Chemical reacting adhesives

In this case, the liquid adhesive applied to the adherends consists of the monomer molecules ready for a chemical reaction (Sections 2.1.2 and 2.1.3). Due to their small size they are mostly liquid. After the application of the adhesive and the joining of the adherends to be bonded, a chemical reaction occurs in the glueline. From the (liquid) monomers the solid ( hard ) adhesive layer develops. This time-dependent process is called curing or setting. Since it is triggered by a chemical reaction, one talks of chemically reacting adhesives or of reactive adhesives. 

Two-component adhesives Chemically reacting adhesives with a second component (hardener) to be admixed to another component (usually the resin component). 

Butadiene or isoprene based block copolymers Chemical reacting adhesives... 

Plasma films are usually highly cross-linked, resistant to higher temperatures, resistant to abrasion and chemical attack, and are highly adherent to the surface. Adhesion to the surface is generally high both because the growing polymer complex can fit the surface contour and thus lock-itself in (physical adhesion), and because in many instances, the species are active enough to chemically react with the surface molecules to chemically bond to the surface. The surface can be prepared so that the chemical reaction is enhanced. 

Effect on the Bulk Property of the Adhesive. Moisture can alter the properties of the bulk material by changing its glass transition temperature, inducing cracks, or chemically reacting with the polymer—a process called hydrolysis. But before these mechanisms occur, the moisture must first find its way into the bulk polymer. 

Hot melts have to be applied hot (above meiting temperature) to wet the surface of the substrate. Then on cooling, the moiten polymer returns to its soiid form, providing good cohesive strength to the bond. They set very quickiy after they are applied, do not chemically react with the substrate, and do not generate solvent emissions. The primary disadvantage of hot melt adhesives is poor performance at elevated temperatures. 

The water present can chemically react with components of the adhesives. Thus, adhesives containing large quantities of isocyanate groups cannot be used for cementing under water if their time and area of contact with water will be considerable because the carbon dioxide released forms pores and pits in the adhesive (Equation 5.1). 

Silicone and butadiene/acrylonitrile elastomers have been successfully incorporated into an addition polyimide adhesive LARC-13. Two approaches were used to accomplish this task. Fluorosilicone (Silastic) and vinyl-terminated (Sylgard) silicone rubbers were physically blended into the adhesive amic acid and aromatic ATBN and aromatic amine-terminated silicone elastomers were chemically reacted into the prepolymer backbone. Each of the four resins displayed a distinct and separate Tg for the resin and elastomer phases. Incorporation of elastomer particles at a concentration of 15% by weight solids resulted in a 6- to 7-fold increase in peel strength and a 3- to 5-fold increase in the fracture toughness of LARC-13. This improvement in toughness was accomplished at a sacrifice in the elevated temperature adhesive strength of the material. 

Reactive— liquid components chemically react with each other to form a solid (two-component epoxy adhesives, cyanoacrylates or super glues react with water, some adhesives react on exposure to light or radiation)... 

To convert this essentially fiquid/semi-solid epoxy into an infusible solid, the adhesive will also contain a hardener (curing agent), which, under the correct conditions, will chemically react with the epoxy to produce a cross-linked, infusible polymer. 

Base polymers are classified as being either thermoplastic or thermosetting. Thermoplastic polymers are polymers that melt when heated and then resolidify when cooled. Thermoset polymers are those that do not melt when heated, but at sufficiently high temperatures they exhibit creep under load and even decompose. Polymers gain their thermosetting nature by a process called cross-linking, where the adhesive molecules chemically react with one another to form a three-dimensional network. The... 

Primers can also chemically react with the adhesive and adherend to provide greater joint strengths. This type of primer is referred to as an adhesion promoter. The use of reactive silane to improve the adhesion of resin to glass fibers in polymeric laminates is well known in the plastic industry. 

Chemical reaction theories propose that chemical reactions occur between the adhesive and the adherent forming primary chemical bonds. While it is unlikely that these theories are universally applicable to adhesives, chemical reactions may be present in some cases. Silanes, for example, are bifunctional molecules that are used as coupling agents [6]. One end of the molecule is intended to interact with a polymeric adhesive. The other end is intended to chemically react with atoms in the adherend s surface layer, such as oxygen in an oxide layer of a metal or the oxygen in a ceramic. 

Adhesives can be separated into two general classes thermoplastics and thermosets. Thermoplastics can be formulated with halogen-containing and non-halogen-containing additives. Thermosets are commonly treated by adding flame retardants that chemically react with a resin precursor. O Table 13.12 lists flame retardants that are typically used. 

Glue layer (adhesion) An intermediate layer between the film and the substrate used to increase adhesion. Also called a bond coat or tie layer. Example The titanium layer in a titanium-gold metallization on an oxide. The titanium chemically reacts with the oxide and alloys with the gold. 

It reacts chemically as if it were either 1,3,5-trihydroxybenzene or the triketone of hexa-hydrobenzene. The trialkyl derivative of the hydroxy-form or the trioxime of the keto-form can be obtained from phloroglucinol by reacting in a suitable manner. In certain cases derivatives of the two forms are interchangeable. Used in printing, photography, adhesives, pharmaceuticals. 

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