The Influence of the Dispersion Method on the Morphological, Curing, and Mechanical Properties of NR/SBR Reinforced with Nano-Calcium Carbonate

There are several reasons for the development of nanopolymer compounds, such as improving physical, mechanical, and chemical properties, increasing lifespan, reducing costs, and decreasing negative environmental impact. The compatibility of two rubbers and mineral nanofillers in nanocomposites is a challenge that needs to be studied, and the effect of nanofillers on morphological, physical, and mechanical properties should be investigated accordingly. In this study, calcium carbonate nanoparticles were added to a polymer compound that included natural rubber (NR), styrene-butadiene rubber (SBR), vulcanization accelerators, and other additives. For mixing nanoparticles in the polymer matrix, various methods were used, including the solvent method in toluene and W410 solvents and the surface modification of calcium carbonate nanoparticles with stearic acid. The effect of dispersion nanoparticles in nanocomposite specimens on morphology, curing characteristics, and mechanical properties was studied. The morphologies of specimens were determined by X-ray diffraction (XRD) analysis and field emission scanning electron microscopy (FESEM). The particle size of the nanocomposite was approximately 34 nm, and the interlayer spacing between crystal plates increased from 2.81 nm to 3.03 nm. These results indicate a uniform dispersion of nanoparticles, specifically with an optimum content of 3.52%, in the compounds prepared through all mixing methods, with no agglomeration observed in the nanocomposites. The results of the nanocomposites’ curing characterization demonstrate that with the addition of nanoparticles, a strong bond is created in the polymer chains, and curing properties are improved. Among the dispersion methods, the highest percentage improvement in curing properties is observed with the solvent method W410. To evaluate the effect of the addition of calcium carbonate nanoparticles and the dispersion method on improving mechanical properties, tensile, tear, hardness, and rebound resilience tests were performed. In tensile tests, the surface modification method showed the highest enhancement in ultimate stress (80%), followed by the W410 method (64%) and toluene method (63.7%). Tear strength improvements were highest in the W410-solvent sample (80%), followed by the surface modification method (57%) and the solvent-toluene method (50%). The W410 method resulted in the hardest samples, while the surface-modified samples had the lowest hardness. The addition of CaCO3 nanofillers reduced rebound resilience, with the W410 method experiencing the largest reduction (10.64%), followed by the toluene method (6.38%), and with the surface-modified samples showing the lowest reduction (4.25%). The results show that in the W410 solvent method, the nanocomposite is more elastic than for other methods. Additionally, for most of the mechanical properties, the W410 method results in the most growth in improvement.