An adhesive is a material used for holding two surfaces together. An adhesive must wet the surfaces, adhere to the surfaces, and by surface attachment that resists separation. Inorganic substances such as portland cement also can be considered adhesives. Natural adhesives have been known since antiquity. In the performance of adhesive joints, the physical and chemical properties of the adhesive are the most important factors.
Types of adhesive raw materials
- Cellulose nitrate
- Cellulose acetate
- Methyl cellulose
- Ethyl cellulose
- Polyvinyl acetate
- Polyvinyl alcohol
- Polyvinyl butyral
- Polyvinyl ether
- Polyvinyl chloride
Mechanism of adhesion process
The main mechanism of adhesion is explained by the adsorption theory.
Adsorption theory can be defined as substances stick because of intimate intermolecular contact. In adhesive joints this contact is attained by intermolecular or valence forces exerted by molecules in the surface layers of the adhesive and adherend.
In addition to adsorption, four other mechanisms of adhesion have been proposed.
It occurs when adhesive flows into pores in the adherend surface or around projections on the surface.
Interdiffusion results when liquid adhesive dissolves and diffuses into adherend materials.
Adsorption & Surface Reaction
In this process bonding occurs when adhesive molecules adsorb onto a solid surface and chemically react with it.
This theory suggests that electrostatic forces develop at an interface between materials with differing electronic band structures
A sealant is the viscous material that has little or no flow characteristics and stay where they are applied or thin and runny so as to allow it to penetrate the substrate by means of capillary action.
The main difference between adhesives and sealants is that sealants typically have lower strength and higher elongation than do adhesives.
Sealants fall between higher-strength adhesives at one end and extremely low-strength putties and caulks at the other. Sealants fill a gap between two or more substrates. It forms a barrier through the physical properties of the sealant itself and by adhesion to the substrate. Sealants maintain sealing properties for the expected lifetime, service conditions and environments.
Dental sealants are a dental treatment consisting of applying a plastic material to one or more teeth, for the purpose of preventing dental caries (cavities) or other forms of tooth decay.