Degradation And Consolidation Of Silk Fabrics Colored By Natural Dyes

Silk is an important material carrier of traditional Chinese painting,where many of the existing paintings and calligraphy works are drawn on the silk.Ancient silk paintings have witness the history of Chinese civilization.The silk painting existed could reflects the social and economic life at that time.Therefore,they have high historical,archaeological,scientific and economic values.However,after being buried under the ground for years or handed down through generations,silk paintings suffered various degrees of deterioration under the influence of temperature,humidity,soil acidity and microorganisms,and so on.The silk fabrics unearthed have suffered from further aging due to environmental changes and influence of light and heat.So it is very urgent to protect those valuable historical relics for further displays and researches.To simulate traditional silk painting,silk fabrics were dyed with the colorant extract of nature dyestuff and(or)treatment with gelatin and alum,then put into a UV aging tester or a temperature-controlled oven for accelerating aging.The color difference,surface morphology,chemical structure,mechanical property and thermal properties of silk fabrics with various aging conditions were investigated.The aging mechanisms were also discussed.Then EGDE/Ala consolidation system was built and used to treat fragile dyed silk fabrics.Properties of fragile dyed silk fabrics treated by alanine(Ala)and ethylene glycol diglycidyl ether(EGDE)have been investigated.The results are as follows:Both gelatin and alum have effects on silk fabrics.Gelatin of a certain concentration postponed the effects of ageing on sized silk fabrics,while the damage of silk fabrics was serious by treating with alum.For light ageing,degradation of silk fabric treated by sizing was divided into two stages.The first stage was the degradation of amorphous area,which was easier to happen.In the meantime,the proportion of crystalline area was increased gradually.Then crystalline region began to degrad in the second stage.Dyeing and sizing accelerated the ageing of silk fabrics,which reduced the color difference and improved the thermal stability of aged silk fabric.For thermal ageing,dyeing promoted the ageing of silk fabrics.While sizing increased the brittleness of silk fabrics,and decreased their tenacity.Thus it plays a positive role in slowing down the degradation of silk fabrics.Alanine has facilitated the consolidated reaction and improved the properties including mechanical strength and crystallinity of fragile dyed silk fabrics.Through comprehensive comparison and analysis,it is concluded that an optimal technological parameters for consolidation is: 2.5 % EGDE,1.7 % Ala.And the solvent is ethanol water,with a volume ratio of 1.2: 1.Under these consolidated conditions,the breaking strength of aged silk fabrics dyed with colorant extract of sohrora japonica increased from 2.5 MPa to 14.87 MPa,with a color difference of 0.72.Application of this consolidation system to fragile undyed and dyed silk fabrics was conducted.Results show that breaking strength and anti-aging stability of fragile silk fabrics are improved after consolidation,while color difference of the fragile dyed silk fabrics is large than that of the fragile undyed silk fabrics.In conclusion,the ageing mechanism of silk fabric samples was studied and a consolidation method of fragile dyed silk fabrics was built in this work,which will provide a new approach for the protection of historic dyed silks or silk paintings.