Preparation, optimization and thermal characterization of a novel conductive thermoset nanocomposite containing polythiophene nanoparticles using dynamic thermal analysis

Polythiophene nanoparticles as a conductive filler was prepared with average diameter of 20-35 nm and its molecular structure was confirmed by the FT-IR, TEM, XRD and UV-vis analysis. A new conductive epoxy nanocomposite was synthesized by curing of diglycidyl ether of bisphenol A/4,4′-(4,4′ Isopropylidenediphenoxy) bis (Phthalic Anhydride) involving various percentages of polythiophene nanoparticles. DSC and DMTA studies revealed that low percentage of the polythiophene nanoparticles, i.e. 1%, results in improved crosslink density as evidenced by increasing in the glass transition temperature. The addition of polythiophene nanoparticles into the epoxy matrix resulted in a significant increment in the electrical conductivity, mechanical properties, thermal stability and activation energy of thermal degradation. The advanced isoconversional method is utilized to describe the curing behavior and thermal degradation process of the neat epoxy and epoxy nanocomposite. We have utilized the Coats-Redfern and Criado methods to find the solid state thermal degradation reaction mechanism. For the nanocomposite, the mechanism was recognized to be two-dimensional diffusion (D₂) reaction and it changes to a nucleation and growth (A₄) for pure epoxy system.     

Calorimetric measurement of the maximum glass transition temperature in a thermosetting resin

The measurement of the maximum glass transitionT _g∞ of a thermosetting resin is usually performed by differential scanning calorimetry in the second scan (T _g2scan), after a previous scan by heating up the sample to a temperature where the exothermic curing reaction has been completed. However, this method can eventually produce thermal degradation, decreasing the crosslinking density and theT _g of the sample. Values ofT _g2scan between 95? and 102?C were found in an epoxy resin based on DGEBA cured with phthalic anhydride. Thermal degradation effects can be avoided if the measurement is performed by isothermal curing and further determination ofT _g. AT _g∞ value of 109?C is achieved, which is the maximum value ofT _g according to the topological limit of conversion.     

Advanced isoconversional and master plot analyses on solid-state degradation kinetics of a novel nanocomposite

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.     

Liquid crystalline and isotropic epoxy thermosets: Mechanism and kinetics of non-isothermal degradation

Thermal non-oxidative degradability of two epoxy thermosets was studied. Investigations were carried out on a non-commercial liquid crystalline structure and its isotropic homologue in order to provide further insight into the mechanism and kinetics of thermal degradation of the proposed systems. The studies were done by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). For the first time the degradation of a liquid crystalline epoxy was studied using an advanced isoconversional kinetic method. The results were used to predict the thermal stability of both types of epoxy networks. GC-MS analysis was applied on evolved gas during degradation to elucidate the degradation mechanism in accordance with the kinetic results. The liquid crystalline structure has a different mechanism of decomposition in comparison with its isotropic homologue. In spite of a higher T_g value, it shows a similar thermal stability but a lower release of degradation compounds.     

Thermal properties and flame retardancy of novel epoxy based on phosphorus‐modified Schiff‐base

Through addition reaction of Schiff‐base terephthalylidene‐bis‐(p‐aminophenol) ( DP‐1 ) and diethyl phosphite (DEP), a novel phosphorus‐modified epoxy, 4,4'‐diglycidyl‐(terephthalylidene‐bis‐(p‐aminophenol))diphosphonate ether ( EP‐2 ), was obtained. An modification reaction between EP‐2 and DP‐1 resulted in an epoxy compound, EP‐3 , possessing both phosphonate groups and C?N imine groups. The structure of EP‐2 was characterized by Fourier transform infrared (FTIR), elemental analysis (EA), ¹H, ¹³C, and ³¹P NMR analyses. The thermal properties of phosphorus‐modified epoxies cured with 4,4'‐diaminodiphenylmethane (MDA) and 4,4'‐diaminodiphenyl ether (DDE) were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The activation energies of dynamic thermal degradation (E_d) were calculated using Kissinger and Ozawa's methods. The thermal degradation mechanism was characterized using thermogravimetric analysis/infrared spectrometry (TG‐IR). In addition, the flame retardancy of phosphorus‐modified epoxy thermosets was evaluated using limiting oxygen index (LOI) and UL‐94 vertical test methods. Via an ingenious design, phosphonate groups were successfully introduced into the backbone of the epoxies; the flame retardancy of phosphorus‐modified epoxy thermosets was distinctly improved. Due to incorporation of C?N imine group, the phosphorus‐modified epoxy thermosets exhibited high thermal stabilities; the values of glass‐transition temperatures (T_gs) were about 201–210°C, the values of E_d were about 220–490 kJ/mol and char yields at 700°C were 49–53% in nitrogen and 45–50% in air. These results showed an improvement in the thermal properties of phosphorus‐modified epoxy by the incorporation of C?N imine groups. Copyright © 2010 John Wiley & Sons, Ltd.     

