Recycling of plaster of Paris

Plaster of Paris (POP) is being used in different ways in the field of medicine, dentistry and rehabilitation. One of its uses is in the manufacture of models of body segments in prosthetics and orthotics. It is used as a one-off procedure in which the used material is dismantled and discarded. The disposal of discarded materials does not allow easy decomposition which then pollutes the environment. It is not known whether this material could be reused if recycled.

The main objective of the study was to recycle POP models and determine its reuse in producing models with identical qualities, and thus reduce environmental pollution.

The procedure adopted was to break discarded models into small pieces, remove impurities and dirt; then the sample models were milled, washed, dried and pulverised. The POP models were heated to evaporate crystalline water in order to determine for how many times it could be recycled while retaining the desired strength, setting time and working characteristics.

The recycled POP reached higher setting temperatures and was stronger in terms of compressive strain and strength than the virgin POP. The highest temperature recorded for recycled POP was 40°C, which was higher than that for virgin powder (32.5°C). Testing compressive strength of all cylinders in all groups showed that the average compressive strength of the recycled powder mixed with water in a ratio of 1:1 was 2407 KN/m² and the ratio of 2:3 resulted in a compressive strength of 1028 KN/m², whereas the average compressive strength of virgin POP powder mixed with water in a ratio of 1:1 was 1807 KN/m² and the ratio of 2:3 resulted in a compressive strength of 798 KN/m². There were no differences in working properties between the recycled POP and the virgin POP.

It was therefore concluded that under controlled conditions, such as grinding size, heating temperature, time and avoidance of contamination, used POP could be continuously recycled, resulting in stronger and workable casts.