Dextrin-based adhesives

This dextrine based adhesive is excellent for cardboard or paper to provide a quick tack and lasting adhesion. Also useful in labeling. 

Polyethylene glycols, chiefly the liquid grades, are used as humectants and plasticizers for dextrin-based adhesives. The addition of PEG prevents embrittlement and reduces the tendency of the bonded papers to curl up. 

Solutions of Natural and Synthetic Polymers in Water. Aqueous Stank- and Dextrin-Based Adhesives. The starch- and dextrin-based adhesives reached their zenith between 1920 and 1935. Since then, they have been increasingly superseded by synthetic resin-based adhesives, and they are now important only in certain applications. However, they are still used in considerable quantities for applications such as labeling adhesives, paper-sack adhesives, and envelope gums. 

The raw materials used for the various types of starch- and dextrin-based adhesives are chiefly potato starch and cornstarch and, to a far lesser extent, tapioca starch and wheat starch. Potato starch is preferred for liquid glues, at least in Europe, where it is widely available. 

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. 

The viscosity of dextrin-based adhesives can be reduced by vigorous stirring. However, the viscosity of dextrin-based adhesives generally undergoes a marked increase after production, so that they have to be left to mature. In most cases, dextrin-based adhesives are marketed only after the maturing process is complete. 

Mixed Glues. Starches and dextrins also are used in combination with other raw materials in adhesives. For example, the resistance to water of starch-based adhesives can be improved by the addition of melamine-formaldehyde or urea-formaldehyde resins. Mixtures of starch-based adhesives or dextrin-based adhesives with synthetic resin dispersions are also used. 

Poly(vinyl alcohol) is utilized as a component of starch-based adhesives.11121114 Other patents report the use of partially oxidized starch,1115 dextrins,1116 dextrins and urea,1117 borax,1118 boric acid,1119 and vinyl methyl ether-maleic acid copolymers.1120 Other patents indicate the use of poly (vinyl alcohol) with partially hydrolyzed poly(vinyl acetate),1121 nonhy-drolyzed poly(vinyl acetate),1122 and poly(vinyl chloride).1123 A few patents have reported such poly acrylic additives as poly (acrylic acid)1124 and its salts,1125 poly(acrylamide),1126 1127 A-methylacrylamide or poly(A-acryl-amide),1128 and polyethyleneimine.1129 Polystyrene has also been used,1130 as well as more complex copolymers such as a maleic acid monobutyl ester-methyl vinyl ether copolymer, together with dextrin and polyacrylamide),1131 carboxylated ethyl acrylate-styrene zinc salt copolymer,1132 ethylene-methyl acrylate-vinyl acetate copolymer,1133 vinyl acetate-vinyl pyr-rolidone copolymer,1134 and ethylene-vinyl acetate copolymer.1135 Some adhesives are compounded with SBR latex1136 1138 and phenol-formaldehyde resins.1139... 

ADHERE-TEX 1500 adhesive is used when pigment printing cotton, cotton blends, and most synthetic fabrics including fiberglass. The problem of mildew formation is eliminated with this adhesive, since it is not a starch or dextrin-base product. 

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]. 

There are two general types of water-based adhesives solutions and latexes.Solutions are made from materials that are soluble only in water or in alkaline water. Examples of materials that are soluble only in water include animal glue, starch, dextrin, blood albumen, methyl cellulose, and polyvinyl alcohol. Examples of materials that are soluble in alkaline water include casein, rosin, shellac, copolymers of vinyl acetate or acrylates containing carboxyl groups, and carboxymethyl cellulose. 

Lamination of Paper and Board. Adhesives based on starch, dextrin, glutin and poly(vinyl alcohol), and also emulsion adhesives, mainly polyfvinyl acetate), are used for the lamination of paper and board. Only when high initial tack and a lay-flat effect are required are hot glues based on glutin still in use. Starch-based adhesives modified with silicate, casein-stabilized copolymer dispersions, and rubber latices are used in the lamination of paper to aluminum foils. Modified polyacrylate solutions and reactive polyurethane adhesives are used mainly for paper-to-plastic lamination. 

Discrete particle, flat gumming, solvent-based adhesives are another method of making remoistenable adhesives. The cold-water-soluble material (usually a dextrin) is suspended in a solvent and applied to the paper and dried. Since the dextrin is not soluble in the solvent, it is deposited in discrete particles. On contact with water, the dextrin swells and will glue two pieces of paper together. The dextrin is usually used at 40% solids and a viscosity of 1000... 

Rubber and cellulosic-type solvent cements are used for attaching gaskets and blotters. Water based adhesives such as sodium silicate, starch, dextrin, and latex are used for a variety of applications such as labeling. 

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

Water-base adhesives are made of materials that can be dissolved or dispersed in water. Both natural (cellulosic, dextrin, starch) and synthetic (phenol formaldehyde, polyvinyl acetate, styrene-butadiene rubber, nitrile rubber) polymer materials are used in manufacturing water-base adhesives. Their primary application is in packaging, with a much smaller percentage usage in construction. Their share of the market, however, has been increasing due to health concerns associated with some of the solvents used in organic-solvent adhesives. 

Sealing tape has 35 to 90 pounds per ream of kraft paper as a substrate, whereas, reinforced sealing tape is based on a bonded laminate of kraft paper, reinforcing fibers, and kraft paper. The adhesives applied to these substrates may be thin-boiling, waxy starches alone, or blended with a soluble dextrin (5). More recently, blends of a soluble dextrin with oxidized potato or a hydrox-ypropyl ether of an oxidized potato starch are being used (9). Also, the acetate or succinate of an oxidized waxy starch may be used (15) as well as specially produced waxy starch acrylamide graft copolymer products (16). 

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