Epoxy systems with improved water resistance, and the non‐fickian behaviour of epoxy systems during water ageing

Abstract

N,N‐Bis (2, 3‐epoxypropyl) aniline and 4,4′‐methylenebis‐[N,N‐bis (2,3‐epoxypropyl) aniline] containing bromo, chloro, trifluoromethyl or polyfluoroalkoxy substituents were synthesised and cured with aromatic diamines in order to investigate the effect of substituted halogen on water absorption. Significant improvements were achieved: thus use of 4,4′‐methylenebis‐[N, N‐bis (2, 3‐epoxypropyl)‐3, 5‐dichloroaniline] and 4,4′‐methylenebis‐[N,N‐bis (2,3‐epoxypropyl)‐3‐(trifluoromethyl) aniline] instead of 4,4′‐methylenebis‐[N,N‐bis (2,3‐epoxypropyl) aniline] reduced the water absorption by about a half. Departures from Fickian behaviour were observed during water immersion ageing at room temperature and were a general feature of the epoxy systems examined. Plots of water absorption against the Fickian parameter (√t/d) usually showed at least mild sigmoid character and were not independent of specimen thickness. Further, slow continued uptake of water occurred during long‐term ageing, and evidence is provided that the associated network distortions are reversible.

Novel phosphorus‐containing hardeners with tailored chemical structures for epoxy resins: Synthesis and cured resin properties

“…This observation can be in part attributed to the relative proximity of the immersion temperature to the glass transition temperature of this wet epoxy system (wet T g = 142°C as determined by DMA). Hence, viscoelastic effects would contribute to an enhanced water transport into the network, in agreement with previous studies in the literature 37, 57, 58. It is worth mentioning at this point that an “initial saturation” value (as indicated by the arrows) was used to fit the experimental water absorption data using Fick's law; therefore, “apparent” diffusion coefficients are calculated and are summarized in Table II.…”

Hygroscopic Behavior of Woven Fabric Carbon-Epoxy Composites

“…Barrie et al [5] included the possibility of clustering of water molecules at high moisture levels. It has also been proposed that the equilibrium water concentration is mainly governed by the available free volume [4,6,7], or that water molecules occupy microvoids and other defects [8][9][10]. Previous studies [11][12][13][14][15][16] show that water molecules are linked by strong hydrogen bonds to hydrophilic groups such as hydroxyl and amine groups.…”

Design and ageing of adhesives for structural adhesive bonding – A review

“…81 Changes in the chemicals composition of the resin alter both the rate at which water is absorbed and the extent of absorption, and this is particularly evident when the epoxy contains chlorine, bromine or fluorine atoms. 82–84 The diffusion coefficients are influenced by the functionality of the epoxy and the amine which in turn influences the free volume. The free volume is reflected in the T g and the diffusion coefficients scale roughly with its value; a high T g material will usually have a low diffusion coefficient.…”

“…Comparison of joints produced using processes involving grit-blast and degreasing (GBD), phosphoric-acid anodising (PAA), and PAA followed by the application of an anti-corrosion primer (PAAP) and subjected to cyclic fatigue tests in liquid water and in 55% relative humidity (RH) has been undertaken. 84 It has been found that there is threshold for the adhesive fracture energy, G th , below which crack growth will not occur. For the GBD pre-treated joints, tested in both the liquid water and in 55% RH environments, failure occurs predominantly by the thermodynamic displacement of the adhesive from the metal substrate.…”