Composites from poly(lactic acid) (PLA) and acetylated microfibrillated cellulose (MFC) were prepared by a solvent casting technique. MFC, mechanically isolated from never-dried bleached birch Kraft pulp, was used as a reinforcement. The acetylation reaction was carried out at 105 C in toluene and proved to be an effective way of increasing the dispersion of MFC in a nonpolar solution of PLA in chloroform. The maximum acetyl content (10.3%) was achieved after 30 min of reaction time. This could be translated to a degree of substitution (DS) of 0.43. The acetylation was confirmed by Fourier transform infrared spectroscopy. MFC with a higher DS exhibited a more pronounced effect on the properties of PLA. Mechanical testing showed that Young's modulus increased by approximately 70% and the tensile strength increased by approximately 60% at a fiber weight fraction of 20%. At an MFC loading of 10 wt %, the strain at break and toughness, expressed as the work of fracture, increased by around 500%. The Young's modulus increased by approximately 15%, whereas the tensile strength remained the same. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 126:E448-E457, 2012

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Composites of poly(lactic) acid (PLA) reinforced with TEMPO-oxidized fibrillated cellulose (TOFC) were prepared to 15, 20, 25, and 30% fiber weight fractions. To aid dispersion and to improve stress transfer, we acetylated the TOFC prior to the fabrication of TOFC-PLA composite films. Raman spectroscopy was employed to study the deformation micromechanics in these systems. Microtensile specimens were prepared from the films and deformed in tension with Raman spectra being collected simultaneously during deformation. A shift in a Raman peak initially located at ~1095 cm(-1), assigned to C-O-C stretching of the cellulose backbone, was observed upon deformation, indicating stress transfer from the matrix to the TOFC reinforcement. The highest band shift rate, with respect to strain, was observed in composites having a 30% weight fraction of TOFC. These composites also displayed a significantly higher strain to failure compared to pure acetylated TOFC film, and to the composites having lower weight fractions of TOFC. The stress-transfer processes that occur in microfibrillated cellulose composites are discussed with reference to the micromechanical data presented. It is shown that these TOFC-based composite materials are progressively dominated by the mechanics of the networks, and a shear-lag type stress transfer between fibers.