Studies On Preparation Of Modified Waterborne Polyurethane And The Protections On Paper Relics

Paper cultural relics are regarded as the treasures of human civilization history.Most of the existing ancient books and cultural relics are seriously aged due to the inherent factors of paper materials such as papermaking raw materials,papermaking additives and external environmental factors such as ultraviolet radiation,which greatly reduces their research value and historical value.Among them,ultraviolet radiation is an important factor to accelerate the aging of fiber and paper materials.Therefore,the enhancement of paper cultural relics and anti-UV protection is particularly important.First of all,this topic uses silane coupling agent KH-550 to modify nano-SiO₂,through a series of dispersion stability tests and hydrophilic oil test to explore the best technology of silane coupling agent modification,obtained that the content of KH-550 is controlled at 25%,the reaction time is 2h,the reaction temperature is 75℃,After modification,the average particle size of SiO₂ remains in the range of 122.4-190.1nm,and the sedimentation volume is the largest.Under the modified process conditions,the modified particles have good dispersion and strong oil-philic and hydrophobic properties.Scanning electron microscopy（SEM）results show that nano-SiO₂ particles are prone to agglomeration before modification and have poor dispersion performance.After modification,the dispersion performance of nano-SiO₂ particles in organic media is obviously improved.XRD results show that KH-550 modified nano-SiO₂ does not change the crystal structure.Subsequently,this topic adopts in situ polymerization method,using isophorone diisocyanate（IPDI）and polypropylene glycol（PPG-1000）as the main raw materials,using the unmodified nano-SiO₂ and the silane coupling agent KH-550 modified nano-SiO₂ to prepare paper cultural relics protection solution of waterborne polyurethane.The experimental results show that the optimal dosage of nano-SiO₂is 0.5%,and the protective liquid with this content has good stability,small particle size and high dispersion.After forming the film,the UV transmittance of the protective liquid in the UVB region can be reduced to less than 5%,the contact Angle increases,the absorption rate decreases,and it has good water resistance and UV shielding effect.At the same time,the apparent viscosity of the protective liquid is small,paper coating operation.Finally,on the basis of the above research,the prepared nano-SiO₂/WPU protective liquid was coated on the simulated rice paper,and the effects of different nano-SiO₂protective liquid contents on the tensile strength,tearing degree,whiteness and water resistance of the rice paper before and after coating and aging were explored.The results show that the strength performance of rice paper is improved obviously.After coating rice paper with protective liquid,the tensile index loss rate of rice paper is mainly distributed in the range of 10.0%～15.6%,the tear loss rate is only 7.8%～10.3%,and the whiteness loss rate is only 1.8%,which is smaller than that of untreated rice paper base paper.After UV aging test,when the content of nano-SiO₂ in the protective solution is 0.5%,the tensile index loss rate is 1.9%,the tear loss rate is 2.6%,and the whiteness loss rate is only 0.2%.The UV aging resistance of the protective solution is significantly improved compared with that of uncoated paper.Combined with scanning electron microscopy analysis,it was found that the coating of protective solution effectively prevented the aging of the fibers,and the protective solution increased the bonding strength between the fibers,which played a good strengthening role.After coating with protective liquid,there is no obvious cover on the appearance of rice paper,and it has good water resistance,which meets the requirements of paper cultural relics protection.