Boric acid wood products

Boric acid is used as an antiseptic in mouthwashes, eye washes, and ointments a preservative in natural products to protect wood against insect damage in washing citrus fruits as a catalyst in hydrocarbon oxidation as a flame retardant in cellulose insulation in nickel electroplating baths and as a buffer in ammonia analysis of wastewaters hy acid titration. 

Inorganic boron compounds are generally good fire retardants (59). Boric acid, alone or in mixtures with sodium borates, is particularly effective in reducing the flammability of cellulosic materials. Applications include treatment of wood products, cellulose insulation, and cotton batting used in mattresses (see Flame retardants). 

Borax pentahydrate is an effective flame retardant for wood/cellulosic materials in terms of surface flammability. However, due to the Na20 moiety, it can promote smoldering combustion in cellulose. Thus, in cellulosic material and wood products, it is commonly used in combination with boric acid, which is an effective smoldering inhibitor. For example, the treatment of wood fibers with a partially dissolved boric acid and borax pentahydrate slurry (-1.75% by wt. of boron) results in Medium Density Fiberboard (MDF) that is claimed to pass the ASTM E-84 Class 1 surface flammability standard.12 The additional examples of using borax pentahydrate and boric acid combination are presented in Section 9.2.2.1. 

Due to their low dehydration temperatures and water solubilities, boric acid and sodium borates (borax pentahydrate and borax decahydrate) are mostly used as fire retardants in wood/cellulosic products such as timbers, plywood, particle board, wood fiber, paper products, and cotton products. In recent years, boric acid has also been used as fire retardant in epoxy intumescent coating, pheno-lics, urethane foam, and so on. When necessary, boric acid can be coated with silicone oil such as silicone to alleviate its water solubility in water-based coating. 

Wood and its related products have been used extensively in the construction and transportation industries. Boric acid, borax, ammonium phosphate, melamine phosphate, dicyandiamide, and urea derivatives are commonly used flame retardants in wood. Depending on the specific application, borax pentahydrate (or borax decahydrate), and boric are normally used together. 

Wood Composites—these are resin-bonded composite boards where the particles are wood shavings, flakes, chips, or fibers bonded with thermosetting adhesives that can be urea formaldehyde, melamine formaldehyde, phenol formaldehyde, or diisocyanate. In recent years, the markets for OSB and MDF board have been rapidly increasing. Most particle board production uses urea-formaldehyde as a binder that is acid setting. Hence, sodium borates (alkaline) can interfere with the setting. As a result, boric acid has been the major boron compound used as the flame retardant in particle board.28 29 Typically, a loading of 12%-15% of boric acid in MDF is required to meet the ASTM E-84 Class A rating. If sodium borate is used as a flame retardant, phenol-formaldehyde binder, that is compatible with alkaline chemicals, is commonly used. 

It is well known that wood samples containing phosphorus compounds can release phosphoric acid that accelerates the dehydration and carbonization of wood (i.e., with decreased threshold temperature and activation energy). As a result, phosphate renders the main decomposition of wood at lower temperatures (<300°C) and results in the formation of less flammable products and correspondingly more char. On the other hand, boric acid can increase the thermal stability of wood via a different pathway (i.e., increase in threshold temperature and activation energy), and thus suppresses the mass loss and stabilizes the char. 

Most FR formulations are not resistant to leaching by water. Therefore, there have been increased efforts to develop leach-resistant chemicals that can be impregnated into wood products for use in exterior or high-humidity applications. Some of the proposed leach-resistant systems include chemical combinations that form insoluble complexes, amino-resin systems, and monomers that polymerize in the wood. A common amino-resin system for exterior use is dicyandiamide phosphoric acid formaldehyde. Guanylurea phosphate-boric acid also is a commonly used organic phosphate salt for modern commercial FR wood. 

Boron compounds have been used in several ways to achieve reduced flammability of wood products. Borax and boric acid can be incorporated into particle board chips before addition of a dicyan-diamide, phosphoric acid, amino-resin system 85). They can also be used to produce a fire-retardant hardboard. Riem and Dwars 86) added water-soluble ammonium borate to wood fibers before the board was formed. A 6-7% boron content produced a hardboard that had a flame spread of 25 or less. 

Other inorganic compounds have also found an application. CNSL has long had an indigenous use as a wood preservative and the employment of boric acid and of arsenic oxide to enhance this action has been studied (ref. 257). It seems most likely that the products are oligomers, hydrogen-bonded (in the case of boric acid)... 

Boric acid and borax are used to produce a large variety of diverse products (Woods... 

Sodium Borates (11). These water-soluble salts, made by U.S. Borax and others, have been known since the eighteenth century as nondvu-able flame retardants for cotton, rope, canvas, and paper. The hydrated salts can act as endothermic heat sinks and moreover the salt fuses to a nonflammable glassy barrier layer. Sodium borates, in particular borax (sodium tetraborate decahydrate [1303-96-4]), are used in disposable paper and nonwoven cellulosic products, and as wood flame retardants where their water solubility can be tolerated. The borate salts are effective on flaming combustion but allow severe afterglow they are best used in formulations with afterglow preventatives, and often used with boric acid. 

Boric acid (H3BO3) 70 4.7 Urethane foams, paper products, cotton batting and wood composite board... 

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