Bioresource Technology 101 (2010) 775–780

Contents lists available at ScienceDirect

Bioresource Technology

journal homepage: www.elsevier .com/locate /bior tech

Chemical composition and pulping of date palm rachis and Posidonia oceanica – Acomparison with other wood and non-wood fibre sources

R. Khiari a,b, M.F. Mhenni a, M.N. Belgacem b,*, E. Mauret b

a Research Unity of Applied Chemistry and Environment, Department of Chemistry, Faculty of Sciences, Monastir 5019, Tunisiab Laboratoire de Génie des Procédés Papetiers UMR CNRS 5518, Grenoble INP-Pagora, B.P. 65, 38402 Saint Martin d’Hères Cedex, France

a r t i c l e i n f o

Article history:Received 29 June 2009Received in revised form 20 August 2009Accepted 21 August 2009Available online 18 September 2009

Keywords:Date palm rachisPosidonia oceanicaChemical compositionPulpingFibre properties

0960-8524/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.biortech.2009.08.079

* Corresponding author. Tel.: +33 04 76 82 69 62; fE-mail address: naceur.belgacem@efpg.inpg.fr (M.

a b s t r a c t

In the present paper, the valorisation of two residues: Posidonia oceanica and date palm rachis was inves-tigated. First, their chemical composition was studied and showed that they present amounts of holocel-lulose, lignin and cellulose similar to those encountered in softwood and hardwood. Extractives indifferent solvents and ash contents are relatively high. Moreover, ash composition assessment showedthat silicon is the major component (17.7%) for P. oceanica. The high ash quantity and the low DP (about370) may be considered as serious disadvantages of P. oceanica, in the pulping and papermaking context.Oppositely, the properties of rachis date palm and those of the ensuing pulp, obtained from a classicalsoda-anthraquinone cooking, demonstrated the suitability of this agricultural by-product for papermak-ing. Preliminary tests conducted on unrefined pulp suspensions and handsheets from date palm rachis interms of freeness, Water Retention Value and mechanical properties allowed confirming the good qualityof date palm rachis fibres.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Paper consumption is continuously increasing in the world evenin countries where wood resources are very limited. Furthermore,the valorisation of agricultural residues or marine biomass throughrational and innovative ways of utilization is of potential interest,in such countries, since they can be considered as new cellulosic fi-bre sources. Such strategies were already applied to valorize vari-ous agricultural crops available for instance in Portugal (Antuneset al., 2000; Cordeiro et al., 2004), India (Dutt et al., 2008), Malaysia(Wan Rosli et al., 2003), Iran (Hedjazi et al., 2008), Sudan (Khristovaet al., 2005) or Tunisia (Aguir and M’henni, 2006; Gezguez et al.,2009). In this work, we investigated the valorisation of twolignocellulosic materials, largely available in Tunisia, as a sourceof cellulosic fibres, namely: Posidonia oceanica balls and date palmrachis.

P. oceanica is the dominant sea grass in the Mediterranean Sea.Important quantities of P. oceanica fragments accumulated onTunisian coasts, which imposes the cleaning of the beaches everysummer. The valorisation of this available and renewable lignocel-lulosic biomass can be considered as a suitable solution for thisproblem. Nowadays, P. oceanica is studied as a low cost and renew-able adsorbent for removing dyes or phenol (Ncibi et al., 2006,

ll rights reserved.

ax: +33 04 76 82 69 33.N. Belgacem).

2008; Gezguez et al., 2009) or as a source of cellulose (Aguir andM’henni, 2006). In that case, P. oceanica is treated in order to ex-tract cellulose and convert it into carboxymethyl cellulose. To thebest of our knowledge, no complete data about the chemical com-position of P. oceanica are available in the literature. Moreover, itspotential use as a source of lignocellulosic fibres for the productionof pulp and paper has never been tested.

Date palm (Phoenix dactylifera) is one of the most cultivatedpalms in the arid and semi-arid regions of the world. Tunisia hasmore than 4 millions date palms which occupy 32,000 ha (statis-tics from the Tunisian Ministry of Agriculture, 2003). After the datefruit harvesting, important quantities of date palm rachis wastesaccumulated every year in Tunisian agricultural lands. Here also,rational ways of valorising this abundant renewable resourceshould be find. For instance, it is well known that the use of natu-ral fibres in composites is a way of meeting the increasing demandin biodegradable and renewable materials. In this context, datepalms agricultural residues (rachis or leaves) can be viewed assources of reinforcing fibres for polymeric matrices in compositematerials. Such way of valorisation has been recently undertaken(Al-Sulaiman, 2002; Abou-Shark and Hamid, 2004; Taha et al.,2007; Bendahou et al., 2008; Sbiai et al., 2008). Oppositely, onlyfew studies evaluated the potential use of date palm by-productsfor pulp and paper manufacturing and most of them are dedicatedto the pulping of date palm leaves (Ezzat, 1974; El Morsy, 1980; ElMorsy et al., 1981). To the best of our knowledge, only Khristovaet al. (2005) compared pulps produced from rachises and leaves.

