Читать книгу Adhesives for Wood and Lignocellulosic Materials - R. N. Kumar - Страница 45

The role of an adhesive for wood is to transfer and distribute loads between components, thereby increasing the strength and stiffness of wood products [6].

This is achieved through the following three basic types of adhesion:

1 Specific Adhesion—Bonding between the adhesive and the adherend is due to chemical reaction.

2 Mechanical Adhesion—occurs due to mechanical anchorage.

3 Effective Adhesion—combines specific and mechanical adhesion for optimum joining strength.

One should distinguish between adhesion and cohesion.

Cohesion as defined earlier is the attraction of molecules and groups within the adhesive (or other material) that holds the adhesive molecules together. The combination of adhesion and cohesive strength determines the bonding effectiveness. An adhesive bond fails if either the adhesive separates from the substrate (interfacial adhesion failure) or the adhesive breaks apart (cohesive failure). The adhesive and cohesive strengths of some adhesives are high enough that the cohesive strength of the substrate fails before the adhesive bond.