Effect of hybridization on the physical and mechanical properties of high density polyethylene–(pine/agave) composites A.A. Pérez-Fonseca a , J.R. Robledo-Ortíz b,⇑ , D.E. Ramirez-Arreola c , P. Ortega-Gudiño a , D. Rodrigue d , R. González-Núñez a a Departamento de Ingeniería Química, Universidad de Guadalajara, Blvd. Gral. Marcelino García Barragán # 1451, Guadalajara, Jalisco 44430, Mexico b Departamento de Madera, Celulosa y Papel, Universidad de Guadalajara, Carretera Guadalajara-Nogales km 15.5, Las Agujas, Zapopan, Jalisco 45510, Mexico c Departamento de Ingenierías, CUCostaSur, Universidad de Guadalajara, Av. Independencia Nacional 151, Autlán de Navarro, Jalisco 48900, Mexico d Department of Chemical Engineering and CERMA, Université Laval, Quebec City, Quebec G1V 0A6, Canada article info Article history: Received 30 May 2014 Accepted 14 July 2014 Available online 23 July 2014 Keywords: Polymer matrix composite Hybrid Mechanical properties Extrusion Injection molding abstract This work reports on the properties of high density polyethylene based hybrid composites made with two natural fibers: agave and pine. The composites were produced by a combination of extrusion and injec- tion molding. The effect of hybridization was analyzed via morphological, mechanical and water immer- sion tests for two total fiber contents, 20 and 30 wt.%, and different pine-agave fiber ratios (100–0, 80–20, 60–40, 40–60 and 0–100). Moreover, the effect of coupling agent (maleated polyethylene) in the hybrid composite formulation was evaluated. The results showed that addition of agave fibers improves tensile, flexural and impact strength, while pine fibers decreases water uptake. As expected, the addition of a cou- pling agent improves substantially the quality of the polymer–fiber interface as well as the mechanical properties, but this effect was more important for composites produced with higher agave fibers content due to the their chemical composition. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction In recent years ecological awareness and other environmental issues led to the development of composite materials based on renewable resources such as natural fibers. These materials are environmentally friendly and low-cost alternatives to replace syn- thetic fibers like glass and carbon fibers [1]. Natural fibers are used as reinforcements for composite materials due to various advanta- ges compared to conventional fibers. The main advantages are lower densities, non-toxicity and lower cost. In addition several fiber varieties are locally available [2]. However, due to hydropho- bic–hydrophilic interactions the combination of natural fibers with most polymer matrices results in poor adhesion and therefore lim- ited stress transfer from the matrix to the reinforcing fibers [3]. For that reason, several investigations explored the possibility of using coupling agents to improve adhesion and consequently properties such as tensile and flexural strength and modulus [4,5]. Lu et al. [6] investigated the effect of maleated polyethylene (MAPE) in wood fiber/high density polyethylene composites and observed that for untreated composites the wood fibers were mainly linked to the thermoplastic matrix through mechanical connections, while evidence of chemical bridges via esterification were present in maleated wood fiber/HDPE composites. Hybrid composites are materials made by combining two or more different types of reinforcements in a common matrix. Hybridization may offset the disadvantages of one component by the addition of another. A requisite for the occurrence of a hybrid effect is that both reinforcements differ in mechanical properties and their interaction with the matrix. The strength of hybrid com- posites is dependent on the properties of each reinforcement such as aspect ratio, content, geometry, orientation, intermingling extent and interfacial bonding [7]. For example, Haq et al. [8] men- tioned that hybridization enables to exploit the synergy between natural fibers and inorganic compounds, leading to properties improvement while maintaining environmental appeal. One advantage of hybridization is cost reduction; some rein- forcements are very expensive and could be combined with less expensive materials maintaining good properties. For example, with the addition of natural fibers, good mechanical properties can be obtained at a lower cost. Ramesh et al. [9] prepared hybrid composites of sisal–jute–glass fibers and found that the incorpora- tion of sisal–jute fibers can improve tensile, flexural and impact strength and used as an alternate material for glass fiber reinforced http://dx.doi.org/10.1016/j.matdes.2014.07.025 0261-3069/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +52 33 3682 0110x233. E-mail address: jorge.robledo@cucei.udg.mx (J.R. Robledo-Ortíz). Materials and Design 64 (2014) 35–43 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes