02769nas a2200229 4500008004100000022001400041245013600055210006900191260000800260300001400268490000700282520195800289653002602247653001002273653002602283653001302309100001902322700002302341700002002364700002702384856012802411 2019 eng d a0969-023900aStructure-property relations in regenerated cellulose fibers: comparison of fibers manufactured using viscose and lyocell processes0 aStructureproperty relations in regenerated cellulose fibers comp cAPR a3655-36690 v263 a

Regenerated cellulose fibers are produced using two industrially dominant technologies: the viscose and lyocell processes. Here, we compare commercially available fibers, prepared using the viscose and lyocell processes. Single fibers are subjected to a variety of mechanical deformations to obtain stress-strain, stress relaxation and stress recovery data. These are fitted to a phenomenological model, whose parameters are interpreted in terms of the fiber semicrystalline microstructure. This simple model does not incorporate the complexities of semicrystalline microstructure. Rather, it represents structure in a semicrystalline polymer fiber in terms of an elastic crystalline phase that coexists with a viscoelastic Voigt-like glassy amorphous phase. Lyocell fibers are characterized by higher values of crystalline modulus relative to viscose. Lyocell fibers also have a higher amorphous phase modulus and a wider relaxation spectrum than viscose, suggesting that amorphous and crystalline phases are dispersed in close connectivity in lyocell. Viscose and lyocell fibers exhibit qualitative similarities in their mechanical response. On stretching, there is a transition in the stress-strain curve from a low strain elastic response at a critical value of strain. This critical strain has been incorrectly attributed to yielding of the fiber. We establish that this critical value corresponds to an apparent yield. When subjected to strains higher than this apparent yield point, the fibers develop a memory of the mechanical deformation. This memory decays slowly, logarithmically with time and is lost over about a day as the fiber structure transitions back to the original as spun fiber. Finally, we demonstrate that on wetting the fibers with water, there is an increase in the apparent yield strain for viscose fibers, but not for lyocell. We interpret these results in terms of the semicrystalline microstructure of the fibers.

10amechanical properties10aModel10aRegenerated cellulose10aYielding1 aSharma, Aakash1 aNagarkar, Shailesh1 aThakre, Shirish1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/structure-property-relations-regenerated-cellulose-fibers-comparison-fibers-manufactured02816nas a2200217 4500008004100000022001400041245011000055210006900165260000800234300001400242490000700256520204500263653001802308653003402326653001702360653002602377100001902403700002002422700002702442856012902469 2020 eng d a0969-023900aMicrostructural differences between Viscose and Lyocell revealed by in-situ studies of wet and dry fibers0 aMicrostructural differences between Viscose and Lyocell revealed cFEB a1195-12060 v273 a

Regenerated cellulose fibers manufactured using Lyocell and Viscose processes exhibit differences in their structural response to mechanical deformation. Here, we study the effect of stretching and stress relaxation on the orientation of crystal and amorphous phases. Our results show that on stretching, orientation in both crystal and amorphous phases increases linearly with strain, correlating with the increase in stress and with the stretching of the crystalline unit cell along the c-axis. On holding after stretching to a particular strain, the stress relaxes logarithmically in time, correlating with a decrease in the strain along the c-axis of the crystal unit cell. The stress relaxation is also correlated with a logarithmic increase in amorphous orientation, while crystalline orientation stays constant. We attribute the stress development during stretching to deformation of the crystal unit cell, while crystal reorientation in the fiber direction results in increase in the crystalline orientation parameter. On holding the fiber at a fixed total strain, the stress relaxes as strain is transferred from crystal to amorphous regions. Thus, the strain on the unit cell c-axis decreases and amorphous orientation increases. There are quantitative differences between the rate of increase in amorphous phase orientation during stress relaxation for Lyocell and Viscose fibers. For dry fibers, Lyocell shows a slower increase in orientation during stress relaxation. On wetting the fibers, their structural response changes qualitatively. We combine wide angle x ray diffraction and birefringence experiments with our model to infer that that on stretching the wet fiber, the crystalline phase is neither strained nor oriented. However, orientation develops in the amorphous phase. During stress relaxation in wet condition, Lyocell fibers shows a faster increase in amorphous orientation than Viscose fibers, in line with the comparison of relaxation time spectra for wet Viscose and Lyocell fibers. Graphic abstract

10abirefringence10aCrystal-amorphous orientation10aIn-situ WAXD10aRegenerated cellulose1 aSharma, Aakash1 aThakre, Shirish1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/microstructural-differences-between-viscose-and-lyocell-revealed-situ-studies-wet-and-dry03020nas a2200289 4500008004100000022001400041245013500055210006900190260000900259300001400268490000600282520205800288653001702346653002502363653001102388653001202399653002302411653002602434653000902460100001902469700002402488700002002512700002302532700002002555700002702575856012802602 2021 eng d a2637-610500aProcess-induced microstructure in viscose and lyocell regenerated cellulose fibers revealed by SAXS and SEM of acid-etched samples0 aProcessinduced microstructure in viscose and lyocell regenerated cMAY  a2598-26070 v33 a

