2.3.2. Mechanical Characterization

Tensile and flexural tests were carried out in a universal testing machine ELIB 30 from S.A.E. Ibertest (Madrid, Spain) at room temperature, according to ISO 527 [42] and ISO 178 [43], respectively. Both tests were performed with a loading cell of 5 kN and a test speed of 10 mm/min, using five samples from each formulation in each test. Moreover, the typical stress-strain curve for each formulation was plotted from one representative curve, which showed the average behavior of the formulation. Furthermore, the toughness of the materials was calculated with the area under this curve using the OriginPro2015 program. Five values of toughness were assessed for each formulation and the average and standard deviation values are reported.

Impact absorbed energy measurements were carried out with a Charpy pendulum machine from Metrotec S.A. (San Sebastian, Spain), using a 6 J pendulum under the ISO 179 [44]. Five specimens were tested, and the mean and standard deviation are reported.

The hardness of PLA/PBAT/GR formulations was measured using a Shore D durometer, Model 673-D, from Instrument J.Bot S.A. (Barcelona, Spain), following the guidelines of ISO 868 [45]. Twenty measurements were taken from aleatory parts of the samples, and the mean and standard deviation are reported as hardness values.

The heat deflection temperature (HDT) was determined by the A method according to ISO 75 [46], which recommends a load of 1.8 MPa and a heating rate of 120 ◦C/h. In addition, the Vicat softening temperature (VST) was assessed using the ISO 306 [47], method B (with a load of 50 N and a heating rate of 50 ◦C/h). Both tests were carried out in a VICAT/HDT station DEFLEX 687-A2 from Metrotec SA (San Sebastián, Spain). For each property, three specimens were tested, and the mean and standard deviation are reported.
