Silk degradation hydrolysis

The silk floss was defatted and hydrolyzed by Saeman s method [10] giving rise to xylose (73 %) and glucose (27 %), Aus indicating the presence of xylan. When the time of hydrolysis was up to 24 h, the presence of rhamnose (5 %) was also evident. However, degradation of xylose was observed after 8 h at 100 °C. 

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. 

Proteins are readily hydrolysed by microbial enzymes, and their preservation requires desiccation, freezing or pickling, to retard microbial action. The key degradation step is peptide-bond hydrolysis, which is temperature dependent. The more highly ordered and cross-linked proteins—such as keratin, fibrinogen (in silk and mollusc-shell matrix) and collagen (comprising... 

As for linen and other natural fibres, silk is sensitive to a variety of environmentally driven degradative processes, though in most cases the actual damage is caused by hydrolysis and/or oxidation. Attack on the polymer chains is generally initiated in the amorphous zones as a consequence of their more open structure and the incidence of reactive amino-acids (specifically histidine, lysine, phenylalanine, proline, threonine, tryptophan, tyrosine and valine). 

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