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1.
The cure-induced phase separation processes of various thermoplastics(TP)-modified thermosetting systems which show upper critical solution temperature (UCST) or lower critical solution temperature (LCST) were studied with emphasis on the temperature dependency of the phase separation time and its potential application in the cure time-temperature processing window. We found that the phase separation time/temperature relationship follows the simple Arrhenius equation. The cure-induced phase separation activation energy Ea(ps) generated from the linear fitting of the Arrhenius equation is irrelevant to the detection means of phase separation time. We also found that Ea(ps) is insensitive to TP content, TP molecular weight and curing rate, but it changes with the cure reaction kinetics and the chemical environment of the systems. With the established phase separation time-temperature dependence relation, we can easily establish the whole cure time-temperature transformation (TTT) diagram with morphology information which is a useful map for the TP/TS composites processing industry. 相似文献
2.
3.
Elena Dibildox-Alvarado Jorge F. Toro-Vazquez 《Journal of the American Oil Chemists' Society》1998,75(1):73-76
Tripalmitin (TP) crystallization in sesame oil solutions (0.98, 1.80, and 2.62%, wt/vol) was investigated by utilizing a modification
of the Avrami equation. The modified equation retains the original correspondence to the nucleation process (i.e., n) and crystal growth and simply corrects the value of the crystallization rate constant (z) by eliminating the influence of n. The energy of activation (E
a
) values for TP crystallization in sesame oil solution, calculated with the modified z, were quite similar to those calculated with the reciprocal of time required to achieve 50% of TP crystallization (t
F
=0.50−1). However, E
a
values calculated with z from Avrami’s original equation were quite different from those obtained with t
F
=0.50−1. Thus, z and E
a
values calculated through the Avrami equation yield erroneous results, especially when comparing crystallization processes
having different magnitudes of n, as in this study. Additional analysis that considered the viscosity of the TP oil solutions concluded that, at equal supercooling
conditions (e.g., 22.0–22.5), the magnitude of z and E
a
became more dependent upon the crystal growth process as oil viscosity decreased. In contrast, as viscosity of the oil phase
increased, the main crystallization process, evaluated through z and E
a′
was nucleation. Furthermore, within the supercooling interval achieved at the temperatures utilized, the increase in supercooling
at constant viscosity conditions (e.g., 5.25–5.5 dynes/cm2) would produce a higher degree of nucleation without an appreciable effect on TP crystal size. The results obtained indicate
that investigating the effects of supercooling, molecular diffusion (i.e., viscosity) and TP concentration on the magnitude
of z and E
a
during TP crystallization in sesame oil requires a multiple variable statistical approach. 相似文献
4.
The nonlinear phase‐separation behavior of poly(methyl methacrylate)/poly(styrene‐co‐maleic anhydride) (PMMA/SMA) blends over wide appropriate temperature and heating rate ranges was studied using time‐resolved small‐angle laser light scattering. During the non‐isothermal process, a quantitative logarithm function was established to describe the relationship between cloud point (Tc) and heating rate (k) as given by Tc = Alnk + T0, in which the parameter A, reflecting the heating rate dependence, is much different for different compositions due to phase‐separation rate and activation energy difference. For the isothermal phase‐separation process, an Arrhenius‐like equation was successfully applied to describe the temperature dependence of the apparent diffusion coefficient (Dapp) and the relaxation time (τ) of the early stage as well as the late stage of spinodal decomposition (SD) of PMMA/SMA blends. Based on the successful application of the Arrhenius‐like equation, the related activation energies could be obtained from Dapp and τ of the early and late stages of SD, respectively. In addition, these results indicate that it is possible to predict the temperature dependence of the phase‐separation behavior of binary polymer mixtures during isothermal annealing over a range of 100 °C above the glass transition temperature using the Arrhenius‐like equation. © 2012 Society of Chemical Industry 相似文献
5.
