Study On UV Aging Mechanismand Aging Resistance Modification Of Stone Cultural Relics Protection Materials

Stone cultural relics have important historical value and artistic value,but the preservation state of stone cultural relics is not optimistic because of various factors.Organic materials have become the most used cultural relic protective materials due to their high ductility,film-forming property,hydrophobicity and cohesiveness.However,the polymer protective material is easy to age,especially the ultraviolet light in the environment is easy to make it fail and lose the protective effect.In this paper,the properties of commonly used stone heritage protection materials epoxy resin（E44）and acrylic resin（B72）during UV aging were tracked and the aging mechanism was explored by means of infrared spectroscopy,X-ray photoelectron spectroscopy,dynamic thermomechanical analysis,nuclear magnetic resonance spectroscopy,gel permeation chromatography,etc.It is found that the interrupt chain of aging process and crosslinking reaction exist at the same time,but the dominant reaction is different in different periods.The active sites of the photochemical reaction in E44 were aromatic ether bond,CH₃-C bond in isopropyl group and C-N bond at the crosslinking point,and the chromogenic group C=O was generated during the reaction process.The active site of the photochemical reaction of B72 was tert-butyl radical.lactone and C=C were generated in the reaction,which changed the properties of B72.In order to improve the UV resistance of E44 and B72,polyhedral oligomeric silsesquioxane（POSS compounds）were synthesized by hydrolysis shrinkage method.The effect of different ratio of raw materials on the structure of POSS compounds was studied and the optimum synthesis conditions were determined.The effects of different kinds and contents of POSS compounds on UV resistance of E44,B72 were explored.It was found that OTES-POSS and KH550-POSS can significantly improve the UV resistance of E44 and B72 and reduce the generation of photochemical reaction products when the dosage of 5%-8%.The effects of POSS compounds on other durability of E44 and B72 were explored through freeze-thaw experiments,salt aging experiments and acid aging experiments,so as to comprehensively evaluate the modification effect of POSS compounds.The experimental results show that POSS compounds play a significant role in improving the UV resistance of E44 and B72,maintaining or improving the properties of E44 and B72 after freezing and thawing aging,soluble salt aging and acid aging.It provides a basis for selection and modification of antiaging polymer materials for cultural relics protection.