NANOCOMPOSITES BASED ON A SYNTHETIC LAYER SILICATE AND POLYAMIDE-12

The swelling behavior of a synthetic three-layer silicate caused by 12 -aminolauric acid is studied by wide angle X-ray scattering. The swell ing process as a function of the 12-aminolauric acid concentration can be separated into two regimes; i) cation exchange of inorganic cation s by protonated 12-aminolauric acid and ii) further diffusion of exces s zwitterionic 12-aminolauric acid into the interlayer space of the si licate. After the cation exchange an interlayer distance of the silica te of about 1.7 nm can be achieved, which can be increased to more tha n 2 nm after additional diffusion of zwitterionic 12-aminolauric acid. Also the distribution of the interlayer distance as a function of the swelling conditions is measured from the full width at half maximum v alues of the d(001) spacing of the silicate. Improvement of the mechan ical properties of polyamide-12 by adding the swollen layer silicate i s only achieved when the silicate is present during the polymerization . This is closely related to the morphology development. It is shown b y transmission electron microscopy and atomic force microscopy measure ments that defoliation of the silicate layers leading to a nanocomposi te occurs only when the layer silicate is present during the polymeriz ation process. As little as 2 wt.% of swollen layer silicate with an i nterlayer distance of about 2.1 nm in the nanocomposites leads to an i mprovement of the tensile modulus of about 1000 MPa without decreasing the impact strength.