Effect of coupling agent on surface free energy of organic modified attapulgite (OAT) powders and tensile strength of OAT/ethylene-propylene-diene monomer rubber nanocomposites

In order to apply attapulgite as a rubber filler, the hydrophobicity and balanced characteristics of attapulgite could be modified by grafting organic groups to control surface energy and dispersive interaction to improve compatibility of attapulgite in rubber matrix. The free energy of immersion could be calculated using the surface energy of organic modified attapulgite (OAT) and rubber matrix. The surface energies of OAT were measured by several different liquids which have different surface energies and polar interactions, and then calculated by Wu's equation. The results showed that the dispersive interaction of fillers and the free energy of immersion between fillers and rubber matrix increased first and then fell with the increase of coupling agent content. The maximized tensile strength of rubber composites and the dispensability of fillers were obtained with the optimal addition amount of coupling agent, and the free energy of immersion reached the maximum value. The above finding could be used as guidance for modification of fillers and tuning properties of rubber composites.