776 R. Khiari et al. / Bioresource Technology 101 (2010) 775–780

Thus, the main objectives of this paper are the characterizationof these two Tunisian cellulosic by-products (P. oceanica balls anddate palm rachis) and the evaluation of their properties, in thepapermaking context. The first part of this work is devoted to thedetermination of the chemical composition. Then, soda-anthraqui-none cooking, which is considered as the most suitable process forpulping annual plants (Antunes et al., 2000), is tested. The ensuingpulps are characterised in terms of yield, kappa number, degree ofpolymerisation (DP) and chemical composition (residual lignin,holocellulose, cellulose and extractives). Finally, the physical andmechanical properties of handsheets are presented and discussed.The obtained results (chemical composition of pulps and physicalproperties of papers) are compared to other wood and non-woodsources thanks to a complete literature review.

2. Materials

2.1. Raw materials

P. oceanica balls and date palm rachis used in this study werecollected in Monastir in August 2007. These wastes were dried un-der natural conditions during September 2007 (average relativehumidity = 65%; average temperature = 25 �C). The date palm ra-chises of about 1 m length and 6–7 cm diameter were then cut into1–3 cm pieces before pulping. The P. oceanica balls were washed inorder to eliminate sand and contaminants and then dried again un-der the same conditions.

2.2. Characterization of raw materials

Chemical composition of P. oceanica balls and date palm rachiswas determined. The evaluation of extractive substances was car-ried out in different liquids according to common standards,namely: cold and hot water (T207 cm-08), 1% sodium hydroxidesolution (T212 om-07) and ethanol–toluene (T204 cm-07). Ashcontent (T211 om-07) was determined and analysis of the mineralfraction was performed at the ‘‘Service Central d’Analyse – Vernai-son (CNRS)”. The amounts of lignin, holocellulose, cellulose, as wellas the kappa number were also assessed by using the followingrespective standard methods: T222 om-06, method of Wise et al.(1946), T203 cm-99 and T236 om-06. As recommended by the var-ious standards used, all the experiments were duplicated and thedifference between the two values was within an experimental er-ror of 5%.

2.3. Pulping

The delignification of date palm rachis was carried out accord-ing to the procedure described by Khristova et al. (2005) with a to-tal alkali charge of 20% expressed in NaOH (based on w/w o.d.rachis), an anthraquinone concentration of 0.1% (w/w with respectto o.d. material) and a cooking time at constant temperature of120 min. The liquor to solid ratio was changed and fixed at 10due to the experimental device used and different temperaturesranging from 150 to 170 �C were tested. All the experiments wereconducted in a 1 L reactor, in which the heating time to reach theconstant temperature was 1 h. The same procedure was applied toP. oceanica balls.

2.4. Pulp and paper characterization

After cooking, the obtained pulps were washed several timesthrough a wire until obtaining a clear filtrate and characterisedin terms of yield, kappa number, residual lignin, holocelluloseand ethanol–toluene extractives. The cooking yield was calculated

as the ratio of the weight of o.d. material after washing to that ofinitial raw material. The residual lignin was determined from boththe Klason lignin and the soluble lignin measured by UV absorptionof a filtrate specimen at 205 nm (Tappi method UM 250). The vis-cosity of pulp (g in mPa s) dissolved in a cupriethylene-diaminesolution was determined according to Tappi standard (T230 om-99). These values were then converted into degrees of polymerisa-tion (DP) thanks to the following relation proposed by Sihtola et al.(1963):

DP ¼ ½0:75ð954Log10g� 325Þ�1:105 ð1Þ

All the experiments were duplicated and the difference between thetwo values was within an experimental error of 5%.

After disintegration (standard method ISO 5263-1), the pulpwere passed through a slotted screen of 0.15 mm aperture size,in order to remove uncooked materials. The screening yields weredetermined as the ratio between the weights of o.d. material beforeand after screening. Morphological properties of the fibres werestudied by SEM observations (results not shown) and by using aMORFI analyzer (Techpap): the main fibre parameters were as-sessed by image analysis of a diluted suspension flowing in a trans-parent flat channel observed by a CCD video-camera. WaterRetention Values (WRV) were also determined by centrifugationof wet pulp samples during 15 min at 3000g according to Silvy’smethod (Silvy et al., 1968). The samples were weighted, beforeand after drying, and the WRV calculated. The pulp drainabilitywas evaluated by measuring the Shopper Riegler degree (SR –ISO 5267-1). The unbeaten screened pulps suspensions were di-luted to 2 g L�1. Then, conventional handsheets with a basis weightof 60 g/m2 were prepared on a Rapid Khöten sheet former follow-ing the standard method IS0 5269-2. Prior to testing, the hand-sheets were conditioned (23 �C, 50% relative humidity – ISO 187)and structural and mechanical properties were determined bymeasuring basis weight, thickness, bulk and permeability, as wellas the tensile, burst and tear strength according to standards ISO536, ISO 534, ISO 5636-3, ISO 1924-3, ISO 2758 and ISO 1974. Asrecommended by the various standards used, all the measure-ments were made 10 times, thus allowing the determination ofstandard deviation. Paper thickness was measured 20 times.

