Study of natural fibers from waste from sponge gourd, peach palm tree and papaya pseudstem
Abstract
Lignocellulosic wastes from agro-industry are usually discarded, despite their technical potential for use to reinforce composites. Because of increasing environmental concerns, scientific interest is growing to characterize fiber residues from peach palm tree trunks, papaya tree trunks and sponge gourds. The peach palm residues were obtained from the portion of the trunk not suitable for hearts of palm, while the papaya trunk residues were obtained from trees cut down after three years of fruit production and the sponge gourd waste material came from leftover gourds not suitable for making bath sponges. The materials were characterized regarding moisture content, density, ash content, lignin and holocellulose content, and soluble content, and were submitted to thermogravimetric analysis, Fourier transform infrared spectroscopy (FTIR), X -ray diffract ion, mechanic property and morphological analysis by scanning electron microscopy. The moisture, extractives and ash contents of the papaya pseudsterm and peach palm wastes were very near each other. The sponge gourd fibers had the highest concentrations o f α-cellulose and hemicellulose and lowest levels of extractable soluble, and ash. The characterization results show that these waste materials are comparable with other agro -industrial residues described in the literature for use in making composites, so they have good potential for use as polymer reinforcement.
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Introduction
Concern over the use of resources from fossil sources has prompted development of composites for various applications containing cellulose as a substitute for synthetic materials derived from petroleum [1]. The cellulosic materials or lignocellulosic fibers obtained from agro-industrial waste can be burned to generate energy (e.g., sugarcane bagasse), but the majority are discarded in dumps/landfills or are burned without proper control, causing environmental problems, especially atmospheric emissions. For this reason, there is a need to find uses for these materials in line with good sustainability practices, involving economic, social and environmental questions [2].
A wide range of lignocellulosic fibers can be used to reinforce polymers. These include agricultural fibers such as stems and leaves as well as wood fibers [1]. Fibers can be considered composites of fibrils bounded by a matrix formed by lignin and hemicellulose. Cellulose is main responsible for the resistance of fibers, because of its high degree of polymerization and molecular orientation. In turn, lignin not only keeps the fibers together, it also acts as a stiffening agent for the cellulose molecules within the fiber wall. Besides these components, fibers contain inorganic compounds and molecules that are extractable with organic solvents, such as pectins, simple carbohydrates, alkaloids, saponins, polyphenols, gums, resins, fats, greases and others. Woody plants typically contain 40-50wt% cellulose, 20-30wt% hemicellulose and 20-28wt% lignin, besides other substances in smaller concentrations [3]. Study of the chemical composition is important to understand the influence of fibers on the characteristics of the composite of interest [4].
It is necessary to investigate the chemical composition of fibers because this can vary according to many factors, such as species, variety, soil type, climate conditions, plant part and age of the plant from which the fiber is extracted. In one study [5], the chemical compositions of fibers from banana plants, sugarcane bagasse and sponge gourds were determined and the samples were also characterized by X-ray diffraction, thermal analysis and microscopy to evaluate morphology. The crystallinity indices, obtained by X-ray diffraction, for the banana tree, bagasse and sponge gourd fibers were 39, 48 and 50%, respectively. All the materials came from Brazil. The morphological study of the fibers revealed different sizes and arrangements of cells composing the fibers, with thick non-spherical cells [5]. Another characterization study was carried out by Tanobe and collaborators [6], who evaluated sponge gourd fiber from southeastern Brazil before and after different chemical treatments (2% NaOH and 3% methacrylamide) for surface modification. They observed that the treatment with NaOH was more effective to prepare the surface for subsequent use as reinforcement of composites. Teixeira and collaborators [7] characterized sugarcane bagasse by thermogravimetry, X-ray diffraction and morphological analysis, concluding that this bagasse can be used to obtain whiskers. Other studies to characterize cellulosic residues from various plant sources and countries can be mentioned, such as: coconut shells [8,9], wheat and rice stalks [10](origin not mentioned), banana plants (India) [11-13] and palm (Thailand) [9].
By looking for in the literature, we verified that no articles have been published about the characterization of fibers extracted from the peach palm or papaya tree trunks for the last ten years. In the case of the peach palm, only part of the trunk is used (to produce hearts of palm), while papaya trees have a short productive lifetime, after which they are cut down. In both cases, the remaining material is generally discarded or burned. For this reason, the research group of the Center for Excellence in Recycling and Sustainable Development (NERDES), located at the Universidade Federal do Rio de Janeiro (UFRJ), has taken the initiative to study these materials. The fibers extracted from the trunks of peach palm (bactris gasipaes) and papaya pseudstem (Carica papaya) were characterized for subsequent use in composites. Waste fibers from mature sponge gourds (Luffa Cylindrica) were characterized as well because they also have technical and commercial potential. Fibers are known to improve properties when added to polymers to produce composites. The reinforcement is highly dependent of the interaction between the polymeric matrix and the filler. To insure that the fiber-filled composite will have better performance, characterization of the fiber is very important as filler and matrix must present special features as to develop a strong interface.
Conclusion
The characteristics of the agro-industrial waste fibers analyzed here, from peach palm trees, papaya trees and sponge gourds, are comparable to those of other studies of natural fibers from waste materials (coconut shells, sponge gourds, sugarcane bagasse and banana plants), even though the materials come from different places. Knowledge of the structure and compositions of these three waste materials will provide data for comparison in future studies, in particular for peach palm and papaya tree, for which this is the first published report . The sponge gourd fiber presented higher hemicellulose and cellulose concentrations than the other two fibers so probably the presence of hemicellulose and cellulose could be directly related to the absorption of water. The sponge gourd fiber had the highest concentrations of holocellulose, and consequently of α-cellulose and hemicellulose, and the lowest levels of soluble extractives and ash. The papaya tree and peach palm fibers had moisture, extractives and ash values very near each other. These waste fibers can be used effectively to reinforce polymers, while reducing the environmental impacts caused by inadequate disposal or burning.
