Starch and dextrin adhesives are readily available, low in cost, and easy to apply from water dispersion. They are considered to be the least expensive class of paper packaging adhesive. Formulated starch and dextrin adhesives can be applied hot or cold. These adhesives are generally provided to the end-user as powder and mixed with water prior to use to form a relatively thick paste.
Dextrin adhesives are manufactured by dry-roasting starch in the presence of an acid catalyst. Through treatments with heat and acid, the starch molecules are hydrolyzed into small fragments, and then repolymerized into highly branched, readily soluble polymer molecules of moderate size. Corn starch is commonly used because of its low cost and ready availability, although other starches are also employed.
RESULTING PROPERTIES
Laminating adhesives must exhibit high tack, low permeation of the substrate, and non-curling behavior. The adhesive must also meet the requirements of the laminating equipment. White dextrin is often used in this application. A typical formulation is shown in Table 7. Sugar, sodium nitrate, or urea is often added at 30-50% of the dextrin to increase solids and to control open time. Foil laminations require resin based adhesive for adhesion and water resistance. Alkaline starch types yield excellent adhesion to aluminum foil and good heat resistance, but poor water resistance.
