Silica-rich regenerated cellulose fibers enabled by delayed dissolution of silica nanoparticles in strong alkali using zinc oxide

Silica nanoparticles (SNPs) dissolve in alkaline media, which limits their use in certain applications. Here, we report a delayed dissolution of SNPs in strong alkali induced by zinc oxide (ZnO), an additive which also limits gelation of alkaline cellulose solutions. This allows incorporating high solid content of silica (30 wt%) in cellulose solutions with retention of their predominant viscous behavior long enough (ca. 180 min) to enable fiber wet spinning. We show that without addition of ZnO, silica dissolves completely, resulting in strong gelation of cellulose solutions that become unsuitable for wet spinning. With an increase of silica concentration, gelation of the solutions occurs faster. Employing ZnO, silica-rich regenerated cellulose fibers were successfully spun, possessing uniform cross sections and smooth surface structure without defects. These findings are useful in advancing the development of functional man-made cellulose fibers with incorporated silica, e.g., fibers with flame retardant or self-cleaning properties.

Nanomaterials for Combined Stabilisation and Deacidification of Cellulosic Materials-The Case of Iron-Tannate Dyed Cotton

The conservation of textiles is a challenge due to the often fast degradation that results from the acidity combined with a complex structure that requires remediation actions to be conducted at several length scales. Nanomaterials have lately been used for various purposes in the conservation of cultural heritage. The advantage with these materials is their high efficiency combined with a great control. Here, we provide an overview of the latest developments in terms of nanomaterials-based alternatives, namely inorganic nanoparticles and nanocellulose, to conventional methods for the strengthening and deacidification of cellulose-based materials. Then, using the case of iron-tannate dyed cotton, we show that conservation can only be addressed if the mechanical strengthening is preceded by a deacidification step. We used CaCO₃ nanoparticles to neutralize the acidity, while the stabilisation was addressed by a combination of nanocellulose, and silica nanoparticles, to truly tackle the complexity of the hierarchical nature of cotton textiles. Silica nanoparticles enabled strengthening at the fibre scale by covering the fibre surface, while the nanocellulose acted at bigger length scales. The evaluation of the applied treatments, before and after an accelerated ageing, was assessed by tensile testing, the fibre structure by SEM and the apparent colour changes by colourimetric measurements.

Evaluation of the Adhesion and Performance of Natural Consolidants for Cotton Canvas Conservation

Recent developments in paper and canvas conservation have seen the introduction of nanocellulose (NC) as a compatible treatment for the consolidation of historical cellulosic artifacts and manuscripts. However, as part of the assessment of these new materials for canvas consolidation, the adhesion of the consolidation treatment (which takes place between the applied material and the substrate) has not yet been evaluated, and as a result, it is poorly understood by both the scientific and conservation communities. After evaluating the potential of NC treatments for the consolidation of cotton painting canvas, we investigate a route to promote the interaction between the existing canvas and the nanocellulose treatment, which is in our case made of cellulose nanofibrils (CNF). This was carried out by introducing a cationic polymer, polyamidoamine-epichlorohydrin (PAAE), as an intermediate layer between the canvas and the CNF. The morphological, chemical, and mechanical evaluation of the canvas samples at different relative humidity (RH) levels demonstrated how the adhesion of the added PAAE layer is a dominant factor in the consolidation process. Improvement in the coating of canvas single fibers by the CNF, higher adhesion energy between the canvas fibers and the CNF treatment, and finally overall stronger canvas reinforcement were observed following the introduction of PAAE. However, an increase in mechanical response to moisture sorption and desorption was also observed for the PAAE-treated canvases. Overall, this study shows the complexity of such systems and, as such, the relevance of using a multiscale approach for their assessment.

Wet Spinning of Flame-Retardant Cellulosic Fibers Supported by Interfacial Complexation of Cellulose Nanofibrils with Silica Nanoparticles

The inherent flammability of cellulosic fibers limits their use in some advanced applications. This work demonstrates for the first time the production of flame-retardant macroscopic fibers from wood-derived cellulose nanofibrils (CNF) and silica nanoparticles (SNP). The fibers are made by extrusion of aqueous suspensions of anionic CNF into a coagulation bath of cationic SNP at an acidic pH. As a result, the fibers with a CNF core and a SNP thin shell are produced through interfacial complexation. Silica-modified nanocellulose fibers with a diameter of ca. 15 μm, a titer of ca. 3 dtex and a tenacity of ca. 13 cN tex^-1 are shown. The flame retardancy of the fibers is demonstrated, which is attributed to the capacity of SNP to promote char forming and heat insulation on the fiber surface.