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Industrial Crops and Products 52 (2014) 32– 37

Contents lists available at ScienceDirect

Industrial Crops and Products

journa l h om epa ge: www.elsev ier .com/ locate / indcrop

ilanthus altissima: An alternative fiber source for papermaking

atrícia Baptistaa, Ana Paula Costaa,b, Rogério Simõesa,b, Maria Emília Amarala,∗

Research Unit of Textile and Paper Materials, University of Beira Interior, 6201-001 Covilhã, PortugalDepartment of Chemistry, University of Beira Interior, 6201-001 Covilhã, Portugal

r t i c l e i n f o

rticle history:eceived 13 August 2013eceived in revised form7 September 2013ccepted 2 October 2013

a b s t r a c t

This work aims at studying the potential of Ailanthus altissima as a raw material for papermaking. For thispurpose, trees of two age groups (2 and 25 years) were studied in terms of wood density and chemicalcomposition. The latter was evaluated at different height levels in the tree. Selected wood samples weresubmitted to kraft cooking under different operating conditions, namely effective alkali charges, in orderto evaluate their pulping potential. The best screened pulp yield was close to 49% (w/w) and was obtained

eywords:ilanthus altissimahemical compositionraft pulpsulp beatingapermaking properties

from the 2 years old trees. Ailanthus pulps were subsequently beaten using a PFI mill at 500, 1500,and 3000 revolutions. An industrial bleached Eucalyptus globulus kraft pulp was used as reference. Bothpulps and papers were fully characterized in terms of morphological and physical properties. The resultsshowed that the properties of the paper obtained from ailanthus are close to those of the reference ones.

© 2013 Elsevier B.V. All rights reserved.

. Introduction

The worldwide consumption of paper and board productsncreased from 125 million tons in 1970 (Jahan et al., 2009; Mousavit al., 2013) to 402 million tons in 2011, and it is expected toeach 521 million tons per annum by year 2021 (Lal et al., 2013). Inrder to meet future demand and to overcome the wood shortage,tudies have been conducted worldwide to evaluate the potentialf new or alternative resources as raw material components forulp and paper production (Samariha et al., 2011). Thus, the usef fast growing species such as Ailanthus altissima (Miller) Swinglean be a promising alternative. This species is a member of theimaroubaceae botanical family, native to China and North Vietnam.t has become invasive on all other continents except AntarcticaKowarik and Säumel, 2007). The word ailanthus, derived fromilanto, an Ambonese word which means “tree-of-heaven” (Kundund Laskar, 2010). Ailanthus is a medium-sized tree which reachesaximum heights of 18–30 m, growing up to 3 cm per day depend-

ng on the growth conditions (Marchante et al., 2005; Kowarik and

äumel, 2007; Kundu and Laskar, 2010; Motard et al., 2011). Itrefers rich and moist soils, but also tolerates poor and dry ones.esides that, the ailanthus supports relatively high levels of airollution and may be able to sequester some pollutants. For this

∗ Corresponding author at: Research Unit of Textile and Paper Materials, Univer-ity of Beira Interior, Rua Marquês d’Avila e Bolama, 6201-001 Covilhã, Portugal.el.: +351 275314740; fax: +351 275314740.

E-mail address: mecca@ubi.pt (M.E. Amaral).

926-6690/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.indcrop.2013.10.008

reason, it has been widely planted in urban areas worldwide toreduce environmental pollution (Ding et al., 2006a,b). However,this tree has become a plague, not only by competing with nativevegetation, but also by causing destruction on roads, sidewalks,structures, piping, and orchards due to its extensive root system.Invasive plants pose a threat to biodiversity and economy of theentire world. Up until now, there has been a limited effort in devel-oping biological control programs against Tree-of-Heaven (Dinget al., 2006b). Ailanthus has been used as an ornamental plant,on shelterbelts, afforestation and reforestation of “difficult sites,”plantations for the culture of silkworms, and biomass productionfor fuel wood and for the production of fodder for goats and cat-tle (Feret, 1985). Moreover, this plant has been studied from thepoint of view of its biological activities and pharmacological appli-cations, proving its use in traditional Chinese medicine and itspotential application in modern medicine (Kowarik and Säumel,2007; Kundu and Laskar, 2010; Luís et al., 2012). To our knowledge,only one study has been made on the evaluation of papermakingpotential of unbleached A. altissima kraft pulp (Ferreira et al., 2013).The present work was aimed at studying ailanthus trees of twoage groups (2 and 25 years old) targeting papermaking potential.Firstly, these wood samples were quantified in terms of chemi-cal composition, and then the optimal conditions in kraft cookingwere investigated. After pulp bleaching, the effect of different lev-els of beating was evaluated. The impact of beating on the fibers’

