Modification of Nitrocellulose Crystal Structure by an Azide Plasticizer: X-ray Diffraction Study

Modification of Nitrocellulose Crystal Structure by an Azide Plasticizer: X-ray Diffraction Study | 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 Modification of Nitrocellulose Crystal Structure by an Azide Plasticizer: X-ray Diffraction Study Vladimir Lomadurov This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8153658/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract The influence of an azide plasticizer on the supramolecular structure of nitrocellulose with different nitrogen content was investigated by Wide-angle X-ray diffraction (WAXD). The penetration of cyclic molecules of a low-molecular-weight plasticizer with increased rigidity into the ordered regions of nitrocellulose has been experimentally established, and this penetration of plasticizer molecules is observed even at low concentrations. It is shown that the nature of interaction is the same for nitrocelluloses with nitrogen content of 12.0-12.1% and 13.0%. Nitrocellulose Azide plasticizer X-ray diffractogram deconvolution Supramolecular structure Interstitial solid solution WAXD Figures Figure 1 Figure 2 Introduction Nitrocellulose (NC, cellulose nitrate) is one of the oldest and most important cellulose derivatives with almost 200 years of research history (Morris et al., 2023 ). Despite its wide industrial applications—from use as an energetic material to membranes in medical test systems—knowledge about its crystalline structure has remained extremely limited, based on data from X-ray diffraction analysis (WAXD) of fibers obtained first half of the 20th century (Herzog, 1926 ; Herzog and Naray-Szabo, 1927 ; Miles and Craik, 1930 ). As with many semi-crystalline polymers, the structure of NC is described within the framework of a two-phase model, assuming the coexistence of regions with ordered arrangement of polymer chains (crystalline domains) and regions with disordered arrangement (amorphous phase). The ratio of these phases is characterized by the degree of crystallinity, which is a key parameter that directly affects the mechanical, thermal, and functional properties of the material (Sturcova et al., 2005 ). The promising performance characteristics of composite materials based on nitrocellulose modified with azide plasticizers determine the growing interest in such systems (Badgujar et al., 2017). However, effective design of these materials requires a deep understanding of the interaction mechanism at the molecular level. A key challenge is the increased rigidity of cyclic molecules of azide plasticizers, which creates significant steric and energy barriers for their introduction into the supramolecular structure of the polymer (Tretyakova et al., 2007 ). Thus, it can be expected that the process of NC plasticization with an azide plasticizer will be associated with significant difficulties related to the penetration of the bulky and rigid plasticizer molecule between the chains of the NC macromolecule. At the same time, the interpretation of the structure modification process itself is complicated by historically established views. On the one hand, NC has long been considered as a largely amorphous or very weakly crystalline polymer (Morris et al., 2023 ), and its few diffraction reflections have often been interpreted without considering their complex nature (Wu et al., 2022 ). On the other hand, the accepted paradigm of plasticization (Ferry, 1980 ; Utracki, 1989 ) of semi-crystalline polymers assumed the penetration of low-molecular-weight plasticizer molecules only into amorphous regions. The complexity of the NC diffraction pattern requires special attention when interpreting data. As shown by Morris et al. ( 2025a ), three strong NC interference lines d ≈ (3.6, 4.1, and 4.4 Å) are superimposed on the broad NC amorphous halo, which significantly complicates the traditional analysis of NC diffractograms. It should be taken into account that changes in the intensity of these NC reflections can lead to an artifact - an apparent shift in the position of the amorphous halo maximum. Accounting for this effect is important for the correct interpretation of NC plasticization data. Thus, the aim of this work is to study the features of modification of the supramolecular structure of nitrocellulose with an azide plasticizer according to X-ray diffraction analysis, taking into account the indicated methodological difficulties. Experimental Section 2.1. Materials and Sample Preparation For the preparation of modified NC samples, NC with a mass fraction of nitrogen of 12.0-12.1% and 13.0% (N = 12.0-12.1% and N = 13.0%, respectively) were used. NC samples modified with an azide plasticizer (AP, 2,4-diazido-6-azidoethoxy symmetric triazine, Tretyakova et al., 2007 ) were prepared according to the method described in the monograph (Fioshina et al., 2004). Plasticization of nitrocellulose with the azide plasticizer was carried out in an aqueous medium. The initial components were mixed in specially prepared water at a module of 1:7 (ratio of the total mass of NC and plasticizer to the mass of water). The process was carried out at an initial temperature of 20°C with subsequent heating to 50°C and continuous stirring for 2 hours. After modification, the NC samples were dried to constant mass. 2.2. Methodology of Wide-Angle X-ray Diffraction Study X-ray diffraction studies of NC modified with azide plasticizer were carried out on DRON series X-ray diffractometers in reflection mode using Cu Kα radiation (λ = 1.5418 Å), monochromatized by a nickel filter, in a scanning mode in the diffraction angle range 2θ from 5° to 55°. The angular range 2θ was divided into two intervals with different scanning steps: in the scattering angle interval 2θ from 5° to 26°, the detector scanning step was Δ2θ = 0.2°, which is necessary for accurate determination of the amorphous halo parameters and strong NC reflections; in the angle interval 2θ from 26° to 55°, the detector scanning step was Δ2θ = 0.4°. To ensure high data accuracy, especially in the 2θ scattering angle interval from 11° to 30°, where intense NC reflections are located, the conditions of the X-ray experiment were chosen so that the relative error δ of intensity measurement, defined as δ = 1/√N (where N is the number of registered pulses) (Gine, 1961 ), did not exceed 0.01. This required accumulation of at least 10,000 pulses at each measurement point, which ensured reliable separation of strong NC reflections during diffractogram deconvolution. The detection intensity reached ~ 20,000 pulses, which provided a high signal-to-noise ratio. Such high accuracy of intensity measurement allowed us to minimize methodological artifacts associated with the overlap of peaks and the amorphous halo. This ensured the reliability of fixing even slight shifts in the position of the Bragg reflections, which is critical for the correct interpretation of structural changes. The Bragg-Brentano focusing scheme was implemented on DRON series X-ray diffractometers. According to classical works (Gine, 1961 ), in this geometry, to exclude the angular dependence of the absorption factor, the sample surface must be strictly flat. In this case, the absorption factor becomes independent of the angle θ. The flat sample surface necessary for X-ray studies in reflection mode was achieved by pressing the studied samples into tablet. The pressing pressure was 1.8 MPa. Similar conditions (diffractogram recording scheme in reflection mode, use of non-textured powder samples pressed into tablets are used in the determination of structural characteristics of cellulose by wide-angle X-ray diffractometry (Ioelovich, 2014 ). 