Vinyl, modified epoxy

Continuous scans of modulus versus temperature utilizing the DuPont Dynamic Mechanical Analyzer (DMA) has provided a comparison of the high temperature service capabilities of radiation-cured experimental formulations of a vinyl-modified epoxy resin. Shell Epocryl-12. These scans were compared to data obtained when the same materials were applied as adhesives on aluminum test panels, radiation-cured with an electron beam, and lap shear strength tested at discrete temperatures. The DMA instrument utilizes a thin rectangular specimen for the analysis, so specimens can be cut from blocks or from flat sheets. In this case the specimens were cured as sheets of resin-saturated graphite-fibers. The same order of high temperature stability was obtained by each method. However, the DMA method provided a more complete characterization of temperature performance in a much shorter test time and thus, it can be very useful for quick analyses of formulation and processing variables in many types of materials optimization studies. The paper will present details of this study with illustrations of the comparisons. 

Pyrotechnic mixtures may also contain additional components that are added to modify the bum rate, enhance the pyrotechnic effect, or serve as a binder to maintain the homogeneity of the blended mixture and provide mechanical strength when the composition is pressed or consoHdated into a tube or other container. These additional components may also function as oxidizers or fuels in the composition, and it can be anticipated that the heat output, bum rate, and ignition sensitivity may all be affected by the addition of another component to a pyrotechnic composition. An example of an additional component is the use of a catalyst, such as iron oxide, to enhance the decomposition rate of ammonium perchlorate. Diatomaceous earth or coarse sawdust may be used to slow up the bum rate of a composition, or magnesium carbonate (an acid neutralizer) may be added to help stabilize mixtures that contain an acid-sensitive component such as potassium chlorate. Binders include such materials as dextrin (partially hydrolyzed starch), various gums, and assorted polymers such as poly(vinyl alcohol), epoxies, and polyesters. Polybutadiene mbber binders are widely used as fuels and binders in the soHd propellant industry. The production of colored flames is enhanced by the presence of chlorine atoms in the pyrotechnic flame, so chlorine donors such as poly(vinyl chloride) or chlorinated mbber are often added to color-producing compositions, where they also serve as fuels. 

Materials. The adhesives and primers used in this study were model and commercial materials that were cured according to conditions appropriate for the specific adhesive chemistry. Adhesives A and B were conventional epoxy/Versamid and epoxy/dlcyandiamlde adhesives, respectively. Adhesives C and D were commercial urethane and epoxy/polyamlde adhesives, respectively. Adhesive E was a conventional two-part epoxy/amldoamlne adhesive. Adhesive F was a vinyl plastlsol adhesive. The adhesive primers used in this study were a urethane crosslinked epoxy electrocoat primer and spray primers based on tall oil modified epoxy ester, and polyesterpolyol/isocyan-ate chemistry. Dicyandlamlde was obtained from Aldrich Chemical Company. Epon 828 was obtained from Shell Chemical Company. 

DMTA is a very interesting tool for characterizing heterogeneous materials in which domains of distinct Tg values coexist. The most interesting cases involve modified thermosets of different types (see Chapter 8). Examples are the use of rubbers (e.g., liquid polybutadiene and random copolymers), or thermoplastics (e.g., polyethersulphone or polyetherimide in epoxy matrices or poly(vinyl acetate) in unsaturated polyesters), as impact modifier (epoxies), or low-profile additives (polyesters). The modifier-rich phase may be characterized by the presence of a new a peak (Fig. 11.10). But on occasions there may be superposition of peaks and the presence of the modifier cannot be easily detected by these techniques. If part of the added polymer is soluble in the thermoset matrix, its eventual plasticizing effect can be determined from the corresponding matrix Tg depletion, and the... 

Many different adhesives have been tested and used in weldbonding. These include both high-strength structural adhesives, such as modified epoxies, and relatively low-strength adhesives, such as vinyl plastisols or epoxy-polysulfides that are commonly used for sealing and vibration damping. Table 14.10 shows that a variety of adhesives and substrates are compatible with the weldbonding process. 

Weldbonded aluminum joints (1-mm aluminum alloy 2036-T4) where compared with spot welded aluminum (1-mm aluminum alloy 2036-T4) and spot welded steel (1-mm steel 1010) joints.45,46 Weldbonded 2036-T4 joints made with a vinyl plastisol adhesive and with a one-part modified epoxy had a fatigue strength about twice that of the spot welded aluminum alloy and approximately the same as that of the spot welded steel. The fatigue strength of the weldbonded aluminum joints with polysufide-epoxy adhesive or with high-peel-strength epoxy adhesive is higher than that of steel spot welds alone. 

C cured film (nitrile-phenolic, vinyl-phenolic, novolac-epoxy) 120°C cured film (modified epoxy, nitrile-epoxy, nylon-epoxy)... 

Vinyl-phenolic Nitrile-phenolic Vinyl-phenolic Neoprene-phenolic Nylon-phenolic Modified epoxy Nitrile-phenolic Epoxy... 

All of the commercial epoxy adhesives presented in App. B bond well to aluminum and to a wide variety of other materials. Sell22 has ranked a number of aluminum adhesives in order of decreasing durability as follows nitrile-phenolics, high-temperature epoxies, elevated-temperature curing epoxies, elevated-temperature curing rubber-modified epoxies, vinyl epoxies, two-part room temperature curing epoxy paste with amine cure, and two-part urethanes. 

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. 

Resinous modifiers. Epoxy resins have the ability to interact with other resins to form heteropolymers. These are also known as plastic alloys. Improved properties can be achieved with modified systems which are otherwise not possible with a single resin for example epoxies can form plastic alloys with poly(vinyl formal) to improve the impact resistance and peel strength of adhesive formulations. 