morphology and on the physical properties of paper handsheetswas assessed. To evaluate the papermaking potential of these twowood age groups, an industrial bleached Eucalyptus globulus kraftpulp was used as reference.

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. Materials and methods

.1. Raw material

The A. altissima trees used in this study were collected in theerra da Estrela region (Portugal). One 25 years old isolated tree,ith an average diameter of 27 cm at breast height level, was har-

ested in a private garden. Representative young trees (2 yearsld) were collected in the university campus. The oldest tree wasivided into four different height levels (15%, 35%, 65%, and 85%),nd the 15% height level was further divided into two portions,eartwood and sapwood. For pulping experiments, all raw materi-ls were manually cut to approximate size of industrial wood chips10–20 mm length; about 10 mm wide and almost 4 mm thick). Thery matter content of the material was determined according toCAN-CM 39. The chip basic density was determined according toappi 258 om-11. For chemical analysis, a small portion of chips wasround and screened to obtain a uniform particle size of a 40–60esh.

.2. Wood chemical composition

The extractives content was determined after successive extrac-ion in a Soxhlet apparatus by dichloromethane (5 h), ethanol (8 h),nd hot water (3 h), according to Tappi 204 cm-97. The 1% sodiumydroxide solubility and ash content were obtained following theappi 212 om-02 and the Tappi 211 om-02 standards. The ligninontent was determined using the NREL/TP-510-42618 proceedingSluiter et al., 2011). The neutral sugars and acetic acid were deter-

ined according the procedure previously reported by Santos et al.2012). At least, a three replicates were performed for each samplend the coefficient of variation is lower than 5%.

.3. Kraft pulping and bleaching

In order to obtain the optimal cooking conditions and eval-ate the potential effect of material origin position in the 25ears old tree, a series of preliminary experiments was carriedut using mini-digesters working with 25 g oven-dry (o.d.) wood.he wood chips were submitted to a kraft cooking process underiverse reaction conditions, reported in Fig. 1. After cooking con-itions optimization, experiments were carried out with 1000 g.d. of wood, in a forced circulation digester, under the followingonditions: effective alkali charge 22% (as NaOH); sulfidity 30%;iquor-to-wood ratio 4:1; heating-up to 165 ◦C for 90 min; cookingt maximum temperature for 90 min.

The cooked chips were disintegrated, washed and screened on acreen with 0.3 mm slot width and the accepted material was col-ected on a 200 mesh screen. The screened pulp and the uncookedrejects) yields were determined. The kappa number and pulpntrinsic viscosity were determined according to ISO 302 and ISO351-1. This part of ISO 5351 specifies a method for the deter-ination of the limiting viscosity number of cellulose in dilute

upri-ethylene-diamine (CED) solution. This method is applicableo CED-soluble samples of cellulose. Selected pulps were bleachedsing a chlorine dioxide based bleaching sequence D0ED1D2 (where-chlorine dioxide and E-alkaline extraction) using a kappa factorf 0.2 and a chlorine dioxide charge (expressed as active chlorine)f 1.3% and 0.6% in D1 and D2, respectively, at medium consistency.