2.3. Processing and Interpretation of X-ray Patterns For the analysis of the NC diffractogram, deconvolution into its constituent interference lines and amorphous halo is currently carried out with determination of their position, half-width and maximum intensity values (Herrmann et al., 2011 , 2012 ). Deconvolution of the modified NC diffractogram into individual interference lines with determination of their parameters was carried out using computer programs. The task of separating NC interference lines was reduced to approximating the experimental diffractogram Iobs(2θ) with a calculated curve Icalc(2θ), in which the amorphous halo and each interference line of the modified NC had the form of a pseudo-Voigt function. The methodology for approximating the experimental NC diffractogram Iobs(2θ) is described in the work (Lomadurov et al., 2021 ). Figure 1 Deconvolution of nitrocellulose (N = 12.0-12.1%) diffractogram into individual interference lines and amorphous halo: solid line - total intensity; dashed line - amorphous halo; four strong reflections are marked with interplanar spacing values. The interplanar spacing values of the four strongest interference lines isolated from the NC diffractogram are presented in the Table. As can be seen from the Table, these data are in good agreement (deviation less than 1.2%) with the values obtained from the X-ray diffraction analysis of specially prepared NC fibers (N = 13.0% and N = 13.9%). Table. Interplanar spacings of the strongest interference lines of NC Sample Mass fraction of nitrogen in NC, % Interplanar spacings, Å 1 12.0–12.1 6.81 4.62 4.11 3.58 2 13.0 7.08 4.57 3.97 3.51 3* 13.0 7.09 4.52 4.01 3.54 4** 13.9 7.10 4.40 4.04 3.66 Note: * - data from Meader et al. ( 1978 ); ** - data from Morris et al. ( 2025a ). Results and Discussion Evaluation of the structural characteristics of the initial NC using the approach applied by Morris et al. ( 2025b ) based on the Segal method showed that the NC sample (N = 12.0-12.1%) is characterized by a significant proportion of the amorphous phase (~ 70%), the proportion of coherent scattering regions (CSRs) of NC is ~ 30%. It should be noted that this approach is one of the numerous methods for determining the degree of crystallinity of NC (Ioelovich, 2014 ) and represents the measurement of the relative intensity of a separate reflection relative to the intensity of the amorphous phase and is not a direct measurement of the percentage content of the crystalline phase (Morris et al., 2025b ). Despite the dominance of the amorphous phase, the presence of ordered regions makes it possible to use X-ray diffraction methods to monitor deep changes in the supramolecular structure. The change in the position of reflections from NC coherent scattering regions can serve as a sensitive indicator of processes occurring in the binary NC-plasticizer system. The authors proceeded from the assumption that nitrocellulose, being a derivative of cellulose and a product of its chemical modification, inherits the property of selective accessibility, according to which amorphous regions are "weak and accessible places", while crystallites are "strong and inaccessible structural elements" (Ioelovich, 2016 ). At the same time, literature data indicate that NC is capable of forming molecular complexes with plasticizers, which is associated with the penetration of their molecules into the NC crystalline domains and subsequent rearrangement of its crystal lattice (Trogus et al., 1932 ; Sviridov et al., 1984 ). Based on the analysis of these literature data, a working hypothesis was formulated describing the expected mechanism of plasticization as a sequence of three stages: (1) Amorphous phase filling: Plasticizer molecules initially interact with easily accessible amorphous regions. Since penetration into crystalline domains does not occur, the interplanar spacing d 110 remains unchanged. (2) Onset of penetration into crystalline domains: After reaching a certain concentration in the amorphous phase, the plasticizer overcomes the energy barrier and begins to penetrate into the crystalline domains, which should manifest itself in a systematic increase in d 110 . (3) Saturation of crystalline domains: Due to the high packing density of the crystalline domains, the penetration process into the crystalline domains should quickly reach a limit, which will lead to the parameter d 110 reaching a constant value (plateau) (Fig. 2). It is important to emphasize that the cyclic molecules of the azide plasticizer (AP) used in the work are characterized by increased rigidity (Tretyakova et al., 2007 ), which creates significant steric hindrances for their introduction into the densely packed structure of the polymer crystalline domains. Thus, for the NC-AP system, there were all prerequisites to expect either predominant accumulation of azide plasticizer AP in amorphous regions, or plasticizer molecules penetrate only into the interstructural spaces of NC macroformations (Tager, 2012). It is critically important that none of these scenarios assumes changes in the crystal lattice parameters of NC crystalline domains. Consequently, within the framework of existing concepts, the value of d 110 should remain constant throughout the entire studied range of AP plasticizer concentrations. 3.1. Influence of Azide Plasticizer on NC Coherent Scattering Regions The behavior of the intense separate interference line of NC, corresponding to the interplanar spacing d 110 ≈ 7 Å, turned out to be key for understanding the interaction in the NC-AP system. Figure 2 Concentration dependence of the interplanar spacing d 110 in the (110) crystallographic direction in modified NC: ■ --- NC (N = 12.0-12.1%); ○ --- NC (N = 13.0%); dashed lines --- hypothesis. The concentration dependence of the interplanar spacing d 110 in the (110) crystallographic direction for modified cellulose nitrate is shown in Fig. 2. It can be seen from the graph that the introduction of the plasticizer leads to an increase in the value of d 110 , i.e., there is a shift of this interference line towards smaller diffraction angles θ. For the initial NC (N = 12.0-12.1%), the value of the interplanar spacing d 110 is 6.93 Å. When 10% AP is introduced, a reliable shift of the reflection is observed, corresponding to an increase in the interplanar spacing d 110 to 7.2 Å. An important result is the monotonic increase in the value of the interplanar spacing d 110 with increasing AP content, observed for all studied NC samples, which indicates the universality of the phenomenon. Thus, for NC (N = 12.0-12.1%), the value of the interplanar spacing d 110 increases from 6.93 to 7.63 Å, and for NC (N = 13.0%) - from 7.08 to 7.93 Å. At the same time, no limiting saturation of NC crystalline domains with plasticizer molecules is observed, upon the onset of which plasticizer molecules no longer penetrate into NC crystalline domains and the value of the interplanar spacing d 110 does not change further. The substantial monotonic increase in the interplanar spacing d 110 (up to 10%) discovered in the experiment demonstrates a fundamental difference in the modification mechanism in the NC-azide plasticizer system, which finds no explanation within the existing theories of polymer plasticization (Tager, 2012). The obtained data indicate the penetration of plasticizer molecules into the NC crystalline domains, which leads to the rearrangement of the supramolecular structure of the polymer. 