Polysulfone A number of adhesives have been found useful for joining polysufone to itself or to other materials. These include 3M Company s EC 880 solvent-base adhesive, EC 2216 room-temperaturecuring epoxy two-part paste, Bloomingdale Division, American Cyana-mid Company BR-92 modified epoxy with DICY curing agent, or curing agent "Z" (both spreadable pastes), vinyl-phenolics, epoxy-nylons, epoxies, polyimide, rubber-based adhesives, styrene polyesters, resorcinol-formaldehyde, polyurethanes, and cyanoacrylates. The EC 880, EC 2216, and the two BR-92 adhesives are recommended by the polysulfone manufacturer. Union Carbide (16) (17). 

RTM is compatible with a variety of thermosetting polymers including polyester, vinyl ester, epoxy, phenolic, modified acrylic, and hybrid polyester-urethane. A convenient typical viscosity of thermoset precursors is in the range of 0.2-0.6 Pa s. The RTM process has the following advantages (i) emissions are lower than in open-mold processes such as spray-up or hand lay-up (ii) it can produce parts faster, as much as 5-20 times faster than open-mold techniques (iii) the mold surface can produce a high quality finish (iv) complex mold shapes can be achieved and... 

Adhesives recommended include modified epoxies, modified phenoUcs, epoxy-phenolics, neoprene-phenolics, second-generation acrylics, cyanoacrylates, silicone rubbers, and vinyl plastisols. Sell has ranked a number of adhesives in the order of decreasing durability with aluminum adherends as follows ... 

Adhesives used to bond acetal homopolymer to itself and to other materials, such as aluminum, steel, natural rubber, neoprene rubber, and Buna rubber, include polyester with isocyanate curing agent, rubber-based adhesives, phenolics, epoxies, modified epoxies, and vinyls. Solvent cementing... 

Cotter has reported the results of weathering conducted at three sites over a period of six years. All adhesives performed best at the desert site, although the epoxy/polyamide bonds were considered the least durable. At the hot, wet tropical site, the epoxy/polyamide bonds lost most of their strength after two years, in sharp contrast to the excellent strength retention of specimens bonded with novolac-epoxy, nitrile-phenolic, and vinyl-phenolic adhesives. It was also found that the combination of environmental exposure and stress was particularly harmful, the effects being more pronounced with certain adhesives. Thus stressed epoxy/polyamide bonds all failed after two years tropical exposure and stressed vinyl-phenolic bonds under the same conditions lost strength rapidly after two years and all specimens had failed after six years. The novolac-epoxy and nitrile-phenolic were less effected by stress, as were an epoxy-phenolic and a modified epoxy. 

Data from U.S. International Trade Commission, Synthetic Organic Chemicals. Data include modified and unmodified epoxy resins. Modified epoxy resins include solid epoxy resin (SER), vinyl ester resins, epoxy acrylates, etc. There appear to be some discrepancies in epoxy resin production and market data as reported by different publications and organizations (7). This is primarily due to the fact that some epoxy resins such as liquid DGEBA resins and epoxy novolacs are used as raw materials to produce modified or advanced epoxy resins, which may be further converted to end-use products. Some pubhcations report only unmodified epoxies. 

Elastomer-modified epoxy resins are used in composites and structural adhesives, coatings, and electronic applications. Similar approach to toughen epoxy vinyl esters using other elastomeric materials has been reported (204). Other elastomer-modified epoxies include epoxy-terminated urethane prepolymers, epoxy-terminated polysulfide, epoxy-acrylated urethane, and epoxidized polybutadiene. Preformed dispersions of epoxy-insoluble elastomers have been developed and reported to achieve toughening without Tg reduction (205,206). 

An elastomer modified epoxy vinyl ester that expands the serviceability of thermoset resins in traditional FRP applications. 

REDUX 775RN a vinyl phenolic film adhesive (hot-cured, 30 min/150 C) from Ciba-Geigy. BSL 312 a modified epoxy film adhesive (hot-cured, 30 min/120 C) from Ciba-Geigy. tt The subscript a is used to indicate a property of the adhesive. 

Chem. Descrip. Polyhydtoxy carboxylic add amides with 20% It. aromatic naphtha, 19% xylene, 5% isobutanol, 5% ethylbenzene Uses Rheology control agent for fumed silica-modified thermoset resin systems, e.g., unsat. polyesters, vinyl esters, epoxy resins wetting agent and dispersant for fumed silica stabilizes thixotropic behavior Features Reduces or prevents separation... 

Epoxy-phenolic Epoxy-polyamide Vinyl-phenolic Modified epoxy paste... 

Heat resistance is an important characteristic of the bond. The strength of typical abrasive stmctures is tested at RT and at 300°C. Flexural strengths are between 24.1 and 34.4 MPa (3500—5000 psi). An unmodified phenoHc resin bond loses about one-third of its room temperature strength at 298°C. Novolak phenoHc resins are used almost exclusively because these offer heat resistance and because the moisture given off during the cure of resole resins results in undesirable porosity. Some novolaks modified with epoxy or poly(vinyl butyral) resin are used for softer grinding action. 

Bisphenol A diglycidyl ether [1675-54-3] reacts readily with methacrylic acid [71-49-4] in the presence of benzyl dimethyl amine catalyst to produce bisphenol epoxy dimethacrylate resins known commercially as vinyl esters. The resins display beneficial tensile properties that provide enhanced stmctural performance, especially in filament-wound glass-reinforced composites. The resins can be modified extensively to alter properties by extending the diepoxide with bisphenol A, phenol novolak, or carboxyl-terrninated mbbers. 

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