Authors:J. M. Salla, J. M. Morancho, X. Ramis, and A. Cadenato
Summary Thermogravimetry was used to study the kinetics of isothermal degradation of an epoxy thermoset powder coating in a nitrogen atmosphere and in oxidizing atmospheres of air and pure oxygen. An integral isoconversional procedure was used to analyse how the activation energy varies depending on the degree of conversion and depending on the atmospheres used. In the case of degradation in a nitrogen atmosphere, in addition to the activation energy, the kinetic triplet was completed using an Avrami reaction model and the pre-exponential factor. With this atmosphere, the conclusion was reached that the isothermal and non-isothermal kinetics are equivalent. It was shown that the thermooxidative degradation process is more complex and consists of a two-stage process. The first stage of degradation is similar whether nitrogen, oxygen or air are present. Chain scission occurs and it seems that there is formation of thermally more stable compounds. The second stage of degradation, involving several phenomena, occurs only in the presence of oxygen or air and leads to the total disappearance of the organic material by thermooxidation. These stages are very similar under non-isothermal or isothermal conditions.
Authors:L. Núñez-Regueira, M. Villanueva, and I. Fraga-Rivas
study of the degradation of a polymer is important because it can determine
the upper temperature limit, the mechanism of a solid-state process, and the
life-time for this system. Since the behavior of thermosets is affected by
the selection of the curing cycle, it is important to investigate the changes
which take place during the thermal degradation of these materials when a
change on the sequence of time and temperature is introduced during the curing
this work, the thermal degradation of two epoxy systems diglycidyl ether of
bisphenol A (BADGE n=0)/1, 2 diamine cyclohexane
(DCH) cured through different sequences of time and temperature was studied
by thermogravimetric analysis in order to determine the reaction mechanism
of the degradation processes, and also to check the influence of the curing
cycle on this mechanism. Values obtained using different kinetic methods were
compared to the value obtained by Kissinger’s method (differential method
which do not require a knowledge of the n-order
reaction mechanism), and to that obtained through Flynn–Wall–Ozawa
method in a previous work.
Resin injection repair is a common method to repair delamination damage in polymer matrix composites (PMCs). To repair high-temperature
PMCs, the resin should have a very low viscosity, yet cure into a compatible adhesive with high temperature stability. Normally,
thermosetting polymers with high glass transition temperatures (Tg) are made from monomers with high room temperature viscosities. Among the high temperature resins, bisphenol E cyanate ester
(BECy, 1,1’-bis(4-cyanatophenyl)ethane), is unique because it has an extremely low viscosity of 0.09–0.12 Pa s at room temperature
yet polymerizes as a cross-linked thermoset with a high Tg of 274°C. BECy monomer is cured via a trimerization reaction, without volatile products, to form the high Tg amorphous network.
In this study, the cure kinetics of BECy is investigated by differential scanning calorimetry (DSC). Both dynamic and isothermal
experiments were carried out to obtain the kinetic parameters. An autocatalytic model was successfully used to model isothermal
curing. The activation energy from the autocatalytic model is 60.3 kJ mol−1 and the total reaction order is about 2.4. The empirical DiBenedetto equation was used to evaluate the relationship between
Tg and conversion. The activation energy of BECy from the dynamic experiments is 66.7 kJ mol−1 based on Kissinger’s method, while isoconversional analysis shows the activation energy changes as the reaction progresses.
Authors:N. Gabilondo, M. López, J. Ramos, J. Echeverría, and I. Mondragon
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.
The exothermal process of curing of thermoset resins in adiabatic conditions cannot be monitored by differential thermal analysis
techniques such as DSC. Starting from the specific reaction rate, heat capacity as function of the temperature and the heat
of reaction at some reference temperature, it is possible to design any adiabatic operation.
In this paper we apply the energy balance to the curing process in adiabatic conditions and solve the basic rate law for the
two empirical kinetic functionsf(α) usually used:nth-order kinetics [f(α)=(1−α)n], and autocatalytic kinetics [f(α)=αm(1−α)n], where α is the degree of conversion andn andm the reaction orders, in order to obtain the heat generation curve (dH/dt) as a function of time, as well as the change of temperature with time, the explosion time, the maximum adiabatic temperature
and the rate of reaction as a function of the degree of conversion.
chapter on Thermosets in Thermal Characterization of Polymeric Materials (E. A. Turi, editor, 1981, 1997). Dr. Prime is a fellow of SPE and NATAS and was the recipient of the Mettler-Toledo Award in Thermal Analysis in 1989. He is a founding member of
The glass transition temperature,Tg is a sensitive and practical parameter for following cure of reactive thermosetting systems. A new equation was developed for predicting theTg-conversion relationship based on the Dillman-Seferis viscoelastic compliance model. It assumes that the changes inTg are primarily due to changes in relaxation time as chain extension and crosslinking reduce the mobility of a polymer network. Such information is essential in combining kinetic and viscoelastic measurements, which monitor transformations of thermosets during cure. The equation derived from the viscoelastic model was shown to be applicable for a variety of experimental data. The success of the methodology was further demonstrated by comparing well-established relations, such as the Fox equation and the Di-Benedetto equation, to predictions made possible by adjusting two viscoelastic model parameters. Finally, the fitting power of the proposed equation was shown by fitting published epoxy data from the literature as well as experimental data on a relatively new resin system such as dicyanates used as a model in this study.
