The pyromellitic dianhydride（PMDA） crosslinked poly（vinyl alcohol）（PVA） was coated on top of the PAN ultrafiltration membrane to form a PVA/PAN composite PV membranes for wastewater desalination. The composite m...The pyromellitic dianhydride（PMDA） crosslinked poly（vinyl alcohol）（PVA） was coated on top of the PAN ultrafiltration membrane to form a PVA/PAN composite PV membranes for wastewater desalination. The composite membranes have high application value in industrial wastewater treatment. By varying the membrane fabrication parameters including the weight percent（wt%） of the PMDA, the crosslink temperature and duration, membrane with the best desalination performance was obtained. The composite membrane with a 2-lm-thick PVA selective layer containing 20 wt% of PMDA and being crosslinked at 100 °C for 2 h showed the highest Na Cl rejection of 99.98% with a water flux of 32.26 L/（m^2 h）at 70 °C using the 35,000 ppm Na Cl aqueous solution as feed. FTIR spectroscopy, wide-angle X-ray diffraction, thermogravimetric analysis and scanning electron microscope have been used to characterize the structures and properties of both the crosslinked PVA dense films and PVA/PAN composite membranes. The effects of the concentrations of PMDA,the crosslinking time and temperature to the membrane water contact angle, swelling degree, salt rejection and water flux were systematically studied.展开更多
Partially replacing polyvinyl-alcohol(PVA)fibers with polypropylene(PP)fibers in strain-hardening cementitious composites(fiber hybridization)modify certain mechanical properties of these materials.The hybridization b...Partially replacing polyvinyl-alcohol(PVA)fibers with polypropylene(PP)fibers in strain-hardening cementitious composites(fiber hybridization)modify certain mechanical properties of these materials.The hybridization based on the introduction of low-modulus hydrophobic polypropylene fibers improves the ductility and the strain-hardening behavior of the cementitious composites containing polyvinyl-alcohol fibers of different types(PVA-SHCC).Pull-out tests indicate that adding PP fibers increases the energy capacity of the hybrid composite with respect to the material containing only PVA fibers under tensile loading,and PP-fiber geometry(i.e.,section shape and length)is a key factor in enhancing the strain capacity.展开更多
Silver nanoparticles were synthesized by chemical reduction method. The Ag nanoparticles (AgNP) were characterized using UV-Vis spectroscopy which shows an absorption band at 420 nm confirming the formation of nanopar...Silver nanoparticles were synthesized by chemical reduction method. The Ag nanoparticles (AgNP) were characterized using UV-Vis spectroscopy which shows an absorption band at 420 nm confirming the formation of nanoparticles. For any practical application of the silver nanoparticles it is necessary to stabilize it which can be done by making a composite. In the present studies three polymers were chosen such that AgNP could be put to some practical use. Polyvinyl Alcohol (PVA), Polypyrrole (Ppy) and Carboxymethyl cellulose (CMC) are important for use in textiles, electronics and food/drug technologies respectively. Polymeric composites of PVA, PPy, and CMC were prepared by mixing the aqueous solutions of the respective polymers and the colloidal suspension of preformed silver nanoparticles. Various compositions containing 1% to 5% of Ag nanoparticles were prepared. Thin films of these composites were characterized by UV-Vis spectroscopy, X-ray diffraction and Scanning electron microscopy. X-ray diffraction showed the presence of the peaks at 2θ values of 38.1°, 44.2°, 64.4 and 78.2° corresponding to cubic phase of silver metal. SEM photographs revealed the presence of Ag nanoparticles of sizes varying from 40 to 80 nm. The electrical conductivity of these materials was studied using the four probe method. The conductivity was found to increase from 10–6 for control samples to 10–3 S/cm after the formation of the nanocomposites.展开更多
The texture of interfacial zone between cement paste and quartz in the cement-based composites containing polyvinyl alcohol (PVA), methylcellulose (MC) and their potyblend in an amount of 10 wt % with respect to cemen...The texture of interfacial zone between cement paste and quartz in the cement-based composites containing polyvinyl alcohol (PVA), methylcellulose (MC) and their potyblend in an amount of 10 wt % with respect to cement, as well as the texture of dehydrated bodies of PVA, MC, and the potyblend solutions, were investigated with SEM. The network texture of the dehydrated polyblend is confirmed by comparing the texture of dehydrated bodies of PVA and MC. The network texture has restrained the movement of polyblend molecules in the cement mortar but is helpful to forming a coherent interface between cement paste and quartz. The key factor of forming the coherent interface is not the neutralization reaction between H + from hydrolysis of quarts: and OH- from hydration of cement, but the electrostatic attraction and the chemical reaction between polar groups on the polyblend molecule and cations and onions from hydrolysis of quartz and hydration of cement, respectively. The model of the coherent interface formation is that excessive [HSiO3]- and [SiO3]2- onions are bonded with the hydrated cations such as Ca2+ and Al3+ , which is confirmed by the gel containing Ca and Si on the quartz surface.展开更多
