Our choice of expressions used for calculation of DD was based on literature recommendations.
Expressions 15 and 17 were chosen because some authors maintain that calculations
based on equations proposed by Baxter et al. [24] are - in a sense - absolute methods.
These equations were set up without comparing the DA values to a range of samples with
known DA and were with good agreement with values from NMR. Next two formulas (16,
18) were taken for DD calculations because: in (16), the stretching band at 2870 cm-1, as
a reference band, is convenient – its position and intensity reportedly do not change with
water content; in (18): DD obtained from the ratio A1320/A1420 was in agreement with DD
determined from 1H NMR and 13C NMR [22] and positions at 1320 cm-1 and 1420 cm-1 do
not change with humidity.