Dynamic behavior and flame retardancy of HDPE/hemp short fiber composites: Effect of coupling agent and fiber loading K. Wang a , F. Addiego a,⇑ , A. Laachachi a , B. Kaouache a , N. Bahlouli b , V. Toniazzo a , D. Ruch a a Department of Advanced Materials and Structures, Public Research Centre Henri Tudor, ZAE Robert Steichen, 5 Rue Bommel, L-4940 Hautcharage, Luxembourg b ICube Laboratory, University of Strasbourg/CNRS, 2 Rue Boussingault, 67000 Strasbourg, France article info Article history: Available online 12 March 2014 Keywords: Polyethylene Hemp Dynamic behavior Flammability Micromechanics Modeling abstract This work aimed at investigating the effect of maleic anhydride-grafted polyethylene (MAPE) as coupling agent and of hemp fiber loading on the compressive dynamic behavior and flammability of high-density polyethylene (HDPE)/hemp short fiber composites. The compressive modulus, the yield stress increased with the presence of MAPE and with the loading of hemp fiber. However, the absorbed energy increased with the presence of MAPE and with the loading of hemp fiber up to 15 wt.%. Halpin–Tsai and Pukánszky models were successfully used to predict the compressive modulus and the yield stress of the composites, respectively. Cone calorimeter measurements showed that the peak of heat release rate (pHRR) was low- ered in the presence of MAPE and hemp fiber in comparison to neat HDPE and that this decrease was higher when the fiber content increased. The compatibilization between hemp fiber and HDPE via MAPE was suitable to improve the dynamic behavior and flame retardancy of the composite. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The increasing use of polymeric materials presents a threat to our environment by bringing huge post-used plastic wastes. There- fore, it is of high importance to integrate the environmental con- cerns in the formulation of new plastics and in particular for polymer-based composites. For example, the use of vegetal fiber to reinforce thermoplastics could reduce the carbon dioxide foot- print of the resulting composites compared to conventional ther- moplastics composite filled with glass fiber due to their low density, biodegradability, and renewability [1–5]. Concerning the mechanical performance of these fibers, they exhibit an elastic modulus of the order of that of glass fiber [6], but a higher ratio be- tween elastic modulus and density. Most of the works dedicated to polymer/natural fiber composites are generally focused on the investigation of the compatibility between the fibers and the poly- mer matrix [7–9], their processing [10,11], their water absorption [12,13], their physical and thermal properties [14,15], and their recycling [16,17]. In this context, maleic anhydride-grafted poly- ethylene (MAPE) was considered as an effective coupling agent for polyethylene/natural fiber composites [8,18]. Zabihzadeh et al. [19] reported that the addition of 2 wt.% of MAPE to HDPE/ wheat straw composites was enough to improve the adhesion between the fiber and the polymer matrix. Lei et al. [8] found that the storage modulus of recycled HDPE/pine (30/70 wt.%) compos- ites increased with increasing MAPE content until 1.8 wt.%. Above 1.8 wt.% of MAPE, the storage modulus of the composite decreased. However, the use of MAPE did not prevent the deformation-in- duced fiber/matrix debonding mechanisms occurring at a tensile strain of 10%, as shown in our previous paper [20]. The use of these vegetal-fibers reinforced composites is hence not suitable for applications requiring extremely high mechanical performance and durability. Nevertheless, it is of fundamental interest to iden- tify the underlying mechanisms to continuously improve the mate- rial formulation. For example, the high strain rate compressive responses of polymer/natural fiber thermoplastics is far from being known, although some polymer/natural fiber systems have been proposed to be used in application subjected to impact loading [21]. The knowledge of compressive dynamic behavior of compos- ite material is of high interest for the automotive industry, as for example for bumper. For this application, if an accident occurs, composite material could be also subjected to fire. Analyzing and reducing the flammability of these new materials is of high scien- tific and technological interest. The aim of this work was to study the effect of the hemp loading and coupling agent on the dynamic compressive behavior and flammability of HDPE/hemp short fiber composites. The dynamic compression behavior was investigated by using Split Hopkinson Pressure Bar (SHPB) technique. Two micromechanical models http://dx.doi.org/10.1016/j.compstruct.2014.03.009 0263-8223/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +352 4259914639. E-mail address: frederic.addiego@tudor.lu (F. Addiego). Composite Structures 113 (2014) 74–82 Contents lists available at ScienceDirect Composite Structures journal homepage: www.elsevier.com/locate/compstruct