Starch or amylum is a polysaccharide carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. Starch is produced by all green plants as an energy store. It is the most important carbohydrate in the human diet and is contained in such staple foods as rice, wheat, maize (corn), potatoes and cassava.

Pure starch is a white, tasteless and odorless powder that is insoluble in cold water or alcohol. It consists of two types of molecules: the linear and helical amylose and the branched amylopectin. Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80% amylopectin. Glycogen, the glucose store of animals, is a more branched version of amylopectin.

Starch can be used as a thickening, stiffening or gluing agent when dissolved in warm water, giving wheatpaste.

Energy store of plants

In photosynthesis, plants use light energy to produce glucose from carbon dioxide. The glucose is stored mainly in the form of starch granules, in plastids such as chloroplasts and especially amyloplasts. Toward the end of the growing season, starch accumulates in twigs of trees near the buds. Fruit, seeds, rhizomes, and tubers store starch to prepare for the next growing season.

Glucose is soluble in water, hydrophilic, binds much water and then takes up much space; glucose in the form of starch, on the other hand, is not soluble and can be stored much more compactly.

Since starch is a reserve sugar for the plant, glucose molecules are bound in starch by the easily hydrolyzed alpha bonds. The same type of bond can also be seen in the animal reserve polysaccharide glycogen. This is in contrast to many structural polysaccharides such as chitin, cellulose and peptidoglycan, which are bound by beta-ties and are much more resistant t

o hydrolysis.

Papermaking is the largest non-food application for starches globally

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consuming millions of metric tons annually. In a typical sheet of copy paper for instance, the starch content may be as high as 8%. Both chemically modified and unmodified starches are used in papermaking. In the wet part of the papermaking process, generally called the “wet-end”, the starc

hes used are cationic and have a positive charge bound to the starch polymer. These starch derivatives associate with the anionic or negatively charged paper fibers / cellulose and inorganic fillers. Cationic starches together with other retention and internal sizing agent help to give the necessary strength properties to the paper web to be formed in the papermaking process (wet strength), and to provide strength to the final paper sheet (dry strength).

In the dry end of the papermaking process the paper web is rewetted with a starch based solution. The process is called surface sizing. Starches used have been chemically, or enzymatically depolymerized at the paper mill or by the starch industry (oxidized starch). The size – starch solutions a

re applied to the paper web by means of various mechanical presses (size press). Together with surface sizing agent the surface starches impart additional strength to the paper web and additionally provide water hold out or “size” for superior printing properties. Starch is also used in paper coating as one of the binders for the coating formulation a mixture of pigments, binders and thickeners. Coated paper has improved smoothness, hardness, whiteness and gloss and thus improves printing characteristics.

Corrugated board adhesives are the next largest application of non-food starches globally. Starch glues are mostly based on unmodified native starches plus some additive such as borax and caustic soda. Part of the starch is gelatinized to carrier slurry of uncooked starches and prevent sedimentation. This opaque glue is called a SteinHall adhesives. The glue is applied on tips of the fluting. The fluted paper is pressed to paper called liner. This is then dried under high heat, which causes the rest of the uncooked starch in glue to swell/gelatinize. This gelatinizing makes the glue a fast and strong for corrugated board production.

Another large non-food starch application is in the construction industry where starch is used in the gypsum wall board manufacturing process. Chemically modified or unmodified starches are added to the stucco containing primarily gypsum. Top and bottom heavyweight sheets of paper are applied to the formulation and the process is allowed to heat and cure to form the eventual rigid wall board. The starches act as a glue for the cured gypsum rock with the paper covering and also provide rigidity to the board.

Adhesives – Starch is used in the manufacture of various glues for book-binding, wallpaper adhesives, paper sack production, tube winding, gummed paper, envelop adhesives, school glues, bottle labeling.

Starch derivatives as yellow dextrins can be modified by addition of some chemical forms to be a hard glue for paper work, some of those forms are Borax, Soda Ash, which mixed with the starch solution at 50-70 °C to gain a very good adhesive, Sodium Silicate can be added to reinforce this formula.