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Electrospun Nanofiber Mat of α-1,3-Glucan Butenoate and Its Surface Modification via Thiol-Ene Reaction

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(1)J. Fiber Sci. Technol., 77(5), 157-165 (2021) doi 10.2115/fiberst.2021-0015 ©2021 The Society of Fiber Science and Technology, Japan. 【Transaction】. Electrospun Nanofiber Mat of α-1,3-Glucan Butenoate and Its Surface Modification Thiol-Ene Reaction Yuki Hori*1, Yukiko Enomoto*1, Satoshi Kimura*1, and Tadahisa Iwata*1,# *1. Science of Polymeric Materials, Department of Biomaterial Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan. Abstract: α-1,3-glucan ester with carbon-carbon double bonds (C=C), namely, α-1,3-glucan butenoate (α13GB) was synthesized from 3-butenoic acid and trifluoroacetic anhydride. Nonwoven nanofiber mat was successfully prepared by electrospinning α13GB / HFIP solution. α13GB had many reactive vinyl groups in its ester groups that could attribute to thiol-ene reaction, making it possible to modify the nanofiber mat surface by one step chemical functionalization using thiol-ene reactions. The surface of nanofiber mat was modified with 1H ,1H ,2H ,2H -perfluorodecanethiol (PFD) or 3-mercapto-1,2-propanediol (MPD) via thiol-ene reactions. Attenuated total reflection-Fourier-transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) analyses revealed that the surface of the nanofiber mat was successfully modified with these thiol compounds. The water contact angle (WCA) of the surface of each nanofiber mat was measured to evaluate its wettability changes, and indicated the mat modified with PFD showed super-hydrophobicity (WCA>150̊). Furthermore, the morphology of nanofiber was successfully maintained even after modification by adjusting reaction time. (Received 15 February, 2021; Accepted 9 March, 2021). 1. Introduction. molded from polymer materials, except for films or fibers.. The development. consisting. of. numerous. renewable resource has been a necessity in the course. great interest due to its appealing properties such as. of. high porosity and large surface area. Several. for. plastic. mat. nanofibers (fiber diameter is within 1μm) has been of. demands. biomass. Nanofiber. from. increasing. of. establishment. of. sustainable and low-carbon society. The abundant. fabrication. natural. been. reported, and they are including drawing, template. polymers,. expected. as. polysaccharides. high. functional. have. for. nanofibers. have. been. plastic. synthesis, phase separation [7], and electrospinning [8].. materials. Esterification is the most efficient way to. Among these, electrospinning process has become the. give. good. most attractive because it is cost-effective and. polysaccharide. solubility. in. bio-based. methods. thermo-plasticity. organic. solvents. and. Among. applicable to a variety of polymer materials [9]. In. polysaccharide ester derivatives, α-1,3-glucan esters. [1‒5].. electrospinning method, there are so many spinning. have outstanding thermal properties (Tm of acetate =. parameters that play a key role in determining the. 338̊C, Tm of propionate = 294̊C, Tm of butylate = 266̊C). morphology of the electrospun fabrics, and many. and exhibit superior thermal stability to conventional. studies on the relationship between the spinning. petroleum. solutions. based. plastic,. PET. or. nylon. [6].. and. the. produced. morphology. were. Furthermore, thermal properties (Tm or Tg) and. reported [10]. Among parameters, the kind of solvent. mechanical properties can be controlled by varying. and polymer concentration of spinning solution are. the chain length of introduced ester groups. It is. thought to be the most important conditions.. expected to broaden the applications of α-1,3-glucan esters in many fields.. Electrospun nanofiber or nanofiber mat have been extensively expected to apply for medical fields.. Nanofiber mat is given as an example of products. Poly-lactic acid and polycaprolactone nanofiber was. # corresponding author: Tadahisa Iwata (E-mail: atiwata@g.ecc.u-tokyo.ac.jp Tel.: +81-3-5841-5266 Fax: +81-3-5841-1304). Journal of Fiber Science and Technology (JFST), Vol.77, No. 5 (2021). 157.