3.2. Interpretation of New Experimental Data in the Context of Classical Concepts of Plasticization The obtained experimental data, in particular, the significant increase in the interplanar spacing d 110 , allow us to propose a refined model of interaction in the NC-azide plasticizer system. Interaction with NC ordered regions. The observed increase in the interplanar spacing d 110 is direct X-ray evidence of the penetration of AP molecules into the ordered domains of NC. This result indicates that the interaction is not limited to the amorphous phase of the polymer, as is often assumed in the literature for many polymer-plasticizer systems (Ioelovich, 2016 ). AP molecules in this system act as an active modifier of the supramolecular structure. Distribution of plasticizer within the polymer volume. The change in the interplanar spacing d 110 is observed even at small additions of AP, which indicates that the interaction process is not staged ("first amorphous phase, then crystalline"). This indicates the distribution of the plasticizer throughout the entire volume of the polymer, including the NC ordered regions, from the very beginning of the modification process. Furthermore, throughout the entire studied concentration range (up to 50% AP), no saturation effect is observed, which is characteristic, for example, of doping processes in metal alloys, when further introduction of impurity atoms into the crystal lattice ceases after reaching a certain limit. The monotonic growth of the interplanar spacing d 110 indicates a fundamentally different, thresholdless mechanism of interaction in the NC-AP system. The observed incorporation of plasticizer molecules into the binary system (NC –AP plasticizer) even at a relatively low estimated degree of crystallinity (≈ 30%) can be explained by the unique structural features of cellulose nitrate. According to generally accepted methodology (Ioelovich, 2021 ), the position of the amorphous halo maximum on the X-ray diffractogram allows for the estimation of the average interchain distance in the disordered (amorphous) phase. The position of the amorphous halo maximum of nitrocellulose is 𝑑=5.41Å (Lomadurov et al., 2021 ). At the same time, the parameters of the crystalline phase's unit cell dictate a distance between the axes of the macromolecules of approximately 7.6–7.7 Å (Meader et al., 1978 ). Thus, the estimated distance between the axes of macromolecules in the disordered region of cellulose nitrate appears to be smaller than that in the ordered region. It is suggested that plasticizer molecules may find it difficult to easily penetrate the dense amorphous phase. Instead, they might preferentially incorporate into the less dense interstices of the crystal lattice or at the interphase boundaries, where the local packing density is potentially lower. This observed effect of "early" plasticizer incorporation may therefore be attributed not to the overall degree of crystallinity, but rather to the relative density and availability of free volume within the various structural regions of the polymer. Overcoming steric limitations. Direct X-ray data convincingly demonstrate that AP molecules, contrary to established views about their steric rigidity (Tretyakova et al., 2007 ), are effectively incorporated into the ordered crystalline domains of NC. This fundamental observation refutes the existing limitations and opens up new possibilities for creating composite materials based on plasticizers with rigid molecules. 3.3. Universality of the Interaction Mechanism and Novelty of the Work The establishment of the same nature of the concentration dependence of the interplanar spacing d 110 for NC with different nitrogen content (12.0-12.1% and 13.0%) indicates the universality of the interaction mechanism between NC macromolecules and azide plasticizer (AP) molecules in the studied range of binary system components. It should be especially emphasized that, despite the significant applied interest in azide plasticizers as energetic components (Badgujar et al., 2017; Wu et al., 2022 ; Zou et al., 2021 ), questions of their fundamental interaction with the polymer matrix at the supramolecular level have remained practically unexplored. The vast majority of publications are devoted to the synthesis of new compounds, the evaluation of their thermal stability and the rheological properties of compositions (Wu et al., 2022 ; Zou et al., 2021 ). At the same time, data on the direct influence of azide plasticizers on the structure of NC's ordered regions, in particular, on the parameters of its crystal lattice, are absent in the available literature. Thus, this study provides direct experimental insight into the mechanism of plasticizer action in semicrystalline polymers. It conclusively demonstrates the capability of the Wide-angle X-ray Diffraction (WAXD) technique to detect and quantify structural changes within the crystalline domains of a polymer. These findings challenge the conventional view of plasticizer localization solely in amorphous regions. They open up prospects for the purposeful design of composite materials with specified structural characteristics. Conclusion The conducted X-ray diffraction study of binary nitrocellulose-azide plasticizer (NC-AP) systems allowed us to establish fundamental aspects of the plasticization mechanism that make adjustments to a number of classical concepts. The key evidence of the active role of the azide plasticizer (AP) as a modifier of the supramolecular structure, and not an inert diluent, is the systematic increase in the interplanar spacing (d 110 ≈ 7 Å) in the NC coherent scattering regions with increasing AP concentration. The obtained data allow us to take a fresh look at the established paradigms: First, it is shown that the interaction of the plasticizer is not limited to the amorphous phase; AP penetrates and modifies areas with three-dimensional order. Second, changes in lattice parameters are observed from the smallest additions of AP, which is characteristic of the formation of an interstitial solid solution and excludes the existence of a concentration threshold. Third, it has been experimentally shown that the steric