3.2.1. Blends and Samples Preparation

Two different binary blends compositions containing, respectively, 15 and 20 wt.% PBSA (see Table 1 for the blends' names and compositions) were produced in pellets using a Comac EBC 25HT (L/D = 44) (Comac, Cerro Maggiore, Italy) twin screw extruder. The samples were named PLA (pure PLA), 85-15 (blend of PLA and PBSA 85/15 by weight) and 80-20 (blend of PLA and PBSA 80/20 by weight). Before the extrusion the materials were dried for 12 h in a DP 604–615 dryer (Piovan S.p.A., Verona, Italy). PLA granules were introduced into the main extruder feeder, while PBSA granules were fed into a specific side feeder. The temperature profiles of the extruder (11 zones) used for blends preparation were 150/175/180/180/180/185/185/185/185/185/190 ◦C, with the die zone at 190 ◦C. A screw rate of 300 rpm and a total mass flow rate of 20 kg/h were set. The strands coming out from the extruder were rapidly cooled in a water bath and then cut into pellets by an automatic knife cutter. All pellets were finally dried again at 60 ◦C.

**Table 1.** Injection molding conditions.


After the extrusion, the extruded pellets were injection molded in a Megatech H10/18 injection molding machine (TECNICA DUEBI s.r.l., Fabriano, Italy) to obtain ISO 527-1A dog-bone specimens (width: 10 mm, thickness: 4 mm, length: 80 mm) for tensile tests. From the injection molding parameters (Table 1), it can be observed that the same temperature profile was adopted for all blends as well as the same cooling time was set. The mold temperature was also lowered progressively with the increasing amount of PBSA from 70 ◦C for pure PLA to 55 ◦C for 80-20. The PBSA addition causes a decrement in viscosity that results in a lowering of the injection pressure [28].

#### 3.2.2. FT-IR Characterization

Infrared spectra of pure PLA, PBSA, and PLA/PBSA blends were recorded in the 550–4000 cm−<sup>1</sup> range using a Nicolet 380 Thermo Corporation Fourier Transform Infrared (FTIR) Spectrometer (Thermo Fisher Scientific, Waltham, MA, USA) equipped with smart Itx ATR (attenuated total reflection) accessory with a diamond plate. Two hundred and fifty-six scans at a 4 cm−<sup>1</sup> resolution were collected. The analysis was performed on the material sampled on the gate region of injection molded specimens.

#### 3.2.3. Mechanical Characterization

Tensile and creep tests were carried out on ISO 527-1A dog-bone specimens using an MTS Criterion model 43 universal testing machine (MTS Systems Corporation, Eden

Prairie, MN, USA) equipped with a 10 kN load cell and interfaced with a computer running MTS Elite Software. Tests were conducted, at room temperature, 3 days after the injection molding process and during this time the specimens were stored in a dry keeper (SANPLATEC Corp., Osaka, Japan) at a controlled atmosphere (room temperature and 50% humidity).

For standard uniaxial tensile tests, at least ten specimens for each blend composition were tested at a constant crosshead speed of 10 mm/min. The average values of the main mechanical properties were reported.

In order to investigate the nature of the deformation process, constant-load creep tests were carried out at room temperature at different stress levels, below the yield stress value, from 10 up to 40 MPa. The initial load for obtaining the set stress was reached by subjecting the specimen to uniaxial test at a speed of 10 MPa/min and, subsequently, maintaining the applied load for 8 h. Once the desired load was reached, the variation in deformation over time was recorded. Furthermore, to estimate the volume change that occurred during the creep test, transversal and axial specimen elongation were recorded with a video extensometer (Genie HM1024 Teledyne DALSA camera) interfaced with a computer running ProVis Software (Fundamental Video Extensometer) which, in turn, is interfaced with the MTS Elite Software. The volume strain (Δ*V/V*0) was calculated, assuming equal the two lateral strain components, according to the following equation [20,50,51]:

$$\frac{\Delta V}{V\_0} = (1 + \varepsilon\_1)(1 + \varepsilon\_2)^2 - 1 \tag{7}$$

where the volume variation is Δ*V*, the starting volume is *V*0, *ε*<sup>1</sup> is the axial (or longitudinal) strain, and *ε*<sup>2</sup> is the lateral strain.

In order to verify the reproducibility of the results obtained, at least 3 tests for stress level were carried out for each formulation.
