Preparation Of Nanocellulose/Water-based Polyurethane Composite Material And Research On Its Coating Properties

Water-based polyurethane coated fabrics have the advantages of environmental protection,low price,and diverse varieties.However,the mechanical properties are worse than solvent-based polyurethane coated fabrics,mainly due to the mechanical properties and thermal stability of water-based polyurethane(WPU)are poor.Nanocellulose includes cellulose nanocrystal(CNC)and cellulose nanofiber(CNF).It has the advantages of large specific surface area,high strength,and good biocompatibility.It can be used to improve the physical and mechanical properties of WPU.In this paper,Microcrystalline cellulose(MCC)was used as raw materials to prepare CNC and CNF by acid hydrolysis and TEMPO oxidation,respectively.The crystal structure,chemical composition,thermal stability and morphology of the prepared CNC and CNF were compared and analyzed.Secondly,CNC and CNF with different mass fractions were added to WPU respectively.CNC/WPU and CNF/WPU composites were prepared by solution blending method.The chemical structure,thermal stability,tensile properties,wear resistance and bending stiffness of nanocomposites with different mass ratios were systematically studied.The mechanism of strengthening and stretching was systematically expounded by studying the microstructure of fracture surface and worn surface.Finally,CNC/WPU and CNF/WPU composite materials were used in coating finishing,and their effects on the tensile properties,anti-pilling resistance,color fastness to rubbing and air permeability of the coated fabrics were investigated.The specific research results were as follows:1.Using MCC as raw material,CNC and CNF were prepared by acid hydrolysis method and TEMPO oxidation method,and their morphology,crystal structure and thermal stability,etc.were compared and analyzed.The results showed that the morphology of CNC and CNF were both rod-like,and the length-diameter ratio of CNC was lower than that of CNF,but the crystallinity and thermal stability of CNC were higher than CNF.Therefore,it was possible to consider using these two different sizes of nanocellulose for the modification study of the physical and mechanical properties of WPU.2.The CNC and CNF obtained from the above preparation were filled into the WPU matrix to prepare two kinds of nanocomposites.The chemical structure,thermal stability,mechanical properties,wear resistance,bending stiffness and microstructure of the two composites were compared and analyzed by Fourier transform infrared spectrometer(FTIR),thermogravimetry(TG),mechanical tensiometer,wear-resistant tester,bending stiffness tester and field emission scanning electron microscope(SEM).The results showed that small amount of CNC or CNF added to the WPU matrix has better dispersibility,and agglomeration will occur when a large amount was added.The tensile strength and elastic modulus of the composites were increased by 179.3% and 216.9%,respectively,and the wear of the composites is reduced by 19% when the optimal CNC content is 1wt%.However,the optimal CNF content was 1.5wt%,and the tensile strength and elastic modulus of the composite material were increased by 226.4% and 121.7%,respectively,and the wear amount was reduced by 25%.Compared with WPU,the thermal stability of CNC/WPU and CNF/WPU nanocomposites were significantly improved,and the bending stiffness was reduced.The results of microstructure study show that CNF can form a relatively dense network structure in CNF/WPU nanocomposites due to its high aspect ratio,which provides a theoretical basis for the subsequent application of coating finishing.3.CNC/WPU and CNF/WPU nanocomposites were applied to the coating finishing of suede fabric,and the tensile properties,pilling resistance,color fastness to friction resistance and air permeability of suede coated fabric were compared and analyzed.Compared with untreated suede fabric,the longitude and weft breaking strength,pilling resistance,and color fastness to rubbing of the coated fabric were significantly improved.Among them,CNC/WPU/ fabric and CNF/WPU/ fabric had higher longitude and weft breaking strength and anti-pilling resistance than WPU/fabric,and the color fastness to dry and wet rubbing reached grade 4～5.However,the air permeability of suede fabric was higher than WPU/fabric,CNC/WPU/fabric and CNF/WPU/fabric.According to the SEM figure,a layer of discontinuous film was formed on the surface of the coated fabric.Compared with WPU/ fabric,the continuity of film formation of CNC/WPU/ fabric and CNF/WPU/ fabric was significantly improved.