Paper and board
Starches provide cost-efficient solutions to improve the quality and processability of paper and corrugated board. The paper and corrugated board industry uses various types of starches at different stages of the manufacturing process for different purposes.
The most common starches used for paper manufacture are from maize, potato, and tapioca. Starch is used in large quantities at three points during themanufacturing 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.
Cationic starch can be added to paper making stock to improve the dry strength of the finished sheet, to improve the retention of fines and fillers, or for a combination of both of these. Cationic starch is preferred because the positive charge that has been introduced onto the starch molecule chain tends to form an electrostatic bond with negative charge sites on the fibres and fines. This in turn results in better retention of the starch in the paper web. The major application of oxidized starch is as a surface sizing agent and a coating binder.
Corrugated board adhesives
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 carry the slurry of uncooked starches and prevent sedimentation. This opaque glue is called a SteinHall adhesive. 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 adhesive for corrugated board production.