PEER-REVIEWED BRIEF COMMUNICATION bioresources.com Oliveira et al. (2019). “Sound absorption composites,” BioResources 14(2), 4806-4813. 4806 Sound Absorption of Recycled Gypsum Matrix Composites with Residual Cellulosic Pulp and Expanded Polystyrene Karina A. de Oliveira, a, * Juliana C. Barbosa, b André L. Christoforo, c Julio C. Molina, a Carolina A. B. Oliveira, a Marilia S. Bertolini, b Maristela Gava, b and Gustavo Ventorim a This work aimed to study the technical feasibility of using industrial gypsum, expanded polystyrene (EPS), and cellulose solid wastes in the production of acoustic insulation panels for buildings. Five traces of acrylic gypsum matrix were produced with variations in the proportions of cellulosic pulp and EPS and always maintaining the same proportion of recycled gypsum and water. The composites produced were tested according to the ISO 10534-2 (2015) standard for the determination of the coefficient of sound absorption and ABNT NBR 14715-2 (2010) for bending tests. The results didn’t show statistically significant differences in the coefficient of sound absorption with variations in the quantities of each material. However, the sonic frequency of the tests directly influenced the results, presenting a better performance at a low frequency (250 Hz). The results qualify the composite produced for use as acoustic insulation and can be used in plates for sound reflection in buildings in places where it doesn’t require resistance to great stresses. Keywords: Solid waste; Recycled gypsum; Acoustic insulation; Composites; Recycled materials Contact information: a: Department of Mechanical Engineering, UNESP - São Paulo State University, Guaratinguetá/SP, Brazil; b: College of Timber Industrial Engineering, UNESP - São Paulo State University, Itapeva/SP, Brazil; c: Departament of Civil Engineering, UFSCar - Federal University of São Carlos, São Carlos/SP, Brazil; *Corresponding author: kari.oliveira@outlook.com INTRODUCTION The constant process of development and urbanization has led to a search for a reduction in the extraction of natural resources and for an increase in the reuse of waste that is otherwise discarded in the generation of new materials. The reuse of waste not only preserves natural resources but also reduces the production costs and pleases consumers who wish to use environmentally sound materials. These new materials may be used as alternatives to those commonly used by industry. In Brazil, the pulp and paper sector has great importance in the economy and generated a high volume of production that results in a high volume of waste that requires final disposition. This material can be incorporated into other materials, forming composites with improvements in its mechanical properties, such as tensile, flexural, acoustic, and thermal resistance (Oliveira 2012; Arenas et al. 2014). Expanded polystyrene (EPS) is another residue scrapped on a worldwide scale and it consists of a rigid cellular plastic expanded by gas. This material is used for various purposes. It has been gaining prominence in civil construction because it can adapt to the needs of the work and has acoustic and thermal properties, in addition to being low cost. Another big generator of environmental impacts in Brazil is the civil construction sector, which besides being responsible for the excessive consumption of natural resources