Extraordinary mechanical behavior of exfoliated montmorillonite/polymer nanocomposite films cast from soap‐free emulsion polymerized latices

The exfoliated montmorillonite (MMT) nanoplatelets tended to re‐stack with each other after casting the MMT/poly(methylacrylate‐ co ‐methylmethacrylate) P(MA‐ co ‐MMA) latex solutions fabricated by soap‐free emulsion polymerization into films as revealed by X‐ray diffraction and transmission electron microscopy. As the content of MMT was increased from 0 to 20 wt %, the T g measured by differential scanning calorimetry was slightly decreased from 19.2 to 17.2 °C, whereas that measured by dynamic mechanical analysis was increased from 22 to 32 °C, indicating that the local motion of polymer segments has been retarded by MMT nanoplatelets. Besides, the elongated elliptical voids appeared during stretching of 1 wt % MMT/P(MA‐ co ‐MMA) film to cracking also illustrated the pinning effect provided by the exfoliated MMT. As the content of MMT was increased more than 10 wt %, the mechanical behavior of MMT/P(MA‐ co ‐MMA) nanocomposite films was changed from ductile to brittle nature with significant increase of Young's modulus and tensile strength owing to the restacking of exfoliated MMT nanoplatelets. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1064–1069, 2010