THE INFLUENCE OF THE CONDITIONS OF BLOWING EXTRUSION OF POLYETHYLENE FILM ON THE CHANGES OF SOME ITS PROPERTIES

摘要

The fundamental problems related to polymer (especially polyethylene) degradation,going during extrusion of the film,are discussed. Various commercial PE-LD and PE-LLD grades,processed in experimental technological line of blowing extrusion (Fig. 1),were the subjects of own investigations. Polymer degradability was evaluated on the basis of melt flow rate (MFR) changes,oxidation induction time (OIT) and DSC thermograms (Table 2). The effects of selected elements of intensive mixing or shear of a screw (Fig. 2) as well as extrusion conditions (normal or extreme ones,dependency on the type of mixing tip,shot degree of plasticizing system and shearing slot height on the degree of polyethylene degradation were determined. Degradation causes lowering of polymer molecular weight what results in changes of mechanical properties of the film especially deterioration of tensile strength (Table 3 and 4). The levels of total migration of the substances from the films to model liquids mimicking the food were determined (Table 3). It was found that the effect of PE degradation degree on migration level was insignificant.