Advanced polymer nanocomposites in packaging applications

1.1 Challenges in utilizing polymer nanocomposites for packaging applications

The practical implementation of PNCs as packaging materials faces several significant challenges. Ensuring cost-effectiveness is a primary concern, as advanced materials can be expensive to produce. ³² The migration of nanofillers into food products raises safety issues that must be carefully managed to protect consumer health. Additionally, the environmental burden of packaging materials, which are typically disposed of after use, has become a critical issue. Society increasingly recognizes the importance of recyclability, necessitating the design of single-material packaging rather than multi-layered or composite materials. ¹¹ This shift toward simpler, recyclable materials aims to reduce the environmental impact and promote sustainable packaging solutions. ⁴⁸

1.2 Current scenario of PNCs in packaging applications

Studies show that packaging waste poses a significant environmental burden, highlighting the need for sustainable alternatives. ⁴⁹ Recyclability and single-material designs are increasingly preferred over multi-layered composites, aligning with sustainability goals and reducing the environmental footprint. ^{48 , 50} These materials attract attention due to their enhanced properties and versatility. Saba et al. (2014) emphasize the importance of developing food packaging materials that are functional, environmentally friendly, and easy to recycle. ⁵¹ Despite challenges, PNCs have promising potential with improved mechanical strength, barrier performance, and thermal stability. Thermoset polymers are vital for structural applications in sectors like marine, automotive, and aeronautical due to their high specific strength and ease of processing. ⁵²

Advances in nanotechnology have led to the development of PNCs with enhanced functionalities, meeting requirements for various industrial applications like packaging, construction, and pharmaceuticals. Nanocomposites offer advantages over traditional materials, including improved sustainability, lightweight, and increased toughness. ⁵³ Common materials used in thermoset nanocomposites include carbon nanoparticles, nanoclays, metal oxides, and polymeric-based nanoparticles. ⁵⁴ However, achieving uniform dispersion of nanoparticles remains a significant challenge. Dybka-Stepien et al. (2020) demonstrated the potential of PNCs in extending the shelf life of perishable goods through improved barrier properties. ⁵⁵

Recent research focuses on cost-effectiveness by developing efficient and scalable production methods. Mittal et al. (2014) suggest that optimizing nanofiller dispersion can reduce production costs while maintaining desired PNC properties. ⁵⁶ Exploring biodegradable and renewable nanofillers, as discussed by Kuzmina et al. (2019), can mitigate environmental concerns and enhance PNC sustainability. ⁵⁷ Hassan et al. (2004) investigated nanotechnology applications in high-performance composites, aiming to reduce weight while enhancing strength. The study mainly focused on improving the toughness of nanomodified thermoset composites, addressing fracture toughness in highly cross-linked brittle thermosets. Results suggested that there is a significant improvement in fracture toughness with reactive butadiene-nitrile rubber-modified thermosets. ⁵⁸

1.3 Strategy for improving the properties of polymeric nanocomposites

Improving the properties of polymeric nanocomposites using carbon-based, metallic, and metal oxide nanoparticles involves several advanced strategies aimed at enhancing their mechanical, opto-electronic, thermal and physico-chemical properties.

Carbon-based nanoparticles, such as carbon nanotubes and graphene, are widely used for their exceptional strength, electrical conductivity, and thermal stability. ⁵⁹ To maximize their benefits, these nanoparticles are often functionalized with various chemical groups like carboxylic, amine, hydroxyl, thiols etc. to enhance their dispersion within the polymer matrix. This functionalization process improves interfacial bonding, leading to significant improvements in the composite’s overall mechanical and thermal properties. ⁶⁰ Additionally, hybrid nanocomposites can be created by combining carbon nanoparticles with other nanofillers, such as metal oxides. ⁵¹ This synergy results in nanocomposites with enhanced strength, conductivity, and other desirable properties. Surface modification of carbon nanoparticles further improves their compatibility with the polymer matrix, leading to better dispersion and enhanced performance. ⁶¹

Metallic nanoparticles, including silver and gold, offer unique properties such as high electrical conductivity and antimicrobial effects. Incorporating these nanoparticles into the polymer matrix can significantly enhance the nanocomposite’s electrical properties and mechanical strength. Alloy nanoparticles, such as silver-copper, provide a combination of improved thermal stability and mechanical performance. ⁶¹ Coating metallic nanoparticles with polymers or other materials enhances their dispersion and stability within the polymer matrix, leading to uniform distribution and consistent properties throughout the composite. ^{62 , 63 , 64}

