Effect of 60Co-γ irradiation treatment on cellulose structure originating from Phragmites communis trim (PCT) was investigated on the basis of irradiation doses of 0 to 2000 kGy at a dose rate of 2 kGy h-1. Scanning electron micrograph images showed that surface morphologies of PCT cellulose could become fragmented after being treated with 60Co-γ irradiation. Based on X-ray diffraction profiles, crystallinity and amorphous region of microcrystalline cellulose treated by irradiation were obviously changed. Fourier transform IR spectroscopy data indicated that a new characteristic peak corresponding to carbonyl (1734 cm -1) appeared after PCT cellulose was treated with 60Co-γ irradiation, which suggested that PCT cellulose was degraded after irradiation treatment

Chen, Jing-ping

Chen, Liang

Liu, Yun

Wang, Ke-qin

Xiong, Xing-yao

English

Wood and Fiber Science (E-Journal)

EFFECT OF GAMMA IRRADIATION ON MICROCRYSTALLINESTRUCTURE OF PHRAGMITES CELLULOSEKe-qin WangProfessorXing-yao Xiong*ProfessorHunan Engineering Laboratory for Alcohol Fuels from BiomassHunan Agricultural UniversityChangsha 410128, ChinaJing-ping ChenResearch AssociateLiang ChenResearch AssociateHunan Institute of Atomic Energy Application in AgricultureChangsha 410125, ChinaYun Liu*Associate ProfessorCollege of Life Science and TechnologyHuazhong University of Science and TechnologyWuhan 430074, China(Received November 2010)Abstract. Effect of 60Co-g irradiation treatment on cellulose structure originating from Phragmitescommunis trim (PCT) was investigated on the basis of irradiation doses of 0 to 2000 kGy at a dose rateof 2 kGy h–1. Scanning electron micrograph images showed that surface morphologies of PCT cellulosecould become fragmented after being treated with 60Co-g irradiation. Based on X-ray diffraction profiles,crystallinity and amorphous region of microcrystalline cellulose treated by irradiation were obviouslychanged. Fourier transform IR spectroscopy data indicated that a new characteristic peak corresponding tocarbonyl (1734 cm1) appeared after PCT cellulose was treated with 60Co-g irradiation, which suggestedthat PCT cellulose was degraded after irradiation treatment.Keywords: Phragmites communis trim (PCT), microcrystalline cellulose, 60Co-g irradiation, SEM,XRD, FT-IR.INTRODUCTIONBioethanol and biodiesel, which are importantalternative bioresource energies, have beenattracting increasing attention because of theproblem of CO2 emissions as well as petroleumenergy security concerns (Liu et al 2010;Remond et al 2010). Current technologies forbioethanol production mainly rely on starch andsugars, and they have been considerably debatedbecause of poor sustainability. In this context,bioethanol produced from lignocellulosic bio-mass is an interesting alternative because ligno-cellulosic raw materials do not compete withfood crops and they are also less expensive thanconventional agricultural feed stocks. This isespecially important for countries with bigpopulations.* Corresponding authors: X. Xiong (xiongxingyao@126.com); Y. Liu (liuyunprivate@sina.com)Wood and Fiber Science, 43(2), 2011, pp. 225-231# 2011 by the Society of Wood Science and TechnologyIn principle, the major technical problem of etha-nol production from lignocellulosic biomass is tohydrolyze lignocellulose into fermentable mono-saccharides. Cellulose pretreatment is an essen-tial step for obtaining potentially fermentablesugars in the hydrolysis step. The aim ofpretreatment is to break down lignin structuresand disrupt crystalline structures of cellulose forenhancing enzyme accessibility to cellulose dur-ing the hydrolysis step (Mosier et al 2005). Sev-eral recent reviews on pretreatment approacheshave been published (Hendriks and Zeeman2009; Alvira et al 2010). In general, pretreatmentcan be conducted with chemical methods (alkalipretreatments, acid pretreatments, ozonolysis,organosolvation method, and ionic liquids pre-treatment) and physicochemical methods (SO2steam explosion, liquid hot water, ammoniafiber explosion, wet oxidation, microwave pre-treatment, ultrasound pretreatment, and CO2explosion). Nevertheless, no information is yetavailable on 60Co-g irradiation treatment effecton structural properties of Phragmites communistrim (PCT) cellulose. Therefore, the purposes ofthis work were to 1) investigate changes in mo-lecular and morphological structure of micro-crystalline cellulose before and after 60Co-girradiation