Key Factors for Adhesive Selection

Key Factors for Adhesive Selection----Technical Principles and Practical Selection Criteria


The fundamental function of adhesives is to coat the surfaces of adherends and bond them together. When manufacturing bonded assemblies, the first priority is to select the suitable adhesive from various types available. Below are several key factors that influence adhesive selection.

1. I. Bonded Assemblies

The entire processing workflow for producing bonded assemblies exerts varying degrees of influence on adhesive selection. Pre-bonding processing creates specific surface conditions on the adherend surfaces, which directly determine the final bonding performance. If such surface conditions cannot be modified, an adhesive compatible with the existing surface must be chosen. Post-bonding machining processes of the finished bonded component also need to be taken into account during adhesive selection. If the bonded assembly serves as a single unit to be mated with other components, the handling properties of the selected adhesive must align with the production rhythm of other working procedures. In addition, the physical form of the adhesive (liquid, paste, film or solid) shall match the manufacturing methods applied to the bonded assembly.

1. II. Properties of Adherend Materials

The physical and chemical properties of adherend materials, as well as the required surface preparation standard prior to bonding, constitute another critical factor for adhesive selection.The target of selection at this stage is to maximize the bonding strength across the joint interface, so that the joint fails cohesively during testing rather than suffering interfacial failure between the adhesive and the adherend. Only in this way can the maximum strength of the adhesive be fully realized.

1. III. Strength of Adherend Materials

Low-strength substrates may be weaker than the adhesive itself, resulting in cohesive failure occurring inside the adherend instead of the adhesive layer.

For such applications, the selected adhesive shall allow the bonded assembly to withstand all physical service conditions that the base material can endure, without risk of bonding failure. In this case, adopting high-strength adhesives would lead to over-specification of the adherend materials and unnecessary extra costs.

1. IV. Thickness of Adherend Materials

Another factor that cannot be overlooked is the physical form of the adhesive. Solvent-based adhesives tend to cause wrinkling at the joint edges when bonding thermoplastic films or their composite laminates; however, when applied to rigid thermoplastics, they often lower the requirements for substrate surface pretreatment. The special geometry of adherends often facilitates the application of specific types of adhesives. For edge bonding between aluminum honeycomb structures and flat metal sheets, liquid primer paired with thermosetting adhesive films reinforced with fiberglass fabric delivers optimal bonding performance. Paste adhesives are convenient for fabricating heat exchangers by joining copper fins and aluminum tubes. For porous substrates, high-viscosity or paste-type adhesives are more suitable

1. V. Compatibility Between Adherends and Adhesives

Incompatibility between the adherend and adhesive will trigger bonding failure of the bonded assembly. This holds true even if only one component of the adhesive is incompatible with the adherend. Examples are as follows: metal parts being corroded by acidic or alkaline adhesives; plasticizers migrating out of flexible plastics into the adhesive and causing interfacial bonding failure; solvents or volatile substances contained in the adhesive attacking plastic films. Therefore, whenever possible, detailed property specifications shall be supplied together with adhesive samples. This will undoubtedly benefit both adhesive manufacturers and technicians performing bonding processes.

1. VI. Storage Requirements for Bonded Assemblies

While service conditions of bonded assemblies usually draw sufficient attention, their storage conditions are often overlooked. The proper practice is to take into account the abnormal extreme temperatures and impact loads that bonded assemblies may encounter during transportation and storage at the stage of adhesive selection.

1. VII. Cost

When evaluating the entire bonding process as a whole, the suitability of an adhesive’s properties carries greater weight than its raw material cost. Beyond the unit price of the adhesive itself, production efficiency and other associated factors must also be factored into the selection process. Solely choosing the cheapest adhesive without considering the relevant criteria listed below will not necessarily deliver favorable economic benefits:

    Overall bonding efficiency

    Ease of acquiring equipment required for application and processing

    Cycle time consumed by the bonding procedure

    Labor costs for adherend assembly and inspection

    Waste generation volume compared with alternative joining technologies

Generally, fast-tack adhesives that enable simplified bonding workflows are cost-effective even at a slightly higher unit price, provided they eliminate the need for complex assembly jigs or molds.