samples were manufactured using an infusion process with and without nanophased epoxy and exposed to UV radiation and UC conditioning for 5, 10, and 15 days respectively. Nanophased epoxy was prepared with 1 wt%and 2 wt% nanoclay. Static compression tests were carried out using MTS test system under displacement control mode at a crosshead speed of 1.27 mm/min. Dynamic compression tests were carried out using modified Split Hopkinson Pressure Bar (SHPB) at different strain rates. The compressive strength and stiffness were evaluated as functions of strain rate. Results of the study showed that samples lost weight when exposed to UV radiation, whereas they gained weight when exposed to UC conditioning. Weight gain or loss was lower for nanophased composites when compared to neat samples. Static and high strain compressive properties reduced for all the nanophased samples when compared with room temperature samples. However, the loss in compressive properties was lowest in nanophased composites with 2 wt% nanoclay.
Book
Clay-Containing Polymer Nanocomposites covers everything from fundamental understanding to real applications of clay-containing polymer nanocomposites, including environmental considerations. The book's coverage of fundamentals and generalities, in addition to in-depth coverage of polymer layered silicate nanocomposites, make it a valuable companion for beginners in the field as well as more seasoned researchers. This book provides a rare coherent approach to this class of materials. This title is ideal for polymer and material scientists, researchers, and engineers, including under- and post-graduate students who are interested in this exciting field of research. This book will also help industrial researchers and R&D managers who want to bring advanced polymeric material based products into the market.
Article
In this work, the design and manufacture of functional composite coatings on plastic substrates were investigated. In particular, graphene nano-platelets and graphene derivatives, that is, graphene reduced oxide modified by amino organo-silane compounds, were used to reinforce a radiation curable cycloaliphatic epoxy resin. The resulting composite materials were deposited on polycarbonate. The chemical structure of the coatings was characterized by FT-IR. Physical properties of the coatings, especially thermal stability, were evaluated by differential scanning calorimetry. Chemical endurance of the coatings was tested by dipping in acidic, saline and basic environments. Special protocols were, then, developed to evaluate the friction of the coatings as well as their potential to prevent the adhesion of contaminants on their surface (i.e., anti-soiling properties). Mechanical performance of the coatings was evaluated by pencil test (pencil hardness), progressive load scratch test (scratch hardness). Graphene-reinforced cycloaliphatic epoxy resins were found to ensure good combination of physical, chemical and mechanical properties. Therefore, they can be considered attractive functional materials to deposit on advanced plastic substrates.
Chapter
This chapter deals with a brief account of thermal degradation of polymer-based blends, composites and nanocomposites. Different synthesising, preparation and characterisation methods of thermal degradation of polymer-based blends, composites and nanocomposites are discussed. Finally the applications, new challenges and opportunities for these thermal degradation of polymer-based blends, composites and nanocomposites are discussed.
Article
The wide range of applications associated with nanocomposites is due to their improved properties when compared to conventional composites. In this study, commercial epoxybased powder coatings were formulated with 2 and 4% (w/w) of an organically modified montmorillonite (OMMT) by incorporation in the melt state (extrusion). These composites were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and X-ray diffraction (XDR). The thermal behavior and stability of the epoxy nanocomposites were studied by TGA and DSC. The nanoparticle structure within the polymer matrix was analyzed by XRD and TEM. A predominantly exfoliated structure was observed by TEM, which was confirmed by XDR analysis. The study demonstrated that the nanoclay increases the glass transition and crosslinking temperatures and also enhances the thermal stability of the coating.
Article
Clay minerals, especially montmorillonite (Mt), have emerged as a subject of enormous scientific interest due to their unique atomic structure, high cation exchange capacity, high aspect ratio and large surface area. Clay polymer nanocomposites have established a unique position among technologically important materials because of their extensive and potential applications. Herein we have fabricated cloisite epoxy nanocomposites (CPNs) from diglycidyl ether of bisphenol A (DGEBA) epoxy and modified nanoclay, cloisite 93A using triethylenetetramine (TETA) as a curing agent. The major objective was to examine the static and dynamic mechanical properties and the performance of these CPNs for barrier resistance and thermal stability. Determination of cross link density (CLD) of CPNs by Flory-Rehner equation and activation energy by Coats-Redfern procedure were also a focus of the present study. The cloisite layer exfoliation in CPNs was monitored by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and further corroborated using transmission electron microscopy (TEM). Static mechanical properties of CPN were characterized in terms of tensile and flexural properties. Moreover, dynamic mechanical and thermal properties were evaluated by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) respectively. XRD and TEM revealed that the cloisite distribution in the epoxy matrix is of the partially exfoliated kind at lower level loadings and intercalated at higher loadings. The enhancement of mechanical properties of CPNs was to the level of 15% increase in tensile strength and 23% in flexural strength at very low cloisite loadings. The interfacial interactions brought about by cloisite 93A also benefited the thermomechanical properties to a large extent in the form of improved glass transition temperature and an impressive enhancement in storage modulus. Results based on equilibrium swelling experiments revealed that a maximum of 61% increase in barrier performance was achieved by the addition of 5 phr (per hundred gram of resin) cloisite. CLD measurements demonstrated an 11% increase in CLD at 1 phr cloisite loading. TGA results revealed that cloisite can impart greater thermal stability to pure epoxy. All the properties were correlated with the dispersion state of the cloisite in the epoxy resin matrix.
