This article describes the synthesis of a liquid crystalline curing agent 4,4′-bis-(4-amine-butyloxy)-biphenyl (BABB), and
its application as a curing agent for the epoxy resin (DGEBA) in comparison with normal curing agent, 4,4′-diaminobiphenyl
(DABP). BABB was investigated with polarized optical microscopy, differential scanning calorimetry, and small-angle X-ray
scatting, and the results showed that BABB displayed smectic liquid crystalline phase. The curing behaviors of DGEBA cured
with BABB and DABP were studied by using differential scanning calorimetry (DSC), polarized optical microscopy (POM), and
dynamic mechanical analysis (DMA). The results indicated that BABB showed a higher chemical reactivity than DABP. The kinetics
was studied under isothermal conditions using an isoconversional method, and the isothermal DSC data can be fitted reasonably
by an autocatalytic curing model. The nematic droplet texture was observed for the resulting polymer network of DGEBA/BABB
system, while the DGEBA/DABP system showed an isotropic state. The storage modulus of DGEBA/BABB system was enhanced in comparison
with DGEBA/DABP system because of the formation of LC phase, whereas the glass transition temperatures decreased because of
the introduction of flexible spacer group. 相似文献
In the present study, TEIA bioresin was blended with the diglycidyl ether bisphenol A (DGEBA) epoxy resin in different ratios (i.e. 10, 20, 30, 40 mass%), cured with methylhexahydrophthalic anhydride curing agent in the presence of 2-methylimidazole catalyst. The optimized composition of DGEBA and TEIA bioresin blends system was employed as an adhesive strength. The adhesive strength of the TEIA-modified DGEBA epoxy resin blend system was increased from 4.14 to 6.31 MPa on an aluminium substrate compared to the DGEBA epoxy resin. The curing kinetics of non-isothermal, DGEBA epoxy resin and its bio-based blend systems were investigated employing differential scanning calorimetry. An increase in the peak temperature and reduction in a heat of curing as well as activation energy in DGEBA epoxy resin were observed with the addition of TEIA bioresin content. The activation energy (Ea) of the DGEBA resin and their bio-based blend system were obtained from Kissinger and Flynn–Wall–Ozawa methods.
The curing kinetics of lignin-novolac and methylolated lignin-novolac resins were studied using non-isothermal methods employing
differential scanning calorimetry (DSC) at different heating rates. The Belichmeier, Ozawa and Kissinger methods were applied,
which give the kinetic parameters of the curing process studied. In addition, the model-fitting Coats-Redfern method was used
to analyze the experimental data. The kinetic study evaluated the effect of the lignin (softwood ammonium lignosulfonate),
methylolated or not, on the resin curing process. Results for lignin-novolac and modified lignin-novolac resins were compared
with a commercial novolac resin as a reference. When lignosulfonate is modified by methylolation and is incorporated in the
novolac resin, there is an important reduction in activation energy. The lignin-novolac showed slightly higher values of activation
energy than methylolated-lignin resins, but lower values than commercial resins. This behavior has been attributed to the
extra methyol groups introduced by lignosulfonate. 相似文献
Diglycidyl ether of 4,4′-dihydroxybiphenol (BPDGE) is a liquid crystalline epoxy. The biphenyl epoxy (diglycidyl ether of 3,3′,5,5′-tetramethyl-4,4′-biphenyl, TMBPDGE) has found great applications in plastic encapsulated semiconductor packaging. Phenol novolac (PN) was used as curing agent. The reaction kinetics of BPDGE/PN and TMBPDGE/PN systems in the presence of triphenylphosphine (TPP) were characterized by an isoconversional method under dynamic conditions using differential scanning calorimetry (DSC) measurements. The results showed that the curing of epoxy resins involves different reaction stages and the values of activation energy are dependent on the degree of conversion. The effects of curing temperature on their phase structure have been investigated with polarized optical microscopy and Wide-angle X-ray diffraction. With proper curing process, BPDGE showed a nematic phase when cured with PN. 相似文献
The effect of both formaldehyde content and catalyst type used in the synthesis of several resole type phenolic resins has
been studied by using differential scanning calorimetry. In this study Kissinger-Akahira-Sunose (KAS), Ozawa-Flynn-Wall (OFW)
and Friedman model-free kinetics are applied in order to correlate the dynamic cure behaviour with the mentioned synthesis
variables. Strong upward dependency of activation energy on conversion has been detected in all cases up to a maximum value.
Lower the formaldehyde content fewer changes in activation energy have been detected, revealing a more homogeneous polymerization.
