Yanzhi Xia

Synthesis, Rapid Responsive Thickening, and Self-Assembly of Brush Copolymer Poly(ethylene oxide)-graft-Poly(N,N-dimethylaminoethyl methacrylate) in Aqueous Solutions

Double hydrophilic brush copolymer poly(ethylene oxide)-graft-poly(N,N-dimethylaminoethyl methacrylate) (PEO-g-PDMAEMA) was successfully prepared via atom transfer radical polymerization (ATRP). We investigated the pH/thermoresponsive behaviors of PEO-g-PDMAEMA brush-shaped copolymer concentrated aqueous solutions by rheology. The observed LCST strongly decreased with increasing pH of the solutions, which was lower than that of linear block copolymer for different pH, indicating rapid thermoresponsiveness of the brush PDMAEMA chains. An unexpected shear thickening behavior was observed and could be tuned by the pH, resulting from the mobile nature and tractive force of the densely grafted hydrophobic chains of PDMAEMA at high pH. Self-assembly of the brush copolymer in a different pH and ionic strength environment was studied by transmission electron microscopy. A wormlike cylinder structure was formed at low pH. Fractals were observed for the brush copolymer aqueous solution in the presence of NaCl. The results showed that by adjusting the pH and NaCl concentration of the dispersions fractal aggregates with different topology were obtained. The observations reported here can supply a better understanding of the molecular self-assembling nature and be used to develop responsive materials with better performance.

The effect of zinc ion content on flame retardance and thermal degradation of alginate fibers

The study employs limiting oxygen index (LOI) measurements, cone calorimetry (CONE) and thermogravimetric analysis (TGA) to examine the catalytic effect of zinc ion content on the flame retardance and thermal degradation of alginate fibers. LOI results show that all zinc alginate fibers are intrinsically flame retardant, with LOI values of over 27.0, as compared with about 24.5 for alginic acid fiber. The heat release rate (HRR) and total heat release values of zinc alginate fibers (obtained from CONE) are significantly less than those of alginic acid fiber, and decrease with increasing zinc ion content. TGA indicates that char formation increases and maximum thermal weight-loss rate is reduced when zinc content in the fibers is increased. The residues of zinc alginate fibers keep their shapes better than those of the alginic acid fiber. Further discussion of the combustion process and flame retardant mechanism is presented.

Influence of Na(+) and Ca(2+) on flame retardancy, thermal degradation, and pyrolysis behavior of cellulose fibers.

Flame-retardant cellulose-Na and cellulose-Ca fibers were successfully synthesized by grafting Na+ and Ca2+ onto cellulose fibers, and confirmed by FTIR. The combustion behavior of the fibers was assessed by the limiting oxygen index (LOI) and cone calorimeter (CONE). The maximum LOI values of cellulose-Na and cellulose-Ca fibers were 31 and 30, which are higher than that (19) of cellulose fibers. The CONE results showed that the values of heat-release rate and total heat release for cellulose-Na and cellulose-Ca fibers were significantly lower than those for cellulose fibers. The thermogravimetric analysis (TG) and differential thermogravimetric analysis (DTG) curves in the continuous and trigger modes showed that the cellulose-Na and cellulose-Ca fibers generated more residues than cellulose fibers. Thermogravimetric analysis-gas chromatography-mass spectrometry was used to detect the characteristic gases produced in the pyrolysis of cellulose-Na and cellulose-Ca fibers.

Functionalized alginate with liquid-like behaviors and its application in wet-spinning

Alginate is a kind of marine-derived plant polysaccharide with useful properties including inherent flame-retardancy and biocompatibility, yet poor flowability and low processing efficiency induced by high viscosity impede its further industrial applications. In this study, PEG-substituted tertiary amines were adapted to functionalize alginate with different molecular weight via acid-base reaction to improve the flowability. Based on alginate with low molecular weight, alginate fluids exhibited excellent flowability at room temperature in the absence of solvent. For alginate with high molecular weight, gelatinous precipitated phase exhibited significant shear-thinning properties and higher solid content despite lack of solvent-free flowability, which was applied to wet-spinning. The alginate fibers exhibited increased tensile strength by 104% and elongation at break by 132% compared with conventional alginate fibers, and the spinning efficiency was significantly improved. The proposed strategy is expected to extend to highly efficient processing of other polysaccharides to obtain high-performance biomedical materials.

Pyrolysis products and thermal degradation mechanism of intrinsically flame-retardant carrageenan fiber

Carrageenan fiber (CAF) was prepared by a wet spinning method to develop an excellent flame-retardant material. In order to investigate the flame-retardant mechanism of CAF, a series of tests were carried out. The values of limiting oxygen index (LOI), total heat release (THR), and total smoke release (TSR) of CAF reached up to 52, 2.9 MJ m−2, and 2.5 m2 m−2, respectively, while there was no Time To Ignition (TTI) in cone calorimeter (CONE). These results indicate that CAF exhibits superior flame-retardant performance than other alginate fibers. Thermogravimetry, differential scanning calorimetry, Fourier transform infrared spectroscopy (TG-DSC-FTIR) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) tests were performed in order to explore the pyrolysis mechanism. The results show that CAF absorbed more heat and produced more carbon residue than calcium alginate fiber (ALF) and agar fiber (AGF) in the process of thermal degradation. In addition, in the current work, we have explored the possible flame-retardant mechanisms which can be attributed to sulfonyl free radical (SFR), carbon residue, barium sulfate, water vapor, and carbon dioxide.