barrier, considered insurmountable for rigid molecules of cyclic structure of the azide plasticizer, is overcome in practice, which indicates the need to revise the thesis about the impossibility of forming stable systems based on them. The universality of the identified mechanism is confirmed by the identical nature of the concentration dependence of d 110 for NC with different nitrogen content (12.0-12.1% --13.0%), which indicates its fundamental nature for the NC-AP system. From a practical point of view, the modification technique in an aqueous environment made it possible to obtain homogeneous monolithic samples of NC-AP compositions (70:30) without pores and cracks, demonstrating the potential of the approach for creating highly filled energetic materials with specified structural characteristics. Thus, this study marks a paradigm shift in the understanding of nitrocellulose plasticization - from the model of passive filling of the free volume of the amorphous region of the polymer to the model of purposeful design of its supramolecular structure. This opens up new ways for creating NC composite materials with programmable characteristics. Declarations Acknowledgments The author is grateful to Dr. Alexander F. Voronkov for the joint work on developing the methodology of nitrocellulose diffractogram decomposition used in this work. The author is also grateful to Dr. V.P. Efremov for the valuable discussion of this work. Funding: Not applicable. The study did not receive external funding. Conflict of interest: The authors declare that they have no conflict of interest. Data availability: Data is available upon request. Author Contribution Vladimir F. 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Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 27 Jan, 2026 Editor assigned by journal 27 Jan, 2026 Submission checks completed at journal 21 Nov, 2025 First submitted to journal 19 Nov, 2025 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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04:10:24","extension":"png","order_by":7,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":100494,"visible":true,"origin":"","legend":"","description":"","filename":"OnlineFigure1.png","url":"https://assets-eu.researchsquare.com/files/rs-8153658/v1/58f5018058a51c1af6e736ca.png"},{"id":100845530,"identity":"d2ac2c82-6b15-4f0d-9ab7-fdaba078c946","added_by":"auto","created_at":"2026-01-22 04:10:24","extension":"png","order_by":8,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":34096,"visible":true,"origin":"","legend":"","description":"","filename":"OnlineFigure2.png","url":"https://assets-eu.researchsquare.com/files/rs-8153658/v1/3897a89dc0d61ed728f56f30.png"},{"id":100845522,"identity":"9572b4fd-3545-4d26-95b4-3ec2e6980b79","added_by":"auto","created_at":"2026-01-22 04:10:24","extension":"xml","order_by":9,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":59521,"visible":true,"origin":"","legend":"","description":"","filename":"cbba30b710824d1a9ebca442d55e7b8c1structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8153658/v1/b5d229b8dbdd624082f712bb.xml"},{"id":100845527,"identity":"c8d8c307-ac04-4f4c-8f25-8cd668365f99","added_by":"auto","created_at":"2026-01-22 04:10:24","extension":"html","order_by":10,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":64310,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8153658/v1/fde38e201eed42f1120a7350.html"},{"id":100845520,"identity":"c03200f0-4bb2-41e3-83b6-ee7d7fd021e3","added_by":"auto","created_at":"2026-01-22 04:10:23","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":70566,"visible":true,"origin":"","legend":"\u003cp\u003eDeconvolution of nitrocellulose (N=12.0-12.1%) diffractogram into individual interference lines and amorphous halo: solid line - total intensity; dashed line - amorphous halo; four strong reflections are marked with interplanar spacing values.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-8153658/v1/229c94e421d5eaec3f241a39.png"},{"id":100845532,"identity":"c23233d4-850b-43cc-9eec-1d0d67c66392","added_by":"auto","created_at":"2026-01-22 04:10:25","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":70585,"visible":true,"origin":"","legend":"\u003cp\u003eConcentration dependence of the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e in the (110) crystallographic direction in modified NC: ■ --- NC (N=12.0-12.1%); ○ --- NC (N=13.0%); dashed lines --- hypothesis.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-8153658/v1/6afd7a3a5e8dfb353bbb8425.png"},{"id":100858990,"identity":"b4959436-8eee-4a0e-b278-cc78a83e6e38","added_by":"auto","created_at":"2026-01-22 07:25:04","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":753216,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8153658/v1/654e6d21-944c-44de-b25c-a62dee14fb6e.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Modification of Nitrocellulose Crystal Structure by an Azide Plasticizer: X-ray Diffraction Study","fulltext":[{"header":"Introduction","content":"\u003cp\u003eNitrocellulose (NC, cellulose nitrate) is one of the oldest and most important cellulose derivatives with almost 200 years of research history (Morris et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Despite its wide industrial applications\u0026mdash;from use as an energetic material to membranes in medical test systems\u0026mdash;knowledge about its crystalline structure has remained extremely limited, based on data from X-ray diffraction analysis (WAXD) of fibers obtained first half of the 20th century\u003c/p\u003e \u003cp\u003e(Herzog, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1926\u003c/span\u003e; Herzog and Naray-Szabo, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1927\u003c/span\u003e; Miles and Craik, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1930\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAs with many semi-crystalline polymers, the structure of NC is described within the framework of a two-phase model, assuming the coexistence of regions with ordered arrangement of polymer chains (crystalline domains) and regions with disordered arrangement (amorphous phase). The ratio of these phases is characterized by the degree of crystallinity, which is a key parameter that directly affects the mechanical, thermal, and functional properties of the material (Sturcova et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe promising performance characteristics of composite materials based on nitrocellulose modified with azide plasticizers determine the growing interest in such systems (Badgujar et al., 2017). However, effective design of these materials requires a deep understanding of the interaction mechanism at the molecular level. A key challenge is the increased rigidity of cyclic molecules of azide plasticizers, which creates significant steric and energy barriers for their introduction into the supramolecular structure of the polymer (Tretyakova et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Thus, it can be expected that the process of NC plasticization with an azide plasticizer will be associated with significant difficulties related to the penetration of the bulky and rigid plasticizer molecule between the chains of the NC macromolecule.