Modified lignin nanoparticles for composite and bio-based/Cu packaging applications

Project Information

PACK-NIN

Grant agreement ID: 101031402

DOI

10.3030/101031402

Project terminated on 28 February 2023

EC signature date 4 March 2021

Start date 1 April 2021

End date 31 March 2023

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 162 040,32

EU contribution

€ 162 040,32

Coordinated by

INNORENEW COE CENTER ODLICNOSTI ZA RAZISKAVE IN INOVACIJE NA PODROCJU OBNOVLJIVIH MATERIALOV IN ZDRAVEGA BIVANJSKEGA OKOLJA
Slovenia

Periodic Reporting for period 1 - PACK-NIN (Modified lignin nanoparticles for composite and bio-based/Cu packaging applications)

Reporting period: 2021-04-01 to 2023-03-31

Summary of the context and overall objectives of the project

The consumption of polymers has grown enormously in the last twenty years, with packaging now accounting for 42 percent of all plastics used worldwide. The extensive use of polymers has had a significant impact on the environment, both on land and in water. While sustainable polymers made from green raw materials like PLA offer a more environmentally friendly alternative, they are often more expensive compared to unsustainable plastic packaging made from polypropylene (PP) and polyethylene (PE). However, PLA provides a more sustainable packaging solution as it is a biopolymer derived from natural sources.
Despite its advantages, PLA faces challenges such as higher costs, poor thermal stability, and slow crystallization, which make it less suitable for long-term food packaging. These limitations can be addressed by incorporating bio-based polymers such as lignin into the PLA matrix.
Lignin, an underutilized by-product obtained from agriculture and forestry biorefineries, poses compatibility issues with the PLA matrix due to its polar functional groups. However, modifying the polar groups in lignin can improve its compatibility with PLA and enhance the mechanical and physicochemical properties of PLA-based biocomposites for packaging applications.
The specific objectives of the project are as follows:
i) Develop novel modification methods (etherification-oxypropylation and esterification with 4-hydroxybenzoic acid) and modified lignin nanoparticles (MLNPs) synthesis for sulfur (kraft) and sulfur-free lignin (Organosolv, soda). The compatibility of these modified lignins with PLA polymer will be compared with the traditional acetylation method.
ii) Enhance PLA packaging composite materials by incorporating modified lignin (PLA/ML) and MLNPs (PLA/MLNPs) and investigate their resulting mechanical and physicochemical properties.
iii) Establish and optimize a novel synthesis route for producing PLA/ML-Cu composites and PLA/MLNP-Cu composites.
iv) Evaluate the antimicrobial activity of the synthesized composites against E. Coli and S. aureus to explore potential end-user applications.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Three different sources of technical lignin (Kraft, Organosolv-ORG, and Protobind lignin - PB) were subjected to modification processes, including acetylation, oxypropylation, and hydroxybenzoylation, in order to alter their chemical structure and enhance compatibility with PLA. Lignin nanoparticles were produced using the solvent-shifting method, with Kraft lignin showing more uniform-sized particles averaging 75 nm compared to PB and ORG. The results indicated that oxypropylation and hydroxybenzoylation reactions were more effective with Kraft lignin than with the other lignin samples (ORG and PB). Based on these findings, PLA composites were prepared using Kraft lignin and oxypropylated Kraft lignin at various weight percentages (1%, 5%, 10%, 20%, and 40%) within the PLA matrix.
Regarding mechanical properties, the addition of more than 10% lignin in PLA matrix resulted in a reduction in tensile strength and elongation at the breakpoint. This can be attributed to increased interaction between stress concentration zones around lignin particles at higher lignin content, leading to diminished mechanical properties.
Unmodified Kraft lignin exhibited higher antioxidant properties and reduced lipid oxidation compared to the modified (oxypropylated) lignin. Migration studies showed that the levels of lignin-derived migratory substances remained below 8.5 mg kg-1 when the lignin content was 10% or less, which is lower than the overall migration limit (60 mg kg-1) for food contact materials. A fungal-based degradation study using Trametes Versicolor was conducted to evaluate the biodegradation of the synthesized composites, with FT-IR and DSC analyses confirming the physical and chemical changes that occurred in the composites.
The prepared nanoparticles (Kraft, oxypropylated Kraft, and hydroxybenzoylated Kraft lignin) were incorporated into the PLA matrix, and their mechanical properties were investigated. The results indicated higher Young's modulus and reduced tensile strength compared to unmodified lignin nanoparticles. Among the different sources, Kraft and PB lignin nanoparticles exhibited better compatibility without aggregation when combined with PLA, while ORG lignin showed poor compatibility and mechanical properties due to its non-uniform particle size.
Copper nanoparticles were synthesized using the NaBH4 method. The mechanical and physical properties of PLA/lignin/Cu and PLA/modified lignin/Cu composite films were analyzed using tensile tests, TGA, and DSC analysis. The antimicrobial activity of the casted composites (5% and 10% lignin-PLA with Cu weight of 5% and 7.5%) was evaluated against food-borne pathogenic bacteria, with higher inhibition efficiency observed against E. coli compared to slight inhibition growth in S. aureus.
The PACK-NIN project was disseminated at an international level to scientific peers through an open-access publication in a peer-reviewed international journal. Two additional publications have been submitted and are currently under peer review, with two publications currently being prepared. During the project, the ER organized ten online webinars, and the presentations can be found on the InnoRenew YouTube channel. As part of the project, the ER conducted a secondment at Stockholm University's Sustainable Materials Chemistry department.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The PACK-NIN project aimed to develop lignin-based PLA composite materials for sustainable packaging applications, promoting the valorization of lignin by incorporating it into the PLA polymer to reduce costs and improve physical and mechanical properties. Anti-oxidation, lipid oxidation, biodegradation, and antimicrobial tests were conducted, and all these studies confirmed the suitability of lignin for use in food-based packaging, with an optimum content of 10% by weight.
To assess people's acceptance of color variation in the material after lignin addition, a survey was conducted, presenting participants with a picture of the material and asking for their acceptance rating. Interestingly, most survey participants were not greatly concerned about the color change and readily accepted it, recognizing the importance and sustainability of packaging. People placed high importance on the safety, recyclability, biodegradability, reusability, source, and price of the material (above 3.5 out of 5). Medium importance was given to permeability, durability, and flexibility (above 2.5 out of 5), while less importance was given to smoothness, transparency, and color (above 1.5 out of 5) of the material.
Overall, the PACK-NIN project advocated for the utilization of underutilized materials like lignin from biorefineries in value-added applications, which significantly contribute to the development of potential applications in various sectors, including polymer composites for medical applications. By replacing fossil-fuel-based resources with biobased materials like lignin, the project addressed global climate concerns, recyclability, and reusability, which are directly linked to society. The comprehensive study on the valorization of lignin with different modifications, as well as its combination with PLA and Cu, was made possible through the fellowship. The achievements of the PACK-NIN project can be integrated and extended in the market to further advance a sustainable bioeconomy and support EU initiatives.

The logo of the PACK-NIN project

Antibacterial activity of Lignin/PLA/Cu composites in E. Coli media

European Researchers’ Night

Survey result: Colours of packaging material. To what extent are these options acceptable to you?

The pages of PACK-NIN project website