If a box of crayons is left in a hot car on a summer afternoon, what change would you expect to observe in the crayons?

1 Answer
Jul 25, 2016

Softening of the wax and therefore of the crayons.


I presume you are referring to wax crayons. These are composed predominantly of paraffin wax (typically 135 - 140 grade, which melts at between 135 and 140 degrees F, or roughly 57 - 60 degrees celcius. The wax is mixed with various pigments and these are dispersed into the wax using relatively high shear mixing. The mixture is pumped out into moulds which are then cooled to form the finished coloured crayons.

Whilst the wax melts at temperatures above about 60 degrees C (i.e. it is liquid above this temperature) there is not really a sharply defined melting point for paraffinic waxes, because they are composed of a number of different chain lengths. It means that some small fractions of the wax become liquid at much lower temperatures, and the wax can soften (i.e. still remain solid, but much softer and able to be deformed by physical stress) at these temperatures.

The temperature inside a car, especially if direct sunlight is coming through the windows onto the crayons, can easily reach 50 degrees C, and this is easily enough to make the wax soft and pliable.