In this study,tannic acid(TA)was investigated as flame retardant agent for PLA.Different strategies to modify its thermal degradation pathway have been explored in order to improve its charring effect.The first one co...In this study,tannic acid(TA)was investigated as flame retardant agent for PLA.Different strategies to modify its thermal degradation pathway have been explored in order to improve its charring effect.The first one consists in combining TA with organomodified montmorillonite(oMMT),and enables limiting the thermo-oxidative degradation of TA and promoting the formation of an effective char layer.Flame-retardant(FR)behavior of PLA-based composition has been found to be positively impacted by this combination since a reduction of the peak of Heat Release Rate(PHRR),more important than the value recorded when oMMT and tannic acid are used separately,has been obtained.The second strategy,in which tannic acid was associated with a biosourced phosphorousbased compounds,i.e.metallic phytate salt,evidenced another alternative allowing enhancing TA flame retardant effect at 30 wt%loading content.The third and last strategy explored aims to chemically modify TA via a chemical grafting of phosphoric acid groups.This phosphorylated TA was shown to present the most effective flame-retardant(FR)effect.However,an important reduction of PLA molecular weight was observed.展开更多
The reality of plastic pollution is no longer under debate:It has invaded our daily lives and is present all around us,with our oceans being no exception.In fact,a seventh“continent”has appeared in the oceans,compos...The reality of plastic pollution is no longer under debate:It has invaded our daily lives and is present all around us,with our oceans being no exception.In fact,a seventh“continent”has appeared in the oceans,composed of plastics and microplastics!Newspapers including Le Monde in France and The Guardian in United Kingdom recently headlined the record rate of microplastic accumulation in the Arctic Ocean.These headlines referred to an article published in Nature Communications[1]that reported the finding of up to 12000 plastic microparticles per liter of water frozen in the sea ice.Given this finding,what future solutions can counteract this particularly insidious pollution?展开更多
A class of bio-based bifunctional phthalonitrile(PN)resins composed of cinnamaldehyde derivatives,aminophenol,and end-capped with a PN moiety is detailed.The cinnamic-imine PN(CIPN)resins were synthesized by utilizing...A class of bio-based bifunctional phthalonitrile(PN)resins composed of cinnamaldehyde derivatives,aminophenol,and end-capped with a PN moiety is detailed.The cinnamic-imine PN(CIPN)resins were synthesized by utilizing environmentally friendly solvents methanol(MeOH)and acetone at ambient temperatures.Characterization of the resins was conducted via proton(1 H)and carbon(13C)nuclear magnetic resonance(NMR)spectroscopy,differential scanning calorimetry(DSC),thermogravimetric analysis(TGA),infrared spectroscopy(IR),mechanical analysis,single crystal X-ray diffraction(XRD),and rheometry.The CIPN resins were self-curing due to the vinylic,imine,and PN moieties present and displayed a range of viscosities from 153−1546 cP at 225℃.The resulting CIPN polymers were prepared by post-curing up to 380℃ and exhibited excellent thermal stability with Td5%above 510℃ up to an 80%char yield.Moderate brittleness ranging from an initial storage modulus(G′at 25℃)of 86−1295 MPa was observed among the CIPN resins.This combination of properties suggests that the bifunctional CIPN resins are excellent materials for high temperature thermosets in composite applications.展开更多
Crystal phase engineering on CulnS2(CIS)nanocrystals,especially polytypic structure,has become one of the research hotspots to design the advanced materials and devices for energy conversion and environment treatment....Crystal phase engineering on CulnS2(CIS)nanocrystals,especially polytypic structure,has become one of the research hotspots to design the advanced materials and devices for energy conversion and environment treatment.Here,the polytypic CIS nanosheets(NSs)including zincblende/wutzite and chalcopyrite/wurtzite types were first time achieved in a hot-injection system using oleic acid and liquid paraffin as the reaction media.As-obtained polytypic CIS NSs exhibit significantly enhanced light-absorption abillty and visible-light-driven photocatalytic performance originating from the rational hetero-crystalline interfaces and surface defect states,which efficiently inhibit the recombination of photo-generated carriers.Meanwhile,the polytypic CIS NSs were spin-coated onto the surface of fluorinated-tin oxide glass substrate and used as the photoelectrode,which shows an excellent photoelectrochemical(PEC)activity in aqueous solution.The present work not only provides a facile,rapid,low-cost,and environmental-friendly synthesis strategy to design the crystal phase and defect structure of ternary chalcogenides,but also demonstrates the relationships between the polytypic structure and photocatalytic/photoelectrochemical properties.展开更多
