Comparison between the molecular mechanics calculated energy of interaction of lignan dimers and trimers with a cellulose I crystallite and the experimental values of Young's modulus obtained by thermomechanical analysis (TMA) of cellulose paper impregnated with low molecular weight lignins showed good correlation between calculated and experimental results. The oligomer composition of the four low molecular weight lignins tested was obtained by MALDI-TOF mass spectrometry. This showed that these lignins were predominantly composed of dimers and trimers rendering them ideal for correlation testing. The lignan/cellulose crystallite interaction energy is determined by the oligomer molecular weight as well as the type of linkage within the lignan oligomers. Lignans with higher molecular weight in which the units are linked as beta-O-4 give interaction energy values indicating stronger attraction with cellulose. (C) Koninklijke Brill NV, Leiden, 2010