Natural Extracts and Their Applications in Polymer-Based Active Packaging: A Review.

At a time when food safety awareness is increasing, attention is paid not only to food and additives but also to packaging materials. Most current food packaging is usually made of traditional petroleum-based polymeric materials, which are not biodegradable and have adverse effects on the environment and health. In this context, the development of new non-toxic and biodegradable materials for extending the best-before date of food is receiving increasing attention. In addition, additives in packaging materials may migrate outward, resulting in contact with food. For this reason, additives are also seen as a transition from synthetic additives to natural extracts. Active extracts from animals and plants having good antioxidant and antibacterial properties are also beneficial for human health. It is indisputable that active extracts are ideal substitutes for synthetic additives. Polymer packaging materials combined with active extracts not only maintain their original mechanical and optical properties and thermal stability but also endow polymers with new functions to extend the shelf life of food. This review paper provides an overview of this promising natural extract-containing polymer-based active packaging, with a focus on plant essential oils (containing phenolics, monoterpenes, terpene alcohols, terpene ketones, and aldehydes), pigments (procyanidins), vitamins (vitamin B), and peptides (nisin). In particular, this paper covers the research progress of such active extracts, in single or compound forms, combined with diverse polymers (mostly biopolymers) for food packaging applications with particular focus on the antioxidant and antibacterial properties of packaging materials.

Modified Biomass-Reinforced Polylactic Acid Composites.

Polylactic acid (PLA), as a renewable and biodegradable green polymer material, is hailed as one of the most promising biopolymers capable of replacing petroleum-derived polymers for industrial applications. Nevertheless, its limited toughness, thermal stability, and barrier properties have restricted its extensive application. To address these drawbacks in PLA, research efforts have primarily focused on enhancing its properties through copolymerization, blending, and plasticization. Notably, the blending of modified biomass with PLA is expected not only to effectively improve its deficiencies but also to maintain its biodegradability, creating a fully green composite with substantial developmental prospects. This review provides a comprehensive overview of modified biomass-reinforced PLA, with an emphasis on the improvements in PLA's mechanical properties, thermal stability, and barrier properties achieved through modified cellulose, lignin, and starch. At the end of the article, a brief exploration of plasma modification of biomass is presented and provides a promising outlook for the application of reinforced PLA composite materials in the future. This review provides valuable insights regarding the path towards enhancing PLA.

Functional electrospun nanofibers: fabrication, properties, and applications in wound-healing process.

Electrostatic spinning as a technique for producing nanoscale fibers has recently attracted increasing attention due to its simplicity, versatility, and loadability. Nanofibers prepared by electrostatic spinning have been widely studied, especially in biomedical applications, because of their high specific surface area, high porosity, easy size control, and easy surface functionalization. Wound healing is a highly complex and dynamic process that is a crucial step in the body's healing process to recover from tissue injury or other forms of damage. Single-component nanofibers are more or less limited in terms of structural properties and do not fully satisfy various needs of the materials. This review aims to provide an in-depth analysis of the literature on the use of electrostatically spun nanofibers to promote wound healing, to overview the infinite possibilities for researchers to tap into their biomedical applications through functional composite modification of nanofibers for advanced and multifunctional materials, and to propose directions and perspectives for future research.

Bio-based epoxidized soybean oil branched cardanol ethers as compatibilizers of polybutylene succinate (PBS)/polyglycolic acid (PGA) blends.

Blending poly(butylene succinate) (PBS) with another biodegradable polymer, polyglycolic acid (PGA), has been demonstrated to improve the barrier performance of PBS. However, blending these two polymers poses a challenge because of their incompatibility and large difference of their melting temperatures. In this study, we synthesized epoxidized soybean oil branched cardanol ether (ESOn-ECD), a bio-based and environmentally friendly compatibilizer, and used it to enhance the compatibility of PBS/PGA blends. It was demonstrated that the terminal carboxyl/hydroxyl groups of PBS and PGA can react with ESOn-ECD in situ, leading to branching and chain extension of PBS and PGA. The addition of ESO3-ECD to the blend considerably diminished the dispersed phase of PGA. Specifically, in comparison to the PBS/PGA blend without a compatibilizer, the diameter of the PGA phase decreased from 2.04 µm to 0.45 µm after the addition of 0.7 phr of ESO3-ECD, and the boundary between the two phases became difficult to distinguish. Additionally, the mechanical properties of the blends were improved after addition of ESO3-ECD. This research expands the potential applications of these materials and promotes the use of bio-based components in blend formulations.