(2) tried to develop for use of artificial blood vessel.. point of preserving the morphology of nanofiber mats.. Polyvinylalcohol, collagen and hyaluronic acid were. Prior to use thiol-ene functionalization, C=C modified. formed to nanofiber for utilizing as cell scaffolds. It. polysaccharide ester should be prepared as raw. was also reported that complex nanofiber mat of. materials for nanofiber mat. In our previous research. chitosan and polyethylene oxide (PEO) exhibited good. on surface modifications of polysaccharide esters-. wound healing effects [11]. There are some reports on. derived films, it was revealed that α-1,3-glucan. making nanofiber mat from polysaccharide such as. butenoate (α13GB), which has C=C groups in its ester. cellulose [12], aliginate [13], and chitosan [14], however,. chains, exhibited high reactivity with thiol reagents. it is still challenging due to polysaccharide s poor. [21].. solubility in common organic solvent. A variety of. In the present research, we firstly attempted to. approaches have been conducted to improve the. investigate the varying morphology of electrospun. solubility, including the chemical modification of. α13GB fibres produced. hydroxyl groups of polysaccharides. However, to our. conditions :. best knowledge, there are very few reports on. (dichloromethane and HFIP), and controlled different. nanofiber or nanofiber mat made from polysaccharide. polymer concentration. The successfully obtained. esters. Polysaccharide esters show good solubility and. α13GB nanofiber mat was subsequently modified via. tunable. one step. thermal. or. mechanical. properties. as. mentioned above, so they are expected to be a new ideal material for nanofiber mat. Polysaccharide esters - derived. nanofiber. mats. could. broaden. use. of. chemical. from two. different kinds. modification. spinning. of. using. solvent. thiol-ene. reaction to adjust the surface wettability.. 2. Materials and methods. nanofiber mat s application, utilizing its high thermal 2.1 Materials. or mechanical properties. Surface modification on nanofiber mat can. α-1, 3-Glucan was synthesized using the method. provide additional functionality to the fabric by. described in the literature [22]. Trifluoroacetic. maximizing the effects of large surface area of. anhydride (TFAA), N,N'-azobisisobutyronitrile (AIBN),. nanofibers. For instances, functional nanofiber mat. 1H, 1H, 2H, 2H - perfluorodecanethiol. has the ability to chemically catch the particular. 3-mercapto-1,2-propanediol (MPD) were purchased. organic matters or ions in solutions and has gathered. from Wako Pure Chemicals (Tokyo, Japan). 3-Butenoic. much attention as absorbents or affinities [15].. acid was purchased from Aldrich, and all the other. Furthermore,. reagents were used as received from commercial. functional. nanofiber. mats. with. (PFD). controlled hydrophobicity, water absorption, and pH. suppliers without further purification.. regulation properties are of special interest for. 2.2 Synthesis of α-1, 3-glucan butenoate (α13GB). and. cosmetic, pharma, and biomedical fields [16]. Recently,. α-1, 3-glucan (500 mg) was added to a premixed. many studies on surface modification of fibers or. solution of TFAA (20 mL) and 3-butenoic acid (10 mL),. nanofiber. [17‒19].. and the solution was stirred at 50̊ C for 30 min. After. Approaches for surface modification are classified into. cooling to 25̊ C, the solution was poured into methanol. two types: one is coating or dipping processes, which. (1.5 L). The precipitate was filtered, washed with. create physical bonds between the coating materials. methanol, and dried in vacuo to produce α13GB (978.2. and the substrates, and the other is chemical grafting,. mg, 87% yield).. which forms covalent bonds between those two. 2.3 Electrospinning of α-1, 3-glucan butenoate. mats. have. been. reported. materials. The former approach has difficulty in terms. (α13GB). of durability due to peeling because the physical bond. Portions of the obtained α13GB was dissolved in. can be easily broken [20]. The latter approach. dichloromethane or hexafluoro-2-propanol (HFIP) in. requires many steps or complicated conditions for. concentration. chemical modification, so development of technically. Electrospinning was performed using a Esprayer ES-. simple, rapid, and modular method for covalent. 2000 (Fuence Co., Ltd) instrument. The applied. functionalization of nanofiber mat is highly needed.. voltage was 20 kV and the syringe pump feed rate. Herein we report a general one step chemical. was 20 µm/min. The diameter of syringe needle was. modification using thiol-ene reaction. One step. 0.51-0.82 mm. Nonwoven mat was collected on a. modification is very important from the perspective. square aluminium foil.. 158. of. 50,. Journal of Fiber Science and Technology (JFST), Vol.77, No. 5 (2021). 75,. 100,. 150. mg / ml..

