| Cultural relics of colored paintings with important historic, artistic and scientific values are common arts in ancient China. However, with the ageing of pigments and resins inside and the influence of humiture and illuminance outside,cultural relics of colored paintings will get diseases like alkalization and exfoliation. Currently, modern polymer materials are frequently applied in the conservation of colored paintings, and its performance will directly affect the effectiveness of conservation and longevity of cultural relics. Among the materials of conservation,Paraloid B72(short for B72), a kind of acrylic materials, is the most commonly used material in conservation. On the other hand, the film of B72will gradually turn yellow and crisp with the influence of environmental factors such as UV irradiation,and as a result limits its performance. Therefore, it is important to improve the materials’properties or make new materials with better properties according to the practice of cultural relics conservation. Nano SiO2is a modified material which is widely used in recent years to improve the properties such as corrosion resistance and anti-ageing of original materials. However, nano SiO2is seldom applied in the conservation of cultural relics, and there is even a vacuum in the study of B72modified by SiO2. There are mainly three parts in this article. In this article, we carry on an experiment that modify the properties of B72with SP1-5702, a nano SiO2material,aiming to discuss the feasibility of B72modified by nano SiO2, improve the anti-photoaging property of B72, and determine the optimal modification conditions.The first part:The study of the modification of SiO2. In the experiment, we use deionized water and anhydrous alcohol as solvent, and set two criteria of the rate of deposition and film forming ability, then we carry on a single factor test and determine the proper proportion of deionized water and anhydrous alcohol. On this basis, we use orthogonal experiment and the rate of deposition as criteria, analyzing the influence of four factors--dosage of coupling agent, dosage of emulsifier,ultrasonic time and ultrasonic temperature--on the dispersion properties of nano materials. The results of L9(34) orthogonal experiment show that the best dispersion conditions of nano materials are:the volume ratio of deionized water and anhydrous alcohol is15:85, the amount of coupling agent KH550is1%of nano materials by mass, the amount of emulsifiers OP-10is3%of nano materials by mass, the ultrasonic temperature is60℃, and the ultrasonic time is120mins.The second part:The study of B72modified by nano SiO2. In the experiment we modify the properties of B72by nano SiO2materials of different mass concentration range from2%to10%, after getting the film of modified B72, we carry on an aging experiment by a254nm UV light. By comparing the change of appearance and wetting angle before and after the experiment, the criteria of weight loss rate, mechanical strength and infrared spectroscopy of modified B72film during the aging, we determine the best concentration of SiO2. We find that the comprehensive properties of modified B72are better than any other modified materials when the content of SiO2is8%,8.5%and9%of B72by mass.The third part:The study of conservation of modified B72on the simulated colored painting samples. To further identify the best content of nano SiO2and to investigate the practical effects of modified materials on the colored paintings, we design a series of experiments, including the conservation of simulated colored paintings and the aging tests, to evaluate the modified B72material by comparing the color and wetting angle before and after the conservation and the criteria of color change of simulated colored painting samples during the UV aging. The experiments show that:the modified material is an excellent surface protection material for colored paintings with excellent properties of UV resistance and small appearance change to samples when the nano SiO2’ s content is8%of B72by mass. |
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