Development of PLA/Lignin Bio-Composites Compatibilized by Ethylene Glycol Diglycidyl Ether and Poly (ethylene glycol) Diglycidyl Ether.

Poly (lactic acid) (PLA) is a promising green substitute for conventional petroleum-based plastics in a variety of applications. However, the wide application of PLA is still limited by its disadvantages, such as slow crystallization rate, inadequate gas barrier, thermal degradation, etc. In this study, lignin (1, 3, 5 PHR) was incorporated into PLA to improve the thermal, mechanical, and barrier properties of PLA. Two low-viscosity epoxy resins, ethylene glycol diglycidyl ether (EGDE) and poly (ethylene glycol) diglycidyl ether (PEGDE), were used as compatibilizers to enhance the performance of the composites. The addition of lignin improved the onset degradation temperature of PLA by up to 15 °C, increased PLA crystallinity, improved PLA tensile strength by approximately 15%, and improved PLA oxygen barrier by up to 58.3%. The addition of EGDE and PEGDE both decreased the glass transition, crystallization, and melting temperatures of the PLA/lignin composites, suggesting their compatabilizing and plasticizing effects, which contributed to improved oxygen barrier properties of the PLA/lignin composites. The developed PLA/lignin composites with improved thermal, mechanical, and gas barrier properties can potentially be used for green packaging applications.

Molecular Dynamics Simulation of Polymer Nanocomposites with Supramolecular Network Constructed via Functionalized Polymer End-Grafted Nanoparticles.

Since the proposal of self-healing materials, numerous researchers have focused on exploring their potential applications in flexible sensors, bionic robots, satellites, etc. However, there have been few studies on the relationship between the morphology of the dynamic crosslink network and the comprehensive properties of self-healing polymer nanocomposites (PNCs). In this study, we designed a series of modified nanoparticles with different sphericity (η) to establish a supramolecular network, which provide the self-healing ability to PNCs. We analyzed the relationship between the morphology of the supramolecular network and the mechanical performance and self-healing behavior. We observed that as η increased, the distribution of the supramolecular network became more uniform in most cases. Examination of the segment dynamics of polymer chains showed that the completeness of the supramolecular network significantly hindered the mobility of polymer matrix chains. The mechanical performance and self-healing behavior of the PNCs showed that the supramolecular network mainly contributed to the mechanical performance, while the self-healing efficiency was dominated by the variation of η. We observed that appropriate grafting density is the proper way to effectively enhance the mechanical and self-healing performance of PNCs. This study provides a unique guideline for designing and fabricating self-healing PNCs with modified Nanoparticles (NPs).

Grafting Polymerization of Long-Chain Hydrophobic Acrylic Monomer onto Lignin and Its Application in Poly(Lactic Acid)-Based Wholly Green UV Barrier Composite Films.

The development of low-cost and high-performance bio-based composites derived from forestry waste lignin and polylactic acid has emerged as a topic of central attention. However, the weak compatibility between lignin and polylactic acid often resulted in high brittleness of the composites. Graft copolymerization is not only the most effective way to modify lignin but also can significantly improve the compatibility of lignin and polylactic acid. In this study, bio-based monomer lauryl methacrylate was grafted onto lignin by feasible radical polymerization to prepare lignin graft copolymers with excellent thermal stability and hydrophobicity, which are expected to improve the compatibility with polylactic acid. Wholly bio-based composites were prepared by compounding this graft copolymer with polylactic acid. The results showed that the crystallization ability of the composite was improved, and the highest crystallinity was increased from 6.42% to 17.46%. With addition of LG-g-PLMA lower than 9%, the thermal stability of the composites was slightly improved. At 5% copolymer addition, the elongation at break and tensile toughness of the composites increased by 42% and 36%, respectively. Observation of the frozen fracture surface of the composite by SEM found that wire drawing and ductile deformation appeared when a small amount of LG-g-PLMA was added. The thus prepared composites also showed excellent UV barrier properties. This approach provides a new idea for the high-value application of lignin.

