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1.
The thermal degradation of samples of cellulose, hemicellulose, and lignin have been investigated using the techniques of thermogravimetric analysis (TGA) and differential thermal analysis (DTA) between room temperature and 600°C. The results calculated from static and dynamic TGA indicated that the activation energy E for thermal degradation for different cellulosic, hemicellulose, and lignin samples is in the range 36–60, 15–26, and 13–19 kcal/mole, respectively. DTA of all the wood components studied showed an endothermic tendency around 100°C in an atmosphere of flowing nitrogen and stationary air. However, in the presence of flowing oxygen this endothermic effect was absent. In the active pyrolysis temperature range in flowing nitrogen and stationary air atmospheres, thermal degradation of Avicel cellulose occurred via a sharp endothermic and a sharp exothermic process, the endothermic nadir and exothermic peak being at 320° and 360°C, respectively. In the presence of oxygen, combustion of Avicel cellulose occurred via two sharp exothermic processes. DTA studies of different cellulose samples in the presence of air showed that the shape of the curve depends on the sources from which the samples were prepared as well as on the presence of noncellulosic impurities. Potassium xylan recorded a sharp exothermic peak at 290°C in a nitrogen atmosphere, and in a stationary air atmosphere it yielded an additional peak at 410°C, while in the presence of oxygen the curve showed two sharp exothermic peaks. DTA traces of periodate lignin in flowing nitrogen and air were the same and showed two exothermic peaks at 320° and 410°C, while in the presence of oxygen there were two exothermic peaks in the temperature range 200°–500°C.  相似文献   

2.
Seven polyesters having different amounts of halogen were studied for kientics of degradation and fire retardant efficiency. Out of them, the polyesters number 1, 2, 3, and 4 had the molar ratios of chlorendic acid to isophthalic acid of 0.25, 0.67, 1.5, and 4.0 respectively. The polyesters number 5, 6, and 7 were based on dimethyl-di-(p-oxyacetoxymethylphenyl)-methane, dimethyl-di-(3,5-dichloro-4-oxyacetoxymethylphenyl) methane and dimethyl-di-(3,5-dibromo-4-oxyacetoxymethylphenyl)-methane respectively. These studies were done with the help of thermogravimetric analysis (TGA), differential thermal analysis (DTA), infra-red spectroscopy and glow rod apparatus. The thermal stability of these polyesters decreased in the following order: 5 > 6 > 7 > 1 > 2 > 3 > 4, taking the threshold temperature as a measure of the thermal stability. The 50% weight loss temperature determined from TGA curves supported this to some extent. These studies further revealed that these polyesters degrade in two stages. The first stage of degradation ranged from 250–450°C. The second stage of degradation is in the range of 450–600°C. In the first stage, the range of temperature for degradation is constricted by increasing the halogen content. Bromination is more effective than chlorination. The activation energy for degradation of these polyesters showed the same trend as the thermal stability. But the flame resistance is somewhat in the reverse order of thermal stability. These studies also confirm a cyclic mechanism for flame retardancy.  相似文献   

3.
Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were conducted on two common types of rye straws (Danko and Kustro) at a heating rate of 20°C/min in an oxidizing atmosphere (15% oxygen and 85% nitrogen, by volume) between ambient temperature and 700°C. The two step nature of the TGA curves and the dual peak characteristics of the DTA curves showed that rye straw had two distinct reaction zones. The initial degradation temperatures, the residual mass at 700°C, the thermal degradation rates in the first and second reaction zones and the kinetic parameters of each reaction zone (order of reaction, activation energy and pre-exponential factor) were determined. Higher thermal degradation rates were observed in the first reaction zone as compared to those in the second reaction zone.  相似文献   