基金supported by the Higher Education and High-quality and World-class Universities (PY201618)the National Natural Science Foundation of China (Contract Grant Number 51373014)the National Natural Science Foundation of China (Contract Grant Number 51403012)
文摘The pyromellitic dianhydride（PMDA） crosslinked poly（vinyl alcohol）（PVA） was coated on top of the PAN ultrafiltration membrane to form a PVA/PAN composite PV membranes for wastewater desalination. The composite membranes have high application value in industrial wastewater treatment. By varying the membrane fabrication parameters including the weight percent（wt%） of the PMDA, the crosslink temperature and duration, membrane with the best desalination performance was obtained. The composite membrane with a 2-lm-thick PVA selective layer containing 20 wt% of PMDA and being crosslinked at 100 °C for 2 h showed the highest Na Cl rejection of 99.98% with a water flux of 32.26 L/（m^2 h）at 70 °C using the 35,000 ppm Na Cl aqueous solution as feed. FTIR spectroscopy, wide-angle X-ray diffraction, thermogravimetric analysis and scanning electron microscope have been used to characterize the structures and properties of both the crosslinked PVA dense films and PVA/PAN composite membranes. The effects of the concentrations of PMDA,the crosslinking time and temperature to the membrane water contact angle, swelling degree, salt rejection and water flux were systematically studied.
文摘Partially replacing polyvinyl-alcohol(PVA)fibers with polypropylene(PP)fibers in strain-hardening cementitious composites(fiber hybridization)modify certain mechanical properties of these materials.The hybridization based on the introduction of low-modulus hydrophobic polypropylene fibers improves the ductility and the strain-hardening behavior of the cementitious composites containing polyvinyl-alcohol fibers of different types(PVA-SHCC).Pull-out tests indicate that adding PP fibers increases the energy capacity of the hybrid composite with respect to the material containing only PVA fibers under tensile loading,and PP-fiber geometry(i.e.,section shape and length)is a key factor in enhancing the strain capacity.
文摘Silver nanoparticles were synthesized by chemical reduction method. The Ag nanoparticles (AgNP) were characterized using UV-Vis spectroscopy which shows an absorption band at 420 nm confirming the formation of nanoparticles. For any practical application of the silver nanoparticles it is necessary to stabilize it which can be done by making a composite. In the present studies three polymers were chosen such that AgNP could be put to some practical use. Polyvinyl Alcohol (PVA), Polypyrrole (Ppy) and Carboxymethyl cellulose (CMC) are important for use in textiles, electronics and food/drug technologies respectively. Polymeric composites of PVA, PPy, and CMC were prepared by mixing the aqueous solutions of the respective polymers and the colloidal suspension of preformed silver nanoparticles. Various compositions containing 1% to 5% of Ag nanoparticles were prepared. Thin films of these composites were characterized by UV-Vis spectroscopy, X-ray diffraction and Scanning electron microscopy. X-ray diffraction showed the presence of the peaks at 2θ values of 38.1°, 44.2°, 64.4 and 78.2° corresponding to cubic phase of silver metal. SEM photographs revealed the presence of Ag nanoparticles of sizes varying from 40 to 80 nm. The electrical conductivity of these materials was studied using the four probe method. The conductivity was found to increase from 10–6 for control samples to 10–3 S/cm after the formation of the nanocomposites.
基金Funded by Natural Science Foundation of China (No. 49802004)
文摘The texture of interfacial zone between cement paste and quartz in the cement-based composites containing polyvinyl alcohol (PVA), methylcellulose (MC) and their potyblend in an amount of 10 wt % with respect to cement, as well as the texture of dehydrated bodies of PVA, MC, and the potyblend solutions, were investigated with SEM. The network texture of the dehydrated polyblend is confirmed by comparing the texture of dehydrated bodies of PVA and MC. The network texture has restrained the movement of polyblend molecules in the cement mortar but is helpful to forming a coherent interface between cement paste and quartz. The key factor of forming the coherent interface is not the neutralization reaction between H + from hydrolysis of quarts: and OH- from hydration of cement, but the electrostatic attraction and the chemical reaction between polar groups on the polyblend molecule and cations and onions from hydrolysis of quartz and hydration of cement, respectively. The model of the coherent interface formation is that excessive [HSiO3]- and [SiO3]2- onions are bonded with the hydrated cations such as Ca2+ and Al3+ , which is confirmed by the gel containing Ca and Si on the quartz surface.
