Blood albumen glue

The literature [5] indicates that there were many adhesives based on blood albumen or combinations of blood albumen with phenol-aldehydes, casein, soybean meal and other protein-based products. However, in aircraft structures blood-based glues would have been almost exclusively used in plywood [6,7]. With the aircraft industry s reluctance to use casein adhesives, due to their poor water resistance, blood albumen glues and/or blood albumen/casein or occasionally blood albumen/soya bean extract became the primary adhesive systems for the preparation of plywood until ousted by the Tego phenol-formaldehyde (P/F) system in the early to mid-1930s. 

There are two general types of water-based adhesives solutions and latexes.Solutions are made from materials that are soluble only in water or in alkaline water. Examples of materials that are soluble only in water include animal glue, starch, dextrin, blood albumen, methyl cellulose, and polyvinyl alcohol. Examples of materials that are soluble in alkaline water include casein, rosin, shellac, copolymers of vinyl acetate or acrylates containing carboxyl groups, and carboxymethyl cellulose. 

Casein, like gelatin and blood albumen, is essentially a protein. It is obtained as a precipitate from skimmed milk, which bas been treated with sulfuric, hydrochloric or lactic acid. The glue is prepared by blending the preeipitated casein (which also contains several milk-product impurities) and alkaline salts (generally of calcium, sodium or boron) in an aqueous medium. To set - i.e. to achieve a solid state - the adhesive solution pH is adjusted to between 9 and 13. 

The active ingredient in blood glues is albumen. It is a protein with a molecular weight of about 69,000 (9). In the adhesives industry, the physical characteristics of the blood, such as solubility and viscosity in solution, are more generally used to characterize it than are more fundamental chemical traits. The suitability of blood for adhesives is generally determined on a supplier-by-supplier and lot-by-lot basis. 

These glues are based on the globular protein, albumen, which would have been extracted from blood essentially as a by-product of the massive meat processing... 

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