treatment using scanning electronmicroscopy (SEM) and X-ray diffraction (XRD);and 2) assess the effect of irradiation treatment ondegradation of microcrystalline cellulose usingFourier transform IR spectroscopy (FT-IR). Inthis study, PCT microcrystalline cellulose waschosen as the raw material because it is one ofthe most important cellulose resources in China,and PCT can be easily obtained from northeastChina plain, inner Mongolia, Xingjiang Province,and northern China plain.MATERIALS AND METHODSMaterialsPCT cellulose and microcrystalline cellulosemade of Phragmites were received as gifts fromYuanjiang Paper Mills of Tai Gelin Group inHunan Province, China. They were both proc-essed before being used in experiments.PCT cellulose was ground to approximately500 mm using a cutting mill (Retsch GmbHSM1, Haan, Germany) with a 500-mm stainlesssteel trapezium-shaped sieve. Then the Phrag-mites cellulose was air-dried, homogenized inseparate lots to avoid compositional differencesbetween batches, and stored in polyethylenebags until use. Chemical compositions ofPCT were measured using procedures fromAnkom Technology (Macedon, NY; protocolsavailable at www.ankom.com). Briefly, ligninwas extracted in 72% H2SO4 in preweighedfilter bags and quantified by weight after rins-ing the acid with water at 90C. Cellulose wasquantified as the difference between acid deter-gent fiber (ADF) and lignin contents, and hemi-cellulose was quantified as the differencebetween ADF and neutral detergent fiber con-tents. With a few modifications, AmericanOil Chemists’ Society methods were used todetermine moisture and ash content of PCT(Firestone 1998). Moisture and ash contentswere calculated by mass balance after PCTwas oven-dried at 105 and 600C, respectively.Chemical composition of PCT material wasdetermined as follows: 50.15% cellulose,23.40% hemicellulose, 20.72% lignin, 10.50%moisture, and 2.23% ash.The isolation method of microcrystalline cellu-lose was as follows: Phragmites cellulose wascooked in the horizontal tube continuouscooking system under conditions of steam pres-sure 0.7 MPa, 165C, and duration 35 min.After cooking, the cellulose slurry was obtained.Then 4% NaOH and 0.3% MgSO4 were addedto the slurry to delignification under pressure of0.5 MPa for 90 min. After delignification,beginning pulp was obtained. Then the begin-ning pulp was oven-dried at 68C for 48 h andground to particle size to obtain microcrystallinecellulose.Rice straw was collected and stored in a store-house with adequate ventilation, allowing anatural dried condition. After it was storedapproximately 3 months, the straw was washedand dried to about 10% moisture content (MC)(untreated sample) before use.226 WOOD AND FIBER SCIENCE, APRIL 2011, V. 43(2)Osmium tetroxide, ethanol, and acetone werebought from Sinopharm Chemical Reagent Co.(Shanghai, China).60Co-g Ray Irradiation TreatmentAll irradiation treatment experiments were per-formed using a 60Co-g ray irradiation deviceat 1.85 1016 Bq in the Hunan Irradiation Cen-ter (Changsha, China). A batch of dry PCT cel-lulose materials in a glass bottle (net weight200 g) was irradiated at room temperature at a60Co-g radiation source intensity of 9.99  1015Bq and dose rate of 2.0 kGy h–1. Specific levelsof 60Co-g irradiation doses used were 0 kGy,400, 800, 1200, 1600, and 2000 kGy.Surface Morphology Observation byScanning Electron MicroscopyIn the case of SEM examinations, treated cellu-lose samples were washed with saline solution atroom temperature for 10 min, fixed withosmium tetroxide, and dehydrated first with eth-anol and then acetone. Then samples werecompletely dried. Dry samples were mountedon sample holders and coated with gold. SEMimages of samples were taken using a JEOLJSM 6360LV SEM microscope (Tokyo, Japan).Crystalline Analysis by X-Ray DiffractionX-ray diffraction patterns with Cu Ka radiation(l¼ 1.5406 Å) at 36 kV and 30 mA wererecorded in the range of 2y ¼ 10-40 with anXRD diffractometer (Siemens D500-XRD,Karlsruhe, Germany). Samples were mountedon a plastic holder 2 mm thick, and the propor-tional counter detector was set to collect data ata rate of 2y¼ 1 min1 with increments of 0.01for 2y values. All samples were cut into particle-like size to erase influence of crystalline orien-tation. The crystalline structure was attributedaccording to authoritative data. Total degree ofcrystallinity (CrI) was estimated by the Segalmethod (Inagaki et al 2010) using height of