\u003c/p\u003e \u003cp\u003eAt the same time, the interpretation of the structure modification process itself is complicated by historically established views. On the one hand, NC has long been considered as a largely amorphous or very weakly crystalline polymer (Morris et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), and its few diffraction reflections have often been interpreted without considering their complex nature (Wu et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). On the other hand, the accepted paradigm of plasticization (Ferry, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1980\u003c/span\u003e; Utracki, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1989\u003c/span\u003e) of semi-crystalline polymers assumed the penetration of low-molecular-weight plasticizer molecules only into amorphous regions.\u003c/p\u003e \u003cp\u003eThe complexity of the NC diffraction pattern requires special attention when interpreting data. As shown by Morris et al. (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2025a\u003c/span\u003e), three strong NC interference lines d \u0026asymp; (3.6, 4.1, and 4.4 \u0026Aring;) are superimposed on the broad NC amorphous halo, which significantly complicates the traditional analysis of NC diffractograms. It should be taken into account that changes in the intensity of these NC reflections can lead to an artifact - an apparent shift in the position of the amorphous halo maximum. Accounting for this effect is important for the correct interpretation of NC plasticization data.\u003c/p\u003e \u003cp\u003eThus, the aim of this work is to study the features of modification of the supramolecular structure of nitrocellulose with an azide plasticizer according to X-ray diffraction analysis, taking into account the indicated methodological difficulties.\u003c/p\u003e"},{"header":"Experimental Section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Materials and Sample Preparation\u003c/h2\u003e \u003cp\u003eFor the preparation of modified NC samples, NC with a mass fraction of nitrogen of 12.0-12.1% and 13.0% (N\u0026thinsp;=\u0026thinsp;12.0-12.1% and N\u0026thinsp;=\u0026thinsp;13.0%, respectively) were used. NC samples modified with an azide plasticizer (AP, 2,4-diazido-6-azidoethoxy symmetric triazine, Tretyakova et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) were prepared according to the method described in the monograph (Fioshina et al., 2004). Plasticization of nitrocellulose with the azide plasticizer was carried out in an aqueous medium. The initial components were mixed in specially prepared water at a module of 1:7 (ratio of the total mass of NC and plasticizer to the mass of water). The process was carried out at an initial temperature of 20\u0026deg;C with subsequent heating to 50\u0026deg;C and continuous stirring for 2 hours. After modification, the NC samples were dried to constant mass.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Methodology of Wide-Angle X-ray Diffraction Study\u003c/h2\u003e \u003cp\u003eX-ray diffraction studies of NC modified with azide plasticizer were carried out on DRON series X-ray diffractometers in reflection mode using Cu Kα radiation (λ\u0026thinsp;=\u0026thinsp;1.5418 \u0026Aring;), monochromatized by a nickel filter, in a scanning mode in the diffraction angle range 2θ from 5\u0026deg; to 55\u0026deg;.\u003c/p\u003e \u003cp\u003eThe angular range 2θ was divided into two intervals with different scanning steps: in the scattering angle interval 2θ from 5\u0026deg; to 26\u0026deg;, the detector scanning step was Δ2θ\u0026thinsp;=\u0026thinsp;0.2\u0026deg;, which is necessary for accurate determination of the amorphous halo parameters and strong NC reflections; in the angle interval 2θ from 26\u0026deg; to 55\u0026deg;, the detector scanning step was Δ2θ\u0026thinsp;=\u0026thinsp;0.4\u0026deg;.\u003c/p\u003e \u003cp\u003eTo ensure high data accuracy, especially in the 2θ scattering angle interval from 11\u0026deg; to 30\u0026deg;, where intense NC reflections are located, the conditions of the X-ray experiment were chosen so that the relative error δ of intensity measurement, defined as δ\u0026thinsp;=\u0026thinsp;1/\u0026radic;N (where N is the number of registered pulses) (Gine, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1961\u003c/span\u003e), did not exceed 0.01. This required accumulation of at least 10,000 pulses at each measurement point, which ensured reliable separation of strong NC reflections during diffractogram deconvolution. The detection intensity reached\u0026thinsp;~\u0026thinsp;20,000 pulses, which provided a high signal-to-noise ratio.\u003c/p\u003e \u003cp\u003eSuch high accuracy of intensity measurement allowed us to minimize methodological artifacts associated with the overlap of peaks and the amorphous halo. This ensured the reliability of fixing even slight shifts in the position of the Bragg reflections, which is critical for the correct interpretation of structural changes.\u003c/p\u003e \u003cp\u003eThe Bragg-Brentano focusing scheme was implemented on DRON series X-ray diffractometers. According to classical works (Gine, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1961\u003c/span\u003e), in this geometry, to exclude the angular dependence of the absorption factor, the sample surface must be strictly flat. In this case, the absorption factor becomes independent of the angle θ. The flat sample surface necessary for X-ray studies in reflection mode was achieved by pressing the studied samples into tablet. The pressing pressure was 1.8 MPa. Similar conditions (diffractogram recording scheme in reflection mode, use of non-textured powder samples pressed into tablets are used in the determination of structural characteristics of cellulose by wide-angle X-ray diffractometry (Ioelovich, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Processing and Interpretation of X-ray Patterns\u003c/h2\u003e \u003cp\u003eFor the analysis of the NC diffractogram, deconvolution into its constituent interference lines and amorphous halo is currently carried out with determination of their position, half-width and maximum intensity values (Herrmann et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDeconvolution of the modified NC diffractogram into individual interference lines with determination of their parameters was carried out using computer programs. The task of separating NC interference lines was reduced to approximating the experimental diffractogram Iobs(2θ) with a calculated curve Icalc(2θ), in which the amorphous halo and each interference line of the modified NC had the form of a pseudo-Voigt function. The methodology for approximating the experimental NC diffractogram Iobs(2θ) is described in the work (Lomadurov et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFigure 1 Deconvolution of nitrocellulose (N\u0026thinsp;=\u0026thinsp;12.0-12.1%) diffractogram into individual interference lines and amorphous halo: solid line - total intensity; dashed line - amorphous halo; four strong reflections are marked with interplanar spacing values.