4.
The thermal degradation behavior of copolymers of methacrylic acid (81.5–17.4 mol%) was studied using thermogravimetry (TGA) and differential scanning calorimetry (DSC) and the degradation products were analyzed using mass spectroscopy and DSC–FTIR. From mass spectroscopy, it was observed that in the copolymers the main degradation products obtained below 280°C included water, ethanol, and methanol, whereas at higher temperature (up to 400°C), CO2, CO, and small olefins were liberated. Elimination of water and ethanol is attributed to anhydride formation, which is believed to result from two routes: (a) anhydride formation involving adjacent acid groups and (b) anhydride formation involving adjacent acid and ester groups. An endothermic transition in the DSC and percent weight loss in the TGA in the same temperature range (140–280°C) support the above proposal. An increase in weight loss with increase in EA content of the copolymer confirms the participation of EA in the anhydride formation. © 1994 John Wiley & Sons, Inc.  相似文献   

5.
Poly(vinyl alcohol) was modified by an aldehyde acetal reaction with 2,4,6‐trinitrophenylacetaldehyde to give a new energetic polymer poly(vinyl 2,4,6‐trinitrophenylacetal) (PVTNP). The structure of PVTNP was characterized by elemental analysis, ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectra. The glass‐transition temperature of PVTNP was evaluated by differential scanning calorimetry (DSC), and the thermal stability of PVTNP was tested by differential thermal analysis (DTA) and thermogravimetric analysis (TGA). DSC traces showed that the PVTNP polymer had one single glass‐transition temperature at 105.3°C. DTA and TGA curves showed that the thermooxidative degradation of PVTNP in air was a three‐step reaction, and the percentage of degraded PVTNP reached nearly 100% at 650°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011  相似文献   

6.
The behavior on thermal degradation of the sericin cocoon consisting of a sericin and a few fibroin has been examined by means of evolved gas analysis (EGA), evolved gas detection (EGD), and differential thermal analysis (DTA). The sericin cocoons produced from the silkworm (Nd, Nd-s/Nd-s,Nd-s/+) and sericin stripped from the silk gland in the silkworm show two endothermic peaks at 220°C and 270°C according to differential thermal analysis. From the x-ray diffraction pattern, dynamic mechanical measurement, and the thermal gravity analysis (TG), the former peak occurs by the scission of the structural state and the change from crystalline to amorphous. Moreover, at 220°C, the weight changes markedly, the yellowness index (L/b) measured by the color difference meter abruptly decreases, and the gas (CO2), evolved from the sericin cocoon, shows increases above 200°C.  相似文献   

7.
Almonds are subjected to thermal processes in the production of processed food and this can affect their thermal stability and lead to oxidation processes. In this work, almond samples from three different cultivars (Spanish Guara and Marcona, and American Butte) were characterized by using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) at different heating rates. Crystallization and melting parameters were determined by DSC; whereas thermal stability was studied by TGA, showing no apparent degradation for all samples up to around 290 °C. Butte samples showed the lowest DSC values and TGA initial degradation temperature. These results were linked with differences in fatty acid profiles between Butte and Spanish almond cultivars, Butte presenting higher linoleic acid content. Successful discrimination was obtained for samples analyzed at 2 and 10 °C min−1 heating rates for DSC and TGA, respectively, by applying multivariate stepwise linear discriminant analysis (LDA). The results obtained proved the suitability of thermal analysis techniques combined with LDA for an easy and fast discrimination among different almond cultivars to control eventual adulteration in food processing.  相似文献   