.4. Pulp fiber characteristics and SEM

The morphological properties of pulp fibers before and aftereing beaten were studied in a MORFI (LB-01) analyzer developedy Techpap-France. The main parameters (fiber length weighted

n length, fiber width, kinked fibers, curl index, coarseness and fine

nd Products 52 (2014) 32– 37 33

elements) were measured by image analysis of a diluted suspensionflowing in a transparent flat chamber observed by a CCD video cam-era, by measuring more than 8000 fibers. Fine elements are definedas particles with size <200 �m. For scanning electronic microscope(SEM) analysis, samples of unbeaten pulps of ailanthus and eucalyptwere fixed in a 2.5% glutaraldehyde solution overnight at 4 ◦C. Theywere then dehydrated in a graded ethanol series, dried with liquidCO2 at critical point and subsequently gold-covered by cathodicspraying. The SEM used was a Hitachi S-2700 operated at 20 kV.Concerning the beaten samples, an optical microscope with darkfield condenser was used to illustrate the fibrillation phenomenaresulting from the pulps beating.

2.5. Paper characterization

The laboratorial pulps from A. altissima and the industrialbleached E. globulus kraft pulp were beaten in a PFI mill at500, 1500 and 3000 revolutions under a refining intensity of3.33 N/mm (ISO 5264-2). The pulp suspension drainability wasdetermined by Schopper–Riegler method (ISO 5267-1). The pulpfibers water retention value (WRV) was determined by centrifu-gation at 3000 × g of wet pulp samples during 15 min, accordingto the method reported by Silvy et al. (1968). Handsheets with abasis weight of 60 g/m2 were prepared and conditioned accordingto ISO 5269-1 and ISO 187 standards. Papermaking properties ofpulp handsheets were examined according to ISO 5270 standard.Pulp optical properties were measured according to ISO 2470-1(for ISO brightness), ISO 2471 (for opacity) and ISO 9416 (for lightscattering coefficient), respectively.

3. Results and discussion

3.1. Raw material characterization

Wood density is related to most of the resistance properties oftimber as well as many aspects of wood processing and productquality (Zobel and Buijtenen, 1989; Santos et al., 2012). The ailan-thus wood density is of 502 kg/m3 for the 2 years old and 495 kg/m3

for the 25 years old (15% height level), respectively. These valuesare slightly lower than those reported for eucalypt (E. globulus –520 kg/m3) by Patt et al. (2006), but they compare well to severaleucalypt species usually used for pulping (Bhat et al., 1990; Mirandaet al., 2001; Santos et al., 2008a).

3.2. Wood chemical composition

Table 1 summarizes the chemical composition of the young(2 years old) and mature (25 years old) wood samples from A.altissima. In general, the experimental data enable us to concludethat no significant differences can be identified between the twomaterials groups in terms of total lignin and extractives contents,despite the significant differences in tree ages. Concerning totallignin content, our values are in accordance with those reported byKhattak and Ghazi (2001) and Samariha et al. (2011) with 22.19%and 25.19%, respectively. Regarding the global extractives content(samples successively extracted with dichloromethane, ethanol,and water), the young trees present slightly lower values (4.42%)than the mature trees (15% height level) analyzed (4.93%). Thesevalues are in agreement with those published by Samariha et al.(2011) for ailanthus and are very close to those obtained for theeucalypt (Pereira, 1988; Miranda et al., 2001). As expected, theextractives content in heartwood (5.07%) is higher than in the sap-

wood (3.77%) for the 25 years old tree at 15% height level; thedifferences are due to the ethanol and hot water extractives. Usinga similar extraction procedure, Lourenc o et al. (2010) have reported3.9% and 9.8%, respectively, for the sapwood and the heartwood of

34 P. Baptista et al. / Industrial Crops and Products 52 (2014) 32– 37

n pul

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Fig. 1. Effect of kraft cooking conditions o

n 18 years old E. globulus tree. The lower values obtained for theilanthus heartwood indicate that this species can generate fewxtractives, which can make it good for pulp production. Our val-es for ash content are in agreement with the value reported byerreira et al. (2013). It seems, however, that the amount of 1%odium hydroxide extractives is higher in young trees than that inature ones. Regarding the neutral sugars and acetic acid wood

ontent, the relative proportion for the mature wood are as fol-ows: glucose: 56%, xylose + mannose + galactose: 33%, acetic acid:1%. The young wood presents slightly lower glucose content. Inummary, the data from chemical composition opens a good possi-ility for using this young material as a source of pulp fibers, mainlyonsidering its very fast growth.

