Monitoring crystallite fusion of nanocellulose during colloid condensation

Monitoring crystallite fusion of nanocellulose during colloid condensation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Monitoring crystallite fusion of nanocellulose during colloid condensation Yoshinori Doi, Kazuho Daicho, Noriyuki Isobe, Reina Tanaka, Satoshi Kimura, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2713577/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Jul, 2023 Read the published version in Cellulose → Version 1 posted 7 You are reading this latest preprint version Abstract The crystallinity of cellulose decreases when bundled microfibrils are dispersed in water as cellulose nanofibers (CNFs) or physically separated into finer nanoscale fibrils or single microfibrils. The crystallinity of these CNFs is recovered when they become densely assembled through the dehydration of the dispersion. In this process, multiple CNFs are assumed to partially fuse, leading to the enlargement of crystallite widths. The mechanism of this CNF fusion is, however, not well understood. In this study, the recovery process of the crystallinity of CNFs was monitored by sampling wet CNF gels during condensation from a dilute dispersion to a dense aggregate, followed by wide-angle X-ray diffractometry (WAXD) and solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy analyses after supercritical drying. In the WAXD analysis, a two-step enlargement in the (2 0 0) crystal size was observed: the first step was a rapid increase in the range of solid content up to 1%, followed by a gradual increase in the range of 1–85%. The crystallinity index estimated by NMR hardly changed in the range of 0.5–30% but gradually increased in the range of 30–85%. A portion of the CNF samples, without drying, were also subjected to small-angle X-ray scattering and viscoelasticity analyses, indicating that the inter-CNF contact points in water significantly increased until reaching a solid content of 1%, and then at solid contents higher than 1%, the contact areas of each point gradually expanded. Finally, a mechanism of CNF fusion was proposed based on these results. cellulose nanofibers crystallinity crystallite fusion condensation aerogels Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Highly fibrillated cellulose is attracting attention as a sustainable “cellulose nanofiber (CNF)” with excellent mechanical and thermal properties (Nishiyama 2009 ; Solhi et al. 2023 ; Heise et al. 2022 ). CNFs are generally produced as aqueous dispersions from bleached wood pulps through wet disintegration. Controlling the dehydration of CNF dispersions results in various bulk structures, including aerogels with a sparse CNF network and films with a dense CNF network. These CNF aggregates exhibit functionalities depending on the network structure, such as heat insulating and gas barrier properties (Fukuzumi et al. 2009 ; Kobayashi et al. 2014 ). The material properties of networked CNF structures correlate with the crystallinity of CNFs (Iwamoto et al. 2007 ; Uetani et al. 2015 ; Ishioka et al. 2023 ). The crystallinity of cellulose is significantly decreased when microfibrils tightly bundled in a pulp disperse as CNFs (Daicho et al. 2018 ). However, the crystallinity is recovered when CNFs are densely assembled through the dehydration of the dispersion (Daicho et al. 2021 ). This recovery of the crystallinity correlates with inter-CNF interactions, and the crystallite widths of CNFs are significantly enlarged through assembly with strong inter-CNF interactions. In this process, multiple CNFs, or cellulose crystallites, are assumed to partially fuse into single crystalline domains (Daicho et al. 2021 ). This is probably the same phenomenon as the “cocrystallization” or “twinning” of crystallites proposed by Newman et al. (2004, 2013 ). The mechanism of this crystallite fusion using CNFs as the structural unit is, however, not yet well understood, and neither is when or how it occurs during the dehydration of CNF dispersions. Herein, we report changes in the crystallinity of CNFs when transitioning from a dilute dispersion to a dense aggregate by condensation at rest. The CNF used in this study was TEMPO-oxidized, and some of the surface C6 hydroxy groups were converted to sodium carboxylates (Saito et al. 2006 ). CNF samples with different solid contents, sampled in the process of condensation, were subjected to supercritical drying, followed by wide-angle X-ray diffractometry (WAXD) and solid-state cross-polarization magic angle spinning (CPMAS) 13 C nuclear magnetic resonance (NMR) spectroscopy analyses. A portion of the CNF samples, without drying, were also subjected to small-angle X-ray scattering (SAXS) and viscoelasticity analyses to trace the networked CNF structure in water. Finally, we proposed a mechanism of the fusion phenomenon. Materials And Methods Materials A TEMPO-oxidized pulp in a wet state was kindly provided by DKS Co. Ltd. and used as the starting material. The carboxylate content of the pulp was determined to be 1.78 mmol g − 1 by conductivity titration. Ethanol (99.5%) and distilled water were purchased from Fujifilm Wako Pure Chemical Co., Ltd. and used as received. CNF dispersion The TEMPO-oxidized pulp was suspended in distilled water at approximately 0.5% w/w and disintegrated into CNFs by passing it through a high-pressure water jet system (HJP-25005X, Sugino Machine Limited, Japan) at 150 MPa twice. The resulting CNF dispersion was passed through a nylon mesh filter with a mesh size of 5 µm to remove an unfibrillated fraction. A part of the dispersion was diluted to 0.1–0.4% w/w by adding distilled water. Condensation A 0.5% CNF dispersion (15 g) was poured into a polystyrene dish (44×44×15 mm) and condensed at rest in a thermohygrostat at 40°C and 80% relative humidity (RH) until the solid content reached a plateau at approximately 85%. Supercritical drying A portion of the starting pulp and the condensed CNF samples were soaked in ethanol (200 mL) and gently shaken for two days using a rotary shaker at 50 rpm. The ethanol bath was replaced with fresh ethanol four times a day. The obtained samples were placed in the chamber of a supercritical dryer (Sanyu-Gijutsu, SYGLCP-8, Japan) under a liquid CO 2 flow (4 mL min -1 ) at 15°C for 9 h. After the flow of liquid CO 2 was stopped, the chamber temperature was increased to 40°C to reach the supercritical phase. After maintaining the supercritical phase for 1 hour, the chamber was gradually depressurized at 40°C for 1 h. The resulting supercritical-dried samples were conditioned at 23°C and 50% RH for more than 1 day before analysis. The moisture contents of the supercritical-dried samples were approximately 5%. WAXD The conditioned samples were pressed at approximately 500 MPa for 1 min using a pelletizing device for WAXD. WAXD measurements were performed using a Rigaku Mini Flex diffractometer with a Ni-filtered Cu Kα beam (λ = 0.1542 nm) at 40 kV and 15 mA in the diffraction angle 2 θ range of 3–45° in reflection mode. The diffraction peaks corresponding to the (2 0 0) and the sum of the (1 1 0) and (1–1 0) planes were deconvoluted after subtracting a linear background from the profiles, according to a previous report (Daicho et al. 2018 ) (see Figure S1 for the peak separation of the WAXD profiles). The crystal size of the (2 0 0) plane was calculated using Scherrer’s equation with a shape factor of K = 0.9. The peak broadening due to the optical system of the instrument was corrected using a silicon monocrystal. CP-MAS 13 C NMR spectroscopy The conditioned samples were packed into a ZrO 2 rotor and analyzed by CP/MAS 13 C NMR spectroscopy. CP/MAS 13 C NMR measurements were performed using a JEOL JNM-ECAII 500 spectrometer equipped with a 3.2 mm HXMAS probe and rotor operating at 125.77 MHz for 13 C. The samples were spun at 15000 Hz and 298 K. The 90° proton decoupler pulse width, contact time, and relaxation delay were set to 2.5 µs, 2 ms, and 5 s, respectively (Daicho et al. 2020 ). Adamantane was used as an external standard for calibration of the chemical shift. The signals in the regions of 92–87 and 87–80 ppm, corresponding to the crystalline and noncrystalline C4 carbon atoms of cellulose, respectively, were separated, and the integral ratio of the C4 crystalline signal to all C4 signals was calculated as the crystallinity index (CI) value. Recovery rate of crystallinity The recovery rate of the crystal size and CI of a condensed sample was defined as follows: $$\text{R}\text{e}\text{c}\text{o}\text{v}\text{e}\text{r}\text{y} \text{r}\text{a}\text{t}\text{e} \left(\text{%}\right)=\frac{{X}_{\text{c}\text{o}\text{n}\text{d}}-{X}_{\text{d}\text{i}\text{s}}}{{X}_{\text{p}\text{u}\text{l}\text{p}}-{X}_{\text{d}\text{i}\text{s}}}\times 100$$ 1 where