Dextrine adhesives

Dextrin adhesive Aqueous adhesive based on catabolized starch. 

In his book The Technology of Adhesives [6], John Dehnonte tells us that the first commercial glue plant was founded in Holland in 1690, that casein glues appear to have been manufactured in Germany and Switzerland in the early nineteenth century, and that the first U.S. patent (number 183,024) on a casein glue was issued in 1876. He mentions that starch adhesives were used on postage stamps when they were first issued in 1840, and that the first U.S. patent (number 61,991) on a dextrin adhesive was issued in 1867. 

The formulation of starch and dextrin adhesives can be viewed more as an art than the result of rigorous scientific study. Not surprisingly, the purpose for whieh the adhesive is to be used and the method by which it will be applied greatly determine the properties needed in the resin. Factors that must be controlled inelude viseosity, solids eontent, stability, tack, slip, substrate penetration, drying rate, flexibility, water and mierobial resistance, and cost. Some of these are determined by the type of stareh or modification, while others require the addition of an additive to give the adhesive the desired properties. In the sections below we diseuss some of the most common additives that are used with starch-derived adhesives. 

Borax (sodium tetraborate) in the presence of small amounts of sodium hydroxide is the most widely used additive to starch-based adhesives. It is commonly used in dextrin adhesives, where it increases the viscosity and acts as a tackifier and viscosity stabilizer. These effects are particularly important in machine application of adhesive to substrate. When used in adhesives, borax is often added in amounts up to 10% based on dry starch before the starch is cooked. Enough sodium hydroxide is added to convert the borax to sodium metaborate, which is the active boron species in thickening. The metaborate is able to hook two starch molecules together, forming a complex (Fig. 5) [10]. If additional sodium hydroxide is added, the complex will dissociate the viscosity of the suspension will begin to decrease with increasing sodium hydroxide [11]. 

Cartons from corrugated board are most often sealed with liquid glues or hot-melt adhesives. However, dextrin adhesives are still used as a result of their low cost and ready availability. Adhesives for sealing cartons must have low and stable viscosity, be able to form strong bonds, and set up quickly. If staining of the carton is not a concern, sodium hydroxide may be added to increase adhesion. A formulation for a white dextrin adhesive is given in Table 5. 

Structural bond—A bond that stresses the adherend to the yield point, thereby taking full advantage of the strength of the adherend. On the basis of this definition, a dextrin adhesive used with paper (e.g., postage stamps, envelopes) which causes failure of the paper, forms a structural bond. The stronger the adherend, the greater the demands placed on the adhesive. Thus, few adhesives qualify as structural for metals. A further requirement for a structural adhesive is that it be able to stress the adherend to its yield point after exposure to its intended environment. 

Dextrin compounds have strong adhesive properties and are used as pastes, particularly for envelopes, gununed paper, and postage stamps. Dextrin adhesives can bond to many different substrates. Paper and paperboard are the most common substrates. Laminating adhesives are usually made from highly soluble white dextrins and contain fillers such as clay. 

Dextrin-based adhesives are available as powdered dextrins, which are dissolved in water before application, and ready-to-use aqueous dextrin adhesives with a dextrin content of 50 - 70 % and viscosities of 3 x 10 to 3 x 10 mPa s. 

Tube Winding. Mainly dextrin adhesives are used and/or plasticized homopoly-meric poly(vinyl acetate) emulsions, but glutin glues are also used in special cases. 

Dextrin adhesives modifier Methyl vinyl United States 3,366,587 1968 GAF... 

It should also be noted that water-based polyvinyl acetate and dextrin adhesives have been replaced by hot melt adhesives, which now have over 50% of the market. The reasons for the high rate of penetration are typical of those mentioned earlier for hot melts in general. But the increased speed and ease of automation are the primaiy ones. 

Formaldehyde resins Starch and dextrin adhesives Styrene-butadiene latex binders Natural rubber latex Flot melts Solvent-based adhesives Pressure-sensitive adhesives Inorganic adhesives. 

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