Development of moisture-absorbing and antioxidant active packaging film based on poly(vinyl alcohol) incorporated with green tea extract and its effect on the quality of dried eel

Sustainable strategies for using natural extracts in smart food packaging

The growing demand for sustainable and eco-friendly food packaging has prompted research on innovative solutions to environmental and consumer health issues. To enhance the properties of smart packaging, the incorporation of bioactive compounds derived from various natural sources has attracted considerable interest because of their functional properties, including antioxidant and antimicrobial effects. However, extracting these compounds from natural sources poses challenges because of their complex chemical structures and low concentrations. Traditional extraction methods are often environmentally harmful, expensive and time-consuming. Thus, green extraction techniques have emerged as promising alternatives, offering sustainable and eco-friendly approaches that minimise the use of hazardous solvents and reduce environmental impact. This review explores cutting-edge research on the green extraction of bioactive compounds and their incorporation into smart packaging systems in the last 10 years. Then, an overview of bioactive compounds, green extraction techniques, integrated techniques, green extraction solvents and their application in smart packaging was provided, and the impact of bioactive compounds incorporated in smart packaging on the shelf lives of food products was explored. Furthermore, it highlights the challenges and opportunities within this field and presents recommendations for future research, aiming to contribute to the advancement of sustainable and efficient smart packaging solutions.

Biodegradable films from the lignocellulosic fibers of wheat straw biomass and the effect of calcium ions

Plastics are hazardous to human health, and plastic waste results in environmental pollution and ecological catastrophe. Biobased polymers from renewable sources have recently become promising for developing biodegradable packaging films. Among them, lignocellulosic residue from agricultural biomass is inexpensive, renewable, and biodegradable. This study aims to develop biodegradable films using lignocellulosic residue from wheat straw biomass. The methodology is a green process that solubilizes lignocellulosic chains using Zn2+ ions and crosslinks with Ca2+ ions of different concentrations (200-800 mM). The results reveal that the increase of Ca2+ ions significantly decreases moisture content, water solubility, water vapor permeability, transparency, and elongation of films. The tensile strength is recorded as 6.61 ± 0.07 MPa with the addition of 800 mM of CaCl2, which is approximately 2.5 times higher than commercial polyethylene films. Around 90 % of films biodegrade within a month in soil containing 20 % moisture content. Overall, lignocellulosic residue from wheat straw biomass could be an excellent replacement for synthetic polymer to fabricate strong, transparent, and biodegradable plastic films.

Carboxymethyl cellulose/poly (vinyl alcohol) based active film incorporated with tamarind seed coat waste extract for food packaging application

Incorporating a bioactive food waste extract into biodegradable polymers is a promising green approach to producing active films with antioxidant and antibacterial activity for food packaging. Active packaging films from carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA) incorporated with tamarind seed coat waste extract (TS) were prepared by solvent casting method using citric acid as a crosslinking agent. The effect of TS content on the film properties was determined by measuring the optical, morphology, mechanical, water vapor transmission rate (WVTR), antioxidant, and antimicrobial attributes. The CMC/PVA-TS films were also tested on fresh pork. The addition of TS did not significantly affect the film structure and WVTR but it improved the mechanical and UV barrier properties. The films possessed antioxidant and antimicrobial ability against bacteria (S. aureus and E. coli). Thus, CMC/PVA packaging was successfully prepared, and the incorporation of TS enhanced the antioxidant and antimicrobial properties of the film, which extended the shelf-life of fresh pork.

Pulp waste extracted reinforced powder incorporated biodegradable chitosan composite film for enhancing red grape shelf-life

Chitosan (CS) is widely used as a natural biopolymer due to its semi-crystalline structure, good film-forming properties, and easy availability. CS-based composite films are widely used in industry, particularly in the food sector as active food packaging. Despite all of these advantages, their wide range of applications are constrained by poor mechanical properties. Therefore, this work introduced refined bamboo cellulose powder (RBCP), a reinforcing material that is extracted from waste bamboo pulp and applied to CS composite films to enhance their mechanical and physicochemical properties. The chemical composition and crystallinity properties of CS composite films with RBCP addition were observed by ATR-FTIR and XRD. The homogeneous and heterogeneous surfaces of the RBCP incorporated films before biodegradation and after biodegradation (20 days) were observed by scanning electron microscopy (SEM). The increase in reinforcing RBCP materials from 0.00 to 5.00 % resulted in an increase in tensile strength for CS/RBCP films from 2.9 to 8.3 MPa. The application of the CS/RBCP/5 composite film as red grapefruit storage was also investigated, which performed much better than commercial plastic and control CS films with 92.8 and 88.6 % viability of S. aureus and E. coli bacteria. Overall achieved properties demonstrated strong potential for usage as active packaging materials to preserve and lengthen the shelf life of red grapefruits.

