2.3.3. Mechanical Properties

Axial and diametral compression tests were carried out with a Hausfield universal mechanical tester. The equipment was set at a load cell capacity of 5 kN at a rate of 20 mm/min (Figure 4). The corresponding strength values were determined as the minimum force at which pellet broke. That way, the resistance of pellet to deformation and breakage when compressed vertically and horizontally were evaluated which are likely scenarios during transport and storage.

**Figure 4.** Axial compressive test.

The axial compressive strength (<sup>σ</sup>*AC*) was calculated using:

$$
\sigma\_{\rm AC}(\rm MPa) = \frac{4P}{\pi d^2} \tag{3}
$$

where *d* is the diameter of the pellet (mm) and *P* (N) is the failure force.

The elongation at break (ε) was defined as:

$$
\sigma(\%) = \frac{s}{l} 100\tag{4}
$$

with *s* the length at break (mm) and *l* the initial length (mm).

The diametral compressive strength (<sup>σ</sup>*DC*) was calculated as:

$$
\sigma\_{\rm DC}(\rm MPa) \,\,=\,\frac{2P}{\pi Ld} \tag{5}
$$

where *L* and *d* are the length (mm) and diameter (mm) of the pellet and *P* (N) is the failure force.

Durability (*D*) tests were performed on commercial RS and RH pellets to measure their friability and their possibility of breaking apart during processing. With this purpose, an initial quantity of material was weighed (*W*i) and placed in a 0.25 L recipient. Then, the recipient was tumbled at 50 rpm for 10 min and sieved afterwards. Finally, the mass of pellets retained on the sieve after tumbling was measured (*W*f). The final weight was compared against its initial value and the difference was expressed as:

$$D(\%) = \frac{\mathcal{W}\_f}{\mathcal{W}\_l} 100,\tag{6}$$
