ABSTRACT
Structural variations (oligolactide segments, functionalized end groups, and different plasticizer cores) were utilized to tailor the performances of biobased plasticizers for polylactide (PLA). Six plasticizers were developed starting from 1,4-butanediol and isosorbide as cores: two monomeric (1,4-butanediol levulinate and isosorbide levulinate) and four oligomeric plasticizers with hydroxyl or levulinate ester end groups (1,4-butanediol-based oligolactide, isosorbide-based oligolactide, 1,4-butanediol-based oligomeric levulinate, and isosorbide-based oligomeric levulinate). Structural variations in plasticizer design were reflected in the thermal stability, plasticizing efficiency, and migration resistance. The monomeric plasticizer 1,4-butanediol levulinate decreased the glass-transition temperature of PLA from 59 to 16 °C and increased the strain at break substantially from 6 to 227% with 20 wt % addition. 1,4-Butanediol-based oligomeric levulinate exhibited better thermal stability and migration resistance, though the plasticizing efficiency was slightly lower (glass-transition temperature = 28 °C; strain at break = 202%). Compared to PLA films plasticized by plasticizers with flexible butanediol cores, those plasticized by plasticizers with rigid isosorbide cores exhibited higher Young's modulus and thermal stability and lower plasticizing efficiency. Furthermore, plasticizers with levulinate ester end groups had improved thermal stability, plasticizing efficiency, and migration resistance compared to the corresponding plasticizers with hydroxyl end groups. Hence, a set of controlled structural variations in plasticizer design were successfully demonstrated as a potent route to tailor the plasticizer performances.
ABSTRACT
Dual-functioning additives with plasticizing and antibacterial functions were designed by exploiting the natural aromatic compound eugenol and green platform chemical levulinic acid or valeric acid that can be produced from biobased resources. One-pot synthesis methodology was utilized to create three ester-rich plasticizers. The plasticizers were thoroughly characterized by several nuclear magnetic resonance techniques (1H NMR, 13C NMR, 31P NMR, HSQC, COSY, HMBC) and by electrospray ionization-mass spectrometry (ESI-MS) and their performances, as plasticizers for polylactide (PLA), were evaluated. The eugenyl valerate was equipped with a strong capability to depress the glass transition temperature (Tg) of PLA. Incorporating 30 wt% plasticizer led to a reduction of the Tg by 43 °C. This was also reflected by a remarkable change in mechanical properties, illustrated by a strain at break of 560%, almost 110 times the strain for the breaking of neat PLA. The two eugenyl levulinates also led to PLA with significantly increased strain at breaking. The eugenyl levulinates portrayed higher thermal stabilities than eugenyl valerate, both neat and in PLA blends. The different concentrations of phenol, carboxyl and alcohol functional groups in the three plasticizers caused different bactericidal activities. The eugenyl levulinate with the highest phenol-, carboxyl- and alcohol group content significantly inhibited the growth of Staphylococcus aureus and Escherichia coli, while the other two plasticizers could only inhibit the growth of Staphylococcus aureus. Thus, the utilization of eugenol as a building block in plasticizer design for PLA illustrated an interesting potential for production of additives with dual functions, being both plasticizers and antibacterial agents.