In this work,azobenzene-containing polyurethane liquid crystal networks(PULCN(AZO)s)were synthesized using a one-pot strategy to demonstrate excellent two-way free-standing thermo-/photo-responsive shape memory effect...In this work,azobenzene-containing polyurethane liquid crystal networks(PULCN(AZO)s)were synthesized using a one-pot strategy to demonstrate excellent two-way free-standing thermo-/photo-responsive shape memory effects.Based on the step-growth nature of hydroxyls and isocyanates,the architectures of the networks were adjusted by controlling the stoichiometries of chemical materials.A uniform monodomain sample was prepared by external stress relaxation via a reversible addition reaction of a dynamic carbamate bond.Two independent transition temperatures assigned to glass transition temperature/melting temperature and liquid crystal phase transition temperature were employed to thermally trigger triple shape memory effects and two-way autonomous actuation.In addition,taking advantage of the trans-cis photoisomerization of azobenzene,the programmed network showed a reversible bending and unbending shape change upon irradiation by visible light at450 and 550 nm,respectively.Coupling the autonomously thermo-induced contraction/extension actuation and reversible photo-induced bending/unbending behaviors of PULCN(AZO)s in one system will expand their potential applications in emerging multifunctional devices.展开更多
We report a novel and easily accessible method to chemically reduce graphene fluoride （GF） sheets with nanoscopic precision using high electrostatic fields generated between an atomic force microscope （AFM） tip an...We report a novel and easily accessible method to chemically reduce graphene fluoride （GF） sheets with nanoscopic precision using high electrostatic fields generated between an atomic force microscope （AFM） tip and the GF substrate. Reduction of fluorine by the electric field produces graphene nanoribbons （GNR） with a width of 105-1,800 nm with sheet resistivity drastically decreased from 〉1 TΩ.sq.^-1 （GF） down to 46 kΩ.sq.^-1 （GNR）. Fluorine reduction also changes the topography, friction, and work function of the GF. Kelvin probe force microscopy measurements indicate that the work function of GF is 180-280 meV greater than that of graphene. The reduction process was optimized by varying the AFM probe velocity between 1.2 μm.s^-1 and 12 μm.s^-1 and the bias voltage applied to the sample between -8 and -12 V. The electrostatic field required to remove fluorine from carbon is -1.6 V.nm-1. Reduction of the fluorine may be due to the softening of the C-F bond in this intense field or to the accumulation and hydrolysis of adventitious water into a meniscus.展开更多
文摘In this study,tannic acid(TA)was investigated as flame retardant agent for PLA.Different strategies to modify its thermal degradation pathway have been explored in order to improve its charring effect.The first one consists in combining TA with organomodified montmorillonite(oMMT),and enables limiting the thermo-oxidative degradation of TA and promoting the formation of an effective char layer.Flame-retardant(FR)behavior of PLA-based composition has been found to be positively impacted by this combination since a reduction of the peak of Heat Release Rate(PHRR),more important than the value recorded when oMMT and tannic acid are used separately,has been obtained.The second strategy,in which tannic acid was associated with a biosourced phosphorousbased compounds,i.e.metallic phytate salt,evidenced another alternative allowing enhancing TA flame retardant effect at 30 wt%loading content.The third and last strategy explored aims to chemically modify TA via a chemical grafting of phosphoric acid groups.This phosphorylated TA was shown to present the most effective flame-retardant(FR)effect.However,an important reduction of PLA molecular weight was observed.
文摘The reality of plastic pollution is no longer under debate:It has invaded our daily lives and is present all around us,with our oceans being no exception.In fact,a seventh“continent”has appeared in the oceans,composed of plastics and microplastics!Newspapers including Le Monde in France and The Guardian in United Kingdom recently headlined the record rate of microplastic accumulation in the Arctic Ocean.These headlines referred to an article published in Nature Communications[1]that reported the finding of up to 12000 plastic microparticles per liter of water frozen in the sea ice.Given this finding,what future solutions can counteract this particularly insidious pollution?
