Property modelling Predictive modeling of creep in polymer/layered silicate nanocomposites Ali Shokuhfar a , Abolfazl Zare-Shahabadi b, * , Ali-Asghar Atai c , Salman Ebrahimi-Nejad a , Mahdie Termeh a a Advanced Materials and Nanotechnology Research Lab, Department of Mechanical Engineering, K.N. Toosi University of Technology,19991-43344 Tehran, Iran b Department of Mechanical Engineering, Yazd Branch, Islamic Azad University, Yazd, Iran c Department of Mechanical Engineering, University of Tehran, Tehran, Iran article info Article history: Received 13 November 2011 Accepted 23 December 2011 Keywords: Polymer/clay nanocomposites Predictive modeling Creep resistance Processing method abstract A predictive creep model is developed which uses the properties of matrix and rein- forcement to predict the creep of polymer/layered silicate nanocomposites. Up to this point, primarily empirical creep models such as Findley and Burgers models have been used for creep of polymer/clay nanocomposites. The proposed creep model is based on the elastic-viscoelastic correspondence principle and a stiffness model of these nano- composites. Also, the added stiffness of polymeric matrix due to the constraining effect of layered silicates on polymer chains in the nanocomposite is considered by a parameter termed constraint factor. The results of the proposed model show good agreement with experimental creep data for different clay contents, stresses and temperatures. Comparing the model predictions with experimental data, a logical relationship between the method of processing and the constraint factor is discovered which shows that in-situ polymeri- zation can be more efficient for improving creep resistance of polymer/layered silicate nanocomposites relative to melt processing. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Polymer/clay nanocomposites have attracted consider- able attention from many researchers over the last few years because of the potentially higher properties that these nanocomposites can exhibit compared to conven- tional composites. Layered silicates or clay minerals are composed of very thin (w1 nm) platelets that have large surface areas and high aspect ratios. In addition, these platelets have very high stiffness (w178 GPa) compared to that of polymers (w3 GPa) [1]. Because of such stiffness and aspect ratios, these materials can be very efficient rein- forcements, and in the last few years numerous studies have shown that minimal amounts of layered silicates can lead to significant enhancement of many mechanical and physical properties, including stiffness [2], strength [3], creep [4], flammability [5], permeability and gas barrier properties [6,7], and thermal stability [8,9]. Because of these attractive properties, polymer/clay nanocomposites are being used for a wide variety of applications, such as in transportation, construction, electronics and consumer products [10], and different types of polymeric materials including addition polymers [11–13], condensation poly- mers [14–16], biodegradable polymers [17,18] and asphalt binders [19,20] have been used as the matrix in these nanocomposites. The structures available for polymer/clay composites and nanocomposites can be divided into four categories: (a) conventional composite structures in which the silicate platelets are agglomerated (Fig. 1a), (b) intercalated nanocomposite structures, where some matrix molecules are inserted between individual silicate layers, but the layers remain parallel (Fig. 1b), (c) partially intercalated and exfoliated nanocomposites in which exfoliated layers and intercalated stacks are randomly distributed in the * Corresponding author. Tel.: þ98 913 250 6474; fax: þ98 351 821 0670. E-mail addresses: zareshahabadi@dena.kntu.ac.ir, zare.shahabadi@ gmail.com (A. Zare-Shahabadi). Contents lists available at SciVerse ScienceDirect Polymer Testing journal homepage: www.elsevier.com/locate/polytest 0142-9418/$ – see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2011.12.013 Polymer Testing 31 (2012) 345–354