Moisture in untreated, acetylated, and furfurylated Norway Spruce monitored during drying below fiber saturation using time domain NMR
Using time domain–nuclear magnetic resonance spectroscopy, the moisture content (MC) in Norway spruce [Picea abies (L.) Karst.] sapwood, subjected to three different treatments (untreated, acetylated, and furfurylated), was studied during drying at 40oC at MCs below fiber saturation. Spin–spin relaxation time distributions were derived from Carr-Purcell-Meiboom-Gill relaxation curves using mulitexponential fitting (CONTIN). After conditioning for 6 wk at 100% RH, the modified wood samples had a MC of about 15%, whereas the MC of the untreated samples was about 30%. Two water populations with different relaxation times were found in all three sample types at this point: 1.1 ms and 0.15 ms (untreated), 0.5 ms and 0.15 ms (furfurylated), and 1.2 – 3.5 ms and 0.1 ms (acetylated). As the MC decreased, the relaxation time of the most slowly relaxing population decreased, whereas it remained more or less constant for the other population. For both the untreated and the furfurylated samples, the two populations merged at 5 – 10% MC, and relaxation times were identical for the two treatments at low MC. The two populations did not merge for the acetylated samples. These results indicate that while acetylation changed the interaction between water and the wood cell wall, furfurylation seemed to mostly affect the amount of water present within the cell wall at the beginning of the drying experiment.