THE PROBLEM OF DRYING POLYETHYLENE SHEATHING COMPOUND PRIOR TO EXTRUSION,

It was determined that steps must be taken to supply the cable sheathing extruders with dry polyethylene to avoid blisters and rough sheath difficulties. The moisture content of polyethylene sheathing compound should not exceed .04. Special care is required in making moisture content determinations. Moisture content - relative humidity equilibrium data were obtained from which curves were drawn with the material at temperatures of 80F and 167F. If material is received at low moisture contents and stored until equilibrium is reached with the atmosphere, the moisture content will be above the optimum extrusion level in either winter or summer. The theory of drying is reviewed. Drying rate equations for thru-circulation do not apply to hopper drying because the beds are deeper and the material is stationary on the bed. Extrusion of dried polyethylene apparently does not result in increased extruder outputs. Further development of heat and mass transfer relations for hopper drying are needed together with a precise value of the critical moisture content of the material. Author