Materials Science and Engineering A 475 (2008) 365–367 Short communication On the strain rate sensitivity of HDPE/CaCO 3 nanocomposites S.M. Zebarjad a,b,∗ , S.A. Sajjadi a a Department of Materials Science and Engineering, Engineering Faculty, Ferdowsi University, Azadi Square, P.O. Box 91775-1111, Mashhad, Iran b Nano Research Center, Ferdowsi University of Mashhad, Iran Received 14 January 2007; received in revised form 7 April 2007; accepted 3 May 2007 Abstract In the current study the role of both nano-sized calcium carbonate and strain rate on the tensile properties of HDPE was studied. For this purpose standard tensile samples of HDPE and HDPE/10 vol.% CaCO 3 were performed using extrusion and injection molding methods. Tensile test was done at different strain rates. The results of tests showed that addition of 10 vol.% of nano-sized calcium carbonate made an increase in both yield stress and Young’s modulus of HDPE unlike its elongation. Also it was concluded that strain-rate sensitivity of HDPE decreased as nano-sized calcium carbonate was added to it. The data obtained from the tests indicated that the variation of Young’s modulus of HDPE nanocomposite could be obtained from the following equation, i.e. E/E 1 = [1.0 + 5ϕ 2 + 15.5ϕ 2 2 ]. © 2007 Elsevier B.V. All rights reserved. Keywords: HDPE; CaCO 3 ; Nanocomposite; Strain rate 1. Introduction Polymer nanocomposites are a new class of particle-filled polymer composites in which at least one dimension of the dispersed particles is in the nanometer range. Among polymer matrix nanocomposites high density polyethylene is much under attention because of its moderate cost and high strength/weight ratio. Regarding its vast applications of HDPE and its nanocom- posites there are many investigations concentrated on HDPE nanocomposites. According to the literature survey the previous studies can be divided into some viewpoints [1–11]. The most important researches concentrated on the role of nano-sized cal- cium carbonate on the mechanical properties of HDPE [1–4]. For example Lazzeri et al. [1] showed that addition of coated nano-sized calcium carbonate could compensate the decrease of the tensile properties compared to the uncoated precipitate cal- cium carbonate. The results of their study show that addition of fatty acids such as stearic acid (SA) or other fatty acid can be a good way to make an uniform dispersion with suitable adhesion [1]. Also according to the report by Sahebian et al. [2] addition of nano-sized calcium carbonate to HDPE causes drastically effect ∗ Corresponding author at: Department of Materials Science and Engineering, Engineering Faculty, Ferdowsi University, Azadi Square, P.O. Box 91775-1111, Mashhad, Iran. E-mail addresses: Zebarjad@ferdowsi.um.ac.ir, Zebarjad@um.ac.ir (S.M. Zebarjad). on stress whitening zone appeared in front of pre-crack during plane-strain fracture toughness test [2]. Another approach focused on the role of filler size on rhe- ological properties of HDPE/CaCO 3 composites [1,5–8]. The results of this approach showed that calcium carbonate has a big significant effect on rheological behaviour of HDPE. Also it is observed that decreasing particle size can play as a barrier during processing of polymer [9–11]. Another viewpoint paid attention on thermal behaviour of HDPE/CaCO 3 nanocomposites [12,13]. Zebarjad et al. [12] reported that nano-sized calcium carbonate has a significant effect on crystallinity, melting point and heat of melting of HDPE [12]. Furthermore the same authors show that dimensional sta- bility of HDPE can be affected by addition of nano-sized calcium carbonate [13]. The details of their study illustrated that thermal expansion coefficient of HDPE would be decreased as nano- sized calcium carbonate was added to it. From the literature review performed by the present author, it was found that some researchers [14–17] have studied the relation between tensile properties of HDPE and strain rate. For example Viana [14] studied the dependency of strain rate, tem- perature and morphology on the yield stress of injection molded semicrystalline polymers. The results showed that the depen- dence of yield stress upon the morphology is significant for higher strain rates and lower test temperatures. As the strain rate increases, the contribution of the morphological parameters of the skin layer saturates and the effect of the core layer becomes 0921-5093/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2007.05.008