Molecular dynamics simulation insight into topological structure dependence of self-healing polymer nanocomposites.

Polymer nanocomposites (PNCs), which exhibit excellent mechanical properties through the incorporation of fillers into polymers, have been extensively studied to achieve enhanced self-healing capability for their next-generation development. However, there is still a lack of investigation into the influence of the topological structures of nanoparticles (NPs) on the self-healing capability of PNCs. In this study, we utilized coarse-grained molecular dynamics simulations (CGMDs) to construct a series of PNC systems composed of NPs with different topological structures, including Linear, Ring, and Cross topologies. We employed non-bonding interaction potentials to examine the interactions between the polymer and NPs, and varied the parameters to simulate different functional groups. Our results indicate that the stress-strain curves and the rate of performance loss validate that the Linear structure is the optimal topology for mechanical reinforcement and self-healing properties. By analyzing the stress heat map during stretching, we observed that the Linear structure NPs experience significant stress, allowing the matrix chains to dominate in small recoverable deformations during stretching. It can be speculated that NPs oriented in the direction of extrusion are more effective than others in enhancing performance. Overall, this work provides valuable theoretical guidance and a novel strategy for designing and manipulating high-performance, self-healing PNCs.

Polylactic Acid/Lignin Composites: A Review.

With the gradual depletion of petroleum resources and the increasing global awareness of environmental protection, biodegradable plastics are receiving more and more attention as a green substitute for traditional petroleum-based plastics. Poly (lactic acid) is considered to be the most promising biodegradable material because of its excellent biodegradability, biocompatibility, and good processability. However, the brittleness and high cost limit its application in more fields. Lignin, as the second largest renewable biopolymer in nature after cellulose, is not only rich in reserves and low in cost, but it also has an excellent UV barrier, antioxidant activity, and rigidity. The molecular structure of lignin contains a large number of functional groups, which are easy to endow with new functions by chemical modification. Currently, lignin is mostly treated as waste in industry, and the value-added utilization is insufficient. The combination of lignin and poly (lactic acid) can on the one hand solve the problems of the high cost of PLA and less efficient utilization of lignin; on the other hand, the utilization of lignocellulosic biomass in compounding with biodegradable synthetic polymers is expected to afford high-performance wholly green polymer composites. This mini-review summarizes the latest research achievements of poly (lactic acid)/lignin composites. Emphasis was put on the influence of lignin on the mechanical properties of its composite with poly (lactic acid), as well as the compatibility of the two components. Future research on these green composites is also prospected.

Enhancing Hydrophobicity and Oxygen Barrier of Xylan/PVOH Composite Film by 1,2,3,4-Butane Tetracarboxylic Acid Crosslinking.

Hemicellulose has potential advantages in food packaging because of its abundant reserves, degradability and regeneration. However, compared with fossil-derived plastic films, hemicellulose-based films show inferior hydrophobicity and barrier properties because of their low degree of polymerization and strong hydrophilicity. Focusing on such issues, this work covers the modification of a xylan/polyvinyl alcohol (PVOH) film using 1,2,3,4-butane tetracarboxylic acid (BTCA) as esterifying agent. The thus prepared composite film was more compact owing to the esterification reaction with xylan and PVOH forming a crosslinked network structure and reducing the distance between molecular chains. The results showed that BTCA had a positive effect on the oxygen barrier, hydrophobicity and mechanical properties of the composite film. The tensile strength of the xylan/PVOH composite film with 10% BTCA content increased from 11.19 MPa to 13.99 MPa. A 20% BTCA loading resulted in an increase in the contact angle of the composite film from 87.1° to 108.2°, and a decrease in the oxygen permeability from 2.11 to 0.43 (cm3·µm)/(m2·d·kPa), corresponding to increase in the contact angle by 24% and a decrease in oxygen permeability by 80%. The overall performance enhancement indicates the potential application of such composites as food packaging.

