A glue can be made from milk by souring it using vinegar (an acid) which separates it into curds and whey. The curds can be neutralised by various bases to produce a variety of different glues. The glue can be tested for strength by sticking together two lolly sticks and attaching weights to them. This activity lends itself to group,investigative and competitive work.
Did you ever wonder why Elmer’s
®
white glue has a picture of a cow on the label? This is because cows make glue. Of course, this statement seems strange until you learn that it is the protein in the milk can be used to make glue. The protein in the milk is casein. So, in reality, cows make milk, but you can use milk to make glue.
Casein is actually a micelle consisting of a protein subunit that somehow stabilizes the micelle so that it limits its growth and stays dispersed in the milk colloid. The other components of casein are calcium and phosphate ions.
When the protein subunit is removed from the casein micelle, they can clot together to form the curd that can be further treated to make cheese or an adhesive suitable for use in paper, plastics, or glues. When mixed with lime, the curds form a material know as whitewash, which was used in colonial times to paint houses.
Elmer’s
® glue used to be made from casein, however, it is now made from a polymer, polyvinylacetate (PVA) since that polymer is more stable and has a long shelf storage life. Elmer’s
®
blue gel glue is made from polyvinylalcohol.
Milk contains casein, a protein that is used in the production of glues, paints and plastics, as well as some food products. If you heat up milk and add an acid, such as vinegar, you will cause a chemical reaction whereby the casein separates from the liquid component of milk. When you add a base, such as baking soda, to the casein extracted from milk, the acid is