Chemical Enhancement of Mechanically Fibrillated Nanocellulose (mCNF) Films for Improved Mechanical Performance

Mechanically extracted cellulose nanofibrils (mCNF), which have not been chemically modified, were used to create mechanically isotropic films. Crosslinking systems like carbodiimides, poly-functional aziridines, blocked isocyanates, and polyamide epichlorohydrin were added to chemically crosslink the nanocellulose films and improve the mechanical properties. The process to make the casting mixtures involved taking 3.1wt% mCNF, DI water, and a premeasured crosslinker solution to create a three to one ratio of solids for the final mixture of crosslinker to mCNF. Two cases were analyzed with each of the different crosslinkers: one with a viscosifier and one without to determine the crosslinking compound. The cast films were left in a dehumidifier chamber to dry, until they were able to be removed from the mold. They were then cured at either 105 or 125oC, depending on the film chemistry. Tensile dog bone specimens were cut from the cured films. A Dynamic Mechanical Analysis (DMA) was used to test the mechanical properties of each sample. One sample reached over 100 MPa, which compared similarly to the base line sample with no crosslinkers. This round of testing was not able to find any crosslinkers that improved the mCNF mechanical properties. The ultimate goal of similar work would be to use the best crosslinker and then implement commercialization using continuous production techniques, like extrusion, that would allow for the mCNF films to be utilized in the packaging and structural industry.