X cond , X dis , and X pulp are the crystal sizes or CI values of the condensed sample, the 0.5% CNF dispersion, and the starting pulp, respectively. The crystal size and CI value of the pulp were 3.0 nm and 41%, respectively. Scanning electron microscopy (SEM) SEM images of the supercritical-dried samples were captured with a Hitachi S-4800 field-emission microscope at 1 kV. The samples were pretreated with a Meiwafosis Neo osmium coater at 2.5 mA for 10 s. SAXS SAXS with synchrotron radiation was carried out on dilute dispersions (0.1–0.5%) at the BL40B2 beamline of SPring-8 (Hyogo, Japan). The dispersions were set into a quartz-windowed metallic folder and mounted on a goniometer head. The X-ray (λ = 1.0 Å) irradiation was maintained for 100 s, and the diffraction pattern was recorded using a photon-counting pixel detector (PILATUS3 S 2M, Dectris, Switzerland). The distance between the sample and the imaging plate (3193 mm) was calibrated using silver behenate powders (d = 5.838 nm) (Stephens et al. 2012 ). SAXS measurements of the condensed samples (0.6–1.0%) were performed using a Rigaku NANOPIX SAXS system with monochromatized and collimated Cu Kα radiation ( λ = 0.1542 nm) at 40 kV and 30 mA and a camera length of 920 mm. The condensed samples were set into a quartz-windowed metallic folder and mounted on a goniometer head. The 2D SAXS pattern was recorded using a hybrid pixel 2-dimensional detector (HyPix-3000, Rigaku, Japan) with an exposure time of 30 min. The camera lengths were calibrated using silver behenate. The recorded patterns were converted to a 1D scattering angle q -intensity profile using Rigaku 2DP software. The cross-sectional radii of gyration, R c , for CNFs in the dispersions and condensed samples were calculated from the profiles in the q range of 0.50–0.94 nm -1 using the following equation (Glatter et al. 1982 ): $${ln}\left(I\left(q\right)\bullet q\right)={ln}\left(I\left(0\right)\bullet q\right)-\frac{1}{2}{{R}_{c}}^{2}\bullet {q}^{2}$$ 2 Dynamic viscoelasticity Dynamic viscoelasticity measurements were conducted using an MCR 302 (Anton Paar GmbH, Graz, Austria) at 25°C. A cone-plate geometry (plate diameter 50 mm, cone angle 2°) and a parallel-plate geometry (plate diameter 25 mm) were used for the dispersions ( 0.5%), respectively. Strain sweep measurements were carried out in advance at strains γ = 0.01–100% and a frequency ω = 10 rad s -1 to estimate the linear viscoelastic region, and frequency sweep measurements were conducted at angular frequencies ω = 0.1–100 rad s -1 within the linear viscoelastic region ( γ = 1%). Results And Discussion Condensation The CNF dispersion was slowly condensed at rest in a thermohygrostat set to 40 ℃ and 80% RH until the desired solid contents were attained. Figure 1 a shows the appearances of the 0.5% dispersion and two condensed samples at the intermediate (1%) and final (85%) stages of condensation. The starting dispersion had fluidity. As the solid content increased to approximately 1%, the CNFs lost fluidity and formed a self-standing gel. Finally, the condensed sample formed a film with a solid content of 85%. A series of condensed CNF samples was then subjected to solvent exchange with ethanol, followed by supercritical drying (Fig. 1 b). Supercritical drying is regarded as the best method for suppressing the dry agglomeration of dispersed CNFs in wet samples (Kobayashi et al. 2014 ). The wet CNF samples showed no obvious shrinkage in the supercritical drying process, and the resulting dried products or “aerogels” appeared to maintain their original volumes in the wet state. The SEM analysis of the sample supercritical-dried at a 0.5% concentration showed a network structure of well-individualized CNFs (Fig. 1 c). Hereafter, the dried samples are referred to by their solid contents in the wet state. Crystallinity The crystallinity of the dried samples was analyzed by WAXD and CP/MAS 13 C NMR spectroscopy. The samples were deformable aerogels and were pelletized by compression for WAXD (see Figure S2 for the appearance of the pellets). The lack of change in the crystallinity after this compression process was confirmed in advance by NMR (Figure S3). Figure 2 a shows the reflection WAXD profiles of the samples. As the solid content increased, the diffraction peaks became sharper. We assumed that the (0 1 2) and (1 0 2) diffractions at approximately 20–21° were negligibly small in the reflection profiles, considering that the CNFs in the pelletized samples were sufficiently oriented to the in-plane direction of the pellets (see Figure S4 for on-edge transmission WAXD profiles of the pellets), so that no (0 0 4) diffraction at approximately 35° was observed in the reflection profiles. According to a simulation study by French and Santiago Cintrón ( 2013 ), cellulose I crystals with the preferred orientation show no (0 1 2) and (1 0 2) diffractions in their reflection profile, which is also accompanied by a significant reduction in the (0 0 4) diffraction. The (2 0 0) diffraction was then separated from these WAXD profiles by peak deconvolution (Figure S1 ), and their crystal sizes were calculated using Scherrer’s equation (Fig. 2 b). The crystal size increased from approximately 1.8 nm to 2.4 nm as the solid content increased from 0.5–85%. Interestingly, this crystal-size enlargement showed two steps: a rapid increase in the range of 0.5–1%, followed by a gradual increase in the range of 1–85%. The slight shift of the (2 0 0) peak position from 21.9° to 22.3° with the solid content can be explained by this crystal-size enlargement (Wada et al. 1997 ; Huang et al. 2018 ). Figure 2 c shows the NMR spectra of the samples. In the C4 region, the crystalline signal at 87–92 ppm increased little by little relative to the noncrystalline signal at 80–87 ppm with increasing solid content. A similar change was also observed in the C6 region; the crystalline tg signal at approximately 65 ppm gradually increased relative to the noncrystalline gt and gg signals at approximately 60–63 ppm. The CI values were calculated as the integral ratio of the crystalline C4 signal to all C4 signals in the NMR spectra. The CI value hardly changed in the range of 0.5–30% but gradually increased from approximately 23–28% in the range of 30–85% (Fig. 2 d). The recovery rates for the crystal size and CI value at each solid content were calculated based on the decrement of these values upon disintegrating the starting pulp into CNFs with a 0.5% concentration (see Methods section for details). The crystal size and CI value were recovered by 41% and 28%, respectively, throughout the whole range of 0.5–85% (Fig. 2 e). The reason for the higher recovery rate of crystal size is discussed later. CNF assembly in water The fact that the obvious enlargement in crystal size occurred for the supercritical-dried samples with low solid contents below 1% implies that the adjacent CNFs dispersed in water started to assemble at such a low solid content. To verify this hypothesis, the cross-sectional radii of gyration, R c , of the CNFs in the wet samples were analyzed by SAXS measurements. Figure 3 a shows the 1D SAXS profiles of the wet CNF samples with solid contents of 0.1–1% (see Figure S5a for the SAXS patterns of all the samples). The shape of the profile changed with the solid content. The R c of the CNFs at each solid content was calculated from the profiles in the q range of 0.50–0.94 nm -1 (Fig. 3 b). The resulting R c value indeed increased with increasing solid content. This result indicates that the CNFs assembled in water, and the inter-CNF contact points increased upon condensation up to 1%. Assuming a cylindrical model, the cross-sectional diameter was estimated to be approximately 3.8‒4.1 nm using the R c values and scaled to a similar extent with the crystal size shown in Fig. 2 b (~ 0.3 nm). Note that the CNFs with these low solid contents were randomly oriented on average (see Figure S5b for 2D SAXS patterns). Network growth The dynamic viscoelasticity of the wet samples with low solid contents was measured to investigate the network formation of CNFs in water. Figure 4a shows the frequency dependency of storage modulus, G’ , and loss modulus, G” , of the wet samples with solid contents of 0.13–0.47%. At 0.13%, the G’ values were lower than the G” values in the frequency range of 0.1–0.2 rad s -1 ; the sample was in a sol state and had fluidity. At 0.25%, the G’ values were nearly equal to G” in the frequency range of 0.1–20 rad s -1 , suggesting the network formation of dispersed CNFs. With a further increase in solid content to ~ 0.5% or above, the G’ values became clearly higher than the G” and were almost constant over the entire frequency range (Fig. 4b). These results show that the wet CNF samples with solid contents of ~ 0.5% or