Degradation of Cellulosic Fibres

Deterioration of each of the fibres various components will affect the mechanical performance, but to different extents and through different mechanisms. Breakdown of the intercellular glue will obviously facilitate slippage of the ultimates, and this is often a particular problem for archaeological linen. Here though, we have chosen to focus mainly on the deterioration of the structural cellulose filler, which may be the more pertinent to the weakened condition of the Victory sailcloth. 

Humidity and Heat. Moisture is crucial to the normal behaviour of cellulosic fibres. Under moderate conditions (relative humidity 45-65%) water is readily absorbed through the network of pores running through a fibre cell, it coats cellulose crystallites and acts as a plasticiser of the amorphous regions, disrupting inter-chain hydrogen bonds. Without this bound water the fibre would be permanently brittle, with an effective glass transition point way above room temperature. 

Soaking in sea spray, of particular relevance to the Victory sail, will have led to increased swelling of the fibres, due to the penetration of hydrated sodium and chloride ions. On drying, swollen fibres will suffer dimensional changes, which in turn can lead to the distortion of the fabric. For the brine-laden sailcloth, further disruption of the linen would have ensued as the salt crystallised within the fibres. 

Desiccation, under drier conditions (RH 30%), will lead to increased cross-linking of the chains in the amorphous zones through secondary bonding, and brittleness. The overt results are shrinkage and loss of flexibility. As the 

There is another key thermally-promoted deterioration mechanism, oxidation. This is driven by free radicals and results in both cross-linking and chain scission, as well as discolouration to yellow/brown. These reactions will occur slowly at normal temperatures, but are accelerated by the presence of pre-existing free radicals, such as those arising from photolysis. Lignin and, to a lesser extent, hemicelluloses are both more susceptible to thermal damage than is cellulose. 

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