.3. Kraft cooking and bleaching

In order to select the optimal settings for kraft cooking, differenteactions conditions were explored. Fig. 1 summarizes the experi-ental results of exploratory cooking tests made with 25 years old

. altissima wood chips taken at several levels of the tree height.sing mild cooking conditions, the screened pulp was low and theulp kappa number and rejects were too high. On the contrary,

erreira et al. (2013) have reported a pulp yield of around 54%,nd a kappa number of ca. 15 using these relatively mild cookingonditions. These different behaviors can certainly be ascribed toifferences in tree age, wood samples chemical composition, and

able 1hemical composition of 25 years old and 2 years old ailanthus wood.

Components (% on o.d. wood) 25 years old Ailanthus altissima (height level

85% 65% 35%

ExtractivesDichloromethane 1.20 0.58 0.66

Ethanol 1.95 1.30 1.17

Water solubility 2.61 3.12 2.96

Total 5.76 4.99 4.78

1% sodium hydroxide solubility 19.49 16.59 19.61

Klason lignin 22.83 20.42 20.58

Acid soluble lignin 4.96 4.95 5.27

Total lignin 27.79 25.37 25.85

Ash content 0.85 0.85 0.89

ping potential of 25 years old A. altissima.

chips dimensions. To decrease the pulp kappa number and improvethe pulp yield, the maximum cooking temperature was increasedfrom 160 ◦C to 165 ◦C, as well as the cooking time (90 min), andalkali charge.

Using a forced circulation digester, 1 kg of wood chips wascooked under the previous selected conditions. Whatever thecooking conditions, the total and screened pulp yield only reached50% and 45.5%, respectively, for the 25 years old A. altissima tree.Interestingly, the 2 years old wood material submitted to simi-lar cooking conditions provided better pulp yield (49.1%), loweruncooked material (2.3%), and a slightly lower pulp kappa number(15.7 vs 17.7). In summary, regardless of the A. altissima wood sam-ple considered (25 years old or 2 years old), the results obtained inthis study suggest that this species exhibits slightly lower pulpingperformance than E. globulus industrial chips, which exhibit a pulpyield in the range of 51–53%, for similar reaction conditions (Santoset al., 2008a,b). In addition to pulping yield, basic wood density alsodetermines the performance of the industrial digesters, but in thiscase those values are closer.

The pulp behavior in bleaching was assessed with a chlorinedioxide bleaching sequence of D0ED1D2. The D0 was applied usingan active chlorine kappa factor of 0.2, while the chorine dioxide

charges (expressed as active chlorine) in D1 and D2 were of 1.3%and 0.6%, respectively, for both pulps. No significant differenceswere detected between the two pulps in terms of final brightness(both of approximately 88% ISO). The pulps’ intrinsic viscosities for

in the tree) 2 years old tree

15%

Total Sapwood Heartwood

0.75 0.71 0.65 0.501.24 0.90 1.56 1.792.93 2.15 2.85 2.134.93 3.77 5.07 4.42

18.67 18.29 18.55 21.9720.98 20.00 20.46 20.95

4.36 4.28 3.91 4.9925.33 24.28 24.37 25.94

0.85 0.76 0.80 0.73

P. Baptista et al. / Industrial Crops and Products 52 (2014) 32– 37 35

Table 2Effect of beating on fibers morphology and on the percentage of fine elements content for ailanthus (A.a.) and eucalypt (E.g.) bleached pulps.

Lengtha (mm) Width (�m) Coarseness (mg/m) Kinked fibers (%) Curl (%) Fine (% length)

0 PFI revs25 years old A.a. 0.791 22.7 0.083 27.5 6.03 22.12 years old A.a. 0.721 23.0 0.083 28.5 6.07 25.3Industrial E.g. pulp 0.798 18.2 0.068 28.7 7.28 25.2

500 PFI revs25 years old A.a. 0.786 22.7 0.091 26.2 6.05 26.82 years old A.a. 0.721 23.1 0.083 26.8 6.06 27.2Industrial E.g. pulp 0.790 18.5 0.069 27.2 6.80 25.8

1500 PFI revs25 years old A.a. 0.778 23.2 0.085 24.5 6.10 29.02 years old A.a. 0.717 23.4 0.084 28.7 6.37 28.0Industrial E.g. pulp 0.782 18.7 0.069 29.0 6.98 26.2

3000 PFI revs25 years old A.a. 0.763 23.6 0.084 26.5 6.54 31.62 years old A.a. 0.703 23.5 0.084 32.0 6.77 28.2

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Industrial E.g. pulp 0.770 19.4 0.0

ilanthus are of 710 cm3/g and 800 cm3/g for 25 years old and 2ears old, respectively. These values compare well to the referenceulp viscosity (750 cm3/g).