above behaved as elastic bodies. The G’ values at 1 rad s -1 in the plateau region were taken as the plateau moduli, G’ p , and were plotted against the solid content in a double logarithmic plot (Fig. 4c). There were two clearly distinguished regions with different slopes in the plot. The following relationship between the G’ p values and solid contents has been proposed for semiflexible fiber networks (Tatsumi et al. 2002 ; Saito et al. 2011 ): $${{G}^{{\prime }}}_{p}=A{c}^{\alpha }$$ 4 where A is a constant that reflects individual fiber properties, such as the aspect ratio and elastic modulus, and the power, α , is related to the network structure and corresponds to the slope of the double logarithmic plots. The α value for the wet CNF samples in this study changed from 3.5 to 1.3 at the threshold of approximately 1%; at this threshold, the contribution of CNFs to the network growth changed as the solid content increased. The threshold value was consistent with the solid content at which the trend in the crystal-size enlargement clearly changed (see Fig. 2 b), indicating a correlation between the crystal-size enlargement and networked CNF structure in water. Figure 4d shows the correlation lengths, L , in the polymer networks, or the segment lengths between entanglements, estimated using the G’ p values (Ferry 1961 ). These L values correspond to the average distances between the inter-CNF contact points in this study and were estimated by the following formula: $$L=\rho RT/{G{\prime }}_{p}$$ 3 where ρ , R , and T are the density or CNF weight per volume of the wet sample, gas constant, and temperature, respectively. The L value drastically decreased with increasing solid content up to 1% but became almost constant at a threshold of approximately 1%. Mechanism Figure 5 illustrates our interpretation of the mechanism of network formation or growth by CNF assembly. Taking into account the results shown in Figs. 3 and 4, we assumed the following mechanism (Fig. 5 a): 1) the inter-CNF contact points significantly increase until reaching a solid content of 1%, at which point the basic skeleton of the CNF network in a wet sample is set, and 2) at a solid content higher than 1%, the inter-CNF contact areas gradually expand in a zip-up manner with the solid content. This mechanism corresponds to the two-step enlargement of the crystal size shown in Fig. 1 b. Another mechanism of CNF assembly, shown in Fig. 5 b, was assumed to explain the preferential recovery of the crystal size at low solid contents in comparison with the CI (see Fig. 2 e). In this assumption, we used an 18-chain model with molecular sheet stacking of 2/3/4/4/3/2 as a single CNF. At low solid contents up to 1%, the CNFs are assumed to preferentially assemble by hydrophobic interactions, where the (2 0 0) surfaces of the CNFs are stacked on top of each other. This CNF assembly explains the crystal size enlargement or “crystallite fusion” observed at low solid contents. At higher than 1%, we assumed that gradual assembly between the hydrophilic surfaces is induced by condensation, exceeding the repulsive force of electric double layers. This latter step of assembly explains the gradual increases in the CI as well as the crystal size. Note that some of the hydroxy groups on the hydrophilic (1 1 0) and (1 − 1 0) surfaces were oxidized to carboxy groups in this study. See also our previous report for the current interpretation of the CI recovery of such partially surface-oxidized CNFs (Daicho et al. 2021 ). Conclusions The recovery of the crystallinity of CNFs transitioning from a dilute dispersion to a dense aggregate by condensation was monitored in this study. The condensed CNF samples were subjected to supercritical drying, followed by WAXD and NMR analyses. In the WAXD analysis, a two-step enlargement in the (2 0 0) crystal size was observed; the first step was a rapid increase in the solid content range of 0–1%, followed by a gradual increase in the range of 1–85%. The CI value estimated by the NMR analysis hardly changed in the range of 0.5–30% but gradually increased in the range of 30–85%. The wet CNF samples were also subjected to SAXS and viscoelasticity analyses without supercritical drying. These analyses of wet samples indicated that the inter-CNF contact points significantly increased until reaching a solid content of 1%, and then at solid contents higher than 1%, the contact areas of each point gradually expanded. Taking into account the preferential recovery of crystal size at low solid contents, we further assumed a mechanism of crystallite fusion; at low solid contents, the hydrophobic (2 0 0) surfaces of CNFs are preferentially stacked on top of each other, followed by gradual assembly between not only the hydrophobic (2 0 0) but also the hydrophilic (1 1 0)/(1 − 1 0) surfaces at high solid contents. The findings in this study will contribute to diverse material designs involving CNF assembly. Declarations Conflict of interest. The authors declare no competing financial interest. Ethical approval. This article does not contain any studies with human participants or animals performed by any of the authors. Funding. This research was partially supported by the JST CREST program (JPMJCR22L3), JST-Mirai R&D Program (JPMJMI17ED), and JSPS Grant-in-Aids for Scientific Research (20K15567; 20K15348; 21H04733; 22J01001; 22H03786; 22K19885). Authors' contributions. T.S. conceived the concept of the study. K.D. and T.S. designed the samples, XRD and NMR experiments. N.I. and S.F. designed the SAXS experiments. R.T. and T.S. designed the rheological experiments. Y.D. and K.D. performed all experiments with help from N.I., R.T., and S.K. All authors analyzed the data. Y.D. and K.D. wrote the first version of the manuscript, and T.S. revised the manuscript with contributions from all the authors. Acknowledgments. The synchrotron radiation experiments were performed at SPring-8 (Proposal Nos. 2021A1240) at BL40B2. We thank Prof. Tomoya Imai at Kyoto University for his help in the synchrotron radiation experiments at SPring-8. References Daicho K, Fujisawa S, Kobayashi K et al (2020) Cross-polarization dynamics and conformational study of variously sized cellulose crystallites using solid-state 13 C NMR. 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Supplementary Files SIDoi.docx Cite Share Download PDF Status: Published Journal Publication published 06 Jul, 2023 Read the published version in Cellulose → Version 1 posted Editorial decision: Major revision 27 Apr, 2023 Reviews received at journal 11 Apr, 2023 Reviewers agreed at journal 27 Mar, 2023 Reviewers invited by journal 27 Mar, 2023 Editor assigned by journal 24 Mar, 2023 Submission checks completed at journal 24 Mar, 2023 First submitted to journal 22 Mar, 2023 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2713577","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":188457597,"identity":"f8106ca6-6583-4f77-9a65-d540cd2aac46","order_by":0,"name":"Yoshinori Doi","email":"","orcid":"","institution":"University of Tokyo","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yoshinori","middleName":"","lastName":"Doi","suffix":""},{"id":188457598,"identity":"d48df869-4ed8-40d6-a1d3-b799fa9fb62c","order_by":1,"name":"Kazuho Daicho","email":"","orcid":"","institution":"University of Tokyo","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Kazuho","middleName":"","lastName":"Daicho","suffix":""},{"id":188457599,"identity":"dd9f4f9d-a7a7-4943-badb-bf8fee368c2b","order_by":2,"name":"Noriyuki Isobe","email":"","orcid":"","institution":"Japan Agency for Marine-Earth Science and Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Noriyuki","middleName":"","lastName":"Isobe","suffix":""},{"id":188457600,"identity":"7b29d293-04f2-4094-88b4-163d9c6f3d08","order_by":3,"name":"Reina Tanaka","email":"","orcid":"","institution":"Forestry and Forest Products Research Institute","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Reina","middleName":"","lastName":"Tanaka","suffix":""},{"id":188457601,"identity":"519f5eaf-430e-44d2-b593-3b0b05985e76","order_by":4,"name":"Satoshi Kimura","email":"","orcid":"","institution":"University of Tokyo","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Satoshi","middleName":"","lastName":"Kimura","suffix":""},{"id":188457602,"identity":"1f9017d2-6fb7-4448-9fde-56b5977800b8","order_by":5,"name":"Shuji Fujisawa","email":"","orcid":"","institution":"University of Tokyo","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Shuji","middleName":"","lastName":"Fujisawa","suffix":""},{"id":188457603,"identity":"f013367f-f1c0-4a8d-8d9b-020b2a9c4a32","order_by":6,"name":"Tsuguyuki