Accepted Manuscript Title: Combined effects of raw materials and solvent systems on the preparation and properties of regenerated cellulose fibers Author: Jinghuan Chen Ying Guan Kun Wang Xueming Zhang Feng Xu Runcang Sun PII: DOI: Reference:

S0144-8617(15)00336-7 http://dx.doi.org/doi:10.1016/j.carbpol.2015.04.027 CARP 9858

To appear in: Received date: Revised date: Accepted date:

4-2-2015 11-3-2015 7-4-2015

Please cite this article as: Chen, J., Guan, Y., Wang, K., Zhang, X., Xu, F., and Sun, R.,Combined effects of raw materials and solvent systems on the preparation and properties of regenerated cellulose fibers, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.04.027 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Combined effects of raw materials and solvent systems on the

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preparation and properties of regenerated cellulose fibers

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Jinghuan Chen, Ying Guan, Kun Wang*, Xueming Zhang, Feng Xu, Runcang Sun*

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Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing 100083,

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China

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AB S TRAC T

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To investigate the combined effects of materials and solvents on the preparation, structural

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and mechanical properties of regenerated cellulose fibers, four cellulosic materials

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(microcrystalline cellulose, cotton linter pulp, bamboo pulp and bleached softwood sulfite

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dissolving pulp) and six non-derivative solvents (NaOH/urea aqueous solution,

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N,N-dimethylacetamide/lithium chloride, N-methyl-morpholine-N-oxide,

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1-butyl-3-methylimidazolium Chloride, 1-allyl-3-methylimidazolium chloride and

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1-ethyl-3-methylimidazolium acetate) were used to prepare fibers with wet spinning

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method. The results showed that the dissolvability of solvent was the determining factor in

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cellulose dissolution, and the dissolving time was influenced by the raw materials’

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properties, such as molecular weight, exposed area and hemicellulose content. The

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crystallinity and elongation at break of the fibers were almost fixed and not affected by the

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materials and solvents. However, the tensile strength of the fibers was directly

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proportional to the molecular weight of the raw materials, and varied with the type of

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solvents through cellulose degradation.

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Keywords: raw material; cellulose solvents; combined effect; regenerated fiber.

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* Corresponding author, Tel. /fax: +861062336903.

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E-mail address: [email protected] (K. Wang), [email protected] (R. Sun).

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1. Introduction

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Cellulose is considered to be the most abundant renewable polymer on the planet, and has attracted much attention because of its outstanding properties, such as biocompatibility, biodegradability, thermal and chemical stability (Tsioptsias, Stefopoulos,

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Kokkinomalis, Papadopoulou, & Panayiotou, 2008). This natural polymer is a linear polysaccharide consisting of β-(1→4)-linked glucose repeating units, and has been extensively used in industries, such as papers, textiles, foods, coatings, etc. (Edgar et al., 2001). However, cellulose is insoluble in water and common organic solvents due to the presence of extensive intra- and intermolecular

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hydrogen bonding (Pinkert, Marsh & Pang, 2010).

A well-known method of cellulose dissolution is the viscose process, which is the most popular technique for producing regenerated

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cellulose fibers. In this process, a prior chemical modification of the macromolecule is needed, leading to the serious environmental pollution and poor health of the human body. Therefore, more environmentally acceptable non-derivative solvent systems have been developed, including N,N-dimethylacetamide/lithium chloride (DMAc/LiCl) (El-Kafrawy, 1982), N-methyl-morpholine-N-oxide

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(NMMO) (Fink, Weigel, Purz, & Ganster, 2001), ionic liquids (Swatloski, Spear, Holbrey, & Rogers, 2002), aqueous alkali solutions (Isogai & Atalla, 1998; Zhou & Zhang, 2000) , etc. DMAc/LiCl could dissolve cellulose with high molecular weight (>106 Da) at the ambient temperature without noticeable degradation (Matsumoto, Tatsumi, Tamai, & Takaki, 2001), and was employed to prepare regenerated cellulose fibers using water as coagulant (Bianchi, Ciferri, Conio & Tealdi, 1989). NMMO has been considered as the superior cellulose solvent among the amine oxides, and was successfully used for the production of man-made cellulose fibers with the

