Bioresource Technology 101 (2010) 775–780 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech Chemical composition and pulping of date palm rachis and Posidonia oceanica – A comparison with other wood and non-wood fibre sources R. Khiari a,b, M.F. Mhenni a, M.N. Belgacem b,*, E. Mauret b a b Research Unity of Applied Chemistry and Environment, Department of Chemistry, Faculty of Sciences, Monastir 5019, Tunisia 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 2009 Received in revised form 20 August 2009 Accepted 21 August 2009 Available online 18 September 2009 Keywords: Date palm rachis Posidonia oceanica Chemical composition Pulping Fibre properties a b s t r a c t In the present paper, the valorisation of two residues: Posidonia oceanica and date palm rachis was investigated. First, their chemical composition was studied and showed that they present amounts of holocellulose, lignin and cellulose similar to those encountered in softwood and hardwood. Extractives in different solvents and ash contents are relatively high. Moreover, ash composition assessment showed that silicon is the major component (17.7%) for P. oceanica. The high ash quantity and the low DP (about 370) 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 classical soda-anthraquinone cooking, demonstrated the suitability of this agricultural by-product for papermaking. Preliminary tests conducted on unrefined pulp suspensions and handsheets from date palm rachis in terms of freeness, Water Retention Value and mechanical properties allowed confirming the good quality of date palm rachis fibres. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Paper consumption is continuously increasing in the world even in countries where wood resources are very limited. Furthermore, the valorisation of agricultural residues or marine biomass through rational and innovative ways of utilization is of potential interest, in such countries, since they can be considered as new cellulosic fibre sources. Such strategies were already applied to valorize various agricultural crops available for instance in Portugal (Antunes et al., 2000; Cordeiro et al., 2004), India (Dutt et al., 2008), Malaysia (Wan Rosli et al., 2003), Iran (Hedjazi et al., 2008), Sudan (Khristova et al., 2005) or Tunisia (Aguir and M’henni, 2006; Gezguez et al., 2009). In this work, we investigated the valorisation of two lignocellulosic materials, largely available in Tunisia, as a source of cellulosic fibres, namely: Posidonia oceanica balls and date palm rachis. P. oceanica is the dominant sea grass in the Mediterranean Sea. Important quantities of P. oceanica fragments accumulated on Tunisian coasts, which imposes the cleaning of the beaches every summer. The valorisation of this available and renewable lignocellulosic biomass can be considered as a suitable solution for this problem. Nowadays, P. oceanica is studied as a low cost and renewable adsorbent for removing dyes or phenol (Ncibi et al., 2006, * Corresponding author. Tel.: +33 04 76 82 69 62; fax: +33 04 76 82 69 33. E-mail address: naceur.belgacem@efpg.inpg.fr (M.N. Belgacem). 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.08.079 2008; Gezguez et al., 2009) or as a source of cellulose (Aguir and M’henni, 2006). In that case, P. oceanica is treated in order to extract cellulose and convert it into carboxymethyl cellulose. To the best of our knowledge, no complete data about the chemical composition of P. oceanica are available in the literature. Moreover, its potential use as a source of lignocellulosic fibres for the production of pulp and paper has never been tested. Date palm (Phoenix dactylifera) is one of the most cultivated palms in the arid and semi-arid regions of the world. Tunisia has more than 4 millions date palms which occupy 32,000 ha (statistics from the Tunisian Ministry of Agriculture, 2003). After the date fruit harvesting, important quantities of date palm rachis wastes accumulated every year in Tunisian agricultural lands. Here also, rational ways of valorising this abundant renewable resource should be find. For instance, it is well known that the use of natural fibres in composites is a way of meeting the increasing demand in biodegradable and renewable materials. In this context, date palms agricultural residues (rachis or leaves) can be viewed as sources of reinforcing fibres for polymeric matrices in composite materials. 