An ultrastrong nanofibrillar biomaterial: the strength of single cellulose nanofibrils revealed via sonication-induced fragmentation.

We report the mechanical strength of native cellulose nanofibrils. Native cellulose nanofibrils, purified from wood and sea tunicate, were fully dispersed in water via a topochemical modification of cellulose nanofibrils using 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) as a catalyst. The strength of individual nanofibrils was estimated based on a model for the sonication-induced fragmentation of filamentous nanostructures. The resulting strength parameters were then analyzed based on fracture statistics. The mean strength of the wood cellulose nanofibrils ranged from 1.6 to 3 GPa, depending on the method used to measure the nanofibril width. The highly crystalline, thick tunicate cellulose nanofibrils exhibited higher mean strength of 3-6 GPa. The strength values estimated for the cellulose nanofibrils in the present study are comparable with those of commercially available multiwalled carbon nanotubes.

Light-scattering analysis of native wood holocelluloses totally dissolved in LiCl-DMI solutions: high probability of branched structures in inherent cellulose.

Three holocelluloses (i.e., cellulose and hemicellulose fractions) are prepared from softwood and hardwood by the Wise method. These holocelluloses completely dissolve in 8% lithium chloride/1,3-dimethyl-2-imidazolidinone (LiCl/DMI) after an ethylenediamine (EDA) pretreatment. After diluting the holocellulose solutions to 1% LiCl/DMI, they are subjected to size-exclusion chromatography/multiangle laser-light scattering/photodiode array (SEC-MALLS-PDA) analysis. All holocelluloses exhibit bimodal molecular weight distributions primarily due to high-molecular-weight (HMW) cellulose and low-molecular-weight hemicellulose fractions. Plots of molecular weight vs root-mean-square radius obtained by SEC-MALLS analysis revealed that all the wood celluloses comprise dense conformations in 1% LiCl/DMI. In contrast, bacterial cellulose, which was used as a pure cellulose model, has a random coil conformation as a linear polymer. These results show that both softwood and hardwood HMW celluloses contain branched structures, which are probably present on crystalline cellulose microfibril surfaces. These results are consistent with those obtained by permethylation analysis of wood celluloses.