Natural rubber/boehmite nanocomposites via latex compounding

Natural rubber (NR) latex was modified with unmodified boehmite alumina (BA) nanoparticles, added in NR up to 15 parts per hundred rubber (phr) amounts. Dispersion of the BA nanofillers was inspected in scanning electron microscopy (SEM). The tensile and fracture mechanical (J-integral approach) properties of the NR/BA nanocomposites were determined. Information on the rubber-BA and possible BA-BA interactions were deduced from dynamic mechanical analysis (DMA) and differential scanning calorimetric (DSC) tests. It was found that BA particles, through agglomerated, were well dispersed in the NR/BA nanocomposites up to a given threshold (7.5 phr). Improvements in the tensile (strength) and fracture mechanical properties (crack initiation- and propagation-related data) were found until this threshold BA content. DMA results confirmed enhanced stiffness and Payne-effect with increasing BA content both in the glassy and rubbery states and in the rubbery state, respectively. The amount of the bound NR fraction on the BA surface was rather small according to DSC results. It was thus concluded that unmodified BA acts as a semi-active nanofiller in NR.