(3) 2.4 Surface modification of nanofiber mat. 2.8 Contact angle measurements. α13GB nanofiber mat was cut into a square (1.0 cm. The static water contact angle of each modified. 1.0 cm) and soaked in 1-propanol containing 5 v/v %. nanofiber mat of α13GB was measured using a Drop. of each thiol compound (36 mol eq to repeat unit of. Master 500 system (Kyowa Interface Science Co., Ltd.,. glucan ester). The AIBN radical initiator was added,. Japan). Water (2.0 µL) was dropped onto three points. and the mixture was stirred at 60 ̊C for 10-30 min.. on the surface of each film, and the average contact. The nanofiber mat was then removed, washed in. angle was calculated.. ethanol for 24 h, and dried in vacuo.. 3. Results and Discussion. The C=C conversion was defined as the ratio of C =C groups that had reacted with the thiol to the total number of ester groups including both 3-butenoyl and 2-butenoyl groups calculated from film weight. 3.1 Syntheses of α13GB α-1,3-glucan was esterified with 3-butenoic acid using TFAA as solvent and a promoter, and α-1,3-. changes according to Equation 1:. glucan (1). butenoate. (α13GB). was. obtained.. The. characterization of α13GB was already conducted by NMR and GPC analyses in our previous paper [21]. In. Mthiol (g/mol) = molecular weight of the thiol compound. our previous research, β-1,3-glucan butenoate (β13GB). MGB (g/mol) = molecular weight of the repeating unit. was also synthesized and the thiol-ene reactivity of its. of α13GB. cast film was compared with. that. of. α13GB.. W (g) = weight of the modified nanofiber mat. Consequently, α13GB showed much higher reactivity. W (g) = weight of the unmodified nanofiber mat. with thiol compounds than β13GB. β13GB forms crosslink structures between C=C of the butenoyl. 2.5 Scanning electron microscopy (SEM). groups after esterification, while α13GB does not, and. The morphological investigations was conducted. this causes the discrepancy in thiol-ene modification. using an S-4800 (Hitachi, Japan). Prior to SEM imaging,. efficiency of these two butenoates [21]. Based on this. the samples were sputtered with platinum using an. results, α13GB was thought to be an ideal start. ion sputter E-1030 (Hitachi, Japan). The applied. material for preparing nanofiber mat by use of. voltage was 1.0 kV. SEM images were taken at. electrospinning. different magnifications: high (scale bar = 10µm) and. functionalization in this research.. low (scale bar = 20µm). Fiber morphology was. 3.2 Electrospinning of α13GB. and. subsequent. thiol - ene. determined directly from multiple SEM images of the. In the preparation of the spinning solutions, two. same sample to determine a representative view. The. solvents and different polymer concentrations were. fiber diameter was determined by calculating the. examined, in order to establish the satisfactory. average fiber diameter of 50 points in SEM image. spinning conditions for making nanofiber mat from. using image J.. α13GB. α13GB was resolved in dichloromethane or. 2.6 Attenuated. total. reflection-Fourier. transform. HFIP with concentration of 50, 75, 100, 150 mg/ml,. infrared spectroscopy (ATR-FTIR). respectively. A summary of the spinning performance. Fourier-transform infrared (FTIR) spectra were. of each polymer solution is given in Table 1, which. obtained using the ATR method on a Nicolet Magna. summarizes the formation of continuous beads or. 6700 spectrometer in the range 500-4000 cm ; the. fibers as a function of processing conditions. Two. resolution was 8 cm­1 and there were 128 scans. ZnSe. kinds of syringe needle were used in accordance with. was used as an ATR accessory.. the solution viscosity: 21 G (0.51 mm) was used for 50,. 2.7 Scanning electron microscopy-energy-dispersive. 75, 100 mg/ml solutions, and 18 G (0.82 mm), a larger. ­1. X-ray spectroscopy (SEM-EDX). one was used for spinning 150 mg/ml solution with. Elemental analyses were conducted using an S-. high viscosity in order to prevent the polymer. 4800 SEM-EDX system (Hitachi, Japan). Prior to. clogging in the needle tip. Fig. 1 shows the SEM. imaging, the samples were sputtered with an. images of the electrospun products and their. electron-conductive carbon layer using a VC-100 S/. morphology were observed.. VC-100 W carbon coater (Vacuum Device Co., Ltd., Japan). The applied voltage was 20 kV.. Bead structures were frequently observed in asspun products from dichloromethane solutions. Beads. Journal of Fiber Science and Technology (JFST), Vol.77, No. 5 (2021). 159.

