1996] NOTES 465

Cellulose extraction from Agave lechuguilla fibers.--Mature and immature leaves of Agave lechuguilla Torr. are gathered in central and northeastern Mexico mainly for the extraction of its fibers used in the elaboration of textiles, cords, and brushes. The earliest evidence of such utilization dates from 6000 B.C. (1). The tradi- tional uses of this agave have been described by Sheldon (2), and include, besides the diverse products from the fiber, its use as construction material, soap, and human food.

This species has one of the most extensive ranges of the agaves, and the number of indi- vidual rosettes probably exceeds those of all oth- er native agaves (3). It grows in such dense clus- ters that human and animal movement is some- times excluded. Plant densities as high as 770/ 100 m 2 have been recorded by the Instituto Na- cional de Investigaciones Forestales in the La Sauceda experimental station, Coahuila, (4), but the average is 210/100m 2 (5). Agave lechuguilla grows in south-eastern New Mexico and south- western Texas in the USA, and occupies almost 20 000 000 ha in the states of Chihuahua, Coa- huila, Nuevo Le6n, Tamaulipas, Durango, Za- catecas, San Luis Potosf, Hidalgo and the state of M4xico, which is 10% of the total territory of Mexico. In that area of Mexico almost one million people depend on A. lechuguilla to pro- duce handicrafts or industrial articles (6). A. le- chuguilla is a characteristic succulent compo- nent of various plant communities between 950 and 2300 MASL. It is associated with limestone soils and is usually absent from volcanic areas. The annual rainfall of the lechuguilla area rang- es between 300 and 500 mm (3).

"La Forestal FCL," which includes more than 600 ejido cooperatives and approximately 200000 people in lechuguilla gathering and pro- cessing is the largest such enterprise in Mexico. This activity is concentrated in the states com- prising the zona ixtlera: Coahuila, Nuevo Le6n, Tamaulipas, Zacatecas and San Luis Potosf (Fig. 1). The industrial exploitation of the lechuguilla dates from the beginning of the nineteen century (7), and peaked in the last quarter of that cen- tury, subsequently falling due to competition with synthetic fibers. In the period 1890-1896, Mexico exported 6000 tons annually (8), while in 1993 the total volume of exported lechuguilla was of only 762 tons, according to the statistics of the Secretarfa de Agricultura y Recursos Hid- ratilicos.

An alternative for the commercialization of this agave is a source of cellulose. New crops in arid lands will have to produce natural products with relatively high value. Such crops should also display good adaptation to dry areas and poor performance in more humid regions (9). A good example of this type of alternative, is the cultivation of sisal (A. sisalana Perrine) in Bra- zil, most of which is destined to the production of paper by the Companhia de Cellusoe (10). This company operates a pulp mill with a pro- duction capacity of 300 tons/day (11). Principal end-products for sisal pulp are newsprint, bag papers, cigarette papers, carbon papers, bank- note papers, filter papers and tea bags. Un- bleached pulp is used for cement bags and sacks, and for electrical-cable and telephone-cable in- sulation (12).

McLaughlin and Schuck (10) compared the dimensions of fiber cells of several species of Agavaceae (among them A. lechuguilla) and an- alyzed their potential in the production of paper which, they noted, requires fibers which have relatively long and thin cells. Their results in- dicated that the fibers of A. lechuguilla have ap- proximately half the length of those from sisal (0.92 -+ 0.1 nun ofA. lechuguilla vs. 1.84 _+ 0.2 mm of A. sisalana), and are also thinner (27.0 --- 1.9 IX of A. lechuguilla vs. 29.1 --- 2.4 ix of A. sisalana). Other characteristics, however, are also important in the evaluation of fibers, such as the quality and the purity of the cellulose ob- tained.

