| Functional films are widely used in various fields of modern industry,but most of these films used in practical applications are prepared based on petrochemical resources.The huge consumption coupled with the non-degradability of material brings huge pressure on both environment and energy.In recent years,research of developing novel functional films based on nanocellulose has drawn increasing attention.But in present,preparing nanocellulose-based functional membranes still faces many challenges,such as low preparing efficiency,poor durability,deteriorating biocompatibility of composite films,etc,which greatly hinder the further development of nanocellulose-based materials.In this study,lignin-containing cellulose nanofibers(LCNFs)were first prepared via a simple and efficient method basing on chemi-mechanical pulp.Then LCNFs were employed to construct various functional films,including UV-blocking film,waterproof film,packaging film,and electromagnetic interference shielding film.The main research work of this dissertation includes:Firstly,we used chemi-mechanical pulp as a raw material.By combining TEMPO-mediated oxidation and microfluidic homogenization method,LCNFs was prepared simply and efficiently.The effect of the dosage of Na Cl O in TEMPO oxidizing system on the oxidation process were studied,as well as the effect of lignin content on the physicochemical properties of LCNFs under the same mechanical treatment.The results showed that the content of retained lignin in LCNFs could be easily controlled by adjusting the dosage of Na Cl O.The content of retaining lignin was negatively correlated with the dosage of Na Cl O.The structure analysis of lignin showed that the β-O-4 linkage in side chain was broken.Guaiacyl units and p-coumarates in aromatic constructure were also degraded in the oxidizing process.Under the same mechanical treatment,the higher retention content of lignin,the more uneven the size of LCNFs.Moreover,most of LCNFs samples exhibited a good dispersion in water except for the 21-LCNFs.Secondly,a highly transparent and UV-blocking lignin-containing cellulose nanopaper(LCNP)was prepared with different LCNFs via a facile filtration method.By compared with the pure cellulose nanopaper(CNP),the effect of lignin retention on the film performance was systematically studied.The results showed that the retaining lignin component did not have adverse effect on visible light transmittance of LCNP,and resultantly endowed the film an excellent UV-shielding capacity.The UV-shielding efficiency of the film increased with the increase content of lignin,especially for the 16-LCNP,which exhibited an ultrahigh visible light transmittance(～91%),ultrahigh haze(～91%),and good UV-blocking efficiency(～87%).Moreover,it was found that the retaining lignin was served as a reinforcing agent filled in LCNP,resulting in a significant improvement on toughness,wet mechanical property,and thermal stability.The fully biobased LCNP with outstanding performance is a promising candidate to apply in automotive decoration,flexible electronics,and protective building materials,etc.Thirdly,in view of the insufficient water stability of the LCNP,water resistant membranes based on LCNP were further developed via a cross-linking strategy of metal ions(M-LCNP).The effect of different metal ions on the properties of cross-linking membranes was studied,and the mechanism on improving water resistance was also explored.The results showed that M-LCNP exhibited a significantly improved water stability than LCNP owing to the formation of coordination bonds between metal ions and lignocellulosic components.In terms of the improvement on water stability,trivalent metal ions were obviously better than that of divalent metal ions.Among these M-LCNP,Fe-LCNP displayed the most excellent water resistance,presented wet mechanical strength of 52 MPa after immersing in water for 24 h,and also possessed the ultralow water uptake ratio of about 35%.Moreover,these M-LCNP also showcased both high visible transmittance and UV-blocking efficiency.Unfortunately,a few colored metal ions exhibited an adverse effect on visible light transmittance.At last,M-LCNP was employed to fabricate a conducted silver line,which indicated it an eligible substrate material for applying in flexible electronics.Fourthly,considering the poor moisture barrier performance and single functionality of CNP,a multifunctional and high barrier-performance packaging film was designed according to the abovementioned research.The effect of metal ion infiltration and the coating amount of chitosan was systematically studied.The results showed that the infiltration of aluminum ion confered the composite an excellent water stability,which significantly improves the water vapor barrier ability of membrane.The following chitosan-coating treatment builded a dense surface for the composite,which endowed the film a decrease of ～ 64% on the oxygen permeability.Furthermore,the composite membrane displayed good optical performance(～ 90%),mechanical performance(～ 90 MPa),antibacterial perfirmance(> 92%),and oil resistance(grade of 12).This composite film with multifunctionality and excellent barrier performance is expected to be novel packaging material to replace traditional plastics.Fifthly,a composite MXene/LCNFs electromagnetic interference(EMI)shielding film with a "brick-mud" structure was constructed based on a vacuum filtration self-assembly method.The differences in structure and physicochemical properties of composite film under different mixing ratios were studied,and the mechanism of EMI shielding performance was also revealed.The results showed that the dry strength,toughness and water stability of composite film were significantly improved with the increasing proportion of LCNFs.In addition,the composite film exhibited high EMI shielding efficiency,which reached a EMI shielding capacity of ～42 d B in the X-band only with a thickness of 34 μm.The composite film presents a potential application in flexible devices,automotive electronics,aerospace,etc. |
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