Mechanical and flame‐retarding properties of styrene–butadiene rubber filled with nano‐CaCO3 as a filler and linseed oil as an extender

A nanosize CaCO3 filler was synthesized by an in situ deposition technique, and its size was confirmed by X‐ray diffraction. CaCO3 was prepared in three different sizes (21, 15, and 9 nm). Styrene–butadiene rubber (SBR) was filled with 2–10 wt % nano‐CaCO3 with 2% linseed oil as an extender. Nano‐CaCO3–SBR rubber composites were compounded on a two‐roll mill and molded on a compression‐molding machine. Properties such as the specific gravity, swelling index, hardness, tensile strength, abrasion resistance, modulus at 300% elongation, flame retardancy, and elongation at break were measured. Because of the reduction in the nanosize of CaCO3, drastic improvements in the mechanical properties were found. The size of 9 nm showed the highest increase in the tensile strength (3.89 MPa) in comparison with commercial CaCO3 and the two other sizes of nano‐CaCO3 up to an 8 wt % loading in SBR. The elongation at break also increased up to 824% for the 9‐nm size in comparison with commercial CaCO3 and the two other sizes of nano‐CaCO3. Also, these results were compared with nano‐CaCO3‐filled SBR without linseed oil as an extender. The modulus at 300% elongation, hardness, specific gravity, and flame‐retarding properties increased with a reduction in the nanosize with linseed oil as an extender, which helped with the uniform dispersion of nano‐CaCO3 in the rubber matrix.