8.
We studied the high temperature performance of soy meal processed to different protein concentrations (flour, concentrate, and isolate), as well as formulated soy-based adhesives, and commercial nonsoy adhesives for comparison. No thermal transitions were seen in phenol-resorcinol-formaldehyde (PRF) or soy-phenol-formaldehyde (SoyPF) or in as-received soy flour adhesive during differential scanning calorimetry scans heating at 10?°C/min between 35 and 235?°C. Heat flow rates decreased in the order soy flour (as received)?>?SoyPF?>?PRF?>?emulsion polymer isocyanate (EPI). In thermogravimetric analysis (TGA) scans from 110 to 300?°C at 2?°C/min, total weight loss decreased in the order soy flour (as-received)>SoyPF?>?PRF?>?casein?>?maple?>?EPI. For bio-based materials, the total weight loss (TGA) decreased in the order soy flour (as-received) > concentrate, casein?>?isolate. Dynamic mechanical analysis from 35 to 235?°C at 5?°C/min of two veneers bonded by cured adhesive showed 30–40% decline in storage modulus for maple compared to 45–55% for the adhesive made from soy flour in water (Soy Flour) and 70–80% for a commercial poly(vinyl acetate) modified for heat resistance. DMA on glass fiber mats showed thermal softening temperatures increasing in the order Soy Flour?<?casein?<?isolate?<?concentrate. We suggest that the low molecular weight carbohydrates plasticize the flour product. When soy-based adhesives were tested in real bondlines in DMA and creep tests in shear, they showed less decrease in storage modulus than the glass fiber-supported specimens. This suggests that interaction with the wood substrate improved the heat resistance property of the adhesive. Average hot shear strengths (ASTM D7247) were 4.6 and 3.1?MPa for SoyPF and Soy Flour compared to 4.7 and 0.8?MPa for PRF and EPI and 4.7 for solid maple. As a whole, these data suggest that despite indications of heat sensitivity when tested neat, soy-based adhesives are likely to pass the heat resistance criterion required for structural adhesives.  相似文献   

9.
Abstract

In order to understand the influence of the inherent chemistry on the relative thermal stability of condensed tannins, the thermal degradation behaviors of various radiata pine bark extracts have been investigated using thermogravimetric analysis (TGA). Generally, results suggest pine bark extract fractions may be readily processed at temperatures below 200°C if co-extracted polysaccharides contents are minimized. Those extracts possessing greater carbohydrate content and lower tannin purity tend to have decreased thermal stability. The initial onset temperature for degradation of relatively crude extracts with high proportions of carbohydrate contents were relatively low (ca. 150°C), whereas extract purification to < 5% carbohydrate content gave increases in thermal stability of at least 50°C. The complicity of the carbohydrate content in the degradation of the tannin samples was also supported by calculated Ozawa activation energies and modulated TGA experiments. While no increase in the thermal stability was gained by acetylating the pendant hydroxyl groups of the pine bark tannin extract, chemical variations such as sulfonation have a large effect on thermal degradation, promoting lower degradation temperatures.  相似文献   

10.
The thermal degradation behaviours of a novel aromatic poly(ester–imide) (PEI) derived from pyromellitic dianhydride and 2,7-bis(4-aminobenzoyloxy)naphthalene have been investigated by thermogravimetric analysis (TGA) and by pyrolysis–gas chromatography/mass spectrometry (pyrolysis–GC/MS). The weight of PEI fell slightly in the temperature range of 350–450 °C in the TGA analysis, but the major weight loss occurred at 520 °C. Evolve gas analysis (EGA) of the PEI showed maximum release of pyrolyzates at 550 °C. The chemical structure of the volatile products resulted from the PEI pyrolysis at different temperatures was identified by pyrolysis–GC/MS. The cleavage of the ester linkage within the polymer chain initiated at 350 °C, and bond scission in the partially hydrolyzed pyromellitimide unit occurred in the temperature range of 450–500 °C. The bonds within the pyromellitimide unit started to cleave at 550 °C. The extensive decomposition of the pyromellitimide segment within the polymer backbone occurred at 600 °C. The possible thermal degradation pathways of this PEI are proposed on the basis of the pyrolysis products.  相似文献   

11.
Carbon nanowires having different functionality has been synthesized through the template assisted approach using poly(vinyl alcohol) (PVA) as precursor polymer at 400?°C, 600?°C, 700?°C and 800?°C in the absence of any catalyst. Carbon nanowires with a diameter range of about 90?C120?nm have been obtained. Scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy are been adopted to characterize the morphology, thermal properties and chemical configuration of the synthesized samples. Raman spectroscopy indicates carbonization of the samples upto 600?°C. Above that carbon-cluster formation is observed at 700?°C and 800?°C. SEM images show the formation of nanowires in alumite template by infiltration of PVA into the pores at 400?°C. The nanowires produced are very flexible at about 700?°C, above which the nanowires tended to retain their rigidity due to the formation of graphite clusters / crystallites.  相似文献   

