**2. Materials and Methods**

### *2.1. Production of Rice Straw Pellet with a Single Press*

Rice straw was provided by Società Agricola Abbazia (45◦2259.34" N 9◦5822.3" E), Orzinuovi (Brescia, Italy). All tests were performed at the *Laboratorio di Ingegneria dei Materiali* (DICCA, UNIGE). Rice straw was initially cut to ge<sup>t</sup> short fibers and then grounded using a chopper with rotating blades for 1 min at 4000 rpm. Sieves with an aperture of 1 mm, 0.85 mm, 0.3 mm, and 0.15 mm were used to obtain the granulometric distribution of the straw powders. The obtained particle size distribution after grinding is presented in Figure 1. A particle size range between 0.5 to 0.7 mm is suggested in literature [15]. Sizes larger than 1 mm could act as preferential breaking points. On the contrary, small particles with large surface area could increase density values and lead to tougher pellets. In this work, only the fraction in the range 0.15–1 mm was used to provide a homogenous sample according to established criteria.

The pellet press consisted of a cylindrical 8 mm diameter die of steel, a fitted piston, and a hydraulic press. The compression of the material was obtained by pressing, with the hydraulic press, against a fixed backstop. A fixed quantity of 0.25 g of rice straw was used. A constant force detected by a 150 kN load cell was applied for one minute at room temperature. After compression, the pressure was released, the bottom of the cylinder removed, and the pellet pressed out of the cylinder. For determination of experimental precision, four replicates were carried out. Pellets had in general a cylindrical shape and are about 8 mm in diameter.

**Figure 1.** Particle size distribution of grounded rice straw.

Different compression forces (1–10 tons) and amount of added distilled water (40–60 mg) were used. Figure 2 shows examples of the produced pellets.

**Figure 2.** Pellets produced using the single press.
