Mengjuan Li

Chemical recycling of waste poly(ethylene terephthalate) fibers into azo disperse dyestuffs

In this study, waste poly(ethylene terephthalate) (PET) fibers were chemically recycled into azo disperse dyestuffs. First, waste PET fibers were glycolytically degraded by excess ethylene glycol utilizing zinc acetate dehydrate as a catalyst. The glycolysis product, bis(2-hydroxyethyl) terephthalate (BHET), was purified through recrystallization and hydrolyzed into terephthalic acid (TPA). Thereafter, BHET and TPA were nitrated, reduced and azotized to obtain diazonium salts. Finally, the obtained diazonium salts were coupled with N,N-dimethylaniline to obtain azo disperse dyestuffs (dye A and dye B, respectively). The depolymerized products (BHET and TPA) and azo disperse dyestuffs (dyes A and B) were characterized by FTIR and 1H NMR spectroscopy. Nylon and polyester filaments were dyed with the synthesized azo dyestuffs with the dye bath pH ranging from 3.6 to 5.8. The performances of the dyestuffs were described by maximum absorption wavelength, K/S, L*, a* and b* values.

Polyaniline-doped TiO2/PLLA fibers with enhanced visible-light photocatalytic degradation performance

A simple and practical strategy has been developed for preparing polyaniline(PANi)-doped TiO2/poly(l-lactide) (P@TiP-C) fibers by a combination of coaxial-electrospinning and in-situ polymerization. The TiO2/PLLA composite fibers with TiO2 located on the surface were fabricated by coaxial-electrospinning, with PLLA as the core phase and a dispersion of TiO2 particles, a well-known photocatalyst, in the sheath phase. The aniline monomers were also located in the core phase and in-situ polymerized by ammonium persulfate (APS) after electrospinning. SEM images show that TiO2 particles were located on the surface of PLLA fibers. Photocatalytic degradation tests show that the P@TiP-C fibers exhibit enhanced photocatalytic activity for degradation of methyl orange under visible light, likely due to the synergistic effect of PANi and TiO2.

A high molecular weight acrylonitrile copolymer prepared by mixed solvent polymerization: I. effect of monomer feed ratios on polymerization and stabilization

A bifunctional comonomer β-methylhydrogen itaconate was synthesized to prepare high molecular weight poly [acrylonitrile-co-(β-methylhydrogen itaconate)] [P (AN-co-MHI)] by mixed solvents polymerization, which was used as carbon fiber precursor instead of acrylonitrile terpolymers. The effect of dimethyl sulfoxide (DMSO)/deionized water ratios on the polymerization, structure and stabilization of P (AN-co-MHI) was studied by elemental analysis, UV-Visible Spectroscopy, fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The highest viscosity-average molecular weight (76.72 × 104 g/mol) of P(AN-co-MHI) was obtained in the mixed solvents of DMSO/deionized water = 10/90 (wt/wt) due to the zero chain transfer constant of deionized water for radical ~ ~ ~AN·, which is 10 times larger than that of P(AN-co-MHI) copolymers prepared in DMSO solution polymerization under the same conditions and is beneficial to improving the tensile strength of resulting carbon fiber. The composition of P(AN-co-MHI) was controlled by the ratio of DMSO/deionized water in the mixed solvents, it is attributed to the changes of AN/MHI ratio taking part in the polymerization reactions, which is caused by the different solubility of AN in the mixed solvents. From elemental analysis and FTIR studies, it can be found out that the content of MHI in P(AN-co-MHI) copolymer becomes larger with the increase of DMSO content in the mixed solvents. The FTIR, XRD and DSC results show that the stabilization of P(AN-co-MHI) copolymer was significantly improved by MHI compared with PAN homopolymer and poly (acrlonitrile-methyl acrylate-acrylic acid) terpolymer, such as larger extent of stabilization, lower initiation temperature and smaller Ea of cyclization, which is beneficial to preparing high performance carbon fiber.

Preparation of Polyaniline/Filter-Paper Composite for Removal of Coomassie Brilliant Blue

Polyaniline/filter-paper (PANI/FP) composite was prepared by in-situ polymerization of polyaniline onto filter-paper and subsequently evaluated for the removal of Coomassie brilliant blue (CBB) from aqueous solution. Scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Fourier-transform infrared (FTIR) spectroscopy were used to investigate the morphology and physicochemical properties of PANI/FP composite. Batch experimental results showed that the pH value and temperature could affect the removal capability of the PANI/FP composite. Langmuir and Freundlich models were used to analyse the equilibrium adsorption. Pseudo-first and pseudo-second order models were used to investigate the kinetics of CBB adsorption onto PANI/FP composite.

