Polarity epoxy resins

CDT is perfoimed by the application of a large electrical field to the fibers through a sharp electrode. The polarity of the fibers and the number of OH and COOH groups increase, and consequently, fiber/polar-epoxy resin matrix adhesion improves after applying this treatment to the fibers. CDT can be applied as a continuous process, which is the common practice in textile or paper industry [6], This treatment can also be apphed as a preparation stage for grafting the cellulosic fiber surface to hydro-phobic, nonpolar polymers [9]. 

Heat-reactive resins are more compatible than oil-soluble resins with other polar-coating resins, such as amino, epoxy, and poly(vinyl butyral). They are used in interior-can and dmm linings, metal primers, and pipe coatings. The coatings have excellent resistance to solvents, acids, and salts. They can be used over a wide range of temperatures, up to 370°C for short periods of dry heat, and continuously at 150°C. Strong alkaUes should be avoided. 

There is, quite clearly, scope or a very wide range of epoxy resins. The nonepoxy part of the molecule may be aliphatic, cycloaliphatic or highly aromatic hydrocarbon or it may be non-hydrocarbon and possibly polar. It may contain unsaturation. Similar remarks also apply to the chain extension/cross-linking agents, so that cross-linked products of great diversity may be obtained. In practice, however, the commercial scene is dominated by the reaction products of bis-phenol A and epichlorohydrin, which have some 80-90% of the market shtu"e. 

The intrinsic moisture sensitivity of the epoxy resins is traceable directly to the molecular structure. The presence of polar and hydrogen bonding groups, such as hydroxyls, amines, sulfones and tertiary nitrogen provides the chemical basis for moisture sensitivity, while the available free volume and nodular network structure represent its physical aspect. 

Composite Particles, Inc. reported the use of surface-modified rubber particles in formulations of thermoset systems, such as polyurethanes, polysulfides, and epoxies [95], The surface of the mbber was oxidized by a proprietary gas atmosphere, which leads to the formation of polar functional groups like —COOH and —OH, which in turn enhanced the dispersibility and bonding characteristics of mbber particles to other polar polymers. A composite containing 15% treated mbber particles per 85% polyurethane has physical properties similar to those of the pure polyurethane. Inclusion of surface-modified waste mbber in polyurethane matrix increases the coefficient of friction. This finds application in polyurethane tires and shoe soles. The treated mbber particles enhance the flexibility and impact resistance of polyester-based constmction materials [95]. Inclusion of treated waste mbber along with carboxyl terminated nitrile mbber (CTBN) in epoxy formulations increases the fracture toughness of the epoxy resins [96]. 

As shown in Table 15.5, the epoxy plastics have fair resistance to high temperatures and have good mechanical properties. Cured epoxy resins are resistant to nonoxidizing acids, alkalis, and salts. Because of the presence of polar hydroxyl pendant groups, these polymers have good adhesion to substrates such as wood or metal. 

Dispersion forces57 , which result from temporary variations in the distribution of electron density in atoms, can account for up to 90 per cent58 of the adhesion forces between non-polar polymers and metal substrates (bond energy 0.5-5 Kcal/ mole)50 . However, for the adhesion of epoxy resins and other polar polymers to metals, dispersion forces are of secondary importance when compared to the electromagnetic and mechanical interactions discussed above. 

LeMay, J. D., Kelley, F. N. Structure and Ultimate Properties of Epoxy Resins. Vol. 78, pp. 113-148. Lindberg, J. J. and Hording, B. Cross Polarization — Magic Angle Spinning NMR Studies of Carbohydrates and Aromatic Polymers. Vol. 66, pp. 1-22. 

The addition of microspheres lowers the glass transition temperature of the epoxy binder (Fig. 13). This seems to be because the filler causes defects in the matrix network. Equal diffusion coefficients of filled and unfilled epoxy binder indicates, therefore, that the diffusion processes are insensitive to binder changes. The sorption of water by epoxy resins is in fact known to depend mainly on their polarity and only slightly on the three-dimensional compactness of the network. 

These findings suggest strongly that the composition of the elastomeric molecule and the nature of the functional groups affect its compatibility and rate of reaction with the epoxy resin, which in turn affect the molecular and morphological structure of the heterophase system. These data indicate the importance of the acrylonitrile comonomer and the carboxyl groups in controlling the polarity of the rubber, and subsequently its compatibility characteristics with the epoxy. We could also... 

Similarly, the hydroxyl equivalent weight is the weight of the resin containing one equivalent of hydroxyl group, and it may also be expressed as equivalents per 100 g. Several studies have demonstrated that the hydroxyl content greatly influences the adhesion of the epoxy resin.3,4 These results are best explained by the polar character of the... 

The phenoxy resin has a chemical structure similar to that of epoxy resin however, the phenoxy is a high-molecular-weight thermoplastic polymer, which needs no further conversion and has an infinite shelf life. Since the phenoxies are strongly polar polyethers, they... 

Because of the highly polar nature of common epoxy resins and their curatives, most formulations can be cured via a microwave environment. A further advantage is that the uncured material absorbs microwave energy more strongly than that which is cured, so the cure occurs uniformly within the material. 

Fig. 16 Schematic representation of an interface-induced segregation scenario. As long as the viscosity of the crosslinking system is low enough, segregation of epoxy resin and curing agent may occur, driven by the polar surface of the Cu component. Conservation of mass requires a depletion zone close to the zone of enrichment. Via the network structure the concentration profile is reflected by the local mechanical properties of the cured epoxy system...

It is made by dimerizing cyanamide in basic aqueous solution, and is a colorless solid melting at 208°C. Dicyandiamide is soluble in polar solvents, but at room temperature is insoluble in bisphenol A epoxy resins. It can be made into a very fine powder and milled into epoxy resins to form stable dispersions. Because the dicy is insoluble in the epoxy, the only possible reaction sites are at the particle surfaces. Although some reaction certainly occurs over a short time, the adhesives easily can have a useful shelf life of six months. On heating to about 150°C, the dicyandiamide becomes soluble in the epoxy resin, and the adhesive polymerizes rapidly. Cure can be accelerated by incorporation of tertiary aromatic amines or substituted ureas. 

To overcome these drawbacks, in recent years much attention has been paid to the development of resins which cem be f2d ricated with the same processes as those for conventional polyester resins, but having superior properties. Vinyl ester resins are the result of such development efforts (4-6). Vinyl ester resins are addition products of Vcurious epoxide resins and ethylenically unsaturated mono-carboxylic acids ( ). It condsines the excellent mechcuiical, chemical cuid solvent resistemce of epoxy resins with the properties found in the unsaturated polyester resins. In general, the cured vinyl ester resin has physical properties superior to the cured conventional ester resin, particulcurly corrosion resistcuice. This arises from the differences in the number and arremgement of polar groups such as ester and hydroxyl groups eind ccurbon-to-ccirbon double bonds present in the polymer chains. 

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