POLYSACCHARIDES IN NATURE

Background

Polysaccharides are very common in Nature serving as plant building material (cellulose) and reserve energy (starch). Polysaccharides may also serve highly special functions such as protective coatings for bacteria and other cells. Polysaccharides are polymers made up from simple sugars such as glucose and fructose.

Polysaccharide have been utilised as a source for food (starches) by animals and man but other uses of polysaccharides can be exemplified by paper (cellulose, wallpaper glue (starch or cellulose derivatives) and thickeners for food products.

Polysaccharides are generally chemically inert and they are all non-toxic and do not cause allergies.

Sacrificial coatings

Polysaccharides are ideally suited for the production of water based sacrificial types of coatings since they readily forms films with or without an intermediate stage of gel formation. When a polysaccharide (or mixture of polysaccharides) forms a gel it means that large amounts of water (generally more than 90%) are trapped in a three-dimensional lattice generated by the polysaccharide. This gel can, upon drying, loose most of its water changing into a film in the process.

When a polysaccharide solution dries into a film (with or without an intermediate gel stage) the forces exerted by the molecular packing will press out water from the film firmly bonding the polysaccharide chains together. This phenomena which is called hysteresis can be strong or weak depending upon the polysaccharide structures.

Polysaccharide coatings are well suited to protect surfaces against contamination such as paints (graffiti) or other oil based contaminants. Polysaccharide coatings also protect surfaces well against most other contaminants such as salts bird droppings insects etc. The protective capacity is due to the fact that even a dry polysaccharide film still contains some water bound in the film. This water acts like „room temperature“ ice layer preventing contaminants to pass through.

The absorption of water is often a slow process at room temperature but it can be speeded up by increasing the temperature. When absorbing water the polysaccharide film swells and becomes soft. The absorption can be stopped at an intermediate gel stage or may be allowed to continue until the film completely dissolves. A gel intermediate stage can be collapsed by increasing temperatures.

Polysaccharide coatings can also contain ingredients, such as buffers, in order to regulate the pH of the surface.