Poly(lactic acid) (PLA)/Poly(butylene succinate-co-adipate) (PBSA) Compatibilized Binary Biobased Blends: Melt Fluidity, Morphological, Thermo-Mechanical and Micromechanical Analysis

Abstract

In this work poly(lactic) acid (PLA)/poly(butylene succinate-co-adipate) (PBSA) biobased binary blends were investigated. PLA/PBSA mixtures with different compositions of PBSA (from 15 up to 40 wt.%) were produced by twin screw-extrusion. A first screening study was performed on these blends that were characterized from the melt fluidity, morphological and thermo-mechanical point of view. Starting from the obtained results, the effect of an epoxy oligomer (EO) (added at 2 wt.%) was further investigated. In this case a novel approach was introduced studying the micromechanical deformation processes by dilatometric uniaxial tensile tests, carried out with a videoextensometer. The characterization was then completed adopting the elasto-plastic fracture approach, by the measurement of the capability of the selected blends to absorb energy at a slow rate. The obtained results showed that EO acts as a good compatibilizer, improving the compatibility of the rubber phase into the PLA matrix. Dilatometric results showed different micromechanical responses for the 80–20 and 60–40 blends (probably linked to the different morphology). The 80–20 showed a cavitational behavior while the 60–40 a deviatoric one. It has been observed that while the addition of EO does not alter the micromechanical response of the 60–40 blend, it profoundly changes the response of the 80–20, that passed to a deviatoric behavior with the EO addition.

Volume Change during Creep and Micromechanical Deformation Processes in PLA–PBSA Binary Blends

“…Pure PLA is a fragile material characterized by an elevated modulus of 3.58 GPa, a high tensile strength of 62 MPa, and a low elongation at break (3.6%). The mechanical results are in accordance to what can be observed in the literature [ 28 , 62 , 63 ]; the introduction of the rubbery PBSA phase at 15 and 20 wt.% led to a decrement in the Young’s modulus and tensile strength counterbalanced by an increment of the elongation at break. These trends are more marked where the PBSA content was higher (20 wt.%).…”

“…From the SEM images shown in Figure 6 , it emerges that the PBSA particle size increases with the PBSA content, in agreement to what is also observed in the literature [ 28 ]. At 10 MPa, for both blends, neither cavitation nor debonding of the PBSA particles appeared.…”

“…In particular, three stress levels were chosen: (I) 10 MPa, which was the lowest value for which both the binary blends underwent the same deformation mechanism and no deviation in the Eyring's slopes occurred; (II) 30 MPa in which the slope variation occurred for both 85-15 and 80-20; (III) 45 MPa, which was the highest stress level tested and for which the micromechanical deformation process should be more marked. From the SEM images shown in Figure 6, it emerges that the PBSA particle size increases with the PBSA content, in agreement to what is also observed in the literature [28]. At 10 MPa, for both blends, neither cavitation nor debonding of the PBSA particles appeared.…”

“…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 ].…”

“…The present paper, starting from one of the author’s own experience [ 27 , 28 ], aimed to explore the micromechanical deformation mechanisms of blends based on polylactic acid (PLA) and polybutylene succinate adipate (PBSA). These blends were recently considered for their potential use in packaging and personal care/sanitary applications [ 29 ], hence, in sectors where products have a short life thus highly contributing to the production of enormous amounts of waste [ 30 ].…”