DSC and curing kinetics of epoxy resin using cyclohexanediol diglycidyl ether as active diluents

Curing reactions of epoxy resin (diglycidyl ether of bisphenol-A) with curing agent polyamido-amine, using cyclohexanediol diglycidyl ether as active diluents, was investigated by non-isothermal differential scanning calorimetry at different heating rates. Activation energy was calculated based on Kissinger method, and the results showed that E _a changed from 68.01 to 54.84 kJ mol^?1 after the diluents was added, which reduced about 20 %. Málek method was used to deduce the probable mechanism function and the results indicated that ?esták–Berggren model is fairly coincident with the experimental data.     

thermal stability of epoxy systems badge (n=0)/1,2-dch and badge (n=0)/ 1,2-dch/vinylcyclohexene dioxide

The thermal degradation of the epoxy system diglycidyl ether of bisphenol A (BADGE n=0)/1,2-diamine cyclohexane (DCH) containing different concentrations of an epoxy reactive diluent was studied by thermogravimetric analysis in order to determine the reaction mechanism of the degradation process and to compare it with the results for the same system without diluent. The value of the activation energy, necessary for this study, was calculated using various integral and differential methods. Values obtained using the different methods were compared to the value obtained by the Flynn-Wall-Ozawa"s method (between 193-240 kJ mol^-1 depending on the diluent concentration) with does not require a knowledge of the nth order reaction mechanism. All the experimental results were compared to master curves in the range of Doyle"s approximation (20-35% of conversion). Analysis of the results suggests that the reaction mechanism could be F₂, F₃, or A₂ type. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of thermal degradation of poly(aryl ether)s containing phthalazinone and life estimation

New special engineering thermoplastics, poly(phthalazinone ether sulfone) (PPES) and poly(phthalazinone ether sulfone ketone) (PPESK), containing phthalazinone are synthesized through step-polymerization. The kinetics of thermal degradation of PPES and PPESK (1/1) in nitrogen is investigated at several heating rates by thermogravimetry (TG). It is concluded that, based on using Satava’s theory, the thermal degradation mechanism of PPESK (1/1) is nucleation and growth, the order of reaction of the degradation process is one (n = 1). In contrast, the thermal degradation mechanism of PPES is a phase boundary controlled reaction and the order of the reaction is two (n = 2). The kinetic parameters, including reaction energy and frequency factor of thermal degradation reaction for PPES and PPESK (1/1) are analyzed using isoconversional Friedman, Kissinger–Akahira–Sunose (K–A–S) and Ozawa method. In addition, the study focus on the influence of heating rate and ratio of ketone/sulfone on thermal stability and the life estimation are described.     

Preparation of nano poly(phenylsilsesquioxane) spheres and the influence of nano-PPSQ on the thermal stability of poly(methyl methacrylate)

The nano poly(phenylsilsesquioxane) spheres (nano-PPSQ) were prepared by the sol?Cgel method and incorporated into poly(methyl methacrylate) (PMMA) by in situ bulk polymerization of methyl methacrylate. The structure of nano-PPSQ was confirmed by transmission electron microscope and thermogravimetry analysis (TG). The interaction between nano-PPSQ and PMMA was investigated by Fourier transform infrared spectra (FT-IR). The influence of nano-PPSQ on the thermal stability of PMMA was investigated by TG and differential scanning calorimetry (DSC) measurements. The results indicated that nano-PPSQ enhanced the thermal stability and the temperatures of glass transition (T _g) of nanocomposites. The effect of the heating rate in dynamic measurements (5?C30?°C?min^?1) on kinetic parameters such as activation energy by TG both in nitrogen and air was investigated. The Kissinger method was used to determine the apparent activation energy for the degradation of pure PMMA and nanocomposites. The kinetic results showed that the apparent activation energy for degradation of nanocomposites was higher than that of pure PMMA under air.     

Non-isothermal kinetics of degradation of ultra-high molecular mass polyethene composite materials

In the present work, the Coats-Redfern method was used to determine the kinetic parameters and the possible reaction mechanism of the thermal degradation of ultra-high molecular mass polyethene and its composites with fiber monocrystals in static air at three different heating rates − 6, 10 and 16 K min⁻¹. The analysis of the results obtained showed that the thermal degradation process of pure ultra-high molecular mass polyethene corresponded to a diffusion controlled reaction (three-dimentional diffusion, mechanism D₃), while its composites with fiber monocrystals degraded by two concurrent mechanisms (diffusion one D₃ and A₁,F₁ mechanism). The fiber monocrystals used increased the thermal stability of the composite materials obtained. The values of the activation energy, frequency factor, the changes of entropy, enthalpy and Gibbs energy for the active complex of the composites were calculated.     

