23 июля, 2015 
Malyar A. Raw Material Source and Preparation
As with blood, the adhesive qualities of casein curd from milk were recognized in relatively ancient times. Mixed with a simple alkali such as lime, casein protein became an important adhesive for furniture and paint pigments and the preferred sizing agent for the canvas of Renaissance paintings [6,55].
Medieval furniture assembly was divided between casein glues and animal gelatin adhesives made from boiled extracts of bone and hide. The gelatin glues were applied to joints as a hot solution and gained bond strength almost immediately on cooling. The casein glues required much longer clamping times to develop adhesion by water loss and insoluble caseinate formation. However, the casein glues had true water resistance, whereas the animal gelatin glues remained forever sensitive to even slight moisture and heat exposure [5]. Thus casein tended to be used where durability was required. This association with water resistance has remained a favorable performance factor for casein glues down to the present.
Casein protein is recovered from skim milk by acid precipitation to pH 4.5. Mineral acids may be used or the milk can be cultured with bacteria that convert lactose (milk sugar) to lactic acid, which in turn precipitates the casein. The precipitated protein curd is washed free of acid with hot or cold water and is then dried and ground. The commercial designation for casein often includes its method of acid precipitation (e. g., ‘‘lactic acid or sulfuric acid casein’’).
Since industrial casein competes directly with the worldwide food uses of milk and its proteins, the price of casein tends to vary widely as the supply/demand economics of milk products rise and fall. In recent years, the cost has remained well over $2 (U. S.) a pound. Even at this price, however, certain casein blend and specialty glues continue to hold a significant place in current markets.
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