Preparation Of Lignin-based Waterborne Polyurethane And Its Application In Wood Varnish And Pesticide Nano Preparation

Alkali lignin(AL)is a kind of natural aromatic polymer from plants,which is derived from the by-products of alkali pulping and papermaking industry.AL has attracted much attention because of its low cost,wide range of sources and renewability.Lignin(AL)is a threedimensional reticular polyphenolic polymer.AL contains multifunctional phenolic hydroxyl groups,which can be used as polymer polyols to synthesize more compact polyurethane materials.In addition,AL molecules have a higher content of carboxyl groups.When synthesizing polyurethane materials,carboxyl groups can be used as hydrophilic groups to impart good hydrophilicity to the polyurethane resin,thereby preparing stable water-based emulsion.Therefore,lignin as a natural polymer raw material is widely used in the preparation of waterborne polyurethane(WPU).At present,the following problems need to be improved in the research reports of lignin as raw material for WPU preparation.Firstly,lignin needs to be chemically modified and then used as a raw material to prepare polyurethane materials.Second,the lignin content in WPU structure is low.In this study,industrial AL without chemical treatment was directly used as hydrophilic chain extender for the synthesis of WPU.A series of lignin-based waterborne polyurethane(LWPU),with different lignin content,were synthesized by copolymerization modification method,and its applications in nano pesticide preparation and wood varnish were expanded.The unmodified industrial Alkali Lignin(AL)was used as a hydrophilic chain extender to prepare a series of LWPU emulsions with different lignin contents by copolymerization modification with polypropylene glycol(PPG)and isophorone diisocyanate(IPDI).The lignin content in the series of LWPUs was determined by elemental analysis,with a maximum content of 24.68 wt%.The infrared spectrum and scanning electron microscope diagram of the LWPU film show that the AL reacts well with isocyanate,the section of the film is flat and smooth,and there are no agglomerated lignin particles in the film,which indicates that the film is homogeneous.With the increase of AL content,the particle size of the LWPU emulsion decreased gradually from 233 nm to 127 nm,the Zeta potential decreased gradually from-44.8m V to-56.9 m V,and the emulsion has good stability in the p H range of 5 to 12.The thermogravimetric analysis of the LWPU film show that the introduction of AL can improve the thermo stability of the polyurethane material,and the mechanical properties test results show that the highest tensile strength of the LWPU film can reach 1.29 times that of the pure polyurethane film.Ultraviolet aging test show that the introduction of AL can significantly improve the UV aging resistance of the polyurethane film.The biodegradation experiments show that the weight loss rate of LWPU film after 125 days of degradation in soil is20.25%?28.29%,which is 7.85?10.97 times of that of WPU film,indicating that LWPU film has good biodegradation performance.A series of LWPU emulsions with different lignin content were used to prepare wood varnishes,and LWPU varnishes with smooth appearance were successfully prepared.The performance test of the varnish shows that the LWPU varnish has excellent pencil hardness and adhesion.Compared with commercial waterborne polyurethane(PU-2890),the LWPU varnish have lower water absorption(13.72%)and larger static contact Angle(85.13°),indicating that the LWPU varnish have better water resistance.In addition,LWPU varnish can still maintain good appearance and excellent properties at 120 °C,and its glass transition temperature increases with the increase of AL content.The highest glass transition temperature of LWPU varnish is-23.28 °C,which is higher than PU-2890.The LWPU varnish has excellent Ultraviolet aging resistance,and its appearance and properties have not changed after 360 hours of Ultraviolet radiation.The results show that the introduction of lignin makes LWPU varnish have excellent Ultraviolet shielding performance,and the Ultraviolet transmittance of LWPU varnish film is 0% in both UVA and UVB regions.Using LWPU as drug-loading material,the photosensitive pesticide emamectin benzoate(EMB)was encapsulated,and 1.8% EMB nano-formulation(EMB@LWPU)was prepared by solvent exchange method.The preparation process of EMB@LWPU was studied,and the EMB@LWPU with particle size of 133?259 nm,Zeta potential of-30.27?-46.63 m V were obtained.The drug loading and encapsulation efficiency of the EMB@LWPU were determined.The results showed that the drug loading decreased and the encapsulation efficiency increased with the increase of the EMB@LWPU ratio.The dispersion stability test shows that the dispersion stability of EMB@LWPU increases first and then decreases with the increase of drug ratio.The storage stability experiments shows that the particle size of EMB@LWPU has a slight increase,and the overall increase is within 6.2%.The UV degradation experiment shows that after 60 hour UV irradiation,the EMB retention rate of EMB@LWPU is 60.35%?81.96%.Compared with the commercial emamectin benzoate microemulsion(C-EMB/ME),the EMB retention rate of EMB@LWPU is increased by 9.14?12.77 times,which shows that EMB@LWPU has excellent photolysis resistance.The affinity of EMB@LWPU to plant leaves was tested,and the results shows that the retention of EMB@LWPU on the leaves and the rain scour resistance performance of EMB@LWPU are greater than that of C-EMB/ME.The test results of the sustained-release performance of EMB@LWPU show that it has remarkable sustained-release performance.In this paper,a series of stable LWPU emulsions with different lignin content were prepared.The study found that the introduction of lignin can significantly improve the mechanical properties and UV aging resistance of polyurethane materials.The prepared LWPU shows excellent application properties in both wood varnishes and pesticide nano preparation.Therefore,the LWPU prepared in this study can be applied as a new type of bio-based polyurethane material.