Guipeng Yu Cheng Liu Bing Li Liwei Wang Jinyan Wang Xigao Jian 《Journal of Polymer Research》2012,19(3):9829
The effect of the incorporation of phenyl-s-triazine units into the main chain of phthalazinone-based polyether sulfones on
initial decomposition temperature, activation energy, thermal-mechanical property and possible degradation mechanism has been
investigated. To this purpose, decomposition of poly(phthalazinone ether sulfone phenyl-s-triazine) copolymers (PPESPs) of
different monomer compositions have been studied by utilizing thermogravimetry and differential scanning calorimetry. Non-isothermal
experiments under nitrogen were performed, and the apparent activation energy (E
a) was calculated by isoconversional and conversional methods including the methods of Flynn-Wall-Ozawa, Friedman and Kissinger.
In the conversion range (5–30%) studied, solid-state decomposition process of PPESPs is found to be a mechanism involving
phase boundary controlled reaction (E
a: 189–201 kJ mol−1) except that phenyl-s-triazine-rich copolymers exhibit a mechanism involving three-dimensional diffusion (E
a: 196–225 kJ mol−1) in terms of Coats–Redfern method. The phenyl-s-triazine-rich copolymers display much higher E
a and slighter mechanical property-change compared to sulfone-rich copolymers and generic aromatic polyether sulfone, suggesting
strong stabilizing effect of the phenyl-s-triazine moieties. 相似文献
6.
Application of arrhenius kinetics to evaluate oxidative stability in vegetable oils by isothermal differential scanning calorimetry 总被引:1,自引:0,他引:1
C. P. Tan Y. B. Che Man J. Selamat M. S. A. Yusoff 《Journal of the American Oil Chemists' Society》2001,78(11):1133-1138
In this study, 10 different vegetable oils were oxidized at four different isothermal temperatures (383, 393, 403, and 413
K) in a differential scanning calorimeter (DSC). The protocol involved oxidizing vegetable oils in a DSC cell with oxygen
flow. A rapid increase in evolved heat was observed with an exothermic heat flow appearing during initiation of the oxidation
reaction. From this resulting exotherm, the onset of oxidation time (T
o) was determined graphically by the DSC instrument. In our experimental data, linear relationships were determined by extrapolation
of the log (T
o) against isothermal temperature. The rates of lipid oxidation were highly correlated with temperature. In addition, based
on the Arrhenius equation and activated complex theory, reaction rate constants (k), activation energies (E
a), activation enthalpies (ΔH
‡), and activation entropies (ΔS
‡) for oxidative stability of vegetable oils were calculated. The E
a′, ΔH
‡, and ΔS
‡ for all vegetable oils ranged from 79 to −104 kJ mol−1, from 76 to −101 kJ mol−1, and from −99 to −20 J K−1 mol−1, respectively. Based on the results obtained, differential scanning calorimetry appears to be a useful new instrumental method
for kinetic analysis of lipid oxidation in vegetable oil. 相似文献
7.
Changsheng Liu Mei Yang Fenghong Huang 《Journal of the American Oil Chemists' Society》2012,89(1):73-78
Rheological behavior of six crude rapeseed oils with different extraction methods including hot-pressing, solvent-extraction
and cold-pressing were studied. Viscosities of the oils were measured with shear rates ranging from 0.1 to 200 s−1 at three different temperatures. The Casson model was used to fit the experimental data and the Arrhenius equation was applied
to estimate the energy of activation for viscosity (E
a). The extraction methods affected the total tocopherol, total phytosterols, total phenols, phosphorus and fatty acid composition.
The hot-pressed medium-erucic rapeseed oil (HMRO) had the greatest viscosity, and the cold-pressed low-erucic rapeseed oil
(CLRO) had the lowest viscosity among all the oils with shear rates >5 s−1 at 10 °C. The crude rapeseed oils exhibited Newtonian behavior at higher shear rates. The significant difference of viscosity
of the six oils was reduced with increasing temperature, and there was no significant change (P > 0.01) among the oils with a shear rate of 100 s−1 at 50 °C. According to the values of E
a, the following order of a change in viscosity was obtained as follows: CMRO > SMRO > HMRO > CLRO > SLRO > HLRO(C, cold pressed;
S, solvent extracted; H, hot pressed; M, medium erucic; L, low erucic; RO, rapeseed oil). Minor components may be the contributing
factors for the values of E
a of rapeseed oils. The higher shear limiting viscosity (ηc) values calculated by the Casson model decreased as the temperature increased, but no significant change (P > 0.01) was observed for ηc by using different extraction methods at 50 °C. 相似文献
8.
