RESEARCH ON THE MOISTURE STATE AND MOBILITY IN WOOD DURING MICROWAVE DRYING BY LF-NMR

In this paper,the LF-NMR technique was used to monitor the rules of moisture state and mobility in wood samples of elm during microwave drying.Study of the moisture content profiles and the state of T2 during different moisture content period showed that there were three kinds of water state in the sample that moisture content was 50%,bound water and two kinds of free water located in different position.When the moisture content was above FSP,the free water mainly moved and transformed to the bound water,and the T2 value of free water decreased accompanying with the increased the T2 value of bound water.The results showed that the moisture gradients presented a similar pattern with higher moisture content in the center and lower moisture content on the surface layer.There was no free water in samples when the moisture content below 20%,and the T2 value of free water showed a tendency of dropping,with the reduced moisture content.Meanwhile,the moisture content profiles inside the samples were flat.With the increased of the microwave power,the moisture content of the inner layers which was slightly lower than that on the surface layer occurred in the samples.