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).

Analyzing the influence of particle size and stiffness state of the nanofiller on the mechanical properties of epoxy/clay nanocomposites using a novel shear-stiff nano-mica

“…with Mg 2? cations in an aqueous suspension [16][17][18]. This Mg-hect with its highly hydrated state in an aqueous dispersion was processed in a stirred media mill in order to exfoliate the nanofiller tactoids by applying mechanical shear forces.…”

“…This Mg-hect with its highly hydrated state in an aqueous dispersion was processed in a stirred media mill in order to exfoliate the nanofiller tactoids by applying mechanical shear forces. After milling, the typical tactoid thickness was found to be (10-15 nm) [18]. As a first approximation of the lateral extension, the hydrodynamic radius obtained from SLS is used [20].…”

“…The homogenous charge density allows for a transformation between highly hydrated shearlabile (lower shear stiffness) and a non-hydrated shear-stiff state (higher shear stiffness) by simple cation exchange. Due to its inhomogeneous layer charge density and amorphous impurities this transformation is not possible for common natural MMT [16][17][18]. Consequently, the influence of stiffness state of the nanofiller on the mechanical properties of the epoxy/clay nanocomposites was analyzed in detail using the shear-stiff K-hectorite (O/K-hect) and the shear-labile (O/Mg-hect).…”

Reduction of aspect ratio of fluoromica using high-energy milling

“…Planetary ball mills are widely used for clay powder preparation, however very few studies investigating the use of stirred ball/bead mills under wet conditions to carry out size reduction on clay nanoparticles have been reported, nor have they considered the commercial necessity of scalability. (Ziadeh et al, 2012). Most of the above mentioned studies used microscopy techniques to characterise the size reduction or the morphological changes, but no effective methods are reported to observe the exfoliated layers and thin platelets due to the agglomerates or clumps, which brings limitations to the accurate measurement of the reduced particle size.…”

Influence of Grinding and Sonication on the Crystal Structure of Talc

“…The temperature of maximum dehydroxylation and the weight loss in the temperature range corresponding to dehydroxylation both showed a linear relationship with decreasing structural order along the c* direction (crystallite thickness) of phyllosilicates after progressive less intensive grinding (Dellisanti and Valdrè, 2008). Ziadeh et al (2012) demonstrated the ability of ball grinding to increase the aspect ratio (crystallite a-b plane dimension over the c* dimension) of synthetic fluorohectorites.…”