What is adhesive?
An adhesive may be described as a substance which is capable of holding materials or adherent together by surface-action. This process of joining the two or more surfaces is known as adhesion.
Ideal adhesive
A good adhesive should have the following desirable properties.
· Maximum mechanical strength of the bond.
· Minimum setting time or quick development of bond.
· Ease and rapidity of application.
· Resistance to moisture.
· Ability to withstand temperature variations.
· Resistance to the deterioration by ageing.
· Chemically inert to the adherent.
· Freedom from objectionable odour.
· Freedom from fire and toxicity hazards.
Types of Adhesives
Different types of the adhesives are availables accordance with their origin or the materials used for their manufacturer. The adhesives may thus be broadly classified as that of animal origin ( animal glue, fish glue and casein), of vegetable origin (starch, cellulose derivatives, rubber and gums etc.) and of synthetic origin(phenolics,vinyls,epoxies etc.) The other system of classification is based on the mode of adhesion, e.g. pressure sensitive, hot melt, chemical-setting and solvent release type etc.
Another system of adhesive classification is based on their physical state, e.g. liquid,paste,solid,frames etc. The liquid based may be further divided into water-based and organic solvent based types.
Physical & Chemical Classification
The physical state of the adhesive determines its method of application. Liquid adhesives can be easily applied by spreading by mechanical spreaders for flat surfaces and, by spraying or brushing for curved or irregularly shaped surfaces. The liquid adhesives can be water emulsions, solvent dispersed or polymerizable liquids.
The most widely used classification for adhesives is on the basis of their origin viz. vegetables,animals and synthetics. These are further classified into sub-groups e.g. cellulose,protein,organic,inorganic etc.
