Thermoset adhesives applications

Adhesive applications, thermosetting epoxy resin based on N-cyanourea-terminated oligomer, 107... 

Thermosetting adhesives are, in general, two-component systems, and may be cured either at ambient or at elevated temperatures. After the components have been mixed, the glue has a limited time of application. Phenol formaldehyde, polyester resins and epoxies are being used the latter show a very strong adhesion to practically all materials. 

Thermosetting adhesives, exhibiting no melting point, consist of highly crosslinked networks of macromolecules. Because of this dense crosslinked structure, they show relatively little creep at elevated temperatures and exhibit relatively little loss of mechanical function when exposed to either elevated temperatures or other degrading environments. Many of these materials are suitable for moderately high-temperature applications. 

Lignin was obtained from an industrial soda bagasse spent liquor as before (5). The lignin was initially evaluated as a thermosetting adhesive by the beech strip test. Prior to its application as adhesive, the lignin was reacted with formaldehyde in alkali at temperatures below 60 °C to afford a hydroxymethylated lignin (fi). The hydroxymethylation reaction was done at pH 12 and 13, and samples of the reaction mixtures were evaluated on beech strips with overlaps of 25 x 25 mm, cured for 4 hours at 90 °C and 12% equilibrium moisture content. 

The phenoloxidase-lignin adhesive is not only applicable as thermosetting adhesive but also as a cold-curing system. 

Many commercial thermosets are quite often used as complex mixtures of several co-reacting monomers and prepolymers, specifically formulated to suit a given end-use application. For example, in coating and adhesive applications, often mixtures of different epoxies, differing in chemical structure and/or molecular weights, are used as required. Even two different thermoset-... 

Layer void impregnation, application of discrete isolated sections of consolidant where laminants have lost adhesion. Lac-querware surfaces separated from their ground or dissociated laminates can often be stabilized with this method. Judicious use of molten waxes or thermosetting adhesives is generally successful because of their unique physical and mechanical properties. 

For glued components for non-structural applications, the same tendency can be seen and one must consider EN 204 (2002) [15] for thermoplastic adhesives and EN 12765 (2002) [16] for thermosetting adhesives. 

These are materials that cannot be heated and melted after the initial cure. Curing takes place by chemical reactions at room temperature or at an elevated temperature, depending on the type of adhesive. Some thermosetting adhesives require considerable pressure, while others require only contact pressure. Solvents are sometimes added to facilitate application. These adhesives are usually available as solvent-free liquids, pastes, and solids. 

Materials bonded include metals, ceramics, glass, and thermosetting plastics. Applications are primarily for high strengths and high temperatures. Examples of alloy adhesives are shown in Table 4.4. 

Factors most likely to influence adhesive selection are listed in Table 7.13. However, thermosetting adhesives such as epoxies, polyurethanes, or acrylics are commonly used for structural application. The adhesive formulations are generally tough, flexible compounds that can cure at room temperature. The reasons that these adhesives have gained most popularity in bonding of plastics are summarized in this section. 

Silver-coated solid and hollow spheres find wide acceptance in applications in which EMI/RFI and ESD control is required. Silver-coated spheres can provide high compressive strength and excellent processing durability for applications requiring conductive thermoplastics. Other uses include conductive thermosets, adhesives, coatings, caulks, and composites. 

Contact adhesives have relatively high shear and peel strengths. Strength and durability approach those of structural thermosetting adhesives. A typical contact adhesive application is the bonding of decorative surface materials to wood for kitchen countertops. Parts must be correctly positioned before bonding because repositioning is difficult or impossible after the bond is made. 

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