3. Results and discussion

3.1. Characterization of the raw material

The chemical composition of P. oceanica and date palm rachisare listed in Table 1, which shows that these raw materials arecharacterised by relatively high amounts of extractives, especiallyfor ethanol–toluene extractives (10.7% and 6.3% for Posidonia anddate palm rachis, respectively). The main difference between Posi-donia and date palm rachis is related to ash content, which is high-er for Posidonia (12%) compared to that of date palm rachis (5%).Cellulose content is similar for both raw materials studied (40%for Posidonia and 45% for date palm rachis). For date palm rachis,chemical compositions from other works are also reported in Table1, which shows that, when available, data are relatively close to ourresults apart from the content in lignin (Bendahou et al., 2007). Dif-ferences may be related to climate conditions, soil chemical com-position. . . Finally, it is worth noting that date palm rachiscontains higher amount of cellulose than leaves, as it can be ob-served in Table 1; it implies that using rachis instead of leaveswould be more profitable for papermaking applications.

Table 2 summarizes chemical compositions collected from liter-ature for various cellulosic biomasses such as hardwood and soft-wood, agricultural residues and other various non-wood sources.The comparison with the present work leads to several comments

Table 1Chemical composition of Posidonia oceanica balls and date palm rachises and leaves – comparison with data collected from previously published studies.

Amounts in % (w/w withrespect to oven driedraw material) (%)

Posidonia oceanica balls Date palm rachis Date palm leaves

This work This work Khristovaet al. (2005)

Bendahouet al. (2007)

El Morsy (1980) Khristovaet al. (2005)

Bendahouet al. (2007)

Ezzat (1974)

Cold water extractives 7.3 5.0 n.d. n.d. n.d. n.d. n.d. n.d.Hot water extractives 12.2 8.1 8.7 n.d. n.d. 10.8 n.d. n.d.1% NaOH extractives 16.5 20.8 25.6 n.d. n.d. 29.9 n.d. n.d.Ethanol–toluene extractives 10.7 6.3 12.8a 4 n.d. 11.7a 3 5.9b

Ash 12 5 5.6 2.5 3.4 9.6 6.5 3.9Lignin 29.8c 27.2c 23.8d 14 25.8 31.2d 27 n.d.Holocellulose 61.8 74.8 n.d. 72 n.d. n.d. 59.5 n.d.Cellulose 40 45 43.1 44 n.d. 30.3 33.5 n.d.

a In ethanol–cyclohexane.b In alcohol–benzene.c Klason lignin.d Residual lignin (Klason and soluble lignin).

Table 2Chemical composition of some lignocellulosic plants.

Reference C.W. H.W. A.B. 1% NaOH Ash Hol. Lign. Hemi. Cell.

WoodBrutia pine Copur and Tozluoglu (2008) 2.2 2.8 1.94 16.1 0.4 75.5 26.1 28.5 47Pine pinasterb Jimenez and Lopez (1990) and

Jimenez et al. (2008)n.d. 2 1–2.6 7.9–10.3 0.3–0.5 69–67 26–28 13. 7 56

Eucalyptus globulusb Jimenez and Lopez (1990) andJimenez et al. (2008)

n.d. 2.8 1.15 12.42 0.6 80.5 19.9 27.7 53

Olive wooda Jimenez and Lopez (1990) andJimenez et al. (1992, 2008)

15.5 17 10.4 30.0 1.4 65.83 15.64 24.33 41.5

Holm Oak (Quercus ilex) Eugenio et al. (2006) n.d. n.d. n.d. n.d. n.d. 71.2 16.3 28.3 43

Non-woodProsopis alba Jimenez et al. (2008) n.d. 4.7 4.65 20.8 n.d. 63.6 19.3 22.0 42Chamaecytisus Jimenez et al. (2008) n.d. 3 3.43 16.1 n.d. 75.3 14.8 31.7 44Phragmites Jimenez et al. (2008) n.d. 5.4 6.36 34.7 n.d. 64.1 23.6 24.4 40Retama monosperma Jimenez et al. (2008) n.d. 3.8 5.03 16.9 n.d. 71.7 21.5 29.0 43Arundo donax Shatalov et al. (2001) n.d. 6.7 9.2 n.d. 4.8 61.2 20.9 32.1 29.2Banana pseudo-stems Cordeiro et al. (2004) n.d. 5.4 2.7 n.d. 14 65.2 12.7 25.2 40Paulownia fortuna Jimenez et al. (1993, 2008) n.d. 9.6 5.5 31.5 n.d. 70.7 22.4 33.3 37

Annual and perennial plantsWheat straw Schott (2000) 5.8–11 14 4.6–9.2 41–42.8 4–9 n.d. 11–21 21–28.5 33–45.5Rice dishes Alcaide et al. (1990) 10.6 13 4.6–5.7 49.1 13–20 n.d. 11–13.5 13–26.2 42–49.8Barley fodder Alcaide et al. (1990) 16 16 4.7 47 4.9–7 n.d. 7–18 24.5 34–48Rye straw Alcaide et al. (1990) 8.4 9.4 3.2–5.2 37.4 4–4.3 n.d. 18.5–19 23–30.5 55Oat straw Alcaide et al. (1990) 13.2 15 4.4 41.8 7–7.5 n.d. 11–19.6 16–27 37–53.6Sorghum stalks Jimenez et al. (1993) n.d. 21.7 7.99 41.6 4.85 71.7 13.4 29.3 42Amaranth Fiserova et al. (2006) 23.5 28 2.51 46.8 12 58.4 13.2 26.1 32Orache Fiserova et al. (2006) 4.6 6.5 1.87 27.5 2 74.9 19.5 38.8 36Jerusalem artichoke Fiserova et al. (2006) 26.6 31 2.86 48.5 3 51.6 14.7 23.1 29Cynara cardunculus L.a Antunes et al. (2000) and Gominho

et al. (2001)n.d. 10 6 n.d. 8 64 20 26 38

Miscanthus sinensis Barba et al. (2002) n.d. 9.1 3.1 n.d. 0.7 72.5 19.9 30.3 42Kenaf (Hibiscus cannabinus) Manfred (1993) n.d. n.d. n.d. n.d. 1.7–5 n.d. 14.5–18.7 n.d. 31–39

C.W.: cold water solubility; H.W.: hot water solubility; A.B.: solubility in various organic solvents; 1% NaOH: 1% sodium hydroxide solubility; Hol.: holocellulose; Lign.: Klasonlignin (%); Hemi.: hemicellulose; Cell.: cellulose.

a Average of 2 or 3 varieties.b Average of 11 varieties.

R. Khiari et al. / Bioresource Technology 101 (2010) 775–780 777

concerning the amount of extractives. Thus, in cold and hot water,the quantity of extractives for both P. oceanica and date palm rachisare higher than those found in hardwood and softwood but compa-rable to the amounts usually encountered in non-wood sources.The 1% NaOH extractives (16.5% for P. oceanica and 20.8% for datepalm rachis) are similar to those of wood sources, i.e. less than 20%,but are lower than those of annual plants. Finally, the amount ofextractives in ethanol–toluene for the raw materials under investi-gation is relatively high, although in the same order of magnitudeas those observed for other annual plants or agricultural crops.

Considering the structural components, Klason lignin for bothmaterials studied was also found to be quite high ( P. oceanica:29%; date palm rachis: 27%), when compared to typical amounts

encountered in annual plants, non-wood and hardwood sourceswhich are close to 20%. Lignin content of these two materials isthen close to that of softwood. In the same way, the amounts ofholocellulose and cellulose for the two raw materials were similarto those found in wood and non-wood plants. These importantfractions allow envisaging the valorisation of such crops as cellu-lose derivatives and/or as lignocellulosic fibres for fibre-reinforcedcomposite materials or papermaking applications like in the cur-rent study.

Concerning now the ash content, it is high for P. oceanica (12%)and comparable to that of rice dishes, Banana pseudo-stems andAmaranth which exhibit the greatest contents, as already reportedin the literature (see Table 2). This can be attributed to the

778 R. Khiari et al. / Bioresource Technology 101 (2010) 775–780

chemical composition of the marine environment in which theplants are growing or/and to a pollution of the balls by sand, evenif intensive washing was performed before analyses. On the oppo-site, ash content in date palm rachis (5%) is lower but remains atthe same order of magnitude as most of the non-wood plants. Con-sidering the important quantity of ashes for these two raw materi-als, their chemical composition was determined. The results aresummarized in Table 3 in which literature data are also reported,for comparison. For date palm rachis, ashes are mainly constitutedby Ca, Cl, K, Cl and Na atoms. The absolute amount of silicon is verylow (0.14% w/w on o.d. raw material) and similar to those reportedby Khristova et al. (2005) for both date palm rachises and leaves(0.06% and 0.56%, respectively). In this case, the high quantity ofashes cannot be considered as problematic, in the context of pul-ping and papermaking processes, since the silicon-based salts arenegligible. Oppositely, silicon is predominant in P. oceanica (abso-lute content of 2.1% w/w on o.d. raw material). This importantamount will negatively impact the chemical recovery processand, therefore, could constitute a serious drawback, if consideringthe valorisation of this marine plant in papermaking stream. Nev-ertheless, it must be kept in mind that a possible pollution by sandcould be responsible. To conclude, comparison with other plants(Amaranth and Banana pseudo-stems) shows that chemical com-position of ashes may considerably vary from one species to an-other, as shown in Table 3.

