Boron in adhesives, caulks, and sealants 

Starch-based adhesives depend on borates to keep performance high 

The adhesive industry moves quickly without much room for disruption. That’s why it’s imperative to include borates in your starch-based or dextrin-based adhesive to reach optimum viscosity, resulting in greater tack, faster bonding, and the right fluid properties. What’s at stake if your adhesive doesn’t possess these qualities?

Manufacturing may experience costly downtime, equipment malfunctions, and unsatisfactory finished products. Insufficient boron levels often result in poor adhesion or deficient solubility, causing water damage on a material’s surface.

That’s why many cellulosic product manufacturers—from paper bag producers to corrugated board—use borates as a fundamental component in starch-based adhesive formulations.

High-quality borates from a reliable supplier such as U.S. Borax are the key for unlocking stronger bonds and ensuring production is right the first time.

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Borates: The trusted additive for starch-and-dextrin based adhesive formulations

Starch and dextrin adhesives for a range of cellulosic-based products benefit from borates’ ability to:
  • Increase tack speed

  • Achieve optimum viscosity

  • Improve fluid properties

  • Avoid gummy, stringy properties

These qualities ensure the adhesive withstands high operating speeds and pressure imposed by production equipment. Manufacturing remains error-free and efficient.

Learn more about how borates work in starch and dextrin adhesives.

Products using boron in adhesives:

  • Corrugated box board
  • Paper bags (grocery and multiwall)
  • Paper boxes
  • Carton and case sealing
  • Paper and board tube winding
  • Laminated paper board
  • Gummed paper and tape
  • Textile sizing

Better bonding starts with correct viscosity

To produce a starch adhesive formulation that meets the demands of industrial applications, starch adhesive’s tack and viscosity must be optimized. Depending on your process, starch is treated with either a hot aqueous solution of soda ash or caustic soda plus a borate compound. Borester anions create a more highly branched chain polymer with a higher molecular weight, which results in improved viscosity and tack.

A closer look at borates’ function in adhesives for paper and other cellulosic products

Borates’ impact on adhesives and overall product quality is felt across several production lines.

Boxes and corrugated cardboard

You’ll find borates in high performing starch-based adhesive for corrugated boxes and cardboard. Borates are used in the patented Stein-Hall process to increase the rate of gelatinization and achieve optimum viscosity.


Box-sealing adhesives

These adhesives must strike a fine balance. A successful box-sealing adhesive is:

  • Thin bodied, but not too gummy or stringy

  • Able to wet the board without soaking it under pressure

  • Low foaming

  • Warp-resistant

  • The right tack speed

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%).

Paper bags

There are two main types of adhesives for paper bags: Seam and bottom.

These are either starch or dextrin-based adhesives and may include borax, sodium metaborate, soda ash, and metasilicate. Excellent fluidity, non-foaming, and stable viscosity are desired attributes.

They should:

  • Be sufficiently thixotropic, keeping the paste roll covered without collapsing under the roll action

  • Adhere sufficiently and release well from the stencil applying the paste

  • Have enough wet tack to hold the bottoms closed until bags are bundled, wrapped, or weighted

  • Form a good dry bond

Tube winding: Whether you’re producing convolute or spiral tubes, you need adhesive with free flow and the correct tack for the speed of the tube run and length of cutoff.

Borates for fire resistant caulks, sealants, and epoxy

Zinc borates, under the Firebrake® product family, can improve tack performance of caulks and sealants. But it’s their excellent fire retardancy performance that can provide unique value as an additive in these applications.

Halogen-containing epoxy

In epoxy formulations, Firebrake ZB can: 

  • Replace 40-100% of antimony trioxide without affecting flame performance

  • Suppress smoke formation, and have a synergistic effect with antimony trioxide, if present 

  • Promote char (intumescent applications of epoxy resins)

Halogen-free epoxy

Firebrake ZB is synergistic and can be used in conjunction with ammonium polyphosphate, alumina trihydrate, and silica for passing fire retardant standards.


If a sealant with Firebrake ZB is exposed to heat, it expands to prevent the spread of fire into openings.

Epoxy adhesives

In both halogen and halogen-free epoxy adhesives, Firebrake ZB is used as a:

  • Flame retardant

  • Smoke suppressant

  • Afterglow suppressant

Why work with U.S. Borax to produce better adhesives, caulks, and sealants?

Pure, consistent, and flexible product options

Quality, consistency, and correct particle size distribution are paramount to controlling an adhesive’s properties. U.S. Borax delivers on all three fronts. We also offer products in special particle sizes, such as borax decahydrate.

Non-stop innovation and improvement

Since our company’s founding, research and development has been fundamental to our success. More recently, we developed a product called Polybor® Flow, a liquid that can be used for starch-based adhesives.

Unmatched technical support and guidance

When you choose U.S. Borax as a partner, you can trust our technical team to offer guidance on specific technical details—from formulation recommendations to navigating evolving regulations to controlling caking effects in borates.

20 Mule Team Borax Products

Recommended for adhesives, caulks, and sealants

Borax decahydrate by U.S. Borax logo

This product improves tack and green strength of an adhesive. It’s commonly used in starch adhesive formulations for corrugated paper and is a peptizing agent in casein-based and dextrin-based adhesives.

Learn More  

Firebrake logo

This product is used in various sealant, caulk, and epoxy formulations for effective fire retardancy, smoke suppression, and in some cases, the promotion of char.

Learn More  

Neobor logo

A concentrated sodium borate, Neobor is found in starch adhesive formulations to improve tack and green strength.

Learn More  

Optibor logo

A pure source of boric oxide, Optibor improves starch adhesive’s physical properties such as tack speed.

Learn More  

Sodium metaborate by U.S. Borax logo

Starch and dextrin-based adhesives benefit from this product’s ability to increase viscosity, speed tack, and enhance fluidity.

Learn More  

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U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 650 customers with more than 1,800 delivery locations globally. We supply around 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles northeast of Los Angeles.  Learn more about Rio Tinto.

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