Effect of short-chain silicones bearing different functional groups on the resistance of pine (Pinus sylvestris L.) and beech (Fagus sylvatica L.) against decay fungi

Malte Pries,Karl-Heinz Kaesler,Holger Militz,Carsten Mai,Roland Wagner

doi:10.1515/hf-2012-0065

Abstract

Abstract Blocks of pine sapwood and beech wood were treated with water-based emulsions containing short-chain silicones with different α-ω-bonded functional groups, such as diamino, carboxyl and carbonyl, betain, and epoxy groups. The weight percent gain upon treatment of the pine wood specimens was relatively high (10%–20%), but their cross-sectional bulking was low (1%–2.5%). Thus, the anti-shrink efficiency (ASE) due to the treatment was also low. The first water-submersion tests revealed some hydrophobation of the treated wood. A second submersion test, however, revealed successful hydrophobation only for betain-functionalised material. The carboxylated silicone even increased the speed of water uptake as compared to the controls. The samples treated with silicones bearing epoxy, diamino, and carboxy functionalities showed a distinct reduction in mass loss compared to the control samples after 16 weeks of incubation with the fungi Coniophora puteana and Trametes versicolor according to EN 113 and CEN/TS 15083-1, whereas the betain-functionalised silicone did not enhance fungal resistance. All silicones tested lowered the mass loss in a soft rot test according to ENv 807. The mode of action of the silicones is discussed.

Highlights

Wood in outside applications, when directly exposed to weathering, needs to be protected either by preservative treatment or by coating
Weight percent gain (WPG), bulking, and water uptake were tested on Scots pine (Pinus sylvestris L.) sapwood specimens [25 mm× 25 mm×10 mm (Radial×Tangential×Longitudinal), shortly named “anti-shrink efficiency (ASE) samples”]
Water uptake was not reduced by most shortchain silicones tested, mass loss due to basidiomycete attack was considerably decreased

Summary

Introduction

Wood in outside applications, when directly exposed to weathering, needs to be protected either by preservative treatment or by coating. Less toxic preservatives and wood modification without biocides are preferable alternatives (Evans 2003) In this context, organosilicon compounds were tested, especially silanes and polydimethylsiloxanes (silicones) (Mai et al 2003; Hill et al 2004; Donath et al 2006a,b). Weigenand et al (2008) treated Scots pine sapwood with an amino silicone microemulsion bearing a chain length of 300–400 dimethylsiloxane (DMS) units. At higher concentrations they found improved dimensional stability and high decay resistance of the treated wood to white and brown rot fungi. The effect is assessed on the basis of water uptake, dimensional stability, and fungal decay of the samples

Materials and methods

Results and discussion

Conclusion