Study On Preparation Of Phosphorylated Nanocellulose And Properties Of Nanopaper

Nanocellulose and nanopaper are ideal alternatives for petroleum based products,and have potential application value in packaging,electronic devices,filtration materials and other fields.However,the hydrophilic property of nanocellulose is strong and easy to burn,which leads to the poor flame resistance and water resistance of nanopaper,which limits its application in some fields.In this paper,the cellulose fiber was modified by phosphate,then the nanocellulose was homogenized at high pressure.The flame retardant nanopaper was made by vacuum filtration.Finally,the nano paper was modified with metal ions and PAE.The charge content,substitution degree of the modified cellulose fibers and the yield increased with warmer reaction temperature and its substitution degree reached 0.135,0.356,0.510 and 0.742,respectively.Phosphorylated cellulose fibers had swelling and some of them had bubbling phenomenon,whose diameter increased from 28.70?m to 30?33.35?m.Fourier transform infrared spectroscopy(FT-IR)and photoelectron spectroscopy(XPS)showed tha the phosphoric acid element of the prepared phosphorylated cellulose was mainly present in the C-O-P structure of the cellulose.X-ray diffraction(XRD)showed that the crystalline structure of phosphorylated cellulose remains cellulose type I.The relative crystallinity decreases with the increase of phosphorylation.In this experiment,the relative crystallinity of cellulose fibers decreased from 75.4%to 61.9%after phosphoric acid treatment.Thermogravimetric analysis(TG)showed that the phosphorylated cellulose fibers have a lower initial thermal degradation temperature compared to cellulose fibers but an increased residual mass.The length of phosphorylated nanocellulose becomes shorter with the increase of phosphorylation,whose relative crystallinity decreases compared with phosphorylated cellulose fibers.Phosphorylated nanocellulose still maintains high quality after thermal decomposition,but its thermal stability decreases.The phosphorylated nanopaper has excellent transmittance and mechanical properties,and all of them can achieve more than88%transmittance at 550 nm,among which PCNF-5P phosphorylated nanopaper exhibits the highest transmittance(91.4%)and the lowest haze(4.21%).PCNF-4P phosphorylated nanopaper has the best mechanical properties,which has tensile strength of 164 MPa,elongation of 6.68%,and modulus of elasticity of 5.9 GPa.The phosphorylated nanopaper has high water absorption capacity and poor water resistance.The phosphorylated nanopaper has excellent flame retardant ability,and its flame retardant performance is enhanced with the increase of phosphorylation,among which PCNF-6P and PCNF-7P are equal to the V0 level of UL94 vertical burning test.After modification of phosphorylated nanopaper with Al³⁺or Ca²⁺,the water absorption decreased from 609.4%before modification to 105.2%(Ca²⁺)and 74.6%(Al³⁺);the wet tensile strength reached up to 53.7 MPa(Al³⁺);the light transmittance of phosphorylated nanopaper after the modification of Al³⁺and Ca²⁺did not decrease significantly,and it still maintained more than 89.0%light transmittance at 550 nm.The water resistance and tensile strength of the phosphorylated nanopaper modified with PAE increased with the increase of PAE content,where the water absorption rate decreased from 609.4%before modification to44.5%at the lowest;the dry and wet tensile strength of PAE modified phosphorylated nanopaper increased with the increase of PAE content.The PAE-modified phosphorylated nanopaper with a light yellow color of the pristine PAE.The light transmittance of PAE-modified nanopaper is slightly reduced,but the transmittance at 550 nm still remains above 87%.The thermal stability of the water-resistant modified phosphorylated nanopaper was improved,and the maximum thermal decomposition of temperature and rate were greatly improved,and the residual mass after thermal decomposition was not significantly reduced.However,their flame retardancy changed significantly.The PAE-modified phosphorylated nanopaper still had excellent flame retardant properties,was difficult to ignite and could end combustion immediately after removing the flame.And the flame retardant properties of Al³⁺or Ca²⁺modified phosphorylated nanopaper were reduced or even lost.PAE can significantly improve the water resistance of phosphorylated nanopaper,and improve its mechanical strength and thermal stability,only making a slight decrease in light transmission,and most importantly,the modified nanopaper still maintains excellent flame retardant propertiesr.