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The β‐phase in polypropylene (PP) induced by shear rate in a single‐screw extruder was studied. PP samples were extruded with and without a breaker plate at the exit of the extruder at five different screw rotational speeds: 20, 40, 60, 80, and 100 rpm. Differential scanning calorimeter was used to observe the melting behavior of the samples. The β‐phase was quantified by wide angle X‐ray diffraction. Extruded samples with a breaker plate showed higher values of β‐phase of PP than those extruded without a breaker plate. With a breaker plate, the maximum percentage of β‐phase was observed at 60 rpm (19.9%), whereas the maximum β‐phase content without breaker plate was observed at 40 rpm (13.6%). The higher level of β‐phase with the breaker plate was attributed to the shear rate induction and to the orientation by shear of the polymer chains through the orifices of the breaker plate. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

The effects of type of processing of polypropylene (PP)/wollastonite composites on mechanical properties and dispersion state were investigated. The concentration in weight of the filler in the compounds was of 2.5%, 5%, and 10%, respectively. Stearic acid was used as an interface modifier for the PP–wollastonite system. Wollastonite was also modified with stearic acid. The infrared spectra did not show any chemical changes between unmodified and modified wollastonites. The interactions between wollastonite and stearic acid were mainly physical. The compounds with interface modifier (stearic acid) showed the higher values in impact strength and elongation at break, as well as the best dispersion state. Qualitative chemical analysis on scanning electronic microscopy detected the presence of the acid stearic in the interface. POLYM. COMPOS., 35:1184–1192, 2014. © 2013 Society of Plastics Engineers

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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. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci.