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Pulping process of Agave americana L. fresh leaves

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par afef tlili
Sousse, institut supérieur agronomique Chott-Mariem - ingénieur d'état 2007

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Pulping process of Agave americana L. fresh leaves

Physical and chemical characterization of Agave americana paper pulp

Tlili Afef*

Laboratoire de chimie, Institut supérieur agronomique de Chott-Mariem,

Université de Sousse, Tunisie.


The abundance of fibers in its composition (Msahli, 2002) legitimises the seek of introducing this specie in cellulose industries especially paper pulping. Throw a comparison established with Alfa (Stipa tenaicissima L.), the referential specie in Tunisia in pulping which is qualified with its availability and strong potentials it was proven the cellulose higher concentration and fewer mineral ashes (Tlili, 2007). Its chemical composition is a persuasion of its suitability to industrial uses especially those who rely on cellulosic fibers.

In fact, making a paper pulp is possible. It requires a concentrated NaOH' cooking' process of its fresh leaves. The designation of this pulp led to physical properties that aren't as convincible as chemical ones. Nevertheless, they didn't declassify it. The paper market admits a pulp with such high level of á-cellulose (87%), such rarity of mineral ashes (0.7%) and such basic pH (7.6) and such less humidity (5.59%). The inefficiency of pulping process is behind the raw and bleached pulp heterogeneity. However, theses pulps very solid. The big reveal about Agave is that even its raw pulp is white despite the NaOH attack which usually darkness it. Agave's pulping efficiency is estimated by 22.9%. these parameters can be improved by developing the pulping process.

Keywords: Agave americana L.; Tunisia; fibers; cellulose; mineral ashes, paper pulp.

slicks show a severe degradation by nearly 1500ha/year (Ksontini et al., 1998). This drop is due to the ecological and environmental perturbations, the Industrial overexploitation and its hard regeneration.

The literature is very poor concerning the Agave pulping process, liquors used and specific steps. Installing a reliable industry would be so risky if we don't mastership the whole formula and distinguish clearly the pulp properties in order to get a better judgement of its suitability.

In this present task, we first established the Agave pulping process. Then we physically and chemically analysed the issued pulp.

2- Material and methods

Pulping process

The collected fresh leaves are washed in order to diminish the risks of pulp impurity. They are peeled and so deprived from their external chlorophyll cover. We make homogeneous samples with 0.5cm thickness; 0.5 cm width and 8cm length.

The pulping process used with Agave leaves is the chemical one also called Kraft. Its principle is fibers isolation with less possible degradation (Edwards, 1998). For preliminary essays, the cooking liquor is concentrated soda (NaOH33% nearly equal to 447.89 g/l). We constantly shake to accelerate the process.

1- Introduction

The changing competitive economic and tech- nologic growth inspires the agronomy a new push. Its time for research and valorisation of existing fauna formerly unexploited. So, came out the national and international interest accorded to Agave americana; a specie for so long given up and depreciated in order to profit its ecologic, agronomic and either economic performances. The curiosity towards Agave was ori-ginnally based on the surprising adaptability of Agave to both of climatic and cultural requirements(Chaieb and Boukhris, 1998) and its easy dissemination (Bertrand,1959).This fauna was introduced from subtropical climates (Lock, 1962) and since belongs to national vegetal patrimony (Cuénod, 1954).

So many uses of Agave on industrial scale are so far recognised which inspires a consideration and a rediscover of this resource in order to intensify the possible profits. Because of the abundance of cellulosed fibers in its tissues (Msahli, 2002), we seek to introduce Agave in industrial use especially if we consider the productions rarity of cellulose fauna and the fact of that many fundamental productions release on this fauna. The pulping industry allows the access to paper making, an important field in tunisian economics for so long established on Alfa grass, the major available source of fibers there. However, its national productions are decreasing, the Alfa grassland

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120 buttons and 150 dark points declassify it (SNCPA, 2007). A pulp homogeneity is governed by several parameters as the introduction of strange corps or the incomplete fibers individualisation. Technically, the pulp aspect is related to cooking conditions. We have to optimise temperature, pressure and liquor concentration that probably doesn't response to fibers decomposition requests. The vegetal material influences the pulp aspect (Walls, 1999); samples dimensions aren't perfect and fibers length doesn't help pulping. Also, we can't ignore the alteration due to strange corps introduced during cooking or the inefficiency of washing process. The simple water throws are in the case of Alfa replaced by successive chemical and physical operations. Even with bleached pulp, heterogeneity doesn't totally disappear. The bleaching agent has no effect on impurities; it only eliminates the lignin rest.

