Effect of controlled drying on the properties of cellulose ester films synthesized in Novel Ionic Liquid [mTBNH][OAc]

Effect of controlled drying on the properties of cellulose ester films synthesized in Novel Ionic Liquid [mTBNH][OAc] | 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 Effect of controlled drying on the properties of cellulose ester films synthesized in Novel Ionic Liquid [mTBNH][OAc] Tanuj Kattamanchi, Heikko Kallakas, Elvira Tarasova, Percy Festus Alao, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4801036/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Cellulose, as a sustainable raw material, holds a promising future as a thermoplastic material. This work focused on fabricating cellulose ester thin films by using both controlled vacuum oven drying and conventional oven drying by the evaporation induced phase separation method (EIPS). A novel distillable ionic liquid (IL) 5-Methyl-1,5,7-triaza-bicyclo- [4.3.0]non-6-enium acetate [mTBNH][OAc]with high dissolving capability of cellulose along with dimethylsulfoxide (DMSO) as a co-solvent are used. The drying methods were compared to investigate their influence on the Cellulose ester films morphological and wettability properties. Based on the results, with increasing the drying rate in the vacuum oven the films have a smoother surface (with CP having 2.14nm RMS value) than the other samples, also indicating higher contact angles of 124 for CP under vacuum drying conditions with denser films. solvent casting vacuum drying [mTBNH][OAc] cellulose esters polymer films EIPS Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Bioplastics are gaining world-wide interest for their numerous applications. Bio-based plastics are typically generated from renewable sources by the action of living organisms, they can be polysaccharides (e.g., regenerated cellulose; pectin, and chitin), lipids etc. (e.g., animal fats) (Bhaladhare and Das 2022 ). The use of plant-based cellulose could be the key, as cellulose is the most abundant biopolymer formed in nature with high chain stiffness, broad chemical modifying capacity and polyfunctionality (Liu et al. 2021 ). Cellulose intrinsically is not a thermoplastic, but with chemical modification desired properties can be achieved. The Hyatt manufacturing company in 1870 demonstrated chemical modification of cellulose on an industrial scale (Balser et al. 2004 ). Chemical modification aims to functionalise and improve processability of cellulose and cellulose esters (CE) are the most popular derivatives of cellulose (Oprea and Voicu 2020 )... Crystallinity of cellulose is an important factor as cellulose is hydrophilic due to the presence of hydroxyl groups and does not actually dissolve in water (Kontturi et al. 2006 ). Whereas the amorphous cellulose swells up in water since water can penetrate by disrupting the intermolecular hydrogen bonds (Müller et al. 2000 ). Cellulose derivatives have been investigated extensively to develop new materials with improved chemical, thermal and physical characteristics (Shaghaleh et al. 2018 ). The esterification of long chain fatty acid cellulose esters is processed in two methods homogeneous and heterogeneous, the conventional method for industrially cellulose esters production is mainly heterogeneous conditions with sulphuric acid acting as catalyst (Hummel 2004 ) (6). The heterogeneous method of cellulose esters production is laborious and time consuming, as the degradation of cellulose is always present along with the low reactivity of cellulose due to its high crystallinity. Conversely, homogeneous transesterification of cellulose creates possibility to synthesis cellulose esters with a high degree of substitution (DS) and long acyl chains. The film preparation from solvent cast method of cellulose acetate (CA) is a simple method (Yang et al. 2013 ), the procedure of solvent casting consists of pouring of the solution on to a substrate which is followed by controlled complete or partial evaporation (Lyytikäinen et al. 2021 ). However, the influence of environmental variables during drying (temperature, pressure etc.) on the film properties have been rarely described from the literature. Recently, (Lyytikäinen et al. 2021 ) have shown drying temperature influence on the film wetting and barrier properties, affecting the morphology of the films and consequently the barriers properties. Harini and Sukumar (Harini and Sukumar 2019 ) compared vacuum drying to open air drying for CA films on Petri dishes and found transparent films dried under vacuum and white films formed under open air drying. The above-mentioned literature pursues the influence of the environment on drying which in turn affect the properties of the film. Vacuum drying is a method that is used to study and compare the results to a conventional oven drying. The sample surface has been studied along with the cross-sectional structure formation. The vacuum drying method should have better film formation with smoother surface that could lead to the film having better hydrophobicity. This study includes the analysis of sample surface topology and the formation of microstructure in the cross section of the films. In this study, we present the physical characterization (FTIR), morphology (SEM), and thermal properties (TGA) of long-chain cellulose ester films prepared by controlled drying solvent casting technique. Experimental Section 2.1. Materials The fibrous cellulose was purchased from Carl Roth GMBH (Karlsruhe, Germany). Vinyl laurate and vinyl palmitate with purity > 98% was purchased from Tokyo chemical Industry Co. (Tokyo, Japan). Ionic liquid 5-Methyl-1,5,7-triaza-bicyclo-[4.3.0]non-6-enium acetate [mTBNH][OAC] was not commercially available and was synthesized by Liuotin Group Oy (Porvoo, Finland). The melting point of IL is 15°C; the flash point is more than 220°C. DMSO with a purity of 99.9% was purchased from Fisher Chemical (Pittsburgh, PA, USA). Diethyl phthalate plasticized (24% DEP) cellulose powder supplied by Sigma Aldrich. Pyridine with purity more than 99% purchased from Sigma Adrich 2.2. Cellulose dissolution in the solvent system Cellulose was dried under vacuum at 105°C for 24 hours before use. 3.5 g of MCC was dissolved in 100 g [mTBNH][OAc] and stirred at 60°C for several hours until the cellulose was completely dissolved to yield 3.5 wt.% solution. To decrease the viscosity which simplifies the processing, a co-solvent DMSO was added in ratio 1:1 to IL. The designed amount of the respective vinyl ester (3 eq./AGU) was added to the cellulose solution in a chemical reactor equipped with a mechanical stirrer and nitrogen flow, and then the reaction was performed at temperature 70°C and reaction time was 3 hours. When the reaction was completed, the obtained cellulose esters were precipitated into 500 ml of water mixed with ethanol (for laurate and myristate) or pure ethanol (for palmitate and stearate). To remove solvent and vinyl ester residuals, the product was washed several times in 100–200 ml of ethanol, next acetone, and finally with hexane. After that the product was dried under a vacuum at 55°C overnight (Table 1 ), the method of preparation was conducted similarly to our previous paper. (Tarasova et al. 2023 ). Table 1 Synthesis parameters for the polymer solution. Nr Derivative name Ester Sample 1 Cellulose acetate - commercial (C2) Acetate CDA 2 Cellulose laurate (C12) Laurate CL 3 Cellulose palmitate (C16) Palmitate CP 2.3. Solvent casting of cellulose films A knife blade was used to spread the polymer solution over a flat glass substrate of 100 mm width. The cast