Saito","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABE0lEQVRIie2QsWrDMBCGTxTsDgKvylK/gowhU1BeRUbgLt0KnUqxCDiL26wO7Uv0DQwGT2myBrrIewd1KZ3aWklaPMihY6H6huOk4+N+CcDh+JOgrCuT3gXuD+yKzICnP0fyC8WMeG1Rhgjn9Vy9vm9Y5s9ajXK4CfAqUnDN4OTevoauEilL/iwy3MSkU8jotogpNALQQ2VXIJEz3ClALjxA+SehGzwm4FWASm4PtmiNshYQvhgFDsrHsALb3ZaKAcEH5akYdwmHFbpt5bJMBfdwGhO+htGyaC5pcifw0FvCxbnSesKmgV+3Wl9BEGDxqPQbO4sGfuybJDd1n+SUmgZH5VEDpr3eV/sA5LjicDgc/4YvydRXSuWPy+gAAAAASUVORK5CYII=","orcid":"","institution":"University of Tokyo","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Tsuguyuki","middleName":"","lastName":"Saito","suffix":""}],"badges":[],"createdAt":"2023-03-20 10:35:02","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2713577/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2713577/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10570-023-05354-x","type":"published","date":"2023-07-06T21:29:56+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":35296575,"identity":"65a3185b-757d-421c-88e2-30e00235136d","added_by":"auto","created_at":"2023-04-04 22:32:45","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":950727,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea \u003c/strong\u003eAppearances of the CNF dispersion (0.5%) and two condensed samples at the intermediate (1%) and final (85%) stages of condensation. \u003cstrong\u003eb \u003c/strong\u003eA supercritical-dried sample prepared from condensed CNF samples. \u003cstrong\u003ec \u003c/strong\u003eCross-sectional SEM images of the supercritical-dried sample prepared at a solid content of 0.5%\u003c/p\u003e","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-2713577/v1/9c239c460cedd0cbcf609926.png"},{"id":35297167,"identity":"2f64632d-0789-4f71-8f22-862918d940d8","added_by":"auto","created_at":"2023-04-04 22:40:44","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":272512,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e WAXD profiles, \u003cstrong\u003eb\u003c/strong\u003e (2 0 0) crystal sizes, \u003cstrong\u003ec\u003c/strong\u003eNMR spectra, and \u003cstrong\u003ed\u003c/strong\u003e CI values of a series of samples. \u003cstrong\u003ee \u003c/strong\u003eRecovery rates of the crystal size and CI.\u003c/p\u003e","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-2713577/v1/37e657c401ac6b7f5011617a.png"},{"id":35296570,"identity":"f030b4ea-2d07-4ad1-86e2-c074f4d0c598","added_by":"auto","created_at":"2023-04-04 22:32:44","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":72070,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea \u003c/strong\u003e1D SAXS profiles of the wet CNF samples and\u003cstrong\u003e b \u003c/strong\u003ethe radii of gyration, \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e, calculated from the 1D profiles.\u003c/p\u003e","description":"","filename":"Onlinefloatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-2713577/v1/b82fb5fe2694934940e43cf0.png"},{"id":35296573,"identity":"1845c545-bc12-4784-a81f-dd9131372e9a","added_by":"auto","created_at":"2023-04-04 22:32:44","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":170601,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea \u003c/strong\u003e\u003cem\u003eG’\u003c/em\u003e and \u003cem\u003eG”\u003c/em\u003e values as a function of frequency for the CNF dispersions with solid contents of 0.13–0.47%, and \u003cstrong\u003eb \u003c/strong\u003e\u003cem\u003eG’\u003c/em\u003e values for the condensed samples with solid contents of 0.47–3.3%. \u003cstrong\u003ec\u003c/strong\u003e Relationship between the \u003cem\u003eG’\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e values and solid contents of the condensed samples.\u003cstrong\u003e d\u003c/strong\u003e Change in the correlation length, \u003cem\u003eL\u003c/em\u003e, estimated from the \u003cem\u003eG’\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e values and solid contents\u003c/p\u003e","description":"","filename":"Onlinefloatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-2713577/v1/33a663be7d4de4d1d488cfb6.png"},{"id":35296572,"identity":"cdb67023-5721-4cf1-ad59-e7664c8eee37","added_by":"auto","created_at":"2023-04-04 22:32:44","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":195750,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea \u003c/strong\u003eMechanism of network formation or growth by CNF assemblyduring condensation, and \u003cstrong\u003eb\u003c/strong\u003e the inter-CNF interactions in water.\u003c/p\u003e","description":"","filename":"Onlinefloatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-2713577/v1/c5fc736e6e978a832386e1e6.png"},{"id":44732428,"identity":"1e458e0f-b9f4-43dd-8027-c4df2a2c8e88","added_by":"auto","created_at":"2023-10-16 21:55:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2400504,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2713577/v1/2c543c7b-d53b-4241-beb6-aafd195db91a.pdf"},{"id":35297168,"identity":"3b987b71-a331-423d-9152-a6042a6bb243","added_by":"auto","created_at":"2023-04-04 22:40:44","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":2150745,"visible":true,"origin":"","legend":"","description":"","filename":"SIDoi.docx","url":"https://assets-eu.researchsquare.com/files/rs-2713577/v1/2d254e8f7d71067809a1bb6d.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Monitoring crystallite fusion of nanocellulose during colloid condensation","fulltext":[{"header":"Introduction","content":"\u003cp\u003eHighly fibrillated cellulose is attracting attention as a sustainable \u0026ldquo;cellulose nanofiber (CNF)\u0026rdquo; with excellent mechanical and thermal properties (Nishiyama \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Solhi et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Heise et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). CNFs are generally produced as aqueous dispersions from bleached wood pulps through wet disintegration. Controlling the dehydration of CNF dispersions results in various bulk structures, including aerogels with a sparse CNF network and films with a dense CNF network. These CNF aggregates exhibit functionalities depending on the network structure, such as heat insulating and gas barrier properties (Fukuzumi et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Kobayashi et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe material properties of networked CNF structures correlate with the crystallinity of CNFs (Iwamoto et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Uetani et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Ishioka et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The crystallinity of cellulose is significantly decreased when microfibrils tightly bundled in a pulp disperse as CNFs (Daicho et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). However, the crystallinity is recovered when CNFs are densely assembled through the dehydration of the dispersion (Daicho et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This recovery of the crystallinity correlates with inter-CNF interactions, and the crystallite widths of CNFs are significantly enlarged through assembly with strong inter-CNF interactions. In this process, multiple CNFs, or cellulose crystallites, are assumed to partially fuse into single crystalline domains (Daicho et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This is probably the same phenomenon as the \u0026ldquo;cocrystallization\u0026rdquo; or \u0026ldquo;twinning\u0026rdquo; of crystallites proposed by Newman et al. (2004, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). The mechanism of this crystallite fusion using CNFs as the structural unit is, however, not yet well understood, and neither is when or how it occurs during the dehydration of CNF dispersions.\u003c/p\u003e \u003cp\u003eHerein, we report changes in the crystallinity of CNFs when transitioning from a dilute dispersion to a dense aggregate by condensation at rest. The CNF used in this study was TEMPO-oxidized, and some of the surface C6 hydroxy groups were converted to sodium carboxylates (Saito et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). CNF samples with different solid contents, sampled in the process of condensation, were subjected to supercritical drying, followed by wide-angle X-ray diffractometry (WAXD) and solid-state cross-polarization magic angle spinning (CPMAS) \u003csup\u003e13\u003c/sup\u003eC nuclear magnetic resonance (NMR) spectroscopy analyses. A portion of the CNF samples, without drying, were also subjected to small-angle X-ray scattering (SAXS) and viscoelasticity analyses to trace the networked CNF structure in water. Finally, we proposed a mechanism of the fusion phenomenon.\u003c/p\u003e"},{"header":"Materials And Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eA TEMPO-oxidized pulp in a wet state was kindly provided by DKS Co. Ltd. and used as the starting material. The carboxylate content of the pulp was determined to be 1.78 mmol g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e by conductivity titration. Ethanol (99.5%) and distilled water were purchased from Fujifilm Wako Pure Chemical Co., Ltd. and used as received.