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generic name of Lyocell (Gao, Shen, & Lu, 2011). The Lyocell process is more desirable than the viscose process since it involves less

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hazardous byproduct formation and higher recovery of solvent (> 99%). Ionic liquids are composed of an organic cation and an inorganic anion with non-volatility and high thermal stability, and have been suggested as the attractive and promising cellulose

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solvents. Some imidazolium-based ionic liquids, such as 1-butyl-3-methylimidazolium chloride ([Bmim]Cl), 1-ethyl-3-methylimidazolium acetate ([Emim]Ac) and 1-allul-3-methylimidazolium chloride ([Amim]Cl), were reported to dissolve cellulose at rather high concentrations (Swatloski et al., 2002). Based on the spinning technology of Lyocell fibers, the regenerated

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cellulose fibers with high tenacity were prepared with ionic liquids (Cai, Zhang, Guo, Shao, & Hu, 2010). Furthermore, the aqueous alkali solutions, such as NaOH/urea (Zhang, Wu, Zhang, & He, 2005), NaOH/thiourea (Ruan, Zhang, Zhou, Jin, & Chen, 2004) and

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LiOH/urea (Cai & Zhang, 2005) have been considered as the economical and eco-friendly solvents, which can rapidly dissolve cellulose in a few minutes. Regenerated cellulose fibers from these systems have been successfully prepared in laboratory and preliminary pilot scale (Li et al., 2010; Wang, Zhang, Zhang, Li, Yu, & Lin, 2013).

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Commonly, the raw materials used for regenerated cellulose fiber product were cotton linter pulp and dissolving wood pulp (Zhang et al., 2013; Olsson & Westman, 2013). However, other regenerated fibers had also been successfully prepared from other materials, such as microcrystalline cellulose (MCC) using [Amim]Cl as solvent (Kim & Jang, 2013), bamboo pulp and sugar cane straw using NMMO as solvent (Yang, Zhang, Shao, & Hu, 2009; Costa, Mazzola, Silva, Pahl, Pessoa, & Costa, 2013). It was reported that the property of the pulps played an important role on the dissolution of cellulose in alkaline solvent systems (Kihlman, Aldaeus, Chedid,

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& Germgard, 2012), and the degree of polymerization of the raw material is crucial to the mechanical properties of the regenerated

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cellulose fibers spun from [Amim]Cl (Kim & Jang, 2013). Meanwhile, the crystal structure, fibrillation behaviors, micromorphology and intensity of the regenerated cellulose fibers were influenced by the solvent systems and technological processes (Jiang et al., 2012a;

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Ingildeev, Effenberger, Bredereck, & Hermanutz, 2013). Therefore, the dissolving process and the structural mechanical properties of the regenerated fibers were significantly affected by the properties of both solvents and raw materials. However, to our knowledge, the combined effect of materials and solvents on the properties of the regenerated fibers was rarely reported. In this study, four cellulosic

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materials and six direct solvents were used to produce the regenerated cellulose fibers by wet spinning method with the fixed cellulose concentration. The solubility of raw materials in solvents, the crystal and microscopic structure as well as the tensile properties of the

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obtained fibers were investigated and comparably discussed. The main purpose of this study was to reveal the combined effect of materials and solvents on the dissolution and regeneration of cellulose to promote the development of regenerated cellulose fibers.

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2. Materials and Methods 2.1. Raw materials

Cotton linter pulp (CP) was acquired from Hubei Chemical Fiber Co. Ltd. (Hubei Province, China). Bamboo pulp (BP) was obtained after delignification with sodium chlorite and alkaline treatment with 25% potassium hydroxide from bamboo. Microcrystalline cellulose (MCC) with a DP of 210-240 was purchased from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China).

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Bleached softwood sulfite dissolving pulp (SP) was kindly provided by CHTC Helon Co., LTD. (Shandong Province, China). All

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these raw materials were oven-dried at 60 °C for 12 h and kept in desiccators until used. Other chemicals and reagents were of

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analytical grade and used without further purification.

