CHARACTERIZATION OF MASSON PINE STONE GROUNDWOOD PULP MODIFIED WITH LACCASE/MEDIATOR SYSTEM

CELLULOSE CHEMISTRY AND TECHNOLOGY CHARACTERIZATION OF MASSON PINE STONE GROUNDWOOD PULP MODIFIED WITH LACCASE/MEDIATOR SYSTEM AI-PING ZHANG, *,** MENG-HUA QIN, **,*** RUN-CANG SUN, *,**** QING-HUA XU, ** YING- JUNA FU ** nd CHUN-FU LIU * * Stte Key Lortory of Pulp Pper Engineering, South Chin University of Technology, Gungzhou 510640, Chin ** Shndong Key Lortory of Pulp Pper Engineering, Shndong Institute of Light Industry, Jinn 250100, Chin *** Key Lortory of Cellulose nd Lignocellulosics Chemistry, Gungzhou Institute of Chemistry, Chinese Acdemy of Sciences, Gungzhou 510650, Chin ****The BioComposites Centre, University of Wles, Bngor, Gwynedd LL57 2UW, UK Received Jnury 9, 2007 The study focuses on the modifiction of Msson pine stone groundwood pulp with lccse in the presence of VIO s meditor ws studied. The lechility nd the physicl properties of the control nd lccse/meditor system (LMS) of the modified pulps were investigted comprtively. The pulp surfce properties were chrcterized y ATR-IR nd ESCA. The results showed tht the lechility nd physicl properties were enhnced fter LMS modifiction. Compred to leched control pulp, the rightness nd the reking length of the LMS-modified pulp with lccse dosge of 5 LAMU g -1, followed y leching with E+P sequences, incresed y 2% ISO nd 500 m respectively. The verge length nd corseness of the modified pulp fiers slightly decresed. The O/C rtio on the pulp surfce incresed from 64.26% to 65.32% fter modifiction, while the lignin content decresed. The physico-chemicl properties of milled wood lignins extrcted from the control nd LMS-modified pulps were chrcterized y elementl nlysis, functionl group mesurement, GPC, FT-IR, 1 H-NMR, nd 13 C-NMR spectroscopy. It ws found out tht the moleculr mss of lignin from LMS-modified pulp ws lower thn tht of the lignin from the control pulp. Compred to the control pulp lignin, the content of methoxyl, phenolic hydroxyl nd liphtic hydroxyl groups in the lignin isolted from the LMS-modified pulp decresed, while the contents of the croxyl nd cronyl groups incresed. Keywords: lccse/meditor system, groundwood pulp, modifiction, milled wood lignin, surfce properties INTRODUCTION In recent yers, there hs een growing world-wide interest in utilizing mechnicl pulp for pulp nd pper production, since the trditionl lignocellulosic source is ecoming less undnt nd more expensive, prticulrly in some developing countries like Chin. 1 Stone groundwood pulping, one of the min types of mechnicl pulping, hs the highest yield nd the lowest mteril losses of ll pulping methods, lso exhiiting the most efficient utiliztion of the lignocellulosic mterils. However, the lower rightness stility nd the physicl properties of the pper produced from stone groundwood pulp re mjor ostcles to its industril ppliction. On the other hnd, ecuse of their highly specific effects on cellulose, hemicelluloses, lignin nd/or extrctives, enzymes hve received incresed industril utiliztion. Numerous ppers hve een devoted to pulping, leching, deinking nd fier modifiction with cellulses, hemicellulses, ligninses, nd pectinses. 2-6 Ligninses, which cn ctlyze the removl of surfce lignin, re promising for fier modifiction of stone groundwood pulp with high lignin content. Ligninses include minly oxidtive enzymes such s lignin peroxidse, mngnese Cellulose Chem. Technol., 41 (1), 67-78 (2007)

