Electrospun Nanosystems Based on PHBV and ZnO for Ecological Food Packaging

Fabrication of Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)/ZnO Nanocomposite Films for Active Packaging Applications: Impact of ZnO Type on Structure-Property Dynamics

Bio-based and biodegradable polyhydroxyalkanoates (PHAs) have great potential as sustainable packaging materials. The incorporation of zinc oxide nanoparticles (ZnO NPs) could further improve their functional properties by providing enhanced barrier and antimicrobial properties, although current literature lacks details on how the characteristics of ZnO influence the structure-property relationships in PHA/ZnO nanocomposites. Therefore, commercial ZnO NPs with different morphologies (rod-like, spherical) and silane surface modification are incorporated into poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) via extrusion and compression molding. All ZnO NPs are homogeneously distributed in the PHBHHx matrix at 1, 3 and 5 wt.%, but finer dispersion is achieved with modified ZnO. No chemical interactions between ZnO and PHBHHx are observed due to a lack of hydroxyl groups on ZnO. The fabricated nanocomposite films retain the flexible properties of PHBHHx with minimal impact of ZnO NPs on crystallization kinetics and the degree of crystallinity (53 to 56%). The opacity gradually increases with ZnO loading, while remaining translucent up to 5 wt.% ZnO and providing an effective UV barrier. Improved oxygen barrier and antibacterial effects against S. aureus are dependent on the intrinsic characteristics of ZnO rather than its morphology. We conclude that PHBHHx retains its favorable processing properties while producing nanocomposite films that are suitable as flexible active packaging materials.

Electrospun Nanofibers for Functional Food Packaging Application

With the strengthening of the public awareness of food safety and environmental protection, functional food packaging materials have received widespread attention. Nanofibers are considered as promising packaging materials due to their unique one-dimensional structure (high aspect ratio, large specific surface area) and functional advantages. Electrospinning, as a commonly used simple and efficient method for preparing nanofibers, can obtain nanofibers with different structures such as aligned, core-shell, and porous structures by modifying the devices and adjusting the process parameters. The selection of raw materials and structural design of nanofibers can endow food packaging with different functions, including antimicrobial activity, antioxidation, ultraviolet protection, and response to pH. This paper aims to provide a comprehensive review of the application of electrospun nanofibers in functional food packaging. Advances in electrospinning technology and electrospun materials used for food packaging are introduced. Moreover, the progress and development prospects of electrospun nanofibers in functional food packaging are highlighted. Meanwhile, the application of functional packaging based on nanofibers in different foods is discussed in detail.

Enhanced Plasmonic Photocatalysis of Au-Decorated ZnO Nanocomposites

The rapid development of technological processes in various industrial fields has led to surface water pollution with different organic pollutants, such as dyes, pesticides, and antibiotics. In this context, it is necessary to find modern, environmentally friendly solutions to avoid the hazardous effects on the aquatic environment. The aim of this paper is to improve the photocatalytic performance of zinc oxide (ZnO) nanoparticles by using the plasmonic resonance induced by covering them with gold (Au) nanoparticles. Therefore, we evaluate the charge carriers’ behavior in terms of optical properties and reactive oxygen species (ROS) generation. The ZnO-Au nanocomposites were synthesized through a simple chemical protocol in multiple steps. ZnO nanoparticles (NPs) approximately 20 nm in diameter were prepared by chemical precipitation. ZnO-Au nanocomposites were obtained by decorating the ZnO NPs with Au at different molar ratios through a reduction process. X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) confirmed the simultaneous presence of hexagonal ZnO and cubic Au phases. The optical investigations evidenced the existence of a band-gap absorption peak of ZnO at 372 nm, as well as a surface plasmonic band of Au nanoparticles at 573 nm. The photocatalytic tests indicated increased photocatalytic degradation of the Rhodamine B (RhB) and oxytetracycline (OTC) pollutants under visible light irradiation in the presence of ZnO-Au nanocomposites (60–85%) compared to ZnO NPs (43%). This behavior can be assigned to the plasmonic resonance and the synergetic effects of the individual constituents in the composite nanostructures. The spin-trapping experiments showed the production of ROS while the nanostructures were in contact with the pollutants. This study introduces new strategies to adjust the efficiency of photocatalytic devices by the combination of two types of nanostructures with synergistic functionalities into one single entity. ZnO-Au nanocomposites can be used as stable photocatalysts with excellent reusability and possible industrial applications.

