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
Starch and dextrin based adhesives are commonly used for bag manufacture. Normally three adhesives are used in this application: seam, cross-pasting, and bottoming. The viscosity and solids content of these adhesives are relatively low. Generally they are made from high soluble white dextrin or acid modified starch. The bottom adhesive is made from a more viscous paste, and it generally has greater tack. Bottom pastes are normally composed of white dextrins or starch. Typical formulations for seam and bottoming adhesives are shown in the tables above.