the(200) peak (I200, 2y ¼ 22.7) and minimumbetween the (200) and (110) peaks (IAM, 2y ¼16.2) by the following equation:CrI ð%Þ ¼ ½ðI200  IAMÞ=I200100 ð1Þwhere I200 is intensity of the 200 peak (at about2y ¼ 22.7) and IAM is intensity correspondingto the peak at about 2y ¼ 16.2.Oxidative Degradation Determination byFourier Transform-IRFT-IR spectra were recorded with a WQF-310FTIR spectrometer (Beijing Second OpticalInstrument Factory, Beijing, China) and using aliquid nitrogen-cooled mercury–cadmium–tellu-rium detector in the regions of 4000-400 cm1.The running conditions were as follows: 4 cm1spectral resolution, 20 kHz scan speed, 128 scancoadditions, and triangular apodization. By set-ting the microscope square diaphragm apertureto 100  100 mm, an excellent spectrum wascollected within a few minutes.RESULTS AND DISCUSSIONMorphology Changes of 60Co-g Irradiation-Treated SampleEffect of 60Co-g irradiation treatment on mor-phologies of cellulose was examined, and sev-eral representative SEM images are shown inFig 1a-f.Before irradiation treatment, the surface of thePCT cellulose was smooth and the conformationwas integrated (Fig 1a). However, significantchanges in the morphology of PCT cellulosewere observed after irradiation treatment(Fig 1b-f). It can be seen that irradiation causedsome fragmentation of cellulose fibers, the sur-face structure of cellulose fibers became loose,and their structure was damaged to increasingdegrees as irradiation doses increased. Theseresults confirm that 60Co-g irradiation wouldbreak the structure of cellulose fibers to variousextents, depending on the irradiation doses.To further support these observations, the dryrice straw sample, the crystalline cellulose fromWang et al—MICROCRYSTALLINE STRUCTURE OF PHRAGMITES CELLULOSE 227rice straw, and the crystalline cellulose fromPCT were also exposed to 60Co-g irradiation at2000 kGy. SEM images are shown in Fig 2. Themorphology of cellulose samples would bedestroyed when treated with 60Co-g irradiation.Crystalline Changes of f 60Co-g Irradiation-Treated Microcrystalline Cellulose FromPhragmites communis TrimCellulose is a complex polymer with crystallineand amorphous areas. XRD was further used toinvestigate effect of irradiation on the crystallinephase of microcrystalline cellulose. Figure 3shows XRD patterns of PCT microcrystalline cel-lulose as a function of diffraction angle as well asirradiation doses changing from 0 to 2000 kGy.Degree of crystallinity was determined by theSegal method from the XRD chart (Fig 4).After irradiation treatment, the CrI of PCT crys-talline cellulose dropped from 78.4 to 40.7%(Fig 4). Hence, XRD indicates that part of crys-talline cellulose was disrupted by irradiation.Figure 4 shows that degree of crystallinity obvi-ously decreased with increasing irradiation dose,which may have been caused by degradation ofhemicellulose or the amorphous regions in cel-lulose as observed from SEM spectra (Fig 1).The lower crystallinity of cellulose makes itmore accessible to chemical reagents, and thusit is easier to hydrolyze to sugars (Mosier et al2005; Driscoll et al 2009). Apparently, irradia-tion more easily cleaves the amorphous regionof cellulose than its crystalline region.Figure 1. Scanning electron micrograph images of Phragmites communis trim (PCT) cellulose sample treated withdifferent irradiation doses ([a] untreated PCT cellulose [0 kGy]; [b] 400 kGy; [c] 800 kGy; [d] 1200 kGy; [e] 1600 kGy;[f] 2000 kGy).228 WOOD AND FIBER SCIENCE, APRIL 2011, V. 43(2)Effect of 60Co-g Irradiation on OxidativeDegradation of CelluloseAs shown in Fig 5, additional shoulder appearedat 1734 cm1 (caused by C ¼ O stretching) onthe O-H bending band. However, a very smallband at 1501 cm1 was noticed for PCT cellu-lose treated with 800 kGy. This band dis-appeared with higher irradiation doses (1200,1600, and 2000 kGy). A reasonable explanationmay be the small band at 1501 cm1, which theyassigned to the N-H absorption band of protein-aceous glues, obviously has to be destroyed inhigher irradiation doses. This observation is inFigure 2. Scanning electron micrograph images of other cellulose samples treated with 60Co-g irradiation of 2000 kGy(RS0, untreated rice straw sample; RS200, rice straw sample treated with 60Co-g irradiation of 2000; CR0, untreatedcrystalline cellulose from rice straw; RS200, crystalline cellulose from rice straw treated with 60Co-g irradiation of 2000;C-PCT0, untreated