12.
In this study, virgin and thermal aged PPS samples were prepared and tested using different techniques such as thermogravimetric analysis (TGA), coupled TGA–Fourier transform infrared spectroscopy (FTIR), and FTIR as well as optical microscopy. Some interesting research results can be summarized as follows: TGA results prove the PPS composite samples aged at 180 and 200°C have been degraded obviously during the aging period in oven. Moreover, accelerated aging leads to the degradation of PPS composite with the observation of increased thermal oxidation layer from outside to inside. There is a plateau standing at about 350 μm for the thermal oxidation layer at oxidation temperature of 200°C. Some thermal decomposition models are applied to clarify the degradation kinetics of PPS composite. According to the activation energy value, it appears degradation more easily at the beginning of the heating process in the atmosphere of oxygen than that of nitrogen. Moreover, the related products of PPS composites during pyrolysis are fully discussed with the combined analysis of TGA–FTIR techniques.  相似文献   

13.
Newly prepared and well-characterized nanocomposite thin films of polyvinylpyrrolidone (PVP) containing 2, 5, 10, and 15 wt% cerium (IV) sulfate have been subjected to structural and thermal stability investigations using the transmission electron microscopy (TEM), atomic force microscope (AFM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The nanostructural nature of the investigated films was confirmed from the estimated average size of the particles. Better crystallinity was achieved with the addition of 15 wt% cerium disulfate to PVP. The thermograms of DSC and its derivative for the investigated composites indicated the development of a new endothermic peak of decomposition nature, and the values of peak position and associated enthalpy were found to be composition dependent, indicating a decrease in thermal stability of PVP with the increase of dopant concentration. Thermograms of TGA and its derivative revealed that the weight loss in the composite samples is composition dependent, and two main steps of degradation were clearly evident, the first assigned mainly to dehydration processes at relatively lower temperature range (30–200 °C) and the second at higher temperatures up to 400 °C attributed to decomposition processes. Thermodynamic parameters, such as activation energy, entropy, enthalpy, and Gibbs free energy, were also determined on the basis of thermogravimetric data.  相似文献   

14.
Transparent polycrystalline Gd3TaO7 ceramics were successfully developed. A sol‐gel process was used to synthesize Gd3TaO7 powder with a uniform composition and an estimated average particle size of 100 nm. Simultaneous thermal gravimetric analysis and differential thermal analysis (TGA/DTA) was used to identify the decomposition sequence as a function of temperature for the as‐synthesized sol‐gel powders. Crystallization was confirmed by X‐ray diffraction (XRD) and a single phase was achieved by calcining at 1000°C. The calcined powders were hot‐pressed at 1400°C to achieve >96% theoretical density with closed pore structure followed by a hot isostatic pressing at 1400°C at 207 MPa to achieve a fully dense structure. Microstructural characterization shows a uniform grain size distribution with an average grain size of about 7 μm. In‐line transmission measurements revealed high transparency in the red and infrared. Thermal conductivity was measured to be >1.6 W/mK at room temperature, decreasing to ~1.3 W/mK by 500°C. Dielectric properties remain stable with relative permittivity values just above 200 and loss tangents <0.005 up to 350°C.  相似文献   

