ABSTRACT
The importance of the cellulose cycle has been increasing during the last decade along the ambitious targets of bioeconomy, however many novel fabrication processes yet lack of technological robustness. We present the optimization process for the fabrication of cellulose fibrous matrix by wet electrospinning via the controlled removal of the ionic liquids in order to avoid the formation of film-like structures. Fibers were produced on a bespoke wet-type electrospinning rig from cotton cellulose solutions of 3% in different types of ionic liquids (BMIMAc/C10MIMCl/EMIMAc). Three stage elution with a range of elution ratios using deionized water were applied to coagulate cellulose and remove residuals of ionic liquid. A variety of fibrous morphologies has been obtained. In case of a high water/IL ratio, the median fiber width across all ionic liquids was 0.4 µm, with the porosity at 92.3% and the pore diameter at 155 µm. The increasing elution ratio positively affected separate cellulose fiber formation, crystallinity, and mechanical strength of formed structures.
ABSTRACT
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.