A novel and general kinetic rate equation combining ultraviolet‐induced (UV‐induced) curing and thermal curing was successfully derived from the conventional thermal‐kinetic rate equation. This proposed novel kinetic rate equation can be applicable to the curing system either simultaneously or individually by UV‐induced and thermal cure methods. This general kinetic rate equation is composed of the reaction order n, activation energy Ea, curing temperature T, energy barrier of photoinitiation EQ, intensity of UV radiation Q, concentration of photoinitiator [I], and a few other parameters. The proposed equation was supported by experimental data based on the curing systems of 4,4′‐bismaleimidodiphenylmethane (BMI) and 2,2‐bis(4‐(4 maleimido phenoxy) phenyl propane (BMIP). The BMI and BMIP systems were isothermally cured at various temperatures, or simultaneously cured with varying intensity of UV radiation (wavelength 365 nm). Conversion levels for the various cured samples were subsequently measured with a FTIR spectrometer. The reaction order n = 1.2, activation energy Ea = 40,800 J/mol, and EQ = 7.5 mW/cm2 were obtained for curing BMI system. The reaction order n = 1.3, activation energy Ea = 53,000 J/mol, and EQ = 9.1 mW/cm2 were obtained for curing BMIP system. The values of n and Ea in the same curing system (BMI or BMIP) are irrespective of the curing method (either simultaneously or individually by UV‐induced and thermal cure methods). The salient results of this study show that UV radiation only enhances the initiation rate and UV ration do not influence the activation energy Ea. The experimental results are reasonably well represented by these semi‐empirical expressions.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
9.
The quality of commercial fish oil products can be difficult to maintain because of the rapid lipid oxidation attributable
to the high number of polyunsaturated fatty acids (PUFA), specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid
(DHA). While it is known that oxidation in fish oil is generally the result of a direct interaction with oxygen and fatty
acid radicals, there are very few studies that investigate the oxidation kinetics of fish oil supplements. This study uses
hydroperoxides, a primary oxidation product, to model the oxidation kinetics of two commercially available fish oil supplements
with different EPA and DHA contents. Pseudo first order kinetics were assumed, and rate constants were determined for temperatures
between 4 and 60 °C. This data was fit to the Arrhenius model, and activation energies (E
a) were determined for each sample. Both E
a agreed with values found in the literature, with the lower PUFA sample having a lower E
a. The oil with a lower PUFA content fit the first-order kinetics model at temperatures ≥20 °C and ≤40 °C, while the higher
PUFA oil demonstrated first-order kinetics at temperatures ≥4 °C and ≤40 °C. When the temperature was raised to 60 °C, the
model no longer applied. This indicates that accelerated testing of fish oil should be conducted at temperatures ≤40 °C. 相似文献
10.
Poly(3‐hydroxybutyrate), PHB, is a widely distributed carbon storage polymer among prokaryotes including Rhizobium. Capacities of Rhizobium etli R13 to produce the bioplastic during growth on media with different carbon sources appeared to be specific carbon‐source. In fed batch fermentation, R. etli R13 resulted in cell dry weight 6.2 g/L and PHB 51.4%. Gas chromatography‐mass spectrometry and gel permeation chromatography analysis revealed that PHB produced from R. etli R13 was solely composed of 3‐hydroxybutyric acid and the molecular mass of the purified PHB was 3.4 × 105 Da with polydispersity 1.47. Dielectric relaxation of PHB has been studied in the temperature and frequency ranges 300–440 K and 10 kHz–4 MHz, respectively. A clear dielectric α and ρ‐relaxation processes are observed in these studied ranges of temperature and frequency. The first process is due to the dipole relaxation in the crystalline phase of PHB. The second one is due to the space‐charge formation or Maxwell‐Wagner‐polarization. The α‐relaxation process has been investigated by semiempirical Havriliak‐Negami relaxation function. The activation energy (Ea) and the relaxation time (τ0) are calculated using the Arrhenius equation. The dielectric relaxation strength (Δε) is strongly temperature dependent. The calculated values of Ea for ac conductivity, ln(σ), of PHB provide information about the presence of electronic conduction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
11.