3.2. Pulping – pulp and paper characterization

3.2.1. Chemical composition of pulps extracted from date palm rachisand P. oceanica

Soda-anthraquinone cookings of P. oceanica and date palm ra-chis were conducted. The experimental conditions as well as thecomposition of the ensuing pulps were listed in Table 4. Whateverthe raw material, a decrease of cooking yield, extractives, lignincontent, kappa number and viscosity occurred, when the cookingtemperature increases from 150 to 170 �C. Oppositely, an increaseof the relative content in holocellulose is observed. Regarding theash contents, they are surprisingly unaffected by the pulping oper-ation. This behaviour has to be taken into account since the per-centage of silicon in P. oceanica is dramatically high. Analysingmore deeply the results, it appears that delignification is more pro-nounced for date palm rachis with a mean cooking yield of 44%compared to 63% for Posidonia, a mean relative content in ligninof 4% compared to 9% for Posidonia and a mean Kappa number of47 compared to 63 for Posidonia. Nevertheless, it is difficult to com-pare the contents in lignin and holocellulose as the sum of compo-nents (ash, lignin, holocellulose) reaches about 93% for P. oceanicapulp and only 80% for date palm rachis pulps. This indicates that

Table 3Ash composition for Posidonia oceanica and date palm rachis (in % w/w with respect to ove

% Posidonia oceanica balls Date palm rachis

This work This work Khristova et al. (2005)

Si 17.7 2.8 1.1Ca 9.12 21.5 n.d.Mg 3.89 3.53 n.d.Fe 3.78 240 ppm n.d.Cu <100 ppm 360 ppm n.d.K 2.04 10.2 n.d.P 0.12 0.7 n.d.S 1.92 1.69 n.d.C <0.3 1.5 n.d.Cl 0.72 18.6 n.d.Na 2.49 6.79 n.d.

Absolute silicon contents in raw materialsSi 2.13 0.14 0.06

some constituents of the pulp are lost during the analysis. Thistrend is also observed for the majority of the non-wood plants,as presented in Table 2. Thus, the total amounts of all the compo-nents is generally comprised between 80% and 95%. This behaviouris probably due to the fact that standard methods designed forwood plants are used without modification for the determinationof chemical composition of non-wood or annual plants. Finally,the DP of the unbleached pulps from date palm rachis is around1200, which is similar to values obtained for unbleached Kraftwood fibres (generally about 1300–1500). The lower value of DPfor P. oceanica pulp (around 500) probably indicates the lowerstrength properties of this material. Table 4 also includes the mainresults taken from previously published works for pulp of datepalm. It clearly appears that, when pulping conditions are close,pulp characteristics are similar: there is a good agreement betweenour experimental values and those arising from the literature, par-ticularly those of Khristova et al. (2005). Cooking conditions usedby El Morsy et al. (1981) seem to be not optimised: even if appar-ent mild conditions of cooking are applied, the ensuing DP is sur-prisingly low. Finally, the better quality of rachis over leaves isonce again demonstrated by comparing yields and viscosity ofthe pulps obtained from these two raw materials. Thus, apart fromthe ash content and the DP of P. oceanica pulp, the characteristics ofthe studied fibres, in terms of cooking yield and Kappa number areclose to those obtained from unbleached kraft pulping of softwoodand hardwood. Their pulping yield is even better than that ob-served for annual plants and agricultural crops, generally around35% (Alcaide et al., 1990; Jimenez and Lopez, 1990; Jimenezet al., 1993, 2008; Schott, 2000; Fiserova et al., 2006).

3.2.2. Physical properties of pulp and paper from date palm rachis andP. oceanica

Pulps of P. oceanica and date palm rachis were then character-ised in terms of physical properties and used for making conven-tional handsheets. Unrefined pulps will be considered in this partwhereas the effect of refining on pulps and papers will be reportedin a next publication. From SEM photographs observations, it ap-pears that the length of P. oceanica fibres is significantly lower thanthat obtained from date palm rachis. This observation is confirmedby morphological measurements collected in Table 5.

Whereas the fibre width is roughly the same for the two rawmaterials studied, the fibre length of date palm rachis pulp isapproximately 60% higher than that of the corresponding fibres ex-tracted from Posidonia. Thus, the aspect ratio (length to diameterratio) is equal to 40 for date palm rachis fibres and reaches only25 for Posidonia fibres, which is rather low. For comparison, thelength of softwood and hardwood fibres is 2–3 mm and 1–2 mm,respectively and the corresponding aspect ratios are around 100

n dried raw material). Comparison with data taken from previously published studies.

Date palm leaves Amaranth Banana pseudo-stems

Khristova et al. (2005) Fiserova et al. (2006) Cordeiro et al. (2004)

5.8 0.25 2.7n.d. 4.17 7.5n.d. 0.035 4.3n.d. n.d. n.d.n.d. 0.01 n.d.n.d. 36.67 33.4n.d. n.d. 2.2n.d. n.d. n.d.n.d. n.d. n.d.n.d. n.d. n.d.n.d. n.d. n.d.

0.56 0.03 0.38

Table 4Pulping conditions and chemical composition of unbleached pulps from Posidonia oceanica and date palm rachis or leaves.

