Interpretation of relaxation and swelling phenomena in lyocell regenerated cellulosic fibres and textiles associated with the uptake of solutions of sodium hydroxide

The uptake of solutions of sodium hydroxide by lyocell fibre results in a phenomenon in textiles described as swelling–shrinkage. The response of woven fabrics in a tensile stress–relaxation experiment shows two time-dependent processes, corresponding to different mechanisms of pressure development. Rapid diffusion has been assigned to osmotic swelling through the interconnected pore structure of the fibre (D = 6–15 × 10⁻¹² m²/s), which is influenced by the extent of ionization of hydroxyl groups at the pore surfaces. A ratio for the cellulose and water dissociation constants (K_cell/K_w) of 70 provides best agreement with experimental data. A second slower diffusion process (D = 2–10 × 10⁻¹⁴ m²/s) is assigned to transport through the cellulose polymer structure, associated with the Na-cellulose transition. This can be modeled assuming an ion-exchange equilibrium, where the cellulose gel converts reversibly between compact hydrogen and expanded sodium forms, with K = 1.04 × 10¹⁴, in favour of the hydrogen form. The model successfully predicts the concentration dependence of the transition and the movement to higher concentration with external constraint. The slow diffusion process only becomes apparent at high alkali concentrations, as the pores in the fibre collapse due to the expansion of the gel. Continued gel-diffusion is only possible through the polymer phase, which then dominates over fast pore-diffusion.     

Degrees of polymerization (DP) and DP distribution of dilute acid-hydrolyzed products of alkali-treated native and regenerated celluloses

Three groups of cellulose II samples, 20% NaOH-treated native celluloses (M-native celluloses), commercial regenerated celluloses and those treated with 20% NaOH (M-regenerated celluloses), were subjected to dilute acid hydrolysis at 105 °C to obtain so-called leveling-off degrees of polymerization (LODP). Molecular mass parameters of the acid-hydrolyzed products were analyzed by SEC-MALLS using 1% LiCl/DMAc as an eluent. The LODP values were in the order of M-native celluloses ≅ M-regenerated celluloses > regenerated celluloses. The LODP values of M-regenerated celluloses are 1.5–1.7 times as much as those of the regenerated celluloses; the cellulose II crystallites in regenerated celluloses increase in size to the longitudinal direction by the alkali treatment and the successive acid hydrolysis at 105 °C. This increase in the longitudinal crystal sizes might primarily occur during acid hydrolysis. All the acid-hydrolyzed products had bimodal SEC elution patterns, i.e. the predominant high-molecular-mass and minor low-molecular-mass components, the latter of which corresponded to DP 20.     

Toughness enhancement of cellulose nanocomposites by alkali treatment of the reinforcing cellulose nanofibers

Nanocomposites were produced with NaOH aqueous solution-treated microfibrillated cellulose (MFC) and phenolic resin, and the mechanical properties were compared with their microcomposite counterparts based on pulp fiber. Tensile tests showed that strong alkali-treated MFC nanocomposites with resin content around 20 wt.% achieved strain at fracture values two times higher than those of untreated MFC nanocomposites and five times higher than those of untreated pulp microcomposites. The improvement in work of fracture of alkali-treated MFC nanocomposites was attributed to the ductility of the nanofibers caused by transformations in the amorphous regions along the cellulose microfibrils.     

Swelling and dissolution of cellulose,Part III: plant fibres in aqueous systems

Raw and refined flax, hemp, abaca, sisal, jute and ramie fibres are dipped into N-methylmorpholine N-oxide (NMMO)–water with various contents of water and into hydroxide sodium (NaOH)–water. The swelling and dissolution mechanisms of these plant fibres are similar to those observed for cotton and wood fibres. Disintegration into rod-like fragments, ballooning followed or not by dissolution and homogeneous swelling are all observed as for wood and cotton fibres, depending on the quality of the solvent. Balloons are not typical of wood and cotton and they seem to be present in all plant fibres. Another interesting result is that the helical feature seen on the balloon membrane is not related to the microfibrillar angle. Plant fibres are easier to dissolve than wood and cotton. This is not related to the molar mass of the cellulose chain. Raw plant fibres keeping most its non-cellulosic components do not show the formation of balloons. Patrick Navard is a Member of the European Polysaccharide Network of Excellence (EPNOE)     

Nanofibrillar Cellulose‐Chitosan Composite Film Electrodes: Competitive Binding of Triclosan,Fe(CN)63−/4−, and SDS Surfactant

Glassy carbon electrodes are modified with a thin film of a cellulose‐chitosan nanocomposite. Cellulose nanofibrils (of ca. 4 nm diameter and 250 nm length) are employed as an inert backbone and chitosan (poly‐D ‐glucosamine, low molecular weight, 75–85% deacetylated) is introduced as a structural binder and “receptor” or molecular binding site. The composite films are formed in a solvent evaporation method and prepared in approximately 0.8 μm thickness. The adsorption of three molecular systems into the cellulose‐chitosan films is investigated and approximate Langmuirian binding constants are evaluated: i) Fe(CN)₆^4? (K_Ferrocyanide=2.2×10³ mol^?1 dm³ in 0.1 M phosphate buffer at pH 6) is observed to bind to ammonium chitosan functionalities (present at pH<7), ii) triclosan (K_Triclosan=2.6×10³ mol^?1 dm³ in 0.1 M phosphate buffer pH 9.5) is shown to bind only weakly and under alkaline conditions, and iii) the anionic surfactant dodecylsulfate (K_SDS=3.3×10⁴ mol^?1 dm³ in 0.1 M phosphate buffer pH 6) is shown to bind relatively more strongly in acidic media. The competitive binding of Fe(CN)₆^4? and dodecylsulfate anions is proposed as a way to accumulate and indirectly determine the anionic surfactant.     

Improvement in the synthesis of (Z)-organylthioenynes via hydrothiolation of buta-1,3-diynes: a comparative study using NaOH or TBAOH as base

Hydrothiolation of symmetrical and unsymmetrical buta-1,3-diynes with sodium organylthiolate anions in reflux, generated in situ by reacting C₄H₉SH with NaOH, afforded (Z)-organylthioenynes in low to good yields (25-80%). By using tetrabutylammonium hydroxide (TBAOH) as base instead of NaOH, the hydrothiolation of buta-1,3-diynes was more rapid and efficient, providing (Z)-organylthioenynes in good to excellent yields (70-95%).