Adhesives reactivity

Reactive adhesives Reactive adhesives are either low molecular weight polymers or monomers that solidify by polymerization and/or cross-linking reactions after application. Cyanoacrylates, phenolics, silicon rubbers, and epoxies are examples of this type of adhesive. Plywood is formed from impregnation of thin sheets of wood with resin, with the impregnation occurring after the resin is placed between the wooden sheets. 

An ingredient added to an adhesive to reduce the concentration of base resin or binder is called a diluent. Diluents are principally used to lower the viscosity and modify the processing conditions of some adhesives. The degree of viscosity reduction caused by various diluent additions to a conventional epoxy adhesive is shown in Fig. 1.5. Diluents do not evaporate as does a solvent, but they become part of the final adhesive. Reactive diluents react with the resin base during cure, so that the final adhesive characteristics are determined by the reaction product of the binder and diluent. Nonreactive diluents do not react with the resin or curing agent and, therefore, more seriously weaken the final properties. Coal and pine tar are common nonreactive diluents. 

Microencapsulated adhesive Reactive adhesive mixture, with the (liquid) components encapsulated by a protective skin in the form of finest drops, preventing a reaction during storage. Only after the destruction of the capsule wall, for example, by screwing a nut onto a suchlike coated screw, does a chemical reaction set in and an adhesive layer develop. 

Chem. Descrip. Phenyl trimethoxy silane CAS 2996-92-1 EINECS/ELINCS 221-066-9 Uses Surf, treatment, pigment/filler treatment in primers, water repellents, paints, inks, and adhesives reactive intermediate tor silicone resin synthesis and org. resin modification adhesion promoter Properties Low-vise, liq. sp.gr. 1.05 vise. 1.7 cSt flash pt. (CC) 29 C 100% act. 

Diluents. These are generally incorporated to reduce the viseosity of the freshly mixed adhesive to offset the effect of the filler. This may be required to improve handling and spreading characteristics or to allow filler additions which tend to reduce cost. Other properties of the fresh and hardened adhesive can be affected by the use of diluents, for example pot life, flexibility and glass transition temperature. If the diluent is non-reactive, such as solvents which remain in the cured system, the net result is a deterioration of chemical and mechanical properties such as increased shrinkage and reduced adhesion. Reactive diluents containing epoxy compounds are capable of combining chemically with the resin/hardener system. 

These are liquid ingredients added to an adhesive to reduce the concentration of the binder component. Diluents are added principally to lower the viscosity and to modify the processing conditions of some adhesives. Reactive diluents do not evaporate, as would solvents. They react with the binder during the cure cycle and are incorporated in the cured adhesive. 

Thermoplastic rubber is a relatively new class of polymer. It has the solubility and thermoplasticity of polystyrene, while at ambient temperatures it has the toughness and resilience of vulcanized natural rubber or polybutadiene. These rubbers are actually block copolymers. The simplest form consists of a rubbery mid-block with two plastic end blocks (A-B-A), as shown in Figure 5.7. Examples of commercial products are Kraton and Solprene . These materials are often compounded with plasticizers to decrease hardness and modulus, eliminate drawing, enhance pressure-sensitive tack, improve low-temperature flexibility, reduce melt and solution viscosity, decrease cohesive strength or increase plasticity if desired, and substantially lower material costs. Low levels of thermoplastic rubbers are sometimes added to other rubber adhesives. These materials are used as components in the following applications PSAs, hot-melt adhesives, heat-activated-assembly adhesives, contact adhesives, reactive contact adhesives, building construction adhesives, sealants, and binders. Two common varieties of thermoplastic rubber adhesives are styrene-butadiene-styrene (S-B-S) and styrene-isoprene-styrene (S-I-S). ... 

Nitrile rubber is used preferably for contact adhesives with improved plasticizer resistance. Polyisobutylene is used in pressure-sensitive adhesives. Butyl rubber is sometimes added to pressure-sensitive and hot-melt adhesives, although it is mainly used in sealing compounds. Epoxy resins and reactive (meth)acrylate adhesives (reactive adhesives) are modified with polychloroprene, butyl, and nitrile rubber. Chlorinated rubber is added in small quantities to contact adhesives and also to rubber-to-metal bonding agents for improving the adhesion properties. 

NF T76-116 1987 Adhesives. Reactive adhesives with organic binders. Determination of conventional reactivity. 

Eliades, T., Katsavrias, E., and Eliades, G. (2002) Moisture-insensitive adhesives reactivity with water and bond strength to wet and saliva-contaminated enamel. Eur. J. Orthod., 24 (1), 35 -42. 

Exceptions include latex adhesives, reactive acrylics and one part epoxides. Freezing of latex adhesives causes the water phase to solidify and the particles to agglomerate. Freeze-thaw stability can be improved by using carboxylate comonomers and adding antifreezes such as ethane diol or glycerol. Blackley (1997) has written a full account of this topic. 

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