Authors:B. Erdoğan, A. Seyhan, Y. Ocak, M. Tanoğlu, D. Balköse, and S. Ülkü
The cure kinetics of epoxy resin and epoxy resin containing 10 mass% of natural zeolite were investigated using differential
scanning calorimetry (DSC). The conformity of the cure kinetic data of epoxy and epoxy-zeolite system was checked with the
auto-catalytic cure rate model. The results indicated that the hydroxyl group on the zeolite surface played a significant
role in the autocatalytic reaction mechanism. This group was able to form a new transition state between anhydride hardener
and epoxide group. The natural zeolite particles acted as catalyst for the epoxy system by promoting its curing rate.
Thin films of 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexane carboxylate were UV irradiated (1.1 J cm-2) under isothermal conditions ranging from 0 to 50C. Under these conditions the polymerization advanced quickly but only
to a conversion level of less than 10% before the reaction rate slowed by more than an order of magnitude. This drop off in
rate was not caused by the glass transition temperature, Tg, reaching or exceeding the reaction temperature, Trxn, since the epoxide's Tg remained at least 40C below Trxn. Raising the sample temperature above 60C caused a sharp increase in the conversion level. At 100C conversion exceeds 80%
and the ultimate Tg approaches 190C. The addition of 10 mass% 1,6-hexanediol, HD, to the epoxy caused the conversion at room temperature to
quintuple over the level obtained without the alcohol present. The heat liberated from this alcohol epoxy blend during cure
on a UV conveyor belt system caused the sample's temperature to increase by about 100C above ambient whereas the epoxy alone
under these conditions only experienced a modest temperature rise of about 26C. If the amount of HD in the blend is increased
above 10% the heat of reaction at 23C decreases due to HD being trapped in a nonreactive crystalline phase. Boosting reaction
temperatures above 50C melts the HD crystals and yields significantly improved conversion ratios. As the level of alcohol
blended with the epoxy is raised its ultimate Tg is lowered and when the concentration of alcohol in the blend nears 30 mass%Tg drops below room temperature.
Authors:D. Chinn, Sang -Beom Shim, and J. C. Seferis
Five epoxy resins of different chemistry and functionality were cured with DDS (4,4′-diaminodiphenyl sulfone) using 2, 8 and 14 h curecycles. Both Differential Scanning Calorimetry (DSC) and Thermomechanical Analysis (TMA) were used to characterize reaction behavior and cured properties of the resin systems. In addition, static mechanical tests and density measurements were integrated with the thermal characterization methods to correlate resin properties with process time. Flexural three-point bending experiments showed that the resins tended to have higher yield stress and toughness values at extended cure times. The improved mechanical properties could be attributed to the full development of the epoxy molecular structure, in the form of cross-linked networks and molecular rearrangement. These results suggest that extended cure times or high temperature post-curing may be required to obtain the resin's ultimate mechanical properties for high performance composites.
A phenomenological approach was used to characterize the cure processes of epoxy resins (a diglycidyl ether of bisphenol A and its modifier CTBN) from dynamic experiments by DSC. Various kinetic parameters were obtained by using a modified Avrami expression. The resulting overall activation energies for the two systems agreed very well with the published data in the whole cure temperature range. In contrast with the isothermal results and the general dynamic models, a change in the exponent and the non-linear temperature dependence of the rate constant were also observed.
Authors:C. Arribas, Rosa Masegosa, C. Salom, E. Arévalo, S. Prolongo, and Margarita Prolongo
Diglycidyl ether of bisfenol-A (DGEBA)/polybenzyl methacrylate (PBzMA)
blends cured with 4,4’-diaminodiphenylmethane (DDM) were studied. Miscibility,
phase separation, cure kinetics and morphology were investigated through differential
scanning calorimetry (DSC) and scanning electron microscopy (SEM). Non-reactive
DGEBA/PBzMA blends are miscible over the whole composition range. The addition
of PBzMA to the reactive (DGEBA+DDM) mixture slows down the curing rate, although
the reaction mechanism remains autocatalytic. On curing, initially miscible
(DGEBA+DDM)/PBzMA blends phase separate, arising two glass transition temperatures
that correspond to a PBzMA-rich phase and to epoxy network. Cured epoxy/PBzMA
blends present different morphologies as a function of the PBzMA content.
Thermal decomposition of polyurethane, epoxy, poly(diallyl phthalate), polycarbonate, and poly(phenylene sulfide) was examined
using a combination of thermal and chemical analysis techniques. Thermal gravimetric analysis with simultaneous analysis of
evolved gases by Fourier transform infrared spectroscopy, differential scanning calorimetry, and gas chromatography coupled
with Fourier transform infrared spectroscopy were used to obtain rate data, determine enthalpy changes, and identify decomposition
products. Examination of the evolved decomposition products indicated a common set of chain scission mechanisms involving
the aromatic moieties in each of the polymer materials studied.
The curing characteristics of adicyandiamide-cured epoxy system under the influence of solvents in a closed environment were
studied by means of isothermal differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR).
The DSC analyses revealed that the presence of solvent results in decreases in the curing exotherm, the initial curing rate,
the glass transition temperature, the reaction rate and the reaction order of the epoxy resin. The greatest decreases were
caused by the solvent with the highest boiling temperature. A change in temperature-dependent curing route due to the heat
absorbed during solvent evaporation is responsible for the difference. The FTIR analyses confirmed that the composition of
the cured resin is affected by the solvent, the curing temperature and the specimen configuration. As compared with those
obtained from open systems, specimens produced in a closed environment have an enhanced curing exotherm, initial curing rate,
glass transition temperature, reaction rate and reaction order because of the retention of volatile catalytic by-products.
Authors:Margarita Prolongo, C. Arribas, Catalina Salom, and Rosa Masegosa
ether of bisfenol-A (DGEBA)/poly(vinyl acetate) (PVAc)/poly(4-vinyl phenol)
brominated (PVPhBr) ternary blends cured with 4,4’-diaminodiphenylmethane
(DDM) were investigated by differential scanning calorimetry (DSC), dynamic
mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM).
Homogeneous (DGEBA+DDM)/PVPhBr networks with a unique Tg
are generated. Ternary blends (DGEBA+DDM)/PVAc/PVPhBr are initially miscible
and phase separate upon curing arising two Tgs
that correspond to a PVAc-rich phase and to epoxy network phase. Increasing
the PVPhBr content the Tgof
the PVAc phase move to higher temperatures as a consequence of the PVAc-PVPhBr
interactions. Different morphologies are generated as a function of the blend
The curing and adsorption behaviors of an epoxy/amidoamine system under the influence of iron, aluminum, and zinc oxides are studied by using differential scanning calorimetry (DSC) and diffuse reflectance infrared spectroscopy (DRIFT). From DRIFT, it is obtained that the amidoamine curing agent is preferentially adsorbed on the three metal oxide surfaces. The amount of amidoamine adsorbed is in the order of iron oxide>zinc oxide>aluminum oxide. Moreover, the iron and zinc oxides adsorb resins more firmly than the aluminum oxide. The results of DSC analyses indicate that more amine related exotherms are found in the specimen filled with the iron oxide but more amide related exotherms are found in the zinc oxide added specimens and they are related to the difference in the preferential adsorption found on three metal oxides. The curing characteristics are also changed in the presence of metallic fillers and the greatest change is obtained from the specimen containing the iron oxide.
Epoxy resins are very used thermoset polymers because of their good combination of high elastic modulus and mechanical strength and good chemical and thermal resistance. One of their main limitations, the low