2.2. Dissolution and preparation of the regenerated fibers

Six different cellulose direct solvents, i.e., NaOH/urea/water, DMAc/LiCl, NMMO, [Bmim]Cl, [Amim]Cl and [Emim]Ac, were

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employed to dissolve the above cellulosic materials. The scheme for preparation of regenerated cellulose fibers was shown in Fig. 1, and the detailed conditions for the dissolution and regeneration process were described below.

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2.2.1. NaOH/urea aqueous solution

NaOH/urea (7/12, wt. %) aqueous solution was prepared and pre-cooled to -12.6 °C according to a previous paper (Qi, Chang, & Zhang, 2008). The cellulosic materials in a desired amount were added into the solvent with stirring at 1500 rpm for 5 minutes to form

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a 4 wt. % transparent cellulose dope. The dope was then subjected to centrifugation at 8000 rpm for 10 min at 10 °C for degasification and removal of the undissolved parts. The supernatant liquor was transferred to a syringe and extruded through a needle with a diameter of 0.21 mm into a coagulation bath consisting of 15 wt. % H2SO4 and 10 wt. % Na2SO4 at room temperature to form regenerated cellulose fibers. Then, the fibers were collected onto a spool without any drafting, and washed with deionized water at room temperature until neutral before air-dried.

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2.2.2. NMMO and ionic liquids ([Bmim]Cl, [Amim]Cl, [Emim]Cl)

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NMMO monohydrate, [Bmim]Cl, [Amim]Cl or [Emim]Cl was firstly heated at 110 °C until completely melted. The cellulosic materials were added to the molten solvents with a fast energetic stirring to obtain transparent cellulose dope with a cellulose

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concentration of 4 wt. %. After ultrasonic and vacuum degassing, the cellulose solutions were transferred to a syringe and extruded through a needle with a diameter of 0.21 mm into a water bath at 80 °C. The regenerated fibers were collected by a spool, washed several times with deionized water at room temperature before air-dried.

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2.2.3. LiCl/DMAc system

Cellulosic material was mixed with DMAc and vacuum evaporated at 60°C for 0.5 h to remove the moisture in the materials and

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solvents. Then the materials were activated by stirring the above mixture at 160 °C for 3 h. After cooling down to 100 °C, LiCl (8 wt. %, based on the solvent) was added with an additional hour stirring. Transparent cellulose solution with concentration of 4 wt. % was obtained after further agitation at room temperature for 12 h. Regenerated fibers were prepared by adopting the above method

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described in 2.2.2.

2.3. Analytical methods

The monosaccharides of the raw materials, which were hydrolyzed with 72% H2SO4 at 30 °C for 1 h and followed by 2.5% H2SO4 at 121 °C for another hour to obtain monosaccharides, were analyzed by high-performance anion-exchange chromatography (HPAEC)

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(Dionex, ISC 3000, US) system as described in a previous literature (Wang, Jiang, Xu, & Sun, 2009). The weight-average (Mw) and

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number-average (Mn) molecular weight of the cellulosic materials and regenerated fibers were determined by gel permeation chromatography (GPC) (Agilent 1200 series, US). Before the analysis conducted, the materials needed to be esterified by isocyanates

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and dissolved in tetrahydrofuran (THF).

The dissolution of raw materials in different solvents was observed with an optical microscope. The crystalline structure of the cellulosic materials and regenerated fibers were measured by an X-ray diffraction on XRD-6000 instrument (Shimadzu, Japan) with a

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scattering angle from 5° to 35° 2 θ at a scanning speed of 2°/min. The crystallinity index (CrI) was calculated from the intensity of the peak corresponding to (002) lattice plane (I002) and the minimum between 110 and 002 lattice planes (Iam) as follows: I 002  I am  100 I 002

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Cr I (%) 

The morphology of the regenerated cellulose fibers was observed by scanning electron microscopy (SEM) (S-3400N, HITACHI, Japan) at acceleration voltages of 5 KV after being fractured in liquid nitrogen and sputtered with gold-palladium in a sputter coater

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(E-1010, HITACHI, Japan) .

