Properties and Morphology of Organoclay/Poly(Styrene-Maleic Anhydride) Nanocomposites: Effect of Copolymer Structure

摘要

For many polymers addition of a nano-phase reinforcing agent such as montmorillonite clay (MMT) could add value to the balance of properties, including increased modulus, heat deflection temperature, and in some cases increased strength and reduced flammability. To realize these potential benefits, it is necessary to be able to exfoliate and disperse the high aspect ratio clay platelets more or less ndividually within the polymer matrix. It has been found that grafting as little as 1% by weight of maleic anhydride to a polyolefin dramatically improves the ability to exfoliate or disperse organoclay platelets; indeed, several commercial products employ just a few percent of a maleated polyolefin as a "compatibilizer" in the formulation to aid clay dispersion in the unmaleated polyolefins. As one example, Hotta and Paul have shown for linear low density polyethylene, the areal density of montmorillonite particles in transmission electron microscope (TEM) images, increases 50-fold as maleic anhydride content is increased from 0 to 1% in the matrix . Maleic anhydride can be copolymerized with polystyrene, and other monomers like acrylonitrile, and it would be important to know if maleic anhydride ncorporation into styrenic polymers facilitates exfoliation in analogy to the case for polyolefins. Compatibilization of montmorillonite in styrenic copolymer nanocomposites using maleic anhydride was previously noted by several authors, who have primarily focused on synthesis and thermal stability [2-4], and to a lesser degree the mechanical properties. This paper explores the use of various styrenic polymers that contain maleic anhydride in varying amounts to form nanocomposites from an organoclay using melt processing. Dispersion of the organoclay was evaluated by transmission electron microscopy combined with digital image analysis and by analysis of the Young's modulus of these composites. Composite modeling allows us to account for the effect of varying matrix modulus and provides a uniform basis for comparison of the reinforcement effect in nanocomposites formed from different copolymers. Wide angle x-ray scattering results are also presented.