Degradation of Silk Fibres

To generate deteriorated fibres for the above experiment, new silk was either thermally or photo-degraded. Silk is particularly susceptible to light damage and it is suspected that this was a significant factor in the case of the Shackleton ensign, particularly for the tin weighted cream-white threads. 

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). 

Acid and Alkaline Hydrolysis. Silk is quite resistant to chemical attack, as a result of its highly crystalline nature. However, some reagents, e.g. those used in the original processing of the cloth and atmospheric pollutants, will affect deterioration, notably over the longer term. 

Fibre-included weighting agents can promote hydrolysis of the fibroin -e.g. over time tin salts are themselves hydrolysed to amphoteric species that can affect both acid and alkaline attack. 

Besides acids and alkalis, strong oxidants used to bleach silk also have the capacity to seriously degrade the fibres. The most significant reactions occur at tyrosine and threonine side-chains, resulting in their oxidation to acids and the breaking of surrounding peptide bonds cross-links are also generated, e.g. between lysine and tyrosine residues. 

---