Shulin An

Evolution of Polyvinylidene Fluoride (PVDF) Hierarchical Morphology during Slow Gelation Process and Its Superhydrophobicity

In the paper, we proposed an evolution process of polyvinylidene fluoride (PVDF) macromolecular aggregation in a mixed solvent through the simple and slow gelation process at room temperature. The mixed solvent is prepared with a room-temperature solvent and a high-temperature solvent. The evolution process can be terminated by quenching and exchanging with nonsolvent in a nonsolvent coagulation bath properly, and then the vivid petal-like nanostructure and microspherulite is formed simultaneously. This hierarchical morphology endows PVDF with superhydrophobic and self-cleaning properties, which is useful to PVDF coating and membrane materials. The evolution processes are investigated through the measurements of differential scanning calorimetry (DSC), X-ray diffraction (XRD). In addition, the rheological properties of solution, dry gel and wet gel, are explored.

Fabrication and properties of poly(tetrafluoroethylene-co-hexafluoropropylene) hollow fiber membranes

Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) hollow fiber membranes have been fabricated for the first time via the melt spinning method. Dioctyl phthalate (DOP) as the diluent and a composite powder (composed of soluble and insoluble particles) as the pore-creating agent were used in this study. The addition of the composite powder brought about a dissolved pore structure and interfacial microvoids (IFMs) in the membrane. The membrane’s corresponding microfiltration performance was characterized in terms of pure water flux, a mechanical strength test, a mean pore size measurement and morphology observations by a field emission scanning electron microscope (FESEM). The results show that the FEP hollow fiber membrane was a kind of homogeneous membrane, with mean pore sizes ranging from 0.4 to 1 μm. The increase of the composite powder addition and the stretching process brought about an obvious enhancement of the pure water flux and porosity. Compared with the available commercial PTFE hollow tube membranes, the smaller size of the FEP hollow fiber membrane provides a higher filled density in the membrane modules. Moreover, the smaller thickness of the membrane improves membrane permeability.

Effects of phenolic antioxidants on ultrahigh molecular weight polyethylene/decalin solution

The degradation of ultrahigh molecular weight polyethylene (UHMW-PE) during its dissolution into decalin is discussed. The stabilization of the solution by three phenolic antioxidants, octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (1076), tetrakis[methylene-β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane (1010), and 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane (CA), and an auxiliary antioxidant, dilaurylthiodipropionate (DLTP) is also discussed. Among the three phenolic antioxidants, 1076 had the greatest effect. The auxiliary antioxidant was effective in stabilizing the solution when combined with one of the three phenolic antioxidants.