Mechanical properties of poly(styrene-co-acrylonitrile) nanocomposites containing organically modified layered double hydroxides

Abstract

Zn2Al layered double hydroxides (LDHs) modified with stearic acid, oleic acid, or caproic acid were synthesized by the co-precipitation method for the compounding with poly(styrene-co-acrylonitrile) (SAN) at 0 to 6wt% contents using a co-rotating twin screw extruder. Melt flow indices (MFI) and mechanical properties of SAN nanocomposites were measured to know the effect of organic modifier. MFI of SAN nanocomposites reinforced with stearic acid modified LDH (SA-Zn2Al LDH) were multiplied by the lubrication effect of considerably released organic modifier over 5wt%. Mechanical properties of SAN nanocomposites showed the maximum values at the contents of organically modified LDH between 1 and 5wt%. The optimum contents of organically modified LDHs (OLDHs) for tensile modulus were measured as 1 or 2wt%, significantly less than the percolation threshold calculated as 4.7wt% for an aspect ratio of 25. Except the flexural strength and notched Izod impact strength, caproic acid modified LDH (CA-Zn2Al LDH) showed the best mechanical performance. SAN nanocomposites containing oleic acid modified LDH (OA-Zn2Al LDH) showed the slightly largest values in both flexural strength and notched Izod impact strength. These results show that the strategy of organically modified LDH (OLDH) can be used to reinforce the SAN polymer without compromising mechanical properties.