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, only few studies evaluated the potential use of date palm by-products for pulp and paper manufacturing and most of them are dedicated to the pulping of date palm leaves (Ezzat, 1974; El Morsy, 1980; El Morsy et al., 1981). To the best of our knowledge, only Khristova et 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 characterization of these two Tunisian cellulosic by-products (P. oceanica balls and date palm rachis) and the evaluation of their properties, in the papermaking context. The first part of this work is devoted to the determination of the chemical composition. Then, soda-anthraquinone cooking, which is considered as the most suitable process for pulping annual plants (Antunes et al., 2000), is tested. The ensuing pulps are characterised in terms of yield, kappa number, degree of polymerisation (DP) and chemical composition (residual lignin, holocellulose, cellulose and extractives). Finally, the physical and mechanical properties of handsheets are presented and discussed. The obtained results (chemical composition of pulps and physical properties of papers) are compared to other wood and non-wood sources thanks to a complete literature review. 2. Materials 2.1. Raw materials P. oceanica balls and date palm rachis used in this study were collected in Monastir in August 2007. These wastes were dried under natural conditions during September 2007 (average relative humidity = 65%; average temperature = 25 °C). The date palm rachises of about 1 m length and 6–7 cm diameter were then cut into 1–3 cm pieces before pulping. The P. oceanica balls were washed in order to eliminate sand and contaminants and then dried again under the same conditions. 2.2. Characterization of raw materials Chemical composition of P. oceanica balls and date palm rachis was determined. The evaluation of extractive substances was carried out in different liquids according to common standards, namely: cold and hot water (T207 cm-08), 1% sodium hydroxide solution (T212 om-07) and ethanol–toluene (T204 cm-07). Ash content (T211 om-07) was determined and analysis of the mineral fraction was performed at the ‘‘Service Central d’Analyse – Vernaison (CNRS)”. The amounts of lignin, holocellulose, cellulose, as well as the kappa number were also assessed by using the following respective standard methods: T222 om-06, method of Wise et al. (1946), T203 cm-99 and T236 om-06. As recommended by the various standards used, all the experiments were duplicated and the difference between the two values was within an experimental error of 5%. 2.3. Pulping The delignification of date palm rachis was carried out according to the procedure described by Khristova et al. (2005) with a total alkali charge of 20% expressed in NaOH (based on w/w o.d. rachis), an anthraquinone concentration of 0.1% (w/w with respect to o.d. material) and a cooking time at constant temperature of 120 min. The liquor to solid ratio was changed and fixed at 10 due to the experimental device used and different temperatures ranging from 150 to 170 °C were tested. All the experiments were conducted in a 1 L reactor, in which the heating time to reach the constant temperature was 1 h. The same procedure was applied to P. oceanica balls. 2.4. Pulp and paper characterization After cooking, the obtained pulps were washed several times through a wire until obtaining a clear filtrate and characterised in terms of yield, kappa number, residual lignin, holocellulose and ethanol–toluene extractives. The cooking yield was calculated as the ratio of the weight of o.d. material after washing to that of initial raw material. The residual lignin was determined from both the Klason lignin and the soluble lignin measured by UV absorption of a filtrate specimen at 205 nm (Tappi method UM 250). The viscosity of pulp (g in mPa s) dissolved in a cupriethylene-diamine solution was determined according to Tappi standard (T230 om99). These values were then converted into degrees of polymerisation (DP) thanks to the following relation proposed by Sihtola et al. (1963): DP ¼ ½0:75ð954Log10 g  325Þ1:105 ð1Þ All the experiments were duplicated