(4) structures are sometimes observed when spinning. a possibility that only fibers could be obtained from. solutions with low polymer concentration [23]. The. dichloromethane solution with higher concentration.. existence of beads cause the mechanical property. However, the polymer solution with concentration of. deterioration in fiber mat, so it is very important to. higher than 200 mg/ml endowed very high viscosity,. prevent the beads forming. Only formless bead. causing the blocking in the syringe needle, and. structures were obtained by spinning 50 mg/ml. continuous spinning was not achieved. Fiber mat that. solution. Electrospun products from 75 and 100 mg/. consisted of only fibers was not obtained from α13GB /. ml solutions were tablet-like bead structures and their. dichloromethane solutions in these four different. size was ranged from 10 to 15 µm. The skin on the. concentrations. On the other hand, fibers were frequently. beads are porous and collapsed, probably due to the rapid removal of solvent from the interior, as the. observed in the as-spun products from α13GB / HFIP. similar structure was reported in the previous. solutions.. research [24,25]. In these three cases, polymer. obtained from 50 mg/ml, the amounts of fibers were. reached the collector without being fully stretched. increased. due to low viscosity of solutions, and as a result, the. concentration. The fiber mat that consisted of only. products were beads not fibers. Fibers were partially. fibers was obtained from 150 mg/ml, as shown in Fig.. observed in the electrospun products of 150 mg/ml.. 2. In this condition, the solution viscosity and the. By increasing the concentration from 100 mg/ml to. applied voltage were thought to be optical to make. 150 mg/ml, the polymer formed entanglement and. fiber.. the solution viscosity increased, resulting in that. 3.3 Surface modification of the nanofiber mat of. Although with. the. only. formless. increase. of. beads the. were. solution. α13GB. polymer was stretched in the spinning process without being torn off. Consequently, fibers were. The nanofiber mat of α13GB was modified with. partially observed between tablet-like beads. There is. PFD and MPD via thiol-ene reactions, following. Table 1 Solvent. Dichloromethane. HFIP. Experimental conditions and morphology of elecropspun α13GB.. Polymer concentration (mg/ml) 50 75 100 150 50 75 100 150. Flow rate (µl/min ). Voltage ( kV ). 20 20 20 20 20 20 20 20. 20 20 20 20 20 20 20 20. Needle diameter (mm) 0.51 0.51 0.51 0.82 0.51 0.51 0.51 0.82. As-spun fibres Formless beads 10 µm tablet-like beads 15 µm tablet-like beads Few fibers and beads Formless beads Fibers and beads Fibers and beads Only fibers. Fig. 1 SEM images of electrospun products of α13GB in different polymer concentration (50, 75, 100, and 150 mg/ml) and two kinds of solvent (dichloromethane and HFIP).. 160. Journal of Fiber Science and Technology (JFST), Vol.77, No. 5 (2021).

