Epoxy resin systems Blends

The polymercaptans can also be used to accelerate the curing of epoxy resins systems blended with polyamines, amidoamines, or amines. The other curatives serve as the base to accelerate mercaptans, and the mercaptans react rapidly, generating the heat to accelerate the cure with the other hardener. 

A modified BMI-epoxy resin system has been introduced by Shell Chemical Company. The system is a highly reactive blend of a bismaleimide, COM-PIMIDE 1206 (55-60% by weight solution of BMI in DMF), and EPON Resin 1151, a polyfunctional epoxy resin (60). In contrast to many polyimide resins on the market, no free MDA is present in the product. This is an important feature, since MDA has been identified as an animal carcinogen and possibly a human carcinogen. This resin system has been fully evaluated for use in multilayer PCB boards (61). 2-Methylimidazole is recommended as a catalyst. However, if required, the processing window can be widened by using 2-phenylimidazole... 

Static and impact fracture data (room temperature measurements) mainly for epoxy resin systems is presented in Table 2. These relatively brittle materials require modification by, for instance, blending with a suitable rubber or thermoplastic to improve fracture toughness. Such improvements, however, depend not only on the types of materials but also on the composition and therefore the type of blend structure (e.g.. continuous-discrete phases. 

Epoxy resins are most widely used for low-pressure laminates and are used for some high-pressure types. Combining a resin (or a blend of resins) with a curing agent and, possibly, with accelerators and flexibilizers, produces an epoxy resin system. 

Sue Sue, H.-J., Earls, J. D., Hefrier Jr., R. E. Fracture behaviour of liquid crystal epoxy resin systems based on diglycidyl ether of 4,4 -dihydroxy-a-methylstilbene. Part 11 Effect due to blending with TACTIX 556 epoxy resin and phenolic monomers. J. Mater. Sci. 32 (1997) 4039 046. 

These tougheners can be physically blended into an epoxy resin system or can be capped with an epoxy resin by pre-reaction and then blended with unmodified epoxies and cure agents, usually using triphenyl phosphine as a catalyst system, which promotes the carboxyl-epoxy reaction at temperatures under 120°C [82]. 

The same basic epoxy resin systems are used as monolithic surfacings and epoxy polymer concrete. In addition to these, epoxy phenol novolac is also used to produce mortars and grouts. This is a higher viscosity resin that requires the inclusion of various types of diluents and resin blends. Table 10.3 lists the atmospheric corrosion resistance of the mortars and grouts. 

Elastomers, plastics, fabrics, wood and metals can be joined with themselves and with each other using nitrile rubber/epoxy resin blends cured with amines and/or acidic agents. Ethylene-propylene vulcanizates can also be joined using blends of carboxylated nitrile rubber, epoxy resin and a reactive metal filler (copper, nickel, cobalt). However, one of the largest areas of use of nitrile rubber modified epoxy systems is in the printed circuit board area [12]. 

When formulating a system for optimum abrasion resistance, both the epoxy/resin hardener binder system and the filler blends used appear to have an influence. The simulation of abrasive service loads on industrial floor toppings in a laboratory is not simple, and numerous wear test machines have been devised. Correlation between different wear test machines is not always good, although most... 

The cloud point curves of the epoxy monomer/PEI blend and BPACY monomer/PEI blend exhibited an upper critical solution temperature (UCST) behavior, whereas partially cured epoxy/PEI blend and BPACY/PEI blend showed bimodal UCST curves with two critical compositions, ft is attributed to the fact that, at lower conversion, thermoset resin has a bimodal distribution of molecular weight in which unreacted thermoset monomer and partially reacted thermoset dimer or trimer exist simultaneously. The rubber/epoxy systems that shows bimodal UCST behavior have been reported in previous papers [40,46]. Figure 3.7 shows the cloud point curve of epoxy/PEI system. With the increase in conversion (molecular weight) of epoxy resin, the bimodal UCST curve shifts to higher temperature region. 

