In a few years, Brazil, which is the world’s leader in the biofuels segment, with its production of billions of liters of ethanol and biodiesel from sugar cane, will have another possible option: producing ethanol from sisal, a vegetable fiber that is abundant in the country, is very resistant and is used for making ropes, carpets and handicraft articles. Furniture, bookshelves, parts for boats and automobile components, like panels and internal finishes, can all use this same fiber as raw material. Studies in this direction are being carried out by chemist, Elisabete Frollini, a professor at the Chemistry Institute in São Carlos, from the University of São Paulo (USP). The team she coordinates is developing polymeric board from vegetable fibers and is obtaining good results with the hydrolysis of sisal, a process related to the first stage of the production of ethanol, when the glucose and other fermentable sugars used in manufacturing alcohol are obtained from the pulp and other components of vegetable fibers.
The work of the researcher is centered on the so-called lignocellulosic fibers and their three main macro-components: lignin, cellulose and hemicellulose. Sisal and sugar cane are examples of this type of fiber. According to the researcher, her interest in sisal started because Brazil is the world’s largest producer and exporter of the fiber. In 2007 global production reached 240,700 tons, of which almost half (113,300 tons) was grown in Brazil, which could easily double its production in a short space of time. Sisal (Agave sisalana) originated in Mexico and is a plant grown in developing countries. In Brazil the plantations are concentrated in the states of Paraíba and Bahia. After being processed, the sisal is exported, mainly to the United States, Canada, Europe, Iran and countries in Eastern Europe. China and Mexico are the main buyers of the raw fiber. Sisal plants are planted over an area of 154,000 hectares in Brazil, with productivity close to 800 kg per hectare.
Other advantages of sisal fiber are the fact that it is not used as a food source and at the same time it has a high concentration of cellulose, almost 10% more than sugar cane bagasse. If the hemicellulose is also considered, almost 90% of the fiber from sisal is material that produces the fermentable sugars used in the process for making ethanol. “These sugars are generated by hydrolysis, which in a simplified way can be considered a reaction in which the bonds that bind the glucose units in cellulose and the units of other sugars in hemicellulose are broken”, explains Elisabete. “In Brazil, the hydrolysis processes for producing ethanol are concentrated on the use of sugar cane. Our work is demonstrating that it’s possible to use sisal for this purpose. We want to contribute so that Brazil can continue to stand out in the biofuel sectors; we believe that sisal can also be used as an important raw material.”
In 2007 researchers from the Chemistry Institute in São Carlos started looking at how to produce ethanol from sisal. They will shortly be joined in a cooperation agreement by researchers from the Wood and Biopolymer Sciences Unit (Unité des Sciences du Bois et des Biopolymères) at the University of Bordeaux I, in France. The purpose of the partnership is to improve the conditions of the hydrolysis process of cellulose from sisal, thereby increasing its efficiency, and studying new methods for extracting lignin from sisal fiber. In the work being done in São Carlos the process they are using is called acid hydrolysis for obtaining glucose from sisal fibers. In the partnership with the French, enzymatic hydrolysis will be investigated, a process in which, instead of acid, enzymes are used to break down the glucose bonds and which may have possible applications in biorefineries. “Acid hydrolysis is still cheaper, but a lot has been invested in enzymatic hydrolysis, with the aim of reducing costs and increasing the efficiency of the process. One of the inconvenient aspects of acid hydrolysis is the corrosion it can cause in refinery equipment when used on a large scale”, explains Elisabete. The project, in cooperation with the French university, also includes studying corn straw for producing biofuels. Straw is a lignocellulosic waste that is abundant in the south of France and in Brazil. For this reason, researchers from both countries are interested in studying how best to make use of it. At the end of 2007 Brazil and France were third and fifth, respectively, in world corn production.
An important aspect of the work of the team from USP is the use of vegetable fibers for producing polymeric compounds, the name given to polymers that are reinforced with other materials. One of the objectives of the research is to use sisal, sugar cane bagasse – waste produced on a major scale in Brazilian agriculture – and other natural vegetable fibers as an agent for reinforcing phenolic polymers to improve the mechanical properties of the compound, such as its impact-resistance. Another advantage of the mixture is the reduction in the cost of the material, because the fibrous reinforcement is cheaper than the polymer itself. “The great challenge is to combine polymeric fibers and matrixes in such a way as to produce an efficient material for use in particular applications”, says the researcher. So far, polymeric boards reinforced with sisal, sugar cane bagasse, curaua fiber from the Amazon region, jute, coconut and banana fibers have been successfully produced in USP’s laboratories.
The researcher’s projects also include the use of lignin and cellulose and their derivatives for preparing and obtaining polymers. In the case of the former, lignin is extracted from sugar cane bagasse and used as a reagent for preparing phenolic resins. These resins, under controlled temperature and pressure, are transformed into polymers and polymeric compounds. “The use of lignin in the resin increases the compatibility between the lignocellulosic fibers, like bagasse, and the polymeric matrix, since it will be present in both”, she explains.
Cellulose extracted from sisal and other fibers is also used for preparing bioplastics, a type of plastic made from a natural polymer that can be used for manufacturing food packaging. “Our goal is to produce this reinforced material on a nanometric scale”, she says. These materials are called bionanocompounds. One of the aspects that makes it difficult for cellulose and its derivatives to compete with synthetic polymers is the fact that this natural polymer is obtained mainly from wood, which has a slow replacement cycle because of the rate at which trees grow. Because of this, the researcher and her team have invested in studying sources that are rich in cellulose, but that have a short growth cycle, like sisal and sugar cane.
Over the last seven years the studies carried out by the researcher with vegetable fibers have already produced five PhD theses, six Master-s dissertations and various scientific undergraduate projects. They have also yielded a patent, one of the depositories of which is FAPESP, and the publication of some 30 scientific articles in international indexed periodicals. The patent shows the possibility of developing polymeric compounds from tannins, substances extracted from certain trees, like the black wattle (Acacia mearnsii) and also found in fruit and red wine. They are used in the leather industry and as a flocculating agent or coagulant in water treatment.
In this patent, the tannin was used as a reagent in the preparation of the polymeric matrix, the same function performed by lignin in other studies carried out by the team. Fibers obtained from the bark of the black wattle, a legume grown mainly in Rio Grande do Sul for its tannin, were used as a reinforcing agent in the compound. “In this way, typical tannin structures form part of the composition of the polymeric matrix and of the reinforcing material, because they are also found in the tree bark fiber”, points out Elisabete, who is confident that compounds obtained from polymers prepared from raw material that comes from a renewable source and natural fibers will be the new and promising materials over the coming years. “This tendency, which started in the closing years of the 20th century, should gradually place these materials almost on a par in the market with synthetic polymers”, she says. “The development of research and the preparation of human resources in this area are important for us to be able to reach this goal more rapidly.”
Natural fibers and macromolecules: studies aimed at different applications (nº 05/56450-8); Modality Regular Research Awards; Coordinator Elisabete Frollini – USP; Investment R$ 143,971.22 and US$ 23,574.47 (FAPESP)
Megiatto Júnior, J. D.; Silva, C. G.; Rosa, D. S.; Frollini, E. Sisal chemically modified with lignins: correlation between fibers and phenolic composites properties. Polymer degradation and Stability. v. 93, p. 1.109-1.121, 2008.