(5) Scheme 1. PFD is a thiol compound with fluorinated alkyl chains, and is used for creating hydrophobic surfaces. MPD has two hydroxyl groups per molecule and is used as a hydrophilic reagent. The reaction time was controlled from 10 min to 30 min to investigate the morphology changes depending on the extent of surface modification. The appearance of the nanofiber mat did not change after reacted with PFD for 10-20 min. The mat shrunk after reacted with PFD for 30 min. On the other hand, the MPD-modified. Fig. 2 Image of α13GB nanofiber mat prepared by electrospinning 150 mg/ml HFIP solution.. nanofiber mat lost fiber textures and turned solid filmlike materials. The extent of C=C conversion was. Scheme 1 Surface modification of α13GB nanofiber mat via thiol-ene reactions with two different thiol compounds (1H ,1H ,2H ,2H ,-perfluorodecanethiol (PFD) and 3-mercapto-1,2-propanediol (MPD)). Table 2. Conversion (%) WCA ( ̊ ). Conversion (%) WCA ( ̊ ). Characterization of surface modified α13GB nanofiber mat.. Nanofiber mat. PFD-modified (10 min). PFD-modified (20 min). PFD-modified (30 min). − 130±2.0. 2.8 151±2.5. − 155±3.0. 18.3 150±4.9. Nanofiber mat. MPD-modified (10 min). MPD-modified (20 min). MPD-modified (30 min). − 130±2.0. 14.9 −. 6.9 −. 60.2 52±12. Fig. 3 SEM images of α13GB nanofiber mat prepared by electrospinning 150 mg/ml HFIP solution, unmodified or modified with PFD (10 min, 20 min, 30 min) and MPD (30 min).. Journal of Fiber Science and Technology (JFST), Vol.77, No. 5 (2021). 161.

(6) calculated by determining the changes in the weights. the nanofiber s characteristic morphology. Therefore,. of the fiber mat before and after modification, as listed. it is significant that the nanofiber morphology is. in Table 2. This value is a direct indication of the. preserved during surface modification process. The. number of C=C groups that have reacted with the. morphology changes of the modified nanofiber mats. thiol compounds. Blank spaces in Table 2 signify that. were investigated by using a scanning electron. a part of mat was lost in the modification and washing. microscopy (SEM). Fig. 3 shows the SEM images of. process, and the correct weight changes were not. unmodified nanofiber mat and modified ones with. measured. The values for the extent of conversion of. PFD-10 min, 20 min, 30 min, and MPD-30 min. It was. α13GB nanofiber mat with PFD-10 min, PFD-30 min,. revealed that PFD-10 min and 20 min modified mat. MPD-10 min, MPD-20 min, and MPD-30 min were. maintained the fiber morphologies, although the fiber. 2.8 %, 18.3 %, 14.9 %, 6.9 %, and 60.2 %, respectively.. diameter became a little larger. Fig. 4 shows the fiber. MPD showed higher reactivity with C=C groups than. diameter change of the nanofiber mat before and after. PFD, which can be explained by the steric hindrance. modified with PFD. The average fiber diameter of the. of thiol groups, as referred in our previous research. unmodified mat and one modified with PFD for 20. on film surface modifications [21].. min was 190 nm and 370 nm, respectively. The. 3.4 Morphology changes of the modified nanofiber. modified fiber s average diameter was about twice. mats. larger than that of unmodified nanofiber mat,. The application of nanofiber mats is strongly. indicating there was a layer of fluoro-alkyl chains on. depended on its large surface area originated from. surface of the nanofiber. The morphology changed. Fig. 4 The fiber diameter distribution of α13GB nanofiber mat prepared by electrospinning 150 mg/ml HFIP solution, (a) unmodified and (b) modified with PFD (20 min).. Fig. 5 Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) spectra of α13GB nanofiber mat, unmodified or modified with PFD and MPD. 162. Journal of Fiber Science and Technology (JFST), Vol.77, No. 5 (2021).