Cellulose is never found pure in nature, but is associated with lignins and hemicelluloses, as well as other substances in a minor proportion. Hemicelluloses comprise a group of polysaccha- rides (excluding pectin) that remains associated with the cellulose after lignin has been removed (13). Hemicelluloses can be separated from cel- lulose with aqueous alkali. They fall into two groups: those which are precipitated from alka- line solution by acid, and those which are not. In the terminology of Cross and Bevan (14), these two groups are known as 13-cellulose and ~-cel- lulose, the term a-cellulose being reserved for what is now universally called cellulose. Highly purified cellulosic pulp is composed of 95-99% of cellulose and is known by such terms as chem- ical cellulose and dissolving pulp.

Few techniques for chemical cellulose extrac- tion from agaves have been reported (11, 15, 16, 17, 18). None have been applied to A. lechu-

466 ECONOMIC BOTANY [VOL. 50

Fig. 1. Areas sampled for Agave lechuguilla fiber analysis.

guilla. In our laboratory, a simple method to ob- tain chemical cellulose from A. fourcroydes Lem. fibers was developed by Cazaurang, Per- aza, and Cruz (19). This high yield method al- lows a product of high purity to be produced employing less drastic treatments than those used in the wood cellulose extraction. We ap- plied this method to A. lechuguilla in order to

evaluate the feasibility of extracting high purity chemical cellulose. The method consists of sub- mitting the fibers to four steps: a prehydrolysis and a hypochlorite treatment, followed by an al- kaline extraction and final bleaching.

In order to evaluate the quality of the chem- ical cellulose extracted, we used five kilograms of hard fiber (type "Care"), obtained from A.

TABLE 1. EXPERIMENTAL SERIES.

Reagent concentrations

NaCIO Alkaline Series Prehydrolysis treatment extraction Bleaching

Series I From 0.5 to 4% 3.5% w/v 20.0% w/v 0.1% w/v v/v H 2 S O 4 free chlorine NaOH free chlorine

Series II 2.0% v/v From 0.5 to 4% 20.0% w/v 0.1% w/v H,SO4 w/v free chlorine NaOH free chlorine

Series III 2.0% v/v 2.5% w/v From 5 to 20% 0.1% w/v H2SO4 free chlorine w/v NaOH free chlorine

Series IV 2.0% v/v 3.5% w/v From 5 to 20% 0.1% w/v H2SO4 free chlorine w/v NaOH free chlorine

Series V 2.0% v/v 2.5% w/v 20.0% w/v From 0.04 to 0.12% H,SO4 free chlorine NaOH w/v free chlorine

Series VI 2.0% v/v 3.5% w/v 20.0% w/v From 0.04 to 0.12% H2SO4 free chlorine NaOH w/v free chlorine

1996] NOTES 467

lechuguilla leaves collected from nine different ecological zones of the "zona ixtlera" in Mex- ico (Fig. 1). These hard fiber (strands of over- lapping libriform fiber cells), initially 200-250 txm in diameter and 30-150 cm in length, were ground and screened, then washed and dried. From this stock, one hundred samples of 100 g each were selected for testing.

The fibers and the chemical cellulose obtained were analyzed and characterized according to the following standard methods: T 204 for al- cohol-benzene solubility; T 207 for water solu- bility; T 222 for the lignin percentage determi- nation; UM 249 for hemicelluloses (a and ~/-cel- lulose) and a-cellulose percentage determination (20). The viscosity-average molecular weight of the chemical cellulose extract was evaluated ac- cording to the method ASTM D-1716-62 (21). The nitrogen content of solutions was determi- nated following Evans (22). The yield of pulp was calculated on the basis of the dry mass of fibers. In order to study the influence of each reagent on purity (a-cellulose content) of the ex- tracted bleached chemical cellulose and its final molecular weight (Mw), six experimental series (Table 1) in 250 ml beaker were performed. Each series was repeated five times.

Our results showed that A. lechuguilla fibers contained 46-48% a-cellulose. This result plac- es these fibers a little higher than wood [40% after Nevell et al. (13)], but lower than A. four- croydes fibers [60% after Cazaurang, Peraza, and Cruz (19), Escolano (23), and Lock (24)]. The hemicellulose content is 30.0 -+ 2.3%, that of lignins 11.0 --- 1.0%, ethanol benzene extract- ables 4.0 + 2.0%, ethanol extractables 5.0 + 1.3% and water extractables 4.0 _ 1.25%.