Mechanical properties of the regenerated fibers were measured on a universal tensile tester (UTM6503, Shenzhen Suns Technology stock CO. LTD. China) according to ASTM D2256-80. The fiber samples were preconditioned for 24 h at 20 °C and 65% relative humidity (RH), and tested with 20 mm gauge length at a speed of 5.0 mm/min.

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3. Results and Discussion

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3.1. Dissolution of cellulosic materials in different solvents

As known, complete dissolving of cellulosic materials in solvents is of the fundamental importance for the spinning process. In this

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study, all the cellulosic materials could be completely dissolved in most solvents except that BP and SP were just swelled in NaOH/urea aqueous solution as shown in Fig. 2. Since it had been demonstrated that only cellulose with a viscosity-average molecular weight below 10.0 × 104 Da could be completely dissolved in NaOH/urea aqueous solution (Qi et al., 2008), the incomplete dissolution

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of BP and SP was probably related to their high Mw value which was listed in Table 1. In addition, SP was easier be swelled in NaOH/urea aqueous solution than BP, although its Mw value was higher than that of BP. From Fig. 2, balloons with a beaded structure

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could be clearly observed in SP fibers, and more insoluble substances were observed in BP. Moreover, SP could be dissolved rapidly in most solvents, while BP needed longer dissolving time (Table 1), suggesting that the Mw value was not the only factor affecting the solubility of materials. The SEM images of the four raw materials are available as Supplementary data. Unlike the small and uniform

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size of MCC as well as the isolated fibers of CP and SP, visible fibril aggregations were observed in BP. This agglomeration was also reflected in the GPC analysis, showed in Supplementary data, in which the molar mass distribution of BP showed a shoulder in the high-molar mass region. These aggregations decreased the accessibility of the solvents, which has been considered as an important factor in the dissolution process (Trygg & Fardim, 2011). The fibrils were linked together by hydrogen bonds between cellulose chains as well as cellulose and hemicelluloses. According to the sugar components summarized in Table 1, the weight percent of xylose,

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relating to the content of hemicelluloses, was significantly higher in BP than other materials. It has been reported that hemicelluloses

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were linked with cellulose by hydrogen bonds which hindered the release of cellulose during dissolution (Moigne & Navard, 2010). The crystallinity of cellulose was also considered to be a critical factor, as high crystallinity could prevent the solvents permeating into

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the cellulose structure by the compact arrangement of cellulose molecular chain and low free energy (Isogai & Atalla, 1998). However, this conclusion was not fully supported by the data in current study, since the crystallinity of BP was the lowest among the four materials (Table 2).

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On the other hand, the dissolvability of the solvents also played an important role in the process of dissolving cellulose. In NaOH/urea aqueous solution, MCC and CP could be dissolved within several minutes at low temperature while BP and SP were

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unsolvable, revealing the limitation of its dissolvability. In the dissolving process, hydroxyl ion plays an important role by forming hydrogen bonding with cellulose, and urea stabilizes the alkali-swollen cellulose molecules by accumulating on the hydrophobic surface (Isobe, Noguchi, Nishiyama, Kimura, Wada, & Kuga, 2013). All the raw materials could be completely dissolved in

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DMAc/LiCl due to its excellent dissolvability. The intermolecular hydrogen bonding networks of cellulose can be broken by the strong hydrogen bonds between the hydroxyl protons of cellulose and the Cl- ions, and homogeneous solution is formed due to the dispersion of cellulose chains in the molecular level (Zhang, Liu, Xiang, Kang, Liu, & Huang, 2014). This solvent has been employed as a suitable eluent to determine the molecular mass distribution of cellulosic substrates by size exclusion chromatography (SEC) (Schelosky, Roeder, & Baldinger, 1999). However, an activation procedure of starting material is required prior to dissolving, and the

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dissolution time, about 16 hours, is much longer than other solvents. Compared to DMAc/LiCl, NMMO and ionic liquids (ILs) are