Gellan Gum and Polyvinyl Alcohol Based Triple-Layer Films Enriched with Alhagi sparsifolia Flower Extract: Preparation, Characterization, and Application of Dried Shrimp Preservation

To meet the demand for biobased packaging and minimize the oxidation of dried aquatic goods during storage, we created a triple-layer film (TF) with antioxidant capacity. The film was produced using polyvinyl alcohol (PVA) as the protective layer, gellan gum (GG)/PVA composite incorporating Alhagi sparsifolia flower extract (AFE) as the anti-oxidative capability layer, and GG as the anti-oxidative capacity slow-release control layer. The TFs with different AFE additions were characterized and compared to a single-layer film (SF) made of the same material. The results demonstrate that adding AFE to films degraded their water vapour and oxygen barrier properties as well as their tensile strength, but increased their light barrier properties, elongation at break, and anti-oxidative capability. The three-layer structure increased the light, water vapour, and oxygen barrier qualities of films, as well as their slow-release anti-oxidative capability. The application experiment revealed that the inclusion of AFE might aid in the preservation of dried prawn quality. Using TF supplemented with 5 (w/v) AFE to package the dried shrimps reduced the TBARS value by 47.5%. Our research indicated that TFs containing AFE have a wide range of possible applications in dried shrimp preservation.

Comparison of chitosan and gelatin-based films and application to antimicrobial coatings enriched with grapefruit seed extract for cherry tomato preservation

Bio-based single, composite, and bilayer edible films were developed based on chitosan and gelatin, including grapefruit seed extract (GSE) as an antimicrobial agent. The physicochemical and antimicrobial properties of films were analyzed, and it was found that compounding and laminating two polymers could enhance their physicochemical properties. The composite film was strong, endurable, and flexible compared with the single ones. In addition, the composite and bilayer films had lower water vapor permeability than the single ones. Edible films and coatings with GSE presented a greater bactericidal effect than the inactive ones. In addition, the hardness, weight, and color changes of the coated cherry tomatoes during 7-day storage did not differ, whereas a bacterial reduction against Salmonella Typhimurium was revealed. Taken together, composite and bilayer films with CH and GL and enriched with GSE were developed for food packaging applications, and it showed improved mechanical, water barrier, and antimicrobial properties.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01254-9.

HPMC films functionalized by zein/carboxymethyl tamarind gum stabilized Pickering emulsions: Influence of carboxymethylation degree

Pickering emulsions are promising systems to act as carriers of active hydrophobic components, and to improve compatibility and the water vapor barrier properties of bio-based films. This study aimed to investigated the effects of cinnamon essential oil Pickering emulsions (CEOEs) using zein/carboxymethyl tamarind gum as stabilizers on the mechanical, barrier, antibacterial and antioxidant properties of Hydroxypropyl methyl cellulose (HPMC) films, and assessed the influence of carboxymethylation degree. In addition, the effect of the packaging was studied on the shelf life of cherry tomatoes. Results showed that the droplet size reduced approximately from 93.03 to 10.59 μm with the increasing degree of substitution (DS), greatly facilitating the droplet uniform distribution in film matrix. Moreover, with the addition of CEOEs, significant increase was observed with the tensile strength from 8.46 to 25.41 MPa, and the water vapor permeability decreased from 6.18 × 10^-10 to 4.24 × 10^-10 g·m^-1·s^-1·Pa^-1. The films exhibited good UV barrier properties without sacrificing the transparency after adding CEO. Furthermore, the antibacterial and antioxidant activities of the prepared films have also been greatly improved. Consequently, the CEOEs was an ideal alternative for incorporation with HPMC based films for increasing the shelf life of cherry tomatoes.