solutions were placed at 25°C and at negative 0.45 bar in a vacuum oven over night. After removal from the oven the cast thin films were immersed in distilled water, peeled from the substrate, and further dried in the vacuum over at 25°C for 8 hours. The final film thickness was dictated by the concentration of the polymer in the solution. Films were cast on laminated glass plates with the blade width of 100 mm (BYK-Gardner GmbH, Germany). With the given knife, the casted thickness of 100 µm was set to achieve the final thickness of 60–80 µm (Kramar et al. 2023 ; Kallakas et al. 2023 ). The above prepared solvent matrix is poured on to a glass substrate (100mm width and 100 micrometre thickness) and was kept in an Memmert universal oven (Memmert GmbH + Co. KG, Germany) at 25°C with a vent open to the ambient room atmosphere (at room pressure), for the evaporation of the solvent. The solvent matrix solution was casted on a glass substrate (100mm width and 100 micrometre thickness) and was kept in a Tefic biotech DZF – 6090 (China) vacuum oven (at 25°C and negative pressure 0.5 bar) for complete evaporation of the solvent. Fig. shows the vacuum drying chamber setup used for the preparation of the films. 2.4 Characterisation 2.4.1 Fourier Transform Infrared (FTIR) Spectroscopy The FTIR spectroscopy was carried out on native cellulose and synthesized cellulose esters to evaluate the acetylation process. Measurements were performed using a Interspectrum FTIR spectrometer Shimadzu (Tõravere, Estonia) with KBr disc method between 500 and 4000 \(\:{cm}^{-1}\) . 32 scans were taken from each sample with a resolution of 4 \(\:{cm}^{-1}\) in absorbance mode. For comparison, spectra were adjusted to the same baseline. 2.4.2 Contact Angle measurement. The contact angles were measured on Data physiscs OCA-20 (Riverside, CA, USA), the sessile drop method with a room temperature of 22°C with the relative humidity of 65%, the water drop is placed on the film surface from a micro syringe (Hamilton-Bonaduz). Measurements were made with three and averaged, each measurement was made on a new spot. The contact angles were measured for 40 s for each measurement. 2.4.3 X-ray diffraction analysis (XRD). The structural analysis of the samples in the powder form was assessed from X-ray diffraction (XRD) measurement using the Ultima IV diffractometer (Rigaku, Tokyo, Japan). The instrument was equipped with a silicon detector, Ni filter, and a Cu Kα irradiation source ( λ = 1.540 Å), anode voltage 40 kV, anode current 40 mA, θ-θ regime, step θ = 0.02 deg. 2.4.4 Scanning electron microscopy (SEM) The cellulose ester films, surface microstructure is understood by Thermo Fisher Phenom XL (Massachusetts, USA) desktop scanning electron microscope (tabletop). Each sample was fixed on a stub using a double-sided adhesive tape after being cryo fractured under liquid nitrogen, the samples were placed at an angle of 90°C. 2.4.5 Atomic force microscopy (AFM) Atomic force micrographs of the ester films were characterised using a Bruker Dimension Edge (Massachusetts, USA) in Tapping mode. The measurements of the samples were taken for the area of 5x5 µm. The roughness average (Ra) and the root mean square (Rq) were calculated to quantitatively estimate the roughness of the films. 2.4.6 Thermogravimetric Analysis (TGA) A Setaram Labsys Evo 1600 thermoanalyzer (Caluire, France) was used. The DTG-DTA experiments were carried out under non-isothermal conditions up to 600°C at the heating rate of 10°C min − 1 in the atmosphere of argon. Standard 100 µL alumina crucibles were used, the mass of the samples was 7.2 ± 0.3 mg, and the gas flow was 20 mL min − 1 . Results and Discussion 5.1. Fourier Transform Infrared (FTIR) Spectroscopy The FTIR spectra of the cellulose films exhibits the absorption bands of the characteristic functional groups of cellulose esters that are dried in the conventional oven and vacuum oven were similar which are shown in the Fig. 1 . The strongest evidence of successful acylation is the appearance of an absorption band at 1740 cm –1 that corresponds to the stretching of the ester carbonyl (> C = O) group, and the band at 720 cm –1 is characteristic for linearly connected –CH2– groups (–(CH2)4– rocking) (Singh et al. 2014 ). Peaks at 2924 cm − 1 and 2854 cm − 1 show the successful introduction of alkyl chains intensities correspond to asymmetric and symmetric stretching of the methylene group of the fatty long chains. The esterification of the cellulose hydroxyl groups is clearly indicated by the decreasing intensity of the wide peak at 3472 cm − 1 that corresponds to the stretching vibrations of the OH group, indicates that a large amount of –OH groups were substituted (Crépy et al. 2011 ). Similar results have been obtained for cellulose esters irrespective of the substituent chain length (Kallakas et al. 2023 ; Tarasova et al. 2023 ). 5.2 Contact Angle measurement. The cellulose ester films were characterised by static contact angle measurement to determine the hydrophobic or the hydrophilic nature, reported in the Table 2 . The contact angles for the films dried in the conventional oven ranged between 80° to 121° Fig. 2 and for the vacuum oven dried thin films the contact angles ranged between 85° to 124°, depending on the fatty acid chain length and in addition with the influence of the drying condition. The thin films are considered hydrophobic depending on the fact that the contact angles between water and the cellulosic films are at least 90°(Bhaladhare and Das 2022 ). Hence, the cellulose ester films are deemed to be hydrophobic. However, the higher contact angles are seen in the vacuum dried cellulosic ester thin films. It is known that long aliphatic side chain is hydrophobic, this is justified with high contact angles of cellulose palmitate and cellulose laurate. Table 2 Average contact angle measurement of cellulose ester films. Ester RO (°) VO (°) CDA 80 (± 5) 85(± 8) CL 106(± 2) 113(± 3) CP 121(± 2) 124(± 3) 5.3. X-ray diffraction analysis (XRD). The film structure has been characterised by XRD to detect the structure of the cellulose ester films. The X- ray diffraction profile of all the film samples is shown in Fig. 3 . All the samples regardless of the drying condition indicate a peak of 2q = 12°- 24°. The intra and intermolecular hydrogen bonds occur in cellulose through hydroxyl groups, which results in various ordered crystalline arrangements (Sheltami et al. 2012 ). According to Miller indices, peaks around 2q = 16.5° and 22.5° represent (110), and (200) crystallographic planes of cellulose I, respectively (French and Santiago Cintrón 2013 ). As seen from Fig. 3 the diffractogram indicates two broad peaks for CDA at 9.32°, and 18.72°. Similarly, the peaks at 9.56°, 19.68°, and 28.69° can be seen for the cellulose esters CL and CP. From the data plot we do not notice any significant effect of the drying conditions on the structure of the films. The peak around 20° is ascribed to (002) of the plane, exhibiting characteristic amorphous phase (Li and Renneckar 2011 ; Fan et al. 2013 ). The weak peak at 28.69° of (040) and 9.56° at (101) reflection appear in CL and CP. The peak at 20° of (002) is broad in CDA and narrower in CL and CP indicating a higher degree of crystallinity (Montane et al. 1998 ). The diffraction peaks that appear around 10° in CDA could be indexed to crystalline peaks of CTA II modification (Sun and Sun 2002 ; Das et al. 2014 ). The diffraction peak at 20° is more intense and the relative intensity has increased, this observation could reveal a better-defined crystalline domain. Lateral chain order is indicated by the decrease of the peak width (2theta = 16°-24°) as the side chain increased as seen in the wide-angle region of the diffractogram a better-defined crystalline domain. 