Fabrication of well-dispersed cellulose nanocrystal reinforced biobased epoxy composites using reversibility of covalent adaptable network.

Cellulose nanocrystal (CNC) shows great potential in reinforced composites but it is difficult to disperse in epoxy thermosets due to its poor dispersity in epoxy monomers. Herein, we reported a novel approach to disperse CNC in epoxidized soybean oil (ESO)-derived epoxy thermosets uniformly by using the reversibility of dynamic imine-containing ESO-derived covalent adaptable network (CAN). The crosslinked CAN was deconstructed by an exchange reaction with ethylenediamine (EDA) in dimethyl formamide (DMF), leading to a solution of deconstructed CAN with plenty of hydroxyl and amino groups, which could form strong hydrogen bonds with hydroxyl groups of CNC and thus facilitated and stabilized dispersion of CNC in the deconstructed CAN solution. Epoxy composite with well-dispersed CNC was finally achieved by a reformation of CAN through the removal of DMF and EDA. In this way, the epoxy composites with CNC content up to 30 wt% were successfully prepared and showed drastically reinforced mechanical properties. The tensile strength and Young's modulus of the CAN were improved by up to ∼70 % and ∼45 times with the incorporation of 20 and 30 wt% CNC, respectively. The composites showed excellent reprocessability without significant loss in mechanical properties after reprocessing.

Synthesis and Characterization of a Novel Composite Edible Film Based on Hydroxypropyl Methyl Cellulose Grafted with Gelatin.

A novel composite edible film was synthesized by grafting gelatin chain onto hydroxypropyl methyl cellulose (HPMC) in the presence of glycerol (used as a plasticizer) using a solution polymerization technique. The reaction was carried out in homogeneous aqueous medium. Thermal properties, chemical structure, crystallinity, surface morphology, and mechanical and hydrophilic performance changes of HPMC caused by the addition of gelatin were investigated by differential scanning calorimetry, thermogravimetric, Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, universal testing machine and water contact angle. The results shows that HPMC and gelatin are miscible and the hydrophobic property of the blending film can be enhanced with the introduction of the gelatin. Moreover, the HPMC/gelatin blend films are flexible, and exhibit excellent compatibility, good mechanical properties and also thermal stability, and could be promising candidates for food packaging materials.

A Hydrotalcite-Based PET Composites with Enhanced Properties for Liquid Milk Packaging Applications.

In the present work, the two-phase mixture (HTLc) of hydrotalcite and its oxide were used to improve the barrier properties, UV resistance and antimicrobial activity of Poly(ethylene terephthalate) (PET) for their application in liquid milk packaging. Firstly, CaZnAl-CO3-LDHs with a two-dimensional layered structure were synthesized by hydrothermal method. CaZnAl-CO3-LDHs precursors were characterized by XRD, TEM, ICP and dynamic light scattering. A series of PET/HTLc composite films were then prepared, characterized by XRD, FTIR and SEM, and a possible mechanism of the composite films with hydrotalcite was proposed. Barrier properties to water vapor and oxygen have been studied in PET nanocomposites, as well as their antibacterial efficacy by the colony technique and their mechanical properties after exposure to UV irradiation for 24 h. By the presence of 1.5 wt% HTLc in the PET composite film, the oxygen transmission rate (OTR) was reduced by 95.27%, the water vapor transmission rate was reduced by 72.58% and the inhibition against Staphylococcus aureus and Escherichia coli was 83.19% and 52.75%. Moreover, a simulation of the migration process in dairy products was used to prove the relative safety. This research first proposes a safe technique for fabricating hydrotalcite-based polymer composites with a high gas barrier, UV resistance and effective antibacterial activity.

Fully biobased poly(lactic acid)/lignin composites compatibilized by epoxidized natural rubber.

