Chemical bond theory believes that in addition to the interaction between the adhesive and the adherend molecules, there are sometimes chemical bonds, such as the bonding interface between vulcanized rubber and copper-plated metal, the effect of coupling agent on bonding, and the bonding of isocyanate to metal and rubber. Studies such as interfaces have demonstrated the formation of chemical bonds. However, the formation of chemical bonds is not common, and it is necessary to form a chemical bond to form a certain quantum member, so that it is impossible to form a chemical bond between the contact point between the adhesive and the adherend. Moreover, the number of chemical bonds per unit adhesion interface is much less than the number of intermolecular interactions, so the adhesion strength from the interaction between molecules is not negligible.
The main agent is the main component of the adhesive, which dominates the adhesive bonding properties and is also an important indicator for distinguishing the adhesive category. The main agent is generally composed of one or two or even three kinds of high polymers, and it is required to have good adhesion and wettability. The substances that can be used as adhesives are:
1. Natural polymers, such as starch, cellulose, tannin, gum arabic and sodium alginate and other plant-based adhesives, as well as animal glues such as bone glue, fish gelatin, blood protein glue, casein and shellac.
2. Synthetic resin, divided into two major categories of thermosetting resin and thermoplastic resin. Thermosetting properties such as epoxy, phenolic, unsaturated polyester, polyurethane, silicone, polyimide, bismaleimide, allyl resin, furan resin, amino resin, alkyd resin, etc.; thermoplastic resin such as polyethylene , polypropylene, polyvinyl chloride, polystyrene, acrylic resin, nylon, polycarbonate, polyoxymethylene, thermoplastic polyester, polyphenylene ether, fluororesin, polyphenylene sulfide, polysulfone, polyketone, polyphenyl ester , liquid crystal polymer, etc., as well as modified resins or polymer alloys thereof. It is the most used type of adhesive.
3. Rubber and elastomer. The rubber mainly includes neoprene rubber, butyl nitrile ethylene propylene rubber, fluorine rubber, polyisobutylene, polysulfide rubber, natural rubber, chlorosulfonated polyethylene rubber, etc.; the elastomer is mainly thermoplastic elastomer and polyurethane elastomer.
4. In addition, there are inorganic binders such as silicates, phosphates, and phosphoric acid-copper oxide.
