Structural elucidation of citric acid cross-linked pectin and its impact on the properties of nanocellulose-reinforced packaging films.

Waste from non-degradable packaging materials poses a serious environmental risk and has led to interest in developing sustainable bio-based packaging materials. Sustainable packaging materials have been made from diverse naturally derived materials such as bamboo, sugarcane, and corn starch. In this study, we made a sustainable packaging film using chitosan extracted from the biomass of yellow mealworm (Tenebrio molitor) shell waste. The extracted chitosan was used to create films, cross-linked with citric acid (CA) and with the addition of glycerol to impart flexibility, using the solvent casting method. The successful cross-linking was evaluated using Fourier-Transform Infrared (FTIR) analysis. The CA cross-linked mealworm chitosan (CAMC) films exhibited improved water resistance with moisture content reduced from 19.9 to 14.5%. Improved barrier properties were also noted, with a 28.7% and 10.2% decrease in vapor permeability and vapor transmission rate, respectively. Bananas were selected for food preservation, and significant changes were observed over a duration of 10 days. Compared to the control sample, bananas packaged in CAMC pouches exhibited a lesser loss in weight because of excellent barrier properties against water vapor. Moreover, the quality and texture of bananas packaged in CAMC pouch remained intact over the duration of the experiment. This indicates that adding citric acid and glycerol to the chitosan structure holds promise for effective food wrapping and contributes to the enhancement of banana shelf life. Through this study, we concluded that chitosan film derived from mealworm biomass has potential as a valuable resource for sustainable packaging solutions, promoting the adoption of environmentally friendly practices in the food industry.

There is an ongoing unmet global need to manufacture novel sustainable liquid packaging materials, that are not based on plastic film or aluminum foil. Superhydrophobic coating technologies have been proposed for developing more sustainable packaging materials. In this study, the underlying engineering principles for fabricating superhydrophobic surfaces proposed for liquid packaging are investigated, including but not limited to the substrates used and engineering properties of the surfaces. Specifically, to improve the engineering performance of superhydrophobic paper for use in packaging, the feasibility of combining platy montmorillonite (MMT, for its barrier properties) and nano-rolling-pin-shaped precipitated calcium carbonate (PCC, for its superhydrophobicity) into multifunctional coating layers is investigated. Water droplet evaporation experiments are performed to identify how subtle changes in the morphological structures of as-prepared superhydrophobic paper samples can produce a useful roughness structure for packaging applications. Paperboard, which is widely utilized in packaging, is chosen as a substrate to study the challenges of fabricating superhydrophobic paperboards for use in packaging. The results of this study provide engineering principles for using sustainable paper-based materials with a dual-scale roughness structure and barrier properties in liquid packaging applications.Graphical abstract

This study investigates the synthesis of potato starch elastomers reinforced with silicon dioxide (SiO2) and citric acid as a crosslinking agent to enhance their mechanical and barrier properties. Surface morphology analysis using optical microscopy revealed that pure potato starch films had uneven surfaces. However, higher SiO2 concentrations increased roughness, while citric acid crosslinked films displayed smoother surfaces overall. Water vapor transmission rates (WVTR) indicated that native starch films were highly hydrophilic, while SiO2 incorporation and citric acid crosslinking significantly reduced WVTR of 17% (30% lower than native film), enhancing the barrier properties. Tensile strength testing revealed that citric acid crosslinking increased the tensile strength by 25%, while SiO2 further reinforced the films but decreased elasticity by 15%. SiO2 had little impact on degradation rates, while citric acid crosslinking delayed microbial growth, extending film longevity by 20%. Biocompatibility assays using SiHa, HT-29, and HEK 293 cell lines revealed that the films had varying degrees of cell confluency. Films with both SiO2 and citric acid showed improved confluency (20% higher) compared to films containing only SiO2. However, citric acid alone resulted in the highest confluency (95% viability), suggesting its significant role in biocompatibility. This eco-friendly approach demonstrates substantial advancements in film properties, offering potential applications in diverse biomedical industries.