peroxidse nd lccse. Lccse is multicopper oxidse enzyme ctlyzing the oxidtion of vrious romtic compounds, especilly phenols, with the concomitnt reduction of oxygen to wter. 7 Lccse hs een found to reduce the kpp numer nd enhnce the leching of the krft pulp when used in the presence of chemicl meditor nd oxygen. 8 The incresed rightness nd lechility of the deinked pulps fter deinking of ONP with lccse were lso reported y Cll et l. 6 Moreover, the ppliction of lccse to improve pulp fier properties hs een explored in recent yers. 9,10 To improve fiers onding strength, lccse ws pplied in medium density fierords, 9,11 nd lso in pperords mde from thermomechnicl pulp. 12 Lund et l. 13 found tht modifiction of high yield unleched krft pulp with lccse/meditor system (LMS) resulted in the enhncement of wet tensile strength. Chndr et l. 14 reported tht tretment of n unleched high-kpp (91) krft pulp with lccse, in the presence of gllic cid, resulted in ovious improvements in urst, tensile nd wet tensile strength, while the fully leched pulps did not respond to the lccse tretment. They lso pointed out tht lignin ws the mjor trget for the fier modifiction of the high-yield pulp with lccse. However, there re only few reports on the mechnism of lccse modifiction. In this pper, the lechility nd physicl properties, s well s the surfce properties of the control nd LMS-modified Msson pine stone groundwood pulps were studied. The possile mechnism of LMS modifiction ws investigted y physicochemicl chrcteriztion of the milled wood lignin (MWL) isolted from the control nd LMS-modified pulps y element nlysis, functionl group determintion, GPC, FT-IR, 1 H-NMR nd 13 C-NMR spectroscopy. EXPERIMENTAL Mterils The Msson pine stone groundwood pulp ws kindly supplied y Gungzhou Pulp nd Pper Mking Co., while lccse (NS 51003) - y Novozymes. 1U is defined s the mount of enzyme which oxidizes 1 mmol of syringldzine per minute, under stndrd conditions (ph 7.5, 30 o C). NS51003 displys optiml ctivity in reltively rod ph intervl, etween 4.5 nd 6.5, evidencing full ctivity under norml conditions t tempertures of up to 65 o C for t lest 30 min. VIO (the violuric cid) used s meditor ws otined from Fluk. Modifiction nd leching of pulp VIO (1%) nd lccse (1-10 LAMU g -1 ) were dded to the Msson pine stone groundwood pulp (30 g) suspension, put in eker with gittion under oxygen tmosphere t 60 o C nd 5% pulp consistency nd the modifiction ws crried out for 45 min. After the required time, the pulp ws wshed thoroughly with distilled wter. The control pulp ws otined under the sme conditions without the ddition of lccse. The control nd lccse/meditor system (LMS) modified pulps were sequentilly leched with lkline extrction nd peroxide (E+P). The lkline extrction stge ws crried out under the following conditions: 2% NOH, 10% pulp consistency, 70 o C, for 90 min. After the extrction, the pulp ws thoroughly wshed with distilled wter. Then, the pulp ws sujected to peroxide leching, under the following conditions: 2% H 2 O 2, 1% NOH, 0.1% MgSO 4, 0.2% DTPA, 2% N 2 SiO 3, 2 h, 70 o C nd 10% pulp consistency. Chrcteriztion of pulps Hndsheets of 60 g/m 2 sis mss were mde on ZQJ-B sheets. The physicl properties, including reking length, ter index nd rightness were determined ccording to the Chinese Stndrd. Averge length, length distriution nd corseness of the pulp fiers were mesured on Kjni FS- 200 instrument. ATR-IR spectr were otined on n FT-IR spectrometer (Bruker Tensor 27) using hndsheets of 60 g/m 2 sis weight. Five different res on ech pper smple were nlyzed. Electron Spectroscopy for Chemicl Anlysis (ESCA) mesurements were performed on PHI- 5300. Hndsheet smples of 80 g/m 2 sis mss were first prepred nd extrcted with cetone nd distilled wter for 4 h in Soxhlet pprtus, respectively, to remove the lipophilic extrctives, lignns nd low-moleculr mss crohydrtes. After extrction, the smples were put on clen glss ord, oven-dried t 60 o C nd then used for ESCA mesurement. 15,16 A monochromtic Mg Kα X-ry (12.5 KV, 20 ma) source ws used to excite the electrons. The turo-moleculr pumps were kept t pressure of 3.1 10-7 P. The content of lignin on pulp surfce cn e clculted ccording to the following eqution: 17 lignin content = (O/C pulp O/C crohydrte ) /(O/C lignin O/C crohydrte ), where O/C crohydrte is 0.83 nd O/C lignin is 0.33. 68

