Adhesive: what it is, types, production and applications

Adhesive is the family of chemical products that bonds two surfaces together and carries the connection without using mechanical fasteners (screws, rivets, welding). In modern manufacturing, bonding is not just a joining method but also a design decision: it spreads the load over a wide area, allows the joining of different materials (metal–plastic, glass–composite), and adds no weight to the structure.

What is an adhesive?

Adhesive is a polymer system applied in liquid or paste form that subsequently cures and solidifies. Bonding occurs through two mechanisms working together: adhesion (the adhesive's attachment to the surface) and cohesion (the adhesive's own internal strength). In a good bond, failure occurs in the material itself rather than in the adhesive layer.

In the industry, "adhesive" and "sealant" are often mentioned together, but their functions differ: adhesive carries load, while sealant fills gaps and provides sealing. Since both products can be manufactured from the same chemical family (polyurethane, silicone, MS polymer), manufacturers usually run both lines together.

How is it produced?

Production is largely a matter of formulation rather than reaction. A base polymer (polyurethane prepolymer, epoxy resin, acrylic dispersion, cyanoacrylate monomer) is taken, and filler, rheological additive, adhesion promoter (silane), plasticizer, curing catalyst and stabilizer are added. The mixture is homogenized under vacuum in high-viscosity mixers — keeping out moisture and air is critical, especially in moisture-curing systems.

There are three main paths depending on the curing mechanism:

• Physical drying: water or solvent evaporates and a polymer film forms (water-based wood glues, contact adhesives).
• Chemical curing: two components mix and react (epoxy, two-component polyurethane).
• Environmentally triggered curing: atmospheric moisture, UV light or an oxygen-free environment initiates the reaction (MS polymer, UV adhesives, anaerobic thread lockers).

Types and varieties

Which sectors use it?

Adhesive is one of the most horizontal product groups in the chemical industry; it has an application in almost every manufacturing branch.

• Automotive: structural bonding, weight reduction and joining of different metals. Battery pack assembly and thermal management tapes in electric vehicles are a fast-growing area.
• Construction and construction chemicals: panel bonding, joint filling, façade systems.
• Packaging: corrugated cardboard, labels, lamination — speed and food-contact compliance are decisive.
• Furniture and wood: edge banding, laminated panel production.
• Footwear, textiles and leather: sole bonding, laminated fabric.
• Electronics: encapsulation, thermally conductive bonding, display assembly.

Turkish market and production

In Türkiye, adhesive and sealant production is an area shaped by demand from the construction and furniture sectors, with numerous domestic formulators active in the field. While a significant portion of base polymers (isocyanate, epoxy resin, acrylic monomer) is imported, formulation, filling and technical service are largely carried out domestically. This structure directly reflects exchange rate volatility onto product costs.

Three topics stand out on the sector's agenda: the shift from solvent-based systems to water-based and solvent-free systems (VOC regulations and occupational health), isocyanate-free chemistries (the growing share of MS polymer and hybrid systems), and debondable adhesion (the ability to separate products at end-of-life, required for recycling). You can follow current developments on these topics in the news feed below.

Technical specifications

When selecting an adhesive, the following headings are the first to be checked on the datasheet. Since values vary widely depending on the product family, the table below should be read as a comparison framework rather than as absolute limits.

All these values are measured on a standard test surface. In actual application, surface energy, cleanliness and joint geometry alter the result significantly; therefore, sample testing does not replace the datasheet but complements it.

Points to consider in selection and procurement

• State the surface pair from the outset. "I will be bonding metal" is not enough — which alloy, whether the surface is oily, whether there is a coating; the supplier's recommendation depends on these factors.
• Define the service condition. Continuous temperature, vibration, chemical contact and UV exposure; if these are not specified, a joint that passes in the laboratory may fail in the field within a year.
• Factor in line speed. If the open time is shorter than the production tempo, the product cannot be used on the floor — no matter how good its strength value is.
• Test the sample on your own part. The standard test coupon is only for comparison purposes.
• Put storage conditions and shelf life in the contract. For moisture-curing products, the gap between delivery date and production date directly affects performance.

Frequently asked questions

What is the difference between an adhesive and a sealant?

Adhesive is designed to carry load; it provides the mechanical strength of the joint. Sealant, on the other hand, is used to fill gaps and provide sealing; it is expected to tolerate movement but is not expected to carry structural load. Both products can be manufactured from the same chemical family.

In which cases is a structural adhesive preferred?

It is preferred when the load needs to be spread over a wide area, when different materials are being joined (such as metal–composite), when drilling/welding would compromise the integrity of the structure, and when weight is critical. Unlike point fasteners, it does not create stress concentration.

Is water-based adhesive as strong as solvent-based adhesive?

In many applications, yes. Water-based systems have longer drying times and are limited on non-porous surfaces; however, they offer a clear advantage in terms of VOC emissions, fire risk and occupational health. On lines where application speed is critical, hot-melt systems offer an alternative.

Why is surface preparation before bonding so important?

Adhesion occurs at the molecular layer where the adhesive contacts the surface. Oil, dust, an oxide layer or mold-release residue blocks this contact, and the joint fails well below the adhesive's own strength. Pretreatments such as cleaning, sanding, flame treatment or plasma treatment are therefore considered part of the formulation.

How is an adhesive's shelf life preserved?

Moisture-curing systems (PU, MS polymer, cyanoacrylate) react with atmospheric moisture once the package is opened; the cap must be sealed tightly and the product stored in a cool, dry environment. In two-component systems, the components have separate shelf lives, and once mixed, the "pot life" is limited.