Determination of the Thermal Degradation Kinetic Parameters of Carbon Fibre Reinforced Epoxy Using TG

In this work, a kinetic study on the thermal degradation of carbon fibre reinforced epoxy is presented. The degradation is investigated by means of dynamic thermogravimetric analysis (TG) in air and inert atmosphere at heating rates from 0.5 to 20°C min⁻¹ . Curves obtained by TG in air are quite different from those obtained in nitrogen. A three-step loss is observed during dynamic TG in air while mass loss proceeded as a two step process in nitrogen at fast heating rate. To elucidate this difference, a kinetic analysis is carried on. A kinetic model described by the Kissinger method or by the Ozawa method gives the kinetic parameters of the composite decomposition. Apparent activation energy calculated by Kissinger method in oxidative atmosphere for each step is between 40–50 kJ mol⁻¹ upper than E _a calculated in inert atmosphere. The thermo-oxidative degradation illustrated by Ozawa method shows a stable apparent activation energy (E _a ≈130 kJ mol⁻¹ ) even though the thermal degradation in nitrogen flow presents a maximum E _a for 15% mass loss (E _a ≈60 kJ mol⁻¹ ). This revised version was published online in July 2006 with corrections to the Cover Date.     

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

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

Thermal degradation behavior of multi-walled carbon nanotubes/polyamide 6 composites

This paper focuses on the thermal degradation behavior of multi-walled carbon nanotubes (MWNTs)/polyamide 6 (PA6) composites under air and nitrogen atmosphere using thermogravimetric analysis (TGA). The results show that the dispersion of amino-functionalized MWNTs (f-MWNTs) in PA6 is more homogeneous than purified MWNTs (p-MWNTs). The presence of MWNTs improves the thermal stability of PA6 under air obviously, but has little effect on the thermal degradation behavior of PA6 under nitrogen atmosphere. The activation energies for degradation under air, E_a, estimated by Kissinger method, are 153, 165 and 169 kJ/mol for neat PA6, p-MWNTs/PA6 and f-MWNTs/PA6 composites, respectively. The p-MWNTs/PA6 composites show two-step degradation not only under air but also under nitrogen atmosphere, however, neat PA6 and the f-MWNTs/PA6 composites exhibit two-step degradation only under air.     

Thermogravimetry of the thermal degradation of Japanese lacquer (urushi) films

The kinetics of the thermal degradation of Japanese lacquer (urushi) films in N₂ and in air were studied by means of thermogravimetry (TG). Thermogravimetric and derivative thermogravimetric curves indicated that the degradation occurred in three stages. The atmosphere influenced the apparent activation energies (E _a) of the three degradation stages. The activation energies (E _a) for the first stage in N₂ and air, obtained from the TG curve, were 19.12 and 10.19 kcal mol^?1, respectively, and the corresponding pre-exponential factors (A) were 6.18 × 10⁵ and 1.24 × 10² min^?1 for 1-year-old urushi films.     

Kinetics of thermo-oxidative and thermal degradation of poly(d,l-lactide) (PDLLA) at processing temperature

Poly(d,l-lactide) (PDLLA) degraded at processing temperature under air and nitrogen. A random chain scission model was established and used to determine the activation energy E_a, and FT-IR, ¹H and ¹³C NMR were used to elucidate the degradation behavior under different atmospheres. Results showed that there were two to three stages. The 1st stage was dominated by the oligomers containing carboxylic acid groups and hydroxyl groups, during which oxygen and nitrogen had little effect on the degradation, thus they share similar E_a. When the oligomers were consumed over or evaporated, the 2nd stage began, and oxygen had a promoting effect on the thermo-oxidation process, resulting in the great decrease in E_a. The third stage of PDLLA was observed when it degraded under nitrogen over 200 °C, which was caused by the appearance of carboxylic acid substance.     

Thermal degradation of γ-irradiated poly(vinyl chloride)

The thermal degradation of unstabilized poly(vinyl chloride) irradiated with γ-rays has been investigated by dynamic thermogravimetry in a nitrogen atmosphere. The overall effect of irradiation is to render PVC more susceptible to thermal degradation. The change in activation energy of degradation with dose showed a behavior parallel with the change of intrinsic viscosity with dose. The minimum and maximum E_a values were found to correspond with the minimum and maximum observed on [η] versus dose curves. This behavior indicates an inverse relationship between the rate of thermal degradation and molecular size.     

