Effect of quenching temperatures on the morphological and crystalline properties of PVDF and PVDF–TiO2 hybrid membranes

Jet-Injection In Situ Production of PVDF/PCM Composite Fibers for Thermal Management

Thermal management protects against external agents and increases the lifetime and performance of the devices in which it is implemented. Because of their ability to store and release a high amount of energy at a nearly constant temperature, phase change materials (PCMs) are promising thermoregulatory materials. Thus, the manufacture of PVDF fibers containing PCMs has advantages since PVDF is already used in elements that are susceptible to thermal management as a binder in batteries or as a base material for fabrics. This work presents a simple, versatile, in situ, cost-effective, and easy-to-scale-up method to produce PVDF-based fibers containing paraffin RT-28HC for thermal management. To achieve that goal, the microfluidic approach of coaxial flows was simplified to gravity-aided laminar jet injection into a bulk fluid, where fibers were produced by the solvent extraction mechanism. With this methodology, hollow PVDF fibers and core-shell PVDF fibers containing paraffin RT-28HC have been produced. The proposed approach resulted in fibers with up to 98 J/g of latent heat, with a hierarchical porous structure. SEM study of the fiber morphology has shown that PCM is in the form of slugs along the fibers. Such PCM distribution is maintained until the first melting cycle, when molten PCM spreads within the fiber under capillary forces, which was observed by an infrared camera. Manufactured composite fibers have shown low thermal conductivity and high elasticity, which suggest their potential application as a thermal insulation material with thermal buffer properties. Leakage tests revealed outstanding retention capacity with only 3.5% mass loss after 1000 melting/crystallization cycles. Finally, tensile tests were carried out to evaluate the mechanical properties of the fibers before and after thermal cycling.

PMMA or PVDF films blended with β-diketonate tetrakis EuIII or TbIII complexes used as downshifting coatings of near-UV LEDs

Luminescent Ln^III complexes incorporated in polymeric films exhibit narrow emission bands and absorption within the near-UV/blue spectral range, and enhanced phostability, which qualify them to be explored for solid-state lighting. Herein, (C₂₆H₅₆N)[Eu(dbm)₄] and Na[Tb(acac)₄], (C₂₆H₅₆N⁺ = didodecyldimethylammonium, dbm^- =1,3-diphenyl-1,3-propanedionate, acac^- = acetylacetonate), were dispersed in PMMA or PVDF films to protect them from degradation, and the obtained blends were applied as downshifting coatings on near-UV emitter LEDs. Upon such excitation, both Eu^III and Tb^III complexes emit red or green light with absolute emission quantum yields of 6.4 and 99%, respectively. The complex amount within films influences the photophysical parameters due to multiphotonic deactivation, and formation of agglomerates. For the PMMA-based LED prototypes, the Ln^III emission is well-observed while for the PVDF ones, only a poor Ln^III emission is detected due to their opacity. Therefore, the PMMA-based systems are better candidates to be used as luminescent coatings of near-UV LEDs for solid-state lighting.

Investigation of antifouling properties of polypropylene/TiO2 nanocomposite membrane under different aeration rate in membrane bioreactor system

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PP/TiO₂ membrane was fabricated via thermally induced phase separation (TIPS) method.

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Effect of aeration rate was investigated on antifouling properties of both membranes in MBR system.

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Fouling properties of membranes under different aeration rates were analyzed using Hermia’s models.

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Nanocomposite membrane showed high antifouling compared to neat membrane.

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Increasing in high aeration rate resulted in sludge floc breakage as well as pore blockage.

This paper presents the results of aeration rate effect on antifouling properties of polypropylene (PP)/TiO₂ nanocomposite membrane in membrane bioreactor (MBR) system in order to oil refinery wastewater treatment. For this purpose, three levels of aeration rate with specific aeration demand per membrane area (SADm) of 0.5, 1, and 1.5 m³/m²h was used. According to the obtained results, PP nanocomposite membrane showed high hydrophilicity, porosity, and high flux compared to neat PP membrane. Also, either low or high aeration rate had a negative influence on permeability and antifouling properties of neat PP and nanocomposite membranes. The analysis of fouling mechanism for both membranes based on Hermia’s model revealed that the cake formation is dominant mechanism for lower aeration rate while by increasing aeration rate, all models couldn’t predict experimental data. Meanwhile, by increasing aeration rate, chemical oxygen demand (COD) removal for activated sludge and both membranes decreased and increased, respectively.

Fabrication of a biconnected structure PVB porous heddle via thermally induced phase separation

Herein, a porous heddle of poly(vinyl butyral) (PVB) was successfully prepared by thermally induced phase separation with PEG400. A phase diagram of PVB was presented, and the effects of various parameters, such as polymer concentration, extrusion temperature, quenching temperature and take-up speed, on the morphology and properties of the PVB porous heddle were investigated. The pore size and porosity of the heddle increase as the extrusion temperature increases. Furthermore, upon increasing the quenching temperature during the TIPS process, the pore size and mechanical properties decrease, whereas porosity increases. In addition, due to the substantially unchanged crystallinity of the PVB heddle, the tensile strength increases since porosity decreases with the increasing take-up speed. The porosity of the prepared PVB porous heddle reached up to 74.63% when the PVB concentration, the quenching temperature and the extrusion temperature were 20 wt%, 0 °C and 170 °C, respectively. Thus, this porous heddle exhibiting a biconnected structure and significant mechanical properties is promising in the field of porous carrier materials.