Chapter
The rapidly-developing nanotechnology and nanoscience in recent years, led to an increase of polymer-based nanocomposites focused on the enhancement of specific properties. Among these, the effect of different nanoparticles, their dispersion and the use of modifiers on the polymer thermal stability are studied. New materials with pre-tailored properties can be manufactured by the incorporation nanoreinforced materials and by the knowledge of the steps involved in their obtention. So, this work focuses on the thermal degradation study of thermosetting nanocomposites materials, evaluating their effect in thermal stability and in thermal degradation steps. Also, the thermal applications of these nanocomposites were also evaluated and the challenges to the nanocomposites field in the following years were also discussed.
Article
A reactive extrusion-calendering process was used in order to manufacture sheets with a nominal thickness of 1 mm of poly(lactic acid) and its nanocomposite with 2.5% of an organo-modified montmorillonite. During processing, the properties of the melt were stabilized and enhanced by the addition of 0.5% of a styrene-acrylic multi-functional-epoxide oligomeric reactive agent. The general analytical equation has been used in order to evaluate the kinetic parameters of the thermal degradation of poly(lactic acid) obtained by reactive extrusion and its nanocomposite. Various empirical and theoretical solid-state mechanisms have been tested to elucidate the best kinetic model. In order to reach this goal, master plots have been constructed by means of standardized conversion functions. Given that it is not always easy to visualize the best accordance between experimental and theoretical values of standardized conversion functions, a new index has been developed to quantitatively discern the best mechanism. By doing that, it has been possible to determine the right activation energy of the thermal degradation. It has been demonstrated that the best theoretical mechanism was the random scission of macromolecular chains within the polymer matrix. This was also in accordance with an empirical kinetic model based on an autocatalytic kinetic model. The presence of montmorillonite nanoparticles has been beneficial and has enhanced the thermal stability of poly(lactic acid).
Article
The variation of physical and chemical structure induced by processing of PLA and PLA/montmorillonite nanocomposites in a pilot plant has been analyzed in this paper. The degree of crystallinity has been evaluated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD) and FTIR spectroscopy. It was found that mechanical processing led to a quasi disappearance of PLA crystal structure, whereas it was recovered after annealing. FTIR spectroscopy has allowed to detect chemical interactions between components in nanocomposites. The thermal stability of the various materials (PLA and its nanocomposites) has been established by calculating various characteristic decomposition temperatures, as determined from TGA thermograms.
Article
In this study, the effects of multi-walled carbon nanotubes (MWCNT), and its hybrids with iron oxide (Fe2O3) and copper oxide (CuO) nanoparticles on mechanical characteristics and thermal properties of epoxy binder was evaluated. Furthermore, simultaneous effects of using MWCNT with TiO2 as pigment and CaCO3 as filler for epoxy composites were determined. To investigate effects of nano- and micro-particles on epoxy matrix, the samples were evaluated by TGA and DTA. It was found that the hybrid of MWCNT with nano metal oxides caused considerable increment in the tensile and flexural properties of epoxy samples in comparison to the single MWCNT containing samples at the same filler contents. Significant improvement in the thermal conductivity of epoxy samples was obtained by using TiO2 pigment along with MWCNT. The TiO2 pigment also caused considerable improvement in mechanical properties of the epoxy matrix and the MWCNT containing nanocomposite. The best mechanical and thermal properties of epoxy nanocomposites were obtained at 1.5 wt % of MWCNT and 7 wt % of TiO2 that it should be attributed to particle network forming of the particles which cause better nano/micro dispersion and properties.
Article
The kinetics of the thermal decomposition of processed poly(lactic acid) has been studied and compared to that of raw material. Processing consisted of two different industrial processes: 1) Injection (with or without further annealing); 2) Extrusion followed by injection (with or without further annealing). For this study, an integral method (based on the general analytical solution), differential methods (based on the first conversion derivative and on the 2nd derivative) and special methods have been used. On the other hand, a method based on the maximum decomposition rate has been considered. By doing that, the kinetic parameters (reaction order, frequency factor and activation energy) have been determined. It has been demonstrated that there was only one first-order reaction for the entire conversion range. A new equation (based on the second conversion derivative plot as a function of temperature) was developed allowing the calculation of the reaction order. This method quantifies peak areas (and not peak heights, as reported by Kissinger). It is very useful because it considers both peak shape and width. Activation energy, as determined by using the general analytical solution, was 318 kJ/mol for unprocessed poly(lactic acid) whereas it was 280 ± 5 kJ/mol for processed materials. All the processed materials had approximately the same thermal stability (T5 = 333.0–335.8 °C, at 95% confidence level), which was slightly lower than that of unprocessed materials (T5 = 337.5 °C). PLA melting (during extrusion and injection) was responsible for depolymerization reactions (the small molecules formed during melting processes can volatilize readily).
Article
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The influence of the resin/diamine ratio on the properties of the system diglycidyl ether of bisphenol A (BADGE n=0/m-xylylenediamine) (m-XDA) was studied. Variation of this ratio resulted in significant effects on the cure kinetics and final dynamic mechanical properties of the product material. The study was made in terms of storage modulus (E′), vss modulus (E″) and molecular mass between cross-links (Mc) at different ratios. Two geometries (cylindrical and rectangular) were considered. The influence of temperature was studied through the activation energy (Ea>), which depends on the epoxy/amine ratio and the geometry of the samples. Glass transition temperatures (Tg>) and glass transition temperatures for thermosets with null degree of conversion (Tgo>) were determined by DSC. Tg> decreases when amounts of curing agent greatly in excess of the stoichiometric composition were used.
Article
Full-text available
The ageing of HDPE/cellulosic fiber composite exposed to drastic weather and the percentages of cellulosic fibers are responsible for some changes in the crystallinity of component matrix (HDPE). Two types of samples have been evaluated during different periods of time (up to 90 days). One in which cellulosic fibers have not been treated and another in which fibers have been given a treatment with a coupling agent, silane type, which favours the fiber adhesion to the matrix. Two instrumental analysis techniques have been used to determine the crystallinity changes of HDPE: Fourier Transform Infrared spectrophotometry (FTIR) and Differential Scanning Calorimetry (DSC).
Article
Full-text available
Amylose content, crystallinity, morphology and the kinetic of thermal degradation to starches from different botanical origins are described based on XRD, SEM, DSC and TG/DTG curves. Applying the non-isothermal isoconversional Wall–Flynn–Ozawa method on the TG/DTG curves average activation energy (0.10 ≤ α ≤ 0.70) E = 144.1 ± 9.8, 171.6 ± 14.6, 158.3 ± 7.4 and 159.4 ± 15 kJ mol−1 could be obtained for thermal degradation of corn, rice, potato and cassava starches, respectively. From E values and the generalized time θ, the Sesták–Berggren (SB) in which f(α) = αm(1 − α)n seems to be most suitable kinetic model in describing physicogeometrically the thermal degradation for the samples regardless of its botanical origins. The determination of the kinetic exponents m and n allows to obtain the pre-exponential factor (0.2 ≤ α ≤ 0.8) ln A = 8.8, 10.4, 9.2 and 8.9 min−1 for corn, rice, potato and cassava starches, respectively. There were not significant differences between values of the kinetic triplet of the starches, indicating that, despite structural differences, these had little influence on the thermal degradation process of the starches.
Article
Diprotonated forms of polyoxypropylene diamines of the type α,ω-[NH3CHCH3CH2(OCH2CHCH3)xNH32+ with x=2.6, 5.6, and 33.1, have been intercalated into montmorillonite and fluorohectorite clays and subsequently evaluated for the formation of glassy epoxy–clay nanocomposites. The intercalated onium ions functioned concomitantly as a clay surface modifier, intragallery polymerization catalyst, and curing agent. Depending on the chain length of the diamine, different orientations of the propylene oxide chains were adopted in the clay galleries, resulting in basal spacings from ∼14 Å (lateral monolayer, x=2.6) to ∼45 Å (folded structure, x=33.1). The initial clay basal spacings were correlated with the formation of intercalated and exfoliated clay–epoxy nanocomposites with improved mechanical properties and high thermal stabilities. In comparison to clay–monoamine intercalates, the use of diamine intercalates greatly reduced the plasticizing effect of the alkyl chains on the polymer matrix, resulting in improved mechanical properties while at the same time reducing the cost and time needed for nanocomposite fabrication.
Article
In this study, we examined the thermal decomposition of polyhydroxyalkanoates (PHAs) such as the homopolymer poly(3-hydroxybutyrate) and the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate). They are biodegradable polymers that can replace plastics produced from nonrenewable resources, such as polypropylene. The biopolymers we analyzed were commercial PHAs [obtained by means of pure cultures, with hydroxyvalerate (HV) contents of 0 and 10.4 mol %] and biopolymers produced in our laboratories (by means of an enriched activated sludge at two different organic loads, 8.5 and 20 gCOD/L, with a HV content of 20 mol %). To process these biopolymers, it is important to know their thermal stability. For this reason, thermal degradation in air by means of dynamic thermogravimetry (TG) was carried out. The TG data were adjusted to the nth-order general analytical equation to evaluate the best order of the reaction, the temperatures of the onset and end of thermal decomposition, and the kinetic parameters. The latter were also calculated by means of other integral and differential methods and compared to those obtained by the general analytical solution. Finally, the influence of the preparation method (pure and mixed cultures and HV content within the biopolymer) on thermal stability was analyzed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2111–2121, 2006
Article
This article studies the influence of the heating rate and sample weight on the thermal decomposition of polystyrene (first-order kinetics). For this purpose, the kinetic parameters (i.e., frequency factor and activation energy), variables at the maximum decomposition rate (such as conversion, reaction rate, and temperature), as well as some characteristic temperatures have been determined for a series of experiments where the heating rate varies (0.5–11.5 K/min) and also, the sample weight (6.0–25.1 mg). Some mathematical equations have been developed that allow: (1) evaluation of the activation energy of thermal decomposition by different ways and comparing the results obtained; (2) relating different parameters between themselves, such as the heating rate with the temperature at the maximum decomposition rate or the frequency factor with the heating rate and sample weight. Finally, some theoretical explanations of the variation of thermal and kinetic parameters have been proposed. © 1996 John Wiley & Sons, Inc.
