Clarity and internal/external structure of blown polyethylene films

The direct transmission factors of linear low density and low density polyethylene blown films were measured as a function of film preparation conditions. The contribution of scattering from the film surface was investigated by separating the overall direct transmission factor into components due to transmission through the bulk film phase and transmission through the surface phase. At lower polymer deformation rate and higher cooling rate the overall direct transmission factor had higher values. The surface phase direct transmission factor dominates the overall direct transmission factor. Surface irregularities of blown PE film are affected by crystallization mechanisms near or at the film surface and flow defects caused by deformations within the die and beyond the die exit. Direct transmission factor of HDPE/PP blend films were also studied as a function of composition. Each phase direct transmission factor showed a mximum near 50 weight percent polyethylene.

Profiles of surface irregularities of the blown films were obtained using a surface profiler and characterized statistically. Scanning electron microscopy was also used to help characterization of surface irregularities. HDPE showed the roughest surface irregularities and LDPE showed the smoothest surface irregularities. A good correlation was found between the standard variation of height deviation of the film surface irregularities and the film's surface phase direct transmission factor.

Orientation in L-LDPE and LDPE films were studied using both birefringence and wide angle X-ray pole figures. Both L-LDPE and LDPE showed a typical a-axis orientation along the machine direction with the b-axes concentrated towards the normal direction.