Rheological behavior of PET/HDPEin situ microfibrillar blends: Influence of microfibrils' flexibility

Polypropylene Hollow Fiber Membrane by Dissolution-Inducing Pore Methods

Plasma leakage limits the development of polypropylene membranes as oxygenated membranes. Here, a new method named the dissolution-induced pore method was adapted to prepare polypropylene hollow fiber membranes: after polypropylene and polyvinyl chloride were melt-blended and extruded, the polyvinyl chloride was removed by N, N-dimethylacetamide to obtain a porous polypropylene membrane material. The variation of membranes has been explored in detail with respect to the influence of different parameters on the flux and mechanical properties of membranes and the feasibility of the polyvinyl chloride recovery. The resulting polypropylene hollow fiber membrane shows that plasma penetration was zero within 6 h of test, gas flux can reach 189,000 L/(m2·h·0.1 MPa), and its strength at break reaches 65 MPa and the elongation at break is 890%; polyvinyl chloride recovery achieves more than 99%. This research has developed a promising and low-cost extracorporeal membrane oxygenation material, which provides benefits for patients with less capacity for medical expenditure.

Relationship between the Processing, Structure, and Properties of Microfibrillar Composites

The relationship between processing, morphology, and properties of polymeric materials has been the subject of numerous studies of academic and industrial research. Finding an answer to this question might result in guidelines on how to design polymeric materials. Microfibrillar composites (MFCs) are an interesting class of polymer-polymer composites. The advantage of the MFC concept lies in developing in situ microfibrils by which a perfect homogeneous distribution of the reinforcement in the matrix can be achieved. Their potentially excellent mechanical properties are strongly dependent on the aspect ratio of the fibrils, which is developed through a three-stage production process: melt blending, fibrillation, and isotropization. During melt blending, the polymers undergo different morphological changes, such as a breakup and coalescence of the droplets, which play a crucial role in defining the microstructure. During processing, various parameters may affect the morphology of the MFCs, which must be taken into account. Besides the processing parameters, the microstructure of the composite is dependent on the composition ratio of the blend and viscosity of the components, as well as the dispersion and distribution of the microfibrils. The objective here is to outline this importance and bring together an overview of the processing-structure-property relationship for MFCs.

The foaming performance evaluation of fibrillated polytetrafluoroethylene and isotactic polypropylene blends

Polypropylene (PP) foamed products have the advantages of heat and chemical resistance, but it is difficult to foam without modified PP. Traditionally, researchers have used chemical modification to increase the melt strength to improve the foaming properties of PP. In this article, we designed four kinds of screw combinations, and five regions are selected for sampling. The polytetrafluoroethylene (PTFE) and isotactic polypropylene (iPP) were blended by one-step fiber forming method, and then we tested the rheological properties and foaming properties. It is found that the rheological properties of the in situ microfiber composite are significantly improved than the iPP, and the crystallization temperature is also increased. The foaming experiment of the composite showed that the foaming performance of the composite with in situ microfiber morphology was significantly improved compared with the pure iPP performance, and the foaming temperature window of iPP was widened from 3°C to more than 6°C.

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Morphology development and size control of poly(trimethylene terephthalate) nanofibers prepared from poly(trimethylene terephthalate)/cellulose acetate butyrate in situ fibrillar composites

Formation of nano-fibrillar composite structures provides an effective method for preparing thermoplastic nanofibers. By mixing two immiscible thermoplastic polymers in a twin screw extruder, poly(trimethylene terephthalate) (PTT) formed nano-fibrillar morphology in cellulose acetate butyrate (CAB) matrix, and then PTT nanofibers were obtained from PTT/CAB in situ fibrillar composites after removing the matrix phase of CAB. Blend ratio, shear rate, and draw ratio were three important parameters in the extrusion process, which could affect the shape and size of nanofibers. By varying the process conditions, average diameter of PTT nanofibers could be controlled in the range of 80-400 nm. Besides this, the mechanism of nano-fibrillar formation in PTT/CAB blends was also studied by collecting samples at different stages in the extruder. The morphology developmental trends of PTT dispersed phase with different blend ratios were nearly the same. From initial to metaphase and later phase development, the PTT dispersed component undergo the formation of sheets, holes, and network structures, then the size reduction and formation of nanofibers.