Bonding, adhesive types

Adhesives. Acryhc emulsion and solution polymers form the basis of a variety of adhesive types. The principal use is in pressure-sensitive adhesives, where a film of a very low T (<—20 " C) acrylic polymer or copolymer is used on the adherent side of tapes, decals, and labels. Acrylics provide a good balance of tack and bond strength with exceptional color stabiUty and resistance to aging (201,202). AcryUcs also find use in numerous types of constmction adhesive formulations and as film-to-film laminating adhesives (qv). 

NR adhesives can be divided in two types wet bonding and dry bonding. Wet bonding adhesives are applied on substrates in a fluid state, the bond being formed by drying. The dry bonding NR adhesives are pressure-sensitive adhesives because the bond is created under pressure. 

Adhesive strength is evaluated at room temperature as well as at the extreme temperatures of —65°F and 180°F. Aircraft structure can reach —65°F at cruise altitudes and 180°F on the ground in a hot, sunny location. The types of toughened epoxies commonly used for metal bond adhesives have glass transition temperatures not much greater than 200°F, so properties fall off drastically at higher temperatures. 

Adhesion promoters are used to achieve the optimum bond adhesion level. The basic unpromoted adhesion system is the RFK system. Addition of cobalt as a promoter to the resin system considerably boosts the adhesion level achieved. The type of salt used determines the cobalt level... 

When solvent welding or thermal welding is not practical or desired, adhesive systems can be used. Adhesive types such as epoxies, urethanes, thermosetting acrylics, nitrile phe-nolics, and cyanoacrylates permit ABS to be bonded to itself and to other substrates. The best adhesives have shown strength greater than that of ABS however, these adhesives provide very rigid bonds. 

Pipe and Pipe Fittings, Adhesive Bonded Joint Type, for Aviation Jet Turbine Fuel Lines... 

Since in the final state these are thermoplastic adhesives, the utilization temper-atiue of the adhesive bonds is Umited to approx. 80°C. Some adhesive types are heat-stable up to 130°C, although the adhesive strength at this temperature is greatly reduced since in this case the inherent strength of the cyanaciylate determines the stability of the plastic bond. 

Instantbond. [Hranonh g.] Cyanoacrylates, ethyl and methyl types instant bonding adhesives. 

There are two types of adhesives by which fluoropolymers bond contact adhesives and bonding adhesives. The distinction between these two adhesives is that contact adhesives can be applied without modification of the surface of the plastic, while bonding adhesives require surface modification. 

Tackifiers can be used to improve the tack properties of thermoplastic polymers, the compatibility between the polymer and substrate, wetting power, or the strength of the permanent bond. Tack is the bond strength that is formed immediately when a given material comes in contact with another surface, or instantaneous adhesion. Types of tackifiers include natural resins, phenolic resins, and polyterpenes. 

Good processing characteristics Adhesives are often used as a contact bond type— either in water- or solvent-based systems—as a hot melt, or as a pressure sensitive, in curing systems, or as heat or solvent reactivatible systems. Block copolymers provide superior pressure sensitive adhesives, but can also be compounded for contact bond adhesive or sealant applications. 

These adhesives are thermoplastic when cured and therefore have a limited temperature capability and chemical resistance. They are suitable for bonding all types of glass, most plastics and metals and are, in general, used for bonding small components. 

The degree of penetration depends on several parameters related to wood, resin and adhesive type, as well as to processing parameters [3], Additionally, a good contact of the adhesive with the lumen wall is needed in order to achieve good bonds [4]. 

MDI Prepolymers with a High Content of Isocyanate This type of adhesive was formulated on the basis of MDI-prepolymer with a relatively high concentration of isocyanate in the uncured adhesive (around 15-16%). This also means a low molecular weight (around 500-600 g/mol). This adhesive type is often used to bond wood. In standard practice, the adhesive is applied under pressure so that most of it flows out between the wood members the thickness of the adhesive layer is virtually zero. 

Phenol-formaldehyde resin is the most common adhesive for exterior applications due to its water resistance, low initial viscosity and its ability to bond various types of wood substrates [1], Because of its resemblance to phenolic moieties, studies on tannin have been oriented towards an alternative formulation to replace the current synthetic phenol-formaldehyde or phenol-resorcinol-formaldehyde adhesives [2-4], A few suitable alternative natural resources such as oil palm shell, pecan shell nut, lignin, starch, rice bran and tannin are also available for this purpose. Among these materials, tannins represent the best immediate substitute for phenol in wood adhesive production [1],... 

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