15.
Zn–Al–NO3–layered double hydroxide (Zn–Al–NO3–LDH) was prepared by the co-precipitation method at a constant pH of 7 and a ratio of Zn/Al = 4. A thermal treatment was performed for LDH at various temperatures. Powder XRD patterns showed that the layered structure of the LDH samples was stable below 200 °C, which was also confirmed by thermogravimetric (TGA) and differential thermal (DTA) analyses. Infrared spectra of the samples showed the characteristic peaks of LDH, and changes of these peaks were observed when thermal treatment was performed above 150 °C. Diffuse reflectance spectroscopy of the samples showed more than one energy gap at calcination temperatures below200 °C. In samples calcined at 200 °C and above only one energy gap was observed at approximately 3.3 eV. The photocatalytic activity was found to increase with the increase of the ZnO crystal size, which can be achieved by increasing the calcination temperature of the samples. Because of the presence of water molecules and anionic NO3 in the interlayer of the LDH, the dielectric response of the calcined LDH can be described by an anomalous low frequency dispersion using the second type of Universal Power Law for calcination temperatures below 200 °C. The dielectric response of the calcined LDH above 150 °C displays the dielectric relaxation behaviour of ZnO because of the formation of a ZnO phase in the LDH within this temperature range.  相似文献   

16.
Epoxidized rubber seed oil (4.5% oxirane content, ERSO) was prepared by treating the oil with peracetic acid generated in situ by reacting glacial acetic acid with hydrogen peroxide. The thermal behavior of the ERSO was determined by differential scanning calorimetry. The effect of the epoxidized oil on the thermal stability of poly (vinyl chloride) (PVC) plastigels, formulated to contain dioctyl phthalate (DOP) plasticizer and various amounts of the epoxidized oil, was evaluated by using discoloration indices of the polymer samples degraded at 160°C for 30 min and thermogravimetry at a constant heating rate of 10°C/min up to 600°C. The thermal behavior of the ERSO was characterized by endothermic peaks at about 150°C, which were attributed to the formation of network structures via epoxide groups, and at temperatures above 300°C, which were due to the decomposition of the material. Up to 50% of the DOP plasticizer in the PVC plastisol formulation could be substituted by ERSO without a marked deleterious effect on the consistency of the plastigel formed. In the presence of the epoxidized oil, PVC plastigel samples showed a marked reduction in discoloration and the number of conjugated double bonds, as well as high temperatures for the attainment of specific extents of degradation. These results showed that the ERSO retarded/inhibited thermal dehydrochlorination and the formation of long (n > 6) polyene sequences in PVC plastigels. The plasticizer efficiency/permanence of ERSO in PVC/DOP plastigels was evaluated from mechanical properties' measurements, leaching/migration tests, and water vapor permeability studies. The results showed that a large proportion of DOP could be substituted by ERSO in a PVC plastisol formulation without deleterious effects on the properties of the plastigels. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.  相似文献   

17.
Differential thermal curves of spurrite-calcite rocks show two characteristic endothermic peaks at 725–850°C and at 845–990°C, both due to decarbonization. A method for determining the amounts of calcite and spurrite when both are present is proposed using DTA analysis in conjunction with the determination of CO2 in the bulk sample. The results of DTA are confirmed by TG and X-ray diffraction studies.  相似文献   

18.
We investigated the thermal decomposition behavior of three commercially available liquid crystalline polymers (LCPs), Vectra A950, Vectra B950, and Xydar SRT-900. The apparent activation energies (Ea) associated with the thermal degradation processes were determined by the Ozawa and Kissinger methods, using data from dynamic thermogravimetric analysis (TGA) experiments. The magnitudes of the Ea for these LCPs follow the order: Xydar > Vectra A > Vectra B in both air and N2 environments. The stability of the samples at the beginning of the degradation processes follows the same order. This order may result from the kink naphthoyl units in Vectra A and a relatively weak bond dissociation energy of C-N in Vectra B. However, at 560°C the weight loss values of these three LCPs in N2 become close (around 37%). After 600°C, the stability order surprisingly changes to Vectra B950 > Vectra A950 > Xydar SRT-900. This suggests that the more stable the sample is at the beginning, the less stable the corresponding residue is. Fourier Transform Infra-red (FTIR) spectra imply that random chain scission and hydrogen abstraction are the degradation mechanisms in N2 atmosphere and the bands of CO stretching for all 3 LCPs decrease after 560°C, indicating the finish of the ester bond rupture process. Further increasing temperature mainly results in carbonization. For all three LCPs, CO2 is the dominant degradation product during the entire testing periods in both N2 and air environments and the change of CO2 amount is consistent with the degradation rate. Residues after TGA experiments in N2 were analyzed and found to have a relatively high percentage of oxygen element, indicating the formations of ether and ketone structures during the thermal degradation of these three LCPs. Forty-seven percent of the nitrogen element remaining in the case of Vectra B950 indicates the formation of the structures containing nitrogen. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2195–2207, 1999  相似文献   