Synthesis of Co/Co3O4 nanoparticles embedded in porous carbon nanofibers for high performance lithium-ion battery anodes

Co/Co3O4-carbon nanofibers (Co/Co3O4-CNFs) with porous structure were prepared using pyrolysis electrospinning cobalt alginate nanofibers (CoA-NFs) derived from brown algae as the raw material. The phase structure and morphology were analyzed by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate Co/Co3O4 nanoparticles with a diameter of about 30–50xa0nm were embedded in the carbon nanofibers. As anode material for lithium-ion battery (LIBs), the Co/Co3O4-CNFs exhibited a high reversible capacity of 720xa0mAhxa0g−1, excellent stability (i.e. 710xa0mAhxa0g−1 at 0.5xa0C over 100 cycles) and good rate performance (310xa0mAhxa0g−1 at a rate of 5xa0C).

Influence of alkaline metal ions on flame retardancy and thermal degradation of cellulose fibers

Cellulose-Na and cellulose-K fibers are obtained by alkalization and etherification of viscose fiber. Flame retardancy and thermal degradation of cellulose-Na and cellulose-K fibers are investigated using limiting oxygen index (LOI), cone calorimetry (CONE), thermal gravimetry (TG), and differential TG (DTG). The LOI values of cellulose-Na and cellulose-K fibers are 33 and 30, compared with about 20 for viscose fiber. In CONE studies, cellulose-Na and cellulose-K fibers show much lower heat release rates, total heat release and effective heats of combustion than viscose fiber does. In addition, TG and DTG studies reveal that the second initial degradation temperature, the temperature of maximum degradation rate and the maximum degradation rate for cellulose-Na and cellulose-K fibers are much lower than those of viscose fiber. Cellulose-Na and cellulose-K fibers generate much more residue or carbonaceous char than viscose fiber does. Scanning electron microscopy studies of combustion residues after LOI testing indicate that cellulose-Na and cellulose-K fibers produce massive, thick residue crusts.

Preparation of carrageenan fibers with extraction of Chondrus via wet spinning process

Traditionally, the carrageenan fibers were prepared by process of extracting, drying, dissolving of carrageenan power and wet spinning process of fibers. However, in this study, carrageenan fibers were prepared by carrageenan solution directly from the extraction of Chondrus, without the steps of precipitation, and drying. The properties of carrageenan powder, spinning solution and carrageenan fibers were characterized with zeta potential, NMR, FTIR, dynamic light scattering (DLS), SEM, tensile testing and energy dispersive spectrometer (EDS). The results showed that the Chondrus contained mainly iota-carrageenan. The extraction of Chondrus was a uniform liquid with good properties of a solution, which was suitable as a spinning solution. The so prepared carrageenan fibers possessed good morphology and tensile properties. The excellent tensile properties of the carrageenan fibers were attributed to the combination of sulfate ester in the carrageenan and barium ions in the coagulation and then form a three-dimensional network structure.

Facile Synthesis of Gold Nanoparticles with Alginate and Its Catalytic Activity for Reduction of 4-Nitrophenol and H2O2 Detection

Gold nanoparticles (AuNPs) were synthesized using a facile solvothermal method with alginate sodium as both reductant and stabilizer. Formation of AuNPs was confirmed by UV-vis spectroscopic analysis. The synthesized AuNPs showed a localized surface plasmon resonance at approximately 520–560 nm. The AuNPs were characterized using transmission electron microscopy, X-ray diffraction and dynamic light scattering. Transmission electron microscopy revealed that the AuNPs were mostly nanometer-sized spherical particles. Powder X-ray diffraction analysis proved the formation of face-centered cubic structure of Au. Catalytic reduction of 4-nitrophenol was monitored via spectrophotometry using AuNPs as catalyst, and further a non-enzymatic sensor was fabricated. The results demonstrated that AuNPs presented excellent catalytic activity and provided a sensitive response to H2O2 detection.

Flame Retardancy and Non-isothermal Crystallization Behaviour of PET/TiO2 Nanocomposites

Titanium dioxide particles (TiO2) have been melt-compounded with poly(ethylene terephthalate) (PET) by using a twin-screw extruder to prepare PET/TiO2 nanocomposites. The flame retardancy and non-isothermal crystallization behaviour of PET and PET/TiO2 nanocomposites have been studied using several techniques. The effects of TiO2 on the combustion behaviour of PET/TiO2 nanocomposites were analyzed by CONE and SEM. The results showed that the HRR, THR and TSR of nanocomposites was reduced significantly. The char residues were examined using scanning electron microscopy, indicating that TiO2 addition produced consistent and compact char crusts. The non-isothermal crystallization behaviour of PET and PET/TiO2 were investigated by differential scanning calorimetry (DSC). Meanwhile, the kinetics of non-isothermal crystallization was analyzed by the Mo Zhishen method. Both results showed that the TiO2 in PET acted as an effective nucleation agent. Not only was the crystallization rate of composites obtained higher than that of the neat PET, but also the crystallization time of the composites obtained was shorter than that of the neat PET. The presence of TiO2 changed the mechanism of the nucleation and accelerated the rate of PET crystallization.