Properties of halloysite nanotubes-filled natural rubber prepared using different mixing methods H. Ismail ⇑ , S.Z. Salleh, Z. Ahmad School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, Nibong Tebal, Penang, Malaysia article info Article history: Received 5 November 2012 Accepted 7 March 2013 Available online 29 March 2013 Keywords: Halloysite nanotubes Natural rubber Mechanical mixing Solution mixing Mechanical properties Morphological properties abstract Two different mixing methods, i.e., mechanical and solution mixing were used in preparation of halloy- site nanotubes/natural rubber (HNTs/NR) nanocomposites with various loading of HNTs. The result showed that the addition of HNTs caused increment in scorch time, cure time and maximum torque for both mixing methods. However, longer scorch and cure time of nanocomposites prepared via solution mixing method than nanocomposites prepared via mechanical mixing method was observed. Nanocom- posites prepared by solution mixing method showed higher tensile strength, tensile modulus, fatigue life and decomposition temperature at lower percentage of weight loss than mechanical mixing method. Scanning electron microscope (SEM) images showed better dispersion of HNTs in nanocomposites pre- pared via solution mixing method than mechanical mixing method. Ó 2013 Published by Elsevier Ltd. 1. Introduction Polymer materials have been filled with several inorganic syn- thetic or/and natural compounds in order to increase several prop- erties like heat resistance, mechanical strength and impact resistance or to decrease other properties like electrical conductiv- ity or permeability for gases like oxygen or water vapor [1]. Cur- rently, nanoclay loaded rubber nanocomposite is one of the fastest developing nanocomposites that has been studied in various fields of study for examples for mechanical, thermal or electrical purposes. Clay minerals are potential nanoscale additives because of their layers consisting of 1 nm thick planar structures [2]. In this study, halloysite nanotubes (HNTs) were chosen as filler. Halloysite is defined as two layered aluminosilicates, chemically similar to kaolin, but it has predominantly hollow tubular struc- ture in the submicron range. Interlayer water in HNTs is one of the most important features distinguish HNTs from kaolinite [3]. The physical appearance of HNTs is very similar to carbon nano- tubes (CNTs), but the cost of HNTs is much lower [4]. This physical characteristic of HNTs has been investigated by TEM images as shown in our previous works [5–7]. HNTs may exist in two forms. Firstly, may exist as hydrated halloysite with basal spacing (d 001 ) of 108 Å. However, due to interlayer water weakly held, halloysite (10 Å) can readily transform to halloysite (7 Å) which also known as methahalloysite [8]. The key factors for the improvement performance of polymer nanocomposites are homogeneous distribution of nanoparticles within the polymer matrix [9], and a strong interfacial adhesion between matrix and nanoparticles. Uniform dispersion of the nanometer particles offers a major specific surface area enhance- ment, compared to the conventional reinforcements of micrometer size [10]. Generally, there are several methods of mixing that are com- monly used in rubber nanocomposites such as melt mixing [11], solution mixing [12,13], and in situ mixing [14] methods. Among them, the melt mixing is the most widely used method [15]. Besides melt mixing, solution mixing is the easiest and frequent mixing method used to obtain better dispersion of filler in rubber matrix. In this study, mechanical and solution mixing methods were used. The properties HNTs/NR nanocomposites prepared via both mixing methods were discussed and compared. Besides, the effects of various HNTs loading on properties of nanocomposites were also discussed. 2. Experimental details 2.1. Materials and chemicals Natural rubber namely SMR L was supplied by Rubber Research of Institute Malaysia (RRIM). Halloysite nanotubes (HNTs) were purchased from Imerys Tableware Asia Limited, New Zealand. The other ingredients such as zinc oxide, stearic acid, sulfur, N-cyclohexyl-2-benzothiazole sulfenamide (CBS) and 2,2- methy- 0261-3069/$ - see front matter Ó 2013 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.matdes.2013.03.038 ⇑ Corresponding author. Tel.: +60 4 599 6113; fax: +60 4 594 1011. E-mail address: hanafi@eng.usm.my (H. Ismail). Materials and Design 50 (2013) 790–797 Contents lists available at SciVerse ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes