Characterization of talc/calcium carbonate ﬁlled polypropylene hybrid composites weathered in a natural environment Y.W. Leong, M.B. Abu Bakar, Z.A. Mohd Ishak*, A. Ariﬃn School of Materials & Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Seberang Perai Selatan, Penang, Malaysia Received 13 May 2003; received in revised form 7 July 2003; accepted 10 August 2003 Abstract Two kinds of composites, namely single-ﬁller polypropylene (PP) composites (containing either talc or calcium carbonate) and hybrid-ﬁller PP composites (consist of a mixture of talc and calcium carbonate) were injection moulded into dumbbells. These specimens were subjected to natural weathering i.e. tropical climate in Penang, Malaysia for 6 months. After 6 months of exposure, the mechanical properties of single-ﬁller PP composites deteriorated due to severe physical and chemical degradation. However, the hybrid-ﬁller PP composites were found to show better retention in mechanical properties albeit having undergone some degree of surface-degradation as well. It is believed that the ‘hybridization’ eﬀect has successfully increased the resistance of the hybrid composite to severe environmental degradation to the extent that it protects the internal structure of the composite from environ- mental damage, even though the surface of the composite gets severely degraded. Surface treatment of ﬁllers was also found to be able to aid in the retention of the composites’ mechanical properties. # 2003 Elsevier Ltd. All rights reserved. Keywords: Polypropylene; Hybrid composite; Photooxidation; Chain scission; Thermal degradation; Natural weathering 1. Introduction Polypropylene (PP) composite is one of the most extensively produced polymers, especially widely used as automotive parts [1] due to its good impact resistance as well as processability. Most automotive parts would either be exposed to the natural environment (e.g. sun- shine, rain, snow and pollutants), or to more extreme environments (e.g. engine heat). In outdoor applications all polymers degrade no matter how strong or tough the materials may be. Many of those parts, having been exposed to sunshine for long periods of time, are heavily photo-oxidized due to the relative high photosensitivity, especially if they were made of PP; hence changes are expected in the thermal behavior, mechanical properties and surface morphology of the products [2]. Although studies on the eﬀect of natural weathering, thermal oxidation and degradation on isotactic and vir- gin PP were extensively covered in various literatures [2–7], similar publications that involve composites, especially hybrid composites that combine two or more diﬀerent types of ﬁllers, are extremely limited. Earlier investigations have been done to determine the mechanical and thermal properties of single-ﬁller and hybrid-ﬁller PP composites [8,9], which have generated very interesting results that demonstrate the eﬀective- ness of hybrid ﬁllers in enhancing the properties of PP. Further exploration on the eﬃcacy of hybrid ﬁllers was done with the treatment of ﬁllers with surfactants [10], which again yielded more promising results to magnify the advantages of using hybrid ﬁllers. In this work, the inﬂuence of natural weathering on the mechanical and morphological properties as well as melting and crys- tallization behaviour of talc and calcium carbonate (CaCO 3 ) ﬁlled PP hybrid composites will be reported. The eﬀects of ﬁller treatments (i.e. with stearic acid and titanate coupling agent Lica-12) on the weatherability of the composites would also be discussed. All composites studied are based on 30 wt.% ﬁller loading. Injection- moulded dumbbells of these composites with varying compositions of talc and CaCO 3 were weathered out- doors in Penang, Malaysia with exposure times varying 0141-3910/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2003.08.004 Polymer Degradation and Stability 83 (2004) 411–422 www.elsevier.com/locate/polydegstab * Corresponding author. Tel.: +60-4-593-7788; fax: +60-4-594- 1011. E-mail address: zariﬁn@eng.usm.my (Z.A. Mohd Ishak).