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eCNF dispersion\u003c/h2\u003e \u003cp\u003eThe TEMPO-oxidized pulp was suspended in distilled water at approximately 0.5% w/w and disintegrated into CNFs by passing it through a high-pressure water jet system (HJP-25005X, Sugino Machine Limited, Japan) at 150 MPa twice. The resulting CNF dispersion was passed through a nylon mesh filter with a mesh size of 5 \u0026micro;m to remove an unfibrillated fraction. A part of the dispersion was diluted to 0.1\u0026ndash;0.4% w/w by adding distilled water.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eCondensation\u003c/h2\u003e \u003cp\u003eA 0.5% CNF dispersion (15 g) was poured into a polystyrene dish (44\u0026times;44\u0026times;15 mm) and condensed at rest in a thermohygrostat at 40\u0026deg;C and 80% relative humidity (RH) until the solid content reached a plateau at approximately 85%.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eSupercritical drying\u003c/h2\u003e \u003cp\u003eA portion of the starting pulp and the condensed CNF samples were soaked in ethanol (200 mL) and gently shaken for two days using a rotary shaker at 50 rpm. The ethanol bath was replaced with fresh ethanol four times a day. The obtained samples were placed in the chamber of a supercritical dryer (Sanyu-Gijutsu, SYGLCP-8, Japan) under a liquid CO\u003csub\u003e2\u003c/sub\u003e flow (4 mL min\u003csup\u003e-1\u003c/sup\u003e) at 15\u0026deg;C for 9 h. After the flow of liquid CO\u003csub\u003e2\u003c/sub\u003e was stopped, the chamber temperature was increased to 40\u0026deg;C to reach the supercritical phase. After maintaining the supercritical phase for 1 hour, the chamber was gradually depressurized at 40\u0026deg;C for 1 h. The resulting supercritical-dried samples were conditioned at 23\u0026deg;C and 50% RH for more than 1 day before analysis. The moisture contents of the supercritical-dried samples were approximately 5%.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003eWAXD\u003c/h2\u003e \u003cp\u003eThe conditioned samples were pressed at approximately 500 MPa for 1 min using a pelletizing device for WAXD. WAXD measurements were performed using a Rigaku Mini Flex diffractometer with a Ni-filtered Cu Kα beam (λ\u0026thinsp;=\u0026thinsp;0.1542 nm) at 40 kV and 15 mA in the diffraction angle 2\u003cem\u003eθ\u003c/em\u003e range of 3\u0026ndash;45\u0026deg; in reflection mode. The diffraction peaks corresponding to the (2 0 0) and the sum of the (1 1 0) and (1\u0026ndash;1 0) planes were deconvoluted after subtracting a linear background from the profiles, according to a previous report (Daicho et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) (see Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e for the peak separation of the WAXD profiles). The crystal size of the (2 0 0) plane was calculated using Scherrer\u0026rsquo;s equation with a shape factor of \u003cem\u003eK\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.9. The peak broadening due to the optical system of the instrument was corrected using a silicon monocrystal.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eCP-MAS \u003csup\u003e13\u003c/sup\u003eC NMR spectroscopy\u003c/h2\u003e \u003cp\u003eThe conditioned samples were packed into a ZrO\u003csub\u003e2\u003c/sub\u003e rotor and analyzed by CP/MAS \u003csup\u003e13\u003c/sup\u003eC NMR spectroscopy. CP/MAS \u003csup\u003e13\u003c/sup\u003eC NMR measurements were performed using a JEOL JNM-ECAII 500 spectrometer equipped with a 3.2 mm HXMAS probe and rotor operating at 125.77 MHz for \u003csup\u003e13\u003c/sup\u003eC. The samples were spun at 15000 Hz and 298 K. The 90\u0026deg; proton decoupler pulse width, contact time, and relaxation delay were set to 2.5 \u0026micro;s, 2 ms, and 5 s, respectively (Daicho et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Adamantane was used as an external standard for calibration of the chemical shift. The signals in the regions of 92\u0026ndash;87 and 87\u0026ndash;80 ppm, corresponding to the crystalline and noncrystalline C4 carbon atoms of cellulose, respectively, were separated, and the integral ratio of the C4 crystalline signal to all C4 signals was calculated as the crystallinity index (CI) value.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eRecovery rate of crystallinity\u003c/h2\u003e \u003cp\u003eThe recovery rate of the crystal size and CI of a condensed sample was defined as follows:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\text{R}\\text{e}\\text{c}\\text{o}\\text{v}\\text{e}\\text{r}\\text{y} \\text{r}\\text{a}\\text{t}\\text{e} \\left(\\text{%}\\right)=\\frac{{X}_{\\text{c}\\text{o}\\text{n}\\text{d}}-{X}_{\\text{d}\\text{i}\\text{s}}}{{X}_{\\text{p}\\text{u}\\text{l}\\text{p}}-{X}_{\\text{d}\\text{i}\\text{s}}}\\times 100$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eX\u003c/em\u003e\u003csub\u003econd\u003c/sub\u003e, \u003cem\u003eX\u003c/em\u003e\u003csub\u003edis\u003c/sub\u003e, and \u003cem\u003eX\u003c/em\u003e\u003csub\u003epulp\u003c/sub\u003e are the crystal sizes or CI values of the condensed sample, the 0.5% CNF dispersion, and the starting pulp, respectively. The crystal size and CI value of the pulp were 3.0 nm and 41%, respectively.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eScanning electron microscopy (SEM)\u003c/h2\u003e \u003cp\u003eSEM images of the supercritical-dried samples were captured with a Hitachi S-4800 field-emission microscope at 1 kV. The samples were pretreated with a Meiwafosis Neo osmium coater at 2.5 mA for 10 s.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003eSAXS\u003c/h2\u003e \u003cp\u003eSAXS with synchrotron radiation was carried out on dilute dispersions (0.1\u0026ndash;0.5%) at the BL40B2 beamline of SPring-8 (Hyogo, Japan). The dispersions were set into a quartz-windowed metallic folder and mounted on a goniometer head. The X-ray (λ\u0026thinsp;=\u0026thinsp;1.0 \u0026Aring;) irradiation was maintained for 100 s, and the diffraction pattern was recorded using a photon-counting pixel detector (PILATUS3 S 2M, Dectris, Switzerland). The distance between the sample and the imaging plate (3193 mm) was calibrated using silver behenate powders (d\u0026thinsp;=\u0026thinsp;5.838 nm) (Stephens et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSAXS measurements of the condensed samples (0.6\u0026ndash;1.0%) were performed using a Rigaku NANOPIX SAXS system with monochromatized and collimated Cu Kα radiation (\u003cem\u003eλ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.1542 nm) at 40 kV and 30 mA and a camera length of 920 mm. The condensed samples were set into a quartz-windowed metallic folder and mounted on a goniometer head. The 2D SAXS pattern was recorded using a hybrid pixel 2-dimensional detector (HyPix-3000, Rigaku, Japan) with an exposure time of 30 min. The camera lengths were calibrated using silver behenate. The recorded patterns were converted to a 1D scattering angle \u003cem\u003eq\u003c/em\u003e-intensity profile using Rigaku 2DP software. The cross-sectional radii of gyration, \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e, for CNFs in the dispersions and condensed samples were calculated from the profiles in the \u003cem\u003eq\u003c/em\u003e range of 0.50\u0026ndash;0.94 nm\u003csup\u003e-1\u003c/sup\u003e using the following equation (Glatter et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1982\u003c/span\u003e):\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$${ln}\\left(I\\left(q\\right)\\bullet q\\right)={ln}\\left(I\\left(0\\right)\\bullet q\\right)-\\frac{1}{2}{{R}_{c}}^{2}\\bullet {q}^{2}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eDynamic viscoelasticity\u003c/h2\u003e \u003cp\u003eDynamic viscoelasticity measurements were conducted using an MCR 302 (Anton Paar GmbH, Graz, Austria) at 25\u0026deg;C. A cone-plate geometry (plate diameter 50 mm, cone angle 2\u0026deg;) and a parallel-plate geometry (plate diameter 25 mm) were used for the dispersions (\u0026lt;\u0026thinsp;0.5%) and condensed samples (\u0026gt;\u0026thinsp;0.5%), respectively. Strain sweep measurements were carried out in advance at strains \u003cem\u003eγ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.01\u0026ndash;100% and a frequency \u003cem\u003eω\u003c/em\u003e\u0026thinsp;=\u0026thinsp;10 rad s\u003csup\u003e-1\u003c/sup\u003e to estimate the linear viscoelastic region, and frequency sweep measurements were conducted at angular frequencies \u003cem\u003eω\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.1\u0026ndash;100 rad s\u003csup\u003e-1\u003c/sup\u003e within the linear viscoelastic region (\u003cem\u003eγ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1%).