Cassava bagasse-Kraft paper composites: analysis of influence of impregnation with starch acetate on tensile strength and water absorption properties
Introduction
Cassava, Manihot esculenta Crantz, is one of the main sources of industrial starch, being cultivated throughout the Brazilian territory, consumed in great quantities, and being important for the preparation of many typical food dishes in Brazil and in other tropical countries (Pandey et al., 2000, Cereda, 1994). In the industrial process to produce cassava starch, the solid residue (bagasse) resulting from the extraction is composed of fibrous materials and starch that has not been extracted. The amount of bagasse produced in industry is significant, being approximately 900 kg of bagasse, with 85% moisture, for each ton of processed root (Leonel, Cereda, & Roau, 1999). The composition of the bagasse depends on the cassava's origin as well as on the processing procedure, but it is predominantly starch (40–60%) and fibre (15–50%) plus small quantities of proteins and lipids (Pandey et al., 2000).
In Brazil, cassava bagasse is a problem for the starch industry because it has a high percentage of water, which makes drying and transport expensive. Because of this problem, many companies deposit this waste on neighbouring land, after which it is carried away to be used in animal feed (Cereda, 1994). The improper disposal of the material represents an environmental problem and the waste of a raw product, which could be used for other purposes.
In recent years, research has been directed towards ways of transforming agro-industrial residues into by-products. Pandey et al. (2000) have used the cassava bagasse as a substrate in microbiological processes, obtaining products of greater additional value, such as aroma and flavour compounds. The use of the bagasse for the production of disposable trays and supports for plants has been presented in symposia, but scientific studies have not been published. It is also important to note that, these trays are biodegradable, reducing the impact caused by the discharge into the environment of materials derived from petroleum.
Cassava starch has also been studied as a raw material for the production of biodegradable films, which are transparent, but with low resistance to direct contact with water and poor mechanical properties (Dufresne and Vignon, 1998, Larotonda, 2002, Lörcks, 1998, Roesser et al., 2000, Tomka, 2000). Starch is a natural polymer consisting of amylose (linear glucose chains) and amylopectin (ramified glucose chains) units, whose percentages can be different depending on the origin of the starch (Buléon et al., 1998, Dufresne and Vignon, 1998).
Starch's hydrophilic nature is the main limitation for the development of biodegradable materials from it (Curvelo, Carvalho, & Agnelli, 2001). Many studies have been directed at the chemical modification of the starch as an alternative way to improve its properties and applications, such as in the acetylation of starch, modifying the molecular structure and allowing the attainment of a thermoplastic and hydrophobic material (Fringant et al., 1996, Graaf et al., 1995, Treadway, 1946, Feuer, 1998).
The objective of this work was to develop biodegradable composites from the cassava bagasse and Kraft paper, and to evaluate the influence of its impregnation with starch acetate on the tensile strength and on the water absorption of these materials.
Section snippets
Materials and methods
Dried cassava bagasse was supplied by AMIFAR Ind. e Com. Ltda., Deodápolis, MS, Brazil, with the following composition: 63.1% starch and 36.9% fibre.
Ten parts of water for each part of bagasse was weighed and heated, under continuous stirring, up to 70 °C and then maintained at this temperature for 40 min by means of a temperature-controlled hot plate. Under these conditions, the starch is gelatinized and adhered to the fibres producing a homogeneous mass, which was then placed in a Meteor
Scanning electron microscopy
Fig. 2 shows a SEM micrograph of the surface and cryo-fractured surfaces of non-impregnated and starch acetate impregnated samples. Fig. 2(a) displays the micrographs of fibre of Kraft paper and bagasse fragments, forming a heterogeneous porous material. The impregnation with starch acetate modified notably the surface of the material, making it more homogeneous, in spite of the presence of fractures on the sample surface, as shown in Fig. 2(b). These fractures were formed during the drying of
Conclusions
Cassava bagasse with 10% Kraft paper added to it can be used for the manufacture of cardboard. The results indicate that impregnation of hygroscopic materials with starch acetate had a great influence on the reduction of water absorption, which decreased to a quarter of the initial absorption in the best of cases. The materials impregnated under atmospheric pressure produced results for water absorption similar to those obtained under vacuum, showing that the impregnation depends on other
Acknowledgements
The authors wish to thank CAPES and CNPq for the financial support provided.
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