Effect of inner and outer chain length in multi-cationic site organoclays on the properties of PU/organoclay nanocomposites

Abstract

Organifiers with multiple cationic sites were synthesized to examine their effect on polyurethane (PU)/organoclay nanocomposites. The number of cationic sites was varied from 1 to 4 and the molecular weight of organifiers was also varied from 4,456 to 10,327. By increasing the number of cationic sites, higher physical ionic crosslinking was observed from the rheometer measurement. In this study, the chain length between two cationic sites was defined as the inner chain, and the chain length attached to the end group of the organifier was defined as the outer chain. The molecular weight of the inner and outer chain was varied to investigate the effect of the inner and outer chain length on the properties of organoclays and nanocomposites. A higher inner chain length led to a better dispersion of clay in the PU matrix, as observed in SEM and TEM images and higher mechanical properties of PU/organoclay nanocomposites, as shown in the tensile test. Lower mechanical properties were observed when the organifier had a shorter inner chain length, even though the organifier has a higher molecular weight and larger number of cationic sites. The tensile strength and glass transition temperature increased from 26 to 59 MPa and from −19.1 to −10.8°C, respectively, with a 3 wt% loading of the 2K-H-2K organoclay because it has the highest organifier inner chain length among the organifiers prepared.