Effect of weight percent gain and experimental method on fiber saturation point of acetylated wood determined by differential scanning calorimetry

This paper evaluates the effects of acetylation level and experimental method on the observed fiber saturation point (FSP) of loblolly pine (Pinus taeda) wood measured using differential scanning calorimetry. To achieve this goal, 1-mm-thick latewood samples were tested over a wide range of equilibrium moisture content (EMC). In this work, the FSP was defined as the non-freezable portion of water of the samples. Two experimental methods were used: the extrapolation of the melting enthalpy to zero and the direct calculation of the non-freezable water amount. For both methods, the FSP decreased with increasing acetylation, varying from about 27% reduced EMC (EMC_R) for control to about 9% EMC_R for the highest level of acetylation. For unmodified samples, the measured FSP was higher with faster scan rates. Moreover, under a specific range of EMC_R, freezing curves revealed the occurrence of two water phase transitions for samples at the highest level of acetylation. Based on previous studies and in present findings, there is strong evidence that the lower temperature freezing peak may result from the homogenous nucleation of water, which is physically separated from water that freezes heterogeneously.