The paper industry uses various types of starches at different stages of the manufacturing process for different purposes. Currently, the most common starches used for paper manufacture are from maize, potato, and cassava.

Cassava starch has very good properties that are highly desirable for the paper manufacturer. Cassava starch, as a dominant source of starch in Nigeria, possesses a strong film, clear paste, good water holding properties, and stable viscosity. It should be the most suitable material for the paper industry in West Africa. In the paper and board industries, starch is used in large quantities at three points during the manufacturing process:

• at the end of the wet treatment, when the basic cellulose fiber is beaten to the desired pulp to increase the strength of the finished paper and to impart body and resistance to scuffing and folding;
• at the size press, when the paper sheet or board has been formed and partially dried, starch (generally oxidized or modified) is usually added to one or both sides of the paper sheet or board to improve the finish, appearance, strength, and printing properties;
• in the coating operation, when a pigment coating is required for paper, starch acts as a coating agent and as an adhesive.

Cassava starch has been widely used as a tub size and beater size in the manufacture of paper, in the past mainly on account of its low price. A high color (whiteness), low dirt and fiber content and, above all, uniformity of lots are needed in this instance. An important new application of starch is in the machine-coating of magazine paper, formerly done exclusively with caseins. There are indications that cassava is particularly well-suited to the purpose; however, definite specifications for the starch still have to be worked out.

Textile industry

In the textile industry, starch is used in three main areas: sizing, finishing and printing. Approximately 80% of the starch used in textiles is used in sizing where individual fibers of yarn must be shaped or formed into a warp that passes through a sizing solution that coats the surface of the twisted warp. The coated yarn is then heated to dry the size and a beam of warp is ready for weaving.

Properties of the starch used are abrasion resistance, flexibility, ability to form a bond to the fiber,to penetrate the fiber bundle to some extent and to have enough water holding capacity so that the fiber itself does not rob the size of its hydration. Finishing is an inclusive term,meaning the transformation of grey goods from the loom to a finished product that is attractive to the consuming public. It includes the process of covering blemishes or defects that may be in the yarn.

Textile printing, or the impression of a design on fabrics, requires a carrier for the dyes and pigments and modified starches have found special uses in these applications. Printing pastes are high viscosity medias that preferably will not change on ageing and will resist the effect of added acids or alkalis as required by color agents. A sharp image is required and thus a short non stringy paste. Modified starches are frequently mixed with other industrial gums to give the required viscosity and paste characteristics.

Glass fiber sizing is a special case among textile fibers sized with starches. Starches finding use as glass fiber sizes are those which have high film strength and are incompletely cooked under normal cooking conditions, but which still form a good film. The characteristic of dispersion instability appears to be one of the more desirable properties. Thus the starch products most frequently found are cross-linked starches, corn and potato, high amylose varieties and their derivatives, as well as some cationic starches. Although most of the glass-sized yarn made goes into fabric uses, a portion is used for electrical insulation and in circuit boards.

Adhesives industry

Starch is a popular base for adhesives, particularly those designed to bond paper in some form to itself or to other materials such as glass, mineral wool, and clay. Starch can also be used as a binder or adhesive for non paper substances such as charcoal in charcoal briquettes, mineral wool in ceiling tiles and ceramics before firing. The starches most commonly used for the manufacture of adhesive pastes are maize, potato, and cassava; of these cassava starch appears more suitable in several respects.

Cassava starch adhesives are more viscous and smoother working. They are fluid, stable glues of neutral pH that can be easily prepared and can be combined with many synthetic resin emulsions. Corn and rice starches take a much longer time to prepare and a higher temperature to reach the same level of conversion. For top-quality work, cassava starch is thought to be ideal, because it is slightly stronger than a potato starch adhesive while being odorless and tasteless, excellent as an adhesive for postage stamps, envelope flaps, and labels. Certain potato pastes have bitter tasting properties while cereal starches exhibit a cereal flavor.

Adhesives from cereal starches have poor mobility and are more suitable for purposes where short parts are required, for example, in the manufacture of corrugated boards. Wheat starch is usually used as a thick paste in the adhesive base for bill posting and the paper bag industry. Poster pastes used for billboards, wallpaper, and other pasting operations that the manual alignment of patterns or edges also tend to utilize high-viscosity starches. Satisfactory texture or slip properties may be achieved via cross-linking. Properties required include low shear resistance or “slip” permitting the paper to be aligned precisely without losing contact with the substrate, good open time (range of tack), and slow setting speed. Gummed tape employs middle-of-the-range viscosities. Properties required include the rapid absorption of water by the dried film, high cohesive strength (tackiness) when wet, limited tendency to curl, stable re moistening properties in the dried film, and low application viscosity.

To meet these requirements it is important that the starch should have little or no tendency to retrograde in the dried film. Using starches low in amylose can most readily achieve this property and/or by subjecting the starch to retrogradation inhibiting treatments on base starches such as cassava, potato, or waxy cereal starches which is the preferred approach. A popular type of bottle labelling adhesive is the “jelly gum” made primarily from cohesive starches (root or waxy cornstarch), which have been cooked in sodium hydroxide. Properties required are that the starch be high in molecular weight, “snappy”, have the ability to pick up the label and anchor it to the bottle even if the bottle is wet, and “ice proof”, resistant to re solubilizing, especially in cold water.

Users of these products are not generally concerned with cyanide content, microbiology, color, taste or odor but would not expect a product to shown signs of mold. Users of paperboard adhesives may have specifications for shelf-life and bonding characteristics but are normally flexible if the price is attractive. Starch-based adhesives in the manufacture of paperboard consist mainly of starch or flour blended with certain chemicals (Tables 1-3). The essential ingredients in starch-based adhesives (SBA) are starch/flour, gelatinization modifier Sodium hydroxide(NaoH), viscosity enhancer/stabilizer (borax) and preservative (sodium formaldehyde). The amount of borax and NaOH must be determined experimentally so as to provide a SBA with the correct viscosity and pasting temperature to meet the requirements.

• Peelers
• Washers
• Graters
• Pressers
• Extruders
• Millers
• Dryers
• Pelletizers
• Sealers
• Packing machines