\u003c/p\u003e \u003cp\u003eThe interplanar spacing values of the four strongest interference lines isolated from the NC diffractogram are presented in the Table. As can be seen from the Table, these data are in good agreement (deviation less than 1.2%) with the values obtained from the X-ray diffraction analysis of specially prepared NC fibers (N\u0026thinsp;=\u0026thinsp;13.0% and N\u0026thinsp;=\u0026thinsp;13.9%).\u003c/p\u003e \u003cp\u003eTable. Interplanar spacings of the strongest interference lines of NC\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMass fraction of nitrogen in NC, %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eInterplanar spacings, \u0026Aring;\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e12.0\u0026ndash;12.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.81\u0026emsp;4.62\u0026emsp;4.11\u0026emsp;3.58\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e13.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7.08\u0026emsp;4.57\u0026emsp;3.97\u0026emsp;3.51\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e13.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7.09\u0026emsp;4.52\u0026emsp;4.01\u0026emsp;3.54\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e13.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7.10\u0026emsp;4.40\u0026emsp;4.04\u0026emsp;3.66\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"3\"\u003e\u003cem\u003eNote: * - data from\u003c/em\u003e Meader et al. (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1978\u003c/span\u003e); \u003cem\u003e** - data from\u003c/em\u003e Morris et al. (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2025a\u003c/span\u003e).\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003eEvaluation of the structural characteristics of the initial NC using the approach applied by Morris et al. (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2025b\u003c/span\u003e) based on the Segal method showed that the NC sample (N\u0026thinsp;=\u0026thinsp;12.0-12.1%) is characterized by a significant proportion of the amorphous phase (~\u0026thinsp;70%), the proportion of coherent scattering regions (CSRs) of NC is ~\u0026thinsp;30%. It should be noted that this approach is one of the numerous methods for determining the degree of crystallinity of NC (Ioelovich, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) and represents the measurement of the relative intensity of a separate reflection relative to the intensity of the amorphous phase and is not a direct measurement of the percentage content of the crystalline phase (Morris et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2025b\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDespite the dominance of the amorphous phase, the presence of ordered regions makes it possible to use X-ray diffraction methods to monitor deep changes in the supramolecular structure. The change in the position of reflections from NC coherent scattering regions can serve as a sensitive indicator of processes occurring in the binary NC-plasticizer system.\u003c/p\u003e \u003cp\u003eThe authors proceeded from the assumption that nitrocellulose, being a derivative of cellulose and a product of its chemical modification, inherits the property of selective accessibility, according to which amorphous regions are \"weak and accessible places\", while crystallites are \"strong and inaccessible structural elements\" (Ioelovich, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). At the same time, literature data indicate that NC is capable of forming molecular complexes with plasticizers, which is associated with the penetration of their molecules into the NC crystalline domains and subsequent rearrangement of its crystal lattice (Trogus et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1932\u003c/span\u003e; Sviridov et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1984\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBased on the analysis of these literature data, a working hypothesis was formulated describing the expected mechanism of plasticization as a sequence of three stages: (1) Amorphous phase filling: Plasticizer molecules initially interact with easily accessible amorphous regions. Since penetration into crystalline domains does not occur, the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e remains unchanged. (2) Onset of penetration into crystalline domains: After reaching a certain concentration in the amorphous phase, the plasticizer overcomes the energy barrier and begins to penetrate into the crystalline domains, which should manifest itself in a systematic increase in d\u003csub\u003e110\u003c/sub\u003e. (3) Saturation of crystalline domains: Due to the high packing density of the crystalline domains, the penetration process into the crystalline domains should quickly reach a limit, which will lead to the parameter d\u003csub\u003e110\u003c/sub\u003e reaching a constant value (plateau) (Fig.\u0026nbsp;2).\u003c/p\u003e \u003cp\u003eIt is important to emphasize that the cyclic molecules of the azide plasticizer (AP) used in the work are characterized by increased rigidity (Tretyakova et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2007\u003c/span\u003e), which creates significant steric hindrances for their introduction into the densely packed structure of the polymer crystalline domains. Thus, for the NC-AP system, there were all prerequisites to expect either predominant accumulation of azide plasticizer AP in amorphous regions, or plasticizer molecules penetrate only into the interstructural spaces of NC macroformations (Tager, 2012). It is critically important that none of these scenarios assumes changes in the crystal lattice parameters of NC crystalline domains. Consequently, within the framework of existing concepts, the value of d\u003csub\u003e110\u003c/sub\u003e should remain constant throughout the entire studied range of AP plasticizer concentrations.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Influence of Azide Plasticizer on NC Coherent Scattering Regions\u003c/h2\u003e \u003cp\u003eThe behavior of the intense separate interference line of NC, corresponding to the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;7 \u0026Aring;, turned out to be key for understanding the interaction in the NC-AP system.\u003c/p\u003e \u003cp\u003eFigure 2 Concentration dependence of the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e in the (110) crystallographic direction in modified NC: ■ --- NC (N\u0026thinsp;=\u0026thinsp;12.0-12.1%); ○ --- NC (N\u0026thinsp;=\u0026thinsp;13.0%); dashed lines --- hypothesis.\u003c/p\u003e \u003cp\u003eThe concentration dependence of the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e in the (110) crystallographic direction for modified cellulose nitrate is shown in Fig.\u0026nbsp;2. It can be seen from the graph that the introduction of the plasticizer leads to an increase in the value of d\u003csub\u003e110\u003c/sub\u003e, i.e., there is a shift of this interference line towards smaller diffraction angles θ.