I. Kelnar, J. Kratochvíl, Z. Padovec
Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic,
Keywords: nanocomposite, blend, melt drawing, microfibrillar composite
Summary:Microfibrillar composites (MFCs) are polymer – polymer composites prepared by drawing of suitable polymer blends, where application of various nanofillers have strong potential to eliminate basic disadvantage of MFC arising from limited parameters of polymer components. The effect of nanofiller (NF) does not only consist in reinforcement of polymer components and improvement of many material parameters, like nonflammability; additional effects on parameters of fibrils and interface, drawing process etc. are also of importance. Due to complexity of NF acting, both synergistic and antagonistic effects may occur. This arises, e.g. from NF-affected interface parameters. This work deals with comparison of the effect of particular, platy and tubular inorganic nanofillers on performance of MFC based on the HDPE matrix with in-situ formed PA6 fibrils. Due to strong hydrophilicity of all nanofillers, their predominant localization inside the PA6 phase was found using different mixing protocols, including NF pre-blending in respective polymer components. In spite of similar final structure, in many cases properties of MFC do not correspond to reinforcement by added NF and fibril formation. At the same time, harmonization of numerous NF-induced effects may lead to fair mechanical behaviour, even exceeding the parameters predicted by Halpin Tsai model . The best results were achieved with organophilized montmorillonite. Tubular halloysite, except of slightly lower mechanical parameters, showed different dependence onthe mixing protocols and composition. Also in the case of nanosized silica spheres, the MFC behaviour exceeded the reinforcing potential of single components, but using functionalized HDPE only. Surprisingly, this system has the best parameters among the undrawn samples. The antagonistic effects reflected in decrease of mechanical properties, including modulus in spite of drawing and resulting fibril formation, were found using some mixing protocols and compositions for all 3 types of NF, but were most marked in the case of spherical NF. These negative effects arise most probably from affecting of crystallinity of semicrystalline polymer components in the interfacial area by different NF localization and ordering caused, e.g. by different extent and course of NF transfer between the polymer components. The explanation of crucial effect of reduced modulus of the thin (~1µm) interfacial layer due to different fraction of PE spherulites at the surface of the PA6 fibrils is based on the finite element analysis. This original concept represents a tool for explanation of analogous antagonistic effects in multicomponent polymer systems and their rational design.