Stearin

Polymer: Natural rubber (NR) RSS I was provided by Torimex-Chemicals Ltd. Sp. z o.o (Konstatntynów Łódzki, Poland). Crosslinking agent: Rubber mixtures were vulcanized with sulfuric crosslinking system consisting of sulfur (Siarkopol, Poland); mercaptobenzothiazole (Sigma-Aldrich, Schnelldorf, Germany); micro-sized zinc oxide (Huta Będzin, Poland); and stearin (SA, Avantor Performance Materials, Gliwice, Poland). Fillers: Cereal straw (several different types of straw mixed together: rye, wheat, triticale and oat) was collected from local farms. Dried straw was crushed using a Pulverisette 5 classic line planetary ball mill (Fritsch, Idar-Oberstein, Germany), grinding time 2 h, speed 300 rpm; chalk–Socal 31 (Solvay GmbH, Hannover, Germany). Talc–Naintsch A-20 (Luzenac Group, Toulouse, France); carbon black–N774 carbon black (MAKROchem S.A, Lublin, Poland); silica – AEROSIL^® A380 (Evonik Degussa GmbH, Essen, Germany).
Composition of typical elastomer mixture: NR rubber (100 phr–parts per hundred rubber), sulfur (2 phr), mercaptobenzothiazole (2 phr), zinc oxide (5 phr), stearin (1 phr), and fillers (0 phr for reference sample or 10, 20, and 30 phr for other composites).

Field horsetail (HT) was delivered by MANU JTC, s.r.o. (Opawa, Poland). Common wheat (WS) was harvested from local farms. Hydrochloric acid (Sigma-Aldrich, Schnelldorf, Germany) and citric acid (Sigma-Aldrich, Schnelldorf, Germany) were used in the hydrolysis process. The polymer matrix was natural rubber (NR) supplied by Torimex-Chemicals Ltd. Sp. z.o.o (Konstatntynów Łódzki, Poland). The cross-linking system consisted of sulfur (Siarkopol, Tarnobrzeg, Poland), 2-mercaptobenzothiazole (MBT), purchased from Sigma-Aldrich (Schnelldorf, Germany), micrometric zinc oxide (ZnO, Huta Będzin SA, Będzin, Poland) and stearin (SA, Avantor Performance Materials, Gliwice, Poland).
The composition of the rubber mixture included (Table 1): natural rubber NR (100 phr-parts per hundred rubber), zinc oxide (5 phr), sulfur (2 phr), 2-mercaptobenzothiazole (2 phr), stearin (1 phr) and a filler (0 phr in in the case of the reference sample and 10 phr in the case of samples filled with the tested bioadditive).