Preprtion of milled wood lignin (MWL) The milled wood lignins were extrcted from the control nd LMS-modified pulps, ccording to the Björkmn method with minor modifictions. 18,19 Dried pulp powders (450-900 µm) were first extrcted with toluene-ethnol (2/1, v/v) for 24 h nd then with distilled wter for 6 h. The extrctivefree powders were then ground for 96 h in virting ll mill, followed y three sequentil extrctions (24 h ech) with dioxne-wter (96/4, v/v). The comined extrct ws concentrted under reduced pressure nd freeze-dried. Purifiction ws ssured y lignin dissolution in 90% cetic cid. The solution ws then dded dropwise to stirred distilled wter. The precipitted lignin ws dissolved in 1,2-dichloroethne-ethnol (2/1, v/v) nd the solution ws dded dropwise to the dried diethyl ether under gittion. The lignin ws centrifuged, successively wshed with dried diethyl ether (twice) nd petroleum ether, nd vcuumdried. Physico-chemicl chrcteriztion of MWL Elementl nlysis (cron, hydrogen nd nitrogen content) of lignins ws crried out on n El Vrio III elementl nlyzer. The methoxyl groups in lignins were determined ccording to Lin s method, 20 while the phenolic hydroxyl groups were nlyzed y ultrviolet spectrum. 21 The croxyl groups were determined y non-queous conductometric titrtion 22 nd the cronyl groups were determined y reduction difference ultrviolet spectrum. 23 Acetyltion of the purified MWL ws crried out ccording to pulished procedure. 24 The moleculr mss of cetylted lignins were determined y gel permetion chromtogrphy (GPC) with tetrhydrofurn s eluent. The column ws clirted using polystyrene stndrds. The FT- IR spectr of the lignins were otined on n FT-IR spectrophotometer (Nicolet 510), with KBr disc contining 1% finely ground smples. Thirty-two scns recorded from 4000 to 400 cm -1 were tken of ech smple t resolution of 2 cm -1 in trnsmission mode. The solution - stte 1 H nd 13 C NMR spectr of the cetylted lignins were otined on Bruker DRX-400 spectrometer t 400.13 MHz. 1 H-NMR spectr were recorded t 25 o C from smples dissolved in chloroform (CDCl 3 ). The 13 C NMR spectr were recorded from the smples dissolved in DMSO-d 6 fter 10,000 scns. RESULTS AND DISCUSSION Pulp rightness nd physicl properties Recently, reserch on lccse-meditor systems hs een focused on the io-deinking of old newsprint nd io-delignifiction of krft pulps with novel environmentlly comptile technologies. It hs een shown tht, to chieve sustntil delignifiction y LMS tretment, meditor nd oxygen must e present in this system. 25 In the study, the stone groundwood pulps were modified with different dosges of lccse, in the presence of meditor, VIO, nd oxygen, followed y leching with E+P sequences, while pulp rightness, reking length nd ter index re listed in Tle 1. As cn e seen, increse of lccse dosge from 0 (the control pulp) to 10 LAMU g -1 led to decreses in pulp rightness from 52.6 to 48.6% ISO. This decrement ws proly cused y the formtion of chromophore during lccse modifiction. 26 Chkr et l. 27 reported similr oservtions in the LMS delignifiction of krft pulp with 1- hydroxyenzotrizole nd N-cteyl-Nphenylhydroxylmine s meditors. They found out tht the pulp ecme drk fter LMS tretment, ttriuting it to the formtion of quinone type structures generted during delignifiction. On the other hnd, compred to the continuous enhncement of the ter index with incresing the lccse dosge from 0 to 10 LAMU g -1, rightness nd reking length of the pulp modified with LMS, followed y E+P leching, exhiited different trends. The increment in lccse dosge from 0 to 5 LAMU g -1 resulted in the enhncement of rightness of the leched pulp from 58.8 to 60.8% ISO nd reking length from 1.66 to 2.16 km, respectively, indicting n improvement in pulp s lechility nd physicl properties, fter LMS modifiction. However, further incresing lccse dosge from 5 to 10 LAMU g -1 led to decrement in the rightness of the leched modified pulp from 60.8 to 58.6% ISO nd in its reking length from 2.16 to 2.05 km. Fier length nd corseness Up to now, no comprehensive study hs een developed on LMS-modified stone groundwood pulp qulity trits, including fier length nd corseness. In this study, fier length, length distriution nd corseness of the control nd LMS-modified pulps with different dosge of lccse, were determined. Tle 2 summrizes the rithmetic length (Ln), length weighted length (L W ), mss weighted length (L WW ) nd corseness of the control nd LMS-modified pulps. It ws found out tht 69