(7) dramatically after PFD-30 min treatment, and fibers. PFD- and MPD-modified nanofiber mat. Red dots. adhered with other fibers, forming a micro-scale web-. were visible on all of the modified nanofiber mat,. like materials as shown in Fig. 3. MPD-30 min. despite extensive rinsing and drying, indicating that. modification converted the fiber mat to film-like. the C=C groups had reacted successfully with the. morphology, probably owing to the high conversion. thiol compounds. PFD-10 min and 20 min modified. value (60.2%), resulting in the adhesion between fibers.. mat were covered with fewer red dots than PFD-30. 3.5 FTIR analyses of the modified nanofiber mat. min modified one. There were markedly more red. Unmodified α13GB nanofiber mat, the PFD- and. dots on the MPD-30 min modified mat than all of PFD-. MPD-modified nanofiber mats were characterized by. modified ones. The conversion rates of the PFD-10, 30. ATR-FTIR, as shown in Fig. 5. MPD-10 min and 20. min and MPD-30 min modified films were 2.8 %,. min modified mat warped after modification and lost. 18.3 %, and 60.2 %, respectively, and the color depth is. the plain surface, so no IR data was obtained. The. a visual indication of this conversion. The results are. peaks at 922, 1680, and 3020 cm. ­1. were assigned to. δ (-C=CH-), ν (-C=C-), and ν (=CH), respectively, for α13GB nanofiber mat. Successful modification by thiol-. consistent with those of the FTIR analyses. 3.7 Water contact angles (WCAs) of the modified nanofiber mats. ene reaction was confirmed by the decrease of these. The wettability changes of the surface of the. vinyl peaks. As shown in Fig. 5, evident decrease of all. modified mats were investigated by determining the. these vinyl peaks was not detected after modification. water contact angles (WCAs); the WCA values are. with PFD for 10 min and 20 min. The peak intensities. listed in Table 2 and the corresponding images are. of. of. shown in Fig. 7. The WCAs of the unmodified α13GB. PFD-30 min modified mat, indicating that a number of. nanofiber mat was 130̊, showing high hydrophobicity,. C=C groups on the surface reacted with this thiol. owing to the surface roughness of nanofiber mat and. compound. The newly advanced peak at 1213 cm­1. this could generally be explained by Cassie theory.. that assigned to ν (CF) also supported the covalent. The WCAs of the hydrophobic PFD-10 min, 20 min,. attachment of PFD reagent. In the spectrum of. and 30 min modified nanofiber mat were 151̊, 155̊,. MPD-30 min modified mat the evident decrease of. and 150̊, respectively. Regardless of reaction time, all. three vinyl peaks and the advance of a peak at 3075-. of them were higher than 150̊, demonstrating super-. that assigned to ν (OH) were observed,. hydrophobicity. In our previous research on film s. the. 3575 cm. olefins. ­1. decreased. in. the. spectrum. indicating successful modification by MPD.. surface modification [21], the achievable maximum. 3.6 Elemental analysis of the nanofiber mat. WCA was 133̊ and super-hydrophobicity was not. Fig. 6 shows scanning electron microscopy-. realized due to film s smooth surface morphologies.. energy-dispersive X-ray spectrometry (SEM-EDX). Unlike the case of film, in this result, both nanofiber. images revealing the distribution of S atoms in the. mat s nanostructure originated from nano-scale fiber. Fig. 6 SEM-energy dispersive X-ray spectroscopy (SEM-EDX) images of α13GB nanofiber mat, unmodified or modified with PFD (10 min, 20 min, 30 min) and MPD (30 min).. Journal of Fiber Science and Technology (JFST), Vol.77, No. 5 (2021). 163.

