Preparation Of Biomass Nanofibers And The Construction Along With Modification Of Their Coatings

With the increasingly serious environmental problems caused by waste polymers,natural polymer materials have been widely studied and developed due to their renewable,degradable and abundant reserves,which can replace traditional polymers.Cellulose and chitin are the most abundant natural polymers in the world,with a wide range of sources and good biocompatibility.Cellulose nanofibers and chitin nanofibers are derivatives of cellulose and chitin,respectively,which have various preparation methods and different preparation methods will produce nanocellulose with different sizes and different properties.At present,the most widely used preparation methods in the world are mechanical method and acid hydrolysis method.However,the mechanical method consumes too much energy,while the acid hydrolysis method causes environmental pollution.So both methods are not conductive to environmental protection and sustainable development strategy.Nanocellulose due to its high specific surface area,high tensile strength and other excellent properities is used to prepare composite films,high transparent coatings and other materials.In this study,the cellulose nanofibers were prepared by selecting purified pulp board as raw material,and using maleic anhydride esterification and ultrasonic crushing methods.The effects of dry esterification,semi-esterification,and wet esterification on the size of cellulose nanofibers were studied.Subsequently,suspensions of cellulose nanofibers and chitin nanofibers were prepared,and the correspongding coatings were prepared with different concentrations of suspensions at different temperatures.Finally,using perfluorooctanoic acid and sodium perfluorooctanoate as modifiers,cellulose nanofibers and chitin nanofibers were modified and the corresponding coatings were prepared.Comparing the different modification methods and performace of their correspoing coatings.Scanning electron microscope(SEM),Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD),Nanometer particle size analyzer and Degree of substitution analysis(DS)test methods were used to characterize and analyze the results of the prepared cellulose nanofibers.Atomic force microscope(AFM),Transmission spectrometer,Ultra-depth 3D microscopy,Paint film adhesion tester,and Contact angle measurement analytical methods were used to characterize the coatings.The main results and conclusions of this study are as follows:(1)Adding different doses of water(0.0 m L,2.5 m L,5.0 m L,7.5 m L,10.0 m L)had a great influence on the final reaction degree of the esterification.The degree of esterification affected the size of cellulose nanofibers.When adding 2.5 m L water into the reaction raw materials,the esterification reaction time was short and the final reaction was complete.Then after treated by 300 W ultrasonication for 30 min,the prepared cellulose nanofibers were uniform in size,with width in 10 nm – 20 nm,and length in 100 nm – 200 nm.Meanwhile,the dispersed solution was light blue,transparent and precipitation-free.(2)Preparing the coatings with cellulose nanofiber dispersion and chitin nanofiber dispersion,respectively.When the dispersion concentration was constant,the drying temperature affected the final effects of the coatings.When the dispersion concentration unchanged,compared with the coatings dried at 50 ?,the surface distribution of the coatings dried at 90 ? was not uniform.There were bumps visible to the naked eye,and the bumps at the highest point could reach 72 ?m.At the same time,The transparency was also reduced,the transmittance was only 56%.However,when the drying temperature was constant,there was no significant difference in the properties of the coatings prepared by 1 wt% and 0.5 wt% cellulose nanofiber dispersions and chitin nanofiber dispersions.When the drying temperature and dispersion concentration were constant,there was no significant difference in the performace characterization of the coatings prepared by cellulose nanofiber dispersions and chitin nanofiber dispersions.(3)Whether the coatings prepated by using cellulose nanofiber dispersion or chitin nanofiber dispersion,the wettability of the coatings was hydrophilic and oleophilic.For the coating prepared after the modification of perfluorooctanoic acid/ethanol solution,the concentration of the modifier had no effect on the coating performance.The water contact angles of the coatings were abnormal,and the coatings became super-hydrophilic.The oil contact angles of coatings were slightly improved.Perfluorooctanoic acid/ethanol solution could not be directly sprayed on the coating surfaces prepared by cellulose nanofiber dispersion and chitin nanofiber dispersion to modify the coatings,but perfluorooctanoic acid/ethanol solution could be directly sprayed on the coating surfaces to modify the coatings.In terms of mechanical properties,the adhesive level of the modified coatings was all changed to first-class.For the occurrence of abnormal phenomena,further and more in-depth research is needed.