Flame-retardant wood polymer composites (WPCs) as potential ﬁre safe bio-based materials for building products: Preparation, ﬂammability and mechanical properties Ehsan N. Kalali a , Lu Zhang a , Marjan E. Shabestari b , Jeremy Croyal c , De-Yi Wang a, * a IMDEA Materials Institute, c/Eric Kandel 2, Getafe, Madrid 28906, Spain b Department of Materials Science and Engineering & Chemical Engineering, Polytechnic School, Carlos III University of Madrid, Avenida Universidad 30, 28911 Legan es, Madrid, Spain c Ecole Polytechnique de l'universit e de Nantes, France ARTICLE INFO Keywords: Wood polymer composite (WPC) Fire performance Mechanical properties Thermal properties ABSTRACT Improving the efﬁciency of traditional ﬂame retardant additives is a challenging task in the ﬁeld of wood polymer composites (WPCs). In this work, novel ﬂame retardant system for WPCs was developed based on the combination of ammonium polyphosphate (APP) with phytic acid modiﬁed layered double hydroxide (Ph-LDH). Thermog- ravimetric analysis illustrated that the incorporation of Ph-LDH resulted in earlier thermal degradation of the WPCs with more thermally stable products during degradation, giving improved char formation. Limiting oxygen index (LOI), vertical burning (UL-94) and cone calorimetry tests were used to study the ﬂammability of WPCs and the results showed that the addition of Ph-LDH had a synergistic effect on their ﬁre performance. The char res- idues of the WPCs after the cone calorimetry tests were characterised by scanning electron microscopy (SEM). Mechanical properties of the ﬂame retardant WPCs were analysed using impact and tensile tests. Partial substi- tution of APP with polypropylene (PP) resulted in a deterioration in the tensile and impact properties, while co- incorporation of nano-ﬁllers led to an enhancement of the mechanical performances of the ﬂame retardant WPCs. This WPC with good ﬂame retardant and mechanical properties could potentially be used in the ﬁelds of building or furniture which require high ﬂame retardancy. 1. Introduction Growing environmental awareness has increased demand for the development of brand new, eco-friendly materials with acceptable properties, high biodegradability and relatively low cost. Wood polymer composites (WPCs) have emerged as the latest generation of construction engineering materials for different interior and exterior applications, such as decking for balconies and terraces, fencing, landscaping timbers, furniture, automobile products, etc. [1–3]. During recent decades, their low cost and superior efﬁciency; including high sustainability, lower water uptake, durability against environmental impacts such as fungi and insects compared with wood, high dimensional stability over their life- time and high relative stiffness and strength, have attracted manufac- turers attention and researchers' interest [4]. However, the main drawback of WPCs is their high ﬂammability which limits their appli- cation in various ﬁelds. Therefore, enhancement of their ﬂame retardant properties is valuable and much effort has been devoted to this area. The incorporation of ﬂame retardants (FRs) during the compounding process is the most efﬁcient method that can be used to modify the ﬂame retar- dant properties of WPCs [5–10]. Ammonium polyphosphate (APP) is one of the conventional, highly effective and widely used environment-friendly ﬂame retardants used for the amelioration of the ﬂame retardant properties of WPCs [11–13]. In order to improve the ﬂame retardant efﬁciency of APP on WPCs, other ﬂame retardants such as expandable graphite [14], SiO 2 or CaCO 3 [15] were combined with APP to obtain effective ﬁre retardancy for WPCs. Besides APP, several kinds of inorganic additives including aluminum hydroxide [16] and magnesium hydroxide [17] were reported as ﬂame retardants for WPCs. Furthermore, some organic ﬂame retardants were also developed to improve the ﬂame retardancy of WPCs through increasing the char yield [18,19]. However, to achieve a satisfactory ﬂame retardant level, high loading of either inorganic or organic ﬂame retardants mentioned above is usually required. Poor compatibility be- tween these ﬂame retardants and polymer matrix resulted in * Corresponding author. E-mail address: deyi.wang@imdea.org (D.-Y. Wang). Contents lists available at ScienceDirect Fire Safety Journal journal homepage: www.elsevier.com/locate/ﬁresaf https://doi.org/10.1016/j.ﬁresaf.2017.11.001 Received 25 January 2017; Received in revised form 1 October 2017; Accepted 4 November 2017 Available online xxxx 0379-7112/© 2017 Elsevier Ltd. All rights reserved. Fire Safety Journal xxx (2017) 1–7 Please cite this article in press as: E.N. Kalali, et al., Flame-retardant wood polymer composites (WPCs) as potential ﬁre safe bio-based materials for building products: Preparation, ﬂammability and mechanical properties, Fire Safety Journal (2017), https://doi.org/10.1016/j.ﬁresaf.2017.11.001