Raw materials for adhesive production

What is an adhesive?

Adhesive is essentially a multi-component system in which different substances form a coherent polymer structure with specific adhesive and cohesive properties. The composition of such a formulation may vary depending on the type of adhesive, its application and working conditions, but it is always based on three groups of components:

• base raw materials – polymers, polyols, resins or dispersions,
• functional additives – stabilisers, surfactants, plasticisers, catalysts,
• solvents or water – determining viscosity and method of application.

From a chemical point of view, the aim is to achieve the right balance between adhesion (adhesion to the substrate) and cohesion (internal cohesion of the adhesive layer). It is the molecular structure of the raw materials – the length of the polymer chain, the type of functional groups or the degree of cross-linking – that determines the durability of the bond.

Polymers and polyols – the basis of adhesive formulations

The most important component of most adhesives are polymers – substances with a high molecular weight that form adhesive bonds with the surfaces of the materials being joined. Depending on the type of adhesive, these can be:

• polyether and polyester polyols, used in polyurethane systems,
• acrylic and styrene copolymers, used in dispersion adhesives,
• epoxy resins, which provide high mechanical and chemical resistance,
• vinyl copolymers, widely used in wood and paper adhesives.

Polyols and polyurethane (PU) adhesives

Polyols, i.e. compounds containing numerous hydroxyl groups (-OH), form the basis of polyurethane adhesive systems. When reacted with isocyanates, they form urethane bonds, which are responsible for high adhesion and resistance to moisture and temperature.
PU adhesives are very versatile and are used in, among others, furniture manufacturing, construction, automotive and footwear industries. They come in single- and two-component forms, and their formulation allows for both flexible and rigid bonds.

In chemical terms, the balance between the hard and soft segments of the polymer plays a key role, determining flexibility and resistance to ageing. Modern PU adhesives increasingly contain partially bio-derived polyols, e.g. from vegetable oils.

Dispersions and resins

Dispersion and acrylic adhesives are based on polymer dispersions, i.e. systems in which polymer particles are evenly dispersed in water. They are an environmentally friendly alternative to solvent-based systems as they do not contain volatile organic compounds (VOCs).

The most commonly used are acrylic, vinyl-acrylic and styrene-acrylic copolymers, which provide very good adhesion to porous substrates (paper, wood, fabrics). In the furniture and packaging industries, they form the basis of modern, safe adhesive formulations.

These dispersions are often modified with cross-linking agents, stabilisers and plasticisers to increase their resistance to water and heat. Chemical control of particle size, viscosity and pH is critical to the application properties and durability of the adhesive.

Epoxy adhesives

Epoxy adhesives are based on the reaction of epoxy resin with a hardener, e.g. amine or anhydrite. The resulting polymer network is characterised by very high mechanical strength, chemical and thermal resistance.

This makes epoxy adhesives suitable for use in construction technologies – they bond metals, glass, ceramics and composites. They are indispensable in the electronics and aerospace industries, where stability over a wide temperature range is required.

From a chemical point of view, the curing of epoxy resins involves the reaction of epoxy rings with amino groups, leading to the formation of a three-dimensional network of covalent bonds. This structure is responsible for their exceptional strength and rigidity.

Additives and modifiers

In addition to the base components, functional additives play an extremely important role in the production of adhesives. They allow for the control of viscosity, setting time, thermal resistance and formulation stability. This group includes, among others:

• surfactants – they facilitate the even distribution of ingredients and stabilise emulsions,
• plasticisers – give adhesives elasticity and resistance to cracking,
• catalysts – accelerate polymer cross-linking processes,
• antioxidants and UV stabilisers – protect the binder from degradation under the influence of light and oxygen,
• thickening and rheological agents – ensure the right consistency and facilitate application.

Additive chemistry is a precise balancing act – too much plasticiser can reduce strength, while too much catalyst will cause the adhesive to set too quickly. Therefore, the adhesive formulation process requires a thorough understanding of chemical reaction mechanisms and interactions between ingredients.