A new spinning solution was synthesized from liquefied wood in phenol by adding hexamethylenetetramine (HMTA) as a synthesis agent, and was easily spun into fibers by melt-spinning. Structure evolution of the spinning solution from liquefied wood (LWS) was investigated by FTIR spectroscopy. Results show the functional groups of LWS were changed from that of liquefied wood by adding HMTA during synthesizing the spinning solution. The effects of various synthesis conditions on the properties of the spun fibers are discussed. Spun fibers with a tensile strength of 90-129 MPa and modulus of elasticity of 8-24 GPa were obtained at a phenol/wood ratio of 6, synthesis agent content of 5%, synthesis temperature of 120°C, and temperature-rising time of 40 min. It was also found that thermal stability of LWS is better than that of liquefied wood, and that the spun fibers from LWS could be a precursor for carbon fibers

Ma, Xiaojun

Zhao, Guangjie

English

Wood and Fiber Science (E-Journal)

STRUCTURE AND PERFORMANCE OF SPINNING SOLUTIONPREPARED FROM LIQUEFIED WOODXiaojun Ma*Department of Packaging and Printing EngineeringTianjin University of Science and TechnologyTianjin 300222, ChinaGuangjie ZhaoDepartment of Material Science and TechnologyBeijing Forestry UniversityBeijing 100083, China(Received January 2008)Abstract. A new spinning solution was synthesized from liquefied wood in phenol by adding hexa-methylenetetramine (HMTA) as a synthesis agent, and was easily spun into fibers by melt-spinning.Structure evolution of the spinning solution from liquefied wood (LWS) was investigated by FTIRspectroscopy. Results show the functional groups of LWS were changed from that of liquefied wood byadding HMTA during synthesizing the spinning solution. The effects of various synthesis conditions onthe properties of the spun fibers are discussed. Spun fibers with a tensile strength of 90–129 MPa andmodulus of elasticity of 8–24 GPa were obtained at a phenol/wood ratio of 6, synthesis agent content of5%, synthesis temperature of 120°C, and temperature-rising time of 40 min. It was also found that thermalstability of LWS is better than that of liquefied wood, and that the spun fibers from LWS could be aprecursor for carbon fibers.Keywords: Liquefied wood, spinning solution, fibers, chemical structure, mechanical properties, thermalanalysis.INTRODUCTIONIn recent years, utilization of biomass resourceshas been gaining importance in environmentalprotection. Therefore, many techniques havebeen developed for using biomass resources ef-fectively (Tatsuhiko and Hirokuni 2001). Woodliquefaction is one of those techniques for con-verting wood into useful liquid materials. As analternative to fossil resources, liquefied wood(LW) has been applied in various chemicalfields (Tsujimoto 1985; Lin et al 1995a 1995b;Yamada et al 1996; Alma et al 1996, 1998;Zhang et al 2004). To increase the use of LWand create “value-added” products, novel utili-zation methods must be developed, such as car-bon fibers and nanostructure fibers. However,there are few studies of fibers from LW becausean appropriate spinning solution could not beeasily obtained (Yoshida et al 2005; Ma andZhao 2007).It is well known that phenol-formaldehyde resincan be developed from LW (Lee et al 2000,2002). Therefore, a liquefied wood spinning so-lution (LWS) could be synthesized according tothe method of Kynol fibers (Liu et al 2005). Thecomponents in LW are rather complex after liq-uefaction. Therefore, the key to prepare fibers ofhigh tensile strength is by synthesis of an opti-mal LWS. At the same time, more detailed stud-ies on structure and performance of LWS arenecessary.In this study, the spinning solution, as raw ma-terial for carbon fiber precursors, was synthe-sized from LW in phenol. The structural evolu-tion and thermal property of LWS was investi-gated by using FTIR spectroscopy andthermogravimetric (TG) analysis, respectively.