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1.
A long-term(about nine months) isothermal degradation experiment of two different commercial polylactide(PLA) samples used for food packaging was carried out at a relatively low temperature(423 K). Thermooxidative degradations of the same polymers were carried out in a thermogravimetric(TG) analyser, at higher temperatures(453 K ≤ T ≤ 523 K), under isothermal heating conditions. The obtained set of experimental TG data was used to determine the apparent activation energy(Ea) of degradation through two isothermal kinetic methods. The results from long-term experiment evidenced considerable mass loss for both PLA samples in the investigated period, but the experimental data were not in agreement with those from the short-term degradations at higher temperatures, thus suggesting a different degradation kinetics, and, then a low reliability of the lifetime predictions for polymers in service or degradation forecasts for the end of their life based on experiments at higher temperatures.  相似文献   

2.
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.  相似文献   

3.
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.  相似文献   

4.
The thermal and rheological behaviour of seven random Cl-ended aromatic PES/PEES copolymers (Mn ≈ 9500 g mol−1), at various PES/PEES repeating unit ratios, was studied. The glass transition temperatures (Tg), 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 (Ti) and the half decomposition temperatures (T1/2) were directly determined by TG curves, while the apparent activation energies of degradation (Ea) were obtained by the Kissinger method. In addition, the complex viscosity (η) of molten copolymers was determined in experimental conditions of linear viscoelasticity. Ti, T1/2, Ea, and η values were depending on copolymer composition, showing a trend similar to that of Tg values. The results obtained were discussed and interpreted.  相似文献   

5.
The thermal and rheological characterizations of seven random, low molecular weight (Mn ≅ 9500 g mol−1), H2N-ended polyethersulfone/polyetherethersulfone (PES/PEES) copolymers, at various PES/PEES ratios, were performed. The glass transition temperatures (Tg) 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 (Ti) and the half decomposition temperatures (T1/2) were directly determined by TG curves, while the apparent activation energies of degradation (Ea) were obtained by the Kissinger method. In addition, the complex viscosities (η) of the molten polymers were determined in experimental conditions of linear viscoelasticity. Tg, Ea and η values increased linearly with PES% content, while Ti and T1/2 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.  相似文献   

6.
Polypropylene/polylactic acid (PP/PLA) blends containing 5 wt% of nanoclay in presence and absence of an ethylene‐butylacrylate‐glycidyl methacrylate terpolymer as compatibilizer were prepared by melt‐mixing process. A matrix‐droplet–type morphology confirmed by transmission electron microscope (TEM) and scanning electron microscopy (SEM) studies is formed in presence and absence of the compatibilizer in which the clay platelets were mainly localized in the polylactic acid (PLA) dispersed phase. Degradation studies by means of thermogravimetry analysis (TGA) and analysis of degradation activation energy (Ea), Tmax (maximum degradation temperature), and ΔT (difference between initial and final degradation temperatures) parameters for each polymer component of the system revealed that incorporation of less stable PLA phase to polypropylene (PP) decreases Ea and Tmax parameters, and hence, reduces the thermal stability of PP phase, while incorporation of clay nanoplatelets to the neat blend further reduces its thermal stability attributed to their lack of localization in PP phase. Compatibilization of the filled system results in migration of clay nanoplatelets toward PP and improves Ea and Tmax of PP phase. On the other hand, the Ea and Tmax of PLA phase of the blend were increased with incorporation of clay and its localization within that phase, while compatibilization of the filled system slightly reduces thermal stability of PLA phase due to migration of clay toward PP. A correlation was found between Ea and intensity of the thermogravimetry analysis Fourier‐transform infrared spectroscopy (TGA‐FTIR) peaks of the evolved products. Using the Criado method, a detailed analysis on degradation mechanism of each component was performed, and the changes in the degradation mechanism of the developed systems were determined.  相似文献   

7.
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.  相似文献   

8.
Initial decomposition temperature (Ti), apparent activation energy of degradation (Ea) and glass transition temperature (Tg) of some low molar mass (Mn ≈ 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 Ti and Tg 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.  相似文献   

9.
Nanocomposites from nanoscale silica particles(NS),diglycidylether of bisphenol-A based epoxy(DGEBA),and 3,5-diamino-N-(4-(quinolin-8-yloxy) phenyl) benzamide(DQPB) as curing agent were obtained from direct blending of these materials.The effect of nanosilica(NS) particles as catalyst on the cure reaction of DGEBA/DQPB system was studied by using non-isothermal DSC technique.The activation energy(E_a) was obtained by using Kissinger and Ozawa equations. The E_a value of curing of DGEBA/DQPB/10%NS system showed a decrease of about 10 kJ/mol indicating the catalytic effect of NS particles on the cure reaction.The E_a values of thermal degradation of the cured samples of both systems were 148 kJ/mol and 160 kJ/mol,respectively.The addition of 10%of NS to the curing mixture did not have much effect on the initial decomposition temperature(T_i) but increased the char residues from 20%to 28%at 650℃.  相似文献   

10.
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 (Ea) 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 Ea values. PVA and blends showed intervals of up to 50% in decomposition degree with nearly constant Ea, and smaller intervals in which Ea varies drastically. The influences of samples irradiation and of surrounding gas in TG analysis on Ea are also shown.  相似文献   

11.
The results of quantum chemical calculations of the potential profile in the LaF3 crystal lattice in the range of superionic phase transition are presented for clusters containing 24 to 1200 ions. It is found that the values of formation energy E a of vacancy-interstitial fluoride ion defects and potential barriers E d hindering the movement of fluoride ions and determining the efficiency of charge transport in the lattice grow monotonously from the minimum values E a = 0.12 eV and E d = 0.22 eV for a 24-ion cluster to the maximum E a = 0.16 eV and E d = 0.26 eV for clusters of 576 and 1200 ions. It is shown that the values of E a and E d obtained for the dielectric phase (T < T c) are several times the values of E a and E d for the superionic state (TT c) of LaF3. The values of E a and E d obtained by quantum chemical calculations from clusters of 576 and 1200 ions agree well with energies E a and E d obtained from the analysis of the data of the Raman and quasielastic light scattering.  相似文献   

