The Evaluation of Polyethylene/Clay Composite from Solid State NMR

Abstract

Polymeric nanocomposites based on polyethylene (PE) and Brazilian natural montmorillonite clay (MN) were obtained by melt processing, using a twin-screw extruder. The main objective of this work is focusing on the characterization of composites materials by solid-state nuclear magnetic resonance (NMR). The solid-state NMR measurements were used to observe both polymer matrix (through carbon-13 and hydrogen nuclei) and the clay (silicon-29 and aluminum-27). The polymer matrix analyses were carried out applying solid state techniques, such as: cross-polarization magic angle spinning (CPMAS), variable contact time (VCT) and by the proton spin-lattice relaxation time in the rotating frame parameter (T_1ρH), detected from the resolved carbon-13 decay of the VCT experiment and through the determination of spin-lattice relaxation time, T₁H (using low field NMR). The clay was analyzed by ²⁹Si and ²⁷Al, employing MAS NMR technique. From those techniques we can have principally response on clay dispersion in the polyethylene matrix, as well as the interactions between both components in the nanostructured material. The T₁H response was an important result which showed, that the materials formed, presented different molecular domains (according to the domain size that varied from 25 to 50 nm, measured by relaxation), considering the clay dispersion mode in terms of intercalation and/or exfoliation in the polymer matrix.