5.4 Thermogravimetric Analysis (TGA) The dynamic thermogravimetric curves of cellulose ester films prepared from [mTBNH][OAc] are given below in Fig. 4 . The analysis showed thermal decomposition process involving rapid loss of weight and towards the end the decomposition zone where the constant weight represents the carbonization of the material. The initial decomposition temperature at 5% weight loss ( \(\:{T}_{5\%}\) ) and the maximum weight loss temperature ( \(\:{T}_{d}\) ), finally the char residue at 600°C are recorded in the following Table 4 . ( \(\:{T}_{d1}\) ) is the initial step of pyrolysis of volatile compounds. Table 3 Thermal stabilities of the cellulose fatty chain esters. Sample T 5% °C Td1 °C Td °C Char % CDA RO 263.2 201.1 360.8 12.2 VO 245.0 210.6 362.0 15.3 CL RO 212.5 232.0 369.2 7.9 VO 212.7 230.8 367.3 6.3 CP RO 303.4 - 360.6 2.6 VO 305.0 - 354.4 0.9 The main degradation range between 250–350°C is due to the crystalline phase degradation of cellulose(Sonia and Priya Dasan 2013 ). The ester groups caused the formation of a specific mass loss in the range between 140–250°C due to decomposition of the alkyl chains grafted to cellulose laurate (CL) and cellulose di acetate (CDA) but the similar trend is absent in case of cellulose palmitate (CP). Mass loss at 5wt% indicates a noticeable difference in the temperature of CDA with the VO dried sample with the mass loss at 245°C compared to the RO sample at 263°C. The cellulose esters CDA and CL two separate degradation steps with initial pyrolysis peak of CL shifted to higher temperature around 230°C compared to CDA at 200°C. The initial pyrolysis peak could be attributed to the degradation of the grafted fatty acid side chains (Jebrane et al. 2017 ), the higher peak of CL can be attributed to the longer chain length compared to CDA with a shorter chain length. In all the samples the main degradation peak of cellulose backbone is seen around 360°C (Jandura et al. 2000 ) (Freire et al. 2006 ; Uschanov et al. 2011 ). Similar degradation temperatures have been observed in the literature with functionalised celluloses fatty acid chlorides (Almasi et al. 2015 ). 5.5. Scanning Electron Microscopy (SEM) SEM has been characterized to study the film formation and structure. The Fig. 5 shows the cross-sectional images of the cellulose ester thin films. From the images, less structures are observed comparing the VO and RO and surfaces indicate dense structure in the film formation. All the sample indicate a top layer which is exposed to the air. The thickness of the films after drying depends on the thickness of the homogeneous solution during casting. The kinetic phase separation during evaporation indicates a polymer lean and a polymer rich phase. The cross-section images reveal that the samples have a homogeneous film composition, and no significant structures are seen in the films prepared which could also be attributed to the long and controlled evaporation times. As the solvent evaporates from the membrane system, the chains lose mobility and adjust to the configurations(Du et al. 2009 ). Longer evaporation time leads to formation of asymmetric structures with denser layer. Table 4 Thickness of cross section of films. Ester Thickness µm CDA RO 116 VO 115.5 CL RO 59.5 VO 60 CP RO 57.5 CO 58 5.6. Atomic Force Microscopy (AFM) The surface morphology and the roughness values of the cellulose ester films are listed in the table 6. The darker areas as observed are associated with depressions on the surface of the films and the lighter areas are the elevations. Surface morphology is characterised by root mean square (Sq), mean roughness (Sa) and the difference between high peaks and low valleys (Z). Observations from the AFM indicated nodular structure, the polymer-rich phase having less ability to deform and thus merge and cause nodular structure due to chain entanglements, while the polymer poor phase become the cavities/depressions(Zhang et al. 2002 ). These nodules are the influencing factor for the roughness of the surface. The effect of evaporation environment is depicted clearly by comparing the surface images and the surface roughness parameters. The average depression size concentration is larger over the area of the films dried in the vacuum oven as compared to the films dried in the conventional oven as seen in the CDA, CP and CL films. The membrane surface, that is the nodule size and distribution could be attributed to the evaporation conditions and environment. The literature reports, with the increase with the nodule size, the surface roughness of the membranes tend to increase(Khulbe et al. 1998 ). The influence of evaporation environment on the surface morphology of the films with average roughness lower and the concentration of the depression area is marginally higher with the vacuum dried samples. However, no nodular structure is seen on the surface of CL films in both dried in the vacuum and the conventional oven. But in this case surface roughness cannot be in proportion to the nodule size, but the depression and the elevation regions could account for the surface roughness. CL on the other hand has a noticeable difference between the conventional oven dried sample and the vacuum dried sample, film surface indicates accumulated area of elevation and depressions. The regions elevation is significant in the vacuum dried film, the isolated nodules have distinct boundaries, and the interstitial regions can be clearly identified. It could be possible that polymer chains present in the interstitial regions are randomly distributed compared to polymer chains present in the nodules(Khulbe et al. 1998 ). Although, a couple of samples indicate circular concentration of peaks which attributed to the released air bubbles during the long drying process. Table 5 AFM surface roughness values of the cellulose fatty chain esters. Sample RMS roughness (Sq)(nm) Mean roughness (Sa)(nm) Max Z range (nm) Drying Method RO VO RO VO RO VO CDA 8.12 6.55 5.83 4.71 76.39 82.40 CL 3.42 5.50 2.32 2.76 43.24 123.24 CP 3.09 2.14 2.30 1.66 31.07 37.19 Conclusions The method of drying the films under vacuum conditions and conventional oven conditions were found to be promising with increased evaporation rate, higher hydrophobicity. The vacuum drying created smoother surface with better hydrophobicity values and create denser films. These evaporation conditions indicate a blend of lamellar and finger like microstructure for better packing structure during drying. The thermal characterisation implied that cellulose films remain stable with similar degradation temperatures. AFM 3D image depicts the depth of the film morphology in context of the surface roughness. Considering our study, vacuum drying showed potential for making films smoother and denser with increased hydrophobicity. Declarations Ethical Approval The author declares no competing interests. Funding This study was supported by ERDF and the Estonian Research Council via project RESTA 10. Author Contribution All authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by E.T., T.K., P.A., and H.K. 