Biobased poly(lactic acid)/lignin (PLA/lignin) composites are limited by poor mechanical properties resulted from poor compatibility and low interfacial adhesion. Herein, we reported a novel approach to improve compatibility and interfacial adhesion of PLA/lignin composites via reactive compatibilization with epoxidized natural rubber (ENR) as a compatibilizer. Interfacial tension calculation indicated that lignin tended to act as interfacial phase between PLA and ENR, but morphology analysis demonstrated lignin was wrapped with a layer of ENR and dispersed in PLA matrix, which was attributed to the interfacial reaction of ENR with both PLA and lignin. The interfacial reaction was confirmed by Fourier transform infrared spectroscopy. The compatibility and interfacial adhesion between PLA and lignin were improved significantly by incorporation and increase in the content of ENR, as evidenced by the reduced interfacial gaps, blurry phase boundaries, and enhanced elastic response. As such, the mechanical properties of PLA/lignin composites were enhanced significantly. The tensile strength and elongation at break of PLA/lignin (W/W, 80/20) were improved by 15 % and 77 %, respectively, with the incorporation of only 1 wt% ENR. We believe this approach to compatibilize PLA/lignin composites is promising because it would not require costly modification of lignin and would not compromise the sustainability of composites.

Elucidation of Non-Intentionally Added Substances from Plant Fiber/Plastic Composites by UPLC-QTOF/MS.

Plant fiber/plastic composites (PPCs) have been widely used in food contact materials (FCMs) for many benefits, such as their claimed better environmental footprint compared to conventional plastics. However, their safety is still not fully understood and must be comprehensively evaluated. Non-volatiles extracted from six PPCs with different plant fibers and polymer matrices were characterized by employing ultra-high-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry in combination with various spectral libraries and manual elucidation, taking into account spectral similarity and characteristic product ions. A total of 115 compounds were tentatively identified, 50 of which were oligomers or their derivatives from the sample with polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT) as the polymer matrix, and some of them were Cramer rules class III substances based on the threshold of toxicological concern (TTC). Seven reaction products between PLA and PBAT monomers, as well as four derivatives of melamine, were elucidated and well detailed for the first time. In addition, bisphenol S was detected in all samples even though its origin remains to be further explored. Isoprothiolane, as an insecticide and fungicide used to control a range of rice pests, was identified in the sample with rice husk as fillers, experimentally confirming the presence of agrochemicals in samples containing plant fibers.

Effects of Quercetin and Organically Modified Montmorillonite on the Properties of Poly(butylene adipate-co-terephthalate)/Thermoplastic Starch Active Packaging Films.

The poly(butylene adipate-co-terephthalate) (PBAT)/thermoplastic starch (TPS) film stands out owing to its acceptable price, low impact on the environment, and excellent mechanical properties. The main objective of this study was to improve the antioxidant properties of the PBAT/TPS film by incorporation of quercetin (Q) through the extrusion blow process. Another specific objective was to incorporate the organically modified montmorillonite (OMMT) to prolong the release of Q and improve the poor barrier properties of the PBAT/TPS/Q film. The films were analyzed in terms of their morphology, mechanical properties, gas and water barrier properties, and antioxidant and anti-UV properties. Optimization of the OMMT content resulted in a fiber-like, co-continuous morphology of the PBAT/TPS/Q film. The incorporation of quercetin enhanced the antioxidant and anti-UV properties of the PBAT/TPS film, while OMMT improved the mechanical properties, ultraviolet barriers, and gas and water barrier properties. The results show that the films incorporating Q and OMMT provided the oxygen and water barrier by up to 94 and 54%, respectively. Also, the amount of polymer required for 50% 2,2-diphenyl-1-picrylhydrazyl (DPPH) inhibition is as low as 0.03 g, and the UV transmission rate was reduced by about 50%. Moreover, PBAT/TPS/Q/OMMT films successfully delayed the decay of the banana and blueberry due to their excellent antioxidant properties and suitable water vapor permeability.

Effect of Biomass as Nucleating Agents on Crystallization Behavior of Polylactic Acid.

Polylactic acid (PLA) is one of the most productive biodegradable materials. Its bio-based source makes it truly carbon neutral. However, PLA is hard to crystallize as indicated by a low crystallization rate and a low crystallinity under conventional processing conditions, which limits its wider application. One of the most effective ways to enhance the crystallization ability of PLA is to add nucleating agents. In the context of increasing global environmental awareness and the decreasing reserves of traditional petroleum-based materials, biomass nucleating agents, compared with commonly used petroleum-based nucleating agents, have received widespread attention in recent years due to their abundance, biodegradability and renewability. This paper summarizes the research progress on biomass nucleating agents for regulating the crystallization behavior of polylactic acid. Examples of biomass nucleating agents include cellulose, hemicellulose, lignin, amino acid, cyclodextrins, starch, wood flour and natural plant fiber. Such green components from biomass for PLA are believed to be a promising solution for the development of a wholly green PLA-based system or composites.