and the difference between the two values was within an experimental error of 5%. After disintegration (standard method ISO 5263-1), the pulp were passed through a slotted screen of 0.15 mm aperture size, in order to remove uncooked materials. The screening yields were determined as the ratio between the weights of o.d. material before and after screening. Morphological properties of the fibres were studied by SEM observations (results not shown) and by using a MORFI analyzer (Techpap): the main fibre parameters were assessed by image analysis of a diluted suspension flowing in a transparent flat channel observed by a CCD video-camera. Water Retention Values (WRV) were also determined by centrifugation of wet pulp samples during 15 min at 3000g according to Silvy’s method (Silvy et al., 1968). The samples were weighted, before and after drying, and the WRV calculated. The pulp drainability was evaluated by measuring the Shopper Riegler degree (SR – ISO 5267-1). The unbeaten screened pulps suspensions were diluted to 2 g L1. Then, conventional handsheets with a basis weight of 60 g/m2 were prepared on a Rapid Khöten sheet former following the standard method IS0 5269-2. Prior to testing, the handsheets were conditioned (23 °C, 50% relative humidity – ISO 187) and structural and mechanical properties were determined by measuring basis weight, thickness, bulk and permeability, as well as the tensile, burst and tear strength according to standards ISO 536, ISO 534, ISO 5636-3, ISO 1924-3, ISO 2758 and ISO 1974. As recommended by the various standards used, all the measurements were made 10 times, thus allowing the determination of standard 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 rachis are listed in Table 1, which shows that these raw materials are characterised by relatively high amounts of extractives, especially for ethanol–toluene extractives (10.7% and 6.3% for Posidonia and date palm rachis, respectively). The main difference between Posidonia and date palm rachis is related to ash content, which is higher 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 Table 1, which shows that, when available, data are relatively close to our results apart from the content in lignin (Bendahou et al., 2007). Differences may be related to climate conditions, soil chemical composition. . . Finally, it is worth noting that date palm rachis contains higher amount of cellulose than leaves, as it can be observed in Table 1; it implies that using rachis instead of leaves would be more profitable for papermaking applications. Table 2 summarizes chemical compositions collected from literature for various cellulosic biomasses such as hardwood and softwood, agricultural residues and other various non-wood sources. The comparison with the present work leads to several comments 777 R. Khiari et al. / Bioresource Technology 101 (2010) 775–780 Table 1 Chemical composition of Posidonia oceanica balls and date palm rachises and leaves – comparison with data collected from previously published studies. Amounts in % (w/w with respect to oven dried raw material) (%) Cold water extractives Hot water extractives 1% NaOH extractives Ethanol–toluene extractives Ash Lignin Holocellulose Cellulose a b c d Posidonia oceanica balls Date palm rachis Date palm leaves This work This work Khristova et al. (2005) Bendahou et al. (2007) El Morsy (1980) Khristova et al. (2005) Bendahou et al. (2007) Ezzat (1974) 7.3 12.2 16.5 10.7 12 29.8c 61.8 40 5.0 8.1 20.8 6.3 5 27.2c 74.8 45 n.d. 8.7 25.6 12.8a 5.6 23.8d n.d. 43.1 n.d. n.d. n.d. 4 2.5 14 72 44 n.d. n.d. n.d. n.d. 3.4 25.8 n.d. n.d. n.d. 10.8 29.9 11.7a 9.6 31.2d n.d. 30.3 n.d. n.d. n.d. 3 6.5 27 59.5 33.5 n.d. n.d. n.d. 5.9b 3.9 n.d. n.d. n.d. In ethanol–cyclohexane. In alcohol–benzene. Klason lignin. Residual lignin (Klason and soluble lignin). Table 2 Chemical composition of some lignocellulosic plants. Reference C.W. H.W. A.B. 1% NaOH Ash Hol. Lign. Hemi. Cell. 2.2 n.d. 2.8 2 1.94 1–2.6 16.1 7.9–10.3 0.4 0.3–0.5 75.5 69–67 26.1 26–28 28.5 13. 