Epoxies/adhesives conclusion

Another indication of hydrolysis is shown by the KR. spectrum Figure II. The change in -CH3 absorption at 2980 cm" at room temperature was followed with a F.T.I.R. employing time lapse technique(7). 3) Functional groups that will interact with acid must be present to obtain maximum adhesion. This conclusion is supported by the fact that epoxy and amine containing silanes are all excellent adhesion promotors as shown in Table V. 

The formation of borophosphate partially explains the good performance when APP and boric acid are mixed together in the epoxy resin. Indeed, in that case good mechanical resistance of the intumescent char is observed as borophosphate is a hard material, which also shows a good thermal stability. As a conclusion, the boron containing compounds provide the good structural properties of the char, whereas the phosphorus ensures the adhesion of the char to the steel. 

Rubber as the Disperse Phase. In polyblend systems, a rubber is masticated mechanically with a polymer or dissolved in a polymer solution. At the conclusion of blending, a rubber is dispersed in a resin as particles of spherical or irregular shape. We can further subdivide this system into three classes according to the major intermolecular forces governing adhesion (a) by dispersion forces—e.g., the polyblend of two incompatible polymers, (b) by dipole interaction—e.g., the polyblend of polyvinyl chloride and an acrylonitrile rubber (56), and (c) by covalent bond—e.g., an epoxy resin reinforced with an acid-containing elastomer reported by McGarry (43). 

Comparison of the results for the HMW PAMAM with those for the LMW PAMAM leads to the conclusion that the optimal concentration of the HB PAMAM that yields the highest shear strength depends not only on the adhesive used but also on the MW and the functionality of the primer. For the epoxy ad-... 

The general conclusions were confirmed by the practical results related to the CO-curing of CEC/ACEC compositions with amines in the presence of BF3-amine complexes [87]. The idea presented here was also applied to the synthesis of novel epoxy compounds which contained epoxy groups differing in structure and reactivity [88-90] to be used in adhesive formulations. 

The above studies showed that, for this particular adhesive system, the rate of diffusion of water through the adhesive to the interface was the rate controlling step. Now, if the diffusion of water through the adhesive is Fickian in nature, then the concentration profile of water as a function of time into the joint may be calculated [6,43,44], and such information may then be readily used in life-prediction models, as discussed below. It should be noted that the values of the diffusion coefficient given in Fig. 12b, which are very typical for structural epoxy adhesives, lead to the conclusion that, at ambient temperatures, it will take at least a year or more for the adhesive layer in a joint, say about 20 mm x 10 mm in size (as often used in single-overlap shear joints), to reach its uniform, equilibrium concentration of water, although of course, depending upon the details of the adhesive system , even complete failure of the joint due to environmental attack may have occurred well before this time is reached. 

The major conclusion was that surface effects but also mechanical properties play an important role in adhesion. The epoxies that showed the best wetdng/adhesion were those with the higher critical surface tension, highest acid parameter and also the largest modulus of elasticity. For the three epoxies for which mechanical properties were studied, adhesion appears to follow the same trend as the one shown in Figure 6.12b. 

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