No abstract

Dynamic shear in the axial direction of a rotor was vertically superposed on the melt flow direction, and its effects on the shear rate and melt strength were investigated theoretically. Polypropylene/high-density polyethylene blends were microcellularly foamed with different vibration parameters. The experimental results were compared with those of a theoretical analysis, and the effects of dynamic shear on the foamability and ultimate cell structure were analyzed in detail. The theoretical results showed that the shear rate and melt strength increased with an increase in the vibration amplitude and frequency. The enhanced melt strength could effectively restrict cell growth, prevent cell rupture, and improve foamability. The experimental results showed that the cell orientation decreased and the cell structure was improved when axial dynamic shear induced by rotor vibrations was superposed on the melt flow direction. Furthermore, the cell diameter decreased and the cell density increased with increases in the vibration amplitude and frequency. The experimental results were very consistent with the theoretical analysis.

The polypropylene (PP) pipes were prepared using a self-made electromagnetic dynamic plasticating extruder, which introduced a vibration force field into the whole plasticating and extrusion process by the axial vibration of the screw. The effects of the vibration frequency and the vibration amplitude on the mechanical properties and microstructure of PP pipes were investigated using bursting pressure testing, tensile testing, impact testing, differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD). The mechanical properties testing showed that the circumferential strength of PP pipes increased significantly, and the biaxial selfreinforcement pipes could be obtained. Also, the impact strength was improved. When compared with the conventional static extruded specimens, the maximum increase of bursting pressure, tensile yield strength, and impact strength were 27.03%, 7.3%, and 16.2%, respectively. DSC and WAXD analysis showed that the PP pipes obtained by vibration plasticating extrusion (VPE) had higher crystallinity, higher melting temperature, more perfect crystals, and smaller crystal sizes, but no new polymeric crystalline peak appeared. The improvement of mechanical properties of the PP pipes prepared by VPE was attributed to the higher crystallinity and the improvement of the molecular orientation and of the crystalline morphology under the action of the vibration force field.

With maleic anhydride grafted polypropylene (PP-g-MAH) as a compatibilizer, composites of block-copolymerized polypropylene (B-PP)/nanoclay were prepared. The effects of the PP-g-MAH and nanoclay content on the crystallization and rheological properties of B-PP were investigated. The microcellular foaming behavior of the B-PP/nanoclay composite material was studied with a single-screw extruder foaming system with supercritical (SC) carbon dioxide (CO 2 ) as the foaming agent. The experimental results show that the addition of nanoclay and PP-g-MAH decreased the melt strength and complex viscosity of B-PP. When 3 wt % SC CO 2 was injected as the foaming agent for the extrusion foaming process, the introduction of nanoclay and PP-g-MAH significantly increased the expansion ratio of the obtained foamed samples as compared with that of the pure B-PP matrix, lowered the die pressure, and increased the cell population density of the foamed samples to some extent. V C 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44094.

We investigated the effect of polydimethylsiloxane (PDMS) on the foaming properties of block-copolymerized polypropylene (B-PP) by blending different contents of PDMS with B-PP in the extrusion process using supercritical CO 2 as the blowing agent. The experimental results indicate that the addition of PDMS greatly increased the expansion ratio of the foamed samples. At the same time, the cell population density of foams obtained from the blends also increased to a certain degree and provided a new perspective on improving B-PP's foaming performance. The addition of PDMS also decreased the die pressure because of the reduced viscosity of the B-PP/PDMS blends compared with that of the B-PP matrix.