LMS modifiction led to slight reduction of fier length nd corseness. Tle 1 Brightness nd physicl properties of the pulps with lccse/meditor system modifiction Pulp P C c Lccse dosge (LAMU g -1 ) 1 3 5 7 10 Brightness (% ISO) 52.6 51.9 50.8 49.9 49.3 48.6 Brightness (% ISO) 58.8 59.3 59.9 60.8 59.0 58.6 Breking length (km) 1.66 1.81 2.07 2.16 2.03 2.05 Ter index (mn m 2 g -1 ) 1.87 2.46 2.57 2.70 2.78 2.82 E+P Brightness of pulps fter LMS-modifiction; Pulp properties fter LMS modifiction followed y leching; c P C represents the control pulp otined without lccse ddition Tle 2 Fier length nd corseness of the pulps with lccse/meditor system modifiction Pulp P C Lccse dosge (LAMU g -1 ) 3 5 10 Ln (mm) 0.36 0.34 0.33 0.33 L W (mm) 0.84 0.82 0.81 0.78 L WW (mm) 1.41 1.39 1.37 1.34 Corseness (mg m -1 ) 3.08 3.04 3.03 3.01 P C represents the control pulp An increse in lccse dosge from 0 (the control pulp) to 10 LAMU g -1 resulted in the reduction of Ln from 0.36 to 0.33 mm, Lw from 0.84 to 0.78 mm, Lww from 1.41 to 1.34 mm nd of corseness from 3.08 to 3.01 mg m - 1. Moreover, the percentge of fiers shorter thn 0.2 mm incresed from 45.71 to 47.30, to 47.43 nd to 48.3% with the increse of lccse dosge from 0 to 3, to 5, nd to 10 LAMU g -1 (dt not shown), respectively, indicting n improved short fier content. These suggested tht the ction of lccse occurred minly on the fier surfce, resulting in slight fier degrdtion under the experimentl conditions given. ATR-IR nlysis To some extent, ttenuted totl reflectnce infrred ry (ATR-IR) spectrometry is surfce-sensitive technique, cple of detecting lignin nd crohydrtes on the sheet surfce. 28 Figure 1 plots the ATR-IR spectr of hndsheets mde from the control pulp (spectrum 1) nd the LMS-modified pulp with lccse dosge 5 LAMU g -1 (spectrum 2). An internl stndrd method ws used to quntify the sorncies. The nd t 1422 cm -1, corresponding to the symmetric ending of CH 2 in crohydrtes, 29 ws used s n internl stndrd. Assignments of the min nds nd their reltive intensity re listed in Tle 3. As cn e seen, the reltive intensity of the pek t 1720 cm -1, relted to the stretching of nonconjugted cronyl groups, incresed from 0.63 (A 1720 /A 1422 ), in the control pulp, to 0.66 in LMS-modified pulp. 30 This indictes tht the LMS tretment resulted in n increse of the non-conjugted cronyl groups in the pulp, which is possily due to the oxidtion of the lignin present in stone groundwood pulp. The reltive intensity of the nd t 1652 cm -1 for the stretching of the conjugted cronyl groups remrkly incresed from 0.80 (A 1652 /A 1422 ) in spectrum 1 to 0.84 in spectrum 70

2, indicting the formtion of new conjugted cronyl groups during LMS modifiction. 31 The incresed numer of non-conjugted nd conjugted cronyl groups present on the pulp surfce, proly due to the oxidtion of lignin with LMS, ws responsile for the decrement of pulp rightness fter LMS tretment. The nds t 1602 nd 1508 cm -1 re relted to the romtic skeletl virtions of lignin. The decresed intensity of the nds in spectrum 2 suggests tht the surfce lignin content decresed fter LMS tretment, which inferred tht lignin degrdtion does occur during LMS modifiction. 0.11 0.10 0.09 0.08 Asornce 0.07 0.06 0.05 1 1652 1602 1508 0.04 0.03 2 1422 0.02 1720 0.01 4000 3000 2000 1000 Wvenumers (cm-1) Figure 1: ATR-IR spectr of the control pulp (spectrum 1) nd LMS-treted pulp with lccse dosge 5 LAMU g - 1 (spectrum 2) Tle 3 Assignments of the min nds nd their reltive intensity in the ATR-IR spectr of control nd LMS-modified pulps Reltive intensity Bnd (cm -1 ) Assignment P C P M c 1720 Non-conjugted cronyl groups 0.6261 0.6594 1652 Conjugted cronyl groups 0.8000 0.8406 1602 Aromtic skeletl virtions 0.7739 0.7664 1508 Aromtic skeletl virtions 0.8758 0.8696 1422 Symmetric ending of CH 2 1 1 The reltive intensity ws clculted s the rtio of ech nd intensity to tht of the nd t 1422 cm -1 P C represents the control pulp c P M represents the LMS modified pulp with lccse dosge of 5 LAMU g -1 ESCA nlysis ESCA could provide quntittive informtion on chemicl composition of surfce. In the present study, the chemicl composition of pulps ws investigted y the ESCA technique. The resulted spectr were 71

