Bioresource Technology 98 (2007) 3487–3490

Characterization of vine shoots, cotton stalks, Leucaena leucocephalaand Chamaecytisus proliferus, and of their ethyleneglycol pulps

Luis Jiménez a,¤, Antonio Pérez a, María Jesús de la Torre b, Ana Moral a, Luis Serrano a

a Departamento de Ingeniería Química, Universidad de Córdoba, Campus de Rabanales, EdiWcio C-3, 14071 Cordoba, Spainb Departamento de Ciencias Ambientales, Universidad Pablo de Olavide, Sevilla, Spain

Received 27 September 2006; received in revised form 2 November 2006; accepted 4 November 2006Available online 3 January 2007

Abstract

We characterized vine shoots, cotton stalks, Leucaena leucocephala and Chamaecytisus proliferus as pulping raw materials and foundC. proliferus and cotton stalks to be the best for the intended purpose on the grounds of their increased contents in holocellulose (79.73%and 72.86%) and �-cellulose (45.37% and 58.48%), and their decreased contents in ethanol–benzene extractables (2.64% and 1.42%), hotwater solubles (2.79% and 3.33%) and 1% soda solubles (16.67% and 20.34%). These properties resulted in increased pulp yields and hencein eYcient use of these two types of raw material.

The previous raw materials were pulped by using an ethyleneglycol concentration of 65% at 180 °C for 75 min, followed by beating at1500 revolutions in a PFI reWner. The paper sheets obtained were characterized and those from C. proliferus found to be the best overallas they exhibited an increased breaking length (4644 m), stretch (2.87%), burst index (2.46 kN/g) tear index (0.33 m Nm2/g) and brightness(49.92% ISO); in addition C. proliferus pulp was obtained with a high-yield (62.88%). On the other hand, vine shoots provided the poorestresults among the studied raw materials.© 2006 Elsevier Ltd. All rights reserved.

Keywords: Non-wood; Pulping; Ethyleneglycol; Pulp; Paper

1. Introduction

For slightly over a century, the use of wood to manufac-ture paper has allowed an increasing output to be obtainedand led to a shortage of wood supplies that has grown withtime (Jiménez, 2005; Jiménez et al., 2006). This has fostereda search for new raw materials in order to avoid uncon-trolled deforestation, which has raised severe ecologicalproblems in some ecosystems. A number of alternativematerials have so far been tested for this purpose includingagricultural residues and plants other than those of agri-food crops, hardwood or softwood.

Also, consumers are becoming increasingly interested inusing paper produced with clean technologies (viz. pulping

* Corresponding author. Tel.: +34 957 218 658; fax: +34 957 218 625.E-mail address: iq1jiall@uco.es (L. Jiménez).

0960-8524/$ - see front matter © 2006 Elsevier Ltd. All rights reserved.doi:10.1016/j.biortech.2006.11.009

processes using no sulphur compounds and bleaching pro-cesses employing non-chlorinated compounds) or obtainedfrom recycled or non-wood Wbre. The use of unconven-tional raw materials and non-sulphur pulping processessuch as those involving organic solvents (viz. organosolvprocesses) (Jiménez et al., 1997; Hergert, 1998; Muurinen,2000; Jiménez, 2005) might help preserve the environmentby reducing polluting loads and the need for wood as a rawmaterial.

Organosolv processes use either low-boiling solvents(e.g., methanol, ethanol, acetone), which can be easilyrecovered by distillation, or high-boiling solvents (e.g.,ethyleneglycol, ethanolamine), which can be used at a low-pressure and hence at available facilities currently used inclassical pulping processes (e.g., soda and kraft processes)(Muurinen, 2000; Jiménez, 2005).

In this work, we characterized various alternative rawmaterials including vine shoots, cotton stalks, Leucaena

3488 L. Jiménez et al. / Bioresource Technology 98 (2007) 3487–3490

leucocephala and Chamaecytisus proliferus, and pulpobtained from each, with a view to identifying potentialeVective substitutes for conventional pulping raw materials.