Terpolymerization of p-acetylpyridine oxime, p-methylacetophenone and formaldehyde, and its thermal studies

A terpolymer resin involving p-acetylpyridine oxime and p-methylacetophenone with formaldehyde (APOMAF) was synthesized by condensation polymerization in the presence of an acid catalyst. The structure of terpolymer was elucidated by FT-IR, ¹H NMR, pyrolysis gas chromatography mass spectrometer (Py?CGC?CMS), nitrogen adsorption/desorption analysis, Ubbelohde viscometer and non-aqueous conductometric titration, TG?CDTG and DSC. Molar fractions of monomer, condensing and comonomer unit (m ₁, m ₂, and m ₃) in APOMAF using ¹H NMR analysis data were calculated as 1.67; 0.27 and 0.66?mol%, respectively. The apparent activation energy of terpolymer by using various degradation models including the Flynn?CWall?COzawa (FWO), Kissinger?CAkahira?CSunose (KAS), and Friedman methods were 140.3; 144.9 and 129.9?kJ?mol^?1, respectively. The results from isoconversional degradation kinetics and Pyrolysis (GC?CMS) indicates that the degradation mechanism of terpolymer are likely limited by at least two-reaction step, the first being associated with the loss of the pendent methyl, acetyl, and oxime groups (side group elimination) while the second mass loss being due to the degradation of the terpolymer backbone (random scission) which clearly indicates that grafting pendant groups to the terpolymer backbone yields polymers with lower thermal stability. From the calculation, the solid state thermal degradation mechanism is proposed to be D₃ (three-dimensional diffusion) at initial stage and F ₁ (Random nucleation with one nucleus on the individual particles) at final stage.     

Understanding of thermal/thermo-oxidative degradation kinetics of polythiophene nanoparticles

The polythiophene nanoparticles (nano-PT) were prepared with average diameter of 20–35 nm. The nanostructurals of polythiophene were confirmed by TEM and SEM analyzes. The kinetics of the thermal degradation and thermal oxidative degradation of nano-PT were investigated by thermogravimetric analysis. Kissinger method, Flynn–Wall–Ozawa method, and advanced isoconversional method have been used to determine the activation energies of nano-PT degradation. The results showed that the thermal stability of nano-PT in pure N₂ is higher than that in air atmosphere. The analyzes of the solid-state processes mechanism of nano-PT by Criado et al. method showed: the thermal degradation process of nano-PT goes to a mechanism involving second-order (F ₂ mechanism); otherwise, the thermo-oxidative degradation process of nano-PT is corresponding to a phase boundary controlled reaction mechanism (R ₂ mechanism).     

Dynamic mechanical analysis

Using dynamic mechanical analysis (DMA) we have studied thermal degradation for a system containing a diglycidyl ether of bisphenol A (DGEBA) and 1,3-bisaminomethylcylohexane (1,3-BAC). The changes of dynamic mechanical properties during thermal degradation indicated a shift of the glass transition temperature (T _g) to higher temperatures and a decrease in the peak value of the dynamic loss factor (tan δ) with an increasing of aging time. The value of dynamic storage modulus (E′) at the rubbery state showed an increase with aging time, whiteE′ at the glassy state only underwent a moderate change with increased thermal degradation. From these results it can be argued that thermal degradation during the stage prior to the onset of the severe degradation involves structural changes in the epoxy system, as further crosslinking and loss of dangling chains in the crosslinked network.     

Kinetics of thermal degradation and thermal oxidative degradation of poly(p-dioxanone)

The kinetics of the thermal degradation and thermal oxidative degradation of poly(p-dioxanone) (PPDO) were investigated by thermogravimetric analysis. Kissinger method, Friedman method, Flynn-Wall-Ozawa method and Coats-Redfern method have been used to determine the activation energies of PPDO degradation. The results showed that the thermal stability of PPDO in pure nitrogen is higher than that in air atmosphere. The analyses of the solid-state processes mechanism of PPDO by Coats-Redfern method and Criado et al. method showed: the thermal degradation process of PPDO goes to a mechanism involving random nucleation with one nucleus on the individual particle (F₁ mechanism); otherwise, the thermal oxidative degradation process of PPDO is corresponding to a nucleation and growth mechanism (A₂ mechanism).     

