Role of hydrogen bonding in cellulose deformation: the leverage effect analyzed by molecular modeling

Abstract

The axial modulus of the cellulose Iβ crystal is as high as 120–160 GPa. The importance of hydrogen bonds is often emphasized in this context, although intrinsic stiffness of the hydrogen bonds is relatively low. Here, hydrogen bond–covalent bond synergies are investigated quantitatively using molecular mechanics and molecular dynamics simulations for the so-called leverage effect, a model introduced recently in which strains for intra-molecular hydrogen bonds are higher than for the cellulose chain as a whole, thereby amplifying their contribution to the total stiffness. The present work also includes simulation of the hydrogen bonding band shifts in vibrational spectra during cellulose deformation, which are compared with FT-IR data. The leverage effect hypothesis was supported by the results, although the total contribution to cellulose stiffness is only 12 %. Hydrogen bonding is still critically important and would lower the modulus much more than 12 %, if “artificially” removed in the model. The reason is that intra-molecular hydrogen bonding preserves the crystal structure and directs axial deformation mechanisms towards higher energy deformation and high stiffness.