Plasticized poly(lactic acid) reinforced with antioxidant covalent organic frameworks (COFs) as novel nanofillers designed for non-migrating active packaging applications

Effect of Different Porous Size of Porous Inorganic Fillers on the Encapsulation of Rosemary Essential Oil for PLA-Based Active Packaging

Essential oils are interesting active additives for packaging manufacturing as they can provide the final material with active functionalities. However, they are frequently volatile compounds and can be degraded during plastic processing. In this work Rosmarinus officinalis (RO) essential oil was encapsulated into Diatomaceous earth (DE) microparticles and into Halloysite nanotubes (HNTs) and further used to produce eco-friendly active packaging based on polylactic acid (PLA). PLA-based composites and nanocoposites films based on PLA reinforced with DE + RO and HNTs + RO, respectively, were developed by melt extrusion followed by cast-film, simulating the industrial processing conditions. As these materials are intended as active food packaging films, the obtained materials were fully characterized in terms of their mechanical, thermal and structural properties, while migration of antioxidant RO was also assessed as well as the compostability at laboratory scale level. Both DE and HNTs were able to protect the Rosmarinus officinalis (RO) from thermal degradation during processing, allowing to obtain films with antioxidant properties as demonstrated by the antioxidant assays after the materials were exposed for 10 days to a fatty food simulant. The results showed that incorporating Rosmarinus officinalis encapsulated in either DE or HNTs and the good dispersion of such particles into the PLA matrix strengthened its mechanical performance and sped up the disintegration under composting conditions of PLA, while allowing to obtain films with antioxidant properties of interest as antioxidant active food packaging materials.

Mechanical reinforcement from two-dimensional nanofillers: model, bulk and hybrid polymer nanocomposites

Thanks to their intrinsic properties, multifunctionality and unique geometrical features, two-dimensional nanomaterials have been used widely as reinforcements in polymer nanocomposites. The effective mechanical reinforcement of polymers is, however, a multifaceted problem as it depends not only on the intrinsic properties of the fillers and the matrix, but also upon a number of other important parameters. These parameters include the processing method, the interfacial properties, the aspect ratio, defects, orientation, agglomeration and volume fraction of the fillers. In this review, we summarize recent advances in the mechanical reinforcement of polymer nanocomposites from two-dimensional nanofillers with an emphasis on the mechanisms of reinforcement. Model, bulk and hybrid polymer nanocomposites are reviewed comprehensively. The use of Raman and photoluminescence spectroscopies is examined in light of the distinctive information they can yield upon stress transfer at interfaces. It is shown that the very diverse family of 2D nanofillers includes a number of materials that can attribute distrinctive features to a polymeric matrix, and we focus on the mechanical properties of both graphene and some of the most important 2D materials beyond graphene, including boron nitride, molybdenum disulphide, other transition metal dichalcogenides, MXenes and black phosphorous. In the first part of the review we evaluate the mechanical properties of 2D nanoplatelets in "model" nanocomposites. Next we examine how the performance of these materials can be optimised in bulk nanocomposites. Finally, combinations of these 2D nanofillers with other 2D nanomaterials or with nanofillers of other dimensions are assessed thoroughly, as such combinations can lead to additive or even synergistic mechanical effects. Existing unsolved problems and future perspectives are discussed.

Application of surface-modified functional packaging in food storage: A comprehensive review

Innovations in food packaging systems could meet the evolving needs of the market; emerging concepts of non-migrating technologies reduce the negative migration of preservatives from packaging materials, extend shelf life, and improve food quality and safety. Non-migratory packaging activates the surface of inert materials through pretreatment to generate different active groups. The preservative is covalently grafted with the resin of the pretreated packaging substrate through the graft polymerization of the monomer and the coupling reaction of the polymer chain. The covalent link not only provides the required surface properties of the material for a long time but also retains the inherent properties of the polymer. This technique is applied to the processing for durable, stable, and easily controllable packaging widely. This article reviews the principles of various techniques for packaging materials, surface graft modification, and performance characterization of materials after grafting modification. Potential applications in the food industry and future research trends are also discussed.

Effect of Operational Variables on Supercritical Foaming of Caffeic Acid-Loaded Poly(lactic acid)/Poly(butylene adipate-co-terephthalate) Blends for the Development of Sustainable Materials

Expanded polystyrene will account for 5.3% of total global plastic production in 2021 and is widely used for food packaging due to its excellent moisture resistance and thermal insulation. However, some of these packages are often used only once before being discarded, generating large amounts of environmentally harmful plastic waste. A very attractive alternative to the conventional methods used for polymer processing is the use of supercritical carbon dioxide (scCO2) since it has mass-transfer properties adapted to the foam morphology, generating different path lengths for the diffusion of active compounds within its structure and can dissolve a wide range of organic molecules under supercritical conditions. The objective of this research was to evaluate the effect of operational variables on the process of caffeic acid (CA) impregnation and subsequent foaming of polylactic acid (PLA) as well as two PLA/poly(butylene-co-terephthalate-adipate) (PBAT) blends using scCO2. The results showed an increase in the degree of crystallinity of the CA-impregnated samples due to the nucleation effect of the active compound. On the other hand, SEM micrographs of both films and foams showed significant differences due to the presence of PBAT and its low miscibility with PLA. Finally, the results obtained in this work contribute to the knowledge of the important parameters to consider for the implementation of the impregnation and foaming process of PLA and PLA/PBAT blends with potential use in food packaging.

