Cross-linking resin adhesion

Elastomeric Modified Adhesives. The major characteristic of the resins discussed above is that after cure, or after polymerization, they are extremely brittie. Thus, the utility of unmodified common resins as stmctural adhesives would be very limited. Eor highly cross-linked resin systems to be usehil stmctural adhesives, they have to be modified to ensure fracture resistance. Modification can be effected by the addition of an elastomer which is soluble within the cross-linked resin. Modification of a cross-linked resin in this fashion generally decreases the glass-transition temperature but increases the resin dexibiUty, and thus increases the fracture resistance of the cured adhesive. Recendy, stmctural adhesives have been modified by elastomers which are soluble within the uncured stmctural adhesive, but then phase separate during the cure to form a two-phase system. The matrix properties are mosdy retained the glass-transition temperature is only moderately affected by the presence of the elastomer, yet the fracture resistance is substantially improved. 

Whilst the properties of the cross-linked resins depend very greatly on the curing system used and on the type of resin, the most characteristic properties of commercial materials are their toughness, low shrinkage on cure, high adhesion to many substrates, good alkali resistance and versatility in formulation. 

Epoxy adhesives are cross-linked resins prepared in two steps. The first step involves SN2 reaction of the disodium salt of bisphenol A with epichloro-hydrin to form a low-molecular-weight prepolymer. This prepolymer is then "cured" into a cross-linked resin by treatment with a triamine such as H2NCH2CH2NHCH2CH2NH2-... 

Thermoset materials Epoxy resins, phenolic resins, polyurethanes (highly cross-linked), anaerobic adhesives. 

Film and tape adhesives are also frequently called two-polymer or alloyed adhesives. With few exceptions, all successful film and tape adhesive are, or have been, one of the types shown in Tables 5.3 and 5.4. The adhesive types based on phenohc cross-linking resins liberate volatiles during cure, while the types based on epoxies only need sufficient pressure to maintain aligmnent and compensate for cure shrinkage. ... 

Adhesive Type Backbone Polymer Cross-Linking Resin Catalyst High-Pressure Cure... 

Epoxy resins n. Plastic or resinous materials used for strong, fast-setting adhesives, as heat resistant coatings and binders, etc. Cross-linking resins based on the reactivity of the epoxides group. One common type is the resin made from epichlorohydrin and bisphenol A. Aliphatic polyols such as glycerol may be used instead of the aromatic bisphenol A or bisphenol F. 

Wood composite products are conventionally manufactured from wood materials having various geometries (eg, fibers, particles, strands, flakes, veneers, and lumber) combined with a thermoset resin and bonded in a press (4). The press applies heat (if needed) and pressme to activate (cross-link) the adhesive resin and bond the wood material into a sohd panel, lumber, or beam having good mechanical (strength and stiffness) and physical (form, dimensional stabihty, etc) properties. 

Unsaturated polymers, prepared from butadiene or isoprene, can be epoxidized with peroxyacids. The peroxyacids used can either be preformed or prepared in situ by reacting hydrogen peroxide with lower aliphatic carboxylic acids. The epoxidized polymers can be reacted with diamines or dianhydrides to give a cross-linked resin useful for adhesive and coating applications. 

For the steel sector, two-component cross-linking polymerization adhesives of polyester, vinyl ester, or acrylate base are important. They are relatively tolerant when it comes to the mixing ratio of resin and hardener and can also be used at low temperatures. They are the most important representatives of polyaddition adhesives including 2-part epoxy and 2-part polyurethane adhesives. 

Adhesive type Backbone polymer Cross-linking resin Catalyst High-pressure cure... 

The use of hydroxyethyl (also hydroxypropyl) methacrylate as a monomer permits the introduction of reactive hydroxyl groups into the copolymers. This offers the possibility for subsequent cross-linking with an HO-reactive difunctional agent (diisocyanate, diepoxide, or melamine-formaldehyde resin). Hydroxyl groups promote adhesion to polar substrates. 

Phenol—formaldehyde (PF) was the first of the synthetic adhesives developed. By combining phenol with formaldehyde, which has exceptional cross-linking abiHties with many chemicals and materials, and a small amount of sodium hydroxide, a resin was obtained. The first resins soHdified as they cooled, and it was discovered that if it was ground to a powder with a small amount of additional formaldehyde and the appHcation of more heat, the mixture would Hquify and then convert to a permanently hard material. Upon combination of the powdered resin mixture with a filler material such as wood flour, the result then being placed in a mold and pressed under heat and pressure, a hard, durable, black plastic material was found to result. For many years these resulting products were called BakeHte, the trade name of the inventor. BakeHte products are still produced today, but this use accounts for only a small portion of the PF resins used. 

Esters. Most acryhc acid is used in the form of its methyl, ethyl, and butyl esters. Specialty monomeric esters with a hydroxyl, amino, or other functional group are used to provide adhesion, latent cross-linking capabihty, or different solubihty characteristics. The principal routes to esters are direct esterification with alcohols in the presence of a strong acid catalyst such as sulfuric acid, a soluble sulfonic acid, or sulfonic acid resins addition to alkylene oxides to give hydroxyalkyl acryhc esters and addition to the double bond of olefins in the presence of strong acid catalyst (19,20) to give ethyl or secondary alkyl acrylates. 

The physical properties of polyurethane adhesives result from a special form of phase separation which occurs in the cross-linked polyurethane stmcture. The urethane portions of polyurethanes tend to separate from the polyol portion of the resin, providing good shear strength, good low temperature flexibiUty, and high peel strength. Catalysts such as dibutyltin dilaurate [77-58-7], stannous octoate [1912-83-0], l,4-diazabicyclo[2.2.2]octane... 

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