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Kattamanchi","email":"data:image/png;base64,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","orcid":"","institution":"Tallinn University of Technology","correspondingAuthor":true,"prefix":"","firstName":"Tanuj","middleName":"","lastName":"Kattamanchi","suffix":""},{"id":360364726,"identity":"4fa41693-e9c4-42ea-bc08-4f85ce0e5395","order_by":1,"name":"Heikko Kallakas","email":"","orcid":"","institution":"Tallinn University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Heikko","middleName":"","lastName":"Kallakas","suffix":""},{"id":360364730,"identity":"58686cfe-237a-48d4-bee8-53cba0079876","order_by":2,"name":"Elvira Tarasova","email":"","orcid":"","institution":"Tallinn University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Elvira","middleName":"","lastName":"Tarasova","suffix":""},{"id":360364734,"identity":"4f127dd3-2a24-4f8d-b7d3-732301481689","order_by":3,"name":"Percy Festus Alao","email":"","orcid":"","institution":"Tallinn University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Percy","middleName":"Festus","lastName":"Alao","suffix":""},{"id":360364737,"identity":"42ddfd4f-49e7-41ff-9134-ff2b0da1604e","order_by":4,"name":"Arvo Mere","email":"","orcid":"","institution":"Tallinn University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Arvo","middleName":"","lastName":"Mere","suffix":""},{"id":360364739,"identity":"0cb2bb9f-0654-4a5e-9d90-9209ec6bdcab","order_by":5,"name":"Andres Krumme","email":"","orcid":"","institution":"Tallinn University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Andres","middleName":"","lastName":"Krumme","suffix":""},{"id":360364742,"identity":"a7567240-f7ae-450b-abe5-e5d7300599e9","order_by":6,"name":"Jaan Kers","email":"","orcid":"","institution":"Tallinn University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Jaan","middleName":"","lastName":"Kers","suffix":""}],"badges":[],"createdAt":"2024-07-25 10:21:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4801036/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4801036/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":67878025,"identity":"933d87e0-bfb9-4e63-b5e0-688c738806f1","added_by":"auto","created_at":"2024-10-30 16:37:47","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":98312,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR of cellulose esters dried in the conventional oven.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4801036/v1/d17a58770fe59335b8277113.png"},{"id":67877582,"identity":"1cd3b15a-ffc1-422c-880b-21fe95642a5a","added_by":"auto","created_at":"2024-10-30 16:29:46","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":56811,"visible":true,"origin":"","legend":"\u003cp\u003eContact angle measurement of cellulose esters.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4801036/v1/9173301efdabc84f2335de3c.png"},{"id":67878026,"identity":"442aa781-4d56-4fb2-8b07-474caf31054d","added_by":"auto","created_at":"2024-10-30 16:37:47","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":154746,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern of both drying method of cellulose esters.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4801036/v1/41a1e25057fa93d50ecc090c.png"},{"id":67877583,"identity":"39440a41-9611-4b9c-9e80-ab6da8354ef8","added_by":"auto","created_at":"2024-10-30 16:29:47","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":89937,"visible":true,"origin":"","legend":"\u003cp\u003eTGA curves of cellulose esters (a) CL, (b) CP, and (c) CDA\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4801036/v1/1b7383d209214b0c4ee02722.png"},{"id":67877586,"identity":"5c792706-e658-485b-bff5-d473bcc3a83c","added_by":"auto","created_at":"2024-10-30 16:29:47","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":280137,"visible":true,"origin":"","legend":"\u003cp\u003eSEM cross section images of cellulose esters at a magnification of 1000x a- CDA RO, b- CDA VO, c- CL RO, d- CL VO, e- CP RO, and f- CP VO.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4801036/v1/d8c85ee1d6d3bedb73b4c85d.png"},{"id":67877584,"identity":"ca30f222-5755-4bb9-a52e-64d806658d45","added_by":"auto","created_at":"2024-10-30 16:29:47","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":919494,"visible":true,"origin":"","legend":"\u003cp\u003eAFM images of cellulose esters 3-D 2-D images of (a-b) CDA RO, (c-d) CDA VO, (e-f) CL RO, (g-h) CL VO, (i-j) CP RO and (k-l) CP VO.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4801036/v1/c5bf09a52434cee9dc9d8d1a.png"},{"id":76420420,"identity":"2633691d-1515-4a2e-a87d-5b5f868946c8","added_by":"auto","created_at":"2025-02-17 04:01:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2861260,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4801036/v1/de03b2c5-cbfc-4da6-b2a7-d3ff4c4cb6e9.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of controlled drying on the properties of cellulose ester films synthesized in Novel Ionic Liquid [mTBNH][OAc]","fulltext":[{"header":"Introduction","content":"\u003cp\u003eBioplastics are gaining world-wide interest for their numerous applications. Bio-based plastics are typically generated from renewable sources by the action of living organisms, they can be polysaccharides (e.g., regenerated cellulose; pectin, and chitin), lipids etc. (e.g., animal fats) (Bhaladhare and Das \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The use of plant-based cellulose could be the key, as cellulose is the most abundant biopolymer formed in nature with high chain stiffness, broad chemical modifying capacity and polyfunctionality (Liu et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Cellulose intrinsically is not a thermoplastic, but with chemical modification desired properties can be achieved. The Hyatt manufacturing company in 1870 demonstrated chemical modification of cellulose on an industrial scale (Balser et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Chemical modification aims to functionalise and improve processability of cellulose and cellulose esters (CE) are the most popular derivatives of cellulose (Oprea and Voicu \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e)...\u003c/p\u003e \u003cp\u003eCrystallinity of cellulose is an important factor as cellulose is hydrophilic due to the presence of hydroxyl groups and does not actually dissolve in water (Kontturi et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Whereas the amorphous cellulose swells up in water since water can penetrate by disrupting the intermolecular hydrogen bonds (M\u0026uuml;ller et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). Cellulose derivatives have been investigated extensively to develop new materials with improved chemical, thermal and physical characteristics (Shaghaleh et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The esterification of long chain fatty acid cellulose esters is processed in two methods homogeneous and heterogeneous, the conventional method for industrially cellulose esters production is mainly heterogeneous conditions with sulphuric acid acting as catalyst (Hummel \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2004\u003c/span\u003e) (6). The heterogeneous method of cellulose esters production is laborious and time consuming, as the degradation of cellulose is always present along with the low reactivity of cellulose due to its high crystallinity. Conversely, homogeneous transesterification of cellulose creates possibility to synthesis cellulose esters with a high degree of substitution (DS) and long acyl chains. The film preparation from solvent cast method of cellulose acetate (CA) is a simple method (Yang et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), the procedure of solvent casting consists of pouring of the solution on to a substrate which is followed by controlled complete or partial evaporation (Lyytik\u0026auml;inen et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, the influence of environmental variables during drying (temperature, pressure etc.) on the film properties have been rarely described from the literature. Recently, (Lyytik\u0026auml;inen et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) have shown drying temperature influence on the film wetting and barrier properties, affecting the morphology of the films and consequently the barriers properties. Harini and Sukumar (Harini and Sukumar \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) compared vacuum drying to open air drying for CA films on Petri dishes and found transparent films dried under vacuum and white films formed under open air drying.