Study On Synthesis And Modification Of UV-curable Waterborne Polyurethane Acrylate

Ultraviolet curable waterborne coatings have attracted much attention due to their advantages of safety,non-toxicity,environmental protection,high efficiency and energy saving.They are the research hotspots in the coatings industry at present and which are widely used in wood,leather and finishing.However,the application of a single free radical ultraviolet curable polyurethane acrylate(UV-WPUA)material is limited due to its poor mechanical properties,water resistance and high product price.In this paper,a series of waterborne polyurethane acrylate(WPUA)oligomers were synthesized from IPDI,PCL-2000,DMPA,BDO and HEMA.After mixing with photoinitiator,a series of waterborne polyurethane acrylate(WPUA)oligomers were initially crosslinked and cured under ultraviolet light,the optimum synthesis process of WPUA was studied.The isocyanate content in the prepolymerization stage was detected by toluene two n-butyl amine method,and the temperature and time of the reaction process were optimized.The effects of R value,DMPA content,inhibitor content and neutralization degree on the properties of the emulsion were also discussed.The results showed that the temperature needed for each step of the pre-polymerization stage ?,? and ? were 65?,85? and 60?,respectively.The reaction time for each step of the pre-polymerization stage ?,? and ? was 2.0h,3.Oh and 5.0h,respectively.The R value was 1.4,the DMPA content was 6.5%,and the inhibitors were p-hydroxyphenyl ether and the amount was 0.05%,the neutralization degree was 110%,the prepared emulsion had better comprehensive properties.Cured film had the highest degree of cure,when the content of photoinitiator was 3%of the solid content of WPUA emulsion.TEOS was used to hydrolyze under acidic conditions,silane coupling agent KH-570 was used to modify SiO2 and then M-SiO2 was obtained.Next,a series of M-SiO2/WPUA oligomers and emulsions were synthesized by WPUA reaction with the above optimum process.After mixing with photoinitiator 2959,a series of UV-M-SiO2/WPUA films were prepared under UV irradiation,and the mechanical properties and thermal properties of the films were tested.FT-IR showed that nano SiO2 successfully introduced unsaturated double bond which could be used for light curing reaction,and M-SiO2 was successfully introduced into WPUA oligomer.The results showed that after adding M-SiO2,the average particle size of M-SiO2/WPUA emulsion increased from 21.Onm to 421.7nm,and the particle size also widened.The hardness of UV-M-SiO2/WPUA film increased from H to 4H,and tensile strength increased from 1.16MPa to 3.96MPa,but adhesion decreased from grade 0 to grade 2,the elongation at break decreases from 379%to 95%.The water absorption of M-SiO2/WPUA film was lower than that of WPUA film,but the alkali resistance of M-SiO2/WPUA film was worse than that of UV-WPUA film.The contact angle of M-Si02/WPUA film increased with the increase of M-SiO2 content,and the calculated surface free energy decreases gradually,indicating that the hydrophobicity becomes better.When the addition amount of M-SiO2 was 10%,the temperature of thermal degradation of 5%was 235.33?,which was higher 42.50C than that of pure WPUA film,showing the best thermal performance.SEM and AFM analysis showed that M-SiO2 was more evenly dispersed in the WPUA film,and agglomeration occurred in a very small part.The nano alumina was modified by acrylic acid,and then the WPUA emulsion was prepared by blending with the above optimum process conditions.After adding the photoinitiator,the AA/Al2O3 containing C=C double bond was grafted onto WPUA under ultraviolet light,and the AA/Al2O3-WPUA composite film was obtained.The structure and properties of the film were characterized by FT-IR,XRD,SEM,and TGA.FT-IR showed that the unsaturated double bonds were successfully introduced on Al2O3,which could be cured by ultraviolet light,the unsaturated double bonds in AA/Al2O3 and WPUA were crosslinked under ultraviolet light.The results showed that the addition of AA/Al2O3 weakened the crystallization diffraction peak intensity of WPUA film.The hardness of AA/Al2O3-WPUA composite film increased from H to 5H,and the adhesion decreased from grade 0 to grade 2,the tensile strength all increased,but the elongation at break decreased from 379%to 145%.When the addition amount of AA/Al2O3 was 3%,the water absorption rate of the film and the degree of expansion of ethanol,acid and alkali were 10.73%,24.61%,15.72%and 3.91%,respectively,showing the best acid and alkali resistance.The results of TGA analysis showed that the temperature of thermal degradation of 5%increased from 192.83? to 221.83? after adding AA/Al2O3,indicating that the heat resistance of AA/Al2O3-WPUA composite film was further improved.