- Liu, Jing
University of Maine
Pressure treatment of transmission poles creates a well-treated outer shell of wood which surrounds an untreated core. The well-treated outer shell is resistant to fungal decay. In practice, however, checks in wood timbers or poles can often form, allowing decay fungi and insects to attack the untreated core and resulting in internal deterioration. Compounding this problem, wood of many refractory species, such as spruce, can not be easily treated by conventional pressure processes because of poor permeability. The treated shell of these species usually is very thin and therefore the wood members are quite susceptible to internal decay. Evidence had previously indicated that fumigant treatments can effectively control internal decay in transmission poles and other large wood timbers. Fumigants are gas phase reagents, and thus can readily penetrate where liquid preservatives cannot.
Diffusion coefficients and effective transfer coefficients in red spruce wood of two commonly used fumigants, methyl isothiocyanate and chloropicrin, were measured. The sorption isotherms of these two fumigants were also determined. A mathematical analysis of capillary flow was conducted, which showed that capillary flow can be described by equations equivalent to Fick's law for diffusion.
Mathematical models were developed to simulate fumigant distribution in red spruce utility poles treated with methyl isothiocyanate or chloropicrin using the parameters measured. The models, based on the finite difference method, are capable of simulating fumigant distribution in spruce poles years after treatment and hence can provide practical information for designing treatments to meet specific application needs.
Volatile chemicals have the potential to escape from wood poles into environment, resulting in a reduction in the effectiveness of the treatment and pollution of the environment. Currently fumigant treated wood poles need to be re-treated periodically to be decay free. Sealing the bottom of a pole with a fumigant impermeable material, and using controlled release technology are potential methods to lengthen re=treatment schedules.