文摘A class of bio-based bifunctional phthalonitrile(PN)resins composed of cinnamaldehyde derivatives,aminophenol,and end-capped with a PN moiety is detailed.The cinnamic-imine PN(CIPN)resins were synthesized by utilizing environmentally friendly solvents methanol(MeOH)and acetone at ambient temperatures.Characterization of the resins was conducted via proton(1 H)and carbon(13C)nuclear magnetic resonance(NMR)spectroscopy,differential scanning calorimetry(DSC),thermogravimetric analysis(TGA),infrared spectroscopy(IR),mechanical analysis,single crystal X-ray diffraction(XRD),and rheometry.The CIPN resins were self-curing due to the vinylic,imine,and PN moieties present and displayed a range of viscosities from 153−1546 cP at 225℃.The resulting CIPN polymers were prepared by post-curing up to 380℃ and exhibited excellent thermal stability with Td5%above 510℃ up to an 80%char yield.Moderate brittleness ranging from an initial storage modulus(G′at 25℃)of 86−1295 MPa was observed among the CIPN resins.This combination of properties suggests that the bifunctional CIPN resins are excellent materials for high temperature thermosets in composite applications.
基金This work was financially supported by the Joint Foundation of National Natural Science Foundation of China(No.U1764254)321 Talent Project of Nanjing,China(No.631783)and 111 Project,China(No.D17003)
文摘Crystal phase engineering on CulnS2(CIS)nanocrystals,especially polytypic structure,has become one of the research hotspots to design the advanced materials and devices for energy conversion and environment treatment.Here,the polytypic CIS nanosheets(NSs)including zincblende/wutzite and chalcopyrite/wurtzite types were first time achieved in a hot-injection system using oleic acid and liquid paraffin as the reaction media.As-obtained polytypic CIS NSs exhibit significantly enhanced light-absorption abillty and visible-light-driven photocatalytic performance originating from the rational hetero-crystalline interfaces and surface defect states,which efficiently inhibit the recombination of photo-generated carriers.Meanwhile,the polytypic CIS NSs were spin-coated onto the surface of fluorinated-tin oxide glass substrate and used as the photoelectrode,which shows an excellent photoelectrochemical(PEC)activity in aqueous solution.The present work not only provides a facile,rapid,low-cost,and environmental-friendly synthesis strategy to design the crystal phase and defect structure of ternary chalcogenides,but also demonstrates the relationships between the polytypic structure and photocatalytic/photoelectrochemical properties.
基金supported financially by the National Natural Science Foundation of China(51773131 and 51721091)the Fundamental Research Funds for the Central Universities。
文摘In this work,azobenzene-containing polyurethane liquid crystal networks(PULCN(AZO)s)were synthesized using a one-pot strategy to demonstrate excellent two-way free-standing thermo-/photo-responsive shape memory effects.Based on the step-growth nature of hydroxyls and isocyanates,the architectures of the networks were adjusted by controlling the stoichiometries of chemical materials.A uniform monodomain sample was prepared by external stress relaxation via a reversible addition reaction of a dynamic carbamate bond.Two independent transition temperatures assigned to glass transition temperature/melting temperature and liquid crystal phase transition temperature were employed to thermally trigger triple shape memory effects and two-way autonomous actuation.In addition,taking advantage of the trans-cis photoisomerization of azobenzene,the programmed network showed a reversible bending and unbending shape change upon irradiation by visible light at450 and 550 nm,respectively.Coupling the autonomously thermo-induced contraction/extension actuation and reversible photo-induced bending/unbending behaviors of PULCN(AZO)s in one system will expand their potential applications in emerging multifunctional devices.
文摘We report a novel and easily accessible method to chemically reduce graphene fluoride （GF） sheets with nanoscopic precision using high electrostatic fields generated between an atomic force microscope （AFM） tip and the GF substrate. Reduction of fluorine by the electric field produces graphene nanoribbons （GNR） with a width of 105-1,800 nm with sheet resistivity drastically decreased from 〉1 TΩ.sq.^-1 （GF） down to 46 kΩ.sq.^-1 （GNR）. Fluorine reduction also changes the topography, friction, and work function of the GF. Kelvin probe force microscopy measurements indicate that the work function of GF is 180-280 meV greater than that of graphene. The reduction process was optimized by varying the AFM probe velocity between 1.2 μm.s^-1 and 12 μm.s^-1 and the bias voltage applied to the sample between -8 and -12 V. The electrostatic field required to remove fluorine from carbon is -1.6 V.nm-1. Reduction of the fluorine may be due to the softening of the C-F bond in this intense field or to the accumulation and hydrolysis of adventitious water into a meniscus.