2. Experimental

2.1. Characterization of raw materials

The raw materials were analysed for holocellulose, �-cel-lulose, lignin, ash, ethanol–benzene extractables, and hotwater and 1% soda solubles, in accordance with the appli-cable TAPPI standards: T-203-0S-61, T-222, T-221, T-204,T-257 and T-T-212, respectively (TAPPI Standards, 1997).

2.2. Pulping

Pulp from each of the previous raw materials wasobtained in a 15 L cylindrical reactor that was heated bymeans of electrical wires. Each raw material was ground topieces 2–5 cm in size and processed in the reactor by usingan ethyleneglycol concentration of 65% at 180 °C for 75 min,followed by beating at 1500 revolutions in a PFI reWner.Pulp yield was determined in each case and the paper sheetsobtained from each type of pulp were characterized forbreaking length, stretch, burst index, tear index and bright-ness in accordance with the applicable UNE standards:UNE-57-054, UNE-57-028, UNE-57-058, UNE-57-033 andUNE-57-062, respectively (Normas UNE, 1989).

3. Results and discussion

3.1. Characterization of raw materials

Table 1 shows the average results of the chemical analysesof L. leucocephala, C. proliferus, vine shoots and cottonstalks. The standard deviations of the three replicates in eachtest with respect to the means were always less than 10%.

Tables 2–4 show previously reported data for some agri-cultural residues viz., olive prunings, wheat straw, sunXowerstalks, sorghum stalks, rice straw and sugarcane bagasse(Jiménez et al., 1990, 1993, 2006), various alternative rawmaterials (Jiménez, 2005), and hardwood and softwood(Alonso, 1976).

Table 1Characterization of L. leucocephala, C. proliferus, vine shots and cottonstalks

Parameter L. leucocephala C. proliferus Vineshoots

Cottonstalks

Hot water solubles (%) 6.81 2.79 16.09 3.331% soda solubles (%) 23.41 16.67 39.21 20.34Ethanol–benzene

extractables (%)8.19 2.64 4.87 1.42

Ash (%) 2.23 2.31 3.49 2.17Holocellulose (%) 68.34 79.73 67.14 72.86�-cellulose (%) 39.41 45.37 41.14 58.48Hemicellulose (%) 28.93 34.36 26.00 14.38Lignin (%) 18.40 16.80 20.27 21.45

Table 2Characterization of various agricultural residues

Analysis (%) Olive pruningsJiménez et al. (1990)

Wheat strawJiménez et al. (1990)

SunXower stalks Jiménez et al. (1990)

Sorghum stalksJiménez et al. (1993)

Rice strawJiménez (2005)

BagasseJiménez (2005)

Hot water solubles 8.16 12.27 22.72 21.70 16.57 4.401% soda solubles 30.04 43.58 47.81 45.58? 46.94 33.92Ethanol–benzene

extractables10.36 4.01 4.07 7.99 1.40 1.73

Ash 1.36 6.49 7.90 4.85 15.39 2.10Holocellulose 61.47 76.20 71.76 65.93 70.60 80.20�-cellulose 35.67 39.72 42.10 41.50 – –Hemicellulose 25.80 36.48 29.66 24.43 – –Lignin 19.71 17.28 13.44 15.64 25.23 19.80

Table 3

Characterization alternative raw materials (Jiménez, 2005)

HWS D Hot water solubles; 1SS D 1% soda solubles; EBED Ethanol–benzene extractables; HOL D Holcellulose; �-CE D �-cellulose; LIG D Lignin.

