Are borates an envi ron me nta I Iy f ri end Iy alternative preseruative?

T HE current "green movement"

I toward more environmentally friendly products continues to gain momentum in the wood preserving industry, leading to an increased interest in alternative wood preservatives of lower toxicity, including borates.

Recent conferences, magazine articles and media advertising have fueled this interest in borate wood preservatives. But what are the real advantages and disadvantages of borate systems and what markets offer the greatest potential for these preservatives?

Borates were first used in wood preservation during the 1930s to protect Australian hardwood lumber from powder post beetle attack. This usage has continued successfully to the present day. Further markets developed for borate preservatives in New Zealand in the early 1950s with dip-diffusion treatments to protect interior building construction pine lumber against borer attack. Later, other treatment processes were added, although dip-diffusion remains the preferred treatment process in that country.

Eventually, the use of borates spread to other parts of the world, including the United Kingdom, Europe, Scandinavia, India, Africa and the United States. Use, however. continues to be limited to certain niches ideally suited for diffusible preservative systems.

Borate preservatives are water

Story at a Glance

Borates have low toxicity, but little effectiveness in high moisture, outdoor applications hardwood, log homeand interior construction materials trcatment possible. good remedial use potential.

soluble solutions of sodium borates made from sodium octaborate or from mixtures of sodium tetraborate and boric acid. These chemicals are highly effective against wood decay fungi, wood boring insects and most species of termites. They are colorless and can be broadly classified as being in the moderate toxicity class (LD50 : l600me/kg).

The high water solubility of borates is highly advantageous in diffusion treatments of "green" wood, as well as for pressure processes of seasoned material. This characteristic also makes borates suitable for treating some refractory wood species and for remedial treatments of decay problems in existing structures.

Unfortunately, this same attribute causes the greatest barrier to the wider use of borates; that is, they tend to migrate out of wood in high moisture applications leaving the wood vulnerable to a variety of wood destroying organisms.

The USDA set up stake tests with borate preservatives in the early 1930s and concluded that borates were ineffective preservatives due to the rapid failure of the stakes. Unfortunately, these tests merely proved that borates will leach in such an environment and were not a test of their fungicidal efficacy. Subsequent research has proven that borates can perform quite well in certain applications; however, until the leaching problem is overcome, the use of these preservatives will remain limited commercially to low exposure applications.

Most preservative-treated wood in the U.S. today (including lumber, poles, piling, crossties, etc.) is used in severe outdoor environments where leachable preservatives would not provide longterm protection. Preservatives for these markets must offer more permanent protection.

Nonetheless, other opportunities for borates exist in the U.S. These include the protection of hardwoods during drying and storage, interior construction where beetle attack is considered a hazard, anti-sapstain additives, and dip-diffusion treatments of log home materials, pallets, etc. Realizable potential may also lie in construction treatments to protect softwood lumber in areas where Formosan termites are prevalent and to protect structures from decay where certain building practices are used. Significant opportunities for diffusible borates also lie in the area of preventive and remedial treatments of existing wooden structures. Borate/glycol coatings (i.e., Boracol and Bora-Care) and fused boron rods (i.e., Impel Rods) have been developed to protect wooden structures from a variety of wood destroying organisms. The highly concentrated, solid boron rods offer a means of slow preservative release for extended protection in high moisture applications. They are applied to wood through a series of drilled holes and depend on moisture for distribution of the boron. Topically applied borate/ glycol solutions have been shown to diffuse very well in both wet and dry conditions and will, therefore, control a wide range of organisms.

If a technological breakthough can be achieved, borate preservatives have considerable potential in the U.S. for commercially treated wood products. However, until an effective, fixed borate preservative is developed and proven, the use of commercial borate treatments for wood exposed outdoors either above-ground or in-ground will remain inappropriate.

We at Chemical Specialties, Inc. are heavily involved in research with both fixed and unfixed borate systems. At this time. we believe the opportunities for borates are limited to relatively smaller, specialty markets, and we are actively pursuing these.