Effect of time‐temperature path of cure on the water absorption of high T_g epoxy resins

Abstract

synopsisThe effect of different time-temperature paths of cure on the water absorption of high Tg epoxy resins has been investigated. The resins were cured isothermally for different times, with the following results:. as extent of cure increased, the glass transition temperature (T,) increased, the room temperature (RT) modulus decreased, the RT density decreased, the RT diffusion coefficient appeared to decrease, and the RT water absorption increased. The decrease in RT density is related to an increase in free volume, which controls the amount of water absorbed. A qualitative model accounts for the increase in RT free volume with increasing cure. The model is based on a restricted decrease of free volume on cure due to the rigid molecular segments in the cured resin systems. The sorption isotherms can be characterized by the dual mode theory at low activities but at high activities the sorption is complicated by penetrant clustering. A thermodynamic approach, independent of the absorption model, can correlate sorption data at different temperatures. The diglycidyl resin was also cured for extended times at three temperatures, in a n effort to achieve full cure at each temperature.For these, the higher the cure temperature, the lower the RT density, which could result from the lower initial density of materials cured at higher temperatures. The equilibrium water absorption increased with increasing cure temperature, consistent with the decrease in RT density. The systems studied were a diglycidyl ether of bisphenol A cured with a n aromatic tetrafunctional diamine, trimethylene glycol di-p-aminobenzoate (Tgm = 156"C), and a triglycidyl ether of tris(hydroxypheny1)methane cured with the same amine (TSm = 268°C).

The TBA torsion pendulum: a technique for characterizing the cure and properties of thermosetting systems

“…Another equation for the versus conversion relationship was based on being T g T g the value of a miscible mixture of Ðnite molecules (the sol), the of which depends on its calculable average molecular T g weight, and network molecules (the gel), the of which T g depends on the calculable crosslink density. 27 ) ; the end of the isothermal vitriÐcation process to conversion ; the constant conversion at gelation to T ; and the temperature e T g gel T g of the transition to conversion. The relationships of other events (e.g.…”

Résines époxy réticulées par des polyamines : structure et propriétés

“…Il a souvent ŽtŽ observŽ quÕˆ tempŽrature ambiante, la masse volumique dÕun syst•me Žpoxy diminue quand la densitŽ de rŽticulation augmente, lorsque celle-ci est contr™lŽe par la cuisson ou par les proportions du mŽlange [42,43,[64][65][66][67][68][69]. Des auteurs [42,43,67,[69][70][71] En revanche, la diminution de la densitŽ de rŽticu-lation par augmentation de la taille des prŽpolym•res [50] ou par lÕajout dÕextendeurs de maille [21] entra"ne une diminution de la masse volumique.…”

The effect of curing conditions on the electrical properties of an epoxy resin

“…In the case of thermosetting epoxy resin systems, it has been shown [1] that the degree of curing depends on the time and temperature of curing. As the curing time increases, so the glass transition temperature, Tg, shifts to higher values.…”

“…The resulting crosslink density impacts the physical properties of epoxy resin, as systems with increased crosslinking have improved mechanical properties [3]. Such variations in the properties of epoxy resin systems are, ultimately, caused by variation in both the time and temperature of curing [1][2][3].…”