A. K. Dordinejad S. H. Jafari H. A. Khonakdar U. Wagenknecht G. Heinrich 《应用聚合物科学杂志》2013,129(1):458-463
In this article, the correlation between the thermorheological behavior and the molecular structure of two grades of metallocene polyethylene, namely linear low density and very low density polyethylene, is studied. The investigated polymers possess the same molecular weight and polydispersity index, but different levels of short branches. Increasing the number of short branches results in enhanced activation energy and delayed relaxation times of the polymers. Four methods including the time–temperature superposition (TTS), van Gurp‐Palmen and activation energy (Ea) as a function of the phase angle, Ea(δ), and the storage modulus, Ea(G′) are employed to study the thermorheological behavior of the samples. The results indicated that the thermorheologically simple behavior is dominant in the specimens. Both the Ea(δ) and Ea(G′) showed independency toward phase angle and the storage modulus. Moreover, the activation energy values obtained from the TTS principle and the Ea(δ) and Ea(G′) diagrams were in good agreement. The zero‐shear rate viscosity of the samples also followed the equation of the linear polyethylene. Regarding the simple thermorheological behavior and the agreement of the zero shear rate viscosity with the relation of the linear polyethylene, one can conclude that long branches do not exist in the investigated metallocene polyethylenes of this article. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
12.
Bleaching kinetics of sunflowerseed oil 总被引:1,自引:0,他引:1
Hüseyin Topallar 《Journal of the American Oil Chemists' Society》1998,75(4):531-533
The bleaching process for sunflowerseed oil follows a rate formula, log (A/A
0)=−κ
, according to absorbance measurements. The dark color of crude oil converts to a light color as the absorbance value decreases.
The activation energy E
a was calculated from the Arrhenius equation as 3 kJ, and other activation thermodynamic parameters were determined as ΔS
⊄=−4.4 J K−1, ΔH
⊄=−31.2 J mol−1, and ΔG
⊄=1.6 kJ mol−1. The study showed that the bleaching process was exothermic, presented a decrease of entropy, and was a nonspontaneous process
during activation. 相似文献
13.
Compatibility,steady and dynamic rheological behaviors of polylactide/poly(ethylene glycol) blends
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Understanding the rheological behavior of plasticized polylactide (PLA) contributed to the optimization of processing conditions and revealed the microstructure–property relationships. In this study, the morphological, thermal, steady and dynamic rheological properties of the PLA/poly(ethylene glycol) (PEG) blends were investigated by scanning electron microscope, differential scanning calorimeter, and capillary and dynamic rheometers, respectively. The results illuminated that the melt shear flow basically fitted the power law, whereas the temperature dependence of the apparent shear viscosity (ηa) or complex viscosity (η*) followed the Arrhenius equation. Both the neat PLA and PLA/PEG blends exhibited shear‐thinning behavior. Because the incorporation of PEG reduced the intermolecular forces and improved the mobility of the PLA chains, the ηa, η*, and storage and loss moduli of the PLA/PEG blends decreased. The PEG content (WPEG) ranged from 0 to 10 wt %, both ηa and η* decreased significantly. However, the decrements of ηa and η* became unremarkable when WPEG exceeded 10 wt %. The reason was attributed to the occurrence of phase separation, which resulted in the decrease in the plasticization and lubrication efficiencies. This study demonstrated that the addition of the right amount of PEG obviously improved the flow properties of PLA. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42919. 相似文献
14.