Recent Advances in PLA-Based Antibacterial Food Packaging and Its Applications.

In order to reduce environmental pollution and resource waste, food packaging materials should not only have good biodegradable ability but also effective antibacterial properties. Poly(lactic acid) (PLA) is the most commonly used biopolymer for food packaging applications. PLA has good physical properties, mechanical properties, biodegradability, and cell compatibility but does not have inherent antibacterial properties. Therefore, antibacterial packaging materials based on PLA need to add antibacterial agents to the polymer matrix. Natural antibacterial agents are widely used in food packaging materials due to their low toxicity. The high volatility of natural antibacterial agents restricts their application in food packaging materials. Therefore, appropriate processing methods are particularly important. This review introduces PLA-based natural antibacterial food packaging, and the composition and application of natural antibacterial agents are discussed. The properties of natural antibacterial agents, the technology of binding with the matrix, and the effect of inhibiting various bacteria are summarized.

In Situ Formation of Microfibrillar PBAT in PGA Films: An Effective Way to Robust Barrier and Mechanical Properties for Fully Biodegradable Packaging Films.

Poly(glycolic acid) (PGA) is a semicrystalline biodegradable polyester with high gas barrier properties. However, due to its poor processability and low ductility, PGA could hardly find applications in the packaging field. Here, a strategy was adopted for in situ generation of high-aspect-ratio flexible microfibrils with strong interface affinity for the PGA matrix. Because poly(butylene adipate-co-terephthalate) (PBAT) possesses impressive ductility, it was selected as the "fibrillar toughening phase" to enhance the ductility of PGA. Moreover, a chain extender was used to enhance the interfacial adhesion between the two polymers. The extrusion blown film technique was then used to develop fully biodegradable PGA/PBAT films with a superior combination of excellent barrier performance and robust mechanical properties. The PBAT phase can in situ form microfibrils under the influence of extensional flow. Simultaneously, the synergetic function of the extensional flow field could effectively promote the motion of the PGA molecular chain to develop an oriented crystalline microstructure. Because of the aligned oriented lamellar crystal of PGA and oriented PBAT fibril structures serving as robust "barrier walls" 60PGA/ADR blown films demonstrated dramatically improved resistance to oxygen and water vapor, with 59 and 44 times lower oxygen permeability and water vapor permeability, respectively, when compared to the neat PBAT blown film. As a result, PGA/PBAT blown films offer a variety of benefits, including superior ductility, toughness, and a strong gas barrier property. The potential of these films to degrade makes them a viable contender for replacing classical nondegradable packing films.

Recent Advances in Cellulose-Based Hydrogels for Tissue Engineering Applications.

In recent years, cellulose has attracted much attention because of its excellent properties, such as its hydrophilicity, mechanical properties, biodegradability, biocompatibility, low cost and low toxicity. In addition, cellulose and its derivatives contain abundant hydrophilic functional groups (such as hydroxyl, carboxyl and aldehyde groups), which are good raw materials for synthesizing biocompatible hydrogels. In this paper, the application prospects of cellulose and its derivatives-based hydrogels in biomedical tissue engineering are summarized and discussed through the analysis of recent research. Firstly, we discuss the structure and properties of cellulose, nano celluloses (NC) from different sources (including cellulose nanocrystals (CNC), cellulose nanofibrils (CNF) and bacterial nano celluloses (BNC)) and cellulose derivatives (including cellulose ethers and cellulose esters) obtained by different modification methods. Then, the properties and preparation methods of physical and chemical cellulose hydrogels are described, respectively. The application of cellulose-based hydrogels as a tissue engineering scaffold (skin, bone and cartilage) in the biomedical field is introduced. Finally, the challenges and prospects of cellulose-based hydrogels in tissue engineering are summarized.