In the manufacture of cellulose nitrate plastic some physical damage of the finished product always results during drying. The drying conditions should be studied and improved.

The purpose of this investigation was to determine the effects of relative water humidity, convection heat and radiant heat on the drying of cellulose nitrate plastic. The conditions causing case-hardening and physical damage were observed, drying rate was determined and drying time compared.

Specimens of cellulose nitrate plastic sheet, plasticized with camphor, were soaked in 95 percent ethyl alcohol. They were first dried in a compartment dryer by conditioned air, with or without radiant heat. Then, they were removed to a zero relative humidity desiccator to be dried until the weight became constant within a one-day period.

The values of relative humidity studied were 30, 40, 50 and 60 percent. The air temperatures studied were 110, 120, 130 and 140 °F. The detailed data were not obtained at 60 percent relative humidity and at 140 °F because these conditions could not be controlled. The radiant heat was supplied from two electric hot plates and used to increase the internal temperature of the plastic.

The effect of increasing the relative humidity was to reduce or avoid damage to the plastic and to reduce the drying rate at higher alcohol content. This effect increased with the increase of air temperature and became less as the alcohol content decreased. It disappeared at 0.225 gram alcohol per gram dry weight as dried at 110 °F and temperature, and at 0.17 gram per gram dry weight as dried at 130 °F.

Increasing the air temperature increased the drying rate and shortened the drying time. The maximum safe air temperature for drying cellulose nitrate plastic without radiant heat was between 130 and 140 °F, physical damage occurring at 140 °F.

Radiant heat could be applied to raise the internal temperature of the wet plastic and to increase the drying rate without causing case-hardening, the effect being slightly greater with a thick plastic of darker color than with a thin plastic of light color.

When the internal temperature of the wet plastic was raised to 128 and 130 °F by supplementary radiant heat, with drying air of 110 °F and 50 and 30 percent relative humidity, respectively, the drying rate was increased, but physical damage to the plastic resulted.