Raw material HWS (%) 1SS (%) EBE (%) HOL (%) �-CE (%) LIG (%)

Luecaena diversifolia 3.24 17.38 4.44 77.88 40.10 19.09Leucaena colinsi 4.30 20.02 4.64 80.79 43.77 17.04Leucaena leucocephala (Honduras) 5.01 20.26 6.01 74.11 41.21 19.39Luecaena leucocephla (India) 3.98 18.44 4.64 75.92 44.43 21.43Chamaecytisus (Australia) 2.96 15.55 2.17 82.16 47.65 15.71Chamaecytisus (New Zealand) 2.99 16.15 3.43 75.36 43.59 14.84Chamaecytisus (La Palma) 2.41 16.62 3.30 76.47 44.99 14.10Retama monosperma 3.84 16.93 5.03 71.76 42.75 21.50Phragmites 5.38 34.77 6.36 64.16 39.76 23.66Arundo donax 4.73 26.80 7.30 70.20 40.46 22.34Prosopis julyXora 6.49 22.56 5.30 62.77 36.55 20.60Prosopis alba 4.67 20.86 4.65 63.56 41.55 19.27Paulownia fortuna 9.6 31.5 5.5 70.7 37.4 22.4

L. Jiménez et al. / Bioresource Technology 98 (2007) 3487–3490 3489

As can be seen, the contents in hot water and 1% sodasolubles, and those in ethanol–benzene extractables, of L.lucocephala exceeded those of other varieties of Luecaena(see (Jiménez, 2005, Table 3)), the opposite being true of itsholocellulose and �-cellulose contents.

The contents in hot water and 1% soda solubles, etha-nol–benzene extractables, holocellulose and �-cellulose ofC. proliferus were intermediate among those previouslyreported for other varieties of Chamaecytisus (Jiménez,2005, Table 3); on the other hand, its lignin content wasslightly higher.

The contents in ash, hot water solubles and 1% soda sol-ubles of vine shoots were somewhat higher than those pre-viously reported by Jiménez et al. (1990), Garoglio (1978)and Lossada et al. (1979); on the other hand, their contentin ethanol–benzene extractables was similar to thoseobtained by Jiménez et al. (1990) and Garoglio (1978), butslightly lower than those reported by Lossada et al. (1979).Their content in holocellulose was intermediate amongthose obtained by Jiménez et al. (1990) and Garoglio(1978), whereas that in �-cellulose was lower than thosereported by the previous authors. Finally, their lignin con-tent was quite similar to those reported by such authors.

The contents in hot water solubles, ethanol–benzeneextractables and ash of cotton stalks were lower than thosereported by several authors (Smith, 1976; Pandey andMehta, 1979; Dhake and Khante, 1981; Patel et al., 1985;Cruz de Cronis, 1985), while those in 1% soda solubles,holocellulose, �-cellulose and lignin were intermediateamong those reported by other authors (Smith, 1976; Pan-dey and Mehta, 1979; Dhake and Khante, 1981; Soemardi,1982; Mobarak, 1982; Patel et al., 1985; Cruz de Cronis,1985). In summary, cotton stalks contain little ash, waterand soda solubles, and ethanol–benzene extractables.

The discrepancies between the reported values for thestudied raw materials may have arisen from the use ofdiVerent procedures, and of raw materials of diverse originand variety.

A comparison of the results for our raw materials (Table1) with those previously reported for various types of agri-cultural residues (Table 2), unconventional plant materials(Table 3), and hardwood and softwood (Table 4), revealsthe following:

(a) The content in hot water solubles is very high in vineshoots and very low in C. proliferus and cotton stalks– the values for which are similar to those for hard-wood, softwood and previously studied alternativeraw materials (Table 3).

(b) The content in 1% soda solubles is very high in vineshoots. Also, those in the other studied materialsare similar to the contents of alternative plants andhigher than those of hardwood and softwood.

(c) The highest content in ethanol–benzene extractables isthat of L. leucacephala and is as high as those of someagricultural residues and higher than those of the otherraw materials studied – which are in turn similar tothose of alternative plants, hardwood and softwood.

(d) The contents in ash of the studied materials are lowerthan those of some agricultural residues, but higherthan those of hardwood and softwood.

(e) The highest content in holocellulose is that of C. pro-liferus and is similar to those of eucalyptus wood, L.collinsi and bagasse; those of the other studied materi-als are similar to the contents of some agriculturalresidues, alternative plants and softwood.

