Research Article Thermal Expansion Behavior of Nonoriented Polypropylene/Clay Composites Fares D. Alsewailem 1 and Metin Tanoglu 2 1 Petrochemicals Research Institute, King Abdulaziz City for Science and Technology (KACST), P.O. Box 6086, Riyadh 11442, Saudi Arabia 2 Mechanical Engineering Department, Izmir Institute of Technology, Gulbahce Koyu, 35430 Urla, Turkey Correspondence should be addressed to Fares D. Alsewailem; fsewailm@kacst.edu.sa Received 11 November 2013; Accepted 24 December 2013; Published 3 February 2014 Academic Editors: A. V. Popov and A. Voronov Copyright © 2014 F. D. Alsewailem and M. Tanoglu. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Linear thermal expansion coefcient (LTEC) was measured for compression molding samples of polypropylene (PP)/clay composites with clay loading of 0 to 7 wt%. Composites were prepared by internal batch mixer and specimens were prepared by compression molding. Tese processing methods are not anticipated to have a preference for orientation; therefore efect of anisotropy was minimal. Te L TEC was measured along three diferent faces of the compression molding sheets, parallel to compression direction S1 and perpendicular to compression directions S2 and S3. Te L TEC for neat PP measured by current research, 1 × 10 −4 mm/mm/ ∘ C, was not found to be altered by direction of the measurements. Similar behavior was observed with composites having very moderate clay content, that is, 5wt%. An interesting fnding by current study was that incorporating clay particles into the PP matrix led to better shrinkage or contraction behavior of the samples prepared by compression molding. 1. Introduction Polypropylene (PP) is a versatile polyolefn that fnds a strong demand in some of the advanced applications such as automotive industry. What makes PP a good candidate for such advanced applications is the excellent chemical and mechanical properties due to its superior crystallinity nature. PP is a highly crystalline polyolefn with relatively higher melting and sofening temperature compared to other commodity vinyl polymers such as polyethylene (PE) and polystyrene (PS). Some of the interior parts of an automotive may be made of PP. Recently, glass fber reinforced PP was introduced to be used in the under-the-hood parts in automotive. Despite this versatility in applications for the PP, this polymer sufers from dimensional instability due to high linear thermal expansion coefcient (LTEC). Neat PP has diferent values of LTEC depending on the orientation of crystalline chain domain [1]. Draw ratio and temperature are the main factors that may afect the LTEC of oriented PP. In general, LTEC is higher for the segment that is perpendicular to the draw direction, while for the segment that is parallel to the draw direction, less values of LTEC may be observed [1]. Jawad et al. [2] have postulated that internal shrinkage stresses may play a major role on the magnitude of LTEC for the oriented PP that was subject to annealing processing. Nonannealed PP samples may exhibit a negative value of LTEC in the axial direction (i.e., parallel to draw direction) as a response to the positive LTEC in the transverse direction (i.e., perpendicular to the draw direction) [3]. Anisotropy in LTEC was also observed in PP blends with elastomeric materials [4]. LTEC for injection molded samples containing 30 vol% of polyethylene-co-octene blended with isotactic PP had higher values of LTEC in the direction normal to fow, and it decreased in the fow direction; however at higher viscosity ratios of PECO to PP the anisotropy became minimum [4]. Low thermal expansion coefcient materials such as inorganic fllers and fbers may be utilized to produce thermally dimensional stable composite systems based on PP matrix [5–7]. Incorporation of glass fbers into PP matrix was seen to reduce LTEC of the resulted composite; however no Hindawi Publishing Corporation ISRN Polymer Science Volume 2014, Article ID 571641, 7 pages http://dx.doi.org/10.1155/2014/571641