\u003c/p\u003e \u003cp\u003eThe above-mentioned literature pursues the influence of the environment on drying which in turn affect the properties of the film. Vacuum drying is a method that is used to study and compare the results to a conventional oven drying. The sample surface has been studied along with the cross-sectional structure formation. The vacuum drying method should have better film formation with smoother surface that could lead to the film having better hydrophobicity. This study includes the analysis of sample surface topology and the formation of microstructure in the cross section of the films.\u003c/p\u003e \u003cp\u003eIn this study, we present the physical characterization (FTIR), morphology (SEM), and thermal properties (TGA) of long-chain cellulose ester films prepared by controlled drying solvent casting technique.\u003c/p\u003e"},{"header":"Experimental Section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Materials\u003c/h2\u003e \u003cp\u003eThe fibrous cellulose was purchased from Carl Roth GMBH (Karlsruhe, Germany). Vinyl laurate and vinyl palmitate with purity\u0026thinsp;\u0026gt;\u0026thinsp;98% was purchased from Tokyo chemical Industry Co. (Tokyo, Japan). Ionic liquid 5-Methyl-1,5,7-triaza-bicyclo-[4.3.0]non-6-enium acetate [mTBNH][OAC] was not commercially available and was synthesized by Liuotin Group Oy (Porvoo, Finland). The melting point of IL is 15\u0026deg;C; the flash point is more than 220\u0026deg;C. DMSO with a purity of 99.9% was purchased from Fisher Chemical (Pittsburgh, PA, USA). Diethyl phthalate plasticized (24% DEP) cellulose powder supplied by Sigma Aldrich. Pyridine with purity more than 99% purchased from Sigma Adrich\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Cellulose dissolution in the solvent system\u003c/h2\u003e \u003cp\u003eCellulose was dried under vacuum at 105\u0026deg;C for 24 hours before use. 3.5 g of MCC was dissolved in 100 g [mTBNH][OAc] and stirred at 60\u0026deg;C for several hours until the cellulose was completely dissolved to yield 3.5 wt.% solution. To decrease the viscosity which simplifies the processing, a co-solvent DMSO was added in ratio 1:1 to IL. The designed amount of the respective vinyl ester (3 eq./AGU) was added to the cellulose solution in a chemical reactor equipped with a mechanical stirrer and nitrogen flow, and then the reaction was performed at temperature 70\u0026deg;C and reaction time was 3 hours. When the reaction was completed, the obtained cellulose esters were precipitated into 500 ml of water mixed with ethanol (for laurate and myristate) or pure ethanol (for palmitate and stearate). To remove solvent and vinyl ester residuals, the product was washed several times in 100\u0026ndash;200 ml of ethanol, next acetone, and finally with hexane. After that the product was dried under a vacuum at 55\u0026deg;C overnight (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), the method of preparation was conducted similarly to our previous paper. (Tarasova et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSynthesis parameters for the polymer solution.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDerivative name\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEster\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSample\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=\"left\" colname=\"c2\"\u003e \u003cp\u003eCellulose acetate - commercial (C2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAcetate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCDA\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=\"left\" colname=\"c2\"\u003e \u003cp\u003eCellulose laurate (C12)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLaurate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCL\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=\"left\" colname=\"c2\"\u003e \u003cp\u003eCellulose palmitate (C16)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePalmitate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Solvent casting of cellulose films\u003c/h2\u003e \u003cp\u003eA knife blade was used to spread the polymer solution over a flat glass substrate of 100 mm width. The cast solutions were placed at 25\u0026deg;C and at negative 0.45 bar in a vacuum oven over night. After removal from the oven the cast thin films were immersed in distilled water, peeled from the substrate, and further dried in the vacuum over at 25\u0026deg;C for 8 hours.\u003c/p\u003e \u003cp\u003eThe final film thickness was dictated by the concentration of the polymer in the solution. Films were cast on laminated glass plates with the blade width of 100 mm (BYK-Gardner GmbH, Germany). With the given knife, the casted thickness of 100 \u0026micro;m was set to achieve the final thickness of 60\u0026ndash;80 \u0026micro;m (Kramar et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Kallakas et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe above prepared solvent matrix is poured on to a glass substrate (100mm width and 100 micrometre thickness) and was kept in an Memmert universal oven (Memmert GmbH\u0026thinsp;+\u0026thinsp;Co. KG, Germany) at 25\u0026deg;C with a vent open to the ambient room atmosphere (at room pressure), for the evaporation of the solvent.\u003c/p\u003e \u003cp\u003eThe solvent matrix solution was casted on a glass substrate (100mm width and 100 micrometre thickness) and was kept in a Tefic biotech DZF \u0026ndash; 6090 (China) vacuum oven (at 25\u0026deg;C and negative pressure 0.5 bar) for complete evaporation of the solvent. Fig. shows the vacuum drying chamber setup used for the preparation of the films.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Characterisation\u003c/h2\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.4.1 Fourier Transform Infrared (FTIR) Spectroscopy\u003c/h2\u003e \u003cp\u003eThe FTIR spectroscopy was carried out on native cellulose and synthesized cellulose esters to evaluate the acetylation process. Measurements were performed using a Interspectrum FTIR spectrometer Shimadzu (T\u0026otilde;ravere, Estonia) with KBr disc method between 500 and 4000 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{cm}^{-1}\\)\u003c/span\u003e\u003c/span\u003e. 32 scans were taken from each sample with a resolution of 4 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{cm}^{-1}\\)\u003c/span\u003e\u003c/span\u003e in absorbance mode. For comparison, spectra were adjusted to the same baseline.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.4.2 Contact Angle measurement.\u003c/h2\u003e \u003cp\u003eThe contact angles were measured on Data physiscs OCA-20 (Riverside, CA, USA), the sessile drop method with a room temperature of 22\u0026deg;C with the relative humidity of 65%, the water drop is placed on the film surface from a micro syringe (Hamilton-Bonaduz). Measurements were made with three and averaged, each measurement was made on a new spot. The contact angles were measured for 40 s for each measurement.