\u003c/p\u003e \u003cp\u003eFor the initial NC (N\u0026thinsp;=\u0026thinsp;12.0-12.1%), the value of the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e is 6.93 \u0026Aring;. When 10% AP is introduced, a reliable shift of the reflection is observed, corresponding to an increase in the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e to 7.2 \u0026Aring;. An important result is the monotonic increase in the value of the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e with increasing AP content, observed for all studied NC samples, which indicates the universality of the phenomenon. Thus, for NC (N\u0026thinsp;=\u0026thinsp;12.0-12.1%), the value of the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e increases from 6.93 to 7.63 \u0026Aring;, and for NC (N\u0026thinsp;=\u0026thinsp;13.0%) - from 7.08 to 7.93 \u0026Aring;. At the same time, no limiting saturation of NC crystalline domains with plasticizer molecules is observed, upon the onset of which plasticizer molecules no longer penetrate into NC crystalline domains and the value of the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e does not change further.\u003c/p\u003e \u003cp\u003eThe substantial monotonic increase in the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e (up to 10%) discovered in the experiment demonstrates a fundamental difference in the modification mechanism in the NC-azide plasticizer system, which finds no explanation within the existing theories of polymer plasticization (Tager, 2012). The obtained data indicate the penetration of plasticizer molecules into the NC crystalline domains, which leads to the rearrangement of the supramolecular structure of the polymer.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Interpretation of New Experimental Data in the Context of Classical Concepts of Plasticization\u003c/h2\u003e \u003cp\u003eThe obtained experimental data, in particular, the significant increase in the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e, allow us to propose a refined model of interaction in the NC-azide plasticizer system.\u003c/p\u003e \u003cp\u003e \u003cb\u003eInteraction with NC ordered regions.\u003c/b\u003e The observed increase in the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e is direct X-ray evidence of the penetration of AP molecules into the ordered domains of NC. This result indicates that the interaction is not limited to the amorphous phase of the polymer, as is often assumed in the literature for many polymer-plasticizer systems (Ioelovich, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). AP molecules in this system act as an active modifier of the supramolecular structure.\u003c/p\u003e \u003cp\u003e \u003cb\u003eDistribution of plasticizer within the polymer volume.\u003c/b\u003e The change in the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e is observed even at small additions of AP, which indicates that the interaction process is not staged (\"first amorphous phase, then crystalline\"). This indicates the distribution of the plasticizer throughout the entire volume of the polymer, including the NC ordered regions, from the very beginning of the modification process. Furthermore, throughout the entire studied concentration range (up to 50% AP), no saturation effect is observed, which is characteristic, for example, of doping processes in metal alloys, when further introduction of impurity atoms into the crystal lattice ceases after reaching a certain limit. The monotonic growth of the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e indicates a fundamentally different, thresholdless mechanism of interaction in the NC-AP system.\u003c/p\u003e \u003cp\u003eThe observed incorporation of plasticizer molecules into the binary system (NC \u0026ndash;AP plasticizer) even at a relatively low estimated degree of crystallinity (\u0026asymp;\u0026thinsp;30%) can be explained by the unique structural features of cellulose nitrate. According to generally accepted methodology (Ioelovich, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), the position of the amorphous halo maximum on the X-ray diffractogram allows for the estimation of the average interchain distance in the disordered (amorphous) phase. The position of the amorphous halo maximum of nitrocellulose is \u0026#119889;=5.41\u0026Aring; (Lomadurov et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). At the same time, the parameters of the crystalline phase's unit cell dictate a distance between the axes of the macromolecules of approximately 7.6\u0026ndash;7.7 \u0026Aring; (Meader et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1978\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThus, the estimated distance between the axes of macromolecules in the disordered region of cellulose nitrate appears to be smaller than that in the ordered region. It is suggested that plasticizer molecules may find it difficult to easily penetrate the dense amorphous phase. Instead, they might preferentially incorporate into the less dense interstices of the crystal lattice or at the interphase boundaries, where the local packing density is potentially lower. This observed effect of \"early\" plasticizer incorporation may therefore be attributed not to the overall degree of crystallinity, but rather to the relative density and availability of free volume within the various structural regions of the polymer.\u003c/p\u003e \u003cp\u003e \u003cb\u003eOvercoming steric limitations.\u003c/b\u003e Direct X-ray data convincingly demonstrate that AP molecules, contrary to established views about their steric rigidity (Tretyakova et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2007\u003c/span\u003e), are effectively incorporated into the ordered crystalline domains of NC. This fundamental observation refutes the existing limitations and opens up new possibilities for creating composite materials based on plasticizers with rigid molecules.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Universality of the Interaction Mechanism and Novelty of the Work\u003c/h2\u003e \u003cp\u003eThe establishment of the same nature of the concentration dependence of the interplanar spacing d\u003csub\u003e110\u003c/sub\u003e for NC with different nitrogen content (12.0-12.1% and 13.0%) indicates the universality of the interaction mechanism between NC macromolecules and azide plasticizer (AP) molecules in the studied range of binary system components.\u003c/p\u003e \u003cp\u003eIt should be especially emphasized that, despite the significant applied interest in azide plasticizers as energetic components (Badgujar et al., 2017; Wu et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Zou et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), questions of their fundamental interaction with the polymer matrix at the supramolecular level have remained practically unexplored. The vast majority of publications are devoted to the synthesis of new compounds, the evaluation of their thermal stability and the rheological properties of compositions (Wu et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Zou et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). At the same time, data on the direct influence of azide plasticizers on the structure of NC's ordered regions, in particular, on the parameters of its crystal lattice, are absent in the available literature.