\u003c/p\u003e \u003c/div\u003e"},{"header":"Results And Discussion","content":"\u003cdiv class=\"Section2\" id=\"Sec14\"\u003e\n \u003ch2\u003eCondensation\u003c/h2\u003e\n \u003cp\u003eThe CNF dispersion was slowly condensed at rest in a thermohygrostat set to 40 ℃ and 80% RH until the desired solid contents were attained. Figure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea shows the appearances of the 0.5% dispersion and two condensed samples at the intermediate (1%) and final (85%) stages of condensation. The starting dispersion had fluidity. As the solid content increased to approximately 1%, the CNFs lost fluidity and formed a self-standing gel. Finally, the condensed sample formed a film with a solid content of 85%.\u003c/p\u003e\n \u003cp\u003eA series of condensed CNF samples was then subjected to solvent exchange with ethanol, followed by supercritical drying (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb). Supercritical drying is regarded as the best method for suppressing the dry agglomeration of dispersed CNFs in wet samples (Kobayashi et al. \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). The wet CNF samples showed no obvious shrinkage in the supercritical drying process, and the resulting dried products or \u0026ldquo;aerogels\u0026rdquo; appeared to maintain their original volumes in the wet state. The SEM analysis of the sample supercritical-dried at a 0.5% concentration showed a network structure of well-individualized CNFs (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec). Hereafter, the dried samples are referred to by their solid contents in the wet state.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec15\"\u003e\n \u003ch2\u003eCrystallinity\u003c/h2\u003e\n \u003cp\u003eThe crystallinity of the dried samples was analyzed by WAXD and CP/MAS \u003csup\u003e13\u003c/sup\u003eC NMR spectroscopy. The samples were deformable aerogels and were pelletized by compression for WAXD (see Figure S2 for the appearance of the pellets). The lack of change in the crystallinity after this compression process was confirmed in advance by NMR (Figure S3).\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea shows the reflection WAXD profiles of the samples. As the solid content increased, the diffraction peaks became sharper. We assumed that the (0 1 2) and (1 0 2) diffractions at approximately 20\u0026ndash;21\u0026deg; were negligibly small in the reflection profiles, considering that the CNFs in the pelletized samples were sufficiently oriented to the in-plane direction of the pellets (see Figure S4 for on-edge transmission WAXD profiles of the pellets), so that no (0 0 4) diffraction at approximately 35\u0026deg; was observed in the reflection profiles. According to a simulation study by French and Santiago Cintr\u0026oacute;n (\u003cspan class=\"CitationRef\"\u003e2013\u003c/span\u003e), cellulose I crystals with the preferred orientation show no (0 1 2) and (1 0 2) diffractions in their reflection profile, which is also accompanied by a significant reduction in the (0 0 4) diffraction.\u003c/p\u003e\n \u003cp\u003eThe (2 0 0) diffraction was then separated from these WAXD profiles by peak deconvolution (Figure \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e), and their crystal sizes were calculated using Scherrer\u0026rsquo;s equation (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb). The crystal size increased from approximately 1.8 nm to 2.4 nm as the solid content increased from 0.5\u0026ndash;85%. Interestingly, this crystal-size enlargement showed two steps: a rapid increase in the range of 0.5\u0026ndash;1%, followed by a gradual increase in the range of 1\u0026ndash;85%. The slight shift of the (2 0 0) peak position from 21.9\u0026deg; to 22.3\u0026deg; with the solid content can be explained by this crystal-size enlargement (Wada et al. \u003cspan class=\"CitationRef\"\u003e1997\u003c/span\u003e; Huang et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec shows the NMR spectra of the samples. In the C4 region, the crystalline signal at 87\u0026ndash;92 ppm increased little by little relative to the noncrystalline signal at 80\u0026ndash;87 ppm with increasing solid content. A similar change was also observed in the C6 region; the crystalline \u003cem\u003etg\u003c/em\u003e signal at approximately 65 ppm gradually increased relative to the noncrystalline \u003cem\u003egt\u003c/em\u003e and \u003cem\u003egg\u003c/em\u003e signals at approximately 60\u0026ndash;63 ppm. The CI values were calculated as the integral ratio of the crystalline C4 signal to all C4 signals in the NMR spectra. The CI value hardly changed in the range of 0.5\u0026ndash;30% but gradually increased from approximately 23\u0026ndash;28% in the range of 30\u0026ndash;85% (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ed).\u003c/p\u003e\n \u003cp\u003eThe recovery rates for the crystal size and CI value at each solid content were calculated based on the decrement of these values upon disintegrating the starting pulp into CNFs with a 0.5% concentration (see Methods section for details). The crystal size and CI value were recovered by 41% and 28%, respectively, throughout the whole range of 0.5\u0026ndash;85% (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ee). The reason for the higher recovery rate of crystal size is discussed later.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec16\"\u003e\n \u003ch2\u003eCNF assembly in water\u003c/h2\u003e\n \u003cp\u003eThe fact that the obvious enlargement in crystal size occurred for the supercritical-dried samples with low solid contents below 1% implies that the adjacent CNFs dispersed in water started to assemble at such a low solid content. To verify this hypothesis, the cross-sectional radii of gyration, \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e, of the CNFs in the wet samples were analyzed by SAXS measurements.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea shows the 1D SAXS profiles of the wet CNF samples with solid contents of 0.1\u0026ndash;1% (see Figure S5a for the SAXS patterns of all the samples). The shape of the profile changed with the solid content. The \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e of the CNFs at each solid content was calculated from the profiles in the \u003cem\u003eq\u003c/em\u003e range of 0.50\u0026ndash;0.94 nm\u003csup\u003e-1\u003c/sup\u003e (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb). The resulting \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e value indeed increased with increasing solid content. This result indicates that the CNFs assembled in water, and the inter-CNF contact points increased upon condensation up to 1%. Assuming a cylindrical model, the cross-sectional diameter was estimated to be approximately 3.8‒4.1 nm using the \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e values and scaled to a similar extent with the crystal size shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb (~\u0026thinsp;0.3 nm). Note that the CNFs with these low solid contents were randomly oriented on average (see Figure S5b for 2D SAXS patterns).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec17\"\u003e\n \u003ch2\u003eNetwork growth\u003c/h2\u003e\n \u003cp\u003eThe dynamic viscoelasticity of the wet samples with low solid contents was measured to investigate the network formation of CNFs in water. Figure 4a shows the frequency dependency of storage modulus, \u003cem\u003eG\u0026rsquo;\u003c/em\u003e, and loss modulus, \u003cem\u003eG\u0026rdquo;\u003c/em\u003e, of the wet samples with solid contents of 0.13\u0026ndash;0.47%. At 0.13%, the \u003cem\u003eG\u0026rsquo;\u003c/em\u003e values were lower than the \u003cem\u003eG\u0026rdquo;\u003c/em\u003e values in the frequency range of 0.1\u0026ndash;0.2 rad s\u003csup\u003e-1\u003c/sup\u003e; the sample was in a sol state and had fluidity. At 0.25%, the \u003cem\u003eG\u0026rsquo;\u003c/em\u003e values were nearly equal to \u003cem\u003eG\u0026rdquo;\u003c/em\u003e in the frequency range of 0.1\u0026ndash;20 rad s\u003csup\u003e-1\u003c/sup\u003e, suggesting the network formation of dispersed CNFs. With a further increase in solid content to ~\u0026thinsp;0.5% or above, the \u003cem\u003eG\u0026rsquo;\u003c/em\u003e values became clearly higher than the \u003cem\u003eG\u0026rdquo;\u003c/em\u003e and were almost constant over the entire frequency range (Fig. 4b). These results show that the wet CNF samples with solid contents of ~\u0026thinsp;0.5% or above behaved as elastic bodies.