*3.1. Biochar Characterization*

Physical characteristics of the biochar samples can be seen in Table 2 below. Carbon content in these samples is very high, although not approaching the >99% purity of CB. Density of these biochars is also nearly identical to the density of CB used (1.7–1.9 g/cm<sup>3</sup> ).

Relative purity of these biochars are also shown in the X-ray diffraction spectra seen in Figure 1. Graphitic d-spacing peaks that are typical in CB and other high-carbon containing materials at 24 and 43◦ 2θ [30] are most prominent in the CB trace, but can also be seen for the biochar samples. No other sharp peaks are seen, meaning there are no appreciable crystalline impurities present in any of the biochar samples.


BC control 87.22 ± 0.50 1.81 ± 0.18 0.12 ± 0.04 6.52 4.33 1.68 BC air 86.42 ± 0.38 1.63 ± 0.20 0.13 ± 0.02 7.93 3.89 1.69

**Table 2.** Material properties of carbon black and biochar samples. BC CO<sup>2</sup> 88.67 ± 0.32 1.49 ± 0.03 0.15 ± 0.03 5.96 3.73 1.69

*C* **2022**, *8*, x FOR PEER REVIEW 4 of 9

<sup>a</sup> oxygen calculated by difference; <sup>b</sup> data supplied by the manufacturer. appreciable crystalline impurities present in any of the biochar samples.

**Figure 1.** X-ray diffraction spectra of CB, biochar control, and gas-treated biochar samples. Graphitic d-spacing peaks at 24° and 43° 2θ are typical of high carbon content materials such as CB and are seen in all four samples. **Figure 1.** X-ray diffraction spectra of CB, biochar control, and gas-treated biochar samples. Graphitic d-spacing peaks at 24◦ and 43◦ 2θ are typical of high carbon content materials such as CB and are seen in all four samples.

### *3.2. Determination of Lauric Acid Coating Concentration 3.2. Determination of Lauric Acid Coating Concentration*

To determine the appropriate amount of LA to use to coat biochar particles, several different concentrations (5, 10, and 20% relative to biochar weight) of LA were milled with a control biochar. The 5, 10, and 20% LA-coated control biochar samples were then molded into rubber composite samples and their tensile properties were measured. Results can be seen in Table 3. To determine the appropriate amount of LA to use to coat biochar particles, several different concentrations (5, 10, and 20% relative to biochar weight) of LA were milled with a control biochar. The 5, 10, and 20% LA-coated control biochar samples were then molded into rubber composite samples and their tensile properties were measured. Results can be seen in Table 3.


**Table 3.** Tensile properties of biochar as a function of LA concentration. **Table 3.** Tensile properties of biochar as a function of LA concentration.

Tensile results over the LA range tested for these rubber composites were similar, but since the 10% LA-coated composite had a slightly higher tensile strength and increased Tensile results over the LA range tested for these rubber composites were similar, but since the 10% LA-coated composite had a slightly higher tensile strength and increased toughness, this concentration was selected to coat all the biochar samples.

toughness, this concentration was selected to coat all the biochar samples. Confirmation of LA coating on biochar samples can be seen by the presence of the characteristic LA C-H stretching vibrations at 2915 and 2847 cm−1 [31] in Figure 2. These biochars were then used to create rubber composite samples for tensile testing. Confirmation of LA coating on biochar samples can be seen by the presence of the characteristic LA C-H stretching vibrations at 2915 and 2847 cm−<sup>1</sup> [31] in Figure 2. These biochars were then used to create rubber composite samples for tensile testing.

**Figure 2.** FTIR spectra for LA-coated vs. uncoated biochar samples showing the presence of LA by the peaks at 2847 and 2915 cm−1 . **Figure 2.** FTIR spectra for LA-coated vs. uncoated biochar samples showing the presence of LA by the peaks at 2847 and 2915 cm−<sup>1</sup> .
