Abstract
Extremely high mechanical performance spun bionanocomposite fibers of chitosan (CHI), and cellulose nanofibers (CNFs) were successfully achieved by gel spinning of CHI aqueous viscous formulations filled with CNFs. The microstructural characterization of the fibers by X-ray diffraction revealed the crystallization of the CHI polymer chains into anhydrous chitosan allomorph. The spinning process combining acidic–basic–neutralization–stretching–drying steps allowed obtaining CHI/CNF composite fibers of high crystallinity, with enhanced effect at incorporating the CNFs. Chitosan crystallization seems to be promoted by the presence of cellulose nanofibers, serving as nucleation sites for the growing of CHI crystals. Moreover, the preferential orientation of both CNFs and CHI crystals along the spun fiber direction was revealed in the two-dimensional X-ray diffraction patterns. By increasing the CNF amount up to the optimum concentration of 0.4 wt % in the viscous CHI/CNF collodion, Young’s modulus of the spun fibers significantly increased up to 8 GPa. Similarly, the stress at break and the yield stress drastically increased from 115 to 163 MPa, and from 67 to 119 MPa, respectively, by adding only 0.4 wt % of CNFs into a collodion solution containing 4 wt % of chitosan. The toughness of the CHI-based fibers thereby increased from 5 to 9 MJ.m−3. For higher CNFs contents like 0.5 wt %, the high mechanical performance of the CHI/CNF composite fibers was still observed, but with a slight worsening of the mechanical parameters, which may be related to a minor disruption of the CHI matrix hydrogel network constituting the collodion and gel fiber, as precursor state for the dry fiber formation. Finally, the rheological behavior observed for the different CHI/CNF viscous collodions and the obtained structural, thermal and mechanical properties results revealed an optimum matrix/filler compatibility and interface when adding 0.4 wt % of nanofibrillated cellulose (CNF) into 4 wt % CHI formulations, yielding functional bionanocomposite fibers of outstanding mechanical properties.
Highlights
IntroductionFibers are structural components with a wide range of applications in medicine, biotechnology, textiles and industrial materials [1]
Suspensions, revealing that the shear-thinning behavior in the latter is governed by the disentanglement of CHI chains and practically not affected by the presence of the cellulose nanofibers (CNFs), which should get oriented in the flow direction [53,55]
Functional chitosan-based fibers were achieved by incorporating small amounts of nanofibrillated cellulose (CNF) into viscous chitosan (CHI) collodion solution in a gel spinning process to yield anisotropic nanofiber-reinforced biocomposite fibers of excellent mechanical properties
Summary
Fibers are structural components with a wide range of applications in medicine, biotechnology, textiles and industrial materials [1]. Common examples of fibers are surgical sutures and medical textile structures. The vast selection of materials, which are used for routine surgical sutures is mainly limited to synthetic polymers, such as polyethylene terephthalate (PET), polyglycolide (PGA), polyamide. 6.6 (PA 6.6), polypropylene (PP), polyvinyl alcohol (PVA), para-aramid and ultra-high molecular weight polyethylene (UHMWPE). Fine control over the mechanical properties is gained via stretching ratio, stretching temperature and thermal treatments, impacting the crystalline microstructure of the polymers with high molecular weight [8]
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