A hierarchical structure and properties of intercalated polypropylene/clay nanocomposites Pham Hoai Nam a , Pralay Maiti a , Masami Okamoto a, * , Tadao Kotaka a , Naoki Hasegawa b , Arimitsu Usuki b a Advanced Polymeric Materials Engineering, Graduate School of Engineering, Toyota Technological Institute, Hisakata 2-12-1, Tempaku, Nagoya 468-8511, Japan b Toyota Central R & D Laboratories, Inc., Nagakute, Aichi 480-1192, Japan Received 9 April 2001; accepted 10 May 2001 Abstract We have prepared the intercalated nanocomposites of polypropylene PP)/clay PPCNs) successfully using maleic anhydride modi®ed PP PP-MA) and organophilic clay via melt extrusion process. The hierarchical structure of the PPCNs from the structure of con®ned PP-MA chains, in the space a few nanometer width between silicate galleries to crystalline lamellae of 7±15 nm thickness and spherulitic texture of 10 mm diameter, were probed using a wide-angle X-ray diffraction, small-angle X-ray scattering, transmission electron microscope, polar- izing optical microscopy and light scattering. After crystallization had taken place at 808C, the PPCNs formed rod-like crystalline texture in the 10 mm length scale which consisted of the inter-®brillar structure including g-phase crystallite caused by the reduction of the PP-MA chains mobility due to the intercalation of the PP chains in the space between silicate galleries and the narrow space surrounded by the dispersed clay particles. The intercalated PPCNs showed an enhancement of moduli compared with PP matrix without clay. The necessity of the intercalating degree of PP-MA chains on the enhancement of the mechanical properties are discussed. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: Polypropylene; Nanocomposite; Intercalation 1. Introduction Development of the polymer/clay nanocomposites is one of the latest evolutionary steps of the polymer technology. The nanocomposites offer attractive potential for diversi®- cation and application of conventional polymeric materials [1±5]. Since the possibility of direct melt intercalation was ®rst demonstrated by Giannelis et al. [6], the melt intercala- tion method has become a main stream for the preparation of the intercalated polymer nanocomposites without in situ intercalative polymerization. It is a quite effective technol- ogy for the case of polyole®n-based nanocomposites [7,8]. In recent years, intensive studies have been devoted to the complete exfoliation of the stacked silicate layers in the polymer matrix under the advanced preparation method [9,10]. We have successfully prepared well-ordered inter- calated polypropylene PP)/clay nanocomposites PPCN)s [7] via direct melt intercalation in an extrusion process, where the layered clay particles were dispersed homoge- neously in the PP matrix and intercalated by extended PP chains. The PP-based intercalated nanocomposites have attractive potentials for continuous expansion of application versatility [11]. Although the dispersed morphology of the clay particles, the excellent mechanical properties [7,8] and the rheological behavior [12,13] of the intercalated PPCNs were investigated, the hierarchical structure for PPCNs viewed on scale from nm to mm length, i.e. from the struc- ture of con®ned PP chains in the space of the silicate galleries of a few nm width to crystalline lamellae of about 10 nm thickness and spherulitic texture of several mm diameter, has not been identi®ed in detail. For innova- tion of PPCNs, we have to understand the structural details and create a technology of controlling the hierarchical struc- ture of the PPCNs. In this study, we prepared the intercalated PPCNs using maleic anhydride modi®ed PP and organophilic clay via melt extrusion processing and conducted identi®cation of the hierarchical structure in detail. We also discuss here the structure±property relationships of the intercalated PPCNs having different clay content. Polymer 42 2001) 9633±9640 0032-3861/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S0032-386101)00512-2 www.elsevier.com/locate/polymer * Corresponding author. Tel.: 181-52-809-1861; fax: 181-52-809-1864. E-mail address: okamoto@toyota-ti.ac.jp M. Okamoto).