* Corresponding author: mxj75@tust.edu.cnWood and Fiber Science, 40(3), 2008, pp. 470 – 475© 2008 by the Society of Wood Science and TechnologyThe effects of the preparation parameters such asphenol/wood ratio, synthesis agent content, syn-thesis temperature, and temperature-rising timeon mechanical properties of the spun fibers arealso discussed.MATERIALS AND METHODSMaterialsWood meal (20–80 mesh) of Chinese fir (Cun-ninghamia lanceolata (Lamb.)) was oven-dried105°C for 24 h and then kept in a desiccator atroom temperature before use. A 37.5% H3PO4aqueous solution was directly used as a catalyst.Phenol and hexamethylenetetramine (HMTA)were purchased from Beijing Chemical Com-pany; 37% hydrochloric acid and 37% formal-dehyde were obtained from Changchun Chemi-cal Company. All other chemicals in the studywere reagent grade and were used without fur-ther purification.Liquefaction of WoodWood meal (20 g), phenol (60–120 g), and37.5% aqueous phosphoric acid (8 wt% for phe-nol) catalyst were mixed together in a 500-mLthree-neck glass flask. The glass flask wasplaced in an oil bath, and liquefaction was con-ducted at 160°C for 2.5 h using various liquidratios (3, 4, 5, and 6 phenol/wood).Synthesizing the Spinning SolutionLW (5 g), together with HMTA (3–6 wt% forLW) as a synthesis agent, were added in a reac-tion tube. Subsequently, according to the chosentemperature-rising time (20–50 min), the mix-ture was heated from room temperature to thesetting synthesis temperature (110–125°C) thenheld for 5 min. LWS was thereby synthesized.Preparation of Fibers from LWSThe LWS was placed in a spinning machine de-signed by our laboratory (Fig 1) and extruded inair through a pinhole under nitrogen pressure.The spun filaments were continuously wound ona bobbin at 36 rpm. The resultant fiber wascured by soaking in a solution containing hydro-chloric acid and formaldehyde as main compo-nents at 95°C for 4 h at a heating rate of 10°C/h,washed with distilled water, and dried.Analysis of the SamplesStructural changes of the LWS were traced withFTIR spectroscopy (Tensor27, Bruker company,France) by using the KBr disk technique. Thesamples were pulverized (150–200 mesh) andmixed with KBr before being pressed into adisk. The concentration of the sample in KBrwas 2.5%, and 0.2 g of KBr was used in thepreparation of the reference and sample disks.The mechanical properties of fibers from lique-fied wood (LWF) were measured by an electri-cal tensile strength apparatus (YG004N, Hongdaspinning apparatus factory, China) with a spanof 10 mm and crosshead speed of 2 mm/min.The data shown are average values for 20samples of the fiber.TG analysis was carried out with a ShimadzuTG-60 instrument. The sample (5–8 mg) wasFIGURE 1. Schemes of the apparatus used for spinning.Ma and Zhao—PERFORMANCE OF SPINNING SOLUTION FROM LIQUEFIED WOOD 471heated in nitrogen from room temperature to800°C at 10°C/min at a flow rate of 40 mL/min.RESULTS AND DISCUSSIONFTIR AnalysisFigure 2 shows the FTIR spectra of Chinese fir,LW, and LWS. The absorption peak attributed toO-H is observed at 3406, 3408, and 3417 cm−1in Chinese fir, LW, and LWS, respectively(Zhang et al 2005). However, the decrease inintensity of these peaks, which is more in LWSthan in LW, is due to the diminishing phenolichydroxyl groups that have occurred as a result ofthe dehydration condensation reaction with phe-nolic hydroxide during synthesization of LWS.The bands at 1595, 1512, and 1454 cm−1, whichare assigned to aromatic ring stretch (Fengel andWegener 1984; Liu et al 2005), are obviouslyweakened in LWS, while a new band appears at1610 cm−1 in LWS.The peak found at 1101 cm−1 in LW, which isassociated with the presence of methylidyneether linkages, begins to intensify in LWS. Atthe same time, the band observed at 1015 cm−1,attributed to the hydroxide methyl bond in LW,shifts to 1039 cm−1 in LWS, and decreases inintensity, indicating that the formation of meth-ylidyne ether in LWS is