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more effective. The highly polar N-O group of NMMO was proposed to disrupt the intra- and inter- molecular hydrogen bonding of cellulose and form new hydrogen bonding network with cellulose molecules, leading to the dissolution of cellulose. In this study, all

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the cellulosic materials were completely dissolved within 4 hours in NMMO, indicating the excellent dissolvability of this solvent. For ILs, a much shorter time, less than two hours, was required, that is probably due to the high polarity of the ions in ILs. The anion tends to form hydrogen bonds with the hydrogen atoms of cellulose and the cation prefers to associate with the oxygen atoms of cellulose

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(Zhang, Zhang, Wu, Zhang, He, & Xiang, 2010). Among the selected ILs, [Emim]Ac is the most effective solvent for all materials, which might be attributed to the shorter alkyl chain by enhancing the connection with cellulose (Zhao, Liu, Wang, & Zhang, 2012;

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Zavrel, Bross, Funke, Buchs, & Spiess, 2009). Based on the above analysis, it could be concluded that the molecular weight and degree of exposure of raw materials, as well as the accessibility and dissolvability of the solvents have an important effect on the

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dissolution of cellulose.

3.2. Crystal and morphological structure of the fibers The crystal features of the regenerated cellulose fibers were examined by powder X-ray diffraction and compared with the raw materials. The XRD patterns of the cellulosic materials and the regenerated fibers are shown in Fig. 3. The raw materials have typical —

cellulose I diffraction angles around 15.4º, 16.2º and 22.4º, corresponding to the diffraction planes 110, 110, 020, respectively. This

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indicated that the delignification and fractional pretreatment of BP did not changed its crystal type. After being dissolved in solvents

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and regenerated in coagulating bath, all materials changed to a cellulose II crystal type with a broad peak around 21.0º and/or a weak

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peak around 12.5º. Additionally, the crystallinity index (CrI) of the raw materials was in the range of 50 - 60%, while the CrI of the regenerated fibers was decreased to an average value of 41.87% with a standard deviation of 1.74% (Table 2). The probable explanation on the uniform CrI value was that all the regenerated cellulose fibers were prepared from the same spinning concentration, orifice diameter and spinner method, as the crystallinity of regenerated fibers was highly depended on the spinning parameters (Wang

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et al., 2013; Jiang et al., 2012b). Consequently, it could be concluded that the crystalline structure of raw materials and the types of solvents have weak influence on the crystal form and crystallinity of the obtained regenerated fibers. According to the above

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discussion, the dissolution and regeneration process of cellulose could be described in a molecule level as that: the cellulose molecular chains in the raw materials were separated by the non-derivative solvents due to the breakage of intermolecular hydrogen bonds, leading to the breaking down the original crystal structure (cellulose I); and during the regeneration process, cellulose molecular chains

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were bonded again in cellulose II crystal type upon the deprivation of solvents in coagulating bath, and the degree of the re-bonding process was closely related to the spinning speed. The morphological structure of the regenerated cellulose fibers prepared from different materials and solvents are shown in Fig. 4. Due to the rapid precipitation of cellulose without any chemical reaction, the cross-sections of all the regenerated fibers were approximately round with a diameter of about 70 μm, which were markedly different from the lobulated shape of the viscose rayon.

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The internal composition of all the fibers were dense and homogeneous, and no visible skin-core structure was observed. This

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morphology was formed during the coagulation stage as a result of the phase separation process, and seemingly not depended on the

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properties of raw materials and solvents.

3.3. Mechanical properties of the fibers

The mechanical properties of the regenerated cellulose fibers prepared from different cellulosic materials and solvents were tested

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on a universal tensile tester. The tensile strength and elongation at the break of these fibers were evaluated from the stress-strain curves and summarized in Table 3. It is clear that the average tensile strength for fibers is in the same order as the Mw values of the cellulosic

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materials, indicating that the tensile strength of the fibers was intimately related with the molecular weight of raw materials. Higher Mw usually leads to higher tensile strength since longer molecular chains could be entangled and withstand the external forces more efficiently (Kim & Jang, 2013). It is noteworthy that for the same material, the tensile strength of the fibers was varied with the solvent