Formation and Investigation of Physicochemical and Microbiological Properties of Biocomposite Films Containing Turmeric Extract Nano/Microcapsules

In the era of growing plastic consumption, food waste by consumers and overproduction caused by economic reasons, the global goal is to decrease these phenomena. Biocomposite films investigated in the past years are creating a promising future toward ecological, intelligent and active packaging. Due to their unique properties, they can be used in many areas of our life and reduce the constantly increasing pollution of our planet. The aim of our study was to obtain innovative and flexible biopolymer films based on sodium alginate and chitosan, as well as to develop methods for generating nanocapsules with turmeric extract in them. Bionanocomposites were analyzed using UV-VIS, FTIR, photoluminescence spectroscopy and SEM microscopy, while contact angles, surface free energy, particle size (DLS) and zeta potential were determined. The mechanical and colorimetric properties of the produced films were investigated, and the water content, solubility and water absorption were determined. Microbiological tests were carried out to analyze the influence of the produced films on the development of microorganisms. The results of the performed analyses allowed us to confirm the presence of curcumin nano- and microcapsules in the alginate-chitosan composite. Moreover, studies have shown that the structure of polysaccharides does not change during capsule manufacturing. The film with the highest concentration of the capsules showed better parameters in tests of solubility, water content, degree of swelling and mechanical properties. The obtained properties of the developed films allow them to be used as active and intelligent packaging materials, or as their parts.

Extrusion-blown starch/PBAT biodegradable active films incorporated with high retentions of tea polyphenols and the release kinetics into food simulants

To reduce thermal degradation of tea polyphenols (TP) in final active packaging materials, poly(butylene adipate-co-terephthalate) (PBAT), starch, plasticizer, and TP were directly synthesized into masterbatches by one-pot method in this study without pre-dispersion, and then blown into active films. TP interacted with starch through hydrogen bonds, with little interaction with PBAT. Barrier properties were improved by incorporating TP into the films, whereas mechanical properties slightly decreased. Blending starch into PBAT greatly accelerated the degradation of the film. And the incorporation of TP slowed down the short-term degradation of the starch/PBAT film, but accelerated the long-term degradation. The initial total polyphenol content in the active film was positively related to the TP loading, whereas the initial retention rate remained above 95 % regardless of TP loadings. The retention rate of TP in active films decreased with storage time, but it was still above 80 % after 12 months, with a favorable stability. TP-loaded films displayed efficient antioxidant and antimicrobial activities with strong dose dependence. The release of TP into food simulants was mainly induced by random diffusion, with little effect from polymer swelling. The short-term release kinetics was well described by Fick's second law. This work has demonstrated the feasibility of TP being incorporated into the active films with high retention through high-throughput fabrication, which provides formula and technical options for the industrial development of active packaging materials.

Polyvinyl alcohol film with chlorine dioxide microcapsules can be used for blueberry preservation by slow-release of chlorine dioxide gas

Introduction

Chlorine dioxide (ClO₂) is a safe and efficient bactericide with unique advantages in reducing foodborne illnesses, inhibiting microbial growth, and maintaining the nutritional quality of food. However, gaseous ClO₂ is sensitive to heat, vibration, and light, which limits its application.

Methods

In this study, a ClO₂ precursor-stabilized ClO₂ aqueous solution was encapsulated by the double emulsion method, and a high-performance ClO₂ self-releasing polyvinyl alcohol (PVA) film was prepared to investigate its performance and effect on blueberry quality during storage.

Results

The self-releasing films had the best overall performance when the microcapsule content was 10% as the film's mechanical properties, thermal stability, and film barrier properties were significantly improved. The inhibition rates of Listeria monocytogenes and Escherichia coli were 93.69% and 95.55%, respectively, and the mycelial growth of Staphylococcus griseus was successfully inhibited. The resulting ClO₂ self-releasing films were used for blueberry preservation, and an experimental study found that the ClO₂ self-releasing antimicrobial film group delayed the quality decline of blueberries. During the 14-day storage period, no mold contamination was observed in the ClO₂ self-releasing film group, and blueberries in the antibacterial film group had higher anthocyanin accumulation during the storage period.

Discussion

Research analysis showed that films containing ClO₂ microcapsules are promising materials for future fruit and vegetable packaging.

