Types of glue are divided into two categories in terms of hardening. The first category is the category that is hardened by chemical reaction and the second category is the category that is hardened without chemical reaction.
Adhesives that harden by chemical reaction
- Epoxy adhesives
Epoxies are the best known construction glue and are the most widely used. The most commonly used epoxy resin is usually called diglyceryl etherase bisphenol A (DGEBA) and is made by reacting the sodium salt of bisphenol A with epichlorohydrin. Aromatic and aliphatic amines are used as hardening agents. These glue adhere well to wood, metals, glass, concrete, ceramics and hard plastics and are resistant to oils, water, dilute acids, bases and most solvents; Therefore, they are more useful in gluing vinyl flooring in services and wet places and to metal surfaces.
- Phenolic adhesives for metals
When phenol reacts with an excess amount of formaldehyde under alkaline conditions in aqueous solution, the product known as resole and oligomeric containing phenols stabilized by heterochromylene on benzene rings is obtained. To prevent the formation of vapor-filled voids, phenolic adhesive joints under pressure are usually hardened between heated steel plates by a hydraulic press. Due to the brittleness of phenolics, polymers such as polyvinyl formal, polyvinyl butyral, epoxides and nitrile rubber are added to make them harder.
- Formaldehyde compression adhesives for wood
Some of the adhesives used for wood are the result of condensation of formaldehyde with phenol and resocinol (1.3 dihydroxybenzene). The rest are condensed with urea or melamine.
- Acrylic adhesives
Structural adhesives containing acrylic monomers harden by free radical addition at ambient temperature. The main monomer is methyl methacrylate (MMA), but others such as methacrylate acid to improve adhesion to metals by forming carboxylate salts and improving heat resistance and ethylene glycol dimethyl acrylate for crosslinking may also be used.
Polyethylene chlorosulfonate is a rubber hardening agent, and cumene hydroperoxide and N,N dimethylaniline are components of a redox initiator. The binders used for strong artificial connections to human bones and porcelain veneers for teeth are also MMA-based and are generally used to bond metals, ceramics, most plastics, and rubbers, creating high-strength connections.
- Anaerobic adhesives
Anaerobic adhesives harden in the absence of oxygen, which is a polymerization inhibitor. These adhesives are often based on dimethacrylates of polyethylene glycol. The application of these adhesives is often at the joint of gears, reinforcing cylindrical joints and for sealing.
- Polysulfide adhesives
Polysulfides were initially used as anti-theft and an important application is the anti-theft of the edges of double mirrors. Both to hold the units together and create a barrier against moisture penetration. They are prepared by bis (2-chloroethyl formal) with sodium polysulfide and mineral fillers are used to reduce the price. Phthalates and silane coupling agents are used as softeners, and their hardening agents include manganese dioxide and chromate.
- Rubber hardening of building adhesives
Many construction adhesives have rubber polymers dissolved in them. When the glue harden, the rubber is deposited as droplets with a diameter of about 1 µm. The rubbers used in this method include polyvinyl formal (pvf) and polyvinyl euthyral (PVB), both of which are made by reacting the appropriate aldehyde with polyvinyl alcohol.
One-component silicone adhesives are often known as room temperature vulcanizing (RTV) adhesives and consist of polydimethylsiloxane (PDMS) with molecular masses in the range of 300-1600 with acetate, ketoxime, or ether end groups. These groups are hydrolyzed by atmospheric moisture, forming hydroxyl groups, which are later condensed by removing water.
Silicone adhesives are soft and desirable and have good environmental and chemical resistance. These adhesives are known as the best coating for use in the bathroom.
Adhesives that harden without chemical reaction
These adhesives include the following three types
Adhesives that harden due to solvent removal
- Contact adhesives:
Contact adhesives are probably the most popular solvent-based adhesives. These are solutions of polymer in an organic solvent that are applied to two surfaces to bond. The main material of these adhesives is polychloroprene rubber (polychloroprene, polychlorobutadiene) and they are used for gluing decorative covers and other strong plastics such as ABS, DVC to wood and metal products, and DIY contact glue for shoe beds.
- Ointment adhesives:
Popular solvent-based glue sold to the public in ointment-like containers are often solutions of nitrile rubber (hemipolymer or butadiene and acrylonitrile) in organic solvents.
Adhesives that harden by losing water
- Aqueous solutions and pastes:
Starch, corn and grains are the main sources for glue use. The main uses are for gluing paper, cardboard and textiles. Its applications include corrugated sheets, paper envelopes, tube punctures, wallpaper gluing and water-rewettable adhesives. Water-wettable adhesives include poly(vinyl alcohol) (DVOH), which are used in postage stamps and are made from the latex of natural gums (e.g., gum and dextrin) and polyvinyl acetate (DVN) with a large amount of stabilizer DVOH. DVOH is the only known polymer that is not made from its own monomer.
- Aqueous emulsions:
The compositional components for emulsion polymerization are: water, monomers, stabilizers and initiator. The product of emulsion polymerization is a leachate of polymer particles with absorbed stabilizers. The most famous example is DIY wood glue, which contains the polymer polyvinyl acetate (DVA) and is widely used in workshop work and in the gluing of arch and tongue joints for doors, windows and furniture in factories, and another example is in emulsion paints. They are based on DVA, which is used to cover the surface or as an glue .
Adhesives that harden by cooling
- Hot melt adhesives:
It is also known as thermal glue, which is a type of thermoplastic glue. Thermoplastic or thermal or heating plastic is a plastic material and a polymer that melts and becomes flexible at a certain temperature and hardens after cooling. The raw material of hot melt adhesives that come out of the molding tool is usually ethylene vinyl acetate (EVA). The application of these glue includes the use in crafts, cardboard boxes, book pages, thermal connections and chipboard. Thermoplastic glue was invented around 1940 by Procter & Gamble. At that time, the glue used for packaging were designed based on water and lost their adhesion due to humidity; Therefore, thermal glue were used as a solution for this issue. Other hot melt glue include polyamide, polyurethane, aliphatic esters, and polyester.
- Pressure sensitive adhesives
Pressure-sensitive glue remain permanently tacky and are popular for use in adhesive tapes and labels. These glue are mainly based on natural rubber, batch and random hemipolymer, styrene-butadiene and acrylic. Softened PVC and polyethylene are common tape materials. One side of the tape is covered with a lining or underlayer. Because of this, the adhesive remains permanently sticky and the other side has a release coating that separates with the adhesive when the tape is opened. The release agent most often used is a hemipolymer of vinyl alcohol and vinyl octadecyl carbamate, which is made by reacting DVOH with octadecyl isocyanate.