Differential Scanning Calorimetry (DSC) — the basics of DSC —DSC of low molecular mass compounds —DSC of thermoplastics —DSC of thermosets —Modulated Temperature DSC —fast scan DSC —instrumentation
Welcome to the Reader!
You, the reader, hold in your hands a valuable journal
issue that contains a number of thermal analysis papers that were presented
at the 32nd annual meeting of the North American Thermal Analysis Society
(NATAS). This conference was held in Williamsburg, Virginia, USA from the
October 4 to 6, 2004. NATAS is known of its dedication in promoting the understanding
and advancement of thermal analysis. NATAS is the largest national thermal
analysis society in the world, and over its more than 30 year existence, it
has represented the interests of numerous scientists, technicians and engineers,
as well as major instrument vendors functioning in the area of thermal analysis.
NATAS is an affiliate of the International Confederation for Thermal Analysis
and Calorimetry (ICTAC), and has been co-operating with ASTM (American Society
for Testing and Materials) for a long time especially Committee E37 on Thermal
Short Course in Thermal Analysis held right before the conference, provide
excellent educational opportunities for technical people, both experienced
in the use of thermal analysis and those expanding their skills to learn thermal
this year's program, by our count, 225 papers were presented in nineteen
different sessions (Kinetics; Fast Scan DSC; Semicrystalline Polymers; Thermal
Conductivity; Pharmaceuticals; Poster Session; Educational Applications; Thermoplastic
Polymers; Combined and Hyphenated Techniques; Composites, Nanocomposites and
Thermosets; Thermal Hazards/Energetic Materials; Wood Materials; Rheology;
Foods; Professional Enhancement; General Session; Flame Retardancy; Films
and Fibers; Medical Polymers). Although thermal analysis is present in all
areas of chemistry, the just described list of 2004 NATAS sessions clearly
indicates that polymers still represent the majority among the materials tested
by thermal analysis, or at least by the NATAS membership. Another phenomenon
that may be seen when comparing these papers with earlier NATAS issues is
some structural change in the type of the papers. As the chemical industry
is inevitably being transformed in the era of globalization, it also affects
thermal analysis. The emphasis is shifted from theoretical papers more to
applications of thermal analysis.
This special issue contains selected papers from
the 2004 Annual NATAS Meeting. Another group of selected papers will be published
in Thermochimica Acta. You may be surprised to see the NATAS material collected
in two special issues of the two thermal analysis journals. However, NATAS
has now decided it is time to return to the good old times and publish together
the selected papers presented at its annual meeting. This year was a trial
year of how the best NATAS papers should be presented to the world. The 2005
NATAS papers will be published in one special issue of Journal of Thermal
Analysis and Calorimetry.
At the annual NATAS meetings, in addition to the classical
conference, there is always an instrument exhibition of a considerable size.
The most important instrument manufacturers of the world are always present
at this exhibition. In addition of being present, they provide funding to
NATAS through financing some of the essential needs of the conference. Thus,
we sincerely thank the following NATAS conference sponsors for their support:
TA Instruments, PerkinElmer Life and Analytical Sciences and Mettler-Toledo.
We are also thankful to both symposia sponsors: ExxonMobil Chemical Company
and Abbott Laboratories. We hope the excellent relationship between NATAS
and its corporate sponsors, and the instrument vendors is permanent. Above
all, we thank all the authors and reviewers for their valuable contribution,
because we feel that re-starting of regular publishing of the papers of the
annual NATAS meetings is extremely important. We express our gratitude to
the editorial offices of both Journal of Thermal Analysis and Calorimetry,
and Thermochimica Acta for providing the opportunity to publish these papers.
Authors:Qing Guo, Yan Huang, Yu-Ying Zhang, Li-Rong Zhu, and Bao-Long Zhang
modifications of epoxy resins have been reported by a lot of researchers [ 1 – 8 ]. Additives, fillers, plasticization, toughening, and blending are usually used to modify epoxy resins. Among the various factors affecting the properties of the thermoset resins