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.4.3 X-ray diffraction analysis (XRD).\u003c/h2\u003e \u003cp\u003eThe structural analysis of the samples in the powder form was assessed from X-ray diffraction (XRD) measurement using the Ultima IV diffractometer (Rigaku, Tokyo, Japan). The instrument was equipped with a silicon detector, Ni filter, and a Cu Kα irradiation source (\u003cem\u003eλ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.540 \u0026Aring;), anode voltage 40 kV, anode current 40 mA, \u003cem\u003eθ-θ\u003c/em\u003e regime, step \u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.02 deg.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.4.4 Scanning electron microscopy (SEM)\u003c/h2\u003e \u003cp\u003eThe cellulose ester films, surface microstructure is understood by Thermo Fisher Phenom XL (Massachusetts, USA) desktop scanning electron microscope (tabletop). Each sample was fixed on a stub using a double-sided adhesive tape after being cryo fractured under liquid nitrogen, the samples were placed at an angle of 90\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e2.4.5 Atomic force microscopy (AFM)\u003c/h2\u003e \u003cp\u003eAtomic force micrographs of the ester films were characterised using a Bruker Dimension Edge (Massachusetts, USA) in Tapping mode. The measurements of the samples were taken for the area of 5x5 \u0026micro;m. The roughness average (Ra) and the root mean square (Rq) were calculated to quantitatively estimate the roughness of the films.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e2.4.6 Thermogravimetric Analysis (TGA)\u003c/h2\u003e \u003cp\u003eA Setaram Labsys Evo 1600 thermoanalyzer (Caluire, France) was used. The DTG-DTA experiments were carried out under non-isothermal conditions up to 600\u0026deg;C at the heating rate of 10\u0026deg;C min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the atmosphere of argon. Standard 100 \u0026micro;L alumina crucibles were used, the mass of the samples was 7.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3 mg, and the gas flow was 20 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e5.1. Fourier Transform Infrared (FTIR) Spectroscopy\u003c/h2\u003e \u003cp\u003eThe FTIR spectra of the cellulose films exhibits the absorption bands of the characteristic functional groups of cellulose esters that are dried in the conventional oven and vacuum oven were similar which are shown in the Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The strongest evidence of successful acylation is the appearance of an absorption band at 1740 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e that corresponds to the stretching of the ester carbonyl (\u0026gt;\u0026thinsp;C\u0026thinsp;=\u0026thinsp;O) group, and the band at 720 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e is characteristic for linearly connected \u0026ndash;CH2\u0026ndash; groups (\u0026ndash;(CH2)4\u0026ndash; rocking) (Singh et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Peaks at 2924 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 2854 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e show the successful introduction of alkyl chains intensities correspond to asymmetric and symmetric stretching of the methylene group of the fatty long chains. The esterification of the cellulose hydroxyl groups is clearly indicated by the decreasing intensity of the wide peak at 3472 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e that corresponds to the stretching vibrations of the OH group, indicates that a large amount of \u0026ndash;OH groups were substituted (Cr\u0026eacute;py et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Similar results have been obtained for cellulose esters irrespective of the substituent chain length (Kallakas et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Tarasova et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e5.2 Contact Angle measurement.\u003c/h2\u003e \u003cp\u003eThe cellulose ester films were characterised by static contact angle measurement to determine the hydrophobic or the hydrophilic nature, reported in the Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The contact angles for the films dried in the conventional oven ranged between 80\u0026deg; to 121\u0026deg; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and for the vacuum oven dried thin films the contact angles ranged between 85\u0026deg; to 124\u0026deg;, depending on the fatty acid chain length and in addition with the influence of the drying condition. The thin films are considered hydrophobic depending on the fact that the contact angles between water and the cellulosic films are at least 90\u0026deg;(Bhaladhare and Das \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Hence, the cellulose ester films are deemed to be hydrophobic. However, the higher contact angles are seen in the vacuum dried cellulosic ester thin films. It is known that long aliphatic side chain is hydrophobic, this is justified with high contact angles of cellulose palmitate and cellulose laurate.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAverage contact angle measurement of cellulose ester films.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEster\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRO (\u0026deg;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVO (\u0026deg;)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCDA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e80 (\u0026plusmn;\u0026thinsp;5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e85(\u0026plusmn;\u0026thinsp;8)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e106(\u0026plusmn;\u0026thinsp;2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e113(\u0026plusmn;\u0026thinsp;3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e121(\u0026plusmn;\u0026thinsp;2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e124(\u0026plusmn;\u0026thinsp;3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e5.3. X-ray diffraction analysis (XRD).\u003c/h2\u003e \u003cp\u003eThe film structure has been characterised by XRD to detect the structure of the cellulose ester films. The X- ray diffraction profile of all the film samples is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. All the samples regardless of the drying condition indicate a peak of 2q\u0026thinsp;=\u0026thinsp;12\u0026deg;- 24\u0026deg;. The intra and intermolecular hydrogen bonds occur in cellulose through hydroxyl groups, which results in various ordered crystalline arrangements (Sheltami et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). According to Miller indices, peaks around 2q\u0026thinsp;=\u0026thinsp;16.5\u0026deg; and 22.5\u0026deg; represent (110), and (200) crystallographic planes of cellulose I, respectively (French and Santiago Cintr\u0026oacute;n \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). As seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e the diffractogram indicates two broad peaks for CDA at 9.32\u0026deg;, and 18.72\u0026deg;. Similarly, the peaks at 9.56\u0026deg;, 19.68\u0026deg;, and 28.69\u0026deg; can be seen for the cellulose esters CL and CP. From the data plot we do not notice any significant effect of the drying conditions on the structure of the films. The peak around 20\u0026deg; is ascribed to (002) of the plane, exhibiting characteristic amorphous phase (Li and Renneckar \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Fan et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). The weak peak at 28.69\u0026deg; of (040) and 9.56\u0026deg; at (101) reflection appear in CL and CP. The peak at 20\u0026deg; of (002) is broad in CDA and narrower in CL and CP indicating a higher degree of crystallinity (Montane et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). The diffraction peaks that appear around 10\u0026deg; in CDA could be indexed to crystalline peaks of CTA II modification (Sun and Sun \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Das et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The diffraction peak at 20\u0026deg; is more intense and the relative intensity has increased, this observation could reveal a better-defined crystalline domain. Lateral chain order is indicated by the decrease of the peak width (2theta\u0026thinsp;=\u0026thinsp;16\u0026deg;-24\u0026deg;) as the side chain increased as seen in the wide-angle region of the diffractogram a better-defined crystalline domain.