.4. Pulp fibers characteristics and SEM

Table 2 presents the fibers’ characteristics of the two pulp sam-les from ailanthus and from industrial bleached E. globulus kraftulp, throughout the beating process. The ailanthus young treesave provided slightly shorter pulp fibers than the mature tree0.72 mm vs 0.79 mm). The values for the pulp fibers produced fromhe mature ailanthus wood are in good accordance with those pre-iously published (Ferreira et al., 2013). The mature ailanthus woodnd the eucalypt exhibit pulp fibers with a comparable length; theilanthus young wood provides slightly shorter pulp fibers. On theontrary, the pulp fibers from A. altissima are wider than those from. globulus (22.7 �m vs 18.2 �m). In general, these values are in goodgreement with those reported by Samariha et al. (2011) for fiber

ood biometry. The fiber coarseness from ailanthus is 22% higher

han that of our reference sample, in line with previous publicationFerreira et al., 2013). The fines content is high and increases witheating, for all pulps, as expected. Regarding curl, the ailanthus pulp

ig. 2. Scanning electron micrographs of 25 years old ailanthus (A), 2 years old ailanthus (Bnd dark field optical micrographs for beaten (3000 PFI revolutions) samples (D–F) with ×

27.6 6.66 28.0

fibers exhibit, in general, lower curl than the eucalypt fibers, prob-ably due to their higher coarseness and fiber width, which inducerigidity. As beating increases both fiber flexibility and collapsibil-ity, the curl of the fibers also increases with beating. The percentageof kinked fibers is around 30% and increases slightly with beating,after a small decrease for the initial beating levels.

Fig. 2 shows scanning electron micrographs (SEM) of the pulphandsheets of ailanthus and eucalypt for unbeaten samples. Theshape of the fibers is similar for both species, but ailanthus fibers arewider; this is in agreement with the results presented in Table 2. Onthe other hand, it can be seen (for beaten pulps, samples D–F) thatthe fibrillation phenomena is resembles. The differences in mor-phological characteristics will certainly impact the pulp beatingand the papermaking potential, as debated below in this paper.

3.5. Papermaking potential

After bleaching, the papermaking potential of the 25 years old

(breast height level) and 2 years old A. altissima was evaluated,using as a reference an industrial bleached E. globulus kraft pulp.Fig. 3 shows that the drainage resistance of E. globulus is consis-tently higher than any of the A. altissima pulp samples considered.

), and industrial E. globulus pulp (C) for unbeaten samples with 300× magnification40 magnification, at the same presentation order.

36 P. Baptista et al. / Industrial Crops and Products 52 (2014) 32– 37

Table 3Effect of beating on physical properties of handsheets.

Apparent paperdensity (kg/m3)

Bendtsen air permeability(�m/(Pa s))

Tensile index (N m/g) Tear index (mN m2/g) Zero-span breakinglength (km)

Dry Wet

0 PFI revs25 years old A.a. 484 25.2 19.4 1.66 12.0 11.02 years old A.a. 473 24.2 19.8 0.95 10.7 9.6Industrial E.g. pulp 597 14.9 35.1 1.95 12.1 11.1

500 PFI revs25 years old A.a. 632 10.7 47.1 3.08 12.3 11.62 years old A.a. 698 7.3 53.6 3.20 11.9 10.2Industrial E.g. pulp 662 8.1 54.8 3.46 12.3 11.1

1500 PFI revs25 years old A.a. 774 0.8 81.0 5.33 14.0 11.12 years old A.a. 829 0.8 78.1 3.62 12.1 9.5Industrial E.g. pulp 767 1.3 84.6 4.28 12.7 10.71

