A non-VOC approach of solvent-based wood preservatives for remedial treatment
M Pallaske, S Hellkamp, P Jüngel
Solvent-based wood preservatives are the workhorses in the field of remedial treatment. Due to new European regulations on the indoor air quality there is an increasing pressure on the VOC-content on these solvent-based product types. The transfer of these European regulations into national law is left up to each European member state and handled in different ways. E.g. France has introduced a VOC-classification system based on ISO 16000 and leaves the product selection up to the customer, in Germany the national building authority has established - based on the AgBB test procedure - binding delay times between treatment and the normal re-use of the facility. The VOC-issues can be approached in two different ways. Either by decreasing the VOC-exposure time by selecting a highly volatile solvent/co-solvent combination or by keeping the VOC-exposure below the regulatory limits by selecting a solvent/co-solvent combination of very low volatility. This study presents two approaches to cope with the VOC-issues of solvent based remedial wood preservatives. The first approach was to decrease the VOC-exposure time by selecting a highly volatile solvent/co-solvent combination. It ended up in wood preservative formulations with non-acceptable inflammability properties.
In the second approach a complete avoidance of VOC-emissions could be achieved by making use of a non-volatile solvent with sufficient dissolving power to directly dissolve the insecticide. This type of product showed a slightly better penetration performance compared to a standard VOC-containing “low odour”-version based on isoparaffins with directly dissolved insecticide. Considerable differences in the distribution of the biocide can be seen between volatile and non-volatile solvent based formulations. While in non-volatile solvents the insecticide stays where the solvent is, the volatile solvent based formulation showed a slight superficial insecticide accumulation resp. a slight depletion inwardly. In addition to the comparative performance test of a volatile solvent- and a non-volatile solvent-based formulation, the impact of the co-solvent on the insecticide penetration of a standard "white spirit"-formulation was demonstrated. Whenever the carrier-solvent is unable to directly dissolve the insecticide, the biocide-distribution becomes determined by the properties of the co-solvent and/or by co-solvent/carrier-solvent interactions. It was shown, that an efficient but unsuited co-solvent in a dearomatised hydrocarbon-carrier solvent could on the one hand side nearly completely stop the insecticide penetration within the first 2.5 mm below the treated surface, but showing no effect on the distribution of the carrier-solvent on the other hand side.