Improving the functionality of biodegradable food packaging materials via porous nanomaterials

Non-biodegradability and disposal problems are the major challenges associated with synthetic plastic packaging. This review article discusses a new generation of biodegradable active and smart packaging based on porous nanomaterials (PNMs), which maintains the quality and freshness of food products while meeting biodegradability requirements. PNMs have recently gained significant attention in the field of food packaging due to their large surface area, peculiar structures, functional flexibility, and thermal stability. We present for the first time the recently published literature on the incorporation of various PNMs into renewable materials to develop advanced, environmentally friendly, and high-quality packaging technology. Various emerging packaging technologies are discussed in this review, along with their advantages and disadvantages. Moreover, it provides general information about PNMs, their characterization, and fabrication methods. It also briefly describes the effects of different PNMs on the functionality of biopolymeric films. Furthermore, we examined how smart packaging loaded with PNMs can improve food shelf life and reduce food waste. The results indicate that PNMs play a critical role in improving the antimicrobial, thermal, physicochemical, and mechanical properties of natural packaging materials. These tailor-made materials can simultaneously extend the shelf life of food while reducing plastic usage and food waste.

Plasticized Mechanical Recycled PLA Films Reinforced with Microbial Cellulose Particles Obtained from Kombucha Fermented in Yerba Mate Waste

In this study, yerba mate waste (YMW) was used to produce a kombucha beverage, and the obtained microbial cellulose produced as a byproduct (KMW) was used to reinforce a mechanically recycled poly(lactic acid) (r-PLA) matrix. Microbial cellulosic particles were also produced in pristine yerba mate for comparison (KMN). To simulate the revalorization of the industrial PLA products rejected during the production line, PLA was subjected to three extrusion cycles, and the resultant pellets (r3-PLA) were then plasticized with 15 wt.% of acetyl tributyl citrate ester (ATBC) to obtain optically transparent and flexible films by the solvent casting method. The plasticized r3-PLA-ATBC matrix was then loaded with KMW and KMN in 1 and 3 wt.%. The use of plasticizer allowed a good dispersion of microbial cellulose particles into the r3-PLA matrix, allowing us to obtain flexible and transparent films which showed good structural and mechanical performance. Additionally, the obtained films showed antioxidant properties, as was proven by release analyses conducted in direct contact with a fatty food simulant. The results suggest the potential interest of these recycled and biobased materials, which are obtained from the revalorization of food waste, for their industrial application in food packaging and agricultural films.

Rosmarinic and Glycyrrhetinic Acid-Modified Layered Double Hydroxides as Functional Additives for Poly(Lactic Acid)/Poly(Butylene Succinate) Blends

Immobilizing natural antioxidant and biologically active molecules in layered double hydroxides (LDHs) is an excellent method to retain and release these substances in a controlled manner, as well as protect them from thermal and photochemical degradation. Herein, we describe the preparation of host-guest systems based on LDHs and rosmarinic and glycyrrhetinic acids, two molecules obtained from the extraction of herbs and licorice root, respectively, with antioxidant, antimicrobial, and anti-inflammatory properties. Intercalation between the lamellae of the mono-deprotonated anions of rosmarinic and glycyrrhetinic acid (RA and GA), alone or in the presence of an alkyl surfactant, allows for readily dispersible systems in biobased polymer matrices such as poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and a 60/40 wt./wt. PLA/PBS blend. The composites based on the PLA/PBS blend showed better interphase compatibility than the neat blend, correlated with increased adhesion at the interface and a decreased dispersed phase size. In addition, we proved that the active species migrate slowly from thin films of the composite materials in a hydroalcoholic solvent, confirming the optimization of the release process. Finally, both host-guest systems and polymeric composites showed antioxidant capacity and, in the case of the PLA composite containing LDH-RA, excellent inhibitory capacity against E. coli and S. aureus.

Processing Compostable PLA/Organoclay Bionanocomposite Foams by Supercritical CO2 Foaming for Sustainable Food Packaging