(f) The highest content in �-cellulose is that of cottonstalks, which is similar to those of hardwood and soft-wood. That of C. proliferusis higher than those ofagricultural residues and alternative plants, and thoseof vine shoots and L. leucocephala are similar to thoseof agricultural residues and alternative plants.

(g) Finally, the lignin content is low – and similar tothose of some agricultural residues such as wheatstraw, sorghum stalks and sunXower stalks – in C.proliferus. Those of the other raw materials studiedare similar to the contents of other agriculturalresidues and alternative plants, but invariably lowerthan those of hardwood and softwood.

Based on the foregoing, C. proliferus and cotton stalks arethe best raw materials among those studied on the groundsof their increased contents in holocellulose and �-cellulose,and their decreased contents in ethanol–benzene extracta-bles, hot water solubles and 1% soda solubles. These charac-teristics can be expected to facilitate their eYcient use as rawmaterials for the obtainment of pulp with a high-yield.

Table 4Characterization of hardwood and softwood (Alonso, 1976)

HWS D Hot water solubles; 1SS D 1% soda solubles; EBE D Ethanol–benzene extractables; ASH D Ash; HOL D Holocellulose; LIG D Lignin;�-CE D �-cellulose; HEM D Hemicellulose.

Parameter Pine pinaster Eleven varietiesof pine

Standarddeviation

Eucalyptus globulus Twenty four varietiesof eucalyptus

Standarddeviation

HWS (%) 1.99 2.04 0.62 2.84 4.19 1.831SS (%) 7.98 10.33 2.10 12.42 14.69 2.37EBE (%) 2.57 1.29 0.58 1.15 2.09 1.03ASH (%) 0.54 0.33 0.16 0.57 0.57 0.23HOL (%) 69.59 67.60 4.70 80.47 77.21 3.97LIG (%) 26.22 28.83 2.62 19.96 25.54 2.45�-CE (%) 55.92 – – 52.79 – –HEM (%) 13.67 – – 27.68 – –

3490 L. Jiménez et al. / Bioresource Technology 98 (2007) 3487–3490

3.2. Pulping

Table 5 shows the pulp yield and the values of the prop-erties of the paper sheets obtained from the diVerent typesof pulp. The operating conditions used, which are describedunder Experimental, were chosen from a previous study(Pérez, 2006) in which they were found to save heatingenergy, pulping chemicals and facility investments by eVectof enabling operation at a lower temperature, and using asmaller amount of solvent for a shorter time than thoseused in the reference work (viz. an ethyleneglycol concen-tration of 70% at 185 °C for 90 min) without signiWcantlydetracting from the properties of the resulting paper sheets.

As can be seen from Table 5, C. proliferus is no doubtthe best raw material among those studied. In fact, it pro-vided paper sheets with better breaking length, stretch,burst index, tear index and brightness than the other mate-rials. Also, it exhibited a high-pulp yield as a reXection ofits amenability to eYcient processing. On the other hand,vine shoots proved the worst raw material as their pulpwas obtained at a low-yield and the resulting papersheets exhibited the poorest properties.

Finally, the paper sheets obtained from cotton stalks hadan increased breaking length, stretch, burst index and tearindex relative to those from L. leucocephala, but exhibiteda low-pulp yield and paper brightness relative to the latter.

Acknowledgements

The authors are grateful to Ecopapel, S.L. (Écija, Sevilla,Spain) and ENCE (Huelva, Spain) for their support, and to

Table 5Properties of pulp and paper sheets from previous raw material studied,obtained by using ethyleneglycol

Property L. leucocephalapulp

C. proliferus pulp

Vine shootspulp

Cotton stalks pulp

Yield (%) 62.37 62.88 49.65 57.24Breaking

length (m)3074 4644 2686 4401

Stretch (%) 1.89 2.87 1.49 2.34Burst index

(kN/g)1.32 2.46 1.05 2.13

Tear index(m Nm2/g)

0.24 0.33 0.18 0.26

Brightness(%)

37.56 40.92 20.97 26.15

Spain’s DGICyT for funding this research within theframework of the Projects PPQ2003-03913-C02-01 andCTQ2004-06564-C04-01.

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