Preserving plant foliage with glycerine - Agriculture Western Australia. Cellulose, the major constituent of the plant 'skeleton' is brittle when dry. About 50 per cent of most plant fresh weight is water, but brittleness is usually only a problem if the water content falls below 10 per cent. Diethylene glycol and the polyethylene glycols have been used as humectants for ornamental foliage. However, their lower water holding capacity means that a greater quantity is needed for a given degree of suppleness.
Polyethylene glycols are available in a wide range of different molecular weights.
Those of interest as humectants have molecular weights ranging from 200 to 1,000. As a general rule, the water holding capacity of glycols decreases as molecular weight increases. Ethylene glycol and propylene glycol are hygroscopic, but are too volatile to be used as humectants for ornamental plant material. Sugars are used as humectants in foods. Sorbitol has approximately half the water holding capacity of glycerol and has potential as an alternative to glycerol because it is cheaper.