This article proposes a foaming method using supercritical carbon dioxide (scCO2) to obtain compostable bionanocomposite foams based on PLA and organoclay (C30B) where this bionanocomposite was fabricated by a previous hot melt extrusion step. Neat PLA films and PLA/C30B films (1, 2, and 3 wt.%) were obtained by using a melt extrusion process followed by a film forming process obtaining films with thicknesses between 500 and 600 μm. Films were further processed into foams in a high-pressure cell with scCO2 under constant conditions of pressure (25 MPa) and temperature (130 °C) for 30 min. Bionanocomposite PLA foams evidenced a closed cell and uniform cell structure; however, neat PLA presented a poor cell structure and thick cell walls. The thermal stability was significantly enhanced in the bionanocomposite foam samples by the good dispersion of nanoclays due to scCO2, as demonstrated by X-ray diffraction analysis. The bionanocomposite foams showed improved overall mechanical performance due to well-dispersed nanoclays promoting increased interfacial adhesion with the polymeric matrix. The water uptake behavior of bionanocomposite foams showed that they practically did not absorb water during the first week of immersion in water. Finally, PLA foams were disintegrated under standard composting conditions at higher rates than PLA films, showing their sustainable character. Thus, PLA bionanocomposite foams obtained by batch supercritical foaming seem to be a sustainable option to replace non-biodegradable expanded polystyrene, and they represent a promising alternative to be considered in applications such as food packaging and other products.

Active PLA Packaging Films: Effect of Processing and the Addition of Natural Antimicrobials and Antioxidants on Physical Properties, Release Kinetics, and Compostability

The performance characteristics of polylactic acid (PLA) as an active food packaging film can be highly influenced by the incorporation of active agents (AAs) into PLA, and the type of processing technique. In this review, the effect of processing techniques and the addition of natural AAs on the properties related to PLA performance as a packaging material are summarized and described through a systematic analysis, giving new insights about the relation between processing techniques, types of AA, physical–mechanical properties, barriers, optical properties, compostability, controlled release, and functionalities in order to contribute to the progress made in designing antioxidant and antimicrobial PLA packaging films. The addition of AAs into PLA films affected their optical properties and influenced polymer chain reordering, modifying their thermal properties, functionality, and compostability in terms of the chemical nature of AAs. The mechanical and barrier performance of PLA was affected by the AA’s dispersion degree and crystallinity changes resulting from specific processing techniques. In addition, hydrophobicity and AA concentration also modified the barrier properties of PLA. The release kinetics of AAs from PLA were tuned, modifying diffusion coefficient of the AAs in terms of the different physical properties of the films that resulted from specific processing techniques. Several developments based on the incorporation of antimicrobial and antioxidant substances into PLA have displayed outstanding activities for food protection against microbial growth and oxidation.

Photocatalytic degradation of organic pollutants through conjugated poly(azomethine) networks based on terthiophene-naphthalimide assemblies

A conjugated poly(azomethine) network based on ambipolar terthiophene–naphthalimide assemblies has been synthesized and its electrochemical and UV-vis absorption properties have been investigated. The network has been found to be a promising candidate for the photocatalytic degradation of organic pollutants in aqueous media.

A conjugated two-dimensional poly(azomethine) network based on ambipolar terthiophene–naphthalimide assemblies has been synthesized and its electrochemical and UV-vis absorption properties have been investigated.

Emerging new-generation hybrids based on covalent organic frameworks for industrial applications

This review highlights the advancement of COF hybrid-based materials for diverse industrial applications.

Hybrid Biocomposites Based on Poly(Lactic Acid) and Silica Aerogel for Food Packaging Applications

Bionanocomposites based on poly (lactic acid) (PLA) and silica aerogel (SiA) were developed by means of melt extrusion process. PLA-SiA composite films were plasticized with 15 wt.% of acetyl (tributyl citrate) (ATBC) to facilitate the PLA processability as well as to attain flexible polymeric formulations for films for food packaging purposes. Meanwhile, SiA was added in four different proportions (0.5, 1, 3 and 5 wt.%) to evaluate the ability of SiA to improve the thermal, mechanical, and barrier performance of the bionanocomposites. The mechanical performance, thermal stability as well as the barrier properties against different gases (carbon dioxide, nitrogen, and oxygen) of the bionanocomposites were evaluated. It was observed that the addition of 3 wt.% of SiA to the plasticized PLA-ATBC matrix showed simultaneously an improvement on the thermal stability as well as the mechanical and barrier performance of films. Finally, PLA-SiA film formulations were disintegrated in compost at the lab-scale level. The combination of ATBC and SiA sped up the disintegration of PLA matrix. Thus, the bionanocomposites produced here show great potential as sustainable polymeric formulations with interest in the food packaging sector.

Nanoscale covalent organic frameworks as theranostic platforms for oncotherapy: synthesis, functionalization, and applications

Cancer nanomedicine is one of the most promising domains that has emerged in the continuing search for cancer diagnosis and treatment. The rapid development of nanomaterials and nanotechnology provide a vast array of materials for use in cancer nanomedicine. Among the various nanomaterials, covalent organic frameworks (COFs) are becoming an attractive class of upstarts owing to their high crystallinity, structural regularity, inherent porosity, extensive functionality, design flexibility, and good biocompatibility. In this comprehensive review, recent developments and key achievements of COFs are provided, including their structural design, synthesis methods, nanocrystallization, and functionalization strategies. Subsequently, a systematic overview of the potential oncotherapy applications achieved till date in the fast-growing field of COFs is provided with the aim to inspire further contributions and developments to this nascent but promising field. Finally, development opportunities, critical challenges, and some personal perspectives for COF-based cancer therapeutics are presented.