With respect to the results of the cellulose ex- traction experiments, we find that the chemical cellulose purity (a-cellulose content) and its deg- radation (molecular weight) depend on the ag- gressiveness of the reaction conditions. In gen- eral, strong conditions of extraction lead to a rise in the grade of purity, however, they increase the degradation of the material. Concentrations of re- agents in the hydrolysis and the hypochlorite treatments, have a marked influence on the con- tent of unattacked fibers in the final product. Con- centrations of 2% sulfuric acid, and 3.5% of free chlorine, in the first and second steps are enough to obtain a chemical cellulose almost free of un- attacked fibers. The final yield of a-cellulose, about 80%-98%, series with the concentration of

free-chlorine in the sodium hypochlorite treat- ment. In hydrolysis and alkaline extraction, the influence of reagent concentration is less notice- able as the range of a-cellulose yield is between 90 and 98%. In bleaching, the effect of reagent concentration is still less as shown by the chem- ical cellulose content of 97 to 98% of a-cellulose. Summarizing, it can be said that, to obtain a chemical cellulose with a 98% of a-cellulose, it is sufficient to use 2% sulfuric acid, and 3.5% free chlorine, in the first and second steps, and a concentration of 20% w/v of soda in the third one.

Cellulose molecular weight falls as the grade of aggressiveness in the extraction increases, be- ing particularly influenced by increase in the con- centration of free chlorine during the sodium hy- pochlorite treatment, as it passes from 450 000 to 120000 g/mole. The hydrolysis and the alkaline extraction grades also produces a decrease in the molecular weight related to the increase in the concentrations of sulfuric acid and soda respec- tively, however it is not so important. Moreover, it is interesting to observe, as a general trend, that the increase in the concentration of reagents led approximately to the same final molecular weight of the cellulose extracted.

The yield, in all cases, is around 40%, except when very low concentrations of free-chlorine are used in the NaC10 treatment, where values of up to 55% were reached because of the high volume of unattacked fibers that persist in the pulp under such conditions.

Using the method proposed here, it is possible to extract chemical cellulose from the A. lechu- guilla fibers with a yield of almost 40% w/w, a content of 98.0% of a-cellulose and a molecular weight between 200 000 to 100 000 g/mole. This is possible using a concentration of 2% of sul- furic acid, 3.5% of free chlorine, and 20% of soda in the first three steps of this method. How- ever, it is important to note that there are two different results available from this process. If a chemical cellulose of high purity (high percent- age of a-cellulose) but with a low molecular weight (consequently low mechanical proper- ties) is required, then a high content of free chlo- rine (3.5%) in the NaCIO treatment should be used. This type of chemical cellulose may be used to produce filter paper, food packing paper, etc. On the other hand, if a chemical cellulose with good mechanical properties, although not very pure (and therefore not very white) is re-

468 ECONOMIC BOTANY [VOL. 50

quired, then an intermediate concentration of 2.5% in the NaC10 treatment should be used. This type of cellulose may be used to produce newsprint paper, bag paper, etc. Moreover, a NaC10 treatment, to bleach the pulp, must be also included as part of the process. Finally, it is important to stress that the entire process does not require specialized equipment, and is safe and easy to follow.

Acknowledgments. We thank La Forestal for the supply of fiber and financial support. We are grateful to Geoffrey Roger Ashburner and Fla- vio V~izquez for useful comments.

