Borates in Adhesives
Borates in Adhesives: Borates are used for home and commercial use. For commercial use, they are commonly used in adhesives by the paperboard and corrugated paper industries. The primary chemical compounds for adhesive applications are sodium decahydrate, borax decahydrate, and boric acid.
Most adhesives come in liquid form. You can find adhesive substances in solid forms, such as powder, pearls, or sticks. Its strength depends on many factors, including cohesion and adhesion, thickness, shape, and thickness.
There are several types of adhesives. The primary criterion is whether a given compound chemically reacts with the materials and causes the entire weld to harden, significantly increasing its mechanical strength. Another essential criterion to consider is the raw material. Some adhesives can be made from a natural material, for instance, animal and plant adhesives.
Starch-based adhesives and dextrin/starch are made from natural polymers from the roots, tubers, or seeds of higher plants. Starch-based adhesives are used primarily in the production of corrugated cardboard. However, they also serve as paper bags, tube winding (paper and board), carton sealing, and textile sizing.
There are also synthetic adhesives, which offer the greatest range of applications. There are many types of synthetic adhesives. These include cyanoacrylates (superglue), acrylic adhesives, and polyurethanes.
Why are Borates Used in Adhesives?
Borates in adhesives serve a primary structural crosslinking function unless used as a catalyst or non-reactive additive. Borate ions in crosslinked adhesive products are bound to the adhesive matrix. Borates in adhesives can also increase viscosity by crosslinking the starch molecule. They also improve film-forming properties and the water-holding capabilities of the bond.
Borates serve different purposes in different types of adhesives. Borated dextrines are used in tube winding toilets, foil rolls, and the kitchen. The adhesive’s constituents, borates, improve its viscosity/tackiness and molecular weight. Caseins are made up of borates, which act as gelling agents for humectants and plasticisers. Glass bottle labels and wallpapers use starches and their derivatives. This adhesive contains borates which increase viscosity, stability and crosslink to give it shear-sensitive properties. Polyvinyl alcohol is commonly used in paper articles like corrugated boards and tubes for toilet paper or foil. Borates are a gelling agent in aqueous solutions of polyvinyl alcohol. Magnesium phosphate can be used to make adhesive grout. It is also helpful in the repair of products. The borates in this adhesive enable products to be sold in liquid form.
Borates in Different Types Of Adhesives
Borax decahydrate and sodium tetraborate are peptising agents for producing starch adhesives that are dextrin and casein-based. Natural starch polymers are made from wheat, tapioca, and maize. Starch polymers are excellent adhesives due to their chemical composition.
However, for many industrial applications, the tack and viscosity of these starch polymers are too slow. Starch can be transformed by hot aqueous solutions of soda ash or caustic soda plus sodium tetraborate to become a highly branched-chain polymer. This improves adhesive viscosity and fluid properties. Boron compounds regulate the adhesive’s viscosity. There are many compositions for adhesives. The borate content can vary from 0.03% to 10%. Adding sodium hydroxide (caustic soda) can lead to more active sodium metaborate, Na2O.B2O3.4H2O. This, in turn, leads to the formation of a borate starch complex.
Starch Adhesive for Corrugated Boards
A flat sheet of paper is first softened by heat and moisture to make corrugated boards. Then, it is passed through a series of corrugating rolling to become flutes. After the adhesive is applied to flute tips on one end, a single-facer linerboard is placed in contact with a fluted medium and heated and pressurized to form a single-facer web. After the adhesive has been applied to the flute tips, the liner can be added to the product and sent to set on a series of hot plates.
The adhesive is a mix of starch and borax and caustic soda. It is suspended in a paste made of cooked starch. Borax is used to buffer caustic soda, but it also serves as a viscosity control agent and provides tackiness to the adhesive. Adhesives constitute around 1-2% of the weight of the corrugated boards. No alternative technology is available to replace borates in adhesives for corrugated panels.
Animal glue is one the oldest known adhesives. Animal glue is water-miscible and is made from animal bones, hides, hoofs, horns, and other proteins by boiling them in water. Boric acid and borax are used in animal glues primarily for their ability to modify rheology, high-temperature tolerance, improved water resistance, and resistance against fungal, bacteria, and insect attacks. The heat can liquefy animal glues, giving them fast-setting properties.
PolyVinyl Alcohol-Based Tile Adhesives
A compound of cellulose ether, polyvinyl alcohol, and boric acid or its salts (preferably borax) is used as a thickener for tile adhesives. Borax or boric acid provides this adhesive with an improved thickening action.
Rubber-Based Contact Adhesives
Rubber-based adhesives can be made by mixing one or more rubbers with elastomers in an emulsifier. These adhesives are made from a mixture of poly-chloroprene emulsion and styrene acrylate latex in an optimized boric acids solution with zinc oxide as a proton inhibitor. In addition to improving the adhesive mix’s shelf life by preventing latex coagulation, the use of boric acid also accelerates the formation of the bond of the poly-chloroprene and styrene-acrylate-based contact adhesives.
Urea-formaldehyde and phenol-formaldehyde adhesives (UF) are used primarily in the wood industry to make plywood, particleboard, and medium-density fibreboard (MDF). Formaldehyde emission is essential for evaluating the health and environmental effects of wood-based boards materials. The optimal level of borax used in UF and PF adhesive formulations reduces formaldehyde emissions without affecting the mechanical strength. Boric acid can be used in polyurethane-based wood glues (PU) for wood protection. This will not affect the bonding strength.
Complex chemical reactions are required to make epoxy adhesives. Many resins can be synthesised by reacting with two or more chemicals. Boron trifluoride is used to homo-polymerize epoxy resins using a cationic catalyst. Epoxies containing boron nitride are superior thermal interface materials to silicones and greases. Two-component epoxy adhesives made from boron nitride are excellent for bonding, sealing, and coating, as well as for potting. Boron nitride-based thermally conductive epoxies have a lower density, making them ideal for aerospace and defence applications and microelectronics.
Hot-melt adhesives consist of thermoplastic solid polymers that are liquefiable at high temperatures. Reactive hot melt adhesives made from curable silicone resins use boron halids or boron complexes as curing agents. This fast-curing, reactive hot-melt glue hardens and stabilises rapidly at ambient temperature. This improves application efficiency. They are therefore instrumental in industry. Tri-phenyl, tri-fluoro-boranes can also be used to make copolymerised aromatic vinyl compounds (e.g., butadiene and styrene) for hot-melt adhesive purposes.
Cyanoacrylates are superglues, which are extremely fast curing adhesives. These adhesives are used when required for a single component. They are rapid curing adhesive with high adhesion, strength, and easy dispensing. Boron oxide and the boron trifluoride complexes can be used as polymerisation inhibitors or stabilisers during the synthesis of cyanoacrylates.
Silicone adhesives boric acid and boron oxide as fillers. Photo-initiators for UV-curable compositions are often organometallic derivatives from boronic acid. Thermally conductive silicone adhesives are made from boron nitride. Boric acid (<0.5 wt%) synthesises self-adhering silicone rubbers with improved surface properties. This is for the production of pressure-sensitive adhesive elastomers. Boric acid is known to improve metal adhesion.