The curing agents of epoxy resin, trimethylsilyl ethers of phenol novolak (TMSPN) and cresol novolak (TMSCN) were prepared
by refluxing phenol novolak and cresol novolak respectively, with the mixture of hexamethyldisilazane and chlorotrimethylsilane
in THF. The curing reaction of epoxy resin with these curing agents and the thermal properties of cured resins were examined.
The Tg values of epoxy resins cured with TMSPN were a little higher than those cured with TMSCN. The maximum of Tg is 118C
for TMSPN-cured epoxy resin against 112C for TMSPN-cured epoxy resin. The water absorption of hydrophobic epoxy resins cured
with TMSPN was a little lower than those cured with TMSCN. The clear decrease of water absorption is attributed to the difficulty
of the micro-void formation caused by the more tight primary structures of TMSPN. The water absorption at 25C containing
trimethylsilyl groups is about one-tenth of that of epoxy resins cured with conventional curing agents and even one-half of
that of the epoxy resins cured with active esters. The low water absorption is attributed to the presence of trimethylsilyl
groups, which are more hydrophobic than ester groups, and to the absence of hydroxyl groups of the cured resins.
The effect of network structure on the glass transition temperature (Tg) was examined by differential scanning calorimetry, thermomechanical analysis and dynamic thermomechanometry for epoxy resins
cured with mixtures of curing agents consisting of an active ester, 1,3,5-triacetoxybenzene (TAB), and a polyfunctional phenol,
1,3,5-trihydroxybenzene (THB). Free hydroxyl groups are formed from THB after curing, whereas acetyl groups are left from
TAB. TheTg value of cured epoxy resins decreased with increasing TAB content in the curing agent, which is attributed to the looser
network structure induced by the steric hindrance of acetyl groups from TAB in the curing reaction and also to the weaker
intermolecular interaction and the internal plasticization of acetyl groups from TAB.
Authors:D. A. Ivanov, V. F. Chuvaev, and M. R. Kiselev
By means of DSC, DTA, TG and NMR it was established that the process of cure of epoxy resins induced by aqueous solutions of heteropolyacids consists of two stages, the first one being connected with a catalytic interaction between oligomer and water, and the second one with epoxy-hydroxyl etherification. Analysis of kinetic data shows that the first reaction is diffusion controlled, the second process can be described by pseudo-first order kinetics with activation energy about 40 kJ/M.
Pentaerythritol diphosphonate melamine-urea-formaldehyde resin salt, a novel cheap macromolecular intumescent flame retardants
(IFR), was synthesized, and its structure was a caged bicyclic macromolecule containing phosphorus characterized by IR. Epoxy
resins (EP) were modified with IFR to get the flame retardant EP, whose flammability and burning behavior were characterized
by UL 94 and limiting oxygen index (LOI). 25 mass% of IFR were doped into EP to get 27.2 of LOI and UL 94 V-0.
The thermal properties of epoxy resins containing IFR were investigated with thermogravimetry (TG) and differential thermogravimetry
(DTG). Activation energy for the decomposition of samples was obtained using Kissinger equation. The resultant data show that
for EP containing IFR, compared with EP, IFR decreased mass loss, thermal stability and Rmax, increased the char yield. The activation energy for the decomposition of EP is 230.4 kJ mol−1 while it becomes 193.8 kJ mol−1 for EP containing IFR, decreased by 36.6 kJ mol−1, which shows that IFR can catalyze decomposition and carbonization of EP.
Authors:L. Barral, J. Cano, A. J. López, J. López, P. Nogueira, and C. Ramírez
The diffusive and dynamic mechanical behavior of the DGEBA/1,3-BAC epoxy resin system was studied during water absorption. The diffusion of water was investigated at 100% relative humidity, by immersion of specimens in water at 60, 80 and 100°C. In all absorption experiments, water diffusion followed Fick's law. Diffusion coefficients and saturated water concentrations are given for these temperatures. The activation energy for diffusion was determined from the relationship between the diffusion coefficient and the reciprocal of the absolute temperature. The value obtained was 31.2 kJ mol−1. Dynamic mechanical analysis of samples immersed in 100°C water and with various water contents showed both a shift of Tg, defined by thetanδ peak, to lower temperatures and a slight decrease in the dynamic modulus in the presence of water. These effects are probably a result of plasticization.
The curing reactions of the epoxy resins tetraglycidyl diaminodiphenyl methane (TGDDM) and tetraglycidyl methylenebis (o-toluidine) (TGMBT) using diaminodiphenyl sulfone (DDS), diaminodiphenyl methane (DDM) and diethylenetriamine (DETA) as curing agents were studied kinetically by differential scanning calorimetry. The dynamic scans in the temperature range 20°–300°C were analyzed to estimate the activation energy and the order of reaction for the curing process using some empirical relations. The activation energy for the various epoxy systems is observed in the range 71.9–110.2 kJ·mol−1. The cured epoxy resins were studied for kinetics of thermal degradation by thermogravimetry in a static air atmosphere at a heating rate of 10 deg·min−1. The thermal degradation reactions were found to proceed in a single step having an activation energy in the range 27.6–51.4 kJ·mol−1.
Authors:I. Blanco, L. Oliveri, G. Cicala, and A. Recca
Epoxyresins are an important class of polymeric materials, characterised by the presence of more than one three-membered ring known as the epoxy (“epoxy” is derived from the Greek prefix “ep,” which means over and
Authors:Jintao Wan, Hong Fan, Bo-Geng Li, Cun-Jin Xu, and Zhi-Yang Bu
Epoxyresins are extensively used in surface coatings, adhesives, laminating, castings, matrices for advanced composites, electronic encapsulation materials, sealants, etc., due to their vast formulation
Epoxyresin is one of the most important polymeric materials widely used in the polymer industry as coatings, structural adhesives, insulating materials, and polymeric composite materials, etc. [ 1 – 3 ]. The
Authors:Zhuofeng Liu, Jiayu Xiao, Shuxin Bai, and Weijun Zhang
Epoxyresin is one of the most used thermosetting polymer matrix for its good mechanical strength and corrosion resistance. It plays an important role in industry. As a matrix of composites, the curing course of