nlyzed for the re under the pek, to determine the reltive quntity of n element. The cron 1 s (C1s) nds were deconvoluted 32 to four component peks: C1 (~285.0 ev) for the non-oxidized crons in the hydrocron (e.g., C-H, C-C nd C=C), C2 (~286.9 ev) for the cron-oxygen single ond (e.g., hydroxyl nd ether groups), C3 (~288.5 ev) for the cron-oxygen doule onds (e.g. O-C-O nd cronyl groups), nd C4 (~289.0 ev) for the croxyl groups (O=C-O). Figure 2 shows the deconvoluted C1s ESCA spectr of the control () nd the LMS-modified pulp with lccse dosge 5 LAMU g -1 (). Anlyses reveled tht the control pulp exhiited cron oxidtion sttes of C1 (20.34%), C2 (16.54%), C3 (42.47%) nd C4 (20.65%), with n O/C rtio of 64.26% nd surfce lignin content of 37.48%. () () () Figure 2: ESCA deconvolution spectr of the C1s signl for the control pulp () nd the LMS-modified pulp with lccse dosge 5 LAMU g -1 () In comprison with the control pulp, the O/C rtio of the LMS-modified pulp incresed from 64.26% to 65.32%, nd the surfce lignin content decresed from 37.48% to 35.36%, indicting lignin degrdtion in the LMS tretment, which ws consistent with the results of ATR-IR nlysis. Becuse of the lower lignin content, the modified pulp fier ecme more flexile nd the fier swelling ecme esier, resulting in improved fier-to- 72

fier onding, which ws consistent with the improved physicl properties of the LMSmodified pulp. On the other hnd, the percentge of the C1 pek (non-oxidized crons), composed of cron signls originting from the non-crohydrtes, decresed to 17.49%, indicting reduction of lignin on the pulp surfce. The C2 percentge of the LMS-modified pulp incresed to 18.86%, which ws due to the improved crohydrte content fter lignin degrdtion. The C3 percentge ws lso seen to increse (from 42.47% to 43.02%), which ment the occurrence of n oxidiztion rection during the LMS tretment. The percentge of C4 remined lmost unltered fter LMS modifiction. Elementl nlysis of MWL The cron, hydrogen nd nitrogen content of lignins were determined y elementl nlysis, while the oxygen content ws clculted y sutrction. Tle 4 lists the elementl composition nd methoxyl content, s well s the pproximte C 9 formul of the milled wood lignins otined from the control nd LMS-modified pulps (L C nd L M, respectively). As shown in Tle 4, the cron content decresed from 62.2% in L C to 61.9% in L M, nd the oxygen incresed from 31.9% in L C to 32.5% in L M, indicting the occurrence of lignin oxidtion in the LMS-modified pulp. The methoxyl content ws lower in L M (14.5%) thn in L C (15.8%), which suggested tht the lignin demethyltion occurred during LMS tretment. 33 The pproximte moleculr formule of the lignins from the control nd LMS-modified pulps, clculted ccording to the results of elementl nlysis nd methoxyl content, were C 9 H 8.37 O 2.87 (OCH 3 ) 0.98 nd C 9 H 7.83 O 3.01 (OCH 3 ) 0.90, respectively. Tle 4 Elementl composition, methoxyl content nd C 9 formul of the lignin preprtions otined from control nd LMS-modified pulps Lignin C (%) H (%) N (%) O (%) -OCH 3 (%) C 9 formul L C 62.2 5.87 0.04 31.9 15.8 C 9 H 8.37 O 2.87 (OCH 3 ) 0.98 L M 61.9 5.49 0.07 32.5 14.5 C 9 H 7.83 O 3.01 (OCH 3 ) 0.90 L C represents the MWL otined from the control pulp L M represents the MWL otined from LMS-modified pulp with lccse dosge of 5 LAMU g -1 Functionl groups nlysis The lignins extrcted from control nd modified pulps, L C nd