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e5.4 Thermogravimetric Analysis (TGA)\u003c/h2\u003e \u003cp\u003eThe dynamic thermogravimetric curves of cellulose ester films prepared from [mTBNH][OAc] are given below in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The analysis showed thermal decomposition process involving rapid loss of weight and towards the end the decomposition zone where the constant weight represents the carbonization of the material. The initial decomposition temperature at 5% weight loss (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{T}_{5\\%}\\)\u003c/span\u003e\u003c/span\u003e) and the maximum weight loss temperature (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{T}_{d}\\)\u003c/span\u003e\u003c/span\u003e), finally the char residue at 600\u0026deg;C are recorded in the following Table \u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{T}_{d1}\\)\u003c/span\u003e\u003c/span\u003e) is the initial step of pyrolysis of volatile compounds.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThermal stabilities of the cellulose fatty chain esters.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eT 5%\u003c/p\u003e \u003cp\u003e\u0026deg;C\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTd1\u003c/p\u003e \u003cp\u003e\u0026deg;C\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTd\u003c/p\u003e \u003cp\u003e\u0026deg;C\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eChar %\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eCDA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e263.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e201.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e360.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e12.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e245.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e210.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e362.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e15.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eCL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e212.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e232.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e369.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e7.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e212.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e230.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e367.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eCP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e303.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e360.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e305.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e354.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe main degradation range between 250\u0026ndash;350\u0026deg;C is due to the crystalline phase degradation of cellulose(Sonia and Priya Dasan \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). The ester groups caused the formation of a specific mass loss in the range between 140\u0026ndash;250\u0026deg;C due to decomposition of the alkyl chains grafted to cellulose laurate (CL) and cellulose di acetate (CDA) but the similar trend is absent in case of cellulose palmitate (CP). Mass loss at 5wt% indicates a noticeable difference in the temperature of CDA with the VO dried sample with the mass loss at 245\u0026deg;C compared to the RO sample at 263\u0026deg;C. The cellulose esters CDA and CL two separate degradation steps with initial pyrolysis peak of CL shifted to higher temperature around 230\u0026deg;C compared to CDA at 200\u0026deg;C. The initial pyrolysis peak could be attributed to the degradation of the grafted fatty acid side chains (Jebrane et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), the higher peak of CL can be attributed to the longer chain length compared to CDA with a shorter chain length. In all the samples the main degradation peak of cellulose backbone is seen around 360\u0026deg;C (Jandura et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2000\u003c/span\u003e) (Freire et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Uschanov et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Similar degradation temperatures have been observed in the literature with functionalised celluloses fatty acid chlorides (Almasi et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e5.5. Scanning Electron Microscopy (SEM)\u003c/h2\u003e \u003cp\u003eSEM has been characterized to study the film formation and structure. The Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the cross-sectional images of the cellulose ester thin films. From the images, less structures are observed comparing the VO and RO and surfaces indicate dense structure in the film formation. All the sample indicate a top layer which is exposed to the air. The thickness of the films after drying depends on the thickness of the homogeneous solution during casting. The kinetic phase separation during evaporation indicates a polymer lean and a polymer rich phase. The cross-section images reveal that the samples have a homogeneous film composition, and no significant structures are seen in the films prepared which could also be attributed to the long and controlled evaporation times. As the solvent evaporates from the membrane system, the chains lose mobility and adjust to the configurations(Du et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Longer evaporation time leads to formation of asymmetric structures with denser layer.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThickness of cross section of films.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" morerows=\"1\" nameend=\"c2\" namest=\"c1\" rowspan=\"2\"\u003e \u003cp\u003eEster\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eThickness\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026micro;m\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eCDA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e116\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e115.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eCL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e59.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eCP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e57.