Article
The transcendent technologies include nanotechnology, microelectronics, information technology and biotechnology as well as the enabling and supporting civil infrastructure systems and materials. These technologies are the primary drivers of the 21st century and the new economy. Mechanics and materials are essential elements in all of the transcendent technologies. Research opportunities, education and challenges in mechanics and materials, including nanomechanics, carbon nanotubes, bioinspired materials, coatings, fire-resistant materials as well as improved engineering and design of materials are presented and discussed in this paper.
Article
The optimum pyrolytic conditions for thermosetting epoxy resin samples were first empirically studied. On the basis of the optimized pyrolytic conditions, epoxy prepolymers and epoxy resin samples cured with and without curing agents, such as diamine and dicarboxylic acid anhydride, were studied using high-resolution pyrolysis-gas chromatography. In addition to some intact prepolymer molecules, various degradation products characteristic of the prepolymers, up to diglycidyl ether of bisphenol A, were detected on the pyrograms of the prepolymers. On the other hand, various phenols characteristic of the prepolymers and a variety of pyrolyzates characteristic of the reacted curing agents, including intact dicarboxylic acid anhydride, were observed on the programs of the cured resin samples. The potential of this technique for studying the curing process of the epoxy resins is discussed.
Article
Epoxy resin prepared from p-aminophenol was cured with six different curing agents, viz. diaminodiphenyl sulfone, diaminodiphenyl methane, diaminodiphenyl ether, benzidine, m-phenylene diamine and diethylenetriamine. Kinetics of thermal degradation of the cured epoxy resins were studied by thermogravimetry in a static air atmosphere at a heating rate of 10°C min−1. The effect of the structure of the curing agent on the thermal stability of the cured epoxy resins was investigated on the basis of temperature characteristics such as initial decomposition temperature, temperature of half volatilization and the integral procedural decomposition temperature, as well as the kinetic parameters. The thermal degradation reactions were found to proceed in a single step having an activation energy in the range 90–122 kJ mol−1. They were first-order reactions.
Article
Diprotonated forms of polyoxypropylene diamines of the type alpha,omega- [NH3CHCH3CH2(OCH2CHCH3)xNH32+ with x=2.6, 5.6, and 33.1, have been intercalated into montmorillonite and fluorohectorite clays and subsequently evaluated for the formation of glassy epoxy-clay nanocomposites. The intercalated onium ions functioned concomitantly as a clay surface modifier, intragallery polymerization catalyst, and curing agent. Depending on the chain length of the diamine, different orientations of the propylene oxide chains were adopted in the clay galleries, resulting in basal spacings from ~14 Å (lateral monolayer, x=2.6) to ~45 Å (folded structure, x=33.1). The initial clay basal spacings were correlated with the formation of intercalated and exfoliated clay-epoxy nanocomposites with improved mechanical properties and high thermal stabilities. In comparison to clay-monoamine intercalates, the use of diamine intercalates greatly reduced the plasticizing effect of the alkyl chains on the polymer matrix, resulting in improved mechanical properties while at the same time reducing the cost and time needed for nanocomposite fabrication.
Article
The curing reactions of liquid epoxy resin based on 1,1'-bis(4-hydroxyphenyl) cyclohexane (DGEBC) with different amine curing agents have been investigated by differential scanning calorimetry. The overall kinetics of curing have been found to follow a simple Arrhenius-type rate-temperature dependence, having an average overall activation energy of 40–97 kJ mol−1. The kinetics of thermal degradation of the cured epoxy resins were studied by thermogravimetric analysis in static air atmosphere at a heating rate of 10°C min−1. The thermal degradation reactions were found to proceed in a single step with an activation energy in the range 30–56 kJ mol−1.
