What Is a Polymer Adhesive?
Polymer adhesives are adhesives that use polymers, which are macromolecules.
They are capable of bonding a wide variety of materials, including metals, plastics, wood, glass, and ceramics. Most polymer adhesives are manufactured from man-made synthetic materials and can be given specific properties such as flexibility, heat resistance, chemical resistance, and electrical conductivity, depending on the application.
Applications of Polymer Adhesives
Polymer adhesives can be used on a wide variety of materials including metals, plastics, ceramics, glass, leather, wood, rubber, and concrete.
They are used in a wide range of industries, including industrial, construction, automotive, marine, and aerospace. Approved products can also be used in the medical field. In addition, adhesives with high electrical insulation properties are suitable for electronic components and are used in electronics, packaging, and other fields.
Principle of Polymer Adhesives
Polymer adhesives are liquid substances that adhere to the surface of an object in a liquid state and later cure to produce an effect. Curing is caused by polymerization, chemical reaction with curing agents, and evaporation of solvents.
Their action consists of both adhesive force, to stick to the base material, and cohesive force, to maintain the structure of the adhesive itself. Adhesive force is the force that sticks different molecules together, while cohesive force is the force that keeps the same type of molecules together.
The adhesive force of polymer adhesives depends on one of the following mechanisms: physical adhesion, chemical adhesion, or dispersion adhesion.
1. Physical Adhesion
Physical adhesion is a mechanism whereby the adhesive adheres mechanically by flowing into holes or adhering to protrusions on the surface of the substrate. It is a particularly effective adhesion method when there are small holes on the surface of the base material.
2. Chemical Bonding
Chemical adhesion is adhesion by chemical bonding. The strongest bonds are ionic and covalent bonds, and the next strongest are hydrogen bonds. Ionic bonding is a bond between a positively charged cation and a negatively charged anion due to electrostatic attraction, while covalent bonding is a bond formed by the sharing of some valence electrons between atoms. Hydrogen bonding is an interaction in which a hydrogen atom covalently bonded to an atom with high electronegativity forms an interaction with a nearby solitary electron pair such as nitrogen, oxygen, sulfur, fluorine, or π-electron framework.
3. Dispersion Bonding
Dispersion adhesion is an adhesive bonding by van der Waals forces (force of electrostatic attraction between two substances due to polarized positively and negatively charged areas within the substance).
Types of Polymer Adhesives
Polymer adhesives include emulsion-type adhesives in the form of a suspended water solution, solution-type adhesives in which the polymer is dissolved in a solvent, reaction-type adhesives in which curing begins when a chemical reaction occurs when exposed to light (ultraviolet light), heat, or pressure, and hot-melt adhesives, which are thermoplastic adhesives.
1. Emulsions
Emulsion-type adhesives are adhesives in which the polymer is emulsified without dissolving and is in the form of a suspension/suspended water solution. Typical substances include vinyl acetate resin emulsions and acrylic resin emulsions. Vinyl acetate emulsions are widely used adhesives for woodworking, while acrylic emulsions are more adhesive and water-resistant adhesives. Synthetic rubber emulsions are used in flooring adhesives. In particular, adhesives that are mainly made of natural or synthetic rubber are called latex adhesives.
2. Solution Type
Solution-type adhesives are made by dissolving polymers in organic solvents. There are several types such as vinyl acetate resin, chloroprene rubber, and natural rubber. Vinyl acetate resin is inexpensive, and chloroprene rubber is a typical rubber-based adhesive used for bonding metals, plastics, and wood. In general, rubber-based adhesives are suitable for bonding soft materials such as leather, rubber, and cloth.
3. Reactive Type
Reactive adhesives are adhesives that cure through a chemical reaction caused by some form of energy such as light (ultraviolet rays, etc.), heat, or pressure. Some are cured using ovens, curing furnaces, UV lamps, etc., while others cure spontaneously at room temperature. Many products become thermosetting polymers after curing.
Since some types of reactions use two or more chemical species, there are not only one-component type products, but also many two-component type products that are mixed just before use. Specific polymer types used include phenolic resins, amino resins, epoxy resins, polyurethane, and acrylic resin systems.