Estudio de compósitos de fibras naturales y arcilla para aplicaciones acústicas
Authors:   , Victoria Martínez Uriel 
Published: March 2023

During the last decade, actions and studies to counteract the effects of noise have increased through the use of insulating or absorbent materials, and civil regulations based on monitoring in urban areas, since exposure to high levels of sound pressure can cause psychological and physiological health problems such as anxiety, depression, stress, fatigue, cardiac, hearing or cognitive problems, as well as irreversible hearing loss. This work aims to develop and study natural compounds made of clay reinforced with coconut or nopal fibers to analyze their acoustic coefficients and determine their applications as insulation or conditioning material. The composites were obtained incorporating 25, 50 and 75% by weight of each fiber with bentonite clay. The physical and chemical characterization of the composites was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy, Fourier transforms infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). The properties of hardness and apparent density of the composites were obtained from samples aged three months. Using XRD, the compounds were identified in the bentonite: montmorillonite, quartz and feldspar. The FT-IR allowed the identification of the functional groups of the clay and for the fibers the presence of lignin and hemicellulose was determined. Micrographs show that coconut fiber is more porous than nopal; the size of the nopal fibers was between 71.8 and 219.7 nm (electron microscopy) and that of the coconut fibers was 0.1613 mm (optical microscopy). The apparent density of the composites follows the model of the mixture rule, while the hardness changes very little in the samples prepared with nopal fiber. Through ATG it was found that bentonite improves the thermal stability of the composites. The acoustic absorption, reflection, and transmission coefficients of the materials were determined using the impedance tube method, in the range of 50 to 10,000 Hz. The samples obtained after the synthesis process was weighed and characterized in the impedance tube; For the humidity tests, a drop was placed on the surface of the sample and the characterization process was repeated. These tests were carried out until 4 drops of water were added to each composite. The results showed an increase in the acoustic absorption properties when adding the fibers in the composites, where it was observed that the coconut fiber presented a higher sound absorption than the nopal fiber. The hardness and density of the material are directly related to a reduction in the absorption coefficient, although the tests carried out show that the nopal fibers in the composites do not increase their hardness and their acoustic properties, unlike coconut fibers. The results obtained from the acoustic characterization carried out in the surface humidity test showed that the absorption, reflection and absorption coefficients of the coconut change with increasing humidity in the samples. While, in the case of nopal, due to its composition and hydrophobic properties, there is no significant variation in its acoustic properties. Composites made from coconut fiber have better acoustic absorption and reduction properties, while those made from nopal fiber stand out in terms of sound reflection.