Long-life Straw And Other Boronated Fibers
January 1997

In 1865, when Joseph Lister pioneered the use of antiseptics in surgery, he started by employing carbolic acid. Later he announced the discovery of a new antiseptic, boracic acid, "highly effective and much less irritating". In doing so, he unwittingly paved the way for significant developments in the 'green' exploitation of renewable resources at the end of the following century.

The bacteriostatic properties that led to the worldwide medical adoption of boracic (boric) acid, as a powder, in solution and in wound dressings for some 70 years, and which were later recruited to protect wood from the infections to which cellulose is prone, are now being invoked to transform natural fibers which have hitherto been under-used or wasted into long-lasting, high performance modern materials.

Borates were largely superseded in hospitals and medicine by more specific antiseptics, but their ability to prevent the growth of micro-organisms remains highly relevant to a world which increasingly embraces the need for resource conservation and waste prevention. Borates control the biodeterioration caused by bacteria, fungi, and insects by combining in solution with groups of biochemicals, such as co-enzymes, that are vital to the metabolic processes of the organisms concerned at the cellular level. These combinations subsequently become unable to take part in the metabolic pathway, and so the cells of the organisms 'starve' and become moribund.

Borates are highly effective broad-spectrum preservatives, giving full control over the fungi and insects responsible for the biodeterioration of natural fiber products. However, borates simultaneously possess very low acute mammalian toxicity, so they pose virtually no risk to pets, let alone their owners.

The reasons behind this are twofold. Mammals are unaffected by borates in the amounts used first because their vast size relative to the fungi or insects means they are not subjected to the same levels of physical exposure. Secondly mammals are safeguarded by efficient kidneys, which excrete borates and so prevent bioaccumulation.

Borates too are generally considered to have a low environmental impact. In the natural environment boron is one of the seven essential plant micronutrients - not only benign, but necessary.

In regard to wood protection, the efficacy of borate treatment has been recognized in many countries for as many as five decades. Special products, notably Tim-borŪ wood preservative, have been developed to optimize this effectiveness. Other natural fibers, susceptible to biodeterioration, can now be given similar protection.

Interest is in fact growing rapidly, for reasons of economy and environmental sustainability, into the options of converting certain fibers - until now, of only low value or even waste products - into efficient materials that meet the high standards of today's manufacturing and construction industries. Many fibers have been rejected until recently not only because they are vulnerable to insect infestation and rot, but also because they are very flammable. In short, they have been regarded as safety hazards which at the same time provide the combination of a comfortable home and ready meal for bacteria, fungi, and insects.

Borate treatment effectively rules out the bug problem, and a somewhat higher concentration also protects against fire risks.

Old newspapers, for example, are hardly worth recycling as even low-grade paper pulp once they are de-inked. But shredded, they become an excellent insulation material and are processed in huge quantities for this purpose. Unfortunately, however, the cellulosic insulation is also highly flammable and very attractive to nesting insects - two problems solved by the addition of boric acid.

Almost unlimited quantities of straw are produced every harvest, and in most countries, it is more or less wasted. Yet compressed into strawboard, it is an excellent material for interior panels in buildings - light, strong, versatile, easy to handle, and cheap. In service it performs well and as it is compressed, it is remarkably fire-resistant: until - all too soon - it can be infested by colonies of the Psocopteran book louse instead.

Treatment with Polybor® disodium octaborate tetrahydrate is very effective against book lice and other insects - the British Standard No. 4046 for strawboard specifies a 0.1 per cent mean boron content.

The use of sheep's wool, effective though it might be as an insulator in the construction industry, has largely been discounted on grounds of its relatively high cost and its susceptibility to attack from carpet beetle and clothes moth larvae. Until recently: a mixture of low-cost short or colored wool fibers treated with Polybor is now a cost effective option in many markets. A five percent borate retention ensures the insulation will not come under carpet beetle or moth attack, and although the material is still relatively expensive it is becoming a viable alternative where there are concerns about safety or environmental impact.

A new development in the use of natural fibers is to take Polybor-treated flax or hemp, and hot press the vegetable fiber with five percent polypropylene filaments to bind the mixture together under high pressure. The result? A cost-effective, robust, lightweight, rot and mold-proof board which is intriguing manufacturing industries the world over. Already it is being tested as an interior panel material for automobiles as total recyclability, which the new board has, is set to become mandatory in some European markets.

Other chemicals have been suggested and tried to bring renewable resources into play; but most fall short on the very safety or environmental grounds they seek to alleviate. Borates, some traditional and some specially developed, are helping to reduce dependence on finite materials, to optimize usage of renewable resources, and to find applications for waste materials. They are advancing the cause of genuinely sustainable technologies and living standards for us all.