Preparation And Properties Of Lignin/Polymer Functional Films

As an abundant natural aromatic polymer,lignin is renewable and biodegradable.Due to its complex structures,lignin has always been regarded as an industrial waste,which not only has not been rationally utilized but also caused serious environmental pollution.In this dissertation,the optical and photothermal properties of lignin are the main research contents.Using the unique chemical structure characteristics of lignin,light conversion composite films,light management composite films and photothermal conversion composite films were prepared,which were respectively applied in the fields of plant photosynthesis,solar cells and photothermal welding.Research on the luminescence and photothermal properties of lignin is conducive to promoting the high-value application of lignin in the field of photoluminescence and photothermal conversion,and is of great significance for the realization of high-value utilization of forest resource wastes.Taking advantage of the inherent fluorescence of lignin,we have incorporated sodium lignosulfonate(LS)into a carboxymethyl cellulose(CMC)matrix to produce a sustainable light-conversion composite film that enhances the photosynthesis of chloroplasts.The optical properties of light-conversion composite films,including UV-Vis absorption spectra and fluorescence emission spectra,were studied.The results showed that the light-conversion composite films efficiently absorbs light in the UV region and emits blue fluorescence,which matches well with the absorption spectrum of chloroplasts.The effect of light-conversion composite films on the photosynthetic efficiency of isolated chloroplasts was analyzed by Hill reaction,ferricyanide reduction assay and measurement of ATP production.The results showed that under irradiation with simulated sunlight,isolated chloroplasts covered with the light-conversion composite film produced 1.4 times more adenosine triphosphate than the control group.The light-conversion composite film was also shown to enhance photosynthetic activity,increasing the electron transfer rate by a maximum of 21%.On these bases,the effect of light-conversion composite films on the photosynthesis of living plants was studied through the chlorophyll fluorescence parameter test.The results showed that our rationally designed light-conversion composite film was able to enhance photosynthesis of Arabidopsis thaliana by～10%.Furthermore,to demonstrate the universality of this simple and efficient strategy for enhancing chloroplast photosynthesis,enzymatic lignin(CEL)was incorporated into polycaprolactone(PCL)matrix to obtain the CEL/PCL composite films.The research results showed that the prepared CEL/PCL composite films can also effectively improve the photosynthesis of chloroplasts by utilizing the characteristics of ultraviolet light down-conversion.Because lignin is a natural biomass material,its optical properties are very unstable.Therefore,certain chemical modification of lignin is required to make it have stable optical properties and endow lignin with more functions.The purified enzymatic lignin was chemically modified by mercapto-olefin.The dopamine was introduced into lignin molecules.The composition,molecular structure and element binding mode of synthesized product were analyzed by Two-dimensional heteronuclear single quantum coherence(2D-HSQC)NMR and X-ray photoelectron spectroscopy(XPS).Then,the modified lignin was then converted into hollow nanoparticles(L-H-NPs)using the solvent exchange-induced self-assembly method.To achieve lignin mesoporous nanoparticles(L-MS-NPs),p H value of as-prepared nanoparticles was adjusted to 10.4,which triggered alkali-catalyzed polymerization of dopamine and eventually crosslinked the L-H-NPs.The micromorphology of L-MS-NPs was analyzed by Transmission electron microscopy(TEM).The optical properties of L-MS-NPs were characterized by UV-Vis double-beam spectrophotometer,spectrofluorometer and photoluminescence spectrometer.The results showed that L-MS-NPs showed strong absorbance in the UV region from 200 nm to 400 nm,and the nanoparticles also showed a stable blue-green fluorescence emission under the excitation wavelength was 365 nm.In addition,L-MS-NPs also have excellent mechanical stability,and the hydrodiameter of L-MS-NPs did not change appreciably after ultrasonic treatment for 5 min.Subsequently,the as-prepared L-MS-NPs were embedded into a polyvinyl alcohol(PVA)matrix to produce an optical film(L-MS-NPs/PVA)with haze,fluorescence and room-temperature phosphorescence(RTP).The transmission haze and transmittance of L-MS-NPs/PVA composite films were measured by UV-Vis-NIR spectrometer.The results showed that the L-MS-NPs/PVA composite film not only possessed high optical haze,but also had high transmittance.The surface morphology and roughness of L-MS-NPs/PVA composite films were analyzed by atomic force scanning probe microscope(AFM),and the formation mechanism of excellent haze of composite films was revealed.Specifically,attributes to the robust morphology in the film matrix,L-MS-NPs cause rough morphology in the surface of L-MS-NPs/PVA composite film,which eventually triggers the great optical haze.The fluorescence and RTP of L-MS-NPs/PVA composite films were analyzed by UV-Vis double-beam spectrophotometer,spectrofluorometer and photoluminescence spectrometer.The results showed that the L-MS-NPs/PVA composite films exhibit excellent fluorescence emission and RTP emission.The combine haze,fluorescence and RTP properties of the L-MS-NPs/PVA composite film enhances the power conversion efficiency(PCE)of dye-sensitized solar cells from～3.9%to～4.1%.In addition to its excellent photoluminescence properties,lignin also has good photothermal conversion properties and is a natural photothermal material.Here,lignin nanoparticles supported copper sulfide(L-NPs@Cu S)were prepared by the solvent exchange-induced self-assembly and physical adsorption method.The microscopic morphology,lattice and surface element composition of L-NPs@Cu S were analyzed by Transmission electron microscopy(TEM),high resolution transmission electron microscope(HRTEM)and X-ray photoelectron spectroscopy(XPS).The results showed that L-NPs@Cu S have a uniform micromorphology with a diameter of 250 nm,and the copper sulfide was successfully supported on the lignin nanoparticles.L-NPs@Cu S exhibited good photothermal conversion properties.The surface temperature of L-NPs@Cu S powder can be increased from 36.6 ~oC to about 79.9 ~oC in 20 min under irradiation with simulated sunlight(150 m W/cm~2).Meanwhile,increasing the light intensity of simulated sunlight can enhance the photothermal conversion effect of L-NPs@Cu S.We have incorporated L-NPs@Cu S into a polycaprolactone(PCL)matrix to produce a L-NPs@Cu S/PCL composite film with photothermal properties.The surface morphology and element distribution of L-NPs@Cu S/PCL composite films were analyzed by scanning electron microscope(SEM).The results showed that the L-NPs@Cu S was uniformly distributed in the PCL matrix.The photothermal conversion properties of L-NPs@Cu S/PCL composite films were investigated.The results showed that the surface temperature of 70%L-NPs@Cu S/PCL composite film could be increased from 36.7 ~oC to about 70.6 ~oC in 20 min under irradiation with simulated sunlight(150 m W/cm~2).The L-NPs@Cu S/PCL composite film was applied to photothermal welding,and the obtained L-NPs@Cu S/PCL composite film after welding was not significantly different from the composite film before welding,which indicated that the L-NPs@Cu S/PCL composite film has good self-healing properties.