02185nas a2200253 4500008004100000022001400041245011300055210006900168260000800237300001600245490000800261520131000269100001501579700001901594700001901613700002801632700001901660700001801679700002501697700002501722700002701747700003101774856012601805 2018 eng d a1932-744700aFluorinated nanocellulose-reinforced all-organic flexible ferroelectric nanocomposites for energy generation0 aFluorinated nanocellulosereinforced allorganic flexible ferroele cJUL a16540-165490 v1223 a

We report here enhanced ferroelectric crystal formation and energy generation properties of polyvinylidene fluoride (PVDF) in the presence of surface-modified crystalline nanocellulose. Incorporation of only 2-5 wt % fluorinated nanocellulose (FNC) in PVDF has been found to significantly induce polar beta/gamma-phase crystallization as compared to the addition of unmodified nanocellulose (carboxylated nanocellulose). A device made up of electrically poled PVDF/FNC composite films yielded 2 orders of magnitude higher voltage output than neat PVDF in vibrational energy harvesting. This remarkable increase in energy generation properties of PVDF at such a low loading of an organic natural biopolymer could be attributed to the tailored surface chemistry of nanocellulose, facilitating strong interfacial interactions between PVDF and FNC. Interestingly, energy harvesting devices fabricated from PVDF/FNC nanocomposites charged a 4.7 mu F capacitor at significantly faster rate and the accumulated voltage on capacitor was 3.8 times greater than neat PVDF. The fact that PVDF/FNC nanocomposites still retain a strain at break of 10-15% and can charge a capacitor in few seconds suggests potential use of these nanocomposites as flexible energy harvesting materials at large strain conditions.

1 aRam, Farsa1 aAmbone, Tushar1 aSharma, Aakash1 aMurugesan, Rajarathinam1 aKajale, Deepak1 aBorkar, Vivek1 aAli, Shaikh, Faruque1 aBalu, Praveen, Kumar1 aKumaraswamy, Guruswamy1 aShanmuganathan, Kadhiravan uhttps://library.ncl.res.in/content/fluorinated-nanocellulose-reinforced-all-organic-flexible-ferroelectric-nanocomposites01782nas a2200169 4500008004100000022001400041245006700055210006700122260000800189300001100197490000600208520123700214100001901451700002701470700002001497856009501517 2018 eng d a2475-995300aModeling the universal viscoelastic response of polymer fibers0 aModeling the universal viscoelastic response of polymer fibers cJUN a0626010 v23 a

Polymer fibers, including natural silk and synthetic fibers, exhibit universal viscoelastic response. On stretching below yield, they show logarithmic stress decay. On unloading fibers with a glassy amorphous phase, the stress recovers. A simple phenomenological model accurately describes data from independent mechanical experiments and provides insights into the micro structural origins of the fiber response. Counter to intuition, the model indicates that it is the crystalline regions, rather than the amorphous glass, that deform first on stretching fibers at high strain rates. On holding a stretched fiber, stress decays as a consequence of relaxations in amorphous regions. Finally, unloading the fiber transfers stress from the amorphous to crystalline regions resulting in stress recovery. Model parameters correlate well with the fiber microstructure. Crystal and amorphous moduli from the model match those from x-ray diffraction. Activation energies for the temperature dependence of the peak relaxation time are similar to those reported in the literature. Thus, a simple model that invokes only crystal-amorphous coexistence can successfully model the mechanical response of a wide variety of polymer fibers.

1 aSharma, Aakash1 aKumaraswamy, Guruswamy1 aThakre, Shirish uhttps://library.ncl.res.in/content/modeling-universal-viscoelastic-response-polymer-fibers02461nas a2200181 4500008004100000022001400041245010600055210006900161260000800230300001400238490000700252520181400259100001902073700001702092700002002109700002702129856012302156 2019 eng d a0024-929700aCharacterizing microvoids in regenerated cellulose fibers obtained from viscose and lyocell processes0 aCharacterizing microvoids in regenerated cellulose fibers obtain cJUN a3987-39940 v523 a

Regenerated cellulose fibers are among the most widely used bio-derived materials. Currently, there is great interest in transitioning from the traditional viscose process to the more environmentally friendly lyocell process for fiber production. Differences between the characteristics of viscose and lyocell fibers can be attributed to microstructural differences that arise due to differences in the processing techniques. Here, we use small-angle scattering to characterize the microvoids in regenerated cellulose fibers that might govern the onset of mechanical failure in these. In regenerated cellulose fibers, scattering of X-rays or neutrons at small angles is largely dominated by scattering from microvoids. We demonstrate that small angle X-ray scattering (SAXS) over the q range that is typical for most commercial instruments arises from Porod scattering from the microvoid surfaces, viz., the scattered intensity scales as q(-4). Therefore, it is not possible to extrapolate this data to lower q to obtain microvoid dimensions and volume fraction. We combine SAXS with medium-resolution small-angle neutron scattering to characterize the microvoids in regenerated cellulose fibers. Specifically, we compare fibers produced using the viscose process with those from the lyocell process. For both viscose and lyocell fibers, microvoids have a high aspect ratio and are elongated in the fiber direction. Also, the volume fraction occupied by the microvoids is comparable for viscose and lyocell fibers (0.04-0.05%). However, there are differences in the microvoid size: Microvoids are more highly oriented in lyocell fibers and have a larger average length and diameter compared with viscose fibers. This result might have important implications for understanding failure of these fibers.