7 47 56 n.d. 2.8 1.15 12.42 0.6 80.5 19.9 27.7 53 15.5 17 10.4 30.0 1.4 65.83 15.64 24.33 41.5 Holm Oak (Quercus ilex) Copur and Tozluoglu (2008) Jimenez and Lopez (1990) and Jimenez et al. (2008) Jimenez and Lopez (1990) and Jimenez et al. (2008) Jimenez and Lopez (1990) and Jimenez et al. (1992, 2008) Eugenio et al. (2006) n.d. n.d. n.d. n.d. n.d. 71.2 16.3 28.3 43 Non-wood Prosopis alba Chamaecytisus Phragmites Retama monosperma Arundo donax Banana pseudo-stems Paulownia fortuna Jimenez et al. (2008) Jimenez et al. (2008) Jimenez et al. (2008) Jimenez et al. (2008) Shatalov et al. (2001) Cordeiro et al. (2004) Jimenez et al. (1993, 2008) n.d. n.d. n.d. n.d. n.d. n.d. n.d. 4.7 3 5.4 3.8 6.7 5.4 9.6 4.65 3.43 6.36 5.03 9.2 2.7 5.5 20.8 16.1 34.7 16.9 n.d. n.d. 31.5 n.d. n.d. n.d. n.d. 4.8 14 n.d. 63.6 75.3 64.1 71.7 61.2 65.2 70.7 19.3 14.8 23.6 21.5 20.9 12.7 22.4 22.0 31.7 24.4 29.0 32.1 25.2 33.3 42 44 40 43 29.2 40 37 Schott (2000) Alcaide et al. (1990) Alcaide et al. (1990) Alcaide et al. (1990) Alcaide et al. (1990) Jimenez et al. (1993) Fiserova et al. (2006) Fiserova et al. (2006) Fiserova et al. (2006) Antunes et al. (2000) and Gominho et al. (2001) Barba et al. (2002) Manfred (1993) 5.8–11 10.6 16 8.4 13.2 n.d. 23.5 4.6 26.6 n.d. 14 13 16 9.4 15 21.7 28 6.5 31 10 4.6–9.2 4.6–5.7 4.7 3.2–5.2 4.4 7.99 2.51 1.87 2.86 6 41–42.8 49.1 47 37.4 41.8 41.6 46.8 27.5 48.5 n.d. 4–9 13–20 4.9–7 4–4.3 7–7.5 4.85 12 2 3 8 n.d. n.d. n.d. n.d. n.d. 71.7 58.4 74.9 51.6 64 11–21 11–13.5 7–18 18.5–19 11–19.6 13.4 13.2 19.5 14.7 20 21–28.5 13–26.2 24.5 23–30.5 16–27 29.3 26.1 38.8 23.1 26 33–45.5 42–49.8 34–48 55 37–53.6 42 32 36 29 38 n.d. n.d. 9.1 n.d. 3.1 n.d. n.d. n.d. 0.7 1.7–5 72.5 n.d. 19.9 14.5–18.7 30.3 n.d. 42 31–39 Wood Brutia pine Pine pinasterb Eucalyptus globulusb Olive wood a Annual and perennial plants Wheat straw Rice dishes Barley fodder Rye straw Oat straw Sorghum stalks Amaranth Orache Jerusalem artichoke Cynara cardunculus L.a Miscanthus sinensis Kenaf (Hibiscus cannabinus) 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.: Klason lignin (%); Hemi.: hemicellulose; Cell.: cellulose. a Average of 2 or 3 varieties. b Average of 11 varieties. concerning the amount of extractives. Thus, in cold and hot water, the quantity of extractives for both P. oceanica and date palm rachis are higher than those found in hardwood and softwood but comparable to the amounts usually encountered in non-wood sources. The 1% NaOH extractives (16.5% for P. oceanica and 20.8% for date palm rachis) are similar to those of wood sources, i.e. less than 20%, but are lower than those of annual plants. Finally, the amount of extractives in ethanol–toluene for the raw materials under investigation is relatively high, although in the same order of magnitude as those observed for other annual plants or agricultural crops. Considering the structural components, Klason lignin for both materials 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 sources which are close to 20%. Lignin content of these two materials is then close to that of softwood. In the same way, the amounts of holocellulose and cellulose for the two raw materials were similar to those found in wood and non-wood plants. These important fractions allow envisaging the valorisation of such crops as cellulose derivatives and/or as lignocellulosic fibres for fibre-reinforced composite materials or papermaking applications like in the current study. Concerning now the ash content, it is high for P. oceanica (12%) and comparable to that of rice dishes, Banana pseudo-stems and Amaranth which exhibit the greatest contents, as already reported in 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 the plants are growing or/and to a pollution of the balls by sand, even if intensive washing was performed before analyses. On the opposite, ash content in date palm rachis (5%) is lower but remains at the same order of magnitude as most of the non-wood plants. Considering the important quantity of ashes for these two raw materials, their chemical composition was determined. The results are summarized in Table 3 in which literature data are also reported, for comparison. For date palm rachis, ashes are mainly constituted by Ca, Cl, K, Cl and Na atoms. The absolute amount of silicon is very low (0.14% w/w on o.d. raw material) and similar to those reported by Khristova et al. (2005) for both date palm rachises and leaves (0.06% and 0.56%, respectively). In this case, the high quantity of ashes cannot be considered as problematic, in the context