Experiments of nonisothermal blown film extrusion were carried out to observe the film blowing process using LDPE (Low Density Polyethylene). Experimental variables were flow rate of melts, pressure difference gradient across the thin film (ΔP/h), and draw ratio. Holding other variables constantly, bubble diameter was decreased with increasing draw ratio, decreasing flow rate of melts, and decreasing ΔP/h. And film thickness was decreased with increasing draw ratio, decreasing flow rate of melts, and increasing ΔP/h. But bubble diameter and film thickness were more sensitive to pressure difference across the thin film than other variables.
Nonisothermal operation of power law model was used for theoretical study. Theoretical values of bubble diameter were equivalent reasonably to experimental results with variation of pressure difference across the thin film except with ΔPmax.
Elongational properties, such as tensile stress and strain at break point, of products were measured. Larger tensile stress and lower strain at break point were shown for larger draw ratio and larger ΔP/h because of chain orientation of polymer.