Paper industry, starch

Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

Nonfood Uses. Native com starch is principally used in nonfood appHcations in mining, adhesives, and paper industries. Pregelatinized starch is chemically unmodified, but it is physically modified. Pregelatinized starches are used to decrease water losses in oil-weU drilling muds, in cold water-dispersable wallpaper pastes, and in papermaking as an internal fiber adhesive. 

Dextrose, obtained from starch, is the raw material for sorbitol and other sugar alcohols and polyols. Isolated starch (usually from corn) can be chemical modified and is used in large amounts as an inexpensive binder in the textile and paper industry. Chemically modified starch can be used as super-absorbers or in polymer manufacturing. 

The paper industry constitutes the largest single industrial market for starch in the world. If the world production of paper is about 235 MM tons, starch production for paper may be estimated at about 3 MM tons. This recognizes that large volume items such as newsprint and tissue are essentially non-starch users. 

Oxidized Starches. Alkaline hypochlorite treatment introduces carboxyl and carbonyl groups, effects some depolymerization, and produces whiter (bleached) products that produce softer, clearer gels. Ammonium persulfate is used in some paper mills with continuous thermal cookers to prepare in situ bigb solids, low viscosity dispersions. Most of the hypochlorite-oxidized starch and all the ammonium persulfate-oxidized starch is used in the paper industry. The low solution viscosity and good binding and adhesive properties of these products make them especially effective in high solids, pigmented... 

Enzymes such as "cellulases" and a-amylases are currently used by several industries to hydrolyze cellulose or starch to products such as dex-trins, syrups, and sugars. Such reactions represent the key first step toward the production of a variety of useful chemicals and sweeteners and are also useful in the pulp and paper industry for fiber modification and de-inking. 

One of the most abundant biopolymers available in nature is starch. Starch is a polysaccharide consistent of glucose monomers and is found in all green plants. Next to its occurrence in food and its use in food-related industries, the major application of starch is in the paper industry, followed by the adhesives industry. 

The paper industry is the main non-food outlet for starch and consumes 17% of the European starch production. Starch-cellulose-starch bonds are created and contribute to the internal cohesion of the paper sheet. 

Advantageously, the viscosity and the gelatinisation temperature are lower than that of native starch. Starch derivatives are used in the paper industry for coating and glues. 

Non-ionic starch ethers are used in the food industry to avoid water release from frozen food and in the paper industry as a coating agent. 

Cationic starch ethers are used in the paper industry to increase the cohesion and rigidity of cellulose fibres and as a flocculant for the selective separation of negatively charged particles. 

The performance and quality of starch can be improved through chemical modification (see Chapter 17). Chemical modifications provide processed foods, such as frozen, instant, dehydrated, encapsulated and heat-and-serve products, the appropriate texture, quality and shelf life (see Chapter 21), and improved processing condition tolerance, such as improved heat, shear and acid stability. Modification also allows starches to be used in the paper industry (see Chapter 19) as wet-end additives, sizing agents, coating binders, and adhesives and as textile sizes. 

Enzymes such as a-amylase and (3-amylase can break the starch chains into maltodextrins and starch sugars such as glucose and maltose. The heat-stable enzymes convert the starch after dissolving the starch by jet-cooking. Enzymatically converted starches are used in the food industry (confectionery, baking products, sweeteners), paper industry (surface sizing) and the fermentation industry. 

Cationic starches are widely used as wet-end additives in the pulp and paper industry to enhance starch and filler retention during papermaking. Use of cationic starches increases paper strength and decreases biological oxygen demand (BOD) of paper mill effluent. Presently only cationic corn and potato starches are used by Canadian paper mills. The degree of substitution (DS) of normal, waxy, high-amylose barley... 

This review has shown that most studies on barley starches have been focused on understanding the fine structures, particle size distribution, chemical composition, gelatinization properties and susceptibility towards enzyme hydrolysis. However, there is a dearth of information on the rheological and retrogradation characteristics of barley starches from different cultivars. Furthermore, the response of small and large barley starch granules towards physical and chemical modification needs investigation. Research in the above areas is underway in our laboratories. It is hoped that this study may improve the utilization of different types of barley starches for specific products within the food and paper industry. 

The major starch sources are corn, potato, waxy maize, wheat and tapioca. Refined starches are supplied in powder form or as slightly aggregated pearl starch.16 Unmodified (native) starch is rarely used in the paper industry, except as a binder for laminates and in the corrugating process. Most starches for use in papermaking are specialty products that have been modified by controlled hydrolysis, oxidation or derivatization.17... 

Recent trends in the paper industry have had an impact on starch supplies. The implementation of statistical process control has led to more awareness that the production of high-quality paper grades depends on the use of high-quality materials. As a consequence, there is increased emphasis on acceptance specifications for starch supplies according to ISO guidelines and more rigorous testing in order to ensure consistently uniform quality. 

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