Size effects of cellulose nanofibers for enhancing the crystallization of poly(lactic acid)

A desirable size of cellulose fibers for enhancing the crystallization of poly(lactic acid) (PLA) in composites was investigated by comparison among cellulose nanofibers with different widths on nanoscales. Namely, the crystallization behaviors of PLA in the presence of cellulose nanofibers were monitored with differential scanning calorimetry and polarized optical microscopy in terms of the crystallization rates of PLA. The smallest width of cellulose nanofibers was found to not necessarily provide better enhancement for the crystallization, presumably because of the preferential self-assembly of smaller cellulose nanofibers in PLA. Namely, when the width was smaller, the better effect expected for nanofibers did not appear in the composites. It is possible that an optimum width range of 60 nm, more or less, in the cellulose nanofibers may exist in balance between the favorable self-assembly as an enthalpy effect and the tendency toward dispersion as an entropy effect.