Wang Huajun,He Junwei,Zou Liming,Wang Chao,Wang Yanli
PVA fibers with high strength and high modulus are very attractive in many potential applications. However, there is a difficulty when enhancing the strength and modulus of PVA fibers. To overcome this difficulty, here we report a method to enhance the strength and modulus of PVA fibers by synthesis of high polymerization degree (DP) and high syndiotacticity diad content (S-diad) PVA polymers with vinyl acetate (VAc)/ vinyl propionate (VPa) as monomers via non-emulsifier emulsion polymerization. The synthesized PVA polymers with different mass ratio of VAc/VPa were characterized by fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance ( 1 H-NMR) and gel permeation chromatography (GPC), it demonstrated that the ratio of VPa monomer has a significant effect on the DP and S-diad of PVA polymers. In addition, a series of PVA fibers have been fabricated using the synthesized polymers by wet spinning method, and the mechanical and thermal properties of PVA fibers have been investigated by tensile tester, differential scanning calorimeter (DSC), thermogravimetric analyzer (TGA), X-ray diffractometer (XRD) and field emission scanning electron microscope (FE-SEM), and it found that there is a substantial increase in strength and modulus of PVA fibers with the increase of DP and S-diad of PVA polymer. However, too high DP and S-diad of PVA polymers had an opposite effect on the spinning fluid, spinnability and properties of PVA fibers.
Huajun Wang,Junwei He,Liming Zou,Chao Wang,Yan Vivian Li
Different vinyl acetate (VAc) and vinyl benzoate (VBz) monomer ratios have been chosen as monomers to create high polymerization degree ( P n ) and high syndiotacticity-diad content ( S-diad ) poly(vinyl alcohol) (PVA) polymers via emulsifier-free polymerization in order to address the problem of limited mechanical capabilities of PVA fibers prepared with low P n and low S-diad polymer. The variations in hydrogen bonding, P n , S-diad , and viscosity of different PVA polymers were investigated and evaluated using Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, gel permeation chromatography, and a viscosity tester. Moreover, various PVA fibers with high strength and modulus have been manufactured using a synthetic polymer as the raw material for dry-wet spinning. The effect of P n and S-diad on the mechanical and thermal characteristics of PVA fibers is evaluated using a variety of characterization techniques, such as the scanning electron microscope, differential scanning calorimetry, thermogravimetric analyzer, X-ray diffraction, and tensile tester. As the ratio of VBz monomer increased, the results suggested that VBz may have a considerable impact on the P n and S-diad of PVA polymers, the OH vibration absorption peak reduced from 3491 to 3442 cm −1 ; the P n increased from 2112 to 17,704; and the S-diad rose from 51.2% to 60.1%. In addition to the fact that P n and S-diad significantly increased the fibers' strength and modulus, the crystallinity increased from 41.8% to 51.7%, and the orientation degree rose from 87.5% to 91.7%, as P n and S-diad increased; the tensile strength and highest elastic modulus increased from 9.71 ± 0.3 cN/dtex to 12.74 ± 0.5 cN/dtex (increased of 31.2%) and 264.52 ± 9.3 cN/dtex to 338.41 ± 8.6 cN/dtex (increased of 27.9%); the elongation at break decreased from 5.63 ± 0.3% to 2.92 ± 0.2%.
Bing Shang,Yaqiong Dong,Bo Feng,Jingyan Zhao,Zhi Wang,Debbie C. Crans,Xiaoda Yang
Background and Purpose Metal-based therapeutic agents are limited by the required concentration of metal-based agents. Hereby, we determined if combination with 17β-oestradiol (E2) could reduce such levels and the therapy still be effective in type 2 diabetes mellitus (T2DM). Experimental Approach The metal-based agent (vanadyl acetylacetonate [VAC])– 17β-oestradiol (E2) combination is administered using the membrane-permeable graphene quantum dots (GQD), the vehicle, to form the active GQD–E2–VAC complexes, which was characterized by fluorescence spectra, infrared spectra and X-ray photoelectron spectroscopy. In db / db type 2 diabetic mice, the anti-diabetic effects of GQD–E2–VAC complexes were evaluated using blood glucose levels, oral glucose tolerance test (OGTT), serum insulin levels, homeostasis model assessment (homeostasis model assessment of insulin resistance [HOMA-IR] and homeostasis model assessment of β-cell function [HOMA-β]), histochemical assays and western blot. Key Results In diabetic mice, GQD–E2–VAC complex had comprehensive anti-diabetic effects, including control of hyperglycaemia, improved insulin sensitivity, correction of hyperinsulinaemia and prevention of β-cell loss. Co-regulation of thioredoxin interacting protein (TXNIP) activation by the combination of metal complex and 17β-oestradiol contributed to the enhanced anti-diabetic effects. Furthermore, a potent mitochondrial protective antioxidant, coniferaldehyde, significantly potentiates the protective effects of GQD–E2–VAC complexes. Conclusion and Implications A metal complex–E2 combinatorial approach achieved simultaneously the protection of β cells and insulin enhancement at an unprecedented low dose, similar to the daily intake of dietary metals in vitamin supplements. This study demonstrates the positive effects of combination and multi-modal therapies towards type 2 diabetes treatment. Graphical
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