Water-reducible epoxy resin

Figure 2.57 Important routes for water-reducible epoxy resin...

VeX 11-548. [Henkel] Water-reducible amidoamine resin epoxy curing agent... 

This review will first present the metal/epoxy resin adhesive system and discuss how the presence of metal oxides influences adhesion secondly, present the reasons why these systems exhibit very good adhesion strength under dry conditions and why this adhesion strength is greatly reduced in the presence of water thirdly, examine possible methods of increasing their durability in wet environments and finally, discuss some of the spectroscopic techniques that are currently being used to aid in the advancement of metal/polymer adhesion technology. 

One method that has shown promise for reducing the permeation of water through epoxy coatings involves the introduction of fluorine into the epoxy network. Highly fluorinated epoxy resins of the form shown below have been developed by Griffith,... 

Decreasing the water absorption mechanically , i.e. by coating the external surface of an article, produces good results. It was shown that coating of epoxy syntactic foams with a thin layer of epoxy resin reduces the water absorption more than tenfold, even under high hydrostatic pressure 140). 

Manson and Chin 151) reported that the addition of filler to an epoxy binder reduces the epoxy s permeability coefficient (P), as well as the solubility of water in the resin (S) and that the reduction is stronger than expected from theory 1 2). Diffusion coefficients calculated from P and S for the unfilled resin were found to be somewhat higher than those for filled resin. The difference seems to be due to the formation of ordered layers, up to 4 pm thick, around every filler particle. The layers form because of residual stresses caused by the difference between the binder and filler coefficients of thermal expansion. The effective activation energy for water to penetrate into these materials, calculated in the 0-100 °C temperature range, is 54.3 kJ/mol151). 

The resins based on glycerol and pentaerythritol are water-soluble and have low viscosity. They can have greater functionality and reactivity than conventional DGEBA resins. Resins based on polytaerythritol are claimed to have excellent adhesive properties including the ability to adhere to wet surfaces. They cure between 2 and 8 times faster than DGEBA epoxy resins and reduce the viscosity of DGEBA by 50 percent when used in concentration of 20 pph. 

Coal tar pitch is the most widely used resinous extender for epoxy resins. It is primarily used in surface coating formulations, but can also be used as a cost reducer and flexibi-lizer in epoxy adhesives and sealants. In addition to the increase in flexibility (and reduction in thermal and chemical resistance), coal tar pitch extenders provide excellent water resistance. Their primary applications, therefore, are often in the marine, pipe, tank, and general industrial maintenance areas. 

Table 14.4 presents formulation information for bisphenol A and polyfunctional epoxy resin emulsions that are cured with an aliphatic amidoamine curing agent. Adhesive performance data are also provided for substrates common to the automotive industry. Both formulas are based on a 1 1 epoxy-amine stoichiometry and they are reduced to 45 percent nonvolatiles with water. The working life of each system is several hours at room temperature. 

Has a reduced solvent content or is solvent free to minimize health effect due to solvents. There have been significant efforts in developing water borne and UV/EB cured epoxy resins to eliminate solvents. 

Epoxy-amino and epoxyacrylate High molecular weight epoxy resins cross-linked with amino or acrylate resins Water reducible for reduced environmental impact Good Limited Universal lacquer for beer and beverage cans (water reducible) Side seam stripes Some food systems... 

Samples of epoxy resin filled with glass microspheres have a reduced elastic modulus after water immersion. The loss of elastic modulus is more pronounced as... 

Figure 11.13 shows that in ajute filled epoxy resin, water intake increases with time of immersion and with the amount of fiber. This jute fibers readily absorb water. A surface treatment of the jute with epoxy silane reduces the water intake. Tensile properties of a composite containing surface treated fiber remain constant up to a moisture content of 5%. 

The fluid dimer polyamides and fatty amido amines also react with phenolic resins (23). These reactions are significantly different from those of epoxy resins. With the heat-reactive phenolic resins, the aminopolyamide portions react with methylol groups. A carbon-nitrogen bond or cross-link is formed and a volatile byproduct, water, is produced. This reaction requires external heat to remove water. At temperatures near 150 °C the reaction proceeds smoothly. Since curing at elevated temperatures is required, the pot life or shelf life at room temperature is relatively long. The liquid dimer polyamide and fatty amido amines also react with alpha, beta unsaturated acids and esters (29) and with polyesters (30). The unsaturated esters reduce viscosity, lengthen useful pot life, and reduce heat of reaction. Thus, they are useful diluents when low viscosity is desired. 

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