Types of Adhesives and Caustic Soda Role in their Production
Adhesives are a group of substances that allow you to bind together different materials, making them impossible to separate. They belong to the group of materials which modify the glued surface, the most important feature of which is to increase adhesion. Depending on the material we want to bind, we can use a wide range of adhesives, which can be divided into different categories. For the production of glue, various additives can be used to improve its adhesive properties, accelerate curing, or reduce viscosity.
Adhesive substances are usually in liquid form. However, you can also find a solid form, e.g. powder, pearls, sticks, or cartridges, forming a weld after melting. Its strength depends on several factors: cohesion, adhesion, shape, and thickness of the adhesive layer, as well as on the so-called depth of penetration of the material by an adhesive substance.
The most important is the adhesion and cohesion that affect the type and strength of the chemical interaction of the adhesive with the bonded surfaces.
Adequate selection of glue for the type and size of materials that are to be bonded makes it easy to glue. The most significant advantages of using adhesive substances in comparison to other material joining techniques include the ability to efficiently distribute stresses throughout the joint. Other benefits include improved joint aesthetics and low mechanization costs for such a process.
Adhesives – classification, raw materials, and production
Adhesives can be categorized according to the type of material joining method. The basic criterion is whether a given compound chemically reacts with the materials and causes the entire weld to harden Another criterion is the type of raw material used. In this case, we deal with glues of natural origin (e.g. plant and animal glues that are used, among others, in the paper and textile industries) or synthetic ones, which have the largest spectrum of applications. We can distinguish many types of synthetic adhesives, such as, for example, cyanoacrylates (colloquially known as “Superglue”), acrylic adhesives, polyurethane, amine, epoxy, silicone, and many others.
Cyanoacrylate adhesives have existed in the industrial market since the 1990s. Their wide application is due to ease of application, rapid hardening at room temperature, heat resistance. The production of this adhesive, although is simple in theory, in practice causes some difficulties. Raw materials, i.e. alkyl cyanoacrylate and formaldehyde, are condensed in the presence of an alkaline catalyst. The obtained polymer is then thoroughly dried and thus deprived of the solvent. The main difficulty in this process is the tendency of the monomer to spontaneously polymerize, which affects the drying and further processing of the polymer.
The basic raw materials for the production of acrylic adhesives are acrylic and methacrylic acids. Other compounds, such as methyl methacrylate, are usually used only as auxiliary monomers. Thanks to the appropriate selection of polymers and monomers as well as the conditions of the polymerization process, a huge palette of acrylic compounds with adhesive properties can be obtained. Acrylic adhesives usually contain a special activator in their composition, which initiates the curing process.
In this group, we can find one-component and two-component adhesives. The former contains prepolymers in their composition and cure under the influence of water or moisture from the air. In order to obtain proper adhesion, binding materials with one-component adhesives are usually carried out in special presses. often at an elevated temperature accelerating the curing time. In contrast, two-component adhesives contain two components and are ready for use after mixing them in appropriate proportions.
Polyurethane adhesives are characterized by excellent adhesion to smooth and porous surfaces, so they effectively bind various materials, such as wood, paper, and cardboard. They can also be used in the construction industry for bonding concrete or sheet metal. Welds made with the use of polyurethane adhesives are characterized by excellent durability.
Caustic Soda Role in their Production
Silicone adhesives are an irreplaceable material used in construction, mainly for the purpose of aesthetic finishing of rooms. They are characterized by excellent flexibility and adhesion to many types of substrates. They prevent material consumption by distributing loads evenly, and reduce production costs, replacing traditionally used mechanical joints, such as screws. Silicone adhesives are extremely versatile. They allow you to bind together a variety of materials, such as metals with plastics or glass. Silicone adhesives are mainly organosilicon compounds produced from sand with gel consistency. One of the main components of high-quality silicone adhesives is water glass, which is formed in the reaction of silica with sodium hydroxide. Silicones, due to their properties, have effectively replaced window putty and various woodwork seals.
Epoxy adhesives, due to their strength and excellent adhesion to many surfaces, belong to the group of universal adhesive products with numerous applications. One of the main components of these adhesives is nonylphenol. It is a mixture of isomers containing mainly p-nonylphenol. Nonylphenol plays the role of an intermediate in many production processes.