Evaluation of Active LDPE Films for Packaging of Fresh Orange Juice

Microbial development, enzymatic action, and chemical reactions influence the quality of untreated natural orange juice, compromising its organoleptic characteristics and causing nutritional value loss. Active low-density polyethylene (LDPE) films containing green tea extract (GTE) were previously prepared by a blown film extrusion process. Small bags were prepared from the produced films, which were then filled with fresh orange juice and stored at 4 °C. Ascorbic acid (AA) content, sugar content, browning index, color parameters, pH, total acidity (TA) and microbial stability were evaluated after 3, 7, and 14 days of storage. The packaging containing GTE maintained the microbial load of fresh juice beneath the limit of microbial shelf-life (6 log CFU/mL) for the bacterial growth, with a more prominent effect for LDPE with 3%GTE. Regarding yeasts and molds, only the CO_LDPE_3GTE package maintained the microbial load of fresh juice below the limit for up to 14 days. At 14 days, the lowest levels of AA degradation (32.60 mg/100 mL of juice) and development of brown pigments (browning index = 0.139) were observed for the packages containing 3% of GTE, which had a pH of 3.87 and sugar content of 11.4 g/100 mL of juice at this time. Therefore, active LDPE films containing 3% of GTE increase the shelf-life of fresh juice and can be a promising option for storage of this food product while increasing sustainability.

Preparation of a Novel Carbon Dot/Polyvinyl Alcohol Composite Film and Its Application in Food Preservation

Carbon dots (CDs) were synthesized with the facile hydrothermal method to produce CDs/polyvinyl alcohol (PVA) active food packaging films. The CDs had a diameter ranging from 2.01 to 5.61 nm and were well-dispersed. The effects of different concentrations of CDs on mechanical strength, water resistance, morphology, optical, and thermal performance of the CDs/PVA films were discussed. The incorporation of CDs in the PVA film improved its mechanical properties, water resistance properties, UV blocking properties, and thermal stability and endowed the composite film with antioxidant and antimicrobial properties. The maximum scavenging rates of 2,2-diphenyl-1-picrylhydrazyl and ABTS free radicals by the 0.50% CDs/PVA film were 72.81 and 97.08%, respectively. The inhibition zone diameters of the 0.50% CDs/PVA solution against Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis), and Escherichia coli (E. coli) were 9.52, 8.21, and 9.05 mm, respectively. Using the 0.50% CDs/PVA film as active packaging, the shelf life of banana, jujube, and fried meatballs was observed to be extended significantly. These results demonstrate the viability of the CDs/PVA composite film as a promising active food packaging material.

Active Flexible Films for Food Packaging: A Review

Active food packaging is a dynamic area where the scientific community and industry have been trying to find new strategies to produce innovative packaging that is economically viable and compatible with conventional production processes. The materials used to develop active packaging can be organized into scavenging and emitting materials, and based on organic and inorganic materials. However, the incorporation of these materials in polymer-based flexible packaging is not always straightforward. The challenges to be faced are mainly related to active agents' sensitivity to high temperatures or difficulties in dispersing them in the high viscosity polymer matrix. This review provides an overview of methodologies and processes used in the production of active packaging, particularly for the production of active flexible films at the industrial level. The direct incorporation of active agents in polymer films is presented, focusing on the processing conditions and their effect on the active agent, and final application of the packaging material. Moreover, the incorporation of active agents by coating technologies and supercritical impregnation are presented. Finally, the use of carriers to help the incorporation of active agents and several methodologies is discussed. This review aims to guide academic and industrial researchers in the development of active flexible packaging, namely in the selection of the materials, methodologies, and process conditions.

Fabrication and characterization of biodegradable active films with modified morphology based on polycaprolactone-polylactic acid-green tea extract

This research focused on developing an eco-friendly packaging for food products through blending polycaprolactone (PCL) and polylactic acid (PLA) as two biodegradable polymers, and green tea extract (GTE) as a natural antioxidant pushing the films toward active packaging; thereby, the morphological, mechanical, thermal, barrier, antioxidant, and biodegradation features of the composite films were analyzed. The films containing 30% PLA exhibited a reduction of 14.96%, 38.89%, 8.75%, and 35.55% in the hydrophilicity, water-solubility, water vapor permeability (WVP), and oxygen transition rate (OTR), respectively. Furthermore, GTE incorporation led to antioxidant behavior as well as better barrier properties (up to 6.25% decrease in WVP and 55.78% in OTR), mechanical properties (an increase of 14.96%, 38.89%, and 8.75% in elastic modulus, tensile strength, and elongation at break, respectively) and biodegradable rate (124.13%). Indeed, the presence of polyphenol compounds in green tea improved molecular interaction between the polymers and launched a co-continuous structure and an unparalleled level of compatibility, which was also approved by the changes in FTIR spectra of the PCL/PLA films. These results demonstrate the benefits of blending PLA with PCL and GTE integration in terms of operational enhancement and film activating, respectively, to provide reliable food packaging.

