Zhangjing Chen
Virginia Polytechnic Institute and State University

Over 400 insects which feed on trees and shrubs have been introduced into the U.S. primarily as a result of the use of cargo containers in world trade. Reducing the spread of forest pests is a national and international priority, the United States along with 133 other countries has been implementing the International Standard for Phytosanitary Measures to slow the spread of wood pests around the globe via forest products such as logs and wood packaging materials. Historically, the most widely used chemical fumigant has been methyl bromide. In addition to preshipment and quarantine uses, Mebr has been used extensively for phytosanitary treatments of food such as dried fruit, nuts, beans, processed foods and pet foods, as well as the treatment of processing facilities. Treating wood products including logs at ports in North American is also major users of MB and use annually. In 2009, about 711,175 lb of methyl bromide was used under PPQ supervision. Oaks log treatment uses 13% and is the second largest consumer next to the grape treatment.
As an environmentally friendly alternative to chemical treatment, this research aimed to establish the vacuum/steam technology to sanitize the logs for export. The steam condensation is one of most effective heat transfer mechanism because the steam carries large amount of heat and the condensation is fast to release the energy. Earlier studies have shown that the vacuum/steam system can heat up the pallets and small logs in a short time. The vacuum treating system consists of a vacuum source (vacuum pump), controlling device, the container and a steam generator. The treatment system initially creates vacuum in the container, it injects steam to the container and maintain the saturation state within the container to increase the temperature to the required setting.Monitoring devices can record and control the process. 
The veneer quality of logs of five common species (Red oak Quercusrubra, Pignut Hickory Caryaglabra, Black Cherry Prunusserotina,American Walnut Juglansnigra, Yellow Poplar Liriodendron tulipifera) from eastern US were treated. Log diameters ranged from 15 to 32 inches in the small end and the logs were about 8.5 to 10.7 feet long. The treatments were done in the commercial rigid chamber to evaluate the vacuum steam efficacy on the logs. Four different treating schedules were used. The treating duration and energy consumption were also measured. During treating, the geometric centers of logs were heated to 60°C and held for 60 minutes. Veneers from treated logs were produced in the veneer manufacturing plant. The effects of vacuum steam treatment on the log quality and the veneer color after treatment were analyzed. The result has shown that the hardwood logs of five important species have been successfully treated with vacuum/steam technology. The steam heat can effectively penetrate logs and raise the internal temperatures to 60°C and held for 60 minutes that is sufficient to kill the any pests. This treatment did exaggerate the end checks in the hickory, red oak and cherry logs by the extension of the existing cracks or checks. However, the treatment did not significantly reduce the veneer yield and values. In general, heat treatments do not have any significant deleterious effects on log quality. The treating time for logs varied from 15 to 40 hours depending on the species, size and treating schedule. That included the vacuum time and hold time of 60 minutes. The energy consumed during the treatment were measured and calculated to vary from 1.79 to 3.09 kwh/kg log depending on the schedule. For hickory, there is no difference in the colors of heartwood veneers for treated and controlled samples. For the sapwood, the veneers from treated logs were darker that from controlled logs. For walnut species, there is no difference in the veneer color between treated and controlled logs. For American cherry, the veneers from the treated logs were darker than from the controlled logs. There is no difference in the veneer colors between the controlled samples and treated samples for both red oak and yellow poplar species.