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used. Generally, the fibers prepared from [Bmim]Cl, [Emim]Ac and NaOH/urea/water system had a lower strength, while fibers prepared from NMMO, DMAc/LiCl and [Amim]Cl had a higher strength. As shown in Table 1, [Emim]Ac is the most efficient solvent in which all the four materials could be completely and rapidly dissolved, suggesting that the tensile strength of the fibers is not directly proportional to the dissolving capacity of the solvents. In order to understand the relationship between the type of solvents and the tensile strength of the regenerated cellulose fibers, the Mw, Mn and polydispersity index (Mw/Mn) of the fibers were listed in Table

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4. As the data shown, the Mw and Mw/Mn of all the cellulosic materials was decreased after dissolution and regeneration process.

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Especially when [Bmim]Cl was used as solvent, the Mw value was reduced by about 30%. The degradation of the cellulose in [Bmim]Cl was caused by the strong polar chloride ions which could attack the inter- and intra-molecular hydrogen bonds of cellulose

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and break the cellulose chains to varying degrees (Chen, Wang, & Liu, 2012), thus ultimately affect the strength of the fibers. The degradation of cellulose in other solvents, such as NMMO, was not as serious as in [Bmim]Cl. In this study, the dissolution of cellulose in NMMO was carried out under nitrogen atmosphere, effectively preventing the formation of byproducts, which has been

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considered as the main reason for the degradation of cellulose in NMMO (Rosenau et al., 2002). In summary, the tensile strength of the regenerated cellulose fibers was critically affected by the molecular weight of the raw materials and the type of the solvents used.

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Unlike the tensile strength, the elongation at break of fibers was in a narrow range from 2.2% to 4.4% and less affected by the properties of the materials and solvents.

In addition, it should be pointed out that in this study all fibers were spun in a wet spinning manner which is not fully exploiting the

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potential of NMMO and ionic liquids. Moreover, the mechanical properties of the fibers were not only relied on the degree of chain extension, also on the overall molecular orientation along the filament axis. The tensile values of all the fibers, which were lower than that of the commercial regenerated cellulose fibers, could be significantly improved by further increasing cellulose concentration and optimizing spinning conditions.

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4. Conclusions

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The dissolution and regeneration of cellulose were influenced by the combined effect of raw materials and solvents. Ionic liquids, especially [Emim]Ac, have a good ability to dissolve cellulose, followed by NMMO and DMAc/LiCl. BP and SP could not be

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dissolved in NaOH/urea/water due to their high molecular weight. BP needs a longer dissolving time because of its tightly clustered morphology and high hemicellulose content. After regeneration, the crystallinity of all the materials were decreased to a uniform value, accompanied by the crystal structure changing from cellulose I to cellulose II. The elongation at break of fibers was unaffected by the

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properties of the materials and solvents. However, the tensile strength of the regenerated cellulose fibers was directly proportional to the Mw of the raw materials, and varied with the type of the solvents. For MCC and CP, the best solvent is NMMO, for BP is

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DMAc/LiCl, and for SP is [Amim]Cl. Therefore, to obtain high strength fibers, the solvent needs to be selected according to the properties of the raw materials.

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Acknowledgements

This work was supported by the Forestry Nonprofit Industry Research of China (201204803) and the National Basic Research Program of China (2010CB732203/4).

Appendix A. Supplementary data

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Supplementary data associated with this article can be found, in the online version, at

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Song, J., Cheng, B.W., Jie, X.J., Liang, Y., Lu, F., & Zhang, F.N. (2011). Study on the coagulation process of cellulose nascent fibers with ionic liquid AMIMCl as a solvent during dry-wet spinning. E-Polymers, 11(1), 401-411. Swatloski, R.P., Spear, S.K., Holbrey, J.D., & Rogers, R.D. (2002). Dissolution of cellose with ionic liquids. Journal of the American

Ac

Chemical Society, 124(18), 4974-4975.

Trygg, J., & Fardim, P. (2011). Enhancement of cellulose dissolution in water-based solvent via ethanol-hydrochloric acid pretreatment. Cellulose, 18(4), 987-994.

