| Wood quarantine treatment is to prevent the forestry quarantine pests distributed around the world via international trade,which has direct influences on trade in wood import and export,and the security of the forest resources and ecological environment.At present,the most common method for quarantine control of insect pests in wood is chemical fumigation with methyl bromide.Due to its negative impact on ozone-layer and human health,many countries have proposed to phase out of insect pests fumigation disinfestation methods with methyl bromide.Thus,it is urgent to develop non-chemical and efficient alternative methods to replace methyl bromide fumigation for disinfesting woods.Radio frequency(RF)treatment as an environmental friendly and non-chemical method can rapidly and volumetrically heat material.In this study,the adult D.armandi(Dendroctonus.armandi)was selected as tested pests,and a pilot-scale 6 kW,27.12 MHz RF system was used to develop a treatment protocol for disinfesting wood.Pine wood blocks were chosen as the tested sample to analyze the RF heating uniformity,then a custom fabricated heating block system was used to study thermal-death kinetics and thermotolerance of the adult D.armandi,and finally the RF heat treatment protocol was validated through insect mortality of D.armandi and wood quality.The main research results are as follows:(1)Exploring thermal mortality kinetics of adult D.armandi.Using a custom fabricated heating block system,effects of various heating rates on D.armandi adult insect mortality were examined between 44 °C to 50 °C at 2 °C intervals.The thermotolerance of the insect showed that low heating rates(0.1 °C/min or 0.5 °C/min)resulted in the enhanced thermotolerance caused by the inducible heat shock protein during the slow heating process.The thermal-death kinetics of D.armandi was determined at a high heating rate of 5.0 °C/min to simulate the rapid dielectric heating of wood products.The required holding times to achieve 100 % mortality were 40,8,4,and 2 min at 44°C,46 °C,48°C,and 50°C,respectively.The thermal death behavior of adult D.armandi followed a 0-order kinetic reaction model.(2)Studying on RF heating uniformity in pine wood samples.The results showed that the best RF heating uniformity occurred when the lower wood moisture content was used and the wood width approached the RF electrode one.RF energy with forced hot air,movement conveyor and holding with hot air can improve RF heating uniformity.The heating time needed only 4.8 min to heat the wood blocks from 25 °C to 50 °C using RF energy under 120 mm electrode gap,but 270 min using hot air.(3)Validating an RF treatment protocol for controlling D.armandi in wood products.After RF heating,the cold spot of the wood block sample was found to be the center on surface of top layer.The temperature of cold spot took 4.9 min to reach 50 °C,resulting in 10.1 m/h of corresponding speed of conveyor belt.The mortality of adult bark beetle increased with an increase in wood temperature as a result of RF treatment and holding time.Complete mortality was achieved by heating to 50 °C with an electrode gap of 120 mm and holding time of 3 min maintained with forced circulation of hot air.The wood quality was not affected significantly by the RF treatment after evaluating the different quality parameters(moisture content,bending properties,and checking). |
