A simple approach for producing high aspect ratio fluorohectorite nanoplatelets utilizing a stirred media mill (ball mill)

Abstract The potential of platy nanofillers like clays in polymer nanocomposites is mostly determined by their aspect ratio. The degree of improvement that may be achieved in respect to reinforcement, gas-barrier properties and flame retardancy critically depends on the aspect ratio. Thus, increasing the aspect ratio is highly desirable in order to explore the full potential of the clay filler. Mechanical shear stress as generated in the grinding chamber of a stirred media mill (ball mill) induced an efficient exfoliation of highly hydrated and therefore ‘shear-labile’ synthetic Mg-fluorohectorite in aqueous dispersion. The attainable degree of exfoliation can be tuned and controlled through the shear forces applied by changing process parameters such as solid content and grinding media diameter. Characterization and evaluation of the exfoliation efficiency during milling was achieved by combining and cross-validating data obtained by powder X-ray diffraction (XRD), static light scattering (SLS), specific surface area measurements applying the Brunauer-Emmett-Teller (BET) equation, and scanning electron microscopy (SEM). This led to the identification of optimal processing parameters, allowing for control of the degree of exfoliation and, consequently, the aspect ratio of the nanoplatelets. Not surprisingly, besides exfoliation, increasing the magnitude of the shear stress also resulted in some reduction in platelet size. The clay platelets obtained showed a high average aspect ratio (>600), several times greater than that of original synthetic fluorohectorite. The increase of aspect ratio was reflected in a significant enhancement of both specific surface area and cation exchange capacity (CEC) of the external basal surfaces. This method has substantial advantages compared to microfluidizer processing with respect to feasibility, batch size and particle diameter size preservation. The exfoliated nanoplatelets obtained by milling have great potential to improve mechanical properties of polymer layered silicate nanocomposites (PLSN).

[1]  C. A. Wilkie,et al.  Shear stiff, surface modified, mica-like nanoplatelets: a novel filler for polymer nanocomposites , 2011 .

[2]  J. Jestin,et al.  Tuning the mechanical properties in model nanocomposites: Influence of the polymer‐filler interfacial interactions , 2011, 1107.1882.

[3]  C. Frances,et al.  Effects of concentration of dispersions on particle sizing during production of fine particles in wet grinding process , 2011 .

[4]  T. Lunkenbein,et al.  Barrier Properties of Synthetic Clay with a Kilo‐Aspect Ratio , 2010, Advanced materials.

[5]  S. Škapin,et al.  The surface properties of clay minerals modified by intensive dry milling — revisited , 2010 .

[6]  M. Möller,et al.  Large scale melt synthesis in an open crucible of Na-fluorohectorite with superb charge homogeneity and particle size , 2010 .

[7]  U. A. Handge,et al.  Tailoring shear-stiff, mica-like nanoplatelets. , 2010, ACS nano.

[8]  H. Heinz,et al.  Nanoscale tensile, shear, and failure properties of layered silicates as a function of cation density and stress , 2010 .

[9]  N. S. Tomer,et al.  Nanoscale particles for polymer degradation and stabilization—Trends and future perspectives , 2009 .

[10]  K. Tamura,et al.  New Age of Polymer Nanocomposites Containing Dispersed High-Aspect-Ratio Silicate Nanolayers , 2008 .

[11]  V. Mittal.  Mechanical and gas permeation properties of compatibilized polypropylene–layered silicate nanocomposites , 2008 .

[12]  F. Bergaya,et al.  Determination of the cation exchange capacity of clays with copper complexes revisited , 2005, Clay Minerals.

[13]  Gerhard Lagaly,et al.  Grafted organic derivatives of kaolinite: II. Intercalation of primary n-alkylamines and delamination , 2005, Clay Minerals.

[14]  Arno Kwade,et al.  A Stressing Model for the Description and Optimization of Grinding Processes , 2003 .

[15]  Emmanuel P. Giannelis,et al.  NEW ADVANCES IN POLYMER/LAYERED SILICATE NANOCOMPOSITES , 2002 .

[16]  Paul Bowen,et al.  Particle Size Distribution Measurement from Millimeters to Nanometers and from Rods to Platelets , 2002 .

[17]  Donald R Paul,et al.  Effect of melt processing conditions on the extent of exfoliation in organoclay-based nanocomposites , 2001 .

[18]  R. Mülhaupt,et al.  Synthesis and thermal behaviour of layered silicate-EVA nanocomposites , 2001 .

[19]  L. Meier,et al.  Determination of the Cation Exchange Capacity (CEC) of Clay Minerals Using the Complexes of Copper(II) Ion with Triethylenetetramine and Tetraethylenepentamine , 1999 .

[20]  P. Long,et al.  The Kinetics of the Smectite to Illite Transformation in Cretaceous Bentonites, Cerro Negro, New Mexico , 1999 .

[21]  C. T. Chiou,et al.  Effects of Exchanged Cation on the Microporosity of Montmorillonite , 1997 .

[22]  I. Chan,et al.  On the estimation of average crystallite size of zeolites from the Scherrer equation: A critical evaluation of its application to zeolites with one-dimensional pore systems , 2009 .

[23]  Jörg Schwedes,et al.  Chapter 6 Wet Grinding in Stirred Media Mills , 2007 .

[24]  P. Scherrer,et al.  Bestimmung der Größe und der inneren Struktur von Kolloidteilchen mittels Röntgenstrahlen , 1918 .