The influence of chain rigidity on the thermal properties of some novel random copolyethersulfones

Some random low molar mass (M_n ≈ 9000 g mol⁻¹) poly(ethersulfoneethersulfone)/poly(ethersulfoneethersulfonebiphenylsulfone) P(ESES)/P(ESESBS) copolymers, with various (25%, 50% and 75%) ESESBS units contents, were synthesized to obtain compounds with higher chain rigidity than PES. The thermal characterization of the prepared copolymers, as well as that of corresponding P(ESES) and P(ESESBS) homopolymers, was performed, and all investigated parameters showed strong dependence on polymer composition.The glass transition temperature (T_g) was calorimetrically determined by DSC technique, and the obtained values increased linearly as function of ESESBS units percentage, thus indicating an increasing chain rigidity.Degradations were carried out in dynamic heating conditions, from 35 °C to 700 °C, in both flowing nitrogen and static air atmosphere, and the characteristic parameters of degradation were determined in order to draw useful information about the overall thermal stability of the studied compounds. The apparent activation energy of degradation (E_a) was obtained by the Kissinger method, and the values found increased linearly as a function of ESESBS content, while the temperature values at 5% mass loss (T_5%) showed an opposite linear trend. The results are discussed and interpreted.     

Kinetic study of the thermal and thermo-oxidative degradations of polylactide-modified films for food packaging

In this study, the thermal degradations of some commercial polylactide (PLA) films, pure and subjected to various superficial treatments, were investigated in both inert (flowing nitrogen) and oxidative (static air) atmospheres. Degradations were carried out in a thermobalance, in the scanning mode, at various heating rates, and the obtained thermogravimetric curves were discussed and interpreted. Experiments, performed in the temperature range of 35–700 °C, showed similar behavior in both the atmospheres used. The initial decomposition temperature (T _i) and the apparent activation energy (E _a) of degradation of the differently treated PLA films were determined and compared with each other and with those of untreated PLA. The E _a of degradation was obtained by Kissinger’s method, and the values were found increased linearly as a function of crystallinity percentage (%c) as well as the T _i values. The glass transition temperature (T _g) was also determined by differential scanning calorimetry. All the investigated parameters showed dependence on different treatments made to the films. The results obtained for the degradations of PLA films were compared with each other, and a classification of thermal stability in the studied environments were made.     

The influence of sulfonation degree on the thermal behaviour of sulfonated poly(arylene ethersulfone)s

Initial decomposition temperature (T_i), apparent activation energy of degradation (E_a) and glass transition temperature (T_g) of some low molar mass (M_n ≈ 8000 g mol⁻¹) sulfonated poly(arylene ethersulfone)s s-(PAES)s were determined to check their dependence on sulfonation degree (SD). The results obtained were compared with those for unsulfonated poly(arylene ethersulfone) PAES. In order to have an accurate control of the chemical structure, a pre-sulfonation route was followed for the preparation of sulfonated compounds. The thermal behaviour of the investigated s-(PAES)s as well as that of PAES appears not to be influenced by the environment (flowing nitrogen or static air atmosphere) of degradation. Both T_i and T_g values of s-(PAES)s were higher than those of PAES and increased quite linearly as a function of sulfonation degree. An analogous linear trend was observed for the apparent degradation energy of s-(PAES)s, but the values found were largely lower than those of unsulfonated homopolymer. The results are discussed and interpreted.     

Thermal behavior of bismaleimide resin

The cure of a bismaleimide (BMI) neat resin modified with an aromatic diamine and a siloxane elastomer, has been studied by ¹³C solid state nuclear magnetic resonance. Two chemical reactions occur during the cure cycle; at a low temperature, Michael's reaction predominates, while at a high temperature the polymerization of the double bond maleimide creates the network. The degradation of this BMI material was characterized with isothermal and dynamic thermogravimetric analyses in air and in nitrogen. The BMI thermal stability is lower in nitrogen than in air. This behavior is an indication of oxygen participating in reactions at high temperatures. The activation energy (E_a) of thermal degradation was determined from isothermal data using an Arrhenius equation (In V vs. 1/T). The global E_a for the weight loss in air was found to be 91 kJ/mol. The nature and the evolution of the thermal degradation products were the combined analyzed by techniques of pyrolysis, gas chromatography and mass spectrometry. The major thermal decomposition products obtained in the temperature range of 300–700°C are identified as benzene, methyl formamide, aniline, toluene and isocyanate-derived products.     

A DSC study on the kinetics of disproportionation reaction of (hfac)Cu(COD)

The kinetics of disproportionation reaction of hexafluoroacetylacetonate-copper(I)-cycloocta-1,5-diene [(hfac)Cu^I(COD)] was investigated by the use of differential scanning calorimetry (DSC) with different heating rates in dynamic nitrogen atmosphere. First, the activation energies (E_as) of the disproportionation reaction were estimated with model-free isoconversional methods, respectively. The E_as were found to fall within the range between 17.6 and 18.7 kJ mol⁻¹, with no temperature and heating rate effects observed. Then, when the E_a was ascertained, the model-fitting methods with least square fitting procedure were adopted to determine the kinetic model for the disproportionation reaction. As a result, the disproportionation reaction follows second-order reaction kinetics.     