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nano-porous composite materials by processing cellulose with ionic liquids and supercritical CO2. Green Chemistry, 10(9), 965-971.

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Wang K, Jiang. J.X., Xu F., & Sun R.C. (2009). Influence of steaming explosion time on the physic-chemical properties of cellulose from Lespedeza stalks (Lespedeza crytobotrya). Bioresource Technology, 100(21), 5288-5294. Wang, W., Zhang, P., Zhang, S., Li, F., Yu, J., & Lin, J. (2013). Structure and properties of novel regenerated cellulose fibers prepared

ed

in NaOH complex solution. Carbohydrate Polymers, 98(1), 1031-8.

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Zhang, C., Liu, R., Xiang, J., Kang, H., Liu, Z., & Huang, Y. (2014). Dissolution Mechanism of Cellulose in N,N-Dimethylacetamide/Lithium Chloride: Revisiting through Molecular Interactions. The Journal of Physical Chemistry B, 118(31), 9507-9514.

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Ac

ce pt

Zhou, J.P., & Zhang, L.N. (2000). Solubility of cellulose in NaOH/urea aqueous solution. Polymer Journal, 32(10), 866-870.

20 Page 20 of 32

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Table 1

Sugar components, molecular weight and solvability of the cellulosic materials.

Mn

D (Mw/Mn)

Ara

MCC

169020

57196

3.0

--

CP

768810

342790

2.2

BP

1353500

151710

8.9

SP

1650500

221000

Glc

Xyl

Na

D

N

B

A

E

--

97.5

2.5

0.5 min

16

1.5

0.5

20 min

15 min

--

--

95.9

4.1

0.5 min

16

2

0.5

0.5

20 min

0.3

--

92.4

7.3

-

16

4

2

2

1.5

--

95.8

4.2

-

16

2

1

1

0.5

ce pt 7.5

Dissolution time (h) c

Gal

ed

Mw

M an

Samples a

Sugar components b

Molecular weight (Da)

--

MCC, microcrystalline cellulose; CP, cotton linter pulp; BP, bamboo pulp; SP, softwood bleached sulfite dissolving pulp.

b

Ara, arabinose; Gal, galactose; Glc, glucose; Xyl, xylose. Values are relative wt% of the total sugar content and the standard

Ac

a

deviations are less than 3%. c

Na, NaOH/urea; D, DMAc/LiCl; N, NMMO; B, [Bmim]Cl; A, [Amim]Cl; E, [Emim]Ac; h, hour: min, minute. - represents the materials

are not completely dissolved in the solvent.

21 Page 21 of 32

ip t cr

Table 2

us

Crystallinity of the cellulosic materials and regenerated fibers.

CrI of the regenerated fibers a FNa

FD

FN

FB

FA

FE

MCC

59.85

44.14

41.54

44.48

39.91

38.66

43.99

CP

59.74

43.31

41.68

42.64

43.48

42.27

39.57

BP

51.15

--

42.38

44.43

43.26

39.51

41.06

SP

55.39

--

40.84

42.55

40.72

40.03

40.85

ed

FNa, fibers prepared from the solvent of NaOH/urea/water; FD, fibers prepared from the solvent of DMAc/LiCl; FN, fibers prepared

ce pt

a

M an

Sample

CrI of the raw materials

from the solvent of NMMO; FB, fibers prepared from the solvent of [Bmim]Cl; FA, fibers prepared from the solvent of [Amim]Cl; FE,

Ac

fibers prepared from the solvent of [Emim]Ac.

