No abstract

Synthesis of polymer nanocomposites with novel shear stiff, mica-like nanoplatelets from a synthetic layered silicate is presented. This novel synthetic clay filler shows high aspect ratios while organophilization may be selectively restricted to external surfaces minimizing the organic content of the filler. The obtained nanocomposite shows superior mechanical, thermal and fire properties as compared to commonly used natural clays. Furthermore, the influence of the blending method on the nanocomposite properties was investigated.

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).

Silsesquioxanes are formed in situ during mixing and curing of a phenolic resin and a molecular silane precursor (3-(triethoxysilyl)-1-propaneamine) yielding a nanocomposite. As indicated by a higher onset temperature, a higher characteristic decomposition temperature, and a lower maximum heat flow, the thermal stability of the nanocomposite is significantly improved over the pristine resin. Moreover, the bending strength and the strain at break could also be enhanced by 36% and 51%, respectively. The nanocomposite was characterized by 29 Si solidstate NMR, STEM/EDS, TGA, DSC, and three point bending tests. The STEM/EDS measurements showed a homogenous distribution of silsesquioxanes in the phenolic resin.

No abstract