Regenerated cellulose fibers represent an important class of bioderived commercial fibers. The traditional viscose process requires the use of environmentally harmful carbon disulfide solvent to produce fibers. Lyocell fibers, produced using a more sustainable recent process, exhibit differences in properties from viscose. These differences arise from their semicrystalline microstructure, formed during fiber spinning. It is widely believed that regenerated cellulose fibers predominantly form fringed fibrillar crystals. We optimize acid etching, followed by SEM as an experimental tool to visualize this fibrillar structure. Acid etching provides sufficient topological contrast to directly visualize similar to O(10 nm) fibrils using field-emission scanning electron microscopy (SEM). We combine SEM with small-angle X-ray scattering (SAXS) to reveal other microstructural details. We observe a Bragg peak, indicating the coexistence of stacked lamellar structure with crystalline fibrils for viscose fibers, but not for lyocell. Viscose and lyocell fibers are characterized by partially oriented semicrystalline microstructure. We present a methodology to calculate the Lorentz correction for such microstructure and employ this to analyze the lamellar scattering from viscose fibers using a 1D correlation function approach. We characterize the lamellar microstructure after swelling viscose fibers with water and observe expansion of the Bragg spacing due to water absorption in the amorphous regions. Our data suggest that the water-induced plasticization of amorphous regions is inhomogeneous. Lamellar stacks that are more misoriented from the fiber direction exhibit lower swelling than those along the fiber direction. The experimental methods described in this work reveal interesting details of semicrystalline microstructure in regenerated cellulose fibers, with important implications for the mechanical response of dry and wet fibers. The methods developed here might find use in investigations of other polymer fibers as well.

10aacid etching10acrystalline lamellae10afibers10afibrils10aLorentz correction10aRegenerated cellulose10aSAXS1 aSharma, Aakash1 aWankhede, Parnashri1 aSamant, Roopali1 aNagarkar, Shailesh1 aThakre, Shirish1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/process-induced-microstructure-viscose-and-lyocell-regenerated-cellulose-fibers-revealed02508nas a2200253 4500008004100000022001400041245012300055210006900178260000800247300001100255490000700266520164100273653002201914653002601936653002101962653002601983653001302009653001602022100001902038700001802057700002402075700003102099856012402130 2023 eng d a0969-023900aSynthesis of N-oxyethylene substituted imidazolium-based zwitterions as a recyclable solvent for cellulose dissolution0 aSynthesis of Noxyethylene substituted imidazoliumbased zwitterio cJAN a87-1090 v303 a

Cellulose is a readily available, renewable, and natural biomaterial that has the potential to replace synthetic fibres. However, their processing to shaped materials such as fibre or film is still complex and restricted due to its insolubility in most conventional solvents. Herein, we present the synthesis and cellulose dissolution characteristics of a new class of recyclable zwitterions composed of tethered N-oxyethylene substituted imidazolium cation and alkyl carboxylate anion. Investigations on cellulose dissolution showed that increasing the alkyl chain length of carboxylate anion and introduction of oxyethylene unit on imidazolium ring led to better cellulose dissolution ability, and up to 12% (w/w) cellulose could be dissolved in aqueous zwitterions at 105 degrees C. The thermal behavior of zwitterions and their cellulose solutions was characterized by TGA and found to be more stable than the NMMO and Lyocell solutions. Rheological characterization of cellulose solutions revealed viscoelastic behavior and zero shear viscosity of 6-12% (w/w) cellulose solution in hexanoate containing aqueous zwitterion was 555 to 5900 Pa.s at 120 degrees C. The characteristics of cellulose solution indicate its potential for processing to cellulose fibre by extrusion through a tiny spinneret. Physico-chemical analysis of regenerated cellulose indicates that zwitterions cause no adverse effect on cellulose structure and morphology during dissolution. The zwitterions are recovered after the cellulose regeneration process, and the recovery was found to be 99.6% after purification using the ion-exchange method.

10aCarboxylate anion10aCellulose dissolution10aOxyethylene unit10aRegenerated cellulose10aRheology10azwitterions1 aJadhav, Sachin1 aGanvir, Vivek1 aSingh, Madan, Kumar1 aShanmuganathan, Kadhiravan uhttps://library.ncl.res.in/content/synthesis-n-oxyethylene-substituted-imidazolium-based-zwitterions-recyclable-solvent