The influence of “two-phase” synthesis conditions on blown film extrusion of LDPE

LDPE synthesized under two-phase conditions is known to have a good balance of blown film properties. Good optical properties and high impact strength are characteristic for two-phase LDPE grades. In order to obtain systematic information, LDPE was synthesized at several different pressures with two different melt index levels. Blown film was extruded at different output rates and melt temperatures. The influence on haze and dart drop impact was studied. Two-phase conditions were found to improve haze and dart drop impact and the improvement was impressive, especially for the low melt index grades. By increasing the output rate, the dart drop values were further improved. The influence of melt temperature on dart drop impact goes through an optimum and overall haze decreases with increasing melt temperature. For films made from two-phase grades, dart drop impact decreases as internal haze increases. For corresponding internal haze values, the films made from single-phase grades have lower dart drop values and they are somewhat scattered.