Improved mechanical, antibacterial and UV barrier properties of catechol-functionalized chitosan/polyvinyl alcohol biodegradable composites for active food packaging

Bioinspired from adhesion behaviors of mussels, we first reported a new strategy to prepare catechol-functionalized chitosan (C-CS)/polyvinyl alcohol (PVA) composite films via a solution blending method in neutral aqueous solution for active food packaging. Compared with pure PVA film, the UV transmittance (at 280 nm) of C-CS/PVA composite films decreases by 67.6 % when C-CS content reaches 10 wt%. Still, all the C-CS/PVA composite films are transparent in the visible range. The maximal tensile strength and elongation at break of C-CS/PVA composite films can reach 45.2 MPa and 153 % respectively, which are 46.3 % and 25.4 % higher than those of pure PVA film. The incorporation of C-CS into PVA matrix increases the antibacterial properties significantly. The water resistance of C-CS/PVA composite films can not be significantly deteriorated by the appropriate amount of C-CS. Therefore, C-CS/PVA composite films show great potential in the field of active packaging due to its good mechanical, antibacterial and UV barrier properties.

Tea polyphenols (TP): a promising natural additive for the manufacture of multifunctional active food packaging films

As a bioactive extract from tea leaves, tea polyphenols (TP) are safe and natural. Its excellent antioxidant and antibacterial properties are increasingly regarded as a good additive for improving degradable food packaging film properties. This article comprehensively reviewed the functional properties of active films containing TP developed recently. The effects of TP addition to enhancing active food packaging films' performance, including thickness, water sensitivity, barrier properties, color, mechanical properties, antioxidant, antibacterial, and intelligent discoloration properties, were discussed. Besides, the practical applications in food preservation of active films containing TP are also discussed. This work concluded that the addition of TP could impart antioxidant and antibacterial properties to active packaging films and act as a crosslinking agent to improve other physical and chemical properties of the film, such as mechanical and barrier properties. However, the effect of TP on specific properties of the active packaging film is complex, and the appropriate TP concentration needs to be selected according to the type of film matrix and the interaction between the components. Notably, the addition of TP improved the efficiency of the active packaging film in food preservation applications, which accelerates the process of replacing the traditional plastic-based food packaging with active packaging film.

Development and characterization of PVA-starch incorporated with coconut shell extract and sepiolite clay as an antioxidant film for active food packaging applications

An active antioxidant film was fabricated by using polyvinyl alcohol (PVA) and corn starch (ST) and incorporated with and 3, 5, 10, and 20% (v/v) coconut shell extract (CSE) and sepiolite clay (SP) for the first time. The microstructure and physical properties of prepared films were characterized and examined. The addition of sepiolite clay to PVA improved the elongation break 15.57 to 69.24%, and water vapor permeability increased with the addition of CSE. In addition to CSE to films, the antioxidant activity properties of the films were enhanced up to 80%. Further, increasing the amount of CSE slightly affected the color of the active films. The thermal properties of films were enhanced with the addition of CSE and SP. The dispersion of SP in the PVA matrix was affected by an increase in CSE concentration in the PVA matrix. Remarkably, PVA-ST film-based sachets successfully improved the oxidative stability of packaged soybean oil. Our results suggest PVA-ST film containing CSE and sepiolite clay can be utilized as a novel antioxidant packaging material in the food processing industry.

Plant-derived antioxidants incorporated into active packaging intended for vegetables and fatty animal products: a review