As formaldehyde content increases, stronger variations of energy values have been observed and the maximum value is shifted
to lower conversions. By comparing triethylamine and sodium hydroxide catalysts similar behaviour has been observed, with
higher energy values and shifting of the maximum in the latter. Friedman approach has been resulted in more convenient and
accurate for the energy values determination and KAS method seems useful for the dynamic cure prediction of that type of thermoset. 相似文献
The mechanism of acid curing of epoxy resins catalyzed with tertiary amines was investigated by using model systems composed of phenylglycidyl ether and benzoic acid or acetic acid anhydrides in the presence of benzyldimethylamine. The reaction was studied by NMR spectrometry, liquid chromatography, and ozone absorption. The main findings are that (1) the tert-amine is bound chemically and irreversibly during the reaction under the formation of a quaternary ammonium salt and (2) 1-phenyloxypropanediol-2,3-dibenzoate or diacetate is the main reaction product. The suggested reaction mechanism involves initiation in which the tertiary amine reacts with the epoxy group, giving rise to a zwitterion that contains a quaternary nitrogen atom and an alkoxide anion; the latter immediately reacts with the anhydride and quaternary salt is formed. In a later stage the carboxy anion of the quaternary salt reacts first with the epoxy group, then with the anhydride. By this reaction diester is formed and the carboxy anion is regenerated. 相似文献
The isothermal course of the reaction of phenylglycidyl ether and N,N-methylglycidylaniline with dibutyl amine at various temperatures was investigated DSC. The data were treated on the basis of a reaction scheme with two processes in parallel, one of them auto-catalyzed. A good fit with the experiment was reached only when the order of both processes with respect to amine had been reduced to half its original value. An assumption that the kinetics of the amine-epoxy resin rection are considerably affected by the formation of various complexes through hydrogen bonds may be an explanation. A simple mathematical model has been suggested to estimate this influence. Because of the relatively high heats of interaction for the formation of complexes, the dependence of the measured heat on the degree of conversion is not linear. The magnitude of the error caused by neglecting this fact in investigation of the kinetics by DSC has been estimated. 相似文献
The cure kinetics of a biphenyl-based liquid crystalline (LC) epoxy resin (LCER) was studied using differential scanning calorimetry (DSC) and polarized optical microscopy. The effects of LC phase formation on the cure kinetics were investigated. Both a model-free isoconversional method and a model-fitting method were used to analyze the DSC data. Results from the isoconversional analysis were applied to develop tentative multi-step kinetic models describing the curing reaction. Kinetic analysis showed that compared to the resins cured in amorphous phase, LCERs exhibited higher values of reaction enthalpy and a complex dependence of activation energy on the degree of cure. The formation of the LC phase resulted in a decrease in activation energy, leading to higher degree of reaction. 相似文献
In this study, the curing kinetics of polyfunctional benzoxazine resins based on arylamine, i.e. aniline and 3,5-xylidine, designated as BA-a and BA-35x, respectively, were investigated. Non-isothermal differential scanning calorimetry (DSC) at different heating rates is used to determine the kinetic parameters and the kinetic models of the curing processes of the arylamine-based polyfunctional benzoxazine resins were proposed. Kissinger, Ozawa, Friedman, and Flynn-Wall-Ozawa methods were utilized to determine the kinetic parameters of the curing reaction. BA-a resin shows only one dominant autocatalytic curing process with the average activation energy of 81-85 kJ mol−1, whereas BA-35x exhibits two dominant curing processes signified by the clear split of the curing exotherms. The average activation energies of low-temperature curing (reaction (1)) and high-temperature curing (reaction (2)) were found to be 81-87 and 111-113 kJ mol−1, respectively. The reaction (1) is found to be autocatalytic in nature, while the reaction (2) exhibits nth-order curing kinetics. In addition, the predicted curves from our kinetic models fit well with the non-isothermal DSC thermogram. 相似文献
Curing kinetics of diglycidyl ether of bisphenol-A (DGEBA) in the presence of novel silicon containing amide-amines were investigated
by the dynamic differential scanning calorimetry. Silicon containing amide-amines were prepared by reacting 2.5 moles of 4,4'-diaminodiphenyl
ether (E)/4,4'-diaminodiphenyl methane (M)/3,3'-diaminodiphenyl sulfone (mS)/bis(m-aminophenyl) methyl phosphine oxide (B) with one mole of bis(4-chlorobenzoyl) dimethyl silane. The multiple heating rate
method (5, 10, 15 and 20°C min-1) was used to study the curing kinetics of epoxy resins in the presence of stoichiometric amounts of amide-amines having molecular
masses in the range of 660 to 760 g mol-1. The peak exotherm temperature depends on the heating rate as well as on the structure of amide-amines. Activation energy
of curing reaction as determined in accordance to the Ozawa's method was found to be dependent on the structure of amine.
The thermal stability of the isothermally cured resins was also evaluated using dynamic thermogravimetry in a nitrogen atmosphere.
The char yield was the highest in case of resins cured with amide-amines having both phosphorus and silicon atoms.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
Reaction of epoxy-diane resin with complex based on monoamide of phosphonic acid and ammonium chloride (MODAF) is studied.
It is established that the MODAF equivalent in the reaction with epoxy resin is equal to 1/5 of its molecular weight. Epoxy
resin is cured via the reactions of both monoamide and ammonium chloride. The dependence of the epoxide and hydroxyl groups
has a stepped character over time, which is probably due to the existence of certain threshold concentrations of the curing
coefficients. The investigated reaction is a new example of macroscopic coherence manifestation. 相似文献
Curing reactions of three cycloaliphatic epoxy resins with methyltetrahydrophthalic anhydride (MTHPA) was investigated by differential scanning calorimetry at different heating rates. Activation energy was calculated based on Kissinger method and varied in the range of 67-72 kJ/mol depending on sample. The curing kinetic behavior was well described by Sestak-Berggren (SB) model and the order of the curing reaction is observed to be from 0.02 to 2.11 according to sample. 相似文献
In this paper, steady-state luminescence spectroscopy is used for the analysis of curing of epoxy resin. The advantage of this method is its rapidity, simplicity and sensitivity. Moreover, this method is contactless, and thus non-invasive. The aim is to analyze epoxy resin, mathematically describe its curing kinetics and determine its storage temperature. Using the photoluminescence method, a rapid procedure for obtaining the necessary technological data is achieved. This method is suitable for continuous measurement in production because there is no contact with the material, and the measurement itself can be performed very quickly. The elaborated mathematical model can serve as a basis for creating algorithms for automated data processing in case of fully robotic workplaces. 相似文献