Starch—a component of almost every plant—has long been used as an adhesive. (According to literature, the ancient Egyptians used a starch adhesive as a bonding agent in the making of papyrus.) Starch is a natural polymeric product, making it a good adhesive. But borate additives can significantly improve its adhesive qualities.
For many industrial applications, the natural tack of starch is too slow, and its viscosity too low. But when treated with a hot aqueous solution of soda ash or caustic soda plus a borate compound, extensive chemical changes occur. Interchain linkages can be formed through borester anions, creating a more highly branched chain polymer with a higher molecular weight. The result is improved viscosity, tack, and fluid properties. The starch and adhesive industry depends on these unique characteristics in the production of numerous products, including:
The patented Stein-Hall process exploits starch’s natural gelatinizing properties to produce a fluid, concentrated suspension of starch granules that is applied to corrugated cardboard and other products, such as convolute or spiral paper or cardboard tubes. When heated, the granules swell and burst, creating adhesion. Among other ingredients that create this suspension, borates are used to increase the rate of gelatinization and achieve optimum viscosity. By speeding tack, borates help to keep machinery running smoothly and quickly. In tube winding, borates’ ability to improve the fluidity of the adhesive is also prized, as the correct flow and tack for the speed of the tube run and length of cutoff are essential.
Borated dextrin is often used to make paper boxes. Here, as in the creation of corrugated cardboard, borates’ ability to improve the viscosity, tack speed, and fluid properties of the adhesive—even at fairly low temperatures—is highly valuable. Box-sealing adhesives must be thin without being gummy or stringy and must wet the board without soaking it under pressure. Starch-based adhesives used during the ending process are usually high-solubility/low-viscosity types blended with borax (10-15%) and high in solids (40-55%). They must have adequate tack, be low-foaming, and impart minimum warping (dimensional changes). Similarly, carton sealing and gummed paper (such as stamps and envelopes) require adhesives with controlled viscosity and viscous stability.
The paper bag industry is a large consumer of starch-based adhesives, with grocery and multiwall bags consuming the most adhesive. In grocery bags, seam adhesive must be fluid, tacky, non-foaming, and fairly stable in viscosity. Bottom pastes should be sufficiently thixotropic, to keep the paste roll covered without breaking down appreciably under the roll action. They should also adhere sufficiently and release well from the stencil applying the paste; have enough wet tack to hold the bottoms closed until the bags are bundled, wrapped, or weighted; and form a good dry bond.
20 Mule Team® borax borates also provide crosslinking to help tackify many caulks and sealants. But they also provide another benefit: fire retardancy. Firebrake® ZB is used in certain sealants that prevent the spread of fire between adjacent rooms, through expansion of the sealant into openings associated with doors, cables, and pipes when heated. In both halogen-containing and halogen-free epoxy adhesives, Firebrake ZB is used as flame retardant, smoke suppressant, and afterglow suppressant. In halogen-containing epoxy, Firebrake ZB can replace 40-100% of antimony trioxide in epoxy formulations without affecting flame performance, and Firebrake ZB is shown to suppress smoke formation even in the presence of antimony oxide. Plus, Firebrake ZB is an effective char promoter, helping with intumescent applications of epoxy resins. In halogen-free epoxy, Firebrake ZB displays synergy in fire test performance when used in conjunction with ammonium polyphosphate, alumina trihydrate, silica, and so on. It is an effective smoke suppressant in many formulations and promotes char formation.
These 20 Mule Team Borax products are developed for use in the manufacture of adhesives, caulks, and sealants.
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