Article
The thermal behavior of epoxy maleate of bisphenol A (EMBA) was investigated by thermogravimetry (TG), derivative thermogravimetry (TDG) and infrared (IR) spectroscopy, in the range of temperatures within 20 and 500°C. The kinetic analysis was carried out using both the “DTG sim” computer software for simulation of DTG curves and the dynamic method for the thermal degradation of polymers at any time. Both TG and DTG curves recorded for 5.5, 9.0, 12.0 and 16.0°Cmin−1 heating rates show three main decomposition stages. The kinetical parameters were evaluated taking into consideration the maximum rate of decomposition (Tmax) as the reference element. The apparent activation energy (Ea) values determined using the dynamic method are 49kJmol−1 for the first stage of decomposition, 106kJmol−1 for the second stage and 159kJmol−1 for the third stage. The kinetical parameters determined in dynamic conditions and data obtained by IR spectroscopy postulate that the thermal degradation mechanism of EMBA involves a scission of the esteric liaison with CO2 elimination in the first stage. This stage is characterized by Tmax values placed between 114 (5.5°Cmin−1 heating rate) and 142°C (16.0°Cmin−1 heating rate). In the second stage with Tmax values between 316 and 343°C, new scissions of the main polymeric chain take place. The third stage, with Tmax values between 363 and 386°C is characterized by the presence of parallel competitive reactions of the polymeric fragments formed in the first and the second stage of degradation. The main important products evolved in the third stage are water and higher phenols.
Article
The diffusive, calorimetric and thermal degradation behavior of different epoxy-amine systems was investigated during water sorption at different temperatures (23, 40 and 70°C). Experimental results showed that the water absorption at these temperatures fitted well to Fick’s law. Influence of water immersion during different periods of time on the glass transition temperatures was studied by differential scanning calorimetry. Thermal degradation of saturated samples was studied by thermogravimetric analysis. Dependence on the selected curing cycle was also checked.
Article
This paper investigates the relationship between cure temperature, morphology, and mechanical properties of di-, tri-, and tetrafunctional high-performance, epoxy layered-silicate nanocomposites. Wide-angle X-ray analysis (XRD) was carried out at different stages of cure to monitor organoclay exfoliation kinetics. It was found that some (small) degree of conversion was required to obtain significant intercalation. The nanocomposite morphology was also probed using transmission electron microscopy, XRD, and positron annihilation lifetime spectroscopy. The bifunctional DGEBA resin gave better exfoliation than the resins of higher functionalities. This is attributed to better catalysis of the intragallery reaction by the organo-ions which reside within the galleries. Higher cure temperatures were also found to improve clay delamination and simultaneously increased toughness and modulus in case of the DGEBA- and TGAP-based materials. Free volume properties did not vary significantly between resins or with cure temperature and generally followed the rule of mixtures, although there was a suggestion that the presence of clay leads to increased free volume. This was consistent with decreased glass transition temperatures upon addition of layered silicate, ascribed to disruption, and decreased cross-link density in interfacial regions of clay and epoxy matrix.
Article
Differential scanning calorimetry in dynamic and isothermal modes was used to study the cure kinetics of the commercial epoxy system Narmco 5208, whose main components are bis[4-(diglycidylamino)phenyl]methane and bis(4-aminophenyl) sulfone. The data were analyzed in terms of a new mechanistic approach described in the preceding paper. The treatment explicitly takes into account both the epoxide-amine reactions and the subsequent etherification reaction. The kinetics can be completely described in terms of three rate constants, which obey the Arrhenius relationship. Excellent agreement with the experimental data is obtained if the etherification reaction is assumed to be first order with respect to the concentrations of epoxide groups, hydroxyl groups, and the tertiary amine groups formed in the epoxide-amine reaction. This model applies over the whole range of conversion up to the point where the resin vitrifies and the reaction becomes diffusion-controlled. The effect of the diffusion control is described very well by an approach based on simple equations proposed in the literature. Altogether, the model allows accurate prediction of the degree of conversion over the whole range of cure and over the temperature range 160-200-degrees-C, which covers the usual curing conditions. Although the rate constants derived are specific to Narmco 5208, the model itself is generally applicable to other epoxy amine systems.
Article
The role of various quaternary ammonium-modified montmorillonites in epoxy/diamine nanocomposite formation is examined to further refine the criteria for selection of organic modifiers necessary to enable fabrication of thermoset resins containing nanoscale dispersions of inorganic phases. Utilization of a hydroxyl-substituted quaternary ammonium modifier affords flexibility to combine both catalytic functionality, which increases the intragallery reaction rate, with enhanced miscibility toward both reagents. The rheological implications of these processing techniques are discussed with regards to using thermoset nanocomposites as a matrix in conventional fiber reinforced composites. The use of a low-boiling solvent to enhance mixability and processability of the initial mixtures is shown not to alter the structure or properties of the final nanocomposite. Also, the use of autoclave techniques enabled fabrication of high-quality specimens containing up to 20 wt % organically modified layered silicate (OLS). Finally, exfoliated and partially exfoliated epoxy/diamine nanocomposites were produced with enhanced heat-distortion temperature and increased flammability resistance.
