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En este trabajo se estudió el proceso de obtención de nanofibras a partir de fique, por el método de hidrólisis ácida utilizando ácido sulfúrico (H2SO4) combinado con ultrasonido (US). A las nanofibras obtenidas se les determinó su morfología (diámetro y longitud) utilizando microscopía electrónica de barrido (SEM) y microscopía electrónica de trasmisión (TEM) respectivamente, la presencia de grupos funcionales por espectroscopia infrarrojo (IR) y la estabilidad térmica por análisis termogravimétrico (TGA). Se obtuvieron tamaños de partícula de 25,2±6,2 nm de diámetro y 483,8±283,2 nm de longitud. La temperatura máxima de degradación de la nanocelulosa fue de 317°C. Las nanofibras de fique se utilizaron como refuerzo en hidrogeles utilizando acrilato de potasio (AK) y acrilamida (AM) como monómeros. Los hidrogeles se sinterizaron por el método de polimerización en solución. La reacción se realizó en un reactor de 500 mL con tapa esmerilada, equipado con reflujo. Se prepararon suspensiones de nanofibras de fique (3, 5, 10% en peso con respecto a la concentración de monómeros) en 80 mL de agua y se dispersaron utilizando ultraturrax a 9000 rpm por 10 min. Por otro lado, se mezclaron 14,0 g de AM con 22,0 g de AK el cual se obtuvo previamente por neutralización de 16,0 g de ácido acrílico (AA) con hidróxido de potasio (KOH) 2,5 M. Posteriormente, se mezcló la solución de nanofibras y la solución de monómeros. La mezcla se agitó por 10 min, a continuación se adicionó el iniciador persulfato de potasio (K2S2O8) (0,3% en peso con respecto a la cantidad de monómeros) y el entrecruzante N,N- Metilen bis acrilamida (NMBA) (0,085% en peso con respecto a la cantidad de monómeros). La adición de nanofibras de fique en una proporción al 3% mejoró la capacidad de hinchamiento en el equilibrio (Qeq) (476±13,26 g/g) en aproximadamente 170 veces más que el hidrogel sin fibra (310±8,71). Hidrogeles con proporciones de nanofibras al 5 y 10% presentan capacidad de hinchamiento (305±12,18 g/g y 292±13,34 respectivamente) similares al del hidrogel sin fibra. La adición de nanofibras de fique en hidrogeles en las proporciones estudiadas incrementaron la capacidad de retención de agua (QR) por encima del 50% en comparación con el hidrogel sin fibra que presenta una QR alrededor del 20%, siendo el hidrogel con una proporción de nanofibras del 5% el de mayor QR (75,3±7,36%). Finalmente, los hidrogeles en proporciones de nanofibras al 5 y 10% mostraron mayor resistencia a la compresión (Rc) en referencia al hidrogel sin nanofibras. El hidrogel con nanofibras al 5% presentó la mayor resistencia a la compresión (16,39±4,3 kPa), 2,5 veces mayor al hidrogel sin nanofibras (6,49±2,48 kPa). //Abstract: In this work the process of obtaining nanofibers from fique by the acid hydrolysis method was studied, and sulfuric acid (H2SO4) combined with ultrasound (US) was used. morphology (diameter and length) of nanofibers were measured using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively, in addition, the presence of functional groups by infrared spectroscopy (IR) and stability thermal analysis by thermogravimetric analysis (TGA) were analyzed. Particle sizes of 25.2 ± 6.2 nm in diameter and 483.8 ± 283.2 nm in length were obtained. The maximum degradation temperature of the nanocellulose was 317 ° C. The fique nanofibers were used as reinforcement in hydrogels, hydrogels potassium acrylate (AK) and acrylamide (AM) as monomers were used. The hydrogels were synthesized by the solution polymerization method. The reaction was carried out in a 500 mL reactor with a ground lid, equipped with reflux. Suspensions of fique nanofibers (3, 5, 10% by weight with respect to the concentration of monomers) in 80 mL of water were prepared, and these were dispersed using an ultraturrax at 9000 rpm for 10 min. On the other hand, 14.0 g of AM with 22.0 g of AK were mixed. AK was previously obtained by neutralization of 16.0 g of acrylic acid (AA) with 2.5 M potassium hydroxide (KOH). Subsequently, the solution of nanofibers and the monomer solution was mixed. The mixture was stirred for 10 min, and subsequently, potassium persulfate initiator (K2S2O8) (0.3% by weight with respect to the number of monomers) and the crosslinker N, N-Methylene bis acrylamide (NMBA) were added (0.085% by weight with respect to the amount of monomers). The addition of fique nanofibers in a 3% ratio improved the swelling capacity at equilibrium (Qeq) (476 ± 13.26 g / g) by approximately 170 times more than the hydrogel without fiber (310 ± 8.71). Hydrogels with proportions of nanofibers at 5 and 10% showed swelling capacity (305 ± 12.18 g / g and 292 ± 13.34 respectively) like hydrogel without fiber. The addition of fique nanofibers in hydrogels increased the water retention capacity (QR) by more than 50% compared to the hydrogel without fiber that presented a QR around 20%, the hydrogel that presented the highest QR was the hydrogel added with 5% nanofibers (75.3 ± 7.36%). Finally, hydrogels with 5 and 10% of nanofibers showed greater resistance to compression (Rc) compared to hydrogel without nanofibers. The hydrogel with 5% nanofibers had the highest compressive strength (16.39 ± 4.3 kPa), 2.5 times greater than the hydrogel without nanofibers (6.49 ± 2.48kPa). Maestría

This paper presents a review on hydrogels applied to agriculture emphasizing on the use of natural fibers. The objectives were to examine, trends in research addressed to identify natural fibers used in hydrogels development and methods for modifying natural fibers, understand factors which determine the water retention capacity of a hydrogel. Consequently, this paper shows some methodologies used to evaluate the hydrogels efficiency and to collect in tables, relevant information in relation to methods of natural fibers modification and hydrogel synthesis. It was found that previous research focused on hydrogels development processed with biodegradable polymers such as starch, chitosan and modified natural fibers, cross-linked with potassium acrylate and acrylamide, respectively. In addition, current researches aimed to obtaining hydrogels with improved properties, which have allowed a resistance to climatic variations and soil physicochemical changes, such as pH, presence of salts, temperature and composition. In fact, natural fibers such as sugarcane, agave fiber and kapok fiber, modified with maleic anhydride, are an alternative to obtain hydrogels due to an increasing of mechanical properties and chemically active sites. However, the use of natural nanofibers in hydrogels, has been a successful proposal to improve hydrogels mechanical and swelling properties, since they give to material an elasticity and rigidity properties. A hydrogel efficiency applied to soil, is measured throughout properties as swellability, mechanical strength, and soil water retention. It was concluded that hydrogels, are an alternative to the current needs for the agricultural sector.