23 Page 22 of 32

ip t cr us M an ed

Table 3

ce pt

Tensile strength and elongation at break of the regenerated fibers prepared from different cellulosic materials and solvents. Tensile strength (cN/dtex)

Sample

D

N

B

A

E

Na

D

N

B

A

E

MCC

0.63 (0.02)a

0.74 (0.03)

0.78 (0.03)

0.59 (0.02)

0.69 (0.03)

0.61 (0.02)

2.2 (0.1)

2.5 (0.1)

2.9 (0.2)

2.4 (0.1)

1.9 (0.1)

2.5 (0.2)

CP

0.93 (0.03)

0.98 (0.03)

1.09 (0.04)

0.86 (0.02)

1.03 (0.04)

0.89 (0.03)

3.6 (0.2)

3.0 (0.1)

3.6 (0.2)

3.4 (0.1)

2.5 (0.1)

2.8 (0.2)

BP

--

1.42 (0.04)

1.35 (0.02)

1.22 (0.03)

1.37 (0.03)

1.28 (0.04)

--

3.2 (0.1)

4.1 (0.2)

4.6 (0.3)

2.6 (0.1)

3.7 (0.2)

Ac

Na

Elongation at break (%)

24 Page 23 of 32

ip t 1.73 (0.03)

1.56 (0.04)

1.77 (0.03)

1.66 (0.02)

cr

1.68 (0.03)

--

4.4 (0.2)

3.8 (0.2)

3.7 (0.1)

3.3 (0.2)

3.1 (0.1)

ce pt

ed

M an

Values in parentheses are the standard errors.

Ac

a

--

us

SP

25 Page 24 of 32

1

Table 4

2

Molecular weight of the regenerated cellulose fibers. Molecular weight (Da)

72265

1.8

FD-MCC

153960

62410

2.5

FN-MCC

156530

64154

2.4

FB-MCC

122040

58697

2.1

FA-MCC

143460

70975

2.0

FE-MCC

132920

76045

1.7

FNa-CP

609330

325620

1.9

FD-CP

643750

319710

FN-CP

709500

344810

2.1

FB-CP

535610

311380

1.7

689100

335790

2.1

587460

305560

1.9

FE-CP FNa-BP

2.0

te

Ac ce p

FA-CP

--

--

--

1216300

180790

6.7

FN-BP

1048400

135240

7.8

FB-BP

977880

150620

6.5

FA-BP

1166650

158110

7.4

FE-BP

983600

124480

7.9

FD-BP

us

130370

d

FNa-MCC

cr

D (Mw/Mn)

an

Mn

M

Mw

ip t

Samples

26 Page 25 of 32

FNa-SP

--

FD-SP

1341300

225260

6.0

FN-SP

1426700

235250

6.1

FB-SP

1164500

205790

5.7

FA-SP

1494600

311640

4.8

FE-SP

1226700

196470

6.2

ip t

--

cr

--

us

3

Ac ce p

te

d

M

an

4

27 Page 26 of 32

4

Figure Captions

5

Fig. 1. Schematic representation of the preparation of regenerated cellulose fibers.

7

Fig. 2. Optical microscopic images of the dissolution of MCC, CP, BP and SP in NaOH/urea/water system.a

9

a

an

(b) is the enlargement of (a); Scale bar 50 um.

us

8

cr

ip t

6

Fig. 3. XRD patterns of the cellulosic materials and regenerated fibers.

11

Fig. 4. SEM micrographs of the regenerated fibers.

M

10

15 16 17

te

14

Ac ce p

13

d

12

18 19

28 Page 27 of 32

20 21

ip t

22

cr

23

us

24

an

25

Ac ce p

te

d

M

26

27 28

Fig. 1.

29

29 Page 28 of 32

ip t cr us an M d te Ac ce p

43 44 45 46 47

Fig. 2.

48

31 Page 29 of 32

49 50

ip t

51

cr

52

Ac ce p

te

d

M

an

us

53

54 55

Fig. 3.

56 57

32 Page 30 of 32

58 59

61 62 63

Fig. 4.

Ac ce p

te

d

M

an

us

cr

ip t

60

64 65

33 Page 31 of 32

65

Highlights

67

► The combined effect of materials and solvents on fibers was investigated in detail.

68

► Cellulose dissolution was mainly determined by the dissolvability of solvents.

69

► Dissolution time was influenced by the properties of raw materials.

70

► The strength of fibers was directly proportional to raw materials’ molecular weight.

71

► For the same material, the fibers’ strength was varied with the type of solvents.

us

cr

ip t

66

Ac ce p

te

d

M

an

72

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