Epoxy resins chemically modified

We have presented an evaluation of epoxy resins chemically modified with poly(di-methyl siloxane) as well as poly(dimethyl-co-diphenyl siloxane) ami poly(dimethyl-co-methyltrifluoropropyl siloxane). The composition of the siloxane modifier, which... 

For polystyrene and related thermoplastic copolymers, this inherent brittleness has been corrected effectively by including rubbery particles, properly modified by grafting with thermoplastic chains, for energy dissipation (6). With crosslinked epoxy resins, chemical attachment of the... 

A highly crosslinked epoxy resin was modified by reactive blending with bisphenol Apolycarbonate. The bisphenol A polycarbonate was dissolved at high temperature in the uncured epoxy resin before the curing process. The physical and chemical interactions between the two components were studied by IR. Isothermal measurements showed that the presence of polycarbonate did not affect the overall curing mechanism but decreased both the initial reaction rate and the final conversion of reactants (278). 

Liquids. Approximately 170,000 railroad tank cars are used in the United States. The interior surfaces of these cars are tailored to carry a wide variety of products and are constmcted of steel which is either unlined or lined with materials to enhance the chemical compatibiUty with a specific product these lining materials include synthetic mbber, phenoHc or modified epoxy resins, or corrosion-resistant materials such as aluminum, nickel-bearing steel, or stainless steel. 

W. A. Romanchick, J. E. Sohn, and J. F. Geibel Synthesis, Morphology, and Thermal Stability of Elastomer-Modified Epoxy Resin, in ACS Symposium Series 221 — Epoxy Resin Chemistry II, R. S. Bauer (ed.), American Chemical Society, Washington DC, 1982, pp. 85-118. 

Of the several types of the polymer-modified mortars and concretes used for various construction applications, latex-modified mortar and concrete are by far the most widely used materials. Latex-modified mortar and concrete are prepared by mixing a latex, either in a dispersed liquid or as a redispersible powder form with fresh cement mortar and concrete mixtures. The polymers are usually added to the mixing water just as other chemical admixtures, at a dosage of 5-20% by weight of cement. Polymer latexes are stable dispersions of very small (0.05-5 pm in diameter) polymer particles in water and are produced by emulsion polymerization. Natural rubber latex and epoxy latex are exceptions in that the former is tapped from rubber trees and the latter is produced by emulsifying an epoxy resin in water by the use of surfactants [87]. 

It is becoming apparent that wood components, especially lignin, are chemically modified by solvents during wood dissolution, and that the resulting wood tars or pastes become highly reactive. Attempts have therefore been made to prepare effective adhesives, moldable resins and other products from wood after dissolution in phenols or polyhydric alcohols. This review presents recent progress on wood dissolution, and on the preparation of epoxy and phenol resin adhesives from kraft lignin. 

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... 

Amines were one of the first hardeners of epoxy resins 1 12), and at present they retain their leading position among all known hardeners of this type. The amine hardeners will most likely also be used in the future because they are fairly accessible, highly reactive, and their properties can be readily modified. The mechanical properties of the cured resins obtained are far better than those of the known polymer binders 2 -4), they have high dielectric characteristics, chemical resistance, etc. 

Sensing mechanism of the modified sensor. The sensing mechanism in this modified sensor should be essentially the same as that of the unmodified one. It is noteworthy that a stationary short circuit current was obtained in spite of such sensor construction that the counter electrode was covered with Epoxy resin. Since the sensing electrode is placed in the same situation as the unmodified sensor, this fact indicates that the cathodic reaction is allowed to take place stationarily at the counter electrode. The proton conductor membrane is as thin as 0.2 mm, so that the reactant 02 and the produced H20 will permeate the membrane as shown in Figure 11. A part of H2 will naturally also permeate through the membrane, but the transfered H2 will be consumed by the reaction with 02 electro-chemically or catalytically at the counter electrode. 

The fabrication of the material that forms when linear polyimides are mixed or coupled with epoxy resins to form three dimensional interpenetrating networks (IPN) is wrought with problems. These can be viewed from a polymer science aspect, where chemically modifying the structure of the components will result in their compatibility or from an engineering viewpoint where modifying existing fabrication methods and formulations will result in the desired composite materials. The following is a summary of research of epoxy and polyimide combinations to date. 