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e58\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e5.6. Atomic Force Microscopy (AFM)\u003c/h2\u003e \u003cp\u003eThe surface morphology and the roughness values of the cellulose ester films are listed in the table 6. The darker areas as observed are associated with depressions on the surface of the films and the lighter areas are the elevations. Surface morphology is characterised by root mean square (Sq), mean roughness (Sa) and the difference between high peaks and low valleys (Z). Observations from the AFM indicated nodular structure, the polymer-rich phase having less ability to deform and thus merge and cause nodular structure due to chain entanglements, while the polymer poor phase become the cavities/depressions(Zhang et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). These nodules are the influencing factor for the roughness of the surface. The effect of evaporation environment is depicted clearly by comparing the surface images and the surface roughness parameters.\u003c/p\u003e \u003cp\u003eThe average depression size concentration is larger over the area of the films dried in the vacuum oven as compared to the films dried in the conventional oven as seen in the CDA, CP and CL films. The membrane surface, that is the nodule size and distribution could be attributed to the evaporation conditions and environment. The literature reports, with the increase with the nodule size, the surface roughness of the membranes tend to increase(Khulbe et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). The influence of evaporation environment on the surface morphology of the films with average roughness lower and the concentration of the depression area is marginally higher with the vacuum dried samples.\u003c/p\u003e \u003cp\u003eHowever, no nodular structure is seen on the surface of CL films in both dried in the vacuum and the conventional oven. But in this case surface roughness cannot be in proportion to the nodule size, but the depression and the elevation regions could account for the surface roughness. CL on the other hand has a noticeable difference between the conventional oven dried sample and the vacuum dried sample, film surface indicates accumulated area of elevation and depressions. The regions elevation is significant in the vacuum dried film, the isolated nodules have distinct boundaries, and the interstitial regions can be clearly identified. It could be possible that polymer chains present in the interstitial regions are randomly distributed compared to polymer chains present in the nodules(Khulbe et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). Although, a couple of samples indicate circular concentration of peaks which attributed to the released air bubbles during the long drying process.\u003c/p\u003e\n\u003cp\u003eTable 5 AFM surface roughness values of the cellulose fatty chain esters.\u003c/p\u003e\n\u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\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\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eRMS roughness (Sq)(nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eMean roughness\u003c/p\u003e \u003cp\u003e(Sa)(nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003eMax Z range\u003c/p\u003e \u003cp\u003e(nm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDrying Method\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eVO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eVO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCDA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e76.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e82.40\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e43.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e123.24\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e31.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e37.19\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe method of drying the films under vacuum conditions and conventional oven conditions were found to be promising with increased evaporation rate, higher hydrophobicity. The vacuum drying created smoother surface with better hydrophobicity values and create denser films. These evaporation conditions indicate a blend of lamellar and finger like microstructure for better packing structure during drying. The thermal characterisation implied that cellulose films remain stable with similar degradation temperatures. AFM 3D image depicts the depth of the film morphology in context of the surface roughness. Considering our study, vacuum drying showed potential for making films smoother and denser with increased hydrophobicity.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eEthical Approval\u003c/h2\u003e\n\u003cp\u003eThe author declares no competing interests.\u003c/p\u003e\n\u003ch2\u003eFunding\u003c/h2\u003e\n\u003cp\u003eThis study was supported by ERDF and the Estonian Research Council via project RESTA 10.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by E.T., T.K., P.A., and H.K. The first draft of the manuscript was written by T.K, and all authors commented on previous versions of the manuscript. Literature research, the analysis, idea of the article, and revision was done by J.K., A.K., P.A, E.T., T.K.,R.L.,A.M., and H.K. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAlmasi H, Ghanbarzadeh B, Dehghannia J, et al (2015) Heterogeneous modification of softwoods cellulose nanofibers with oleic acid: Effect of reaction time and oleic acid concentration. Fibers and Polymers 16:1715\u0026ndash;1722. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s12221-015-4294-1\u003c/span\u003e\u003cspan address=\"10.1007/s12221-015-4294-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBalser K, Hoppe L, Eicher T, et al (2004) Cellulose Esters. In: Ullmann\u0026rsquo;s Encyclopedia of Industrial Chemistry. 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J Appl Polym Sci 86:3389\u0026ndash;3395. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/app.11344\u003c/span\u003e\u003cspan address=\"10.1002/app.11344\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"solvent casting, vacuum drying, [mTBNH][OAc], cellulose esters, polymer films, EIPS","lastPublishedDoi":"10.21203/rs.3.rs-4801036/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4801036/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCellulose, as a sustainable raw material, holds a promising future as a thermoplastic material. This work focused on fabricating cellulose ester thin films by using both controlled vacuum oven drying and conventional oven drying by the evaporation induced phase separation method (EIPS). A novel distillable ionic liquid (IL) 5-Methyl-1,5,7-triaza-bicyclo- [4.3.0]non-6-enium acetate [mTBNH][OAc]with high dissolving capability of cellulose along with dimethylsulfoxide (DMSO) as a co-solvent are used. The drying methods were compared to investigate their influence on the Cellulose ester films morphological and wettability properties. Based on the results, with increasing the drying rate in the vacuum oven the films have a smoother surface (with CP having 2.14nm RMS value) than the other samples, also indicating higher contact angles of 124 for CP under vacuum drying conditions with denser films.\u003c/p\u003e","manuscriptTitle":"Effect of controlled drying on the properties of cellulose ester films synthesized in Novel Ionic Liquid [mTBNH][OAc]","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-10-30 16:29:42","doi":"10.21203/rs.3.rs-4801036/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a74a5e01-9e62-4b96-a7c7-d52ef703ca9f","owner":[],"postedDate":"October 30th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-02-17T03:53:45+00:00","versionOfRecord":[],"versionCreatedAt":"2024-10-30 16:29:42","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4801036","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4801036","identity":"rs-4801036","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}