The pulp is consistent and isn't deteriorated despite the mediocre cooking conditions, inappropriate washing and non sophisticated equipment. This consistency takes its origin from fibers properties which, even dissociated, keep certain rigidity and a considerable length (Pfaffli, 1995). We can stipulate that a good paper can be produced from this pulp. With bleaching agent, the pulp is more compact. Its fibers are submitted to additional degradation. This is due to the possible depolymerization (Han and al., 1995). The excessive alteration can be related to the bleaching agent itself or its concentration; they might be inadequate for Agave pulp.

The residual lignin of a chemical pulp (3 to 6%) has a brownish colour, it's due to lignin double carbon links C=C. however, Agave row pulp is much whiter than Alfa one. Its remarkable colour can lead to a high quality paper with less chemical addicts and wastes.

The Agave efficiency in dry pulp is 22.9%, less than Alfa 33%. Despite the leaf wetness and its massive water contain, there is no remarkable difference. Agave can be a reliable paper making alternative.

Pulp chemical properties

The average dry material rate in Agave pulp is about 94.41%, higher than Alfa pulp (87.09% to 89%). Technically, a paper pulp is rejected if this rate is under 88%. Avery dry material rate augmentation is rewarded by a clear improvement of paper efficiency. Essentially, it's related to extracted paper weight, its thickness and amount. This clue informs also about pulp aptitude to several following manipulations without being deteriorated especially during refining. The higher it is, the more stable are the physico-chemical paper properties.

We get back the pulp. After it gets colder, we dilute it in 10 containers with hot water. We vacuum filtrate it with distilled hot water. The washing efficiency is pronounced by the pulp whitening and so the evacuation of soda. The result pulp is called raw. To get a bleached one, we used NaClO 21.3g/l. we dehydrate the pulp, we introduced it in the steamroom 40°C (1h).

Pulp physical properties

We studied the homogeneity based on simple observations; we introduce a spoon tool within the wet pulp in order to reveal all anomalies frequency as black points or darker strings. It's easier to detect such impurities in dehydrated pulp. They are harder and darker. Throw a comparison with Alfa pulp aspect, we judge the consistency: the particles cohesion of Agave pulp; its softening and individualised fibers structure. We precise the pulp whiteness throw a comparison with two samples of Alfa raw and bleached pulp. The quantity of collected pulp doesn't allow the use of appropriate device.We estimate Agave pulp efficiency E(%)=(Wv*Dv*100)/(Wp*Dp);Wv: vegetable weight; Dv: vegetable dryness; Wp: pulp weight; Dp : pulp dryness.

Pulp chemical properties

We studied dryness D(%); profitableness P(%); humidity H(%) by introducing the samples 3 hours in steamroom 105°C heat. D(%)=(Wf*100)/Wd; P(%)=W*D(%); H(%)=(Wf-Wd)*100/Wf.

Mineral ashes content A(%) is obtained by severe calcination after introducing dry samples 1 h in mitten oven 800#177;25°c. A(%)=(W2*100)/W1*D(%) (Wf: fresh weight; Wd: dry weight; W2: final weight; W1: primary weight).

pH is revealed by putting a 4g sample in 100ml of distilled water within 3 days while the osmotic exchange happens.

In order to specify the á-cellulose amount

á-c (%)=(Wf*100)/Wi; Wf: final weight; Wi: initial weight. We take 5g of pulp; we add 100ml of concentrated soda (212 g/l) we shake 15mn until the whole pulp solution. The homogeneous blend is vacuum filtrated. We add 100ml of acetic acid (20%) and we wash with hot distilled water. The container is put 24h in the steamroom 105°C.

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