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Fire Properties of Wood Materials Treated With Ammonia Compounds

In this study, fire and water absorption properties of solid wood and plywood treated with commercial fire retardants, monoammonium phosphate (MAP), diammonium phosphate (DAP) and ammonium sulphate (AS) as well as quaternary ammonia compounds, didecyl dimethyl ammonium chloride (DDAC) and didecyl dimethyl ammonium tetrafluoroborate (DBF) of which fire properties have not studied yet were evaluated.

Solid wood specimens were obtained from sapwood portions of a scotch pine (Pinus sylvestris l.) log, whilst plywood specimens were cut from plywood panels manufactured with birch and spruce veneers by applying phenol formaldehyde resin at a rate of 200 g/m2 and using a pressure of 1.2 N/mm2 at 140C for 12 min.

All specimens were treated with 1% and 4% aqueous solutions of the chemicals stated above. For fire properties, ASTM E 69 and ASTM 1354 standard methods were followed. Water absorption properties were determined based on TS EN 317 standard method. In the tests according to ASTM E 69 standard method, mass losses in the specimens during the tests were determined; however, more detailed investigations were performed following ASTM 1354 standard method such as mass loss in the specimens, heat release rate, time for sustained ignition, effective heat of combustion, specific extinction area, peak heat release rate, residual mass fraction and flame spread index (FSI).

For statistical analyses of the data, one way variance analysis (ANOVA) were used to compared several groups of observations and all data were then statistically compared by tukey’s test. The results from the study were also compared with previous results done by several researchers.

In the fire tube tests based on ASTM E 69 standard method, 84% and 87% mass losses were found in the solid wood specimens treated with 1% and 4% DDAC, respectively. DBF, however, was resulted in slightly less mass losses in the solid wood specimens treated with the same concentration levels. In the tests with MAP, DAP, and AS, considerably less mass losses occurred in the solid specimens treated with 4% of the chemicals. 54%, 67%, and 71% mass losses were obtained in those specimens; however, mass losses increased when the specimens were treated with 1% solutions of the same chemicals. Control specimens had 82% mass loss in the tests and similar results were obtained in the plywood specimens.

In the cone calorimeter tests based on ASTM 1354 standard method, no specimens were rated as class a which is the most restrictive requiring fire retardant treatment of wood products. In MAP, DAP and AS-treated specimens, FSI values increased from class C to class B as solution concentrations increased from 1% to 4%. However in the plywood specimens treated with as, no class change was determined as the concentration level increased to 4%. In the specimens treated with the quaternary ammonia compounds, DDAC and DBF, only DDAC-treated specimens were class B and all other specimens treated with dbf showed poor fire properties based on the FSI evaluations.

Total heat release rate curves over the duration of the tests showed that total heat release rates of the specimens treated with MAP, DAP, and AS were much lower than those of both DDAC and DBF-treated specimens and untreated control specimens. With increase in the solution concentration in MAP, DAP, and AS, total heat release rates of the specimens decreased.

Water absorption tests revealed that no clear relationships were determined due to probably low retention levels of the chemicals in the specimens.

Overall, MAP, DAP, and AS showed better fire performance as fire retardants; however, DBF and DDAC chemicals showed poor fire properties based on both ASTM E 69 and ASTM 1354 standard tests. In this study, considerably less retention levels of the chemicals when compared to commercial applications. It is likely that higher retention levels of DBF and DDAC may result in better fire performance in both solid wood and plywood panels.