Development of a method to fix a Boron-based preservative into timber

Abstract

Boron, in spite of its exceptional properties as a timber preservative, is not widely used for this purpose. The three key agents that contribute to the destruction of timber are insects, fungi and ultraviolet radiation. Boron is a good fungicide and insecticide and the acrylic/styrene polymer blend resists ultraviolet attack. Treating timber with boron compounds is very easy and, in most instances, does not require sophisticated equipment. The movement of boron into timber is diffusion driven and requires moisture of between 30-50% in the timber. Unfortunately, this superb mobility of boron results in one major disadvantage, namely, the leaching of boron when moisture enters timber. Various methods have been used to impede the movement of boron out of timber (wax coating, paints, varnishes and water-based polymer coatings. None of them have been completely successful. For instance, varnishes, used to prevent boron from leaching out of timber are unsuitable because they also prevent moisture leaving the timber. This results in blistering of the coatings used to contain the boron. In this project, an all-in-one system was developed by systematically varying the nature of the boron compound and the polymer. The successful formulation, which contained disodium octaborate tetrahydrate, as the source of boron and a styrene acrylic polymer blend, has been found to: Allow the uninhibited diffusion of boron into timber. Form a clear continuous polymer film on curing on the surface of the timber. o Display good resistance to ultraviolet attack on the polymer and the timber substrate The product developed has been formulated with the following concentrations: 60 grams per litre of boric acid equivalent 150 grams per litre of boric acid equivalent 200 grams per litre of boric acid equivalent The efficiency of the acrylic/styrene polymer barrier was shown by performing qualitative tests for the presence of boron on the surface of the timber treated with the all-in-one formulation. Furthermore, leaching tests were performed by submerging the treated timber in water and thereafter, analyzing the water for leached boron at regular intervals. The results of these tests showed that the new formulation (60 gIL, 150 gIL and 200 gIL) is suitable for treatment of timber that is destined for above - ground applications. The preservative containing a concentration equivalent to 60 gIL of boric acid was sufficient for remedial treatment. The preservative containing an equivalent of 150 gIL and 200 g/L of boric acid was ideal for treating freshly felled timber. The patent application for this preservative has been accepted.