Copper-octanoate - a potential reference preservative replacement for CCA in field test standards?

IRG/WP 22-20688

R Ringman, M Westin, M Klamer, A Christof, F Friese

Finding a CCA reference replacement for use in standardised test methods is of high priority since this chemical is being phased out and may in the near future be banned also for experimental and approval purposes. In this paper we assess the possibility to replace CCA reference preservative with an historical copper octanoate product. There is a huge amount of lab and field test data available for a copper octanoate preservative, “Cuprinol Tryck”, which was in use in the Nordic countries during the 70s and 80s showing that it might work as a substitute for CCA in test standards. We managed to reproduce the production process for this preservative in laboratory scale. In this study, we have examined the copper octanoate product from an impregnation point of view as well as from a wood protection point of view. Impregnation related results show that copper octanoate has a liquid uptake in wood that is significantly better than water (as measured with Wilhelmy plate), that the impregnation liquid readily penetrates the sapwood in samples mimicking poles of 15 x 15 cm cross-section. ENV 807 tests showed that a retention of 1,9 kg Cu/m³ (21 kg product/m³) fully protected the wood against biological attack in both soft-rot dominated garden compost soil and brown rot dominated sandy soil, to a level equal to CCA 9 kg/m³ and CC 10 kg/m³, while a retention of 0,6 kg Cu/m³ reduced mass loss to approximately the same extent as CCA at low retention level (2 kg/m³). These results are in accordance with old results from field test with Cuprinol Tryck in several Nordic test fields. In order to evaluate the correlation in degradation between CCA and Cuprinol Tryck in field testing according to EN 252, series of retentions reflecting the sample copper levels have been prepared for a Round Robin test. These will be installed in a number of test sites during spring 2022. Results from these experiments will be reported in future papers. Based on our current results, we conclude that the copper-octanoate preservative product would be a potential substitute for CCA in standardized durability testing.

Keywords: Copper octanoate, preservative reference, Cuprinol Tryck, CCA, CC, EN 252, ENV 807.

Conference: 22-05-29/06-02 Bled, Slovenia

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