2.3.4. Thermal and Thermomechanical Characterization

The thermal properties of the PLA/PBAT/GR formulations were obtained by using two analyses, differential scanning calorimetry (DSC) (Mettler-Toledo model 821, Schwerzenbach, Switzerland) and thermogravimetric analysis (TGA) (Linseis, model TGA 1000, Linseis Messgeraete GmbH, Selb, Germany). In the programming of the DSC system, the thermal cycles were carried out, under a nitrogen atmosphere, with a heating and cooling rate of 10 ◦C/min. The purpose of the first heating was to eliminate the thermal history and was carried out from 25 ◦C to 200 ◦C. Later it was cooled down to −50 ◦C and finally, the second heating was carried out to 250 ◦C. The degree of crystallinity (Xc), obtained from the DSC thermograms, was calculated using Equation (1).

$$\chi\_{\rm c} \left( \% \right) = 100 \times \frac{\Delta \text{H}\_{\rm m} - \Delta \text{H}\_{\rm cc}}{\Delta \text{H}\_{\rm m} (100\%)} \times \frac{1}{\text{W}\_{\rm PLA}} \,\tag{1}$$

where ∆H<sup>m</sup> and ∆Hcc are the melting and the cold crystallization enthalpies, respectively, ∆H<sup>m</sup> (100%) is the calculated melting enthalpy of purely crystalline PLA (93 J/g) [49]. WPLA is the weight fraction of PLA in the formulation.

The mass loss obtained by TGA was carried out at a heating rate of 10 ◦C/min, measured in the range of 30 ◦C to 800 ◦C, under a nitrogen atmosphere and with a flow rate of 30 mL/min. The T5% was taken at the temperature where the 5% of mass loss was reached. The Tmax, the temperature where the degradation rate was maximum, was obtained at the peak of the first derivative of the TGA curve (DTG curves). Additionally, dynamic mechanical thermal analysis (DMTA) was performed in torsion mode, from −90 ◦C to 120 ◦C at a heating rate of 2 ◦C/min, a frequency of 1 Hz, and 0.1% of maximum deformation. The test was done on rectangular samples sizing 40 <sup>×</sup> <sup>10</sup> <sup>×</sup> 4 mm<sup>3</sup> in an oscillatory rheometer AR G2 from TA Instruments (New Castle, DE, USA) equipped with a special clamp system for solid samples.