L M, were sujected to the nlysis of the principl functionl groups, the results eing summrized in Tle 5. The content of phenolic hydroxyl groups in the L M of the LMS-modified pulp (3.52%) ws lower thn in the L C of the control pulp (4.88%), which indictes tht the phenolic hydroxyl groups were reduced during the LMS tretment. In contrst to this decresing trend, L M showed higher content of cronyl groups (8.39/100C 9 ) thn L C (6.59/100C 9 ), which indictes tht some new cronyl groups were formed during the LMS tretment. This my explin the decrese in pulp rightness upon LMS modifiction. Tle 5 Functionl group contents in lignins extrcted from control nd LMS-modified pulps Lignin PhOH (%) C=O /100C 9 -COOH (%) L C 4.88 6.59 4.21 L M 3.52 8.39 5.00 Corresponding to the milled wood lignin preprtions in Tle 4 The croxyl groups in L M (5.00%) were lso higher thn in L C (4.21%). Becuse of the more numerous croxyl groups in the LMSmodified pulp lignin, hydrophilicity nd 73

swelling of lignin incresed, resulting in improved fier onding, 34 which my e one of the resons for which the strength properties of the LMS-treted pulp were higher thn those of the control pulp. Moleculr mss The weight-verge (M w ) nd numerverge (M n ) moleculr mss vlues nd the polydispersity (M w /M n ) of L C nd L M re given in Tle 6. As clirtion ws crried out with polystyrene stndrds, the results shown in this tle cn e used only in comprtive nlysis. As seen, the LMS tretment resulted in decrese of weight-verge moleculr weight, numer-verge moleculr weight nd polydispersity of lignin decresed from 16670 to 13602, 7146 to 6796, nd from 2.33 to 2.00, respectively, which indictes tht the lignin ws sustntilly degrded during LMS modifiction. Tle 6 Weight-verge (M w ) nd numer-verge (M n ) moleculr mss, nd polydispersity (M w /M n ) of the lignins extrcted from control nd LMS-modified pulps Lignin M n M w M w /M n L C 7146 16670 2.33 L M 6796 13602 2.00 Corresponding to the milled wood lignin preprtions listed in Tle 4 FT-IR spectr The FT-IR spectr of the lignins extrcted from control (spectrum 1) nd modified (spectrum 2) pulps re shown in Figure 3. The nd t 1508 cm -1, corresponding to the lignin romtic skeletl virtions, ws used s n internl stndrd. The reltive intensities of the peks were clculted s the rtio of sorption intensity to tht of the nd t 1508 cm -1. 35 The ssignments of the min nds nd their reltive intensity re listed in Tle 7. 100 95 90 1 85 80 1664 %Trnsmittnce 75 70 65 2 1730 60 55 50 1421 45 40 1508 4000 3000 2000 1000 Wvenumers (cm-1) Figure 3: FT-IR spectr of the lignins extrcted from control (spectrum 1) nd LMS-modified (spectrum 2) pulps 74

Tle 7 FT-IR sorption nds nd reltive intensity vlues of lignins Bnd (cm -1 ) Assignment Reltive intensity 1730 Stretching of non-conjugted cronyls in lignin 0.2966 0.3663 1664 Stretching of conjugted cronyls in lignin 0.4436 0.4554 1508 Aromtic skeletl virtions 1.0000 1.0000 1421 Aromtic skeletl virtions comined with OCH 3 in-plne 0.6436 0.6378 deformtions Reltive intensity ws clculted s the rtio of ech nd intensity to tht of the nd t 1508 cm -1 Corresponding to the lignin preprtions listed in Tle 4 L C L M The sornce t 1730 cm -1 rises from the C=O stretching of the non-conjugted cronyl groups in lignin. As seen from Tle 7, the reltive intensity of the nd t 1730 cm -1 (A 1730 /A 1508 ) incresed from 0.30 in spectrum 1 to 0.37 in spectrum 2, indicting the formtion of non-conjugted cronyl groups in lignin fter the LMS tretment, which ws possily due to lignin oxidtion. The pek t 1664 cm -1 corresponds to the conjugted cronyl groups in lignin, nd the reltive intensity of this nd (A 1664 /A 1508 ) incresed from 0.44 to 0.46 fter the LMS tretment, which suggested tht some new cronyl groups were formed during it. The nd t 1421 cm -1 reltes to the romtic skeletl virtions, comined with methoxyl group in-plne deformtions. 36 The slight decrement in the reltive intensity of this sornce, fter the LMS tretment, shows tht some methoxyl groups were prtilly removed during it, which is consistent with the results of the functionl group nlysis. 1 H-NMR spectr Figure 4 plots the 1 H-NMR spectr of the cetylted lignins isolted from control (left) nd LMS-modified (right) pulps. The verge numer of ech functionl group per C 9 unit of cetylted lignins cn e estimted ccording to Lundquist s method, the results eing shown 36,37 in Tle 8. ppm ppm Figure 4: 1 H-NMR spectr of cetylted lignins otined from the control (left) nd LMS-modified (right) pulps Tle 8 75

