Adhesive chemistry and development

Just as there is no such thing as the "universal screw" or the "global rivet," there is no such thing as an "all-purpose adhesive." Modern adhesives are highly specialized products of the chemical industry, suitable for a specific range of applications and meeting a specific set of requirements. The chemical industry receives challenges from all industrial sectors, such as the automotive industry, aviation, shipbuilding, rail vehicle construction, electronics, medical technology or construction, and formulates a wide variety of adhesive types and hundreds of thousands of products from the broad toolbox of polymer chemistry and the necessary additives.

The research and development work in the area of adhesive chemistry and development deals with all chemical issues arising from the application of adhesive bonding and thus supports adhesive producers and users of adhesives.

• Formulation of adhesives for special applications
• Property improvements through nanocomposites
• Adhesives made from novel raw materials
• New polymeric materials: biobased and biodegradable

Formulation of adhesives for special applications

There are always special applications for which no suitable adhesives are available on the market: on the one hand, special formulations are often necessary when effective production and high product safety are required; on the other hand, when adhesives and other reactive polymers are needed only in small quantities. In both cases, Fraunhofer IFAM is the ideal development partner. Examples from the past include adhesives for medical technology which are resistant to special sterilization methods, pre-applicable adhesives (PASA®; "Pre-Applicable Structural Adhesives") for bonding bolts or for local reinforcement of sheet steel, as well as potting compounds for electronics with adapted coefficients of thermal expansion and conductive adhesives. Work is also being done on pressure-sensitive adhesives and adhesives for medical applications.

Often, however, it is also a matter of demonstrating new principles through to the development of new raw materials to make adhesives more effective or to integrate new functions. Here, knowledge from general polymer chemistry is transferred and tested for practical applicability. These include, for example, novel catalysts that ensure rapid adhesive curing with improved storage stability, or new resin systems such as benzoxazines or semi-crystalline resins. Other examples are pressure-sensitive adhesive tapes with which metal surfaces can be locally pickled or anodized, or pressure-sensitive adhesives that can be cured to form a structural adhesive.

Property improvements through nanocomposites

In adhesive bonds, adhesion is often greater than cohesion, i. e. the inherent strength of the material. The question arises as to how this can be exploited in material development. The answer to this is the use of nanoparticles, through which a large surface area is introduced into the polymer. Here, the surface modification of the particles is at least as decisive for the resulting properties as the correct processing technique.

The modified particles are used for the formulation of adhesives, coatings, matrix resins for composites or potting compounds. The particles can be used to achieve property improvements such as simultaneous improvement of strength and elongation at break, low curing shrinkage, and coefficient of thermal expansion (CTE). In addition, the rheological properties and fire behavior can be adjusted with their help.

Adhesives made from novel raw materials

When developing new adhesives or coating materials, we first check whether the given requirement profile can be met with commercially available components. If this is not the case, we develop new raw materials for specific applications. These include, for example, new polymers for toughening, fire protection additives or functionalized fillers. Our cooperation with raw material manufacturers often involves the development of sample formulations based on new raw materials.

In the development of new additives – such as catalysts for accelerated curing, functionalized colorants or indicators for controlling the curing state – the adhesive properties can be significantly improved even with small quantities. This enables our customers to differentiate themselves from competitive products.

Already during the selection of the active ingredients to be prepared and the synthesis routes, care is taken to ensure that subsequent implementation in industrial production is possible. These considerations take into account both the anticipated quantity of raw material required and the complexity of production, as well as an initial toxicological assessment.

New polymeric materials: biobased and biodegradable

Companies are feeling pressure from consumers and policymakers to make their products and semi-finished products sustainable. The first step towards a better life cycle assessment is often to replace existing plastics with new polymers that are biobased and/or biodegradable. Fraunhofer IFAM often takes the approach of developing new plastics within the framework of polymer systems already used by companies. This offers the advantages that known material properties can be retained and processing procedures do not have to be changed.