Properties of Poly(lactic acid) Nanocomposite Film Containing Modified Cellulose Nanofibers

Abstract

ICellulose nanofibers (CNF)-reinforced poly(lactic acid) (PLA) nanocomposite was prepared by casting method. In order to improve the compatibility and miscibility of the whole system with respect to PLA matrix, CNFs were treated with oleic acid. The resulting modified nanofibers (MCNF) exhibited reduced polarity and crystalline structure as compared with unmodified CNF. These MCNF were subsequently introduced into a PLA polymeric matrix and the effect of nanofiller on physicochemical properties of the nanocomposites was studied. Surface morphologies of PLA films studied by atomic force microscopy and it was revealed that the surface roughness of nanocomposites increased by increasing the nanofiber content. The morphology of fracture surface, evaluated by scanning electron microscopy, confirmed the uniform dispersion of MCNF at low levels. However, a higher level of MCNF (12 wt%) led to less dispersion uniformity and more agglomeration of the nanofibers. The thermal analysis by differential scanning calorimetry showed that the melting temperature of the PLA-MCNF nanocomposites was significantly higher than that of pure PLA film. Also, the degree of crystallinity increased with an increase in MCNF content. X ray diffraction patterns confirmed that the addition of MCNF resulted in increased crystalline structure in PLA matrix. At MCNF content of 12 wt%, the tensile strength and Young’s modulus of the nanocomposites increased by 2.5 and 2 folds than those of pure PLA films, respectively. These improvements were primarily attributed to the effect of surface modification and uniform dispersion of the MCNF in the PLA matrix. However, the MCNF formed aggregates in the higher loading levels (12 wt %).

Keywords

• poly(lactic acid)
• cellulose nanofibers
• surface modification
• crystalline structure
• thermal properties