*2.2. Mechanical and Thermal Characterization*

The effect of ECO on mechanical properties was studied using standard tensile, impact test, and hardness. Tensile properties were obtained in a universal test machine ELIB 30 from S.A.E Ibertest (Madrid, Spain). Five different samples were tested using 5 kN load cell and a crosshead speed of 10 mm·min−<sup>1</sup> according to ISO 527. Furthermore, an axial extensometer from S.A.E Ibertest (Madrid, Spain) was used to obtain tensile modulus with high accuracy. The impact strength was tested in a 1 J Charpy pendulum from Metrotec S.A. (San Sebastián, Gipuzkoa, Spain), as is indicated in ISO 179. Shore D hardness was carried out following the guidelines of the ISO 868 using a durometer 673-D from J. Bot S.A (Barcelona, Spain). In both tests, a minimum of 5 samples were used and the results shown are the obtained average.

Thermomechanical properties were assessed by using standard Vicat softening temperature (VST) by using a load of 5 kg and a heating rate of 50 ◦C·h <sup>−</sup><sup>1</sup> according to ISO 306. Moreover, heat deflection temperature (HDT) was obtained following the guidelines of ISO 75 with a load of 296 g and a heating rate of 120 ◦C·h −1 . Both values were obtained in a Vicat-HDT station mod. DEFLEX 687-A2 from Metrotec S.A. (San Sebastián, Gipuzkoa, Spain). At least five different specimens for each composition were tested and average values were calculated.

Additionally, storage modulus (G') and damping factor (tan δ) were evaluated in torsion mode by dynamic mechanical thermal analysis (DMTA) in an oscillatory rheometer AR-G2 from TA instrument (New Castle, DE, USA). Shaped samples (4 <sup>×</sup> <sup>10</sup> <sup>×</sup> 40 mm<sup>3</sup> ) were evaluated with a dynamic program from 30 to 110 ◦C using a heating rate of 2 ◦C·min−<sup>1</sup> . The maximum deformation was set to 0.1% with a constant frequency of 1 Hz.

Thermal transitions of PLA plasticized with different contents of ECO were obtained by differential scanning calorimetry (DSC) in a DSC mod. 821 from Mettler-Toledo Inc. (Schwerzenbach, Switzerland). Samples with an average weight of 6–8 mg were subjected to the following temperature program: 1st heating program from 25 to 300 ◦C at 10 ◦C·min−<sup>1</sup> to remove thermal history, 2nd cooling program from 300 to 25 ◦C at <sup>10</sup> ◦C·min−<sup>1</sup> , and 3rd heating program from 25 to 300 ◦C at 10 ◦C·min−<sup>1</sup> . All thermal cycles were performed in a nitrogen atmosphere with a flow rate of 66 mL·min−<sup>1</sup> . The percentage of crystallinity of different PLA formulations with ECO was determined by Equation (1):

$$X\_{\rm c} \left( \% \right) = \left[ \frac{\Delta H\_{\rm m} - \Delta H\_{\rm cc}}{\Delta H\_{m(100\%)}} \right] \cdot \frac{1}{w\_{sample}} \times 100 \tag{1}$$

where ∆*Hcc* and ∆*H<sup>m</sup>* represent cold crystallization and melting enthalpies (J·g −1 ), respectively. The weight amount of PLA is represented by *wsample* (g). Theoretical melting of PLA 100% crystalline (∆*Hm*(100%) ) was 93 J·g −1 , as is reported [10].

Thermogravimetric analysis was carried out in a TGA/SDTA 851 thermobalance from Mettler-Toledo Inc (Schwerzenbach, Switzerland). A heating ramp from 30 to 700 ◦C at constant heating rate of 10 ◦C·min−<sup>1</sup> and constant flow rate of nitrogen (66 mL·min−<sup>1</sup> ) were set to evaluate samples with average weight of 10 mg. The temperature when a 5% weight loss has been reached and the maximum degradation were obtained in order to evaluate thermal stability of the different samples of PLA plasticized with ECO.