Photoluminescence and Photocatalytic Properties of MWNTs Decorated with Fe-Doped ZnO Nanoparticles

The present work reports the photoluminescence (PL) and photocatalytic properties of multi-walled carbon nanotubes (MWCNTs) decorated with Fe-doped ZnO nanoparticles. MWCNT:ZnO-Fe nanocomposite samples with weight ratios of 1:3, 1:5 and 1:10 were prepared using a facile synthesis method. The obtained crystalline phases were evidenced by X-ray diffraction (XRD). X-ray Photoelectron spectroscopy (XPS) revealed the presence of both 2+ and 3+ valence states of Fe ions in a ratio of approximately 0.5. The electron paramagnetic resonance EPR spectroscopy sustained the presence of Fe³⁺ ions in the ZnO lattice and evidenced oxygen vacancies. Transmission electron microscopy (TEM) images showed the attachment and distribution of Fe-doped ZnO nanoparticles along the nanotubes with a star-like shape. All of the samples exhibited absorption in the UV region, and the absorption edge was shifted toward a higher wavelength after the addition of MWCNT component. The photoluminescence emission spectra showed peaks in the UV and visible region. Visible emissions are a result of the presence of defects or impurity states in the material. All of the samples showed photocatalytic activity against the Rhodamine B (RhB) synthetic solution under UV irradiation. The best performance was obtained using the MWCNT:ZnO-Fe(1:5) nanocomposite samples, which exhibited a 96% degradation efficiency. The mechanism of photocatalytic activity was explained based on the reactive oxygen species generated by the nanocomposites under UV irradiation in correlation with the structural and optical information obtained in this study.

Recent Development of Polyhydroxyalkanoates (PHA)-Based Materials for Antibacterial Applications: A Review

The diseases caused by microorganisms are innumerable existing on this planet. Nevertheless, increasing antimicrobial resistance has become an urgent global challenge. Thus, in recent decades, bactericidal materials have been considered promising candidates to combat bacterial pathogens. Recently, polyhydroxyalkanoates (PHAs) have been used as green and biodegradable materials in various promising alternative applications, especially in healthcare for antiviral or antiviral purposes. However, it lacks a systematic review of the recent application of this emerging material for antibacterial applications. Therefore, the ultimate goal of this review is to provide a critical review of the state of the art recent development of PHA biopolymers in terms of cutting-edge production technologies as well as promising application fields. In addition, special attention was given to collecting scientific information on antibacterial agents that can potentially be incorporated into PHA materials for biological and durable antimicrobial protection. Furthermore, the current research gaps are declared, and future research perspectives are proposed to better understand the properties of these biopolymers as well as their possible applications.

Influence of the Alcohols on the ZnO Synthesis and Its Properties: The Photocatalytic and Antimicrobial Activities

Zinc oxide (ZnO) nanomaterials are used in various health-related applications, from antimicrobial textiles to wound dressing composites and from sunscreens to antimicrobial packaging. Purity, surface defects, size, and morphology of the nanoparticles are the main factors that influence the antimicrobial properties. In this study, we are comparing the properties of the ZnO nanoparticles obtained by solvolysis using a series of alcohols: primary from methanol to 1-hexanol, secondary (2-propanol and 2-butanol), and tertiary (tert-butanol). While the synthesis of ZnO nanoparticles is successfully accomplished in all primary alcohols, the use of secondary or tertiary alcohols does not lead to ZnO as final product, underlining the importance of the used solvent. The shape of the obtained nanoparticles depends on the alcohol used, from quasi-spherical to rods, and consequently, different properties are reported, including photocatalytic and antimicrobial activities. In the photocatalytic study, the ZnO obtained in 1-butanol exhibited the best performance against methylene blue (MB) dye solution, attaining a degradation efficiency of 98.24%. The comparative study among a series of usual model dyes revealed that triarylmethane dyes are less susceptible to photo-degradation. The obtained ZnO nanoparticles present a strong antimicrobial activity on a broad range of microorganisms (bacterial and fungal strains), the size and shape being the important factors. This permits further tailoring for use in medical applications.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV))/Bacterial Cellulose (BC) Biocomposites for Potential Use in Biomedical Applications

The aim of this study was to obtain biocomposites consisting of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), bacterial cellulose (BC) and α-tocopherol by a melt processing technique for potential use in biomedical applications. The melt processing and roughness of biocomposites were evaluated and compared to sample without BC. The degradation rate of PHBV/BC biocomposites was measured in phosphate buffer saline (PBS) by determining the mass variation and evidencing of thermal and structural changes by differential scanning calorimetry (DSC) and attenuated total reflectance-Fourier transformed infrared spectrometry (ATR-FTIR). The cell viability, cell morphology, cell cycle distribution and total collagen content were investigated on murine NCTC fibroblasts. Overall, the adding of BC to polyester matrix led to an adequate melt processing of biocomposites and increased surface roughness and cytocompatibility, allowing the cells to secrete the extracellular matrix (collagen) and stimulate cell proliferation. Results showed that the PHBV/BC biocomposites were favorable for long-term degradation and could be used for the design of medical devices with controlled degradability.