of pulping and papermaking processes, since the silicon-based salts are negligible. Oppositely, silicon is predominant in P. oceanica (absolute content of 2.1% w/w on o.d. raw material). This important amount will negatively impact the chemical recovery process and, therefore, could constitute a serious drawback, if considering the valorisation of this marine plant in papermaking stream. Nevertheless, it must be kept in mind that a possible pollution by sand could be responsible. To conclude, comparison with other plants (Amaranth and Banana pseudo-stems) shows that chemical composition of ashes may considerably vary from one species to another, as shown in Table 3. 3.2. Pulping – pulp and paper characterization 3.2.1. Chemical composition of pulps extracted from date palm rachis and P. oceanica Soda-anthraquinone cookings of P. oceanica and date palm rachis were conducted. The experimental conditions as well as the composition of the ensuing pulps were listed in Table 4. Whatever the raw material, a decrease of cooking yield, extractives, lignin content, kappa number and viscosity occurred, when the cooking temperature increases from 150 to 170 °C. Oppositely, an increase of the relative content in holocellulose is observed. Regarding the ash contents, they are surprisingly unaffected by the pulping operation. This behaviour has to be taken into account since the percentage of silicon in P. oceanica is dramatically high. Analysing more deeply the results, it appears that delignification is more pronounced for date palm rachis with a mean cooking yield of 44% compared to 63% for Posidonia, a mean relative content in lignin of 4% compared to 9% for Posidonia and a mean Kappa number of 47 compared to 63 for Posidonia. Nevertheless, it is difficult to compare the contents in lignin and holocellulose as the sum of components (ash, lignin, holocellulose) reaches about 93% for P. oceanica pulp and only 80% for date palm rachis pulps. This indicates that some constituents of the pulp are lost during the analysis. This trend is also observed for the majority of the non-wood plants, as presented in Table 2. Thus, the total amounts of all the components is generally comprised between 80% and 95%. This behaviour is probably due to the fact that standard methods designed for wood plants are used without modification for the determination of chemical composition of non-wood or annual plants. Finally, the DP of the unbleached pulps from date palm rachis is around 1200, which is similar to values obtained for unbleached Kraft wood fibres (generally about 1300–1500). The lower value of DP for P. oceanica pulp (around 500) probably indicates the lower strength properties of this material. Table 4 also includes the main results taken from previously published works for pulp of date palm. It clearly appears that, when pulping conditions are close, pulp characteristics are similar: there is a good agreement between our experimental values and those arising from the literature, particularly those of Khristova et al. (2005). Cooking conditions used by El Morsy et al. (1981) seem to be not optimised: even if apparent mild conditions of cooking are applied, the ensuing DP is surprisingly low. Finally, the better quality of rachis over leaves is once again demonstrated by comparing yields and viscosity of the pulps obtained from these two raw materials. Thus, apart from the ash content and the DP of P. oceanica pulp, the characteristics of the studied fibres, in terms of cooking yield and Kappa number are close to those obtained from unbleached kraft pulping of softwood and hardwood. Their pulping yield is even better than that observed for annual plants and agricultural crops, generally around 35% (Alcaide et al., 1990; Jimenez and Lopez, 1990; Jimenez et al., 1993, 2008; Schott, 2000; Fiserova et al., 2006). 