4.2.1. Rheometric Properties

The BDC filler clearly affected the curing characteristics of the SBR mixtures. The kinetic parameters of the BDC-based compounds differed significantly from those of the unfilled compound, as shown in Table 2. The incorporation of BDC into the SBR compound resulted in higher viscosity and stiffness, as reflected in the torque values (LH, ΔL), which are much higher than those of the SBR samples. The incorporation of the biofiller resulted in higher cross-link density, as the ΔL parameter is an indirect measurement of the degree of elastomer cross-linking. The unfilled sample exhibited shorter time of vulcanization and scorch time than the filled composites. The scorch and vulcanization times increased with increasing concentrations of BDC, showing the highest values for 30 phr concentration (<sup>τ</sup>02 = 3.5 and τ90 = 38.5). It can be concluded that the sulfur cross-linking system was partially adsorbed onto the outer surface of the BDC filler, resulting in a slower curing process [12,13].


**Table 2.** Influence of BDC on the rheometric properties of SBR compounds.

LL—minimum torque moment (dNm); ΔL—the decrease of torque moment (dNm) (ΔL = LHR − LL); <sup>τ</sup>02—scorch time (min); <sup>τ</sup>90—time of vulcanization (min).