Date palm rachis Posidonia oceanica Date palm rachis Date palm leaves

This work Khristovaet al. (2005)

El Morsy(1980)

El Morsy et al.(1981)

Khristovaet al. (2005)

El Morsy et al.(1981)

Ezzat(1974)

Total alkali charge expressedin NaOH, %a

20 20 23 12 15 13 20 12 18c

Anthraquinoneconcentration

0.1 0.1 0 0 0.1 0 0

Time at constanttemperature, min

120 120 120 20 120 20 300

Temperature, �C 150 160 170 150 160 170 165–170 100 150 165 150 150Cooking yield, %a 46.8 44.8 41.8 66.0 63.6 59.9 44.2 42.3 78.5 58.5 39.7 29.5 22.6 38.5Screening yield, %a 94 96 43.1 42 n.d. n.d. 39.7 28.2 n.d. n.d.Ethanol–toluene extractives,

%bn.d. 1.81 0.91 n.d. 0.57 0.26 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.

Ash, %b 4 12 n.d. n.d. 2.2 1.8 n.d. n.d. 3.6 6.15Holocellulose, %b n.d. 69.3 75.2 n.d. 71.4 72.4 n.d. n.d. n.d. n.d. n.d n.d. n.d. n.d.Lignin, %b n.d. 5.2 3.4 n.d. 9.1 8.5 n.d. n.d. 22.2 6.3 n.d. n.d. 10.8 2.2Kappa-number 59 54 47 75 65 63 25.5 20.7 n.d. n.d. 50 20.9 n.d. n.d.Pulp viscosity (mPa s) or

(mL g�1)n.d. 15.7d 15.3d n.d. 5.4d n.d. 937e 845e n.d. n.d. 618e 780e n.d. n.d.

DP (pulp) n.d. 1203 1188 n.d. 513 n.d. 1403 1252 n.d. 880 886 1146 510 n.d.

a w/w With respect to oven dried raw material.b w/w With respect to oven dried pulps.c Sulfidity 25%.d Pulp viscosity in mPa s.e Pulp viscosity in mL g�1.

Table 6Paper properties made from date palm rachis (average values and standard deviation)– comparison with data by Khristova et al. (2005).

This work Khristova et al. (2005)

Shopper Riegler degree (�SR) 14 15.5Basis weight (g/m2) 63.9 ± 1.9 n.d.Thickness (lm) 141 ± 6 n.d.Bulk (cm3/g) 2.21 n.d.Permeabilty (cm3/s Pa m2) 450 ± 0.042 n.d.Breaking length (km) 3.13 ± 0.23 4.40Elongation (%) 1.09 ± 0.09 n.d.Specific energy (mJ/g) 221 ± 37 n.d.Young modulus (GPa) 2.51 ± 0.14 n.d.Burst index (kPa m2/g) 1.32 ± 0.05 1.9Tear index (mN m2/g) 4.4 ± 0.37 10Dry zero-span breaking length (km) 13.4 ± 0.91 n.d.Wet zero-span breaking length (km) 10.8 ± 0.66 n.d.Internal bond strength (J/m2) 94 ± 8.8 n.d.Short-Span Compression Test (kN/m) 1.32 ± 0.13 n.d.

Table 5Main properties of the pulps of Posidonia oceanica and date palm rachis (average ofthree experimental data).

Date palmrachis

Posidoniaoceanica

Shopper Rieglerdegree (�SR)

14 10

Fibremorphology

Fibre lengtha (mm) 0.89 0.55Fibre width (lm) 22.3 21.3Fine elements (% in length) 30.8 7.5

WRV % (w/w on o.d. pulp) 138 110

a Weighted mean.

R. Khiari et al. / Bioresource Technology 101 (2010) 775–780 779

and 60. Then, date palm rachis fibres present length to diameter ra-tio comparable to that of certain hardwood pulps. Date palm rachispulp is also characterised by a great content of fines (30% in length)compared to Posidonia pulp for which it is much lower (around 7%).Finally, Water Retention Value (WRV) of date palm rachis pulp ismore important than that of Posidonia counterpart (see Table 5).We can note that WRV for date palm rachis (138%) is significantlyhigher than that of unrefined pulps arising from softwood andhardwood (90–100%). This property allows predicting a high levelof flexibility of the fibres and consequently good mechanical prop-erties of the ensuing paper. Drainability of both pulps is similar tothat of unrefined softwood fibrous suspensions and better thanthat of other non-wood sources and plants like Cynara cardunlusL. (Antunes et al., 2000; Gominho et al., 2001) or hemp and bamboo(Khristova et al., 2005). P. oceanica pulp exhibits very high draina-bility (10 �SR), which is probably related to its low content in fineelements. Concerning the date palm rachis pulp, combination of agood drainability with a high WRV is surprising and difficult tounderstand especially since morphological properties of the pulpshow a high content of fine elements. Unfortunately, no data areavailable in the literature for a better understanding of such behav-iour. Ezzat (1974) obtained a pulp with a Schopper Riegler degreeof 18.5, but the pulping conditions do not allow comparing the re-sults. Only Khristova et al. (2005) produced a pulp in similar exper-imental conditions of cooking which exhibits a Schopper Riegler

degree of 15; no further characterization was done apart from anestimation of the morphological properties of the fibres throughmicroscopic analysis. Nevertheless, it confirms the high drainabil-ity of this pulp.

