Preparation And Characterization Of Nanocellulose-based Superhydrophobic Materials

Superhydrophobic surfaces have attracted substantial interest due to their unique properties such as self-cleaning,water repellency,anti-corrosion.These properties endow superhydrophobic materials with great potentials in numerous applications including automobile windshields,microfluidic devices,and architectural materials.However,most of the superhydrophobic materials are derived from petroleum-based polymers with the disadvantages of high cost,toxicity,and non-biodegradation.Therefore,the development of biomass-based superhydrophobic surfaces is currently a hot topic.Cellulose has been demonstrated as good candidate for the fabrication of superhydrophobic surfaces,owing to the hierarchical structure and tailorable surface chemical nature by the modification of hydroxyl groups on cellulose.In this study,lignocellulose fiber with different lignin content was prepared from wheat straw.Lignocellulose nanofibrils(LCNFs)were initially prepared from lignocellulose fiber by mechanical grinding,and then superhydrophobic surface was prepared through coating fluoroalkyl silane modified LCNFs on the glass and filter paper.The effects of lignin on the fibrillation and superhydrophobic modification were investigated.1.The preparation and characterization of lignocellulose nanofibrils by the supermasscolloider: lignocellulose nanofibrils were produced from unbleached wheat straw fibers using a supermasscolloider and characterized by transmission electron microscopy(TEM),X-ray diffraction(XRD),contact angle analyzer,and Zeta potential.The diameter distrubtion of LCNFs was in the range of 5-40 nm.The optimal fibrillation results were obtained after 2 passes through a grinder at 1500 r/min with the gap between two disks of-150 ?m.XRD results revealed that LCNF samples did not exhibit any evolution in the crystal structures.Residual lignin inhibited the fibrillation degree of lignocellulose.The LCNF samples with high lignin content possessed nonuniform structures and poor stability in water.Among the LCNF samples,the hydrophobicity was increased with the lignin content.2.The preparation and characterization of lignocellulose nanofibrils by microfluidization: lignocellulose nanofibrils were prepared from unbleached wheat straw fibers by microfluidization and characterized by TEM,XRD,contact angle analyzer,and Zeta potential.The results indicated that the diameter of lignocellulose nanofibrils decreased with lignin content decreasing.TEM results showed nano-lignin particles were getting agglomerated during the mechanical fibrillation process.Lignocellulose nanofibril produced by microfluidization possessed relatively low dispersion stability.XRD results showed that the mechanical fibrillation kept the crystalline structure of cellulose I.Lignocellulose nanofibrils with a greater lignin content showed higher hydrophobicity.In terms of fiber morphology,wettability,dispersion stability,and crystalline structure,there was no significant difference between the lignocellulose nanofibrils prepared by super-masscolloider and those prepared by microfluidization.3.Effect of lignin on performance of lignocellulose nanofibrils based superhydrophobic surface: lignocellulose nanofibrils were initially prepared from pretreated wheat straw by microfluidization,and then the superhydrophobic surface was prepared through coating silanes(PFTS and APTS)modified lignocellulose nanofibrils on glasses and filter papers.The superhydrophobic surface was characterized by contact angle analyzer,scanning electron micron microscopy(SEM),and X-ray photoelectron spectroscopy(XPS).The superhydrophobic surface can be obtained by modifying lignocellulose nanofibrils with the fluoroalkyl silane at an extremely low dosage(0.31 v/v%)owing to the inherent hydrophobic nature of lignin.The nanofibrils created micro-and nanoscale roughness to the superhydrophobic surface.The XPS analysis results showed that the residual lignin in nanofibrils exhibited an inhibitory effect on the chemical modification reaction.The presence of lignin in nanofibrils had an adverse effect on the abrasion resistance of the superhydrophobic surfaces when subjected to strong destruction treatments,however,the abrasion resistance was well maintained under weaker damage.The as-prepared superhydrophobic materials exhibited remarkable water repellency and self-cleaning property.4.Superhydrophobic surfaces modified by different silane systems: lignocellulose nanofibrils prepared by the super-masscolloider were modified with silane mixtures,followed by coating on the glasses and filter papers.The superhydrophobic surface was characterized by contact angle analyzer,SEM,and XPS.The results suggested that the optimal dosage of PFTS and KH550 was 0.3 v/v% and 1.5 v/v%,respectively.Futhermore,the superhydrophobic surfaces showed excellent self-cleaning property and abrasion resistance.The residual lignin in nanofibrils hindered the coupling reaction between silane reagents and cellulose nanofibrils.Compared with the superhydrophobic surface modified with PFTS/KH550,the superhydrophobic surface modified with PFTS/APTS showed superior water repellency.Nanofibrils obtained from different mechanical treatments possessed similar microstructure.Overall,the silanes mixture of PFTS and APTS was more suitable for the preparation of superhydrophobic surfaces.