Effects of wollastonite on fire-retarding and some physical properties of beech wood (Fagus orientalis L.)

Abstract
Background and objectives: Fire is one of the most important wood destructive elements, causing irreparable damages. Fire retardancy of combustible materials such as wood is a mechanism in which the building materials of wood are protected from exposure to oxygen atmospheres, or reduction of heat transfer; this would ultimately delay the ignition time. The compounds which have been found to be most effective in producing flame retardance are compounds containing bromine, chlorine, or phosphorous, or combination of two or more of the compounds. Many of these compounds may affect other properties in wood. For example, fire-retardants in wood often increase water absorption, cause color changes, or lead to wood degradation. Generally, if treatment with a particular fire-retardant lead to an increase in resistance to decay, and to an improvement in the dimensional stability of wood, it is considered the best. In this study, it is aimed to investigate the possibility of using wollastonite as a fire-retardant in improving the fire resistance properties and dimensional stability in beech wood, as well as determining the optimal level of its consumption.
Materials and methods: Beech wood (Fagus orientalis L.) was used in this study. Impregnation of the specimens was carried out with wollastonite suspension at four consumption levels of 4, 6.3, 10 and 12%, using Bethel method (full-cell process). Five fire-retarding properties were measured, including weight loss (%), time to onset of ignition (s), duration of flame after removing of the piloted ignition (s), duration of glow after removing the piloted ignition (s), and the burnt area (%). Water absorption and volumetric swelling of the specimens were also measured.
Results: The results showed that fire-retarding properties were improved as the concentration of wollastonite suspension increased. The best results in terms of improving the fire properties were observed in specimens impregnated with wollastonite suspensions of 10 and 12%; these two consumptions were statistically grouped together in most of the fire properties measured. Furthermore, the treated wood specimens showed a decreasing trend in volumetric swelling with the increase in the consumption of wollastonite suspension, though the decreasing values were not statistically significant (6.3, 10 and 12 percent).
Conclusion: It was concluded that impregnation with wollastonite at 10% consumption would provide the optimum results in beech wood to be recommended to the industry. Depending on the type of wood application, and taking into account the economic aspects, other wollastonite consumptions of wollastonite suspension (even 6.3%) can also be used to improve fire properties and dimensional stability to a favorable extent in beech wood. Therefore, it can be concluded that wollastonite can be recommended as a flame retardant in wood protection.