| Lignin is one of the main components of biomass resources.Its high value-added utilization is of great significance for the high efficient utilization of biomass resources and the green and sustainable development of industrial society.Lignin has amphiphilic structure and natural properties such as antibacterial,anti-oxidation and UV protection.As a macromolecule surfactant or functional material,it has great value in the fields of construction,agriculture and energy.Alkali lignin?AL?accounts for more than 85%of industrial lignin produced from paper and biorefinery industry.However,the disadvantages such as poor water solubility and serious agglomeration restrict its high value and efficient utilization in polymer materials and energy.Silica is an important inorganic powder material,which has been widely used in polymer materials,building materials,medicine,optical materials,etc.However,its practical application performance is seriously restricted by the severe aggregation,difficult dispersion and poor compatibility with substrate of pure silica particles.Organic/inorganic composite particles are novel materials formed on nanoscale,which can significantly improve the compatibility with material matrix and application performance of inorganic components.In this study,AL was combined with silica to solve the problem of aggregation of AL,as well as the issues of serious agglomeration and poor dispersity of silica.Meanwhile,the recombination mechanism of lignin and silica was studied.The use of lignin/silica composite as functional additives and fillers in polymer materials showed that it could improve the anti-UV aging and mechanical properties of aqueous polyurethane?PU?and high density polyethylene?HDPE?.In addition,lignin/silica composite showed promising application in a novel energy storage device,aqueous Zn/LiMn2O4 battery,which provided new application field for the high value-added application of lignin.In this paper,a series of lignin/silica composites were prepared by in situ one-pot synthesis based on the electrostatic interaction between quaternized alkali lignin?QAL?and silica.The structures of them were characterized by particle size distribution,SEM,TEM,FT-IR,XPS,XRD,BET,TG,static contact angle,etc.The positively charged quaternary ammonium groups in QAL could tightly couple with the negatively charged primary crystal nucleus of silica by strong electrostatic interaction,so that the growth of silica nucleus and the hybridization of silica and QAL were conducted in situ.At the same time,the aggregation of QAL was also weakened,leading to the formation of spherical lignin/silica composite with small size?350nm?and light yellow color.The morphology,lignin content and surface hydrophilicity and hydrophobicity of lignin/silica composites could be adjusted by changing the dosage of lignin and modifying the QAL via alkylation.The applications of lignin/silica composites in polymer materials and aqueous Zn/LiMn2O4 battery were studied.The main conclusions are as follows:?1?A series of hydrophilic lignin/silica composite microspheres?QAL/SiO2?were prepared by in situ one-pot synthesis using QAL and sodium metasilicate as raw materials.The lignin content and particle size of QAL/SiO2 could be regulated and controlled,so that the QAL/SiO2with 40.5 wt%of lignin had minimum average particle size of 345 nm.The use of QAL/SiO2in PU to improve the anti-UV aging and mechanical properties of PU was studied.0.6 wt%of QAL/SiO2 containing 40.5 wt%of lignin was added into PU by stirring to prepare PU-based composite film.Compared to the pure PU film,the tensile strength and elongation at break of composite film increased to 1.10 MPa and 934.3%from 0.87 MPa and 662.5%,respectively.Meanwhile,the UV transmittance at 315 nm and 400 nm decreased to 0.3%and 31.7%from13.4%and 74.8%,respectively,with a decreasing amplitude of 97.8%and 57.6%.This was due to the tight coupling of QAL/SiO2 and PU and the monodispersity of QAL/SiO2 in PU,which enabled the UV-absorbent functional groups?cinnamyl alcohol,cinnamaldehyde,carbonyl,phenolic hydroxyl,etc.?in QAL to be uniformly dispersed in PU.This contributed to the improvement in mechanical properties and ability of UV protection of composite film.In addition,the ability of UV protection of composite film was still much stronger than pure PU film after 