In this study, polyvinyl alcohol (PVA) films were reinforced with lignocellulosic nanofibers (LCNFs) extracted from bamboo shoot shells using a choline chloride-based deep eutectic solvent (DES). A filler loading of 10 wt% was identified as the optimal condition for enhancing film performance. To improve interfacial compatibility between the PVA matrix and LCNFs, three surface modification treatments were applied to the nanofibers: hydrochloric acid (HCl) hydrolysis, citric acid (CA) crosslinking, and a dual modification combining both methods (HCl&CA). Among all formulations, films incorporating dual-modified LCNF at 10 wt% loading exhibited the most significant improvements. Compared to neat PVA, these composites showed a 79.2% increase in tensile strength, a 15.1% increase in elongation at break, and a 33.1% enhancement in Young's modulus. Additionally, thermal stability and barrier properties were improved, while water swelling and solubility were reduced. Specifically, the modified films achieved a thermal residue of 9.21% and the lowest degradation rate of 10.81%/min. Water vapor transmission rate and oxygen permeability decreased by 18.8% and 18.6%, respectively, and swelling and solubility dropped to 14.26% and 3.21%. These results highlight the synergistic effect of HCl hydrolysis and CA crosslinking in promoting uniform filler dispersion and strong interfacial adhesion, offering an effective approach to valorizing bamboo shoot shell waste into high-performance, eco-friendly packaging materials.

In this study, a novel cellulose insulation with low dielectric constant and loss is prepared by implementing citric acid (CA) crosslinking. In the modified cellulose insulation, the existence of network structure is confirmed by X-ray photoelectron, Fourier transform infrared spectra and dispersion experiments. Moreover, the effect of different CA concentrations on the dielectric properties and other crucial properties of cellulose insulation is investigated through molecular modeling and simulation and experiments. The results show that CA crosslinking reduces the polarizability of cellulose because the hydroxyl groups on cellulose chains are consumed. Moreover, the network structure effectively hinders the motion of the cellulose chains, which further reduces the orientation polarization. The dielectric constant and loss in cellulose insulation decrease by CA crosslinking. The dielectric constant of 0.4 mol/L CA-treated cellulose decreases from 4.89 to 4.12, and the dielectric loss decreases by 32.6% at 50 Hz as compared to the unmodified cellulose insulation. When the CA is completely crosslinked, the permittivity and dielectric loss decrease with the increase in the concentration of CA. Additionally, CA crosslinking modification does not deteriorate the properties of the cellulose insulation. Thus, CA crosslinking modification can be potentially used for preparing cellulose insulation with low dielectric constant and loss.

Thermoplastic starch (TPS), derived from renewable resources, offers advantages such as biodegradability and lower production costs compared to petroleum-based plastics. However, its limited mechanical properties pose a challenge for broader applications. This research aims to explore the potential of enhancing the mechanical and barrier properties of TPS films through the incorporation of silicon dioxide as a reinforcement filler and citric acid as a crosslinking agent. By introducing silicon dioxide as a reinforcement filler, the mechanical strength of the TPS films is expected to be improved. Additionally, the incorporation of citric acid as a crosslinking agent is anticipated to enhance the barrier properties of the films. The combination of these additives holds promise for creating TPS films with improved performance, contributing to the development of sustainable and environmentally friendly materials in various industries. The results reveal that SiO2 improves the stiffness of the films at lower concentrations but causes brittleness at higher concentrations. In contrast, citric acid crosslinked films exhibit improved flexibility and density. Scanning electron microscopy demonstrates the morphological changes in the films, with SiO2 affecting surface roughness and aggregate formation. SiO2 reduces film thickness and transparency, while citric acid enhances water resistance and barrier properties. X-ray diffraction analysis shows a reduction in crystallinity due to the plasticization process. Fourier-transform infrared spectroscopy highlights chemical changes and antimicrobial activity is observed with citric acid against specific bacteria. The soil burial test reveals that citric acid crosslinked films exhibit slower degradation due to antimicrobial properties. The combination of SiO2 reinforcement and citric acid crosslinking enhances the overall performance of the films, promising sustainable and environmentally friendly materials for various applications.

