Effect of solvent plasticization on polypropylene microcellular foaming process and foam characteristics

In this research, the effect of crystalline fraction of polypropylene (PP) on cell nucleation behavior was overcome by an introduction of solvent‐plasticized step to the microcellular foaming in a solid‐state batch‐foaming process. Utilizing the plasticization performance of the solvent facilitated the PP to be foamed at the temperatures lower than its melting point with the dramatic development in the cellular morphology of the final foams. In consequence of the heterogeneous cell nucleation sites induction and the crystalline loss, which were induced by solvent, a high cell density (i.e., 10⁹–10¹⁰ cells/cm³) was promoted without the cell sacrificing at the elevated temperatures (155 and 165°C) and favorable PP microcellular foams were accomplished. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Morphology and tensile properties of polypropylene‐multiwalled carbon nanotubes composite fibers

In this work, we analyzed tensile properties of polypropylene‐multiwalled carbon nonotubes composite fibers. The multiwalled carbon nanotubes (MWCNTS) were used in different contents of 0, 1, 2, 3, 4, and 5 wt %. Dispersing agents were used to disperse MWCNTs in polypropylene matrix. After the dispersing agent was removed, the mixture was melt mixed. The fibers were spun by a home‐made melt spinning equipment and stretching was done at a draw ratio of 7.5. By using 1–5 wt % of MWCNTs, the modulus of composite fibers increased by 69–84% and tensile strength increased about 39% when compared with the virgin polypropylene fibers. In addition, the MWCNTs dispersion in the matrix was monitored by scanning electron microscopy and transmission electron microscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of die geometry on foaming behaviors of high‐melt‐strength polypropylene with CO2

This article reports on a systematic study that was conducted to investigate the effects of die geometry (i.e., pressure and pressure drop rate) on the cell nucleation and growth behaviors of noncrosslinked high‐melt‐strength (HMS) polypropylene (PP) foams blown with supercritical CO₂. The experimental results showed that the cellular morphologies of PP foams were sensitive to the die geometry. Furthermore, the initial expansion behavior of the foam extrudate at the die exit was recorded using a high‐speed CCD camera. This enabled us to achieve a more thorough understanding of the effect of die geometry on both the initial expansion behavior and the final cellular morphology of HMS PP foams. The effect of die temperature on cell morphology was also studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

The relationship of crystallization behavior,mechanical properties,and morphology of polypropylene nanocomposite fibers

This study aimed at the fabrication of lightweight and high performance nanocomposite fibers. Polypropylene/multiwalled carbon nanotubes (PP/MWCNTs) nanocomposite fibers (0–5 wt% of MWCNTs) were prepared via melt spinning process. The MWCNTs were dispersed in the dispersing agent before mixing with PP powder. After mixing, the dispersing agent was removed. Then the nanocomposites were spun into fibers. The fibers were spun and stretched with 7.5 draw ratios. Crystallization behavior and thermal properties of PP/MWCNTs nanocomposite fibers were studied using the differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA). The DSC curves of PP/MWCNTs nanocomposite fibers showed the crystallization peak at a temperature higher than that of neat PP fibers. These results revealed that the MWCNTs acted as nucleating sites for PP crystallization. The additions of MWCNTs into PP leaded to an increase in both crystallization temperature and crystallization enthalpy. However, no significant changes in the melting temperatures of the PP nanocomposites were detected. Degradation temperature of samples obtained from the TGA curves showed increase thermal degradation behavior for the PP/MWCNTs with the content of MWCNTs. It was found that the increase of tensile strength and modulus corresponded well with the increase of crystallinity of the composite fibers.