Fig. 4

Characteristic ZTE images of cross-sectional slices taken from z = 15 mm from the front of the Populus wood chips, both untreated and pretreated in a steam gun at 180 °C for 4 and 18 min followed by conditioning at 100 % RH for 14 days. Red the highest proton density and water content. The z direction corresponds to the chip length and the x direction corresponds to chip thickness