Over the last two decades, there has been growing interest from all stakeholders (government, manufacturers, and consumers) to make packaging more sustainable. Paper is considered one of the most environmentally friendly materials available. A qualitative study investigating consumers’ expectations and opinions of sustainable paper-based packaging materials was conducted where 60 participants took part in focus group sessions organized in two stages. In the first stage, participants expressed their opinions about currently available packages in the market and their expectations about a sustainable packaging material. In the second stage of the study, they evaluated five paper-based prototype packages for two product categories (biscuits and meat). Too much plastic and over-packaging were the key issues raised for current packages. Price and quality were the main driving forces for consumers’ purchase intent. While participants were impressed by the sustainable nature of the prototypes, the design did not necessarily meet their expectations, and they were not willing to pay more for a sustainable package. The key message that emerged from the discussions was the “3Rs”—Reduce, Reuse, and Recycle”—which should be the main points to consider when designing a sustainable packaging.

Sustainable food packaging paper with high barrier and strength properties was developed with rice straw nanocellulose materials. Pulping and bleaching of rice straw were performed using an organosolv pulping and DED (D: chlorine dioxide bleaching; E: sodium hydroxide extraction) bleaching sequence. Bleached rice straw pulp was refined to 90°SR using a laboratory Valley beater. The laboratory handsheets were prepared using pulp slurry at 40°SR and 90°SR. The handsheets of cellulose nanofibrils (CNFs) made of highly refined pulp (90°SR) were surface sized using alkyl ketene dimer (AKD) wax to increase the barrier properties of paper for selective food packaging applications. The paper samples were tested for mechanical, optical, surface, and barrier properties, including tensile index, burst index, tearing index, bending stiffness, elongation, porosity, apparent density, opacity, Cobb value, water vapor transmission rate (WVTR), oil and grease resistance, and contact angle. The refined pulp (90°SR) was analyzed using field-emission scanning electron microscopy (FE-SEM), and it was observed that the morphology of the developed fibers changes to the nanoscale (<100 nm) for at least one dimension. The particle size distribution of the refined pulp using DLS analyzer also confirmed the cellulose fibers to near nanoscale. It was concluded that nanofibers were formed by a high degree of the mechanical pulp refining process and found to be much more economical than alternative processes in this direction. The sample handsheets of CNFs showed good strength and barrier properties. The barrier properties further increased when surface sizing was done using low-cost, nontoxic, and biodegradable AKD wax.

Preparation and characterization of citric acid crosslinked konjac glucomannan/surface deacetylated chitin nanofibers bionanocomposite film

Chitosan/hydroxyethyl cellulose-based sustainable food packaging composite films (CS/HEC/NC) crosslinked with citric acid (CA) and containing organophilic nanoclay were prepared using the solvent casting method. The physical, thermal, mechanical and barrier properties of as-synthesized composite films were evaluated toward their use as an alternative to petroleum-based polymers. A considerable improvement was observed in surface hydrophobicity, water resistance, barrier properties, tensile strength, and thermal stability of the composite films with increasing nanoclay ratio. CS/HEC/NC3 film loaded with 5 wt% nanoclay exhibited the best physical properties with percent enhancements of 22.94°C, 52.56% and 36.53° in maximum degradation temperature, tensile strength, and water contact angle, respectively, over the neat CS/HEC film. In addition, low permeabilities against water vapor (1.240 × 10−11 gs−1m−1Pa−1) and oxygen (1.12 × 10−16 m3s−1m−1Pa−1), and also strong antibacterial activity against Staphylococcus aureus and Escherichia coli were obtained for this film. The food preservation effects of CS/HEC/NC composite films against cherry tomatoes were also studied, and less than 20% mass loss was achieved in five weeks. Consequently, CS/HEC/NC composite films can be considered competitive packaging materials with great potential to improve safety and quality and extend the shelf life of packaged foods.

Perspectives on sustainable food packaging:– is bio-based plastics a solution?

