CHARACTERIZATION OF HIGH DENSITY POLYETHYLENE/ORGANOCLAY NANOCOMPOSITE BY X-RAY DIFFRACTION AND LOW FIELD NMR Tathiane C. Rodrigues 1 *, Maria I. B. Tavares 1 , Victor J. R. R. Pita 1 , Igor L. Soares 1 and Ana Moreira 2 1 Instituto de Macromoléculas Professora Eloisa Mano – Universidade Federal do Rio de Janeiro (IMA/UFRJ). Centro de Tecnologia, Bloco J, Ilha do Fundão. PO Box: 68525, 21945-970, Rio de Janeiro, RJ, Brazil 2 Rio Polímeros S/A Rua Marumbi 1001 Duque de Caxias, RJ, Brazil tathiquimcr@uol.com.br The purpose of this study was preparing polymer/organoclay nanocomposite based on high-density polyethylene and organically modified montmorillonite by melt processing using twin-screw extruder at different processing parameters (60 and 90 rpm). The x-ray diffraction (XRD) was employed to characterize the formation of the nanocomposite and organoclay dispersions. A new technique was applied by low-field nuclear relaxation study using the proton spin-lattice relaxation time (T 1 H) to understand changes in the molecular mobility after processing, when organoclay was incorporated on polymer matrix. From the T 1 H results, it was observed that samples presented different molecular domains after processing and after clay dispersion on polymer matrix. The XRD characterization of organoclay dispersion on polyethylene matrix indicated that an effective surface layer and delamination at nanoscale level could be obtained from different processing parameters applied. Introduction The technology of polymer nanocomposites is described as one of the most important frontier of materials science since sensible improvements in mechanical, thermal, dimensional, and barrier properties can be obtained with minimum amounts of filler [1-3]. The properties of a nanocomposite are strongly dependent on the final morphology of the material, which depends on the dispersion of the nano particles in the polymer matrix. Polymer/organoclay composites can be intercalated, but the best nanocomposite properties only would be obtained from completely exfoliated systems [4-6], because the increase in the interfacial contact results in a large improvement of the properties. Melt processing is the most appropriate technique for the industrial preparation of polymer-layered silicate nanocomposites of thermoplastic polymers [7]. The success of this way is related with the identification of optimal melt processing conditions; which should be able to promote the intercalation and/or exfoliation of organic layered silicate. In this case, the final level of filler dispersion could characterize the effect of processing condition on the material produced. Interest in polyolefin nanocomposites has emerged due to their promise of improved performance in packaging and engineering applications [8]. Consequently, polyethylene (PE) is one