96 hours of UV radiation.?2?Alkylated QAL(QALC12)was synthesized by modifying QAL via alkylation.A series of hydrophobic lignin/silica composite microspheres(QALC12/SiO2)were prepared by in situ one-pot synthesis using QALC12 and sodium metasilicate as raw materials.The lignin content and surface hydrophobicity of QALC12/SiO2 could be regulated and controlled,so that the QALC12/SiO2 with 40.5 wt%of lignin and particle size of 200500 nm had maximum hydrophobicity.The static contact angle of QALC12/SiO2 could reach to 130°.Furthermore,abundant holes were found on the surface of some QALC12/SiO2 particles,because the hydrophobic C12 alkyl chain in QALC12 molecules prevented the in situ growth of hydrophilic silica nucleus and enhanced the local hydrophobicity of some particles,resulting in the formation holes on the surface of QALC12/SiO2 particles.10 g of QALC12/SiO2 was added into HDPE to prepare HDPE-based composite material by melt mixing.Compared to the pure HDPE material,the tensile strength and elongation at break of composite material increased to24.54 MPa and 1096.3%from 22.18 MPa and 959.3%,respectively.The C12 alkyl chains on the surface of QALC12/SiO2 particles intertwined with the HDPE molecular chains and the binding area between QALC12/SiO2 and HDPE significantly increased due to the abundant holes on the surface of QALC12/SiO2 particles.Therefore,the QALC12/SiO2 could improve the intensity and toughness of HDPE simultaneously.?3?A mesoporous lignin/silica composite microspheres?LSC?with pore size of 3.45 nm were prepared by in situ one-pot synthesis using QAL and sodium metasilicate as raw materials.LSC was used as additive to modify the cathode of aqueous Zn/LiMn2O4 battery.According to the results of electrochemical tests,LSC could significantly decrease the float charge capacity of battery because the mesopores of LSC could adsorb Mn2+produced by the disproportionation reaction of Mn3+,which might suppress the in-depth proceeding of disproportionation reaction.Thus,the stability of cathode material,LiMn2O4,was improved.However,the discharge capacity of battery decreased due to the insulation of LSC.Graphene?GR?with excellent conductivity was added to solve this problem.It was found that LSC could work cooperatively with LSC.When the total dosage of LSC and GR was 3 wt%and the mass ratio of them was1:1,the float charge capacity of battery decreased to 7.2 mAh·g-1 from 14.3 mAh·g-1,which is accounted for a decrease of 50%.Meanwhile,the discharge capacity at 1 C rate of battery increased to 122.3 mAh·g-1 from 114.7 mAh·g-1.?4?A novel lignin/silica nanocomposite was prepared by in situ one-pot synthesis using QAL and fumed silica?FS?as raw materials.It showed excellent electrochemical performances when used as novel gel electrolyte for aqueous Zn/LiMn2O4 battery.The results indicated that the battery using QAL/FS based gel electrolyte had better rate performance and cyclability when the FS was coated by 5 wt%of QAL.The results of scale-up experiment presented that the capacity retention of battery using QAL/FS based gel electrolyte was as high as 81.8%after1000 cycles at 4 C rate,which was 14%higher than that of battery using reference aqueous electrolyte.This was mainly attributed to the fact that the corrosive functional groups?Si—OH and Si—O–?on the surface of FS were partially shielded by QAL,leading to the efficient inhibition of corrosion on zinc anode.At the same time,the growth of zinc dendrite was efficiently suppressed by QAL/FS based gel electrolyte via controlling the uniform deposition and dissolution of Zn2+.In this study,a series of lignin/SiO2 composites were successfully prepared by in situ one-pot synthesis.They have promising applications in the fields of functional additives for polymer materials and aqueous Zn/LiMn2O4 battery.This provides an effective way for the high value-added development and utilization of industrial lignin and is of great significance for the green and sustainable development of industrial society.Results of this study is of great importance for widening the utilization of lignin as functional material in polymer materials and energy storage materials,as well as for the compounding technique and formation mechanism of plant derived random polymers and organic particles. |
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