\u003c/p\u003e\n \u003cp\u003eThe \u003cem\u003eG\u0026rsquo;\u003c/em\u003e values at 1 rad s\u003csup\u003e-1\u003c/sup\u003e in the plateau region were taken as the plateau moduli, \u003cem\u003eG\u0026rsquo;\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e, and were plotted against the solid content in a double logarithmic plot (Fig. 4c). There were two clearly distinguished regions with different slopes in the plot. The following relationship between the \u003cem\u003eG\u0026rsquo;\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e values and solid contents has been proposed for semiflexible fiber networks (Tatsumi et al. \u003cspan class=\"CitationRef\"\u003e2002\u003c/span\u003e; Saito et al. \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e):\u003c/p\u003e\n \u003cdiv class=\"Equation\" id=\"Equ3\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e$${{G}^{{\\prime }}}_{p}=A{c}^{\\alpha }$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003ewhere \u003cem\u003eA\u003c/em\u003e is a constant that reflects individual fiber properties, such as the aspect ratio and elastic modulus, and the power, \u003cem\u003e\u0026alpha;\u003c/em\u003e, is related to the network structure and corresponds to the slope of the double logarithmic plots. The \u003cem\u003e\u0026alpha;\u003c/em\u003e value for the wet CNF samples in this study changed from 3.5 to 1.3 at the threshold of approximately 1%; at this threshold, the contribution of CNFs to the network growth changed as the solid content increased. The threshold value was consistent with the solid content at which the trend in the crystal-size enlargement clearly changed (see Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb), indicating a correlation between the crystal-size enlargement and networked CNF structure in water.\u003c/p\u003e\n \u003cp\u003eFigure 4d shows the correlation lengths, \u003cem\u003eL\u003c/em\u003e, in the polymer networks, or the segment lengths between entanglements, estimated using the \u003cem\u003eG\u0026rsquo;\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e values (Ferry \u003cspan class=\"CitationRef\"\u003e1961\u003c/span\u003e). These \u003cem\u003eL\u003c/em\u003e values correspond to the average distances between the inter-CNF contact points in this study and were estimated by the following formula:\u003c/p\u003e\n \u003cdiv class=\"Equation\" id=\"Equ4\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e$$L=\\rho RT/{G{\\prime }}_{p}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003ewhere \u003cem\u003e\u0026rho;\u003c/em\u003e, \u003cem\u003eR\u003c/em\u003e, and \u003cem\u003eT\u003c/em\u003e are the density or CNF weight per volume of the wet sample, gas constant, and temperature, respectively. The \u003cem\u003eL\u003c/em\u003e value drastically decreased with increasing solid content up to 1% but became almost constant at a threshold of approximately 1%.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec18\"\u003e\n \u003ch2\u003eMechanism\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e illustrates our interpretation of the mechanism of network formation or growth by CNF assembly. Taking into account the results shown in Figs. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e and 4, we assumed the following mechanism (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea): 1) the inter-CNF contact points significantly increase until reaching a solid content of 1%, at which point the basic skeleton of the CNF network in a wet sample is set, and 2) at a solid content higher than 1%, the inter-CNF contact areas gradually expand in a zip-up manner with the solid content. This mechanism corresponds to the two-step enlargement of the crystal size shown in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb.\u003c/p\u003e\n \u003cp\u003eAnother mechanism of CNF assembly, shown in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb, was assumed to explain the preferential recovery of the crystal size at low solid contents in comparison with the CI (see Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ee). In this assumption, we used an 18-chain model with molecular sheet stacking of 2/3/4/4/3/2 as a single CNF. At low solid contents up to 1%, the CNFs are assumed to preferentially assemble by hydrophobic interactions, where the (2 0 0) surfaces of the CNFs are stacked on top of each other. This CNF assembly explains the crystal size enlargement or \u0026ldquo;crystallite fusion\u0026rdquo; observed at low solid contents. At higher than 1%, we assumed that gradual assembly between the hydrophilic surfaces is induced by condensation, exceeding the repulsive force of electric double layers. This latter step of assembly explains the gradual increases in the CI as well as the crystal size. Note that some of the hydroxy groups on the hydrophilic (1 1 0) and (1 \u0026minus;\u0026thinsp;1 0) surfaces were oxidized to carboxy groups in this study. See also our previous report for the current interpretation of the CI recovery of such partially surface-oxidized CNFs (Daicho et al. \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe recovery of the crystallinity of CNFs transitioning from a dilute dispersion to a dense aggregate by condensation was monitored in this study. The condensed CNF samples were subjected to supercritical drying, followed by WAXD and NMR analyses. In the WAXD analysis, a two-step enlargement in the (2 0 0) crystal size was observed; the first step was a rapid increase in the solid content range of 0\u0026ndash;1%, followed by a gradual increase in the range of 1\u0026ndash;85%. The CI value estimated by the NMR analysis hardly changed in the range of 0.5\u0026ndash;30% but gradually increased in the range of 30\u0026ndash;85%. The wet CNF samples were also subjected to SAXS and viscoelasticity analyses without supercritical drying. These analyses of wet samples indicated that the inter-CNF contact points significantly increased until reaching a solid content of 1%, and then at solid contents higher than 1%, the contact areas of each point gradually expanded. Taking into account the preferential recovery of crystal size at low solid contents, we further assumed a mechanism of crystallite fusion; at low solid contents, the hydrophobic (2 0 0) surfaces of CNFs are preferentially stacked on top of each other, followed by gradual assembly between not only the hydrophobic (2 0 0) but also the hydrophilic (1 1 0)/(1 \u0026minus;\u0026thinsp;1 0) surfaces at high solid contents. The findings in this study will contribute to diverse material designs involving CNF assembly.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflict of interest.\u003c/strong\u003e The authors declare no competing financial interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval.\u003c/strong\u003e This article does not contain any studies with human participants or animals performed by any of the authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding.\u0026nbsp;\u003c/strong\u003eThis research was partially supported by the\u0026nbsp;JST CREST program (JPMJCR22L3), JST-Mirai R\u0026amp;D Program (JPMJMI17ED), and\u0026nbsp;JSPS Grant-in-Aids for Scientific Research (20K15567;\u0026nbsp;20K15348; 21H04733; 22J01001;\u0026nbsp;22H03786; 22K19885).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions.\u0026nbsp;\u003c/strong\u003eT.S. conceived the concept of the study. K.D. and T.S. designed the samples, XRD and NMR experiments. N.I. and S.F. designed the SAXS experiments. R.T. and T.S. designed the rheological experiments. Y.D. and K.D. performed all experiments with help from N.I., R.T., and S.K. All authors analyzed the data. Y.D. and K.D. wrote the first version of the manuscript, and T.S. revised the manuscript with contributions from all the authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments.\u0026nbsp;\u003c/strong\u003eThe synchrotron radiation experiments were performed at SPring-8 (Proposal Nos. 2021A1240) at BL40B2. We thank Prof. Tomoya Imai at Kyoto University for his help in the synchrotron radiation experiments at SPring-8.