Preparation Of Superhydrophobic Structure Using Lignin Fatty Acid Esters And Its Application On Wood Surface

Superhydrophobic surfaces have a great potential for applications in aerospace,national defense,biomedical science,and energy fields due to its self-cleaning,anti-corrosion,anti-fog,and anti-fouling properties.Biomass materials,such as cellulose,lignin,proteins,chitosan,and so on,have been gaining attention increasingly in the preparation of superhydrophobic surfaces owing to their advantages of friendly-environment and recyclability in recent years.Lignin,the second-largest renewable polymer in nature,possesses hydrophobic benzene rings,modifiable hydroxyl groups,and has functional properties such as UV resistance and anti-bacterial properties,which makes it become ideal materials for developing high value-added products.In this dissertation,the lignin fatty acid esters superhydrophobic surfaces were prepared by modifying the industrial lignin with octanoyl chloride,dodecanoyl chloride,palmitoyl chloride and stearoyl chloride.The influencing factors of hydrophobic properties and self-assembled structures were investigated.The lignin stearoyl ester（LSE）/epoxy resin（ER）/silicon dioxide（Si O₂）composite superhydrophobic woods were prepared and tested for their anti-mold and anti-decay properties.The main contents and results of this dissertation are as follows:（1）Using lignin（dealkaline）as raw material,lignin octanoyl ester（LOE）,lignin dodecanoyl ester（LDE）,lignin palmitoyl ester（LPE）,and lignin stearoyl ester（LSE）were synthesized by esterification with four fatty acid chlorides at 100°C/3 h including octanoyl chloride,dodecanoyl chloride,palmitoyl chloride and stearoyl chloride.Then,a solvent-nonsolvent method using tetrahydrofuran（THF）as a solvent and ethanol as a nonsolvent was carried out to obtain suspensions of lignin fatty acid esters.And then the lignin fatty acid esters（super）hydrophobic surfaces were prepared by spraying.The contact angles of the obtained LOE,LDE,LPE,and LSE surfaces were 110.1±4.2°,119.6±6.9°,148.8±3.4°,and 161.9±1.9°,respectively.The LSE surfaces had the best superhydrophobicity.（2）LSE-1.5,LSE-2.5 and LSE-3.5 with increasing amounts of stearyl chloride addition were prepared by adjusting the amount of stearoyl chloride.By using the solvent-nonsolvent self-assembly method,LSEs with different grafting amounts can form lignin petal-like nanoflakes（LPNFs）or lignin spherical nanoparticles（NPs）structures with THF as a solvent while ethanol,acetone,or water as non-solvent.Using ethanol as a nonsolvent,LSE-1.5 with low stearyl content formed NPs structures;LSE-2.5 and LSE-3.5 with higher stearyl content formed LPNFs structure at lower THF/ethanol ratios（1:0.25 and 1:0.5）.Using acetone as a nonsolvent,LSE-3.5 can form LPNFs structures under different THF/acetone ratios（1:0.25-1:5）.In the meantime,LSE-3.5 merely formed NPs structures through water as a nonsolvent.The formation of the LPNFs structure is owing to the ordered self-assembly of the stearyl side chains of the LSE molecules,while the formation of the NPs structure is attributed to the disordered assembly of the LSE molecules.In addition,the water contact angle of the surface with LPNFs structure or NPs structures are above 150°,which have a good hydrophobicity.（3）In view of the weak mechanical robustness of the LSE superhydrophobic surface,superhydrophobic surfaces with enhanced robustness were prepared by compounding with LSE,epoxy resin,and Si O₂.And the superhydrophobic wood was constructed by spraying on the fast-growing poplar as the substrate.The contact angles on the cross-section and the tangential section of the superhydrophobic wood were 161.4±3.9°and 159.1±4.0°,which decreased to 141.2±7.5°and 138.9±2.9°after 100 times of abrasion with sandpaper,respectively.After 100 times of tape peeling,the contact angles became 147.2±3.8°and 145.3±4.5°,respectively.After the anti-fungi test,the contact angles of the wood surface remained above 140°after aspergillus niger and brown rot infection,which proved that the superhydrophobic coating could protect the wood from aspergillus niger and brown rot infection to certain extent.However,water droplets could infiltrate the wood after the white rot fungus test and the surface lost its hydrophobic property,which proved that the LSE/ER/Si O₂ composite superhydrophobic wood was resistless to white rot fungus.In this dissertation,lignin fatty acid esters with different carbon-chain lengths were synthesized by esterification with four fatty acid chlorides,and the self-assembled hydrophobic structures were regulated by a solvent-nonsolvent method to prepare a（super）hydrophobic surface of lignin fatty acid esters.Then the superhydrophobic wood was prepared by compounding with ER/Si O₂.The influencing factors of self-assembled structure and hydrophobic properties and the anti-mildew and anti-decay properties of superhydrophobic wood were explored,which provided research ideas and an experimental basis for the preparation and application of lignin-based superhydrophobic surfaces.