Article
The tetrafunctional epoxy resins were prepared starting from diaminodiphenylmethane, diaminodiphenylether, and diaminobibenzyl. The obtained resins were characterized by IR and 1H-NMR spectroscopy, rheological and thermal techniques. The polymerization reaction was investigated by viscosimetry. The flow activation energy and the polymerization activation energy were evaluated from the rheological data and from the critical parameters (critical time and critical viscosity at gel point). The viscosity measurements and gel time determination showed slight differences between the synthesized resins. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2430–2436, 2000
Article
A study was conducted on the curing process of a nanocomposite consisting of a trifunctional epoxy resin, a hardener containing reactive primary amine groups, and montmorillonite (MMT) nanoparticles, previously treated with octadecyl ammonium. Three levels of MMT content were used: 2, 5, and 10%. The curing was carried out following the cycle: 4 h at 100°C, 2 h at 150°C, and 2 h at 200°C. Isothermal trials were also considered at three levels (120, 150, and 200°C) to conduct a kinetic study. The curing conversion was determined by FTIR spectroscopy by selecting the suitable bands for epoxide and primary amine functional groups. The study demonstrated that the MMT nanoparticles accelerate the curing process, especially at the initial stages of the thermal cycle, being this influence quasi negligible at the end of the cycle. Curing conversions were also evaluated by differential scanning calorimetry and compared to those obtained by FTIR spectroscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Article
The epoxy resin/curing agent/montmorillonite nanocomposite was prepared by a casting and curing process. The intercalation and exfoliation behaviors of epoxy resin in the presence of organophilic montmorillonite were investigated by X-ray diffraction (XRD) and dynamic mechanical thermal analysis (DMTA). For the diethylenetriamine curing agent, the intercalated nanocomposite was obtained; and the exfoliated nanocomposite would be formed for tung oil anhydride curing agent. The curing condition does not affect the resulting kind of composite, both intercalation or exfoliation. For intercalated nanocomposite, the glass transition temperature Tg, measured by DMTA and affected by the curing temperature of matrix epoxy resin is corresponded to that of epoxy resin without a gallery. The ′ peak of the loss tangent will disappear if adding montmorillonite into the composite. It was also found that the Tg of the exfoliated nanocomposite decreases with increasing montmorillonite loading. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 842–849, 2002; DOI 10.1002/app.10354
Article
New nanocomposites based on a vinylester resin (VER) and the organo-montmorillonites (ODA-M, BHL-M, DEM-M, BHLV-M) modified with octadecylammonium, bis(2-hydroxyethyl)lauryl ammonium, diethyl[2-(methacryloyloxyl)ethyl]ammonium, and bis(2-hydroxyethyl)lauryl(vinylbenzyl)-ammonium chlorides, respectively, were prepared by dispersing the organoclays in VER, and subsequent crosslinking at finally 120°C. X-ray diffraction studies and morphological studies using transmission electron microscopy revealed that exfoliation occurs for the VER/ODA-M and BHL-M composites, intercalation occurs for the VER/BHLV-M composite, and neither intercalation nor exfoliation occur for the VER/DEM-M and unmodified montmorillonite composites. On the whole, although the enhancement in flexural modulus was observed for the exfoliated ODA-M and BHL-M composites, the flexural strength was rather lowered. Dynamic viscoelastic measurement revealed that the ODA-M, BHL-M, and BHLV-M nanocomposites have significantly higher storage modulus at the rubbery state than the other composites. Polym. Eng. Sci. 44:2041–2046, 2004. © 2004 Society of Plastics Engineers.
Article
A new nanofiller containing layered organo-modified montmorillonite (oMMT) and spherical silica (SiO2) was prepared by an in situ deposition method and coupling agent modification. Fourier transform infrared spectrometry, X-ray diffraction and transmission electron microscopy show that there are interactions between oMMT and SiO2, and the spherical SiO2 particles are self-assembled on the edge of oMMT layers, forming a novel layered–spherical nanostructure. An epoxy resin (EP)/oMMT–SiO2 nanocomposite was obtained by adding oMMT–SiO2 to EP matrix. Morphologies and mechanical and thermal properties of the new ternary nanocomposite were investigated. For purposes of comparison, the corresponding binary nanocomposites, i.e., EP modified with either oMMT or SiO2, were also tested. The results for the mechanical properties show that oMMT obviously improves the strength of EP, and SiO2 enhances the toughness of EP, but oMMT–SiO2 exhibits a synergistic effect on toughening and reinforcing of EP. The toughening and reinforcing mechanism is explained by scanning electron microscopy. In addition, the thermal resistance of EP/oMMT–SiO2 is better than that of EP/SiO2, but it is worse than that of EP/oMMT. Copyright © 2006 Society of Chemical Industry
Article
Epoxy–clay nanocomposites were prepared by the dispersion of an organically modified layered clay in an epoxy resin (diglycidyl ether of bisphenol A) and curing in the presence of methyl tetrahydro acid anhydride at 80–160°C. The nanometer-scale dispersion of layered clay within the crosslinked epoxy-resin matrix was confirmed by X-ray diffraction and transmission electron microscopy, and the basal spacing of the silicate layer was greater than 100–150 Å. Experiments indicated that the hydroxyethyl groups of the alkyl ammonium ions, which were located in the galleries of organically modified clay, participated in the curing reaction and were directly linked to the epoxy-resin matrix network. Experimental results showed that the properties of epoxy were improved, evidently because of the loading of organically modified clay. The impact strength and tensile strength of the nanocomposites increased by 87.8 and 20.9%, respectively, when 3 wt % organic clay was loaded, and this demonstrated that the composites were toughened and strengthened. The thermal-decomposition and heat-distortion temperatures were heightened in comparison with those of pure epoxy resin, and so were the dynamic mechanical properties, including the storage modulus and glass-transition temperature. Moreover, experiments showed that most properties of the composites were ameliorated with low clay contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2649–2652, 2004