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eDaicho K, Fujisawa S, Kobayashi K et al (2020) Cross-polarization dynamics and conformational study of variously sized cellulose crystallites using solid-state \u003csup\u003e13\u003c/sup\u003eC NMR. J Wood Sci 66:62. https://doi.org/10.1186/s10086-020-01909-9\u003c/li\u003e\n\u003cli\u003eDaicho K, Kobayashi K, Fujisawa S, Saito T (2021) Recovery of the irreversible crystallinity of nanocellulose by crystallite fusion: a strategy for achieving efficient energy transfers in sustainable biopolymer skeletons. Angew Chemie Int Ed 60:24630\u0026ndash;24636. https://doi.org/10.1002/anie.202110032\u003c/li\u003e\n\u003cli\u003eDaicho K, Saito T, Fujisawa S, Isogai A (2018) The crystallinity of nanocellulose: dispersion-induced disordering of the grain boundary in biologically structured cellulose. ACS Appl Nano Mater 1:5774\u0026ndash;5785. https://doi.org/10.1021/acsanm.8b01438\u003c/li\u003e\n\u003cli\u003eFerry JD (1961) Viscoelastic properties of polymers. Wiley, Yew York\u003c/li\u003e\n\u003cli\u003eFrench AD, Santiago Cintr\u0026oacute;n M (2013) Cellulose polymorphy, crystallite size, and the Segal Crystallinity Index. Cellulose 20:583\u0026ndash;588. https://doi.org/10.1007/s10570-012-9833-y\u003c/li\u003e\n\u003cli\u003eFukuzumi H, Saito T, Iwata T et al (2009) Transparent and high gas barrier films of cellulose nanofibers prepared by TEMPO-mediated oxidation. Biomacromolecules 10:162\u0026ndash;165. https://doi.org/10.1021/bm801065u\u003c/li\u003e\n\u003cli\u003eGlatter O, Kratky O, Kratky HC (1982) Small angle X-ray scattering. Academic press, London\u003c/li\u003e\n\u003cli\u003eHeise K, Koso T, King AWT et al (2022) Spatioselective surface chemistry for the production of functional and chemically anisotropic nanocellulose colloids. J Mater Chem A 10:23413\u0026ndash;23432. https://doi.org/10.1039/d2ta05277f\u003c/li\u003e\n\u003cli\u003eHuang S, Makarem M, Kiemle SN et al (2018) Dehydration-induced physical strains of cellulose microfibrils in plant cell walls. Carbohydr Polym 197:337\u0026ndash;348. https://doi.org/10.1016/j.carbpol.2018.05.091\u003c/li\u003e\n\u003cli\u003eIshioka S, Isobe N, Hirano T et al (2023) Fully wood-based transparent plates with high strength , flame self-extinction , and anisotropic thermal conduction. 11:2440\u0026ndash;2448. https://doi.org/10.1021/acssuschemeng.2c06344\u003c/li\u003e\n\u003cli\u003eIwamoto S, Nakagaito AN, Yano H (2007) Nano-fibrillation of pulp fibers for the processing of transparent nanocomposites. Appl Phys A Mater Sci Process 89:461\u0026ndash;466. https://doi.org/10.1007/s00339-007-4175-6\u003c/li\u003e\n\u003cli\u003eKobayashi Y, Saito T, Isogai A (2014) Aerogels with 3D ordered nanofiber skeletons of liquid-crystalline nanocellulose derivatives as tough and transparent insulators. Angew Chem Int Ed 53:10394\u0026ndash;10397. https://doi.org/10.1002/anie.201405123\u003c/li\u003e\n\u003cli\u003eNewman RH (2004) Carbon-13 NMR evidence for cocrystallization of cellulose as a mechanism for hornification of bleached kraft pulp. Cellulose 11:45\u0026ndash;52. https://doi.org/10.1023/B:CELL.0000014768.28924.0c\u003c/li\u003e\n\u003cli\u003eNewman RH, Hill SJ, Harris PJ (2013) Wide-angle X-ray scattering and solid-state nuclear magnetic resonance data combined to test models for cellulose microfibrils in mung bean cell walls. Plant Physiol 163:1558\u0026ndash;1567. https://doi.org/10.1104/pp.113.228262\u003c/li\u003e\n\u003cli\u003eNishiyama Y (2009) Structure and properties of the cellulose microfibril. J Wood Sci 55:241\u0026ndash;249. https://doi.org/10.1007/s10086-009-1029-1\u003c/li\u003e\n\u003cli\u003eSaito T, Nishiyama Y, Putaux JL et al (2006) Homogeneous Suspensions of individualized microfibrils from TEMPO-catalyzed oxidation of native cellulose. Biomacromolecules 7:1687\u0026ndash;1691. https://doi.org/10.1021/bm060154s\u003c/li\u003e\n\u003cli\u003eSaito T, Uematsu T, Kimura S et al (2011) Self-aligned integration of native cellulose nanofibrils towards producing diverse bulk materials. Soft Matter 7:8804\u0026ndash;8809. https://doi.org/10.1039/c1sm06050c\u003c/li\u003e\n\u003cli\u003eSolhi L, Guccini V, Heise K et al (2023) Understanding Nanocellulose-Water Interactions: Turning a Detriment into an Asset. Chem Rev 123:1925\u0026ndash;2015. https://doi.org/10.1021/acs.chemrev.2c00611\u003c/li\u003e\n\u003cli\u003eStephens PW, Kaduk JA, Blanton TN et al (2012) Structure determination of the silver carboxylate dimer [Ag(O\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e20\u003c/sub\u003eH\u003csub\u003e39\u003c/sub\u003e)]\u003csub\u003e2\u003c/sub\u003e, silver arachidate, using powder X-ray diffraction methods. Powder Diffr 27:99\u0026ndash;103. https://doi.org/10.1017/S0885715612000309\u003c/li\u003e\n\u003cli\u003eTatsumi D, Ishioka S, Matsumoto T (2002) Effect of fiber concentration and axial ratio on the rheological properties of cellulose fiber suspensions. Nihon Reoroji Gakkaishi 30:27\u0026ndash;32. https://doi.org/10.1678/rheology.30.27\u003c/li\u003e\n\u003cli\u003eUetani K, Okada T, Oyama HT (2015) Crystallite size effect on thermal conductive properties of nonwoven nanocellulose sheets. Biomacromolecules 16:2220\u0026ndash;2227. https://doi.org/10.1021/acs.biomac.5b00617\u003c/li\u003e\n\u003cli\u003eWada M, Okano T, Sugiyama J (1997) Synchrotron-radiated X-ray and neutron diffraction study of native cellulose. Cellulose 4:221\u0026ndash;232. https://doi.org/10.1023/A:1018435806488\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"cellulose","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cels","sideBox":"Learn more about [Cellulose](https://www.springer.com/journal/10570)","snPcode":"10570","submissionUrl":"https://submission.nature.com/new-submission/10570/3","title":"Cellulose","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"cellulose nanofibers, crystallinity, crystallite fusion, condensation, aerogels","lastPublishedDoi":"10.21203/rs.3.rs-2713577/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2713577/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe crystallinity of cellulose decreases when bundled microfibrils are dispersed in water as cellulose nanofibers (CNFs) or physically separated into finer nanoscale fibrils or single microfibrils. The crystallinity of these CNFs is recovered when they become densely assembled through the dehydration of the dispersion. In this process, multiple CNFs are assumed to partially fuse, leading to the enlargement of crystallite widths. The mechanism of this CNF fusion is, however, not well understood. In this study, the recovery process of the crystallinity of CNFs was monitored by sampling wet CNF gels during condensation from a dilute dispersion to a dense aggregate, followed by wide-angle X-ray diffractometry (WAXD) and solid-state \u003csup\u003e13\u003c/sup\u003eC nuclear magnetic resonance (NMR) spectroscopy analyses after supercritical drying. In the WAXD analysis, a two-step enlargement in the (2 0 0) crystal size was observed: the first step was a rapid increase in the range of solid content up to 1%, followed by a gradual increase in the range of 1–85%. The crystallinity index estimated by NMR hardly changed in the range of 0.5–30% but gradually increased in the range of 30–85%. A portion of the CNF samples, without drying, were also subjected to small-angle X-ray scattering and viscoelasticity analyses, indicating that the inter-CNF contact points in water significantly increased until reaching a solid content of 1%, and then at solid contents higher than 1%, the contact areas of each point gradually expanded. Finally, a mechanism of CNF fusion was proposed based on these results.\u003c/p\u003e","manuscriptTitle":"Monitoring crystallite fusion of nanocellulose during colloid condensation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-04-04 22:32:40","doi":"10.21203/rs.3.rs-2713577/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revision","date":"2023-04-27T09:17:49+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2023-04-11T14:45:38+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"d5d85569-70ba-4418-98a8-bc6f44a0a85b","date":"2023-03-27T11:29:45+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2023-03-27T11:22:55+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-03-24T13:32:13+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2023-03-24T07:53:59+00:00","index":"","fulltext":""},{"type":"submitted","content":"Cellulose","date":"2023-03-23T01:33:40+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"cellulose","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cels","sideBox":"Learn more about [Cellulose](https://www.springer.com/journal/10570)","snPcode":"10570","submissionUrl":"https://submission.nature.com/new-submission/10570/3","title":"Cellulose","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"87a99888-4d6e-40ae-9d30-cfa6e69e60f7","owner":[],"postedDate":"April 4th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-10-16T21:41:12+00:00","versionOfRecord":{"articleIdentity":"rs-2713577","link":"https://doi.org/10.1007/s10570-023-05354-x","journal":{"identity":"cellulose","isVorOnly":false,"title":"Cellulose"},"publishedOn":"2023-07-06 21:29:56","publishedOnDateReadable":"July 6th, 2023"},"versionCreatedAt":"2023-04-04 22:32:40","video":"","vorDoi":"10.1007/s10570-023-05354-x","vorDoiUrl":"https://doi.org/10.1007/s10570-023-05354-x","workflowStages":[]},"version":"v1","identity":"rs-2713577","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2713577","identity":"rs-2713577","version":["v1"]},"buildId":"FbvkV6FR0MCFSLy54lSbu","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}