Thermal and thermo-oxidative degradations of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)/copoly(aryl ether sulfone) P(ESES-co-EES) block copolymers: a kinetic study

The thermal degradation of a series of three novel ABA block copolymers of different molar mass (M _n), were the block A is a poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), while the block B is a random copoly(aryl ether sulfone) P(ESES-co-EES), was studied in both inert (flowing nitrogen) and oxidative (static air) atmospheres, to investigate the effects of M _n of the central block on the thermal stability. Copolymers were synthesized with a two step method: in the first stage, a linking molecule is selectively attached as end group to the P(ESES-co-EES) which reacts in the second step with the phenolic hydroxyl group of PPO. Degradations were carried out into a thermobalance, in the scanning mode, at various heating rates, and the characteristic parameters of thermal stability, namely initial decomposition temperature (T _i) and the activation energy (E _a) of degradation, of the various copolymers were determined. Both T _i and degradation E _a values increased exponentially as a function of M _n of copolymers. The results were discussed and interpreted.     

Synthesis and thermal properties of new dumbbell-shaped isobutyl-substituted POSSs linked by aliphatic bridges

Five new dumbbell-shaped polyhedral oligomeric silsesquioxanes (POSSs), in which two identical silicon cages are linked to various length aliphatic bridges, were prepared by corner capping reaction between hepta isobutyltricycloheptasiloxane trisilanol (HIBT) and suitable bis(triethoxysilyl) derivatives. The products obtained were characterized by elemental analysis and ¹H NMR spectroscopy, and the results were in very good agreement with the expected ones. Degradations were carried out in flowing nitrogen and in static air atmosphere, and temperatures at 5 % mass loss (T _5 %) and residues at 700 °C were determined to investigate the resistance to the thermal degradation. The T _5 % values were lower in oxidative atmosphere than in inert environment, and increased linearly as a function of organic bridge length in either used atmosphere. The residues at 700 °C were higher in static air than in flowing nitrogen. The results obtained for various dumbbell-shaped POSSs were discussed and compared with each other. A comparison with the results previously obtained with the corresponding un-bridged phenyl, hepta isobutyl-POSSs showed a higher resistance to the thermal degradation of bridged POSSs.     

Thermal degradation of poly(vinyl chloride) synthesized with a titanocene catalyst

PVC was synthesized using a trichloroindenyltitanium-methylaluminoxane catalyst at room temperature, and its degradation was monitored along with a commercial sample at 160, 170 and 180 °C under air or nitrogen atmosphere. The process was followed by HCl evolution, yellowing index, colour formation and thermogravimetric analysis. The produced polymer had a lower molecular weight and higher surface area, compared with a commercial PVC, while ¹H NMR and T_g values show minimal differences between materials. The HCl evolution degradation studies indicate that produced PVC has a lower thermal resistance than commercial PVC, while TGA reveals the opposite behaviour. Yellowing index and colour evaluation give evidence that nitrogen atmosphere and high surface area in produced PVC allow the polyene growth, whereas low surface area and air atmosphere generate shorter polyenes and chromophoric species. Differences in degradation performance are thought to be due to chemical origin, inherent morphology and differences in instrumentation.     

Thermal and rheological behaviour of some random aromatic polyethersulfone/polyetherethersulfone copolymers

The thermal and rheological behaviour of seven random Cl-ended aromatic PES/PEES copolymers (M_n ≈ 9500 g mol⁻¹), at various PES/PEES repeating unit ratios, was studied. The glass transition temperatures (T_g), determined by DSC experiments, showed a dependence on copolymer composition significantly different from the ideal linear behaviour expected on the basis of Fox equation. Degradations were carried out in the scanning mode, under flowing nitrogen, in the temperature range 35-650 °C and a single degradation stage was observed for all copolymers. The initial decomposition temperatures (T_i) and the half decomposition temperatures (T_1/2) were directly determined by TG curves, while the apparent activation energies of degradation (E_a) were obtained by the Kissinger method. In addition, the complex viscosity (η^∗) of molten copolymers was determined in experimental conditions of linear viscoelasticity. T_i, T_1/2, E_a, and η^∗ values were depending on copolymer composition, showing a trend similar to that of T_g values. The results obtained were discussed and interpreted.     

A kinetic study of the thermal and thermal oxidative degradations of new bridged POSS/PS nanocomposites

The thermal degradation of a series of three novel bridged polyhedral oligomeric silsesquioxanes (POSS)/polystyrene (PS) nanocomposites, at different POSS content (3%, 5% and 10%), was studied in both inert (flowing nitrogen) and oxidative (static air) atmospheres, in order to investigate the effects of this new dumbbell-shaped structure on the filler–polymer interaction and then on the thermal stability of the obtained materials. Nanocomposites were synthesized by in situ polymerization of styrene in the presence of POSS which has not polymerizable groups, aiming to obtain well dispersed POSS/PS systems. The actual filler concentration in the obtained nanocomposites was checked by ¹H NMR spectroscopy. Scanning electron microscopy (SEM) and FTIR spectroscopy evidenced the presence of filler–polymer interactions. Degradations were carried out into a thermobalance, in the scanning mode, at various heating rates, and the characteristic parameters of thermal stability, namely temperature at 5% mass loss (T₅%) and the activation energy (E_a) of degradation, of the various nanocomposites were determined. The results were discussed and interpreted.     

Kinetic study of the thermal degradation of PS/MMT nanocomposites preparedwith imidazolium surfactants

Styrene and montmorillonite organically modified with imidazolium surfactants (MMT) at various alkyl chain lengths (C₁₂, C₁₆ and C₁₈) were used to prepare the corresponding PS/MMT/C₁₂, PS/MMT/C₁₆ and PS/MMT/C₁₈ nanocomposites by in situ polymerization. XRD and TEM analyses evidenced the formation of both intercalated and exfoliated structures. The glass transition temperatures (T _g) of nanocomposites, as well as that of neat PS, were obtained by DSC measurements. The thermal degradations were carried out in the scanning mode, in both inert and oxidative environments, and the initial temperatures of decomposition (T _i) and the apparent activation energies of degradation (E _a) were determined. Due to an oxidative degradation mechanism, the T _i and E _a values in air atmosphere were lower than those under nitrogen. The results indicated that nanocomposites are more thermally stable than polystyrene, and suggested an increasing degree of exfoliation as a function of alkyl chain length of surfactant, associated with enhancing thermal stability.     

Thermal and rheological behaviours of some random aromatic amino-ended polyethersulfone/polyetherethersulfone copolymers

The thermal and rheological characterizations of seven random, low molecular weight (M_n ≅ 9500 g mol⁻¹), H₂N-ended polyethersulfone/polyetherethersulfone (PES/PEES) copolymers, at various PES/PEES ratios, were performed. The glass transition temperatures (T_g) were determined by DSC. Degradations were carried out in a thermobalance, under flowing nitrogen, in dynamic heating conditions from 35 °C to 650 °C. The initial decomposition temperatures (T_i) and the half decomposition temperatures (T_1/2) were directly determined by TG curves, while the apparent activation energies of degradation (E_a) were obtained by the Kissinger method. In addition, the complex viscosities (η^∗) of the molten polymers were determined in experimental conditions of linear viscoelasticity. T_g, E_a and η^∗ values increased linearly with PES% content, while T_i and T_1/2 values showed opposite behaviour. In every case both PES and PEES homopolymers felt outside linearity. The results obtained are discussed and interpreted, and compared with those of corresponding Cl-ended copolymers previously studied.     

Thermal decomposition reactions of metal carboxylato complexes in the solid state. I.: Thermographic and differential thermal studies of metal oxalato,malonato and succinato complexes

Thermal investigation of metal carboxylato complexes of the first transition metals, Mn(II), Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) and non-transition metals like Zn(II) and Cd(II) in the solid state has been carried out under non-isothermal conditions in nitrogen atmosphere by simultaneous TG and DTA. TG and DTA curves inferred that the thermal stability of the complex decreased approximately with the increase of the standard potential of the central metal ion. The thermal parameters like activation energy, E_a, enthalpy change, ΔH, and entropy change, ΔS, corresponding to the dehydration and decomposition of the complexes are determined from TG and DTA curves by standard methods. A linear correlation is found between ΔH and ΔS and E_a and ΔS in dehydration and decomposition processes. DTA curves show an irreversible phase transition for Na₂Mn(mal)₂], Na₂[Cu(mal)₂] and Na₂,[Co(suc)₂] complexes. The residual products in these decomposition processes being a mixture of two oxides, of oxide and carbonate or a mixture of two carbonates.     

Kinetic study of the thermal decomposition of poly(vinyl alcohol)/kraft lignin derivative blends

A kraft lignin derivative (KLD) obtained by reaction with p-aminobenzoic acid/phthalic anhydride, was blended with poly(vinyl alcohol) (PVA) by solution casting from DMSO. PVA and PVA/KLD films were exposed to ultraviolet radiation (Hg lamp, 96 h) and analyzed by thermogravimetry (TG) in inert and oxidative atmosphere. Typical multi-step decomposition profiles were obtained. The apparent activation energy (E_a) of the thermal degradation of the samples was computed by the Vyazovkin method. The KLD degradation presented only small intervals of decomposition degree with constant E_a values. PVA and blends showed intervals of up to 50% in decomposition degree with nearly constant E_a, and smaller intervals in which E_a varies drastically. The influences of samples irradiation and of surrounding gas in TG analysis on E_a are also shown.