due to the condensationreaction with the hydroxymethyl group duringsynthesization of LWS (Ozaki et al 2000).In addition, the bands at 692, 754, and 832 cm−1,assigned to the out-of-plane CH deformation,appear in LW after liquefaction (Zhang et al2005). However, the peak at 692 cm−1 basicallydisappears while the bands at 832 and 754 cm−1decrease in intensity after synthesization ofLWS, indicating that the amount of substitutedbenzene ring increases due to the appearance ofa new addition reaction on the phenolic ring ofLW, adding HMTA (Masahiko et al 2004).Effects of Spinning Solution Factors onMechanical Properties of FibersFigure 3 shows effects of the liquid ratio (phe-nol/wood) on mechanical properties of LWF. Asshown in the figure, tensile strength and modu-lus of LWF linearly increase with increasing liq-uid ratio (phenol/wood).When the phenol/woodratio increases from 3 to 6, tensile strength ofLWF increases from 2.5 to 43 MPa while themodulus increases from 1.3 to 5.9 GPa. Underthe same liquefaction condition, the greater theliquid ratio, the more crosslinking occurs in thecuring reaction due to the unreacted phenol inliquefaction (Alma et al 1995). On the otherhand, it was found that the higher the viscosityof the spinning solution, the lower the phenol/FIGURE 2. FTIR spectra of wood, LW, and LWS: (a) Chi-nese fir; (b) liquefied wood; (c) spinning solution from liq-uefied wood.FIGURE 3. Effects of liquid ratio (phenol/wood) on me-chanical properties of LWF.WOOD AND FIBER SCIENCE, JULY 2008, V. 40(3)472wood ratio. The fibers have large diameters fromthe high viscosity of LWS and are difficult tospin, resulting in low crosslinkage and tensilestrength of LWF.Figure 4 shows effects of synthesis agent contenton mechanical properties of LWF. With the in-crease of synthesis agent, tensile strength andmodulus of LWF gradually decrease. In particu-lar, when the synthesis agent content increases5–6%, the changes of mechanical properties ofLWF are the greatest. It has been known thathigh crosslinkage between phenolic rings in thenetwork leads to good mechanical properties offibers (Liu et al 2005). However, the number ofcrosslinked groups decreases in curing with theincrease of synthesis agent content, indicatingthat phenolic rings react with the overuse of syn-thetic agent in the synthesization of LWS. As aresult, tensile strength and modulus of LWF de-crease with an increase of synthesis agent.Figure 5 shows effects of synthesis temperatureon mechanical properties of LWF. With increas-ing synthesis temperature from 110 to 125°C,tensile strength of LWF increases from 20 to 25MPa while the modulus increases from 2.5 to 4.3GPa. This indicates that mechanical propertiesof LWF increase only slightly over a small rangeof synthesis temperature. However, LWS is verysensitive to the change of synthesis temperature.It was found that synthesization of the spinningsolution is difficult when the synthesis tempera-ture is below 100°C or above 130°C. In addition,the viscosity of LWS becomes increasingly lowas the temperature rises.Figure 6 shows effects of temperature-risingtime on mechanical properties of LWF. Tensilestrength and modulus of LWF reached a maxi-mum of 49 MPa and 6.3 GPa, respectively,when the temperature-rising time was 40 min.Shorter or longer times lead to a decrease oftensile strength and modulus. It was found thatmicropores (see the arrow in Fig 7a) are devel-oped due to the release of NH3 gas during theshorter synthesis process of LWS (Ozaki et al2000). Therefore, mechanical properties of LWFdecrease due to these micropores.FIGURE 4. Effects of synthesis agent content on mechanicalproperties of LWF.FIGURE 5. Effects of synthesis temperature on mechanicalproperties of LWF.FIGURE 6. Effects of temperature-rising time on mechani-cal properties of LWF.Ma and Zhao—PERFORMANCE OF SPINNING SOLUTION FROM LIQUEFIED WOOD 473TG AnalysisAs shown in Fig 8, both LW and LWS havesimilar TG curves. A