Mechanical Properties and Mullins Effect of Ethylene Propylene Diene Monomer Vulcanizes Reinforced with Silica Powders with Different Micropore Structures

Ethylene propylene diene monomer (EPDM) was filled with silica aerogel (AS), spherical silica (SS) and fumed silica (FS), which have different micropore structures and closed particle size. The mechanical properties and Mullins effect of EPDM vulcanizates before and after reinforced were analyzed. It was found that, AS with 3 times more specific surface area and pore volume than FS had a much higher reinforcement efficiency for EPDM. The tensile strength of EPDM vulcanizates reinforced with AS is 928% higher than that of pure EPDM and 4.3% higher than that of FS/EPDM. The tear strength of AS/EPDM is 411% higher than that of pure EPDM and 65.5% higher than that of FS/EPDM. SS did not improve the mechanical properties of vulcanizate. AS and FS have similar reinforcement mechanism in reinforcing EPDM. Above a critical content, Self-similar, rigid clusters formed through a diffusion-controlled cluster-cluster aggregation (CCA) with similar fractal dimension (1.75-1.80) and EPDM chains are connected by the bound molecular segments absorbed in the pore or on the cluster surface through van der Waals force to form physical cross-linking networks. The amount of bound segments, strongly depends on the specific surface area and pore volume of filler, determines the strength of physical networks and the consequent reinforcement efficiency. Therefore, AS shows a higher efficiency in reinforcing EPDM. [GRAPHICS] .