Influence of TEMPO-oxidized cellulose nanofibril length on film properties

Various mechanical disintegration conditions in water were applied to 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose to prepare TEMPO-oxidized cellulose nanofibrils (TOCNs) of uniform widths ∼4 nm but with three different average lengths, 200, 680, and 1100 nm. The viscosity average degrees of polymerization of the TOCNs were 250, 350, and 400, respectively. Self-standing TOCN and TOCN-coated poly(ethylene terephthalate) (PET) and poly(lactic acid) (PLA) films were prepared, and the optical, mechanical and gas-barrier properties of the films were evaluated in terms of nanofibril length. Only small differences in density, water content, and elastic modulus of the films were observed but TOCN films prepared from longer nanofibrils clearly showed higher tensile strengths, elongations at break and crystallinity indices. The oxygen barrier properties of the TOCN-coated PET and PLA films increased with increasing nanofibril length. In contrast, nanofibril length had almost no influence on water vapor-barrier properties.