Inter-relationship between processing conditions and mechanical properties of blown film from different polypropylenes and high melt strength polypropylene blends



The aim of this study is the improvement of process stability and film properties of various matrix polymers by the addition of long chain branched (LCB) polypropylene (PP) in the blown film process. Three commercially available PP grades were dry-blended with two different high melt strength (HMS) PP grades with varying weight content in the range of 5, 10, and 20%. Maximum solid output was determined on a Hosokawa blown film line with a film thickness of 50 μm. Thickness was adjusted by proper relation between output and take-up ratio (TUR). The blow-up ratio (BUR) was varied from 1 : 2 to 1 : 3 and 1 : 4 in connection to the output rate and HMS-PP content. Research showed an increase of the output due to the additon of HMS-PP in various matrix polymers and different processing conditions. Influences on mechanical properties related to process parameters concerning stiffness and impact energy were found. Due to the addition of HMS-PP in a heterophasic PP-copolymer (PP-I) the maximum solid output increases up to 50% as well as tensile properties were enhanced. Stiffness of the blown film is independent of the output and the BUR both in machine direction (MD) and transverse direction (TD). In contrast a reduction of the process stability and solid state properties were determined with homo-PP (PP-H) and random-PP (PP-R) mixtures. Decreasing impact energy of the heterophasic copolymer was determined with increasing HMS-PP content. In comparison to the enhanced stiffness, toughness decreases which refers to a higher brittleness due to the addition of HMS-PP. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010