• bioplastic
• extrusion compounding
• green chemistry
• mechanical characterization
• plasticizers
• poly (lactic acid)
• thermal characterization

Poly (lactic acid) (PLA) is a bio-based and biodegradable polymer which presents properties comparable to traditional fossil-fuel based polymers, such as polystyrene (PS), polyethylene (PE) and polypropylene (PP). However, PLA applications are limited due to its fragility at room temperature. Generally speaking, the introduction of a plasticizer into a rigid polymeric matrix leads to a decrease of the glass transition temperature, a reduced stiffness of the material, the lowering of the yielding strength and to an increase in the elongation at break. Ideal plasticizers for PLA should be non-volatile, compatible, non-toxic and eco-friendly materials.
Following this approach, three low environmental impact copolymers, containing poly(ethylene glycol) PEG, oligomers of lactic acid (OLA, PLA) and poly(caprolactone) (PCL), i.e. PEG-OLA and two PEG-PCL-PLA, were synthetized and used as plasticizers for PLA 2003D.
PEG-OLA was synthetized by bulk transesterification reaction, while PEG-PCL-PLA co-polymers have been polymerized following different reaction strategies to obtain random and block structures, (PEG-PCL-PLA random, PEG-PCL-PLA block) but maintaining comparable PLA and PCL content. Synthesized materials were characterized in terms of molecular weight, molecular weight distribution and molecular structure.
Blends of PLA 2003D with different weight fractions of the three synthesized plasticizers (5, 10, 20 wt%) were prepared by means of extrusion compounding. Mechanical characterization of the compounds in different concentration was carried out (tensile test, Dynamic Mechanical Thermal Analysis (DMTA) and Charpy impact test) to define how the yielding strength, elongation at break, modulus and impact resistance vary with the plasticizer’s structure and weight fraction. Thermal analysis was performed by Diffraction Scanning Calorimetry (DSC) to evaluate the glass transition temperature and the melting temperature of the different blends. Moreover, glass transition temperatures were also detected and measured by DMTA.
In all cases, the 5 wt% of plasticizers didn’t show any significant improvement in neither thermal nor mechanical properties of PLA 2003D. The addition of random and block PEG_PCL_PLA co-polymers to PLA 2003D resulted in significant improvement of the mechanical properties when 20wt% of PEG-PCL-PLA random plasticizer was used. PEG-OLA showed interesting results, in terms of elongation at break and impact resistance, even with a weight fraction of 10%. All plasticizers, noteworthy, lowered the glass transition temperature, the yielding strength and the E-modulus of PLA 2003D.