One-step tannin fixation of non-toxic protein borates wood preservatives

Abstract

Materials and methods Ten specimens for each case of Pinus sylvestris sapwood of dimensions 50 • 15 x 5 mm were treated under 15 minutes vacuum (-1 bar) and 30 minutes at atmospheric pressure with solutions of (1) boric acid (5% weight/volume) + Pinus radiata tannin extract (1% w/v) + egg albumin (1% w(v), (2) boric acid (5% w/v) + Pinus radiata tannin extract (1% w/v) + collagen (animal glue AT 400, 1% w/v), and (3) boric acid (5% w/v) + Pinus radiata tannin extract (1% w/v). Untreated specimens were also prepared. The specimens were dried at 103 ~ for 4 hours. Half of the untreated and treated specimens were leached for 5 days in 20~ water using lots of 50 ml water for each specimen, changed each day with a fresh 50 ml volume of water. The leaching waters were analysed for leached proteins (Li; Tanner; Larkin) (no proteins leached), leached boric acid (Li; Tanner; Larkin) and leached tannin (Thevenon; Pizzi; Haluk); [all of the tannin was still in the wood after 5 days leaching for cases (1) and (2), while 97.2% of the tannin remained in the wood for case (3)]. Leached and unleached specimens were incubated for I month at 25 ~ on agar medium in Petri dishes inoculated with Coniophera puteana, Gloeophyllurn trabeum and Poria placenta.On each plate a leached or unleached untreated control specimen was also evaluated for % mass loss.Results and discussion The results in Table 1 indicate that the combination of tannin and proteins helps to fix the boric acid or at least to greatly retard its leaching when comparing the results to a boric acid/tannin system. While the top-performing albumin borate does not show any marked improvement when tannin is added in relation to albumin borate alone (Thevenon; Pizzi; Haluk), the collagen borate performance improves markedly when tannin is present in relation to soluble collagen borate alone (Thevenon; Pizzi; Haluk). This is due to the insolubilization of collagen by reaction with tannin by a reaction identical to what occurs in leather tanning. If not coupled with tannin, collagen based animal glue and collagen borates have instead been proved to remain soluble (Thevenon; Pizzi; Haluk)and thus to lead to much worse performances. Both albumin borate and collagen borate were added together with the tannin solution in a single impregnation step into the wood, the stability at ambient temperature of the mixed solutions being due to the low tannin concentration (at much higher tannin concentrations this would not be possible). This allows then a single step water-borne treatment with its consequent economic and technical advanFig. 1. Fungal attack on pine sapwood impregnated with boric acid (5%) + tannin (1%) + collagen (1%) as well as untreated controls (specimens at bottom) Bild 1. Pilzbefall auf Kiefernspllntholz nach Impriignierung mit einem Gemisch aus Bors~iure, Tannin und Collagen sowie unbehandelte Kontrollproben (untere Reihe) L~: 2 .r Fig. 2. Fungal attack on pine sapwood impregnated with boric acid (5%) + tannin (1%) without protein Bild 2. Pilzbefall auf Kiefernsplinth...

EFICIÊNCIA DE EXTRATO TÂNICO COMBINADO OU NÃO COM ÁCIDO BÓRICO NA PROTEÇÃO DA MADEIRA DE Ceiba pentandra CONTRA CUPIM XILÓFAGO

“…Apesar de alguns estudos justificarem a alta durabilidade natural de algumas madeiras por causa de taninos presente nas mesmas (JORGE et al, 2001;MELO et al, 2010), outros citam que os taninos possuem baixa toxicidade como preservativos, mas que podem fixar biocidas pelas suas excelentes propriedades quelantes, o que significa que possuem habilidade em formar complexos com metais (LAKS;MCKAIG, 1988;THEVENON et al, 1998;BRAND et al, 2006), dificultando sua posterior lixiviação.…”

Characteristics, Industrial Application, and Prospects of Continuous Extrusion Technology

“…Pizzi and Baecker [22] believed that boric acid could be used to induce the self-condensation of flavonoids and tannic acid, so that some boric acid could be stably fixed in the wood network. Thevenon et al [23] further revealed that tannins binding to proteins could better fixe boric acid or at least significantly delay its leaching. Mazela et al [24] found that 95% boric acid could be fixed by treating wood with protein preservatives and then tannic acid, and that wood treated with a mixture of boric acid and tannic acid could resist the attack of brown-rot fungi [25] .…”

Wood products and green chemistry

“…Wood preservatives based on protein borates, both obtained by just mixed water solutions of protein and boric acid, as well as in the case of premanufactured protein borate salts were shown to be a good method of greatly retarding the leaching of boron from treated timber (Thevenon et al 1997(Thevenon et al , 1998aThevenon and Pizzi 2003). Thus, just premixed albumin + boric acid, premanufactured protein borate, and soy protein + boric acid all showed good preservative performance and much retarded leaching of boron.…”