Dual-Functioning Antibacterial Eugenol-Derived Plasticizers for Polylactide

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.

Tailoring Oligomeric Plasticizers for Polylactide through Structural Control

“…A similar decreased thermal stability because of a higher amount of active groups was previously observed in eugenol-based oligomeric plasticizers, as the T 5 value of plasticizers with a higher phenolic content was 20 °C lower than that of the plasticizer with less phenolic content. 35 Ketone groups were previously proven to increase the thermal stability of plasticizers. 28 In general, the thermal stabilities of the synthesized plasticizer candidates were quite comparable to other PLA plasticizers.…”

Zein-Based Films Containing Monolaurin/Eugenol or Essential Oils with Potential for Bioactive Packaging Application

“…The effects of plasticizers depend on several factors, such as the chemical structure, ratio of polar and non-polar groups, molecular shape (linear or branched), and molecular weight. These aspects affect the miscibility of individual components and final homogeneity [ 50 ]. Generally, the mutual compatibility between the base polymer and added components, including the plasticizers, is controlled in biopolymer-based films and layers.…”

Developments of biobased plasticizers for compostable polymers in the green packaging applications: A review

“…Furthermore, T g , melting point, cold crystallization, and the enthalpy of PLA decreased with increasing the content of POLYSORB ID 37. Recently, using isosorbide plasticizers with other compostable polymers such as starch, 137–140 PLA‐based systems 12,141,142 are reported where most of these studies reveled the improvement in plasticization performance required for food packaging application.The utilization of biobased plasticizers not only showed a remarkable performance that comparable to many traditional petroleum‐based plasticizers but offers additional functionality in many cases. Most of them had met the safety requirements to be used in food packaging applications.…”

“…Various efforts for producing more eco‐friendly plasticizers have been carried out by using biobased sources such as diester succinates, which display better biodegradation behavior and comparable plasticization properties to these of 2‐ethylhexyl phthalate (DEHP) 7,8 . Various types of plasticizers may be derived from biobased building blocks such as tung oil, 9,10 levulinic acid, 11 eugenol‐levulinic acid or valeric acid, 12 tartaric acid, 13 glycerol‐adipic acid, 14 2,5‐bis‐(hydroxymethyl furan) derived from crop plants, 15 5‐hydroxymethyl‐2‐furancarboxylic acid, 16 castor oil, 17,18 tributyl citrate/propargyl ether tributyl citrate/oleic acid/poly (dimethylsiloxane) diglycidyl ether terminated, 19 among others were developed. Although, the biodegradability and toxicological assays for those compounds are still limited, and their effectiveness is assessed in PVC.…”

“…These materials may act as functional additives in compostable polymers, in particular to enhance flowability, flexibility, processability, decrease hardness, and dramatically enhance elongation at break 20 . Additionally, some recent efforts demonstrate the ability of certain bioplasticizers to provide compostable polymers with dual functionality as in the study conducted by Xuan et al, 12 who developed an additive with dual function (plasticization and antimicrobial functionality), which has shown a remarkable change in mechanical properties, reduction in T g of polylactic acid (PLA) as well as antimicrobial characteristics 12 . However, the literatures still have limitation studies on the potential biodegradability to some of these plasticizers.…”