19.
Hexamethylenetetramine dinitrate (HDN) is a rather weak explosive but is used as a precursor for the synthesis of RDX, one of the most important secondary nitramine explosives. HDN has limited application because of its hygroscopic character. This paper reports on the synthesis and characterization of HDN in high yield and purity by the reaction of hexamine with nitric acid at temperatures below 15 °C. It was characterized by FTIR and 1H NMR spectroscopy, Scanning Electron Microscopy (SEM) and Liquid Chromatography/Mass Spectrometry (LC/MS) measurements. The thermal characteristics of HDN were determined by DSC and TG/DTA. The DSC curve of HDN shows an endothermic peak at 170.5 °C corresponding to the melting point of HDN, followed by two exothermic peaks at 174.0 °C and 200.5 °C due to the decomposition. The differences in the thermal behavior of HDN samples, which were thermally aged at 50 °C, 100 °C, and 150 °C in a nitrogen atmosphere were examined. Additionally, some quantum chemical properties of the nitration of hexamethylenetetramine were calculated.  相似文献   

20.
Epoxy resin of 9,9′-bis-(3,5-dibromo-4-hydroxyphenyl) anthrone-10 (EANBr, EEW 490) was synthesized and was characterized by IR and 1HNMR . EANBr and EPK3251 cured resin (EANBrC) were characterized by DSC and TGA at 10°Cmin?1 under nitrogen atmosphere. Broad DSC endothermic transitions of EANBr (265.3 °C) and EANBrC (291.4 °C) are due to some physical change and further confirmed by no weight loss in their TG thermograms. EANBr and EANBrC are thermally stable up to 340 °C and 310 °C, respectively. EANBr has followed single step degradation kinetics, while EANBrC has followed two step degradation kinetics. EANBr followed apparently zero order kinetics, while EANBrC followed apparently second order (1.80) and first order (0.89) degradation kinetics, respectively. Ea and A values of EANBrC (299.7 kJmol?1 and 6.32?×?1020 s?1) were found higher than that of EANBr (201 kJmol?1 and 2.45?×?1013 s?1) due to more rigid nature of EANBrC. The ΔS* value of the first step degradation of EANBrC (146.3 JK?1 mol?1) was found much more than that of EANBr (4.6 JK?1 mol?1). Jute – EANBr composite (J-EANBr) was prepared by compression molding technique at 120 °C for 5 h and under 20 Bar pressure. The observed tensile strength, flexural strength, electric strength and volume resistivity of J-EANBr are 24.7 MPa, 19.0 MPa, 1.8 kVmm?1 and 3.5?×?1012 ohm cm, respectively. Water absorption in J-EANBr was carried out at 30 ± 2 °C against distilled water, 10% NaCl, 10% HCl, 10% HNO3, 10% H2SO4, 10% NaOH, and 10% KOH and also in boiling water. The equilibrium time and equilibrium water content for J-EANBr in different environments are 384–432 h; 12.7–15.2%, respectively. The observed equilibrium water content and diffusivity trends of J-EANBr are KOH>H2SO4>HCl>NaOH>H2O>NaCl and H2O>NaCl>NaOH>H2SO4>HCl>KOH, respectively. Good thermo-mechanical, electrical properties and excellent hydrolytic stability of J-EANBr may be useful for high temperature applications in diverse fields.  相似文献   

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