crystalline cellulose from Phragmites communis trim [PCT]; RS200, crystalline cellulose from PCTtreated with 60Co-g irradiation of 2000).Figure 3. X-ray diffraction (XRD) images of crystallinecellulose of Phragmites communis trim (PCT) treated withdifferent irradiation doses (untreated crystalline cellulose ofPCT [CK]).Figure 4. Variation of crystallinity index calculated fromX-ray diffraction (XRD) chart.Wang et al—MICROCRYSTALLINE STRUCTURE OF PHRAGMITES CELLULOSE 229good agreement with reported results in which anew characteristic peak of carbonyl groups(1734 cm1) was observed when the textile wasexposed to irradiation (Fōldváry et al 2003).Degradation of cellulose treated with 60Co-girradiation was characterized by measurementof the content of carbonyl groups using FT-IR(C ¼ O stretching vibration) at approximately1740 cm1 (Takács et al 2000). It was shownthat PCT cellulose exhibited oxidative degrada-tion after irradiation treatment, which could beattributed to hydrolysis of cellulose.CONCLUSIONSIrradiation treatment using high-energy 60Co-gwas found to be an energy-efficient and environ-mentally benign method to decrease crystallin-ity of microcrystalline cellulose by partiallydestroying the morphological structure of cellu-lose. Irradiation treatments on PCT cellulosecould result in oxidative degradation and leadto an increase in carbonyl groups. Thesechanges in structure and properties of PCT cel-lulose would make it more amenable to treatcellulose instead of using other chemical agentsand thus to allow cellulose to be easily used as araw material for production of sugars, ethanol,and other chemicals.ACKNOWLEDGMENTSThe authors gratefully acknowledge thefinancial support provided by National KeyBasic Research Program (973 Program)(2009CB226108), National Natural ScienceFoundation of China (NSFC) (31070709), andIndustry Scientific Research Program in PublicInterests of Ministry of Agriculture in China(200803034).REFERENCESAlvira P, Tomás-Pejó E, Ballesteros M, Negro MJ (2010)Pretreatment technologies for an efficient bioethanolproduction process based on enzymatic hydrolysis:A review. Biores Technol 101(13):4851-4861.Driscoll M, Stipanovic A, Winter W, Cheng K, Manning M,Spiese J, Galloway RA, Cleland M (2009) Electronbeam irradiation of cellulose. Radiat Phys Chem 78(7-8):539-542.Firestone D (ed.) (1998) Official methods and recommendedpractices of the American oil Chemists’ Society, 5th ed.American Oil Chemists’ Society, Champaign, IL.Fōldváry CsM, Takács E, Wojnárovits L (2003) Effect ofhigh-energy radiation and alkali treatment on the proper-ties of cellulose. Radiat Phys Chem 67(3-4):505-508.Hendriks ATWM, Zeeman G (2009) Pretreatments toenhance the digestibility of lignocellulosic biomass.Biores Technol 100(1):10-18.Inagaki T, Siesler HW, Mitsui K, Tsuchikawa S (2010)Difference of the crystal structure of cellulose in woodFigure 5. Fourier transform-IR spectra for the oxidative gradation of Phragmites communis trim (PCT) microcrystallinecellulose treated with different irradiation doses ([a] untreated microcrystalline cellulose [0 kGy]; [b] 400 kGy; [c] 800kGy; [d] 1200 kGy; [e] 1600 kGy; [f] 2000 kGy).230 WOOD AND FIBER SCIENCE, APRIL 2011, V. 43(2)after hydrothermal and aging degradation: A NIR spec-troscopy and XRD study. Biomacromolecules 11(9):2300-2305.Liu Y, Tan H, Zhang X, Yan YJ, Hameed BH (2010) Effectof monohydric alcohols on enzymatic transesterificationfor biodiesel production. Chem Eng J 157(1):223-229.Mosier N, Wyman CE, Dale BD, Elander RT, Lee YY,Holtzapple M, Ladisch CM (2005) Features of promisingtechnologies for pretreatment of lignocellulosic biomass.Biores Technol 96(6):673-686.Remond C, Aubry N, Cronier D, Noel S, Martel F,Roge B, Rakotoarivonina H, Debeire P, Chabbert B(2010) Combination of ammonia and xylanasepretreatments: Impact on enzymatic xylan and cellu-lose recovery from wheat straw. Biores Technol 101(24):6712-6717.Takács E, Wojnaárovits L, Foéldvaáry CS, Hargittai P,Borsa J, Sajo I (2000) Effect of combined gamma-irradi-ation and alkali treatment on cotton–cellulose. RadiatPhys Chem 57(3-6):399-403.Wang et al—MICROCRYSTALLINE STRUCTURE OF PHRAGMITES CELLULOSE 231

Effect of Gamma Irradiation on Microcrystalline Structure of Phragmites Cellulose

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Effect of Gamma Irradiation on Microcrystalline Structure of Phragmites Cellulose

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