Polypropylene composites based on lignocellulosic fillers: How the filler morphology affects the composite properties Ilhem Naghmouchi a , Francesc X. Espinach b , Pere Mutjé c , Sami Boufi a,⇑ a University of Sfax, Faculty of Science, LMSE, BP 1171-3000 Sfax, Tunisia b Design, Development and Product Innovation, Dept. of Organization, Business, University of Girona, c/M. Aurèlia Capmany, n° 61, Girona 17071, Spain c Group LEPAMAP, Department of Chemical Engineering, University of Girona, c/M. Aurèlia Capmany, n° 61, Girona 17071, Spain article info Article history: Received 3 August 2014 Accepted 16 September 2014 Available online 28 September 2014 Keywords: Composites Wood flour Olives residue Mechanical properties abstract In this research, composite materials were made from wood flour (WF) or olive stone flour (OSF) as reinforcement, polypropylene (PP) as polymer matrix, and maleated polypropylene (MAPP) as coupling agent, by using injection molding. The effects of the filler loading and coupling agent on the physical properties of the composites, in terms of tensile and impact strength, water absorption and wear resistance were studied. The macromechanical properties were explained by the morphological features of the reinforce- ments. Composites containing coupling agents exhibited the best mechanical properties, and reduced the negative impacts of water absorption. The difference in the morphology of the two lignocellulosic fillers was found to be a key factor controlling the properties of the composites and the evolution of their prop- erties against water absorption. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Biomass-fiber-reinforced polymer composites have received much attention because of their low density, nonabrasive, combus- tible, nontoxic, low cost, and environmentally friendly properties [1–3]. Another important property of these reinforcing elements is their ability for noise insulation, making them candidates for the manufacture of lightweight soundproofing solutions. The pos- sibility for energetic recycling at the end of their life is also to be considered as lignocellulosic fillers are used [4]. Because of all these attributes, lignocellulosic based composites gained increas- ing interest of both academic and industrial communities. Poten- tial markets include: automotive parts for light-weight elements with soundproofing properties, building profiles such as decking, siding, fencing, deck boards, wearing surfaces, and window frames [5]. However, in addition to these advantages, natural fillers have some disadvantages as well, such as the wide dispersion of their properties (tensile and flexural strengths, stiffness, morphology...) according to their origin [6]. Furthermore, natural fibers, unlike the synthetic fibers, are thermally unstable, and its use is limited to temperatures below 220 °C [7]. Another major drawback concern- ing natural fillers is their inherent hydrophilic and polar nature, making necessary the use of coupling agents to improve the inter- facial adhesion between the fibers and the hydrophobic matrixes, and accordingly to benefit of their reinforcing potential [8]. Agriculture generates co-products, by-products and waste streams that are currently not properly taken care of both in envi- ronmental and economic terms. The use of such agricultural mate- rials, that are largely available throughout the world, as a source of fillers or reinforcements to the industry not only provides a renew- able source, but could also generate a non-food source of economic development for farming and rural areas [9,10]. Furthermore, the use of biomass for the production of composite materials can be an interesting option for countries with few wood resources. In the case of the Mediterranean regions’ olive oil producing countries, the olive oil extraction processes generates huge amounts of solid lignocellulosic residue, representing 30% by weight of the olive fruit. Given the chemical composition of this residue, mainly lignin, hemi- cellulose and cellulose, different strategies have been developed for its exploitation, being the most common its incineration for energy generation [11]. Nonetheless, alternative uses of agricultural wastes, such as their exploitation as a sustainable reinforcement for composites, are regarded as potentially important within the field of materials technology [12–15]. In fact, polypropylene (PP) ground olive stone residue (OSF) reinforced composite are expected to show high stiffness values, due to the high hardness of the olive stones. This has been corroborated by other publications that http://dx.doi.org/10.1016/j.matdes.2014.09.047 0261-3069/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +216 74 276 400; fax: +216 74 274 437. E-mail address: Sami.Boufi@fss.rnu.tn (S. Boufi). Materials and Design 65 (2015) 454–461 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes