Silk degradation mechanism

A comparison of the state of degradation of historical silk fabrics with those of artificially aged contemporary fabrics would be very useful in any effort to determine the mechanisms by which naturally aged silk is degraded. Such knowledge would also aid in the selection and evaluation of stabilizers to slow the degradation process. For these reasons, the historical fabrics were evaluated. 

Silk deterioration takes place via two main mechanisms oxidation and hydrolysis. Harris (15) has shown that degradation by exposure to light results largely from oxidation and is accompanied by the formation of ammonia nitrogen. Degradation by hydrolysis, on the other hand, is accompanied by the formation of amino nitrogen. In this way, Harris has been able to separate the portions of fiber deterioration that can be attributed to oxidation and hydrolysis. 

Effect of Fiber Degradation on the Corrosion Solution. Hydrolysis and oxidation of protein and cellulose have been described in the literature primarily with the focus on degradation in industrial processing conditions. In alkaline conditions, amino acids are released from silk in a chain unzipping mechanism in acidic conditions, the scissions are random (8,9). As the polymer deteriorates, free carboxyl and amine end groups are formed. Tyrosine oxidizes to a quinone this reaction gives aged silk its yellow coloration. Amorphous areas of the fiber are attacked first. 

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