Crystalline properties and decomposition kinetics of cellulose fibers in wood pulp obtained by two pulping processes

In this study two cellulose fibers, Eucalyptus grandis (CEG) and Pinus taeda (CPT), obtained through the kraft and sulfite pulping processes, respectively, were characterized. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were carried out. From the XRD analysis the interplanar distance, crystallite size and crystallinity index were calculated and the degradation kinetics parameters were determined by TGA at heating rates of 5, 10, 20 and 40 °C min⁻¹ using the Avrami, Flynn-Wall-Ozawa (FWO) and Criado methods. The results obtained by FTIR showed that the composition of the fibers is similar, while from the XRD analysis slight differences in the crystallinity were observed. The thermogravimetric analysis showed higher thermal stability for CPT than CEG while the values for the activation energy (E_a) were higher for CEG than CPT. The results obtained by Avrami and Criado methods showed that the degradation mechanism in the CEG samples involves a diffusion process while in the case of CPT the degradation process is a phase boundary controlled reaction. The degradation mechanisms demonstrated that the difference between thermal stability and E_a may be due to differences in the type of crystalline structure of the samples obtained through the two pulping processes.     

Poly(ether ether ketone)/poly(aryl ether sulphone) blends: thermal degradation behaviour

The thermodegradative behaviour of blends of poly(ether ether ketone) (PEEK) and poly(aryl ether sulphone) (PES) was studied by dynamic thermogravimetry in order to analyze their thermal stability. The Freeman-Carrol differential approach was used to determine the kinetic parameters i.e. the apparent activation energy (E_a) and order of reaction (n), of the degradation process. The results indicate that the presence of one component influences the thermal stability of the other. Both, temperature for 5% weight loss (T₅) and E_a for blends show a negative deviation from the linear behaviour, which signifies a lowering of thermal stability compared to homopolymers. The decrease in the thermal stability at low concentration of PES in PEEK has been explained on the basis of chemical interactions of the degradation products of PES, which has lower induction temperature for degradation, with PEEK and also on the reduction of viscosity of the medium. But the decrease in thermal stability at low concentration of PEEK in PES is unusual and at present, without the complete elucidation of degradation mechanism in these blends, is difficult to explain.     

The thermal properties of monochloro-para-xylylene

The three thermal properties that describe the heat transfer in a material were determined for a thin, tough, transparent, highly crystalline film of poly-monochloro-para-xylylene (PCPX). These three properties, viz. thermal conductivity (K), thermal diffusivity (α), and specific heat (C_p) were determined using a transient heating method.The experimental method used involved the heating of a sample of stacked polymer sheets by an ultrathin heating foil. The heating foil, located in the center plane of the stack provided a source of constant heat flux when a current of known amperage was passed through it. By careful consideration of sample dimensions, the sample simulated an infinite solid. The thermal properties were calculated using standard solutions of the heat transfer equations of an infinite solid over a temperature range of ?192 to 130°C. The experimental method was repeated to check the reproducibility of the results and compared with differential scanning calorimeter results.A data acquisition system was developed to facilitate data handling for the transient experiments. The system included hardware capable of punching data on paper tape and a software package to analyze these data.The conclusions drawn include: (1) the reproducibility of the experiments was well within the experimental errors; (2) the data acquisition system greatly facilitates acquisition of thermal data; (3) an incremental change occurs in C_p of PCPX in the vicinity of the γ relaxation reported by dynamical relaxation measurements and its occurrence indicates that this relaxation involves a cooperative motion of molecules; (4) owing to the significant magnitude of the C_p jump and the appreciable degree of crystallinity of PCPX, these internal motions occurring at the γ transition probably involve both amorphous and crystalline regions; (5) a direct relationship between thermal expansion and specific heat was indicated in PCPX as well as for polystyrene (PS) at relatively low temperatures (?200 to ?20°C); (6) the overall low values of thermal conductivity (1.0 to 2.5 × 10^?4 cal sec^?1 cm^?1) and thermal diffusivity (9.5 to 5.3 × 10^?4 cm² sec^?1) of PCPX indicate that it is ideally suited for insulation applications.     

Thermogravimetry study of pyrolytic characteristics and kinetics of the giant wetland plant Phragmites australis

The pyrolytic characteristics and kinetics of wetland plant Phragmites australis was investigated using thermogravimetric method from 50 to 800?°C in an inert argon atmosphere at different heating rates of 5, 10, 25, 30, and 50?°C?min^?1. The kinetic parameters of activation energy and frequency factor were deduced by appropriate methods. The results showed that three stages appeared in the thermal degradation process. The most probable mechanism functions were described, and the average apparent activation energy was deduced as 291.8?kJ?mol^?1, and corresponding pre-exponential factors were determined as well. The results suggested that the most probable reaction mechanisms could be described by different models within different temperature ranges. It showed that the apparent activation energies and the corresponding pre-exponential factors could be obtained at different conversion rates. The results suggested that the experimental results and kinetic parameters provided useful information for the design of pyrolytic processing system using P. australis as feedstock.