Multifunctional lignin-poly (lactic acid) biocomposites for packaging applications

Abstract

Lignin is the most abundant aromatic biopolymer with many promising features but also shortcomings as a filler in polymer blends. The main objective of this work was to improve the processability and compatibility of lignin with poly (lactic acid) (PLA) through etherification of lignin. Commercial kraft lignin (KL) and oxypropylated kraft lignin (OPKL) were blended with PLA at different weight percentages (1, 5, 10, 20, and 40%) followed by injection molding. Low lignin contents between 1 and 10% generally had a favorable impact on mechanical strength and moduli as well as functional properties of the PLA-based composites. Unmodified lignin with free phenolic hydroxyl groups rendered the composites with antioxidant activity, as measured by radical scavenging and lipid peroxidation tests. Incorporating 5–10% of KL or OPKL improved the thermal stability of the composites within the 300–350°C region. DSC analysis showed that the glass transition temperature values were systematically decreased upon addition of KL and OPKL into PLA polymer. However, low lignin contents of 1 and 5% decreased the cold crystallization temperature of PLA. The composites of KL and OPKL with PLA exhibited good stabilities in the migration test, with values of 17 mg kg−1 and 23 mg kg−1 even at higher lignin content 40%, i.e., well below the limit defined in a European standard (60 mg kg−1). These results suggest oxypropylated lignin as a functional filler in PLA for safe and functional food packaging and antioxidant applications.

Elucidating intermolecular forces to improve compatibility of kraft lignin in poly(lactic acid)

“…Furthermore, a recent prediction from Lin et al, proposed T g values for various amorphous systems and the obtained T g value exhibited an error value of around 20.5°C. Therefore, considering the predicted value of pure PLA is 359.5 K (86.4°C) which is consistent with the values obtained from our experimental value of 46.29°C and literature values of around 60°C by taking into account with the error, around 20.5°C ( Kim et al, 2017 ; Esakkimuthu et al, 2022a ). Moreover, the trend observed from the simulation for all T g values associated with the different wt% can be correlated directly to the experiments.…”

“…We obtained a Young’s modulus value of 1,400 MPa for PLA, which is lower than our previously proposed value of approximately 2,100 MPa ( Esakkimuthu et al, 2022a ). It has been noted that the mechanical properties of composites are significantly influenced by the processing methods employed during fabrication.…”

“…It is noted that the Young’s modulus obtained from the MD simulations aligns with previous literature results where composites were prepared using the extrusion method ( Gordobil et al, 2014 ; Esakkimuthu et al, 2022a ). There are disparities between the mechanical properties obtained from MD simulations and experimental values in the present study.…”

A systematic study on the processes of lignin extraction and nanodispersion to control properties and functionality

“…The small peak at 3670 cm −1 experienced by Fraun-Org, Acid-Org, and Phenol-AH is attributed to free hydroxyl groups that are not involved in hydrogen bonding and are quite common in lignin. 37 These free hydroxyl groups could be a side product from the cleavage of ether linkages during the extraction process. Organosolv lignin, however, is extracted through the dissolution of lignin under relatively milder conditions in organic solvents, sometimes with the addition of a base or an acid.…”

New Insights into Green Food Preservation: “Armored” Lignin Nanoparticles as Promising Antioxidant-cum-Antimicrobial Agents

“…For example, Esakkimuthu et al synthesized a composite material of poly­(lactic acid)/lignin, which has the ability to effectively absorb UV light. This property makes it suitable for preventing food oxidation and decomposition when used in food packaging materials . The gas barrier, antioxidant activity, and biodegradability of PHB/PHA films were significantly enhanced by incorporating lignin into PHB/PHA films, as demonstrated by Vostrejs et al The lignin-zinc oxide (LZn) hybrid particles, prepared by Xiao et al, demonstrated a strong ability to kill Escherichia coli (E.…”