(8) Fig. 7 Water contact angles on surfaces of α13GB nanofiber mat, unmodified or modified with PFD (10 min, 20 min, 30 min) and MPD (30 min). and the decrease of surface energy caused by. by. introduction of fluorinated alkyl chains attributed the. nanostructure and low surface energy caused by the. super - hydrophobicity.. calculated. introduction of fluoro-alkyl layer. The MPD-modified. conversion value (18.3 %) for PFD-30 min modified. mat showed hydrophilicity. The present study. mat was higher than that of PFD-10 min (2.8 %), the. demonstrated the successful preparation of surface. WCA was almost the same. This is probably because. tunable nanofiber mat from α13GB and control of the. the extent of surface roughness decreased due to the. wettability by one step thiol-ene functionalization.. Although. the. both. the. morphological change, from nano-scale to micro-scale. preservation. of. nanofiber. mat s. References. structure, as observed in Fig. 3. It is noteworthy that the WCAs on the PFD-10 min and 20 min modified mat were fully improved while they successfully maintained its nanofiber morphology. This results suggests 10 min was sufficient to make superhydrophobic surface with PFD. The WCA of the. 1. L. Crépy, V. Miri, N. Joly, P. Martin, and J. Lefebvre, Carbohydr. Polym., 83, 1812 (2011). 2. Y. Enomoto-Rogers, Y. Ohmomo, and T. Iwata, Carbohydr. Polym. 92, 1827 (2013).. MPD-30 min modified mat was 52̊, demonstrating. 3. N. G. V. Fundador, Y. Enomoto-Rogers, A.. hydrophilicity resulting from the introduced hydroxyl. Takemura, and T. Iwata, Polymer (Guildf)., 53,. groups. The wettability of the α13GB nanofiber mat was successfully adjusted from hydrophilicity to super-hydrophobicity by attachment of the functional groups via the thiol-ene reaction.. 4. Conclusions. 3885 (2012). 4. T. Danjo, Y. Enomoto-Rogers, A. Takemura, and T. Iwata, Polym. Degrad. Stab., 109, 373 (2014). 5. H. Gan, Y. Enomoto, T. Kabe, D. Ishii, T. Hikima, M. Takata, and T. Iwata, Polym. Degrad. Stab., 145, 142 (2017). 6. S. Puanglek, S. Kimura, and T. Iwata, Carbohydr.. The aim of this study was to prepare the nanofiber mat from α13GB by use of electrospinning and modify its surface via thiol-ene reaction. The nanofiber mat that consisted of only nanofibers was successfully obtained by electrospinning 150 mg/ml HFIP solution. The obtained nanofiber mat was subsequently functionalized by attaching fluoro-alkyl chains or hydroxyl groups to its surface via thiol-ene reaction. The nanofiber morphology was successfully preserved even after surface modification process by adjusting the reaction time. The WCAs on the PFDmodified nanofiber mat were higher than 150̊, displaying super-hydrophobicity, which was achieved. 164. Polym., 169, 245 (2017). 7. P. X. Ma, R. Zhang, and J. Biomed. Mater. Res., 46, 60 (1999). 8. D. H. Reneker and I. Chun, Nanotechnology., 7, 216 (1996). 9. K. Y. Lee, L. Jeong, Y. O. Kang, S. J. Lee, and W. H. Park, Adv. Drug Deliv. Rev., 61, 1020 (2009). 10. B. Ghorani, S. J. Russell, and P. Goswami, Int. J. Polym. Sci., 2013, 256161 (2013). 11. K. Sakurai, Y. Kishida, and T. Sasaki, Chitin and Chitosan Research., 18, 3 (2012). 12. C. W. Kim, D. S. Kim, S. Y. Kang, M. Marquez, and Y. L. Joo, Polymer (Guildf)., 47, 5097 (2006).. Journal of Fiber Science and Technology (JFST), Vol.77, No. 5 (2021).