Epoxy-nitrile Nitrile-epoxy adhesives are composed of solid epoxy resin modified with carboxyl-terminated butadiene nitrile (CTBN) copolymer. The CBTN is introduced into die epoxy resin at elevated temperatures. The modification provides toughness and high peel strength without sacrificing heat and chemical resistance. The film adhesives are widely used in the aerospace industry in the construction of jetliners. 

Adhesives formulated with epoxy-modified latex retain the tack and conformability of the original latex but show improvements in green bond strength and fully cured bond strength. Cured epoxy latex epoxy resin systems also exhibit improved water and chemical resistance over unmodified latex systems. 

The semi-Gaussian stiffness profile indicates diffusion processes occurring before the gelation of the reactive mixture of epoxy resin and curing agent. The diffusion processes are expected to modify the local structure of chemical crosslinks. Due to its finite width of 3/c=280 nm, the gradient zone has to be considered as a volume rather than as an area and, hence, it deserves to be called interphase. 

There are numerous types of paint employed in the protection of steel and they are designed to meet the conditions imposed by the environment in which they are expected to function. For steel exposed to the atmosphere, the most common type of paint system is based on alkyl resin and this may be mixed with other types or may itself be chemically modified for a specific purpose, e.g. vinyl toluenated or styrenated to give rapid drying. Other generic types are chlorinated rubber, vinyl, acrylic, epoxy, and polyurethane. All have particular attributes and limitations and selection is usually a matter of discussion between user and supplier. 

Thermoset plastics have also been pyrolysed with a view to obtain chemicals for recycling into the petrochemical industry. Pyrolysis of a polyester/styrene copolymer resin composite produced a wax which consisted of 96 wt% of phthalic anhydride and an oil composed of 26 wt% styrene. The phthalic anhydride is used as a modifying agent in polyester resin manufacture and can also be used as a cross-linking agent for epoxy resins. Phthalic anhydride is a characteristic early degradation product of unsaturated thermoset polyesters derived from orf/io-phthalic acid [56, 57]. Kaminsky et al. [9] investigated the pyrolysis of polyester at 768°C in a fiuidized-bed reactor and reported 18.1 wt% conversion to benzene. 

Pure epoxy resins, so-called basic resins, are unsuited to building applications because of their high viscosity. Modifications are necessary to achieve the required viscosity, wettability, carbonate resistance, curing rate, cost reduction and numerous other properties. However, the modifiers must be chosen so as not to impair the other valuable attributes of the epoxy resins. For example volatile solvents are unsuitable for thick coatings, because any solvent retained in the cured system will reduce the mechanical and thermal properties and the corrosion resistance. The specific property needs for a particular application may be tailored to each system to maximise the remarkable potential of epoxy resins (Dow Chemical Company, undated c). 

Chemical resistance. Unmodified epoxy resins have excellent resistance to dilute acids, alkalis and certain solvents. The incorporation of an LP component into the epoxy resin extends this resistance to a wide variety of oils, aromatic and aliphatic hydrocarbons, esters and ketones. Coatings and adhesives based on polysulphide-epoxy resins exhibit reduced swell and maintenance of flexibility and adhesion when immersed in these fluids. In view of this, LP-modified epoxies are used on oilrigs, fuel-storage installations and chemical plants (Figure 10.4). 

Figure 10.4 The chemical resistance of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin modified with LP-3 (50 parts LP-3 per 100 parts resin). A 5 cm x 3 cm x 2 mm coupon was immersed in the liquid for 28 days at 23°C. Open boxes = percentage volume swell shaded boxes = percentage weight change. Reproduced with permission from Morton International Ltd, Coventry, UK...

Another development has been reported by P.A. Lucas, W.E. Stamer and S.G. Musselman of Air Products and Chemicals Inc. (Lucas et al., 1994). An acrylate functional urethane flexibiliser has been used to modify epoxy resin, which optimises reactivity and is more compatible with epoxy. Urethane-acrylate flexibiliser offers very tough hybrid epoxy systems meeting the more demanding requirements of civil engineering applications. 

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