Synthesis and evaluation of phosphortriamidates in wood for thermal and fungal decay protection

Abstract

It is estimated that there are almost 500 000 residential structure fires every year attended by US fire depart­ ments. These fires killed approximately 3700 people in 1995 (Hoebel 1998). Proper treatment of wood products with fire retardants would reduce the damages to build­ ings and save lives. Phosphate fire retardants have been used in wood products (Juneja 1972; Juneja and Rich­ ardson 1974; AWPA standard 2004); however, they decrease the wood strength over time (LeVan and Winan­ dy 1990; LeVan et al. 1990). One method to minimize the strength loss is to replace phosphate with phosphor­ amidates (phosphoramides) as fire retardants. The P-N bonds in aromatic and some aliphatic phosphoramidates are stable to alkaline and some acidic conditions (Chao et al. 1995) and have been shown to be better dehydra­ tion agents and phosphorylation catalysts for cellulose (Langley et al. 1980). It has been demonstrated that phosphoramidates in cellulose promote retention of phosphorus in char and increase char yield after pyroly­ sis (Hendrix et al. 1972; Pandya and Bhagwat 1981). Our previous studies proved that wood reacted with phosphoramidates produced in situ from phosphorus pentoxide and aromatic and aliphatic amines at 1158C had an elevated resistance to thermal and fungal deg­ radation. Wood treated in this way degraded thermally at lower temperatures in the range of 254–3048C at maxi­ mum pyrolysis rate loss (control 3778C) and char yields increased to 32.0–44.7% (control 20.1%) (Lee et al. 2004a). Phosporamidate reacted wood prevents decay by a brown-rot fungus Gloeophyllum trabeum (Pers.: Fr.) Murr. MAD-617 at concentrations of 8.1–19.2 mmol/100 g wood. Wood destruction by the white-rot fungus Trametes versicolor (L: Fr.) Quel. MAD-697 was also prevented at concentration levels between 2.9 and 13.3 mmol/100 g wood (Lee et al. 2004b). However, the preparation of treated woods needs 4–24 h reaction time in N,N-dimethylformamide and it is too complicated for practical applications. The objective of this study was to evaluate the possi­ bility of simplification of the process. The question in focus was simply whether phosphortriamidates impreg­ nated wood would be as effective concerning fire resis­ tance and fungal decay as phosphoramidate bonded wood.