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891.
With differential scanning calorimetry measurements, the nonisothermal crystallization of biocomposites of poly(?‐caprolactone) (PCL) reinforced with silk fibroin fiber (SF) was investigated. With the gradual addition of SF, the strengthening of the heterogeneous nucleation reagent effect of SF led to the acceleration of PCL crystallization, and secondary crystallization occurred and became more remarkable with increases in the cooling rate and SF content. Moreover, with the introduction of SF and an increase in the cooling rate, the nucleation and growth mode of the PCL crystalline phase was slightly changed. Because of the confinement of the fiber network structure, the crystallite size of PCL was reduced, the crystallization exothermicity of PCL decreased, and the crystallization activation energy of PCL increased. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
892.
N,N‐Diglycidylaniline was reacted with aniline (yielding polymer EP‐1) and the newly synthesized chromophore 4‐(phenylazo)aniline (yielding polymer EP‐2). The curing kinetics of these two epoxy resin systems was studied in dynamic experiments by means of differential scanning calorimetry. Kinetic parameters such as the activation energy and frequency factor were estimated with the Ozawa method [E(O) and A(O), respectively], the Kissinger method [E(K) and A(K), respectively], and the modified Avrami method [E(A) and A(A), respectively]. The activation energy and frequency factor of EP‐1 were much lower than those of EP‐2 estimated with the Ozawa, Kissinger, and Avrami methods. The activation energy and frequency factor for EP‐1 determined with the Ozawa method [E(O) = 55.8 kJ/mol, A(O) = 10 × 103 1/s] and the Avrami method [E(A) = 56.4 kJ/mol, A(A) = 9.2 × 103 1/s] were higher than those determined with the Kissinger method [E(K) = 51.0 kJ/mol, A(K) = 2 × 103 1/s]. In the case of EP‐2, the kinetic parameters calculated with the Ozawa model [E(O) = 140.4 kJ/mol, A(O) = 12.3 × 1013 1/s] and the Kissinger model [E(K) = 139.9 kJ/mol, A(K) = 10.9 × 1013 1/s] were higher than those calculated with the Avrami model [E(A) = 130.4 kJ/mol, A(A) = 7.9 × 1012 1/s]. The obtained polymers were characterized with Fourier transform infrared, 1H‐NMR, differential scanning calorimetry, and ultraviolet–visible spectroscopy. The polymers exhibited low glass‐transition temperatures in the range of 57–79°C and good solubility in common organic solvents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
893.
The cure kinetics of medium reactivity unsaturated polyester resin formulated for Liquid Composite Molding process simulation was studied by Differential Scanning Calorimetry (DSC) under isothermal conditions over a specific range of temperature. For isothermal curing reactions performed at 100, 110, and 120°C, several influencing factors were evaluated using the heat evolution behavior of curing process. We propose two‐ and three‐parameter kinetic models to describe the cure kinetics of thermoset resins. Comparisons of the model solutions with our experimental data showed that the three‐parameter model was the lowest parameter model capable of capturing both the degree of cure and the curing rate qualitatively and quantitatively. The model parameters were evaluated by a non‐linear multiple regression method and the temperature dependence of the kinetic rate constants thus obtained has been determined by fitting to the Arrhenius equation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
894.
B. C. Ennis 《The Journal of Adhesion》1989,30(1):57-62
Thermal analysis (TA) is practically indispensable to the study and characterisation of modern structural adhesives, particularly those based on epoxies. Because a recent paper in this journal-“Linking Cure Process to Adhesive Bulk Strength by Differential Thermal Analysis” by Jozavi and Sancaktar1-advocates TA to those familiar with aspects of adhesion other than analysis and chemistry of adhesives, it is more open to comment than is usual. 相似文献
895.
The effect of molecular weight (MW) and thermal history on the heat capacity (cp) of amorphous polystyrene over the temperature range from 200–440 K has been measured using differential scanning calorimetry (d.s.c.) General equations are given that show the influence of MW on cp in both the glassy and liquid states. An enthalpic definition of the glass temperature reflects changes in the glass structure, due to thermal history, that are not found using conventional d.s.c. constructions. Thermodynamic and statistical mechanical theories give reasonable approximations to the observed Tg-MW curve but small systematic deviations are found. The effect of thermal history on Tg can be reproduced using a MW-dependent activation enthalpy. 相似文献
896.
897.
Markov DI Zubov EO Nikolaeva OP Kurganov BI Levitsky DI 《International journal of molecular sciences》2010,11(11):4194-4226
We compared thermally induced denaturation and aggregation of two isoforms of the isolated myosin head (myosin subfragment 1, S1) containing different "essential" (or "alkali") light chains, A1 or A2. We applied differential scanning calorimetry (DSC) to investigate the domain structure of these two S1 isoforms. For this purpose, a special calorimetric approach was developed to analyze the DSC profiles of irreversibly denaturing multidomain proteins. Using this approach, we revealed two calorimetric domains in the S1 molecule, the more thermostable domain denaturing in two steps. Comparing the DSC data with temperature dependences of intrinsic fluorescence parameters and S1 ATPase inactivation, we have identified these two calorimetric domains as motor domain and regulatory domain of the myosin head, the motor domain being more thermostable. Some difference between the two S1 isoforms was only revealed by DSC in thermal denaturation of the regulatory domain. We also applied dynamic light scattering (DLS) to analyze the aggregation of S1 isoforms induced by their thermal denaturation. We have found no appreciable difference between these S1 isoforms in their aggregation properties under ionic strength conditions close to those in the muscle fiber (in the presence of 100 mM KCl). Under these conditions kinetics of this process was independent of protein concentration, and the aggregation rate was limited by irreversible denaturation of the S1 motor domain. 相似文献
898.
R.L. Almeida M.A.S.S. Ravagnani A.N. Modenes 《Chemical Engineering and Processing: Process Intensification》2010
This work presents a mathematical model for soybean oil extraction in a belt extractor with miscella recirculation. The mathematical model consists of partial differential and algebraic equations and it takes into account the extractor dimension and the physical properties of the solid and miscella. Experimental data collected in an industrial process in Stead State were used to check the model validity. The model was solved using the Finite Difference Method in a computational routine developed in Maple™ and it was compared with the Method of Ideal Stages. The results are coherent and consistent with the extraction phenomena and they can be used to evaluate the influence of several parameters and to obtain the soybean oil concentration profile in any of the phases and parts of the extractor, either in vertical or horizontal arrangement. 相似文献
899.
900.
Three samples of vinyl ester resins (VERs) were synthesized using bisphenol‐A‐based epoxy resins of varying epoxide equivalent weights (EEW) and acrylic acid in presence of triphenylphosphine as a catalyst at 80 ± 2°C. The cresyl glycidyl ether was used as reactive diluent during the synthesis of VERs. A suitable reaction mechanism was proposed and discussed for the reactions involving epoxide group and acid groups. This was further confirmed by infrared spectroscopic analysis. The maximum peak temperature from DSC were at 106.05°C, 114.20°C, and 128.86°C for benzoyl peroxide initiated VERs viz. samples V1CV, V2CV, and V3CV, respectively, increased with the increase of EEW of the parent epoxy resin. It has also been found that the films of VER having highest EEW of bisphenol‐A epoxy resin showed best chemical resistance amongst all other VERs in this study. The mechanical properties such as hardness and flexibility also showed a similar trend. The thermal stability was found to decrease with the increase of EEW of bisphenol‐A epoxy resin in the VERs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献