3000 PFI revs88.6 5.00 14.0 10.384.5 3.67 13.2 9.391.6 5.07 12.8 9.2

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25 years old A.a. 875 < 0.28

2 years old A.a. 937 < 0.28

Industrial E.g. pulp 851 < 0.28

his behavior can be due to the higher fine elements content of thendustrial E. globulus pulp, but considering the substantially higheroarseness of A. altissima species, we would also expect a lowerpecific surface area and consequently lower drainage resistance.imilar values were obtained with unbleached A. altissima pulpsFerreira et al., 2013). Regarding the water retention values, eval-ated by submitting the pulp at 3000 × g centrifugation force, the

years old pulp fibers exhibit consistently higher values (rangingrom 1.45 g/g to 2.02 g/g with beating), regarding the 25 years oldulp and E. globulus, which exhibit similar values (1.28–1.06 g/g,espectively, before beating and 1.81–1.84 g/g, after beating).

The 2 years old A. altissima pulp densified more easily andore extensively than the 25 years old A. altissima and E. globu-

us, as shown Fig. 4. This is a consequence of the lower fiber lengthroduced from the 2 years old trees. Despite the higher paper den-ity of the 2 years old ailanthus pulp, the corresponding paperensile strength can be slightly lower than the one exhibited byhe other two pulp samples (Table 3). Moreover, the represen-ation of tensile strength as a function of paper density (Fig. 5)learly discloses the superior performance of the 25 years oldilanthus and of the industrial bleached E. globulus kraft pulp,egarding the pulp provided by the 2 years old trees, which pointso the role of the fiber length, and the intrinsic fiber strength. In

act, both dry and wet zero-span tensile strength of the 2 yearsld ailanthus is over 12% lower than the other two pulps. Theower performance of the pulp provided by the 2 years old trees

ig. 3. Evolution of Schopper–Riegler degrees (◦SR) at different beating levels, forilanthus (A.a.) and eucalypt (E.g.).

Fig. 4. Evolution of apparent paper density as a function of different beating levels,for ailanthus (A.a.) and eucalypt (E.g.).

was also revealed for tear (Table 3), which can be justified withthe lower fiber length, in addition to the lower intrinsic fiberstrength. Air permeability as a function of apparent paper den-sity exhibits very similar values, which point to similar structuralproperties (Table 3). However, the light scattering of the papers pro-duced from the 2 years old tree pulp can be slightly higher (Fig. 6(a)),

as a natural consequence of the higher number of fibers per gram,due to the lower fiber length. On the other hand, Fig. 6(b) shows thatthe drainage rate of the E. globulus pulp suspension is substantially

Fig. 5. Evolution of tensile index as a function of apparent paper density, for ailan-thus (A.a.) and eucalypt (E.g.).

P. Baptista et al. / Industrial Crops a

Fig. 6. Specific light scattering coefficients (a) and pulp suspension drainage resis-t ◦

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liptp

4

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ance ( SR) (b) as a function of apparent paper density, for ailanthus (A.a.) anducalypt (E.g.).

ower than the corresponding A. altissima pulps when the objectives a paper structure with a given apparent density. In summary, theapermaking potential of the bleached kraft pulp produced fromhe A. altissima trees compare very well to the bleached E. globulusulp kraft, a reference pulp for printing and writing papers.

. Conclusions

In this work we have studied the papermaking potential of fast growing species, A. altissima (Miller) Swingle. The youngood (2 years old trees) exhibits a pulping behavior close to euca-

ypts, while the mature wood (25 years old) shows a lower pulpield and required more severe cooking conditions. The ailan-hus pulp fibers are coarser and wider than the eucalypt pulp;he fiber length of mature wood is similar to the one of euca-ypts, but the young pulp fibers are shorter. The papermaking

otential of mature fibers is comparable to those from euca-

ypts, but the young show lower tensile strength and tear index,ainly due to their shorter fiber length and lower intrinsic fiber

trength.

nd Products 52 (2014) 32– 37 37

Acknowledgements

The authors wish to thank FCT (Fundac ão para a Ciência e a Tec-nologia) for awarding a graduation grant to Patrícia Baptista, withinPEst-OE/CTM/UI0195/2011.

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