Effects of copolymerization temperatures on structure and properties of melt-spinnable acrylonitrile-methyl acrylate copolymers and fibers

Covalent organic framework functionalized smart membranes with under-liquid dual superlyophobicity for efficient separation of oil/water emulsions

The smart membrane with under-liquid dual superlyophobicity, which can achieve on-demand separation of oil/water emulsions only by simple liquid pre-wetting, is of essential value for the treatment of complicated real oil/water systems. Here, we first fabricated a stable suspension of imine-linked covalent organic framework nanospheres (TPB-DMTP-COF), and subsequently fabricated COF functionalized smart membranes with under-liquid dual superlyophobicity by immersing polyacrylonitrile-based (PAN-based) membranes into TPB-DMTP-COF nanosphere suspension. Accordingly, effective switchable separation of both oil-in-water and water-in-oil emulsions by TPB-DMTP-COF/PAN membranes can be achieved by employing pre-wetting processes (both the oil contact angle under water and the water contact angle under oil are over 150°). Specifically, the separation flux and the separation efficiency are higher than 1200 L/m2‧h and 98.0 %, and 2100 L/m2‧h and 97.4 % for the surfactant-stabilized oil-in-water and water-in-oil emulsions, respectively. Furthermore, the ultralow adhesions in liquid contributed to the outstanding reusability and antifouling resistance of the prepared TPB-DMTP-COF/PAN membranes. This work provides a feasible approach for fabricating a smart membrane with under-liquid dual superlyophobicity for oily wastewater treatment.

The Photocatalysis-Enhanced TiO2@HPAN Membrane with High TiO2 Surface Content for Highly Effective Removal of Cationic Dyes

The elimination of dye pollutants from wastewater is a significant concern that has prompted extensive research into the development of highly efficient photocatalytic membranes. A novel method was proposed to prepare photocatalysis-enhanced poly(acrylonitrile-methyl acrylate) (PAN-based) membranes in this study. In detail, the blended membrane containing SiO₂@TiO₂ nanoparticles with a shell-core structure was first prepared via thermal-induced phase separation. The SiO₂ nanoshells were dissolved, and the released TiO₂ nanoparticles migrated to the membrane surface during a simple hydrolysis process, which prevents the TiO₂ nanoparticles from directly contacting or interacting with the polymer matrix. The hydrogen bonds bind the exposed TiO₂ with the PAN membrane surface, resulting in the formation of the TiO₂@HPAN hybrid membrane. The photocatalytic efficiency of the TiO₂@HPAN membrane doubled compared with that of nonhydrolyzed membranes. In the presence of UV light, the hybrid membrane can degrade 99.8% of methylene blue solution in less than 2 h, compared to only 86.1% for the blended membranes. Further, the TiO₂@HPAN membrane showed excellent photocatalytic activity for cationic dyes due to electrostatic attraction. Moreover, the high-flux recovery rate and recycling stability of the TiO₂@HPAN membrane lead to an excellent antifouling property. The facile preparation method proposed in this work shows extraordinary potential for the development of highly efficient selective photocatalytic materials for cationic dyes to be used in wastewater treatment applications.

Melt-Spinning of an Intrinsically Flame-Retardant Polyacrylonitrile Copolymer

Poly(acrylonitrile) (PAN) fibers have two essential drawbacks: they are usually processed by solution-spinning, which is inferior to melt spinning in terms of productivity and costs, and they are flammable in air. Here, we report on the synthesis and melt-spinning of an intrinsically flame-retardant PAN-copolymer with phosphorus-containing dimethylphosphonomethyl acrylate (DPA) as primary comonomer. Furthermore, the copolymerization parameters of the aqueous suspension polymerization of acrylonitrile (AN) and DPA were determined applying both the Fineman and Ross and Kelen and Tüdõs methods. For flame retardancy and melt-spinning tests, multiple PAN copolymers with different amounts of DPA and, in some cases, methyl acrylate (MA) have been synthesized. One of the synthesized PAN-copolymers has been melt-spun with propylene carbonate (PC) as plasticizer; the resulting PAN-fibers had a tenacity of 195 ± 40 MPa and a Young’s modulus of 5.2 ± 0.7 GPa. The flame-retardant properties have been determined by Limiting Oxygen Index (LOI) flame tests. The LOI value of the melt-spinnable PAN was 25.1; it therefore meets the flame retardancy criteria for many applications. In short, the reported method shows that the disadvantage of high comonomer content necessary for flame retardation can be turned into an advantage by enabling melt spinning.

