TTT‐cure diagram of an anhydride‐cured epoxy system including gelation, vitrification, curing kinetics model, and monitoring of the glass transition temperature

Abstract

ABSTRACT:The curing reaction of an epoxy resin [diglycidyl ether of bisphenol A (DGEBA)] combined with a methyl-hexahydrophtalic anhydride (MHHPA) hardener and a benzyldimethylamine (BDMA) accelerator was studied over a temperature range of 60 -140°C to build its isothermal time-temperature-transformation (TTT)-cure diagram. This includes gelation and vitrification measurements using rheological measurement techniques, monitoring of the glass transition temperature and the reaction kinetics by differential scanning calorimetry, and determination of the following critical glass transition temperatures: T g0 , Gel T g , and T gϱ . A new curing kinetics model, based on the Sesták-Berggren model, was developed including both chemicaland diffusion-controlled stages of reaction. Then, the TTTcure diagram was built by numerical integration of the kinetics model, and good agreement was obtained by comparison with experimental data. Additionally, for the first time, this model takes into account the incomplete cure, which occurs when the thermosetting system is cured below its ultimate glass transition temperature, leading to a more realistic description of the cure evolution after vitrification.

Reaction Kinetics of Polyurethane Formation Using a Commercial Oligomeric Diisocyanate Resin Studied by Calorimetric and Rheological Methods

“…Another important cure property of a material, measurable through rheological investigations is gelation. Gelation is a critical component in thermosetting systems as it describes the formation of an infinite molecular network and hence the start of the crosslinking reaction 16, 35. Investigation of gel times will help elucidate the reaction kinetics of the polyurethane reaction, providing further information on the workability time of the coating.…”

Master curve and time–temperature–transformation cure diagram of lignin–phenolic and phenolic resol resins

“…The methodology employed with other materials can be applied for constructing the TTT cure diagrams of lignin-phenolic and phenolic resol resins, 16,25,[30][31][32] which are shown in Figure 6. In short, the TTT cure diagram of a polymeric material displays the characteristic thermal properties of the glass-transition temperatures: T g0 , gel T g , and T g1 .…”

“…In the literature, the elaboration of TTT diagrams of different systems can be found, which present their respective characteristic values of T g0 , gel T g , and T g1 , as shown in Table III. 25,[32][33][34][35][36] Although each material presents a different TTT cure diagram, because there are remarkable differences between the materials, the information supplied allows optimization of the curing conditions for thermosetting polymers for their final applications. This issue would allow knowing the minimum time and temperature that the material needs to cure in the final application.…”

Time–temperature–transformation cure diagrams of phenol–formaldehyde and lignin–phenol–formaldehyde novolac resins

“…In the literature, the k values found varied from 0.17 to 0.78; this was in accordance with the resulted obtained for novolac samples. 7,14,17,20,[36][37][38][39] A higher k value was obtained for PF curing in relation to LN and MLN curing. This fact, combined with the definition of the k value, suggests that lignosulfonate incorporated into formulations as an extender or filler presented less mobility among its chains at the beginning and end of the curing process of the resins.…”

“…7,36,37 This equation assumes that the resins reach full curing (a ¼ 1). Thus, the empirical DiBenedetto equation makes it possible to relate T g to the a of the resin as follows: 7,14,16,17,20,38,39 …”