1 H signl ssignments of lignins nd verge numers of protons per C 9 unit δ (ppm) Assignment L C Protons/C 9 7.32-7.70 H α in romtic nd side chins 0.35 0.28 6.25-7.20 Aromtic protons 2.38 2.25 5.75-6.25 H α in β-o-4 nd β-1 structures 0.41 0.35 5.00-5.75 H α in β-5 0.25 0.20 4.50-5.00 H β, H γ in β-o-4 0.67 0.65 4.05-4.50 H γ in β-o-4, β-5 nd β-1 1.32 1.26 3.10-4.05 Protons in methoxyl groups 4.08 3.96 2.50-3.10 H β in β-β structures 0.15 0.13 2.20-2.50 Aromtic cettes 0.77 0.72 1.58-2.20 Aliphtic cettes 4.06 3.80 0.38-1.58 Hydrocron contminnt 0.06 0.03 Corresponding to the lignin preprtions listed in Tle 4 L M Compred to the lignin extrcted from the control pulp, the LMS-modified pulp lignin hd lower content of methoxyl, phenolic hydroxyl nd liphtic hydroxyl groups per C 9, which is similr to the results determined y the functionl groups nlysis, suggesting gin the prtil degrdtion of lignin during the LMS tretment. 13 C-NMR spectr The structure of the milled wood lignins ws lso chrcterized y 13 C-NMR spectroscopy, the spectr of the cetylted lignins from control (L C ) nd modified pulps (L M ) eing shown in Figure 5. The signls for the romtic prt of the lignin could e oserved in the region etween 110 nd 160 ppm. The guicyl units were detected 38,39 y signls t 150.5 (C-3 in etherified guicyl units), 147.3 (C-4 in etherified guicyl units), 145.4 (C-4 in non-etherified guicyl units), 139.5 (C-1 in etherified guicyl units), 130.9 (C-1 in non-etherified guicyl units), 123.1 (C-5 in non-etherified guicyl units), 120.1 (C-6 in guicyl units), 117.5 (C-5 in etherified guicyl units), nd 112.1 ppm (C-2 in guicyl units). The p-hydroxyphenyl (H) residues were identified t 128.8 ppm (C-2/C- 6, H). These signls reveled tht the lignin could e verified s GH lignin. In ddition, three signls t 170.6 (C=O in esters from primry hydroxyl groups with cetyl), 169.8 (C=O in esters from secondry hydroxyl groups with cetyl) nd 169.1 ppm (C=O in ester phenolic hydroxyl groups with cetyl) were oserved. The spectr lso showed the β- O-4 (73.7 ppm for C α, 79.7 ppm for C β, nd 62.6 ppm for C γ ), 5-5 (87.1 ppm for C α, 50.1 ppm for C β, nd 64.7 ppm for C γ ), nd β-β linkges (85.2 ppm for C α nd C β nd 62.0 ppm for C γ ), which re the mjor linkges etween structurl units of lignin. The strong signl t 55.7 ppm origintes from the methoxy groups in the guicyl unit. As shown, the two spectr evidence similr signls, which mens no significnt chnges occured in the lignin structure fter LMS modifiction. The reson for this similr structure of the two lignin smples determined y 13 C-NMR spectroscopy ws proly tht lower time (10,000 scns) ws recorded during the nlysis. Tle 9 Content of lignin functionl groups clculted y 1 H-NMR Functionl group/c 9 Methoxyl 1.36 1.32 Phenolic hydroxyl 0.26 0.24 Aliphtic hydroxyl 1.35 1.27 OH totl 1.61 1.54 Corresponding to the lignin preprtions listed in Tle 4 L C L M 76

ppm Figure 5: 13 C-NMR spectr of the cetylted lignins otined from the control nd LMS-modified pulps Tle 10 Chemicl shift ssignment for the 13 C-NMR spectr of cetylted lignins Pek numer δ (ppm) Assignment 1 170.6 C=O in (esters from primry hydroxyl groups with cetyl) 2 169.8 C=O in (esters from secondry hydroxyl groups with cetyl) 3 169.1 C=O in (esters phenolic hydroxyl groups with cetyl) 4 147.3 C-4 in etherified G 5 145.4 C-4 in non-etherified G 6 139.5 C-1 in etherified G 7 130.9 C-1 in non-etherified G 8 128.8 C-2/C-6 in H 9 123.1 C-5 in non-etherified G 10 120.1 C-6 in G 11 117.5 C-5 in etherified G 12 112.1 C-2 in G 13 87.1 C α in 5-5 14 85.2 C α nd C β in β-β linkges 15 79.7 C β in β-o-4 16 73.7 C α in β-o-4 17 64.7 C γ in 5-5 18 62.6 C γ in β-o-4 19 62.0 C γ in β-β 20 55.7 -OCH 3 21 50.1 C β in 5-5 CONCLUSIONS Bsed on the ove studies, the lechility nd the physicl properties of Msson pine stone groundwood pulp incresed fter modifiction with lccse/meditor system (LMS). Lccse ction my occur 77

