Tensile properties and micromechanical analysis of stone groundwood from softwood reinforced bio-based polyamide11 composites H. Oliver-Ortega a, * , Granda L.A. a , Espinach F.X. b , Mendez J.A. a , Julian F b , Mutj  eP a a Group LEPAMAP, Department of Chemical Engineering, University of Girona, C/M. Aur elia Capmany, nº61, Girona 17071, Spain b Design, Development and Product Innovation, Dpt. of Organization, Business Management and Product Design, University of Girona, C/M. Aur elia Capmany, nº61, Girona 17071, Spain article info Article history: Received 12 May 2016 Received in revised form 1 July 2016 Accepted 4 July 2016 Available online 9 July 2016 Keywords: Short-fibre composites Mechanical properties Interface Injection moulding Photoelectronic spectroscopy (XPS) abstract Bio-polyamides (BioPA) reinforced with natural fibres are one of the most promising bio-based com- posites. However the principal challenge of polyamides (PA) is their high melting temperature close to the degradation temperature of the natural fibres. Polyamide 11 (PA11) is a 100% BioPA with a melting point lower than cellulose temperature degradation. Nonetheless, few researches about PA11 reinforced with natural fibres composites had been performed. In this work, PA11 was reinforced with stone groundwood fibres (SGW) ranging 20% up to 60% of fibre contents. The composites were prepared, extruded, injected moulded and their tensile properties were characterised. An enhancement of 66.8% was obtained for the tensile strength of the composites, besides the strain and the toughness decreased as expected. The significant enhancement of the tensile strength leads to consider a relatively good interface between the fibre and the polymer matrix which was determined in the micromechanical studies. Moreover a morphology analysis of the fibre and its chemical composition study at surface were carried on, in order to discuss the micromechanical analysis results. The average orientation factor and intrinsic tensile strength of the fibres were also determined in the micromechanical analysis. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Composites materials reinforced with natural fibres had been a common field of research in the last decades. The significant enhancement of the mechanical properties and low density of this composites are some of their attractiveness for the industry [1e3]. In order to reduce the petrol-based dependence, the use of bio- based polymers for the production of composite materials has become an increasing research topic in the last years [2,4,5]. One type of these bio-based polymers is biopolyamides (BioPA). BioPA are non biodegradable polymers that could be totally or almost completely bio-based. Some examples are polyamide 11 (PA11) which is 100% bio-based, polyamide 10.10 (PA10.10) which could have a bio-based content up to 99%, or polyamide 6.10 (PA6.10) which has a 62% of bio-content, depending on the carbon per- centage from natural resources. BioPA has been successfully rein- forced with synthetic cellulosic fibres [5]; however some special requirements are necessary for the processing of its composites caused by its melting which is close to the degradation temperature of the cellulose fibres. This hinders processing BioPA composites while conserving the natural fibres because short time processes are mandatory to preserve the natural fibres properties [6,7]. PA11 is a 100% bio-based polyamide biotechnologically obtained from 11-aminoundecanoic acid, derived from castor oil [8,9]. Additionally, PA11 has a smaller footprint in the global warming than other polymers [8,10]. PA11 is a thermoplastic polymer with a low melting point regarding other polyamides (about 200  C). This allows PA11 to be natural fibre reinforced with relatively low or inexistent thermal degradation of the natural fibres and becoming a promising polymer matrix for composites. In addition, its non biodegradability, recyclability, good mechanical properties and high water and chemical resistance enables their use for long-life applications such as pipes, automotive, commodities, etc [2,11,12]. However, to the best knowledge of the authors, there is a lack of PA11 studies in the field of natural fibres reinforced composites [13]. Stone groundwood (SGW) is a commercial easily available pulp usually used in papermaking. SGW is obtained high yield process (about 98.5%) and at a relatively low price (less than 0.5V/kg). This * Corresponding author. E-mail address: helena.oliver@udg.edu (H. Oliver-Ortega). Contents lists available at ScienceDirect Composites Science and Technology journal homepage: http://www.elsevier.com/locate/compscitech http://dx.doi.org/10.1016/j.compscitech.2016.07.004 0266-3538/© 2016 Elsevier Ltd. All rights reserved. Composites Science and Technology 132 (2016) 123e130