In the previous papers, we elucidated enhancement of concentration fluctuations, phase separation, and crystallization induced by steady state or step-up shear flow, as observed by shear small-angle light scattering, optical microscopy, and birefringence, for a semidilute solution of ultrahigh molecular weight polyethylene in paraffin as an athermal solvent. However the studies were done only at a given temperature of 124 °C, which is higher than the nominal melting temperature of the quiescent solution Tnm (115–119 °C). It is crucial to extend the studies over a wider temperature range in order to generalize shear-induced phase behavior of the solution. Thus in this work we constructed a kind of phase diagram in the parameter space of temperature (T) and shear rate (). The temperature range covered was higher than Tnm, so that the phase diagram is strictly concerned with shear-induced phase behavior (i.e., without shear the solution is homogeneous and in a single-phase state). The diagram identified Regimes I–III in the T– space as will be detailed in the text. In constructing the phase diagram we found the following new points also. (i) The critical shear rate cx which defines the boundary between Regimes I and II was independent of T. (ii) Regime III identified previously through the dependence of the integrated scattered intensity only at a particular temperature T = 124 °C was further separated into two regimes of IIIa and IIIb below and above a critical temperature (147 °C), respectively, through the observation of the dependence as a function of T: In Regime IIIa, the sheared solution developed the optically anisotropic fibrous structures, indicative of the shear-induced crystallization triggered by the shear-induced concentration fluctuations in Regime II; In Regime IIIb, the solution is so stable that it did not show a trend of the shear-induced crystallization even at the highest shear rates accessible in this experiment, but it only showed the shear-induced phase separation. (iii) The critical shear rates c,streak and cz, which define respectively the boundary between Regimes II and IIIa and that between Regimes II and IIIb, are sensitive to temperature. 相似文献
15.
Ewa Ostrowska‐Ligeza Witold Bekas Dorota Kowalska Marta Lobacz Malgorzata Wroniak Boleslaw Kowalski 《European Journal of Lipid Science and Technology》2010,112(2):268-274
Four samples of olive oil were oxidized under polythermal (dynamic) conditions in the cell of a normal‐pressure differential scanning calorimeter (DSC) and in the Metrohm Rancimat apparatus. The DSC experiments were carried out in an oxygen flow atmosphere using different linearly programmed heating rates in the range of 4–20 °C/min. Through DSC exotherms, the extrapolated onset temperatures were determined and used for the assessment of the thermal‐oxidative stabilities of the samples. Using the Ozawa‐Flynn‐Wall method and the Arrhenius equation, the activation energies (Ea), pre‐exponential factors (Z) and reaction rate constants (k) for oil oxidation under DSC conditions were calculated. The Rancimat measurements of oxidation induction times were carried out under isothermal conditions in an air atmosphere at temperatures from 100 to 140 °C with intervals of 10 °C. Using the Arrhenius‐type correlation between the inverse of the induction times and the absolute temperature of the measurements, Ea, Z, and k for oil oxidation under Rancimat conditions were calculated. The primary kinetic parameters derived from both methods were qualitatively consistent and they help to evaluate the oxidative stabilities of oils at increased temperatures. 相似文献
16.
Two latex interpenetrating polymer networks (LIPNs) were synthesized with methyl methacrylate (MMA) and octyl acrylate (OA) as monomers, respectively. The apparent kinetics of polymerization for the LIPNs was studied. This demonstrates that network II does not have a nucleus formation stage. The monomers of network II were diffused into the latex particles of network I and then formed network II by in situ polymerization. It indicates that the polymerization of network I obeys the classical kinetic rules of emulsion polymerization. But the polymerization of network II only appears a constant‐rate stage and a decreasing‐rate stage. The apparent activation energies (Ea) of network I and network II of PMMA/POA were calculated according to the Arrhenius equation. The Ea values of POA as network I (62 kJ/mol) is similar to that of POA as network II PMMA/POA (60 kJ/mol). However, the Ea value of PMMA as network II POA/PMMA (105kJ/mol) is higher than that of PMMA as network I (61 kJ/mol). Results show that the Ea value of the network II polymerization is related to the properties of its seed latex. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
17.
An amine‐containing borate (labeled NBD) was obtained by a one‐step esterification using neopentyl glycol, boric acid and N,N‐dimethylethanolamine (DMEA) as reactants, and nuclear magnetic resonance as well as Fourier transform infrared (FTIR) measurements were used to characterize its chemical structure. The thermally latent curing properties of NBD were confirmed by differential scanning calorimetry (DSC), FTIR and gelation time results. The cure processes of bisphenol A diglycidyl ether epoxy resins (E51) using NBD as a latent hardener in comparison with a common hardener, DMEA, were studied by DSC measurements. The Avrami and Arrhenius methods as well as the Horowitz‐Metzger method were used to calculate kinetic parameters. These methods also revealed a transition at which the cure reaction mechanism showed a marked change and provided the apparent activation energy Ea associated with the cure reaction at different reaction stages. Copyright © 2012 Society of Chemical Industry 相似文献
18.
A series of semi-interpenetrating polymer networks (semi-IPN) have been prepared from acetylene-terminated sulfone (ATS-C) oligomer and high-performance thermoplastic (TP) blends. The cure characteristics and thermal properties of ATS-C and semi-IPNs are presented in this paper. The addition of thermoplastics has no effect on the mechanism of ATS-C cure reaction and thermal behavior of cured systems. The glass-transition temperature (Tg) and heat distorsion temperature (HDT) of thermoplastics are remarkably decreased with adding ATS-C. The higher the Tg and HDT of the thermoplastics, the more obvious the reduction of Tg and HDT. In the case of fully cured semi-IPNs, the Tg and HDT value of the TP phase are higher than or equal to the Tg and HDT of pure TP. The thermal stabilities of semi-IPNs decrease as the content of ATS-C oligomer increases. © 1993 John Wiley & Sons, Inc. 相似文献
19.
A. Petrauskas L. Grincevi?ien? A. ?e?ūnien? 《Journal of Applied Electrochemistry》2009,39(9):1579-1585
The phase composition of Zn–Ni alloys electrodeposited from acetate-chloride plating solutions containing Zn+2 and Ni+2 ions at ratio of 1–12.8 at 50 °C was investigated by the potentiodynamic stripping method. Two anodic current density (i
a) peaks emerged in potentiodynamic stripping curves (PDC) at E < 0.0 V and E > 0.0 V (vs. Ag/AgCl/KClsat), that were attributed to oxidation of certain phases of the Zn–Ni alloy. The ratio of these phases in deposited Zn–Ni alloys
under potentiodynamic conditions was affected by the potential sweep rate (ν) and maximum cathodic current density (i
c) The ratio of Zn and Ni in certain phases of Zn–Ni alloy was determined by the partial potentiodynamic stripping technique.
Experimental data show that Zn–Ni alloy, containing 6.5 at.% Zn and 93.5 at.% Ni and dissolved in i
a peak H (E > 0.0 V), provides the black coloration of the Zn–Ni alloy. 相似文献
20.
The corrosion behaviour of mild steel in 0.5 M H2SO4 solution containing various concentrations of a p-toluene sulphonic acid doped copolymer formed between aniline and o-toluidine was investigated using weight loss, polarization and electrochemical impedance techniques. The copolymer acted
as an effective corrosion inhibitor for mild steel in sulphuric acid medium. The inhibition efficiency has been found to increase
with increase in inhibitor concentration, solution temperature and immersion time. Various parameters like E
a for corrosion of mild steel in presence of different concentrations of inhibitor and ΔG
ads, ΔH
0, ΔS
0 for adsorption of the inhibitor, revealed a strong interaction between inhibitor and mild steel surface. The adsorption of
this inhibitor on the mild steel surface obeyed the Langmuir adsorption equation. 相似文献