small weight loss is ob-served below 200°C. However, LW showsslightly greater weight losses around 100°C thanLWS, which is mainly due to most of the freephenol and moisture in LW. LWS rapidly de-composes between 200 and 400°C, correspond-ing to a weight loss of around 34.6% at 400°C.Meanwhile, a 40.1% weight loss of LW wasrecorded at 400°C. After this sharp weight loss,there was a gradual weight loss up to 800°C.Weight loss at 800°C is 62 and 58% for LW andLWS, respectively, indicating that thermal sta-bility of LWS is better than that of LW.CONCLUSIONSLiquefied wood was converted to a spinning so-lution by adding HMTA. As carbon fiber pre-cursors, the spun fibers were prepared fromLWS after melt-spinning. It is clear that thefunctional groups of LWS have been changedfrom that of liquefied wood by adding HMTAduring synthesization. As the phenol/wood ratioand synthesis temperature increase, tensilestrength and modulus of the fibers from LWSincrease. However, tensile strength and modulusof the fibers gradually decrease with the increaseof synthesis agent content and temperature-rising time. Spun fibers with tensile strength of90–129 MPa and modulus of 8–24 GPa are ob-tained from LWS at phenol/wood ratio of 6, syn-thesis agent content of 5%, synthesis tempera-ture of 120°C, and temperature-rising time of 40min. It is found that weight loss at 800°C was 62and 58% for LW and LWS, respectively, indi-cating that the thermal stability of LWS is betterthan that of LW.ACKNOWLEDGMENTSThis research was financially supported by Na-tional Natural Science Foundation of PR China(No. 30471351).REFERENCESALMA MH, YOSHIOKA M, YAO Y, SHIRAISHI N (1995) Prepa-ration and characterization of the phenolated wood usingFIGURE 7. SEM photographs of LWF: (a) temperature-rising time of 30 min, (b) temperature-rising time of 50 min.FIGURE 8. TG curves of (a) LW and (b) LWS.WOOD AND FIBER SCIENCE, JULY 2008, V. 40(3)474hydrochloric acid as a catalyst. Wood Sci Technol 30(1):39–47.———,———, ———, ——— (1996) The preparationand flow properties of HCl catalyzed phenolated woodand its blends with commercial novolak. Holzforschung50(1):85–90.———, ———, ———, ——— (1998) Preparation ofsulfuric acid-catalyzed phenolated wood resin. 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Mater Chem Phys 90(23):315–321.MA XJ, ZHAO GJ (2007) Preliminary study on preparation ofcarbon fiber from wood-phenol liquefaction products.Chem Indu Fore Prod 27(5):29–32.MASAHIKO K, TOSHIYUKI A, MIKIO K, BUNICHIRO T (2004)Analysis on residue formation during wood liquefactionwith polyhydric alcohol. J Wood Sci 50(5):407–414.OZAKI J, OHIZUMI W, OYA A (2000) A TG-MS study of poly(vinyl butyral) /phenol-formaldehyde resin blend fiber.Carbon 38(10):1499–1524.TATSUHIKO Y, HIROKUNI O (2001) Characterization of theproducts resulting from ethylene glycol liquefaction ofcellulose. J Wood Sci 47(5):458–464.TSUJIMOTO N (1985) Study on wood-phenol resin fiber. 1985International Symposium on Wood and Pulping Chemis-try. Pp. 19–20.YAMADA T, ONO H, OHARA S, YAMAGUCHI A (1996) Char-acterization of the products resulting from direct lique-faction of cellulose. Mokuzai Gakkaishi 42(11):1098–1104.YOSHIDA C, OKABE K, YAO T, SHIRAISHI N, OYA A (2005)Preparation of carbon fibers from biomass-based phenolformaldehyde resin. J Mater Sci 40(2):335–339.ZHANG QH, ZHAO GJ, JIE SJ (2004) Effects of phosphoricacid on liquefaction of wood in phenol and optimumliquefaction processing parameters. For Stud Chin 6(3):50–54.———, ———, ——— (2005) Liquefaction and productidentification of main chemical compositions of wood inphenol. For Stud Chin 7(2):31–37.Ma and Zhao—PERFORMANCE OF SPINNING SOLUTION FROM LIQUEFIED WOOD 475

Structure and Performance of Spinning Solution Prepared from Liquefied Wood

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Structure and Performance of Spinning Solution Prepared from Liquefied Wood

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