This study addresses the urgent need for sustainable alternatives to conventional plastics by focusing on modification of thermoplastic starch (TPS) derived from renewable biomass sources. Despite TPS's biodegradability and cost advantages, its limitations in mechanical strength and water resistance prompted the investigation of physical and chemical modifications. Ultrasonication, autoclaving, and cross-linking with substances like citric acid and STMP (sodium trimetaphosphate)/STPP (sodium tripolyphosphate) were employed, with citric acid crosslinking standing out for its significant enhancement of transparency, especially beneficial for packaging applications. Film thickness varied with modification methods, with ultrasonicated films exhibiting thinner structures. Differential scanning calorimetry revealed insights into molecular interactions, with citric acid crosslinked film showing a substantial increase in thermal stability of the polymer at 164 °C, while moisture content analysis showed the impact of ultrasonication on reducing water absorption and citric acid crosslinking enhancing dimensional stability. Water vapor transmission rate data highlighted the effectiveness of ultrasonication in creating films with reduced permeability, and citric acid cross-linked films demonstrated potential for tailored water vapor barrier properties. Static water contact angle results indicated the hydrophobicity of films, with citric acid crosslinked films showing significantly more hydrophobic surfaces. The study also delved into water solubility, emphasizing the influence of depolymerization in ultrasonicated films and strengthened starch networks in crosslinked films, affecting their biodegradability. In conclusion, this comprehensive exploration demonstrates the feasibility of producing robust starch films with improved physicochemical properties through physical and chemical modifications, offering potential solutions in the quest for environmentally friendly alternatives to traditional plastics.

The improper disposal of plastics is a growing concern due to increasing global environmental problems such as the rise of CO2 emissions, diminishing petroleum sources, and pollution, which necessitates the research and development of biodegradable materials as an alternative to conventional packaging materials. The purpose of this research was to analyse the properties of biodegradable polymer blends of thermoplastic potato starch (TPS) and polylactide, (PLA) without and with the addition of citric acid (CA) as a potential compatibilizer and plasticizer. The prepared blends were subjected to a comprehensive physicochemical characterization, which included: FTIR-ATR spectroscopy, morphological analysis by scanning electron microscopy (SEM), determination of thermal and mechanical properties by differential scanning calorimetry (DSC), water vapour permeability (WVP), as well as biodegradation testing in soil. The obtained results indicate an improvement in adhesion between the TPS and PLA phases due to the addition of citric acid, better homogeneity of the structure, and greater compatibility of the polymer blends, leading to better thermal, mechanical and barrier properties of the studied biodegradable TPS/PLA polymer blends. After conducting the comprehensive research outlined in this paper, it has been determined that the addition of 5 wt.% of citric acid serves as an effective compatibilizer and plasticizer. This supplementation achieves an optimal equilibrium across thermal, mechanical, morphological, and barrier properties, while also promoting material sustainability through biodegradation. In conclusion, it can be stated that the use of thermoplastic starch in TPS/PLA blends accelerates the biodegradation of PLA as a slowly biodegradable polymer. While the addition of citric acid offers significant advantages for TPS/PLA blends, further research is needed to optimize the formulation and processing parameters to achieve the desired balance between mechanical strength, thermal and barrier properties and biodegradability.

Novel edible films of pectins extracted from low-grade fruits and stalk wastes of sun-dried figs: Effects of pectin composition and molecular properties on film characteristics

The development of green, eco-friendly and sustainable packaging materials is a major challenge in the field of nanoscience and nanotechnology. Advancements in the designing biopolymeric nanocomposites for packaging applications have been established by considering features like biodegradability, environmental friendliness, mechanical properties, cost, safety, etc. Other properties such as thickness, weight, transparency, practicability, recyclability, antimicrobial, porosity, leaching effect, light protective capability, etc. need to be considered during the fabrication of next-generation packing materials for multifaceted applications. Of these, the ultraviolet (UV) protective properties of the designed nanocomposites for sustainable packaging applications are extremely important. The UV protective properties of the packaging materials can be modulated by adding a minute amount of biocompatible nanomaterials with maximum absorption properties in the UV region (200–400 nm). UV light absorption is very important to avoid loss or changes in intrinsic chemical, physical, and biological properties/content of foods, pharmaceuticals, beverages, and so forth during storage and transportation. In the current review, we highlight the principle of UV light protection, the selection of nanomaterials, and the design of nanocomposite films, including the properties and applications of biopolymeric nanocomposite materials for UV protective sustainable packaging. Lastly, the current challenges and prospects of sustainable UV protective packaging are also discussed to provide insights into the future of next-generation packaging technologies.