*2.4. Creation and Tensile Testing of Rubber Composite Samples*

Table 1 below contains the recipe for the rubber composite masterbatch used to make rubber composite samples. Amounts listed are in parts per hundred (phr). Each sample was differentiated according to which biochar filler was used; see the following list with their shorthand notation in parentheses: (1) biochar control (BC control); (2) air-oxidized biochar (BC air); (3) carbon dioxide treated biochar (BC CO2); (4) biochar control coated with lauric acid (BC control LA); (5) air-oxidized biochar coated with lauric acid (BC air LA); (6) carbon dioxide treated biochar coated with lauric acid (BC CO<sup>2</sup> LA).


**Table 1.** Rubber composite formulation (phr).

SBR: styrene butadiene rubber; CB: carbon black; MBTBM: 2,20 -methylenebis(6-tert-butyl-4-methylphenol); SA: stearic acid; ZnO: zinc oxide; CBTS: *N*-cyclohexyl-2-benzothiazolesulfenamide.

Tensile properties were measured on an Instron 55R1123C5420 (Instron, Inc., Norwood, MA, USA) and data was processed using Bluehill Universal Software version 4.32. For each rubber composite sample at least 4 replicates were run.