Nowadays, the food industry is focused on improving the shelf life of products by controlling lipid oxidation using natural antioxidants. The study of natural antioxidants is a field that attracts great interest because of their greater safety compared to synthetic ones. Plant-derived antioxidants being eco-friendly and effective are increasingly playing an important role in food preservation. When incorporated into active packaging, plant-derived antioxidants have no direct contact with foods, and will not change the colour or taste of the foods. They will, however, inhibit the development of rancidity, retard formation of toxic oxidation products, maintain nutritional quality, and prolong the shelf life of products. This review summarises research on the development of plant-derived antioxidants in food packaging. Antioxidants are found in plants such as green tea, olive leaves, ginkgo leaves, rosemary, Indian gooseberry, cinnamon, savoury, bay leaves, mango leaves, sage and clove etc. Antioxidants can scavenge free radicals and inhibit the activity of polyphenol oxidase. Therefore, they can inhibit lipid oxidation and browning of fruit and vegetables. These active substances can be obtained through extracting the plants using solvents with different polarities. The oxidation resistance of active substances can be determined by DPPH radical scavenging capacity, oxygen radical absorbance capacity, PPO enzyme inhibition capacity and other methods. In recent years, research on the preparation of food packaging with plant-derived antioxidants has also made significant progress. One development is to encapsulate plant-derived antioxidants such as tea polyphenols with capsules containing inorganic components. Thus, they can be blended with polyethylene granules and processed into active packaging film by industrial production methods such as melting, extrusion and blowing film. This research promotes the commercial application of active packaging incorporated with plant-derived antioxidants.

Mussel-Inspired Approach to Constructing Dual Network Coated Layered Clay for Enhanced Barrier and Antibacterial Properties of Poly(vinyl alcohol) Nanocomposites

Inspired by complexation and mussel adhesion of catechol groups in tannic acid (TA), organophilic layered double hydroxides (LDHs@TA-Ti) were synthesized by forming a one-pot assembled TA-titanium (Ti) dual network coating on the surface of layered clay for the first time. LDHs@TA-Ti/poly(vinyl alcohol) (PVA) nanocomposites were prepared by the solution casting method. The results show that TA-Ti(IV) and TiO2 coordination compounds are simultaneously formed due to hydrolysis of titanium tetrachloride and complexation of TA in aqueous solution. Upon TA-Ti coatings onto the surface of LDHs, the antibacterial rate of LDHs@TA-Ti is up to 99.98%. Corresponding LDHs@TA-Ti/PVA nanocomposites also show outstanding antibacterial properties. Compared with pure PVA, LDHs@TA-Ti/PVA nanocomposites show a 40.9% increase in tensile strength, a 17.5% increase in elongation at break, a 35.9% decrease in oxygen permeability and a 26.0% decrease in water vapor permeability when adding 1 wt % LDHs@TA-Ti. UV transmittance (at 300 nm) of LDHs@TA-Ti/PVA nanocomposites decrease by 99.4% when the content of LDHs@TA-Ti reaches 3 wt %. These results indicate that PVA matrix incorporated with LDHs@TA-Ti could be used as a potential active packaging material to extend the shelf life of food products.

Electrospun Functional Materials toward Food Packaging Applications: A Review

Electrospinning is an effective and versatile method to prepare continuous polymer nanofibers and nonwovens that exhibit excellent properties such as high molecular orientation, high porosity and large specific surface area. Benefitting from these outstanding and intriguing features, electrospun nanofibers have been employed as a promising candidate for the fabrication of food packaging materials. Actually, the electrospun nanofibers used in food packaging must possess biocompatibility and low toxicity. In addition, in order to maintain the quality of food and extend its shelf life, food packaging materials also need to have certain functionality. Herein, in this timely review, functional materials produced from electrospinning toward food packaging are highlighted. At first, various strategies for the preparation of polymer electrospun fiber are introduced, then the characteristics of different packaging films and their successful applications in food packaging are summarized, including degradable materials, superhydrophobic materials, edible materials, antibacterial materials and high barrier materials. Finally, the future perspective and key challenges of polymer electrospun nanofibers for food packaging are also discussed. Hopefully, this review would provide a fundamental insight into the development of electrospun functional materials with high performance for food packaging.

Preparation and Performance of Radiata-Pine-Derived Polyvinyl Alcohol/Carbon Quantum Dots Fluorescent Films

