Tuning the Tensile Strength of Cellulose through Vapor-Phase Metalation

The infiltration of transition metals into biopolymers by means of vapor-phase processes has been shown to unusually change the bulk mechanical properties of those materials. Here, for the first time, a novel, single precursor infiltration process was applied to cellulose. The mechanical properties, as measured through uniaxial tensile testing, showed improvement as a function of the total number of infiltration cycles as well as the precursor used. For cellulose infiltrated with diethyl zinc with only four infiltration cycles, the ultimate tensile strength was seen to nearly double from ∼160 to ∼260 MPa. A significant increase was also seen in the elastic modulus, with values increasing ∼2.5×, from ∼1.8 to ∼4.5 GPa. In contrast, cellulose infiltrated with trimethyl aluminum showed very little improvement in mechanical properties. By choosing the appropriate precursor and/or number of cycles, the mechanical properties become tunable. The chemical changes in the cellulose structure were measured with Raman spectroscopy and a novel semi in situ X-ray photoelectron spectroscopy experiment. The results of both spectroscopic techniques were used to propose a reaction scheme.