minly on the surfce of pulp fier during LMS modifiction, which results in only slight reduction of fier length nd corseness. ATR-IR nd ESCA nlyses on the control nd LMS-modified pulp surfce indictes tht cronyl groups incresed nd the lignin content decresed fter LMS modifiction. The pproximte moleculr formule of the milled wood lignins extrcted from control nd LMSmodified pulps, clculted ccording to element nlysis, were C 9 H 8.37 O 2.87 (OCH 3 ) 0.98 nd C 9 H 7.83 O 3.01 (OCH 3 ) 0.90, respectively. The content of methoxyl, phenolic hydroxyl nd liphtic hydroxyl groups decresed fter LMS modifiction. ACKNOWLEDGEMENTS: The uthors re grteful for the finncil support of this reserch provided y the Ntionl Nturl Science Foundtion of Chin (Nos. 20576065, 20376042 nd 30430550) nd Shndong Nturl Science Foundtion (No. Y2002B08). REFERENCES 1 E. C. Xu, Appit J., 52, 121 (1999). 2 C. Ekld, B. Pettersson, J. Zhng, S. Jernerg nd G. Henriksson, Cellulose Chem. Technol., 39, 95 (2005). 3 J. W. Prk nd K. N. Prk, Biotechnol. Tech., 13, 49 (1999). 4 M. Ricrd, I. Reid nd J. A. Orccotom, Pulp Pp. Cnd, 106, 78 (2005). 5 Q. H. Xu, M. H. Qin, S. L. Shi, L. Q. Jin nd Y. J. Fu, Enzyme Micro. Tech., 39, 969 (2006). 6 H. P. Cll nd G. Strittmtter, Ppier, 46, 32 (1992). 7 L. Ginfred, F. Xu nd J. M. Bollg, Biorem. J., 3, 1 (1999). 8 R. Bouronnis nd M. G. Pice, Appl. Microiol. Biot., 36, 823 (1992). 9 C. Fely, L. S. Pedersen nd B. R. Nielsen, Holzforschung, 51, 281 (1997). 10 K. K. Y. Wong, K. B. Anderson nd R. P. Kilewhite, Enzyme Micro. Tech., 25, 125 (1999). 11 A. Khrzipour, A. Hüttermnn nd H. D. Luedemnn, Annu. Rev. Immunol., 11, 19 (1997). 12 H. Ymguchi, Y. Med nd I. Skt, Mokuzi Gkkishi, 40, 185 (1994). 13 M. Lund nd C. Fely, Enzyme Micro. Tech., 28, 760 (2001). 14 R. P. Chndr, L. K. Lehtonen nd A. J. Rgusks, Biotechnol. Progr., 20, 255 (2004). 15 K. Li nd D. W. Reeve, J. Pulp Pp. Sci., 28, 369 (2002). 16 L. Bors nd P. Gtenholm, Holzforschung, 53, 188 (1999). 17 P. Frdim nd N. Durn, Holzforschung, 56, 615 (2002). 18 A. Bjökmn, Svensk Ppperstid., 60, 243 (1957). 19 T. Tokimtsu, S. Miyt nd T. Umezw, Jpn Wood Res. Soc., 42, 173 (1996). 20 C. L. Chen, in Methods in Lignin Chemistry, S. Y. Lin nd C. W. Dence (Eds.), Berlin, Springer- Verlg, p. 465 (1992). 21 O. Goldschmid, J. Anl. Chem., 26, 1421 (1954). 22 H. Poiner, Anl. Chim. Act, 155, 57 (1983). 23 E. Alder nd J. Mrton, Act Chem. Scnd., 13, 75 (1959). 24 X. J. Pn nd Y. Sno, Holzforschung, 53, 511 (1999). 25 R. Bouronnis, D. Leech nd M. G. Pice, B.B.A.-Gen. Sujects, 1379, 381 (1998). 26 J. Seley nd A. J. Rgusks, Enzyme Micro. Tech., 23, 422 (1998). 27 F. S. Chkr nd A. J. Rgusks, Holzforschung, 54, 647 (2000). 28 P. Kokkonen, P. Frdim nd B. Holmom, Nord. Pulp Pp. Res. J., 19, 318 (2004). 29 J. X. Sun, R. C. Sun, X. F. Sun nd Y. Q. Su, Crohyd. Res., 339, 291 (2004). 30 J. B. Gdhe, R. B. Gupt nd T. Elder, Cellulose, 13, 9 (2006). 31 N. N. Chipnin, Y. R. Mirskov, S. A. Medvedev, I. V. Volchtov, V.A. Bkin, Chem. Nt. Compd., 31, 474 (1995). 32 W. Shen nd I. H. Prker. Cellulose, 6, 41 (1999). 33 R. Bouronnis nd M.G. Pice, Tppi J., 79, 199 (1996). 34 T. Lindstrom, Nord. Pulp Pp. Res. J., 181 (1992). 35 J. Line nd P. Stenius, Pp. Puu-Pp. Tim., 79, 257 (1997). 36 K. Lundquist, Act Chem. Scnd., B33, 27 (1979). 37 K. Lundquist, Act Chem. Scnd., B33, 418 (1979). 38 K. M. Holtmn, H. M. Chng nd J. F. Kdl, J. Agr. Food Chem., 52, 720 (2004). 39 K. M. Holtmn, H. M. Chng, H. Jmeel nd J. F. Kdl. J. Wood Chem. Technol., 26, 21 (2006). 78