Shear effect in beta-phase induction of polypropylene in a single screw extruder

In this work, we investigated the effect of four different configurations at the exit of a single-screw extruder on the induction of beta phase in PP for four different rotational speeds. The configuration of a breaker plate with 120 orifices of 1-mm diameter and 7-mm length each, give the highest content of beta-phase (56.92%), for a screw rotational speed of 20 rpm. It was due to the shear caused separation of the melt when it passes through the orifices of the breaker plate. The breaker plate of configuration 4 (breaker plate with the greatest number of orifices) provided the largest number of contacts between the melt and the orifice walls resulting in chain alignment. The results show that the beta-phase can be induced in the polymer without any further additives, especially without any nucleating agents, but rather by using a special breaker plate configuration at the exit of the single-screw extruder. The skin-core structure of the polymer was only developed with one type of extruder configuration. (c) 2013 Wiley Periodicals, Inc.