Pulps were then used for making handsheets. First, it is worthnoting that it was not possible to produce paper from P. oceanicapulps as the strength of the wet web was dramatically low andimpeeded to undergo the ensuing operations of pressing and dry-ing. This can be due to the low DP previously mentioned but alsoto the morphological characteristics of the fibres reported in Table5 and especially the very low aspect ratio of the fibres. Thus, no fur-ther investigation was conducted with this raw material alone. Thevalorisation of this marine biomass in papermaking field may beconsidered by blending it with other pulps, for example or by test-ing the leaves instead of the balls. However, paper sheets from datepalm rachis based papers were made and their physical propertiesare reported in Table 6. The obtained data shows that this rawmaterial could be considered as a promising raw material forpapermaking applications. Considering the structural paper

780 R. Khiari et al. / Bioresource Technology 101 (2010) 775–780

properties, it appears that the bulk is high but this property maypartially result from an overestimation of the thickness of the sheetdue to the presence of impurities not fully eliminated by thescreening operation. The permeability is also high despite the pres-ence of fine elements in the pulp. All the mechanical propertiestested exhibit very good values for an unrefined pulp: breakinglength (km), elongation (%), specific energy (mJ/g), Young modulus(GPa), burst index (kPa m2/g), tear index (mN m2/g). The intrinsicstrength of the fibres (zero-span breaking length – wet) is about10 km which is quite significant and witnesses about the appropri-ate conditions of cooking. No comparison with data arising fromthe literature may be done as the previously published works didnot describe the properties of unrefined pulps apart from a partialcharacterization conducted by Khristova et al. (2005), which con-firmed the good quality of date palm rachis based papers (see Table6).

4. Conclusions

The chemical composition of two alternative sources of fibreswas established. The obtained results showed that the two rawmaterials studied contain high amount of cellulose which justifiestheir valorisation in cellulose derivatives or as a source of fibres forcellulose fibres-reinforced composites or in papermaking applica-tions. Thus, several chemical pulps were prepared and character-ised, in terms of yields and morphology. Pulps from date palmrachis gave paper sheets with good properties, without the needof refining operations. This feature can be considered as a seriousadvantage when looking for new alternative sources of fibres forpapermaking.

Acknowledgements

The authors would express sincere thanks to ‘‘IFC”, Institut deCoopération Francais de l’ambassade de France en Tunisie and‘‘MIRA”, Mobilité Internationale du région Rhône-Alpes for itsfinancial support.

References

Abou-Shark, B., Hamid, H., 2004. Degradation study of date palm fibre/polypropylene composites in natural and artificial weathering: mechanicaland thermal analysis. Polymer Degradation and Stability 85 (3), 967–973.

Aguir, C., M’henni, Med.F., 2006. Experimental study on carboxymethylation ofcellulose extracted from Posidonia oceanica. Journal of Applied Polymer Science98, 1808–1816.

Alcaide, L.J., Parra, I.S., Baldovin, F., 1990. Characterization of Spanish agriculturalresidues with a view to obtaining cellulose pulp. TAPPI Journal 73 (5), 173–176.

Al-Sulaiman, F.A., 2002. Mechanical properties of date palm fibre reinforcedcomposites. Applied Composite Materials 9 (6), 377–396.

Antunes, A., Amaral, E., Belgacem, M.N., 2000. Cynara cardunculus L.: chemicalcomposition and soda-anthraquinone cooking. Industrial Crops and Products12, 85–91.

Barba, C., De la Rosa, A., Vidal, T., Colom, J.F., Farriol, X., Montane, D., 2002. TCFbleached pulps from Miscanthus sinensis by the impregnation rapid steampulping (IRSP) process. Journal of Wood Chemistry and Technology 22 (4), 249–266.

Bendahou, A., Dufresne, A., Kaddamai, H., Habibi, Y., 2007. Isolation and structuralcharacterization of hemicelluloses from palm of Pheonix dactylifera L.Carbohydrate Polymers 68, 601–608.

Bendahou, A., Kaddami, H., Sautereau, H., Raihane, M., Erchiqui, F., Dufresne, A.,2008. Short Palm tree fibres polyolefin composites: effect of filler content and

coupling agent on physical properties. Macromolecular Materials andEngineering 293 (2), 140–148.

Copur, Y., Tozluoglu, A., 2008. A comparison of kraft, PS, kraft-AQ and kraft-NaBH4pulps of Brutia pine. Bioresource Technology 99 (5), 909–913.

Cordeiro, N., Belgacem, M.N., Torres, I.C., Mourad, J.C.V.P., 2004. Chemicalcomposition and pulping of banana pseudo-stems. Industrial Crops andProducts 19, 147–154.

Dutt, D., Upadhyaya, J.S., Tyagi, C.H., Kumar, A., Lal, M., 2008. Studies on Ipomeacarnea and Cannabis sativa as an alternative pulp blend for softwood: anoptimization of kraft delignification process. Industrial Crops and Products 28,128–136.

El Morsy, M.M.S., 1980. Studies on the rachis of Egyptian date palm leaves forhardboard production. Fibre Science and Technology 13 (4), 317–321.

