399 ISSN 1229-9197 (print version) ISSN 1875-0052 (electronic version) Fibers and Polymers 2020, Vol.21, No.2, 399-406 Hybrid Polyester Composites Reinforced with Curauá Fibres and Nanoclays Gilberto García del Pino 1 , Antonio Claudio Kieling 1 , Abderrezak Bezazi 2 , Haithem Boumediri 2 , Juliana Fontolan Rolim de Souza 3 , Francisco Valenzuela Díaz 3 , Jose Luis Valin Rivera 4 , Jamile Dehaini 5 , and Tulio Hallak Panzera 6 * 1 Department of Mechanical Engineering, State University of Amazonas (UEA), 69065-001 Manaus-AM, Brazil 2 Laboratory of Applied Mechanics and New Materials (LMANM), University 08 Mai 1945 Guelma, 24000, Algeria 3 Department of Materials Engineering and Metallurgy, University of São Paulo (USP), 05508-030, São Paulo-SP, Brazil 4 School of Mechanical Engineering, Pontifical Catholic University of Valparíso (PUCV), Quilpué, Valparaíso, Chile 5 Department of Meteorology, State University of Amazonas (UEA), 69065-001, Manaus-AM, Brazil 6 Centre for Innovation and Technology in Composite Materials (CITeC), Department of Mechanical Engineering, Federal University of São João Del Rei (UFSJ), 36307-352, São João del Rei-MG, Brazil (Received May 13, 2019; Revised July 16, 2019; Accepted July 28, 2019) Abstract: This work investigates a hybrid polyester composite consisted of Curauá natural fibres and organophilic clay nanoparticles. A Taguchi method is used to identify the effects of fibre fraction (10, 20 and 30 wt%), alkaline treatment concentration (NaOH, 2.5, 5 and 10 wt%), treatment time (2, 4 and 8 h) and nanoparticle content (2.5, 5 and 10 wt%) on the mechanical behaviour of the hybrid composites under tension and three-point bending. X-ray, FTIR and microstructural analysis are performed to assess the treated and untreated fibre surfaces. The optimum combination of the process parameters for the tensile and flexural properties is: fibre content at 30 wt%, NaOH concentration at 5 wt%, treatment time at 8 h and nanoclay inclusions at 5 wt%. A mean tensile and flexural strength of 36.13 MPa and 32.55 MPa are obtained, which represents percent increases of 39.22 % and 25.43 % compared to the polyester polymer in pristine condition. Keywords: Hybrid composite, Natural fibres, Organophilic nanoclay, Mechanical properties, Taguchi Introduction In recent years, due to increasing environmental concerns, there has been a growing renewal of interest in composite materials derived from lignocellulosic feedstock. A significant amount of research has been conducted on different types of plant fibres, identifying some promising substitutes for the traditional composite reinforcement, specifically E-glass. In addition to biodegradability, availability and low cost, natural fibres can bring technical advantages, such as high specific mechanical properties, damping and acoustics properties [1-5]. The hybridisation process in composite materials has been used when a particular or multifunctional performance is required. In this case, the system is composed of two different dispersive phases, i.e. different fibres, particles or fibre-particle. In this work, nano clay particles are combined with natural fibres in a polyester matrix phase. The advantages of using micro and/or nano particles in laminated composites are sometimes controversial in the literature. Basically, the inclusion of rigid particles in laminates is focused on increasing their mechanical properties and durability [6-8]. In theory, there are two effects attributed to the incorporation of rigid particles on laminated composites: (i) the interlocking effect and (ii) the increase in matrix phase stiffness [9]. The interlocking effect occurs when the particles lead to increased shear stress in the interlaminar region attributed to additional friction against the fabric surfaces. The incorporation of rigid particles in the matrix phase makes it stiffer, which contributes to the effective properties of the composites [10]. The amount of particles within the laminates is extremely important to obtain such benefits, and is also related to particle size and geometry [7]. Not only nano particles, e.g. clays [11], carbon nano tube (CNT) [12], silica [13], but also micro particles, e.g. alumina [14], silica [15], silicon carbide [16], Porland cement [17], have been added to composite materials. The fracture mechanism is also affected by the shape, size and distribution of the particle in the system. In general, the presence of particles delays the crack propagation which enhances the composite’s toughness [18]. In contrast, these ceramic particles lead to increased matrix stiffness, which makes it more brittle with a consequent premature failure [9]. Organophilic nano clays is a hydrophobic material which has been used as filler in polymers to enhance their mechanical properties and thermal durability. This particular type of particle can change the morphology of the polymer crystallising with fine grain structure [19-21]. The concentration and the processing conditions should be selected so that the bulk of the clay tactoids are intercalated by the thermosetting polymer and the clay layers are separated from each other, i.e., exfoliated or delaminated [22]. Araujo et al. [20] obtained mecanically improved films of polypropylene nanocomposites (PP) containing 1 % by mass of organically modified bentonite. Oliveira et al. [21] *Corresponding author: panzera@ufsj.edu.br DOI 10.1007/s12221-020-9506-7