Literature Cited. (1) Crane, H. R., and J. B. Griffin. 1958. University of Michigan radiocarbon dates III. Science 128:117-1123; (2) Sheldon, S. 1980. Eth- nobotany of Agave lechuguilla and Yucca came- rosana in Mexico's Zona |xtlera, Economic Botany 34:376-390; (3) Gentry, H. S. 1982. Agaves of Continental North America. The University of Ar- izona Press, Tucson, AZ.; (4) P6rez-Rosales, S. 1964. Los suelos y la vegetaci6n del campo exper- imental La Sauceda en la Zona Arida de Coahuila. Boletfn T6cnico No. 16. Instituto Nacional de In- vestigaciones Forestales, M6xico, D.E; (5) Martf- nez, M. 1936. Plantas fitiles de M6xico. Ediciones Botas. M6xico; (6) Zapi6n-Barrag~in, M. 1981. Ev- aluaci6n de la producci6n de ixtle de lechuguilla en cuatro sitios diferentes. Publicaciones Especiales del Instituto Nacional de Investigaciones Foresta- les. M6xico; (7) Kirby, R. H. 1950. Brush-making fibers. Economic Botany 4:243-252; (8) Romero, M. 1898. Geographical and Statistical Notes on Mexico. Putnam's Sons, New York; (9) Mc- Laughlin, S. P. 1985. Economic prospects for new crops in the southwestern United States. Economic Botany 39:473-481; (10) McLaughlin S. P., and S. M. Schuck. 1991. Fiber properties of several spe- cies of Agavaceae from the Southwestern United States and Northern Mexico. Economic Botany 45: 480-486; (11) Corradini, E T. 1979. Companhia de celulose de bahia. Pages 70-74 in L. E. Haas, ed., New pulps for the paper industry: proceedings of the Symposium on New Pulps for the Paper Indus- try, Brussels, Belgium, May 1979. Miller Freeman,

San Francisco; (12) da Silva, N. M., and A. D. Pereira. 1985. Experience of a pioneer-sisal-simul- taneous resource for pulp and energy. Pages 63-69 in A. J. Seaquist, and E. C. Cobb, compilers, Non- wood plant fiber pulping: Progress Report no. 15. TAPPI Press, Atlanta; (13) Nevell, T. R, and S. H. Zeronian. 1985. The functions and biogenesis of native cellulose. Pages 15-29 in T. P. Nevell and S. H. Zeronian, ed., Cellulose Chemistry and its Ap- plications, Ellis Horwood Limited, West Sussex, England; (14) Cross, C. E, and E. J. Bevan. 1905. Researches on Cellulose. Longmans, London; (15) Bryce, J. R. G. 1980. Sulfite pulping. Pages 291- 376 in J. P Casey, ed., Pulp and Paper: Chemistry and Chemical Technology, Vol I. John Wiley and Sons, New York; (16) Kaneko, Y., S. Tamasaki, and J. Takemoto. 1982. Dissolving Pulp from Agave fi- bers, Japanese Patent Kokai 11,291/82; (17) Libby, C. E. 1980. Ciencia y Tecnologfa sobre pulpa y papel. Vol. 1 Compania Editorial Continental S. A. Mexico; (18) Zepeda-Castillo E. 1981. Producing fermentable powdered syrup and alpha cellulose from xerophyte plants, British Patent, 1-484-310; (19) Cazaurang M. N., S. R. Peraza, and C. A. Cruz. 1990. Dissolving-grade pulps from Henequen fibers. Cellulose Chemistry Technology 24:629- 638; (20) TAPPI. 1992. TAPPI Standard Methods, Vol liB, D. Van Nostrand Company; (21) ASTM. 1994. American Society for Testing and Materials Methods, Annual Book of ASTM standards, Sec- tion 15, Vol. 15.04, Philadelphia; (22) Evans R., and A. E A. Willis. 1989. Cellulose molecular weights determined by viscometry, Journal of Ap- plied Polymer Science. 37:2331-2339; (23) Esco- lano E. U., P. C. Francia, and L. A. Ynalvez. 1971. The proximate chemical composition of some Aga- ve and Furcraea fibers, The Philippine Lumber- man, Sept: 21-25; (24) Lock G. W. 1969. Sisal: Thirty Years' Sisal Research in Tanzania. Long- mans, London.

--Alfredo Mdrquez, Nohemf Cazaurang, lvdn Gonzdlez, and Patricia Colunga- GarcfaMarth, Centro de Invest igacidn Cientifica de Yucattin, A. C. Apartado Pos- tal 87, Cordemex, M~rida, Yucatdn, M~xico 97310.