INVESTIGATION OF NANODISPERSION IN POLYSTYRENE -MONTMORILLONITE NANOCOMPOSITES BY SOLID STATE NMR
S Bourbigot, Jeffrey W. Gilman, David L. VanderHart, W H. Awad, Rick D. Davis, A B. Morgan, C A. Wilkie
Nanocomposites result from combinations of materials with vastly different properties at the nanometer scale. These materials exhibit many unique properties, such as improved thermal stability, reduced flammability, and improved mechanical properties. Many of the properties associated with polymer clay nanocomposites are a function of the extent of exfoliation of the individual clay sheets. They have been shown to be directly proportional to the degree of exfoliation, or the quality of the nano-dispersion. This work demonstrates that solid state NMR can be used to characterize quantitatively the degree of nanodispersion of montmorillonite (MMT) clay in polystyrene matrices. The direct influence of the paramagnetic Fe3+, embedded in the aluminosilicate layers of the MMT, on protons within 0.4 nm of clay surfaces creates relaxation sinks which, via spin diffusion, significantly shorten the overall proton longitudinal relaxation time (T1H). We therefore used T1H as a probe to estimate the nanodispersion of the clay in PS. This approach correlates well with XRD and TEM data. A model is proposed which allows calculation of the distance between MMT platelets and the percentage of exfoliation. Finally, this approach is applied to the characterization of 27 PS/MMT nanocomposites prepared by extrusion. As a part of the development of high throughput methods, we show that the combination of extrusion with these NMR techniques gives a factor of 5 to 10 improvement in analysis efficiency, compared to conventional methods (e.g., TEM). These methods were used for evaluating two parameters (screw speed, MMT loading) associated with processing of PS/MMT nanocomposites.
high throughput, montmorillonite, nanocomposites, paramagnetic Fe3+, relaxation time, solid state NMR
, Gilman, J.
, VanderHart, D.
, Awad, W.
, Davis, R.
, Morgan, A.
and Wilkie, C.
INVESTIGATION OF NANODISPERSION IN POLYSTYRENE -MONTMORILLONITE NANOCOMPOSITES BY SOLID STATE NMR, Journal of Polymer Science Part B-Polymer Physics, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=861256
(Accessed July 31, 2021)