History: earlier used for decorating walls
»A house built on a deposit of gypsum near Paris burnt down; the rain fell on the baked mud of the floors –> footprints in the mud set rock-hard like plaster; this led to the discovery of practice of heating GYPSUM to make the smooth covering for walls.
» Henry III visited Paris in 1254, admired the smooth whiteness of walls & made it popular in England as “Plaster of Paris” for use on walls.
»It came to use for Orthopaedic cast only in 1800s.
Chemical Composition: Gypsum[2(CaSO4.2H2O)] is heated to drive off water & then the powder is made. When water is added to the powder, it changes to the original mineral with the release of heat.
2(CaSO4.2H2O) + Heat ——> 2(CaSO4.1/2H2O) + 3H2O
Ca-sulphate dihydrate + Heat
Plaster of Paris(POP) bandages:
»Manually coating of the powder on bandages & then making the roll of it.
»By automatic machine- powder suspended in volatile additives- slurry coated onto special woven cloth called Leno–>solvent removed in a drying oven–> bandages cut, rolled & packed in the moisture-resistant pack.
Water-resistant Cast: Melamine synthetic resin mixed with Plaster of Paris makes it water-resistant.