Article
The curing process was studied for a trifunctional epoxy resin, triglycidyl-p-aminophenol, using the hardener 4,4′-diaminodiphenylsulfone. Two curing cycles were carried out: one following the manufacturer's guidelines (2 h at 80°C, 1 h at 100°C, 4 h at 150°C, and 24 h at 200°C) and another proposed in this study, in which the two stages at low temperatures were excluded. Fourier transform IR spectroscopy was used to quantify the conversion of different functional groups (primary amine, secondary amine, epoxide, hydroxyl and ether functional groups), and these conversions could be used to infer the type of reactions that took place. These results allowed us to analyze the evolution of the curing process over time and the influence of the curing cycle. Furthermore, the enthalpy of the curing process was determined using differential scanning calorimetry, and from this the thermal conversion for the whole process was evaluated. By taking into account the autocatalytic kinetic model, the rate constants were evaluated. The glass-transition temperatures were also estimated by applying different curing cycles to the resin. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1524–1535, 2005
Article
An overview about the use of nanoparticles in epoxy resins is given. Deaggregated fumed silica, sol gel materials and other spheroidic nanoparticles improved the abrasion resistance and the mechanical properties of filled epoxides, and several properties can be improved by specific particles. Combustion properties, strength and permeation can be improved by organically modified layered silicates. The proper characterisation of the nanocomposites is still an art. TEM analysis of the cured materials and light scattering with 3D cross-correlation for the liquid samples were sufficient methods for the characterisation of filled epoxides.
Article
Epoxy–clay nanocomposites were synthesized using different types of modified montmorillonite, either with a classic quaternary ammonium salt or with protonated adducts synthesized by reacting resorcinol diglycidyl ether with monoamines (benzylamine or cyclohexylamine). The chemical structure was investigated using Fourier transform infrared and 1H NMR spectrometry. The nanocomposite structures were confirmed using X-ray diffraction analysis and transmission electron microscopy. The influence of the montmorillonite modifier on the glass transition temperature of the cured composites was studied using dynamic mechanical analysis. Copyright © 2007 Society of Chemical Industry
Article
This paper studies polymer composites formed by a polystyrene matrix (PS) and a block copolymer of poly(styrene-butadiene) (SBS). Two series of polymer composites with different compositions have been prepared: the first by extrusion followed by injection and the second by dissolution and evaporation of the solvent from the injected samples. The comparison of the FTIR spectra of the polymer composites with those simulated by addition of the spectra of the component polymers allows the detection of differences attributed to the existence of interactions between both polymers that cause partial miscibility between them. The results obtained are corroborated by differential scanning calorimetry.
Article
Thermal decomposition of polyurethane, epoxy, poly(diallyl phthalate), polycarbonate, and poly(phenylene sulfide) was examined using a combination of thermal and chemical analysis techniques. Thermal gravimetric analysis with simultaneous analysis of evolved gases by Fourier transform infrared spectroscopy, differential scanning calorimetry, and gas chromatography coupled with Fourier transform infrared spectroscopy were used to obtain rate data, determine enthalpy changes, and identify decomposition products. Examination of the evolved decomposition products indicated a common set of chain scission mechanisms involving the aromatic moieties in each of the polymer materials studied.
Article
The procedure for the fabrication of epoxy-based polymer layered silicate nanocomposites is important in respect of the nanostructure that is developed. To further our understanding of this, the influence of an organically modified clay (montmorillonite, MMT) on the curing kinetics of an epoxy resin has been studied by differential scanning calorimetry. Clay loadings of 10 and 20 mass% are used, and isothermal as well as dynamic cures have been investigated. For both cure schedules the effect of the MMT is to advance the reaction. Kinetic analysis yields values for the activation energy, but shows that the reaction cannot be described simply by the usual autocatalytic equation. The glass transition of the cured nanocomposites is lower than that for the cured neat resin, a result that is attributed to homopolymerisation taking place in addition to the epoxy–amine reaction.
Article
Artificial aging of high-density polyethylene exposed to UV irradiation, with wavelength close to 350 nm, in the presence of air, has been studied in this paper. Such irradiation is one of the environmental factors which affect most to weather exposed polyethylene. The structural modifications and chemical changes experienced by the polymer by the application of Fourier-transform infrared spectrophotometry (FTIR), mainly polymeric chain breaking, branching and oxidation, have been studied. The variation of crystallinity has also been determined by FTIR. Finally, the evolution of the mechanical properties versus the irradiation time has been closely followed.