Decoloration of waste PET alcoholysis liquid by an electrochemical method

Disperse Red 60 simulated polyester alcoholysis liquid decoloration by electro-Fenton with Fe3O4 catalyst was studied. The influences of the main operating parameters such as catalyst dosage (0.3-0.9 g/L), current density (60-120 mA/cm2) and pH (1-7) were optimized by response surface methodology (RSM) based on Box-Behnken surface statistical design (BBD). In optimal conditions, the initial concentration of 25 mg/L disperse red polyester alcoholysis liquid was catalyzed by 0.6 g/L Fe3O4, and the decoloration efficiency was 97.18% with the current density of 90 mA/cm2 and initial pH of 4.6. There was a relative error of 1.18% with the predicted model when the predictive value was 98.25% under the same conditions. In addition, ultraviolet-visible absorption spectra (UV-Vis), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to study the degradation mechanism during decoloration. The intermediates were identified and the proposed degradation pathways were investigated by liquid chromatography-mass spectrometry (LC-MS) analysis.

Synthesis and sizing performances of water-soluble polyester based on bis(2-hydroxyethyl) terephthalate derived from depolymerized waste poly(ethylene terephthalate) fabrics

This work aimed at effective chemical recycling of waste poly(ethylene terephthalate) (PET) fabrics into water-soluble polyester (WSP). For this, PET fabric waste was depolymerized using excess ethylene glycol (EG) in the presence of zinc acetate as catalyst. The glycolysis product of PET, bis(2-hydroxyethyl) terephthalate (BHET) was then used to synthesize WSP by a three-step method, that is, transesterification, esterification and polycondensation. The structures of BHET and WSP were identified by Fourier transform infrared spectra. Sizing performances of WSP were studied, and it was found that the surface tension of WSP size (57 mN/m, 22℃, 0.5% of weight) was lower than common sizes, the viscosity of WSP size was 1–2 mPa·S (95℃, 6% of weight) and the viscosity stability was larger than 90% at this temperature. The mixture of WSP and starch showed stronger adhesion to polyester–cotton roving and polyester roving than onefold starch. K/S values of fibers before sizing and after desizing showed a slightly difference, which indicated that WSP would not influence the color of yarns when used as the sizing agent.

Adsorption and catalytic oxidation of poly(vinyl alcohol) textile by MnxOy/γ-Al2O3 nanoparticle catalyst:

Mn x O y /γ-Al2O3 nanoparticles were prepared by a wet impregnation–calcination method and characterized using X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, scanning electron microscopy, energy dispersive spectrometry, and gel permeation chromatography. The heterogeneous Fenton-like process with appropriate amounts of Mn x O y /γ-Al2O3 as catalyst was observed. The variation in polyvinyl alcohol removal rate as a function of calcination temperature, adsorption temperature, Mn x O y /γ-Al2O3 dosage, H2O2 dosage, and initial polyvinyl alcohol concentration was investigated. Results showed that polyvinyl alcohol can be removed by the adsorption of Mn x O y /γ-Al2O3; the removal ratio increased with higher adsorption temperature as well as increased Mn x O y /γ-Al2O3 dosage. Moreover, the degradation of polyvinyl alcohol was promoted by increasing calcination temperature and H2O2 dosage and decreasing initial polyvinyl alcohol concentration. In this paper, Mn x O y /γ-Al2O3 nanoparticles were able to remove more than 90% polyvinyl alcohol at an initial concentration below 50 g/L, temperature of 80℃, pH of 3.0, and H2O2 and catalyst doses of 120 mL/L and 1 g/L, respectively. Gel permeation chromatography also confirmed that polyvinyl alcohol could be effectively oxidized with a molecule decreasing rate of about 99%, from 100,773 to 1637. The nanocatalyst could be recycled by filtration and calcination, and maintained favorable catalytic ability during four uses.

Degradation and kinetic modeling of polyvinyl alcohol in aqueous solutions by a H 2 O 2 /Mn(II) system

This paper is about the degradation of polyvinyl alcohol (PVA) in aqueous solutions using a H2O2/Mn(II) system. Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) were applied to analyze the degradation products of PVA, and the results revealed that the backbone chain of PVA could be effectively broken and oxidized. Several unsaturated degradation products, including carboxylic acids, ketones, aldehydes, olefins, and alkynes were also detected and identified by gas chromatography-mass spectrometry (GC-MS), which indicated that higher treatment temperatures would considerably promote the generation of lower molecular weight degradation products. According to the work presented in this paper, the degradation efficiency of PVA increased from 55 % at 60 oC to 99 % at 90 oC after treatment when the initial PVA concentration was 5 %, at pH=3 with a H2O2 and Mn(II) dose of 100 ml/l and 0.6 mol/l, respectively. In addition, kinetic modeling indicated that the experimental results were best fitted by the Page-modified model with an activation energy of 48.78 kJ/mol.