(9) 13. J. W. Lu, Y. L. Zhu, Z. X. Guo, P. Hu, and J. Yu, Polymer (Guildf)., 47, 8026 (2006). 14. Y. Zhou, D. Yang, X. Chen, Q. Xu, F. Lu, and J. Nie, Biomacromolecules., 9, 349 (2008). 15. M. Miyauchi, J. Miao, and T. J. Simmons, J. Chromatogr. Sep. Tech., 2, 1000110 (2011). 16. Y. Dan, M. Buzhor, D. Raichman, E. Menashe, O. Rachmani, and E. Amir, J. Appl. Polym. Sci., 138, 1 (2021).. 20. B. Deng, R. Cai, Y. Yu, H. Jiang, C. Wang, J. Li, L. Li, M. Yu, J. Li, L. Xie, Q. Huang, and C. Fan, Adv. Mater., 22, 5473 (2010). 21. Y. Hori, Y. Enomoto, S. Kimura, and T. Iwata, Polym. Int., doi:10.1002/pi.6157 (2020). 22. S. Puanglek, S. Kimura, Y. Enomoto-Rogers, T. Kabe, M. Yoshida, M. Wada, and T. Iwata, Sci. Rep., 6, 1 (2016). 23. H. Fong, I. Chun, and D. H. Reneker, Polymer. 17. W. W. Gao, G.X. Zhang, and F. X. Zhang, Cellulose., 22, 2787 (2015).. (Guildf)., 40, 4585 (1999). 24. P. Bébin and R. E. Prud Homme, J. Polym. Sci. Part. 18. J. Zhao, Q. Shi, S. Luan, L. Song, H. Yang, H. Shi, J. Jin, X. Li, J. Yin, and P. Stagnaro, J. Memb. Sci., 369, 5 (2011).. B Polym. Phys., 39, 2363 (2001). 25. A. Celebioglu and T. Uyar, Mater. Lett., 65, 2291 (2011).. 19. C. Zhou, Z. Chen, H. Yang, K. Hou, X. Zeng, Y. Zheng, and J. Cheng, ACS Appl. Mater. Interfaces., 9, 9184 (2017).. Journal of Fiber Science and Technology (JFST), Vol.77, No. 5 (2021). 165.

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Fig. 1 SEM images of electrospun products of α 13 GB in different polymer concentration (50, 75, 100, and 150 mg/ml) and two kinds of solvent (dichloromethane and HFIP).
Fig. 3 SEM images of α 13 GB nanofiber mat prepared by electrospinning 150 mg/ml HFIP solution, unmodified or modified with PFD (10 min, 20 min, 30 min) and MPD (30 min).
Fig. 4 The fiber diameter distribution of α 13 GB nanofiber mat prepared by electrospinning 150 mg/ml HFIP solution, (a) unmodified and (b) modified with PFD (20 min).
Fig. 6 shows scanning electron microscopy- microscopy-energy-dispersive X-ray spectrometry (SEM-EDX) images revealing the distribution of S atoms in the
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In the specific case of the α -stable branching process conditioned to be never extinct, we get that its genealogy is given, up to a random time change, by a Beta(2 − α, α −

Because of this property, it is only necessary to calculate a small range of cohomology groups, namely the even dimension and the odd dimension of cohomology groups, in order

In this paper the classes of groups we will be interested in are the following three: groups of the form F k o α Z for F k a free group of finite rank k and α an automorphism of F k

proof of uniqueness divides itself into two parts, the first of which is the determination of a limit solution whose integral difference from both given solutions may be estimated

Showing the compactness of Poincar´e operator and using a new generalized Gronwall’s inequality with impulse, mixed type integral operators and B-norm given by us, we

In our model we take into account only diffusion and velocity of chemical reaction near the surface of the crystal and suggest applying non-linear reaction-diffusion equation with