El Morsy, M.M.S., Riad, B.Y., Mohamed, M.A.S., 1981. Pulp and paper from theEgyptian date palm leaves. Fibre Science and Technology 14 (2), 157–161.

Eugenio, M.E., Alaejos, J., Diaz, M.J., Lopez, F., Vidal, T., 2006. Evaluation of Holm oak(Quercus ilex) wood as alternative source for cellulose pulp. Cellulose Chemistryand Technology 40 (1–2), 53–61.

Ezzat, S., 1974. Leaves of date palm tree (Phoenix dactylifera) as a technical feasiblesource of raw material for paper production. Cellulose Chemistry andTechnology 8, 627–634.

Fiserova, M., Gigac, J., Majtnerova, A., Szeiffova, G., 2006. Evaluation of annual plants(Amaranthus caudatus L., Atriplex hortensis L., Helianthus tuberosus L.) for pulpproduction. Cellulose Chemistry and Technology 40 (6), 405–412.

Gezguez, I., Dridi-Dhaouadi, S., Mhenni, F., 2009. Sorption of yellow 59 on Posidoniaoceanica, a non-conventional biosorbent: comparison with activated carbons.Industrial Crops and Products 29 (1), 197–204.

Gominho, J., Fernandez, J., Pereira, H., 2001. Cynara cardunculus L.: a new fibre cropfor pulp and paper production. Industrial Crops and Products 13, 1–10.

Hedjazi, S., Kordsahia, O., Patt, R., Latibrai, A.J., Tschirner, U., 2008. Anthraquinone(AS/AQ) pulping of wheat straw and totally chlorine free (TCF) bleaching ofpulps. Industrial Crops and Products 62 (2), 142–148.

Jimenez, L., Lopez, F., 1990. Characterization of Spanish agricultural residues with aview to obtaining cellulose pulp. TAPPI Journal 73 (8), 173–176.

Jimenez, L., Sanchez, I., Lopez, F., 1992. Olive wood as a raw material for papermanufacture. TAPPI Journal 11, 89–91.

Jimenez, L., Lopez, F., Martınez, C., 1993. Paper from sorghum stalks. Holzforschung47, 529–533.

Jimenez, L., Rodriguez, A., Perez, A., Moral, A., Serrano, L., 2008. Alternative rawmaterials and pulping process using clean technologies. Industrial Crops andProducts 28 (1), 11–16.

Khristova, P., Kordsachia, O., Khider, T., 2005. Alkaline pulping with additives of datepalm rachis and leaves form Sudan. Bioresource Technology 96, 79–85.

Manfred, J., 1993. Non-wood plant fibres, will there be a come-back in paper-making? Industrial Crops and Products 2, 51–57.

Ncibi, M.C., Mahjoub, B., Seffen, M., 2006. Biosorption of phenol onto Posidoniaoceanica seagrass in batch systems: equilibrium and kinetic modelling.Canadian Journal of Chemical Engineering 84 (4), 495–500.

Ncibi, M.C., Mahjoub, B., Seffen, M., 2008. Investigation of the sorption mechanismsof metal-complexed dye onto Posidonia oceanica (L.) fibres through kineticmodeling analysis. Bioresource Technology 99 (13), 5582–5589.

Sbiai, A., Kaddami, H., Fleury, E., Maazouz, A., Erchiqui, F., Kouba, A., Soucy, J.,Dufresne, A., 2008. Effect of the fibre size on the physicochemical andmechanical properties of composites of epoxy and date palm tree fibres.Macromolecular Material and Engineering 293 (8), 684–691.

Schott, S., 2000, Valorisation de la pâte de paille de blé obtenue par le procédéd’explosion en phase vapeur, pour une application en papeterie. Thesis. InstitutPolytechnique de Grenoble, France.

Shatalov, A.A., Quilho, T., Pereira, H., 2001. Arundo donax L. reed: new perspectivesfor pulping and bleaching. 1. Raw material characterization. TAPPI Journal 84(1), 96.

Sihtola, H., Kyrklund, B., Laamanen, L., Palenius, I., 1963. Comparison and conversionof viscosity and DP-values determined by different methods, special number 4a.Paperi ja Puu 225, 232.

Silvy, J., Romatier, G., Chiodi, R., 1968. Méthodes pratiques de contrôle du raffinage.Revue ATIP 22 (1), 31–53.

Taha, I., Steurnagel, L., Ziegmann, G., 2007. Optimization of the alkali treatmentprocess of date palm fibres for polymeric composites. Composite Interfaces 14(7–9), 669–684.

Wan Rosli, W.D., Leh, C.P., Zainuddin, Z., Tanaka, R., 2003. Optimisation of sodapulping variables for preparation of dissolving pulps from oil palm fibre.Holzforschung 57 (1), 106–113.

Wise, L.E., Murphy, M., D’Addieco, A.A., 1946. Chlorite holocellulose: itsfractionation and bearing on summative wood analysis and on studies on thehemicellulose. Paper Trade Journal 122 (2), 35–43.