In this study, the low-cost processing residue of Radiata pine (Pinus radiata D. Don) was used as the lone carbon source for synthesis of CQDs (Carbon quantum dots) with a QY (The quantum yield of the CQDs) of 1.60%. The CQDs were obtained by the hydrothermal method, and +a PVA-based biofilm was prepared by the fluidized drying method. The effects of CQDs and CNF (cellulose nanofibers) content on the morphology, optical, mechanical, water-resistance, and wettability properties of the PVA/CQDs and PVA/CNF/CQDs films are discussed. The results revealed that, when the excitation wavelength was increased from 340 to 390 nm, the emission peak became slightly red-shifted, which was induced by the condensation between CQDs and PVA. The PVA composite films showed an increase in fluorescence intensity with the addition of the CNF and CQDs to polymers. The chemical structure of prepared films was determined by the FTIR spectroscopy, and no new chemical bonds were formed. In addition, the UV transmittance was inversely proportional to the change of CQDs content, which indicated that CQDs improved the UV barrier properties of the films. Furthermore, embedding CQDs Nano-materials and CNF into the PVA matrix improved the mechanical behavior of the Nano-composite. Tensile modulus and strength at break increased significantly with increasing the concentration of CQDs Nano-materials inside the Nano-composite, which was due to the increased in the density of crosslinking behavior. With the increase of CQDs content (>1 mL), the water absorption and surface contact angle of the prepared films decreased gradually, and the water-resistance and surface wettability of the films were improved. Therefore, PVA/CNF/CQDs bio-nanocomposite films could be used to prepare anti-counterfeiting, high-transparency, and ultraviolet-resistant composites, which have potential applications in ecological packaging materials.

Polyurethane Aerogels Based on Cyclodextrins: High-Capacity Desiccants Regenerated at Room Temperature by Reducing the Relative Humidity of the Environment

Polyurethane aerogels were prepared from a rigid aromatic triisocyanate (tris(4-isocyanatophenyl)methane) and cage-shaped α- and β-cyclodextrins as rigid polyols. Gelation was carried out in DMF using dibutyltin dilaurate as catalyst. Wet-gels were dried to aerogels (abbreviated as α- or β-CDPU-xx) with supercritical fluid CO₂. "xx" stands for the percent weight of the two monomers in the sol and was varied at two levels for each cyclodextrin: 2.5% and 15%. All aerogels were characterized with solid-state ¹³C and ¹⁵N NMR, CHN analysis, FTIR, XPS, SEM, and gas (N₂ and CO₂) sorption porosimetry. α- and β-CDPU-xx aerogels were investigated as desiccants at room temperature. All materials had relatively higher capacities for water adsorption from high-humidity environments (99%) than typical commercial desiccants like silica or Drierite. However, α-CDPU-2.5 aerogels did stand out with a water uptake capacity reaching 1 g of H₂O per gram of material. Most importantly though, adsorbed water could be released quantitatively without heating, by just reducing the relative humidity of the environment to 10%. All α- and β-CDPU-xx aerogel samples were cycled between humid and dry environments 10 times. Their unusual behavior was traced to filling smaller mesopores with water and was attributed to a delicate balance of enthalpic (H-bonding) and entropic factors, whereas the latter are a function of pore sizes.

Development of New Multilayer Active Packaging Films with Controlled Release Property Based on Polypropylene/Poly(Vinyl Alcohol)/Polypropylene Incorporated with Tea Polyphenols

The polypropylene/poly(vinyl alcohol)/polypropylene (PP/PVA/PP) multilayer active films with controlled release property were developed, of which the intermediate PVA layer was incorporated with 4% (w/w) tea polyphenols (TP) and the microporous PP films with different pore size were used as the internal controlled release layer. The SEM results showed that each layer of these films was agglutinated tightly. With increasing pore size from 171.05 to 684.03 µm, there were little effect on the films' color and opacity, the tensile strength (TS) and elongation at break (EAB) decreased slightly, the gas barrier (O₂ and water vapor) property of the film reduced faintly, the time of achieving the release equilibrium in 50% ethanol decreased from 75 hours to 30 hours. The diffusion coefficient for the films increased with the increase of pore size, from 2.06 × 10^-11 cm² /s to 8.06 × 10^-11 cm² /s, suggesting that the release rate of TP increased as the pore size increased. The results were indicated that its release rate could be controlled by adjusting the size of pore. The films also exhibited different antioxidant activities due to their different release profiles of TP. It showed promise for developing the controlled release active packaging film based on this concept. PRACTICAL APPLICATION: Controlled release packaging is propitious to extension of food shelf life. The microporous polypropylene films with different pore size used as the internal layer of polypropylene/poly(vinyl alcohol)/polypropylene (PP/PVA/PP) multilayer active films was proved that the release rate of tea polyphenols in the intermediate PVA layer released from the films into the food simulant can be controlled by adjusting the size of pore in this study. It showed a good prospect for using microporous or perforation-mediated film as the internal layer of multilayer film to develop the controlled release active packaging film for food packaging.