3.2.2. Physical properties of pulp and paper from date palm rachis and P. oceanica Pulps of P. oceanica and date palm rachis were then characterised in terms of physical properties and used for making conventional handsheets. Unrefined pulps will be considered in this part whereas the effect of refining on pulps and papers will be reported in a next publication. From SEM photographs observations, it appears that the length of P. oceanica fibres is significantly lower than that obtained from date palm rachis. This observation is confirmed by morphological measurements collected in Table 5. Whereas the fibre width is roughly the same for the two raw materials studied, the fibre length of date palm rachis pulp is approximately 60% higher than that of the corresponding fibres extracted from Posidonia. Thus, the aspect ratio (length to diameter ratio) is equal to 40 for date palm rachis fibres and reaches only 25 for Posidonia fibres, which is rather low. For comparison, the length of softwood and hardwood fibres is 2–3 mm and 1–2 mm, respectively and the corresponding aspect ratios are around 100 Table 3 Ash composition for Posidonia oceanica and date palm rachis (in % w/w with respect to oven dried raw material). Comparison with data taken from previously published studies. % Posidonia oceanica balls Date palm rachis This work This work Si Ca Mg Fe Cu K P S C Cl Na 17.7 9.12 3.89 3.78 <100 ppm 2.04 0.12 1.92 <0.3 0.72 2.49 2.8 21.5 3.53 240 ppm 360 ppm 10.2 0.7 1.69 1.5 18.6 6.79 Absolute silicon contents in raw materials Si 2.13 0.14 Date palm leaves Amaranth Banana pseudo-stems Khristova et al. (2005) Khristova et al. (2005) Fiserova et al. (2006) Cordeiro et al. (2004) 1.1 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 5.8 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.25 4.17 0.035 n.d. 0.01 36.67 n.d. n.d. n.d. n.d. n.d. 2.7 7.5 4.3 n.d. n.d. 33.4 2.2 n.d. n.d. n.d. n.d. 0.06 0.56 0.03 0.38 779 R. Khiari et al. / Bioresource Technology 101 (2010) 775–780 Table 4 Pulping conditions and chemical composition of unbleached pulps from Posidonia oceanica and date palm rachis or leaves. Date palm rachis Posidonia oceanica This work Total alkali charge expressed in NaOH, %a Anthraquinone concentration Time at constant temperature, min Temperature, °C Cooking yield, %a Screening yield, %a Ethanol–toluene extractives, %b Ash, %b Holocellulose, %b Lignin, %b Kappa-number Pulp viscosity (mPa s) or (mL g1) DP (pulp) a b c d e 20 150 46.8 Date palm rachis Khristova et al. (2005) El Morsy (1980) El Morsy et al. (1981) Khristova et al. (2005) El Morsy et al. (1981) Ezzat (1974) 20 12 15 13 12 18c 23 20 0.1 0.1 0 0 0.1 0 0 120 120 120 20 120 20 300 0.26 165–170 44.2 42.3 43.1 42 n.d. n.d. 100 78.5 n.d. n.d. 150 58.5 n.d. n.d. 39.7 39.7 n.d. 165 29.5 28.2 n.d. 150 22.6 n.d. n.d. 150 38.5 n.d. n.d. n.d. 160 44.8 94 1.81 170 41.8 150 66.0 0.91 n.d. 160 63.6 96 0.57 170 59.9 n.d. n.d. 59 n.d. 4 69.3 5.2 54 15.7d 75.2 3.4 47 15.3d n.d. n.d. 75 n.d. 12 71.4 9.1 65 5.4d 72.4 8.5 63 n.d. n.d. n.d. n.d. 25.5 937e n.d. n.d. n.d. 20.7 845e 2.2 n.d. 22.2 n.d. n.d. 1.8 n.d. 6.3 n.d. n.d. n.d. n.d n.d. 50 618e n.d. n.d. n.d. 20.9 780e 3.6 n.d. 10.8 n.d. n.d. 6.15 n.d. 2.2 n.d. n.d. n.d. 1203 1188 n.d. 513 n.d. 1403 1252 n.d. 880 886 1146 510 n.d. w/w With respect to oven dried raw material. w/w With respect to oven dried pulps. Sulfidity 25%. Pulp viscosity in mPa s. Pulp viscosity in mL g1. Table 5 Main properties of the pulps of Posidonia oceanica and date palm rachis (average of three experimental data). Shopper Riegler degree (°SR) Fibre morphology a Fibre length (mm) Fibre width (lm) Fine elements (% in length) WRV % (w/w on o.d. pulp) a Date palm leaves Date palm rachis Posidonia oceanica 14 10 0.89 22.3 30.8 138 0.55 21.3 7.5 110 Weighted mean. and 60. Then, date palm rachis fibres present length to diameter ratio comparable to that of certain hardwood pulps. Date palm rachis pulp 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 is more important than that of Posidonia counterpart (see Table 5). We can note that WRV for date palm rachis (138%) is significantly higher than that of unrefined pulps arising from softwood and hardwood (90–100%). This property allows predicting a high level of flexibility of the fibres and consequently good mechanical properties of the ensuing paper. Drainability of both pulps is similar to that of unrefined softwood fibrous suspensions and better than that of other non-wood sources and plants like Cynara cardunlus L. (Antunes et al., 2000; Gominho et al., 2001) or hemp and bamboo (Khristova et al., 2005). P. oceanica pulp exhibits very high drainability (10 °SR), which is probably related to its low content in fine elements. Concerning