Rheology of Polyacrylonitrile/Lignin Blends in Ionic Liquids under Melt Spinning Conditions

Lignin, while economically and environmentally beneficial, has had limited success in use in reinforcing carbon fibers due to harmful chemicals used in biomass pretreatment along with the limited physical interactions between lignin and polyacrylonitrile (PAN) during the spinning process. The focus of this study is to use lignin obtained from chemical-free oxidative biomass pretreatment (WEx) for blending with PAN at melt spinning conditions to produce carbon fiber precursors. In this study, the dynamic rheology of blending PAN with biorefinery lignin obtained from the WEx process is investigated with the addition of 1-butyl-3-methylimidazolium chloride as a plasticizer to address the current barriers of developing PAN/lignin carbon fiber precursors in the melt-spinning process. Lignin was esterified using butyric anhydride to reduce its hydrophilicity and to enhance its interactions with PAN. The studies indicate that butyration of the lignin (BL) increased non-Newtonian behavior and decreased thermo-reversibility of blends. The slope of the Han plot was found to be around 1.47 for PAN at 150 °C and decreased with increasing lignin concentrations as well as temperature. However, these blends were found to have higher elasticity and solution yield stress (47.6 Pa at 20%wt BL and 190 °C) when compared to pure PAN (5.8 Pa at 190 °C). The results from this study are significant for understanding lignin-PAN interactions during melt spinning for lower-cost carbon fibers.

Investigation of the effect of some variables on terpolymerization process of vinyl monomers in CSTR by design of experimental method

Aqueous slurry free radical terpolymerization of acrylonitrile (AN) with vinyl acetate (VAc) and a constant amount of 2-acrylamido-2-methylpropane sulfunic acid (AMPS) using K2S2O8/NaHSO3 redox initiator was carried out in a 15-l continuous stirred tank reactor at constant temperature (60°C) and atmospheric pressure. A three-level response surface method based on central composite design was applied to investigate the effect of VAc concentration (wt%) in monomer mixture, bisulfite- to-persulfate ratio in redox initiator system $\left( {\frac{{{\text{[HSO}}_3^ - ]}}{{[{{\text{S}}_2}{\text{O}}_8^{ - 2}]}}} \right)$ and bisulfite-to-monomer mixture ratio $\left( {\frac{{[{\text{HSO}}_3^ - ]}}{{{\text{AN}} + {\text{VAc}}}}} \right)$ on the monomer conversion percentage to polymer, intrinsic viscosity [(η)] and sulfur end groups (SEG) index of the prepared polymers. Experimental results showed that the optimum conditions for synthesis of AN-VAc-AMPS system can be addressed as VAc=9 wt%, $\left( {\frac{{[{\text{HSO}}_3^ - ]}}{{[{{\text{S}}_2}{\text{O}}_8^{ - 2}]}}} \right) = 9.6$ and $\left( {\frac{{[{\text{HSO}}_3^ - ]}}{{{\text{AN}} + {\text{VAc}}}}} \right) = 0.027.$ Monomer conversion percentage to polymer, intrinsic viscosity and SEG index under optimum conditions were 75%, 1.38 dl/g and 190, respectively. The synthesized polymer under these optimum conditions can satisfy the requirements for acrylic fiber production in which its characterization was confirmed with Fourier transform infrared spectroscopy, nuclear magnetic resonance, elemental analysis, X-ray diffraction, differential scanning calorimetry and scanning electron microscope.