Article
A polycationic bentonite clay (PB) was organically modified with a quaternary organic salt and added to isotactic polypropylene (PP). The compounds were prepared by melt intercalation using a twin extruder then characterized by X-ray diffraction (XRD), thermogravimetry (TG) and scanning electron microscopy (SEM) for clarifying the composite nanostructure. Compression moulded films were exposed to a thermal oxidative environment at 110 °C in an attempt to evaluate the thermal stability of PP matrix after chemical modification of bentonite. The carbonyl index results, as obtained by infrared spectroscopy, showed that the modified clay had higher thermal stability in the solid state than the natural clay. This may be connected to a higher dispersion of clay particles, reducing oxygen diffusion through the sample. On the other hand, the degradation of the composites was more intense than the unfilled polymer and this may be due to the presence of acidic sites on the clay surface that act as a catalyst to the polymer oxidation, and/or due to salt decomposition, initiating the free radical degradation of PP.
Article
The cure process of a composite formed by a trifunctional epoxy resin filled with glass beads has been analyzed using Fourier transform infrared spectroscopy (FTIR). With this technique it was possible to follow the curing reactions, studying and quantifying the conversion of different representative functional groups. The evolution of concentration of primary and secondary amines as well as epoxide groups has been followed as a function of the applied curing process. The primary amines were found to be the most useful band in the monitoring process due to the absence of overlapping. The introduction of the rigid phase had a remarkable influence on the curing process, especially when the glass beads where treated with a silane coupling agent. In this latter case the rate of amine conversion was faster than that observed in the unfilled matrix or for the untreated glass-filled composite. However, the filler treatment with a coupling agent was revealed to be inefficient in terms of mechanical properties, probably due to the high temperatures involved during the epoxy curing process. The mechanical properties like Young’s modulus and composite stress at break where found to largely increase and hold its original value, respectively, on the contrary, the strain at break decreased at a value near 50% of the neat matrix. The mechanical composite properties were also evaluated in terms of the stress intensity factor (KI) and the energy release rate (GI). Both values achieved a maximum around the 20%v of glass-beads and were found to decrease slightly with higher volumes of filler. Scanning electron microscopy (SEM) was carried out in order to assess the toughening mechanism associated with the presence of glass beads.
Article
Epoxy–clay nanocomposites were synthesised using two montmorillonite clays (MMT) with different cation-exchange capacities (CEC) (94 and 140 meq/100 g). The purpose was to investigate the influence of the CEC of the clay on the synthesis and structure of epoxy–clay nanocomposites. The dispersion of the 1 nm thick clay layers was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Although XRD data did not show any apparent order of the clay layers in the nanocomposite, TEM revealed parallel clay layers with interlamellar spacing of 90 Å (MMT of high CEC) and 110 Å (MMT of lower CEC) and the presence of remnant multiplets of non-exfoliated layers. A mechanism responsible for the influence of CEC on nanocomposite interlamellar spacing is discussed. The dispersion of the clay was investigated by SEM and found to be finer in the nanocomposites as compared with in conventional composites although the nanocomposites still have clay aggregates at the microscale rather than a monolithic structure.
Article
Epoxy–clay nanocomposites were synthesised by swelling an organophilic montmorillonite in a diglycidyl ether of bisphenol A resin with subsequent polymerisation. Three different curing agents were used: an aliphatic diamine and two cycloaliphatic diamines. The cure kinetics of these systems was evaluated by differential scanning calorimetry and the structure of the nanocomposites was characterised by X-ray diffraction and transmission electron microscopy. Successful nanocomposite synthesis was dependent not only on the cure kinetics of the epoxy system but also on the rate of diffusion of the curing agent into the galleries because it affects the intragallery cure kinetics. The nature of the curing agent influences these two phenomena substantially and therefore the resulting structure of the nanocomposite. The curing temperature controls the balance between the extragallery reaction rate of the epoxy system and the diffusion rate of the curing agent into the galleries. Thus, the choice of curing agent and curing conditions controls the extent of exfoliation of the clay in the material.
Article
The influence of an organically modified clay on the curing behavior of three epoxy systems widely used in the aerospace industry and of different structures and functionalities, was studied. Diglycidyl ether of bisphenol A (DGEBA), triglycidyl p-amino phenol (TGAP) and tetraglycidyl diamino diphenylmethane (TGDDM) were mixed with an octadecyl ammonium ion modified organoclay and cured with diethyltoluene diamine (DETDA). The techniques of dynamic mechanical thermal analysis (DMTA), chemorheology and differential scanning calorimetry (DSC) were applied to investigate gelation and vitrification behavior, as well as catalytic effects of the clay on resin cure. While the formation of layered silicate nanocomposite based on the bifunctional DGEBA resin has been previously investigated to some extent, this paper represents the first detailed study of the cure behavior of different high performance, epoxy nanocomposite systems.
  • F Carrasco
  • P Pagès
F. Carrasco, P. Pagès / Polymer Degradation and Stability 93 (2008) 1000e1007
Thermal stability of nanocomposites based on polypropylene and bentonite
  • F G Ramos-Filho
  • Tja Mélo
  • M S Rabello
  • Sml Silva
Ramos-Filho FG, Mélo TJA, Rabello MS, Silva SML. Thermal stability of nanocomposites based on polypropylene and bentonite. Polym Degrad Stab 2005;89(3):383e92.