Mechanical Properties of Thermoplastic Polyolefin (TPO) /Clay Nanocomposites
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Mechanical Properties of Thermoplastic Polyolefin (TPO) /Clay Nanocomposites Yong-Hong Ruan, and Sie-Chin Tjong Dept. of Physics and Materials Science, City University of Hong Kong, Hong Kong, China, People's Republic of ABSTRACT: Thermoplastic polyolefin (TPO) contained 30 wt.% PP and 70 wt.% SEBS-g-MA, and its nanocomposites were reinforced with 0.3 -1.5 wt.% organoclay (OMMT; Cloisite 30B) by a two-step melt mixing followed by injection molding. The microstructure and mechanical behavior of the TPO/OMMT nanocomposites were investigated. X-ray diffraction measurements revealed the absence of basal diffracting peak of OMMT in TPO/OMMT, suggesting formation of intercalated/exfoliated nanocomposites. Tensile tests showed that the stiffness, yield strength and tensile strength of TPO can be enhanced by adding low loading levels of OMMT. Thus, OMMT can reinforce TPO due to their large aspect ratios. Moreover, there was no reduction in the impact strength of the TPO/OMMT nanocomposites associated with the clay additions. INTRODUCTION Thermoplastic olefin (TPO) refers to elastomeric alloy consisting of elastomers and thermoplastics. TPO blends undergo plastic deformation like thermoplastics but also exhibit resilience and elasticity like elastomers. Their excellent weather resistance, low density, and relatively low cost make them attractive materials for the automotive, electrical and footwear industries Their main shortcomings are poor mechanical properties especially at low temperatures and low chemical resistance. In this regard, inorganic fillers are commonly added to TPO blends to achieve desired mechanical stiffness and strength. Recently, layered silicate clays such as montmorillonite (MMT) and vermiculite have gained considerable attention due to their ability to reinforce polymers at very low loading levels [1-7]. The resulting polymer nanocomposites generally exhibit enhanced tensile modulus and strength but poor tensile ductility and impact toughness. The reinforcing effect arises from homogeneous dispersion of exfoliated clay platelets with large aspect ratios within polymeric matrix. To achieve an optimum balance of stiffness and toughness in the polymer nanocomposites, elastomers, e.g. EPDM and SEBS, have been incorporated into polypropylene [8-12]. However, these studies are mainly focused on the structure and mechanical property of TPO/clay nanocomposites having PP-rich matrix. In contrast, less information is available on the mechanical behavior of the elastomer-rich TPO/clay nanocomposites [11-13]. This work aims to study the structure and mechanical behavior of TPO/organoclay nanocomposites.
EXPERIMENTAL Materials The organically modified montmorillonite (OMMT) used was Cloisite 30B [(bis(2-hydroxyethyl) methyl tallow ammonium montmorillonite)] supplied from Southern Clay Products (USA). Polypropylene (Profax 6331) with a melt flow index of 12g/10min and poly(styrene-ethylene-butylene-styrene) grafted with 1.84 wt% of maleic anhydride (SEBS-g-MA; Kraton FG 1901X) were purchased from Hi
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