Recent advances in biobased and biodegradable polymer nanocomposites, nanoparticles, and natural antioxidants for antibacterial and antioxidant food packaging applications

Inorganic nanoparticles (NPs) and natural antioxidant compounds are an emerging trend in the food industry. Incorporating these substances in biobased and biodegradable matrices as polysaccharides (e.g., starch, cellulose, and chitosan) and proteins has highlighted the potential in active food packaging applications due to more significant antimicrobial, antioxidant, UV blocking, oxygen scavenging, water vapor permeability effects, and low environmental impact. In recent years, the migration of metal NPs and metal oxides in food contact packaging and their toxicological potential have raised concerns about the safety of the nanomaterials. In this review, we provide a comprehensive overview of the main biobased and biodegradable polymer nanocomposites, inorganic NPs, natural antioxidants, and their potential use in active food packaging. The intrinsic properties of NPs and natural antioxidant actives in packaging materials are evaluated to extend shelf-life, safety, and food quality. Toxicological and safety aspects of inorganic NPs are highlighted to understand the current controversy on applying some nanomaterials in food packaging. The synergism of inorganic NPs and plant-derived natural antioxidant actives (e.g., vitamins, polyphenols, and carotenoids) and essential oils (EOs) potentiated the antibacterial and antioxidant properties of biodegradable nanocomposite films. Biodegradable packaging films based on green NPs-this is biosynthesized from plant extracts-showed suitable mechanical and barrier properties and had a lower environmental impact and offered efficient food protection. Furthermore, AgNPs and TiO₂ NPs released metal ions from packaging into contents insufficiently to cause harm to human cells, which could be helpful to understanding critical gaps and provide progress in the packaging field.

Maleic Anhydride Polylactic Acid Coupling Agent Prepared from Solvent Reaction: Synthesis, Characterization and Composite Performance

In the present work, a functionalization of polylactic acid (PLA) has been carried out to anchor maleic anhydride onto the main polymer chain to promote improvement in the compatibility of this polymer matrix with cellulose fibres. Low-molecular-weight PLA has been reacted with maleic anhydride following different procedures: a bulk reaction in an internal mixer and a solution reaction. The presence of oxygen during bulk processing did not allow for functionalization, guiding the reaction towards a decrease in the molecular weight of the material. On the contrary, a controlled reaction under an inert atmosphere in the presence of dioxane as the solvent, at reflux temperature, led to the functionalization of the polymer reaching different yields depending on the percentage of radical initiator and maleic anhydride added and reaction time. The yield of functionalization has been monitored by acid number titration as well as 1H NMR, with optimal yield values of functionalization being up to 3.5%. The PLA-functionalized formula has been used to make commercial PLA compatible with cellulose fibres derived from a thermomechanical treatment. The addition of 10% w/w of fibres to PLA increases the ultimate tensile strength (UTS) of PLA by up to 15%. The incorporation of 4 w/w of the already-functionalized coupling agent to the composite produces improvements in UTS of up to 24% regarding PLA, which confirms the functionalization from a performance point of view.

Extrusion and Injection Molding of Poly(3-Hydroxybutyrate-co-3-Hydroxyhexanoate) (PHBHHx): Influence of Processing Conditions on Mechanical Properties and Microstructure

Biobased and biodegradable polyhydroxyalkanoates (PHAs) have great potential as sustainable packaging materials. However, improvements in their processing and mechanical properties are necessary. In this work, the influence of melt processing conditions on the mechanical properties and microstructure of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) is examined using a full factorial design of experiments (DoE) approach. We have found that strict control over processing temperature, mold temperature, screw speed, and cooling time leads to highly increased elongation at break values, mainly under influence of higher mold temperatures at 80 °C. Increased elongation of the moldings is attributed to relaxation and decreased orientation of the polymer chains together with a homogeneous microstructure at slower cooling rates. Based on the statistically substantiated models to determine the optimal processing conditions and their effects on microstructure variation and mechanical properties of PHBHHx samples, we conclude that optimizing the processing of this biopolymer can improve the applicability of the material and extend its scope in the realm of flexible packaging applications.