\u003c/p\u003e \u003cp\u003eThus, this study provides direct experimental insight into the mechanism of plasticizer action in semicrystalline polymers. It conclusively demonstrates the capability of the Wide-angle X-ray Diffraction (WAXD) technique to detect and quantify structural changes within the crystalline domains of a polymer. These findings challenge the conventional view of plasticizer localization solely in amorphous regions. They open up prospects for the purposeful design of composite materials with specified structural characteristics.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe conducted X-ray diffraction study of binary nitrocellulose-azide plasticizer (NC-AP) systems allowed us to establish fundamental aspects of the plasticization mechanism that make adjustments to a number of classical concepts.\u003c/p\u003e \u003cp\u003eThe key evidence of the active role of the azide plasticizer (AP) as a modifier of the supramolecular structure, and not an inert diluent, is the systematic increase in the interplanar spacing (d\u003csub\u003e110\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;7 \u0026Aring;) in the NC coherent scattering regions with increasing AP concentration.\u003c/p\u003e \u003cp\u003eThe obtained data allow us to take a fresh look at the established paradigms:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eFirst, it is shown that the interaction of the plasticizer is not limited to the amorphous phase; AP penetrates and modifies areas with three-dimensional order.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eSecond, changes in lattice parameters are observed from the smallest additions of AP, which is characteristic of the formation of an interstitial solid solution and excludes the existence of a concentration threshold.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThird, it has been experimentally shown that the steric barrier, considered insurmountable for rigid molecules of cyclic structure of the azide plasticizer, is overcome in practice, which indicates the need to revise the thesis about the impossibility of forming stable systems based on them.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eThe universality of the identified mechanism is confirmed by the identical nature of the concentration dependence of d\u003csub\u003e110\u003c/sub\u003e for NC with different nitrogen content (12.0-12.1% --13.0%), which indicates its fundamental nature for the NC-AP system.\u003c/p\u003e \u003cp\u003eFrom a practical point of view, the modification technique in an aqueous environment made it possible to obtain homogeneous monolithic samples of NC-AP compositions (70:30) without pores and cracks, demonstrating the potential of the approach for creating highly filled energetic materials with specified structural characteristics.\u003c/p\u003e \u003cp\u003eThus, this study marks a paradigm shift in the understanding of nitrocellulose plasticization - from the model of passive filling of the free volume of the amorphous region of the polymer to the model of purposeful design of its supramolecular structure. This opens up new ways for creating NC composite materials with programmable characteristics.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe author is grateful to Dr. Alexander F. Voronkov for the joint work on developing the methodology of nitrocellulose diffractogram decomposition used in this work. The author is also grateful to Dr. V.P. Efremov for the valuable discussion of this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable. The study did not receive external funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest:\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability:\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eData is available upon request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eVladimir F. Lomadurov: conceptualization, methodology, formal analysis, investigation, data curation, writing \u0026ndash; original draft, writing \u0026ndash; review \u0026amp; editing.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBadguzhar, D. M., Talavar, M. B., Zarko, V. E., \u0026amp; Makhulikar, P. P. (2017). 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Hanser Publishers.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu, Y., Li, C., Gao, J., Cai, L., Jiang, C., \u0026amp; Liu, H. (2022). Preparation and properties of azide-modified nitrocellulose and its click reaction curing elastomer. \u003cem\u003eCellulose\u003c/em\u003e, \u003cem\u003e29\u003c/em\u003e, 6009\u0026ndash;6020.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZou, X., Zhang, W., Zhang, Z., Gu, Y., Fu, X., Ge, Z., \u0026amp; Luo, Y. (2021). Study on properties of energetic plasticizer modified double-base propellant. \u003cem\u003ePropellants, Explosives, Pyrotechnics\u003c/em\u003e, \u003cem\u003e46\u003c/em\u003e, 1662\u0026ndash;1671.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"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":"Nitrocellulose, Azide plasticizer, X-ray diffractogram deconvolution, Supramolecular structure, Interstitial solid solution, WAXD","lastPublishedDoi":"10.21203/rs.3.rs-8153658/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8153658/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe influence of an azide plasticizer on the supramolecular structure of nitrocellulose with different nitrogen content was investigated by Wide-angle X-ray diffraction (WAXD). The penetration of cyclic molecules of a low-molecular-weight plasticizer with increased rigidity into the ordered regions of nitrocellulose has been experimentally established, and this penetration of plasticizer molecules is observed even at low concentrations. It is shown that the nature of interaction is the same for nitrocelluloses with nitrogen content of 12.0-12.1% and 13.0%.\u003c/p\u003e","manuscriptTitle":"Modification of Nitrocellulose Crystal Structure by an Azide Plasticizer: X-ray Diffraction Study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-22 04:10:19","doi":"10.21203/rs.3.rs-8153658/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-01-28T04:30:12+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-01-28T04:25:44+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-11-21T12:56:46+00:00","index":"","fulltext":""},{"type":"submitted","content":"Cellulose","date":"2025-11-19T09:41:48+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":"bcea2c0b-ec4a-44b4-9c66-30be8ce57d65","owner":[],"postedDate":"January 22nd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-02-11T11:53:58+00:00","versionOfRecord":[],"versionCreatedAt":"2026-01-22 04:10:19","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8153658","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8153658","identity":"rs-8153658","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}