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
The above formulation is for a dextrin adhesive with 42% solids and viscosity of 2500-3500 cps. It is commonly used for sealing cartons. Today most paperboard cartons are sealed with liquid glues or hot melt adhesive. These are generally preferred because of their high speed of operation and ability to bond strongly to many different substrates. However, dextrin adhesives are used in certain applications where low cost must be achieved. Carton sealing adhesive require a low and stable viscosity, and they must set quickly. A formulation for a white dextrin adhesive for carton sealing is provided above.
