Effect of the Elongational Flow on the Morphology and Properties of Polymer Systems: A Brief Review

Polymer-processing operations with dominating elongational flow have a great relevance, especially in several relevant industrial applications. Film blowing, fiber spinning and foaming are some examples in which the polymer melt is subjected to elongational flow during processing. To gain a thorough knowledge of the material-processing behavior, the evaluation of the rheological properties of the polymers experiencing this kind of flow is fundamental. This paper reviews the main achievements regarding the processing-structure-properties relationships of polymer-based materials processed through different operations with dominating elongational flow. In particular, after a brief discussion on the theoretical features associated with the elongational flow and the differences with other flow regimes, the attention is focused on the rheological properties in elongation of the most industrially relevant polymers. Finally, the evolution of the morphology of homogeneous polymers, as well as of multiphase polymer-based systems, such as blends and micro- and nano-composites, subjected to the elongational flow is discussed, highlighting the potential and the unique characteristics of the processing operations based on elongation flow, as compared to their shear-dominated counterparts.

Continuous Preparation and Properties of Silica/Rubber Composite Using Serial Modular Mixing

In order to efficiently prepare high-performance silica/rubber composites for use in the tread of semi-steel radial tires, a serial modular continuous mixer was designed according to the principle of modular functionalization. The modular structure and serial process helped control the accuracy of the silanization reaction. Synchronous four-wing serrated rotors and reverse meshing reaction mixing twin-rotors utilized shear flow and elongation flow to improve the dispersion. In this paper, the mechanism of serial modular continuous mixing was analyzed, and the influence of the core reaction mixing zone (various mixing elements) on silica-filled compounds was investigated by cooling visualization experiments, including dispersion, and the silanization reaction degree. Meanwhile, a comparative experiment between serial mixing and two-stage mixing was conducted, which showed that the serial process comprehensively improved the dispersion, mechanical properties, and dynamic mechanical properties of silica/rubber vulcanizate.

Preparation and characterization of poly(lactic acid)/sisal fiber bio-composites under continuous elongation flow

In this study, poly(lactic acid) (PLA) matrix bio-composites reinforced with various quantities of sisal fibers (SFs) (from 10% to 50% in weight) were fabricated by using a self-made vane mixer, which can generate continuous elongation flow. The morphology, crystallization, and mechanical properties of PLA/SF bio-composites under continuous elongation flow were investigated. Scanning electron microscopic images showed that SFs were uniformly dispersed in the matrix and oriented along the extrusion direction. Meanwhile, it was found that the diameter of SFs decreased from 250 to 20 μm, which certified that continuous elongation flow remarkably affected the separation of elementary fibers from fiber bundles. Wide-angle X-ray diffraction and differential scanning calorimetry measurements indicated that the addition of SFs promoted the crystallization of PLA as well as increased the crystallinity of PLA. The mechanical tests exhibited that both impact strength and tensile modulus were significantly enhanced (about 64% and 94.63%, respectively) with SFs loading at 40%, which was due to the well dispersion and separation of elementary fibers.