12.
Two novel algorithms are presented for processing thermogravimetric (TG) data obtained during the degradation of a polymer in a single step mechanism under non-isothermal conditions. The first algorithm assesses three characteristics computed from the TG profile against a theoretical data set, and identifies likely kinetic models to fit the experimental data. The second algorithm provides an iterative arithmetic method to extract the apparent activation energy, Ea, and Arrhenius A-factor, A, from TG data without simplifying assumptions. The algorithms are validated using model data and applied to data for the non-isothermal degradation of poly(ethylene adipate), poly(lactic acid) (PLA) and a food packaging PLA composite formulation containing kenaf, a natural fibre. The analysis of poly(ethylene adipate) produced Ea = 137 kJ mol−1 and log10A = 8.71 (first-order kinetic model). The kenaf fibre destabilizes PLA, lowering its Ea from 190 kJ mol−1 to 150 kJ mol−1 (contracting volume model).  相似文献   

13.
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 Ea, 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 Ea. 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 Ea. 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.  相似文献   

14.
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 (Ea) of degradation, of the various nanocomposites were determined. The results were discussed and interpreted.  相似文献   

15.
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 (Ea) 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 Ea 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.  相似文献   

16.
Densities for aqueous solutions of magnesium tetraborate MgB4O7(aq) at the molalities of (0.00556–0.03341) mol·kg?1 were measured with an Anton Paar Digital vibrating-tube densimeter at temperature intervals of 5 K from 283.15 to 363.15 K and 0.1 MPa. Apparent molar volumes were obtained based on the experimental density data, and the 3D diagrams of the apparent molar volume (V ? ) of MgB4O7(aq) against temperature (T) and molality (m) were plotted. On the basis of the Vogel–Tamman–Fulcher equation, the coefficients of the correlation equation for densities of MgB4O7(aq) against temperature and molality were parameterized. According to the Pitzer ion-interaction model of the apparent molar volume, the temperature correlation equations of Pitzer single-salt parameters F(i,p,T)?=?a0?+?a1?×?T?+?a2?×?T 2?+?a3/T?+?a4?×?ln(T)?+?a5?×?T 3 (where T is temperature in Kelvin, a i are model parameters) for MgB4O7 were obtained for the first time.  相似文献   

17.
Degradation of commercial polysulfones (PSF) was investigated in air and in inert atmosphere (nitrogen) using thermogravimetric (TG) method. It has been found that the degradation of Udel P-1800 PSF is initiated about 400°C, both in air and in nitrogen. The activation energy of degradation of PSF, (E a), has been calculated by the Kissinger and Ozawa methods. The value ofE a about 200 kJ·mol?1 has been found for both air and nitrogen atmosphere. Experimental results concerning thermal properties of PSF (T g andT d,1/2) were compared with those obtained by the computer modeling technique, and a good agreement has been found.  相似文献   

18.
In this study, the thermal behavior in terms of glass transition (T g), degradation, and thermal stability of four commercial new-generation posterior bulk fill composites (Surefill SDR, Dentsply; Quixfill, Dentsply; Xtrabase, Voco; and Xtrafill, Voco) activated by light-emitting diodes (LEDs) was analyzed by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The activation energies (E a) for the decomposition of the dental resins were calculated based on the Kissinger and Doyle kinetic models from the peaks of the endothermic curves obtained when the specimens were heated at four different temperatures (5, 10, 15, and 20 °C min?1) during DSC. The results show that the Xtrabase composite displayed the highest T g (120 °C at a 5 °C min?1 heating rate) and E a (157.64 kJ mol?1) values associated with thermal degradation from the main chain of the polymer.  相似文献   

19.
In this work, poly(methyl methacrylate) films 1% additivated with new thiophosphate esters antioxidants derived from technical Cashew Nutshell Liquid (CNSL), a byproduct of the cashew nut (Anacardium occidentale L.) industry, were investigated by thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC) measurements under inert (N2) and oxidative (synthetic air) atmospheres. Three new products were synthesized and characterized by GC/MS, 1H and 31P NMR. The analyses were focused on the onset (T e) and offset temperature (T o) of degradation of the films, and on the maximum degradation temperature (T MAX). It was observed that the thermal stability of the films increased with the addition of the thiophosphate ester antioxidants, which indicates that CNSL could be used as a natural source of phenolic material for the synthesis of antioxidants.  相似文献   

20.
This article studies the thermokinetics and safety parameters of cumene hydroperoxide (CHP) manufactured in the first oxidation tower. Vent sizing package 2 (VSP2), an adiabatic calorimeter, was employed to determine reaction kinetics, the exothermic onset temperature (T 0), reaction order (n), ignition runaway temperature (T C, I), etc. The n value and activation energy (E a) of 15?mass% CHP were calculated to be 0.5 and 120.2?kJ?mol?1, respectively. The heat generation rate (Q g) of 15?mass% CHP compared with hS (cooling rate)?=?6.7?J?min?1?K?1 of heat balance, the T S,E and the critical extinction temperature (T C, E) under 110?°C of ambient temperature (T a) were calculated 111 and 207?°C, respectively. The Q g of 15?mass% CHP compared with hS?=?0.3?J?min?1?K?1 of heat balance was applied to determine the T C, I that was evaluated to be 116?°C. This article describes the best operating conditions when handling CHP, starting from the first oxidation tower.  相似文献   

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