Recently, alternative theoretical expressions have been developed by using classical thermodynamic treatments to describe the compositional dependence of the glass transition temperature in miscible blends and further extended also to the epoxywater systems 2S,27). The studies carried out on DGEBA epoxy resins of relatively low glass transition have shown that the plasticization induced by water sorption can be described by theoretical predictions given by ... 

The lower-viscosity grades have an EEW of about 175 and are virtually pure diglycidyl ethers of bisphenol A. They are so pure, however, that they will crystallize on storage. The crystals melt on warming above 40°C, and heating can be used to restore a crystallized resin to its previous form. Special crystallization-free resins systems have been formed by blending low-viscosity DGEBA resins with more conventional bisphenol A-based epoxy resins. 

Solid epoxy resins are usually formulated as solvent solutions and blends with lower-MW resins for the production of liquid adhesive systems. However, solid epoxy resins are also often employed in the manufacture of adhesive systems having solid form. There are several forms of solid epoxy adhesives that find application. The most common are supported or unsupported film, powder, and solder stick. Formulations for these adhesives are detailed in Chap. 13. 

A variety of polymers, both thermosets as well as thermoplastics, can be blended and coreacted with epoxy resins to provide for a specific set of desired properties. The most common of these are nitrile, phenolic, nylon, poly sulfide, and polyurethane resins. At high levels of additions these additives result in hybrid or alloyed systems with epoxy resins rather than just modifiers. They differ from reactive diluents in that they are higher-molecular weight-materials, are used at higher concentrations, and generally have less deleterious effect on the cured properties of the epoxy resin. 

These blends can take a number of different forms. The added resin may be reacted with the epoxy resin, or it may be included as an unreacted modifier. The modifier may be blended into a continuous phase with the epoxy resin (epoxy alloys) or precipitated out as a discrete phase within the epoxy resin matrix (as is generally done in the case of toughening modifiers). Epoxy hybrid adhesives are often used as film (supported and unsupported) or tape because of the ease with which formulated systems can be dissolved into solvent and applied to a carrier or deposited as a freestanding film. Some systems, notably epoxyurethanes and epoxy-poly sulfides, can be employed as a liquid or paste formulation because of the low-viscosity characteristics of the components. 

The first group, resins that are used primarily to toughen epoxy adhesive systems, is described in Chap. 8. This chapter focuses on the resinous modifiers that are used as alloy blends. Characteristics of commercially available epoxy alloy adhesives are presented in Table 7.1. Tensile shear and peel strengths that are typical of these hybrid adhesives are compared in Table 7.2. 

For adhesive systems, the liquid epoxy resins most widely used with LP-3 polymers are liquid unmodified and diluent-modified bisphenol A resins and liquid blends of bisphenol A and bisphenol F resins. Solid bisphenol A, multifunctional, and aliphatic diepoxy resins have also been used. Ratios of liquid polysulfide polymer to epoxy are in the range of 1 2 to 2 1. The effect of various degrees of polysulfide on cure properties of a DGEB A epoxy is shown in Table 7.7. An increase in elongation and impact strength is the result of increased amounts of the liquid polysulfide polymer. 

Silyl-terminated polyether can be blended with epoxy resins to form elastic adhesives at room temperature.9 In this system, small rigid epoxy particles are chemically linked by an elastic poly ether phase. A typical formulation is shown in Table 8.4. Elongation and peel... 

Typically tape or film epoxy adhesives are modified with synthetic thermoplastic polymers to improve flexibility in the uncured film and toughness in the cured adhesive. Epoxy resins can also be blended with phenolic resins for higher heat resistance. The most common hybrid systems include epoxy-phenolics, epoxy-nylon, epoxy-nitrile, and epoxy-vinyl hybrids. These hybrid film adhesives are summarized in Table 13.2, and structural properties are shown in Table 13.3. 

It can be expected, then, that one of the major problems in adhesives technology is the development of adhesives that must withstand both elevated temperatures as well as periodic excursions to low temperatures. Several solutions have been developed. Certain adhesive systems, notably blends of epoxy resin with more elastic resins, have been formulated with a very broad glass transition temperature range or with multiple glass transitions at both high and low temperatures. These have found some success in the applications discussed in this chapter. 

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). 

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