the date palm rachis pulp, combination of a good drainability with a high WRV is surprising and difficult to understand especially since morphological properties of the pulp show a high content of fine elements. Unfortunately, no data are available in the literature for a better understanding of such behaviour. Ezzat (1974) obtained a pulp with a Schopper Riegler degree of 18.5, but the pulping conditions do not allow comparing the results. Only Khristova et al. (2005) produced a pulp in similar experimental conditions of cooking which exhibits a Schopper Riegler degree of 15; no further characterization was done apart from an estimation of the morphological properties of the fibres through microscopic analysis. Nevertheless, it confirms the high drainability of this pulp. Pulps were then used for making handsheets. First, it is worth noting that it was not possible to produce paper from P. oceanica pulps as the strength of the wet web was dramatically low and impeeded to undergo the ensuing operations of pressing and drying. This can be due to the low DP previously mentioned but also to the morphological characteristics of the fibres reported in Table 5 and especially the very low aspect ratio of the fibres. Thus, no further investigation was conducted with this raw material alone. The valorisation of this marine biomass in papermaking field may be considered by blending it with other pulps, for example or by testing the leaves instead of the balls. However, paper sheets from date palm rachis based papers were made and their physical properties are reported in Table 6. The obtained data shows that this raw material could be considered as a promising raw material for papermaking applications. Considering the structural paper Table 6 Paper properties made from date palm rachis (average values and standard deviation) – comparison with data by Khristova et al. (2005). Shopper Riegler degree (°SR) Basis weight (g/m2) Thickness (lm) Bulk (cm3/g) Permeabilty (cm3/s Pa m2) Breaking length (km) Elongation (%) Specific energy (mJ/g) Young modulus (GPa) Burst index (kPa m2/g) Tear index (mN m2/g) Dry zero-span breaking length (km) Wet zero-span breaking length (km) Internal bond strength (J/m2) Short-Span Compression Test (kN/m) This work Khristova et al. (2005) 14 63.9 ± 1.9 141 ± 6 2.21 450 ± 0.042 3.13 ± 0.23 1.09 ± 0.09 221 ± 37 2.51 ± 0.14 1.32 ± 0.05 4.4 ± 0.37 13.4 ± 0.91 10.8 ± 0.66 94 ± 8.8 1.32 ± 0.13 15.5 n.d. n.d. n.d. n.d. 4.40 n.d. n.d. n.d. 1.9 10 n.d. n.d. n.d. n.d. 780 R. Khiari et al. / Bioresource Technology 101 (2010) 775–780 properties, it appears that the bulk is high but this property may partially result from an overestimation of the thickness of the sheet due to the presence of impurities not fully eliminated by the screening operation. The permeability is also high despite the presence of fine elements in the pulp. All the mechanical properties tested exhibit very good values for an unrefined pulp: breaking length (km), elongation (%), specific energy (mJ/g), Young modulus (GPa), burst index (kPa m2/g), tear index (mN m2/g). The intrinsic strength of the fibres (zero-span breaking length – wet) is about 10 km which is quite significant and witnesses about the appropriate conditions of cooking. No comparison with data arising from the literature may be done as the previously published works did not describe the properties of unrefined pulps apart from a partial characterization conducted by Khristova et al. (2005), which confirmed the good quality of date palm rachis based papers (see Table 6). 4. Conclusions The chemical composition of two alternative sources of fibres was established. The obtained results showed that the two raw materials studied contain high amount of cellulose which justifies their valorisation in cellulose derivatives or as a source of fibres for cellulose fibres-reinforced composites or in papermaking applications. Thus, several chemical pulps were prepared and characterised, in terms of yields and morphology. Pulps from date palm rachis gave paper sheets with good properties, without the need of refining operations. This feature can be considered as a serious advantage when looking for new alternative sources of fibres for papermaking. 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