1 aSharma, Aakash1 aSen, Debasis1 aThakre, Shirish1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/characterizing-microvoids-regenerated-cellulose-fibers-obtained-viscose-and-lyocell02769nas 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-revealed01868nas a2200229 4500008004100000245011600041210006900157260000800226300001200234490000700246520108600253100001901339700002301358700001801381700001801399700001901417700001801436700001601454700002001470700002001490856012801510 2025 eng d00aSANS and SAXS investigation of the melt state structure in disentangled ultrahigh molecular weight polyethylene0 aSANS and SAXS investigation of the melt state structure in disen cMAR a349-3530 v143 a

Disentangled ultrahigh molecular weight polyethylene exhibits a time-dependent increase in rheology modulus when molten. This originates from its kinetically evolving heterogeneous microstructure consisting of disentangled and entangled regions. We report a quantitative analysis of this microstructure using X-rays and neutrons that capture the signatures of these regions. We analyze the absolute intensities to obtain the volume fraction and size distribution of the disentangled domains in the melt. Employing neutrons, we follow the changes in these parameters with time. The trends are qualitatively similar to those of the previous rheological observations. Our methodology also provides an experimental verification of the theoretical report by McLeish, T. C. B. Soft Matter 2007, 3 (1), 83-87, which predicts the presence of high density disentangled domains in a low density entangled matrix. The analysis presented here is a useful instrument for unveiling the origin of differences in the properties of polymers obtained through different processing routes.

1 aSharma, Aakash1 aKruteva, Margarita1 aWillner, Lutz1 aRomano, Dario1 aPorcar, Lionel1 aDulle, Martin1 aZhou, Fuhai1 aRastogi, Sanjay1 aRichter, Dieter uhttps://library.ncl.res.in/content/sans-and-saxs-investigation-melt-state-structure-disentangled-ultrahigh-molecular-weight02417nas a2200241 4500008004100000022001400041245010900055210006900164260000800233300001400241490000700255520158900262100001901851700002301870700001901893700002001912700002101932700001701953700001901970700002801989700002702017856013102044 2026 eng d a0897-475600aDynamic janus hydrogen bond mimicry unlocks tough, flexible supramolecular elastomers for strain sensing0 aDynamic janus hydrogen bond mimicry unlocks tough flexible supra cMAR a2699-27110 v383 a

Flexible and wearable electronics demand stretchable sensors with polymer elastomers as key matrixes for mechanical flexibility and durability. However, despite their excellent elasticity, their limited mechanical strength remains a challenge. To address this limitation, in this study, we report the rational design of supramolecular polyurethane elastomers (SPUs) incorporating nucleobase-inspired aminopyrimidinedione with DDA-AAD (G-C mimic) reversible triple hydrogen bonds. This dual-domain architecture gives rise to a durable supramolecular network with enhanced mechanical properties, yielding elastomers that are soft, stretchable, and tough. By tuning of the density of dynamic cross-links, mechanical properties were systematically modulated. SPU-0.5 exhibited a maximum tensile strength of 16.14 MPa, representing a 67-fold strength enhancement over that of SPU-0. Although increasing the aminopyrimidinedione (APD) content reduced elongation, SPU-0.2 retained a high elongation of 1060% and showed the lowest residual strain during cyclic tests. To be of great interest, the activation energy increased with increasing hydrogen bonding content up to SPU-0.1, whereas beyond SPU-0.2 it decreased, likely due to extensive hydrogen bond formation. Furthermore, SPU-0.2-SP, a conductive variant, demonstrated a promising strain-sensing performance even after hundreds of cycles. Overall, the insights gained from this study advance the development of intelligent soft materials and lay the groundwork for next-generation flexible and wearable electronic devices.

1 aLakshmi, Durga1 aWagh, Mahendra, A.1 aSharma, Aakash1 aAlam, Md, Shafi1 aSelvan, Muthamil1 aTorris, Arun1 aMondal, Titash1 aSanjayan, Gangadhar, J.1 aNair, Kiran, Sukumaran uhttps://library.ncl.res.in/content/dynamic-janus-hydrogen-bond-mimicry-unlocks-tough-flexible-supramolecular-elastomers-strain02056nas a2200241 4500008004100000022001400041245009200055210006900147260000800216300001400224490000700238520127500245653001601520653002801536653001401564653000901578100001801587700001601605700001901621700001901640700003101659856012401690 2026 eng d a0969-023900aSimple two-step gelation process to strengthen 3D printed carboxy methyl cellulose gels0 aSimple twostep gelation process to strengthen 3D printed carboxy cMAR a2015-20300 v333 a

Carboxymethyl cellulose (CMC) is a water-soluble cellulose ether that is widely utilized in hydrogel applications due to its exceptional water absorption and biocompatibility. This study reports a simple two step strategy to make mechanically robust CMC gels without any additional chemical crosslinkers and how it could be leveraged to strengthen 3D printed CMC gels. These hydrogels, prepared through acid-induced gelation followed by freeze-thawing, exhibited a compressive modulus of 12.4 +/- 0.92 kPa and a compressive strength of 491.0 +/- 18.1 kPa. They could be leveraged for strengthening 3D printing hydrogels of intricate shapes by direct ink writing. Small amplitude oscillatory shear (SAOS) tests indicated an order of magnitude higher storage modulus for freeze-thawed gels (FC) as compared to only acid-induced CMC gels (HCMC). Nonetheless, stress relaxation experiments revealed that FC, as well as HCMC gels, relax at similar time scales. FC gels exhibited clear birefringence under crossed polarizers, indicating molecular ordering that is consistent with the presence of ordered/crystalline domains. Such ordered domains likely contribute to the higher elastic modulus and compressive strength observed in FC gels as compared to HCMC gels.

10a3D printing10aCarboxymethyl cellulose10acellulose10aGels1 aRajput, Tejas1 aSathe, Asmi1 aGopal, Animesh1 aSharma, Aakash1 aShanmuganathan, Kadhiravan uhttps://library.ncl.res.in/content/simple-two-step-gelation-process-strengthen-3d-printed-carboxy-methyl-cellulose-gels