Metal oxide nanoparticles, such as titanium dioxide (TiO₂) and zinc oxide (ZnO) and silicon dioxide (SiO₂), are renowned for their excellent mechanical, thermal, and barrier properties. Advanced dispersion techniques, such as ultrasonication and high-shear mixing, are employed to achieve uniform distribution of these nanoparticles within the polymer matrix. ⁶⁵ Surface treatment of metal oxide nanoparticles with surfactants like CTAB, AOT or coupling agents improves their compatibility with the polymer, leading to enhanced mechanical and thermal properties. ⁶¹ Additionally, creating core–shell structures with metal oxide nanoparticles like CdSe/SiO₂, TiO₂/ZnO etc. can further enhance their functionality, providing improved stability and performance in the nanocomposite. ⁶⁶

These strategies collectively contribute to the development of polymeric nanocomposites with superior opto-electronic, mechanical, thermal and physico-chemical properties, making them suitable for a wide range of advanced applications, including packaging, electronics, and structural materials. Continuous research and innovation in this field promise even greater enhancements in the future.

The review stands out for its innovative aspects and advantages for the comprehensive integration of various categories of nanofillers, such as metal oxides and semiconductors based, ceramics, carbon-based materials, polymers, and hybrids, offering a broad perspective by examining the unique characteristics of different nanofillers. It provides a detailed summary of recent research on PNC fabrication methods and nanofiller properties, with a focus on packaging. It focuses specifically on packaging applications, allowing for an in-depth analysis of PNC properties and performance. The review also explores the detailed advanced functionalities of PNCs, including their mechanical, thermal, optical, and barrier properties. Emphasizing environmental impact and sustainability, the review highlights the importance of eco-friendly and biodegradable materials. It offers valuable insights into the latest advancements, technologies, and strategies to improve the overall properties of PNCs that showcase their potential for durable and sustainable packaging solutions, making them valuable materials in the packaging industry.

By incorporating these innovative aspects, this review not only provides a comprehensive and focused analysis of PNCs in packaging applications but also emphasizes the environmental and societal benefits of adopting such advanced materials. This makes the paper a significant and timely contribution to the ongoing discourse on sustainable packaging technologies.

2.1 Solvent casting method

Polymer nanocomposites are often produced in laboratories using the solvent or solution casting approach. Tetrahydrofuran, toluene, acetone, cyclohexane, dimethylformamide, and numerous other solvents can all dissolve this polymer. Usually, applying it involves allowing the nanofillers to mix with the polymer solution once they have been dispersed in the proper solvent (ethanol in this case). The nanocomposites are separated from the solvent using the latex system’s solvent coagulation or solvent evaporation. Which solvent is preferable depends in large part on how soluble the polymer matrix is. The same solvent can be applied to both the nanofibers and the matrix preparation. This method may be used to produce a well-dispersed nanofiller in the appropriate solvent. ^{67 , 68}

Specifically, Marroquin et al. developed the solution-mixing approach to produce Fe₃O₄/multiwalled carbon nanotube (MWCNT)/CHIT hybrid composites, based on chitosan (CHIT). The mixture was then supplemented with CHIT and acetic acid following an hour of sonication of Fe₃O₄ and MWCNT in distilled water. Ultrasonication and a magnetic stirrer were then used to agitate the mixture. The mixture was degassed and vacuum dried in order to create the nanocomposite for the following reasons. ⁶⁹

2.2 Sol–gel method

A wet chemical method called the sol gel process is used to incorporate polymer nanocomposites in thin sheets. One may argue that the dispersion of nanoparticles across the polymer matrix is homogeneous. To summarize, the precursors in sol–gel synthesis are highly reactive metal alkoxide or monomers of polymers. The starting ingredient in the process is an inorganic salt. After blending the basic ingredients in the vapor phase, a sol is produced by controlling the amount of germane constituents and then hydrolyzing the mixture. After heating it to a specific sol temperature, it solidifies into a polymer. According to the method, covalent or hydrogen bonds bind the organic polymers and inorganic nanoscale portions and components of the polymer nanocomposites. Its potential application is limited by the fact that most precursors are pricy and dangerous. Crystalline composites including polymers and inorganic oxide nanoparticles (NPs) are difficult to produce since these polymers are thermally unstable and the sol–gel process might take days or weeks. The primary problem with this process is contraction and brittle fracture caused by the volatile nature of the solvent, the presence of small molecules, and the presence of water. ^{70 , 71} For example, the sol–gel approach was used to synthesize a nanocomposite of TiO₂ and poly-vinyl alcohol (PVA). Triethanolamine was added directly to the mixture to create a homogenous sol, and water was added gently and slowly after that. After introducing and mixing the above-discussed sol, the suspension was prepared at room temperature for the production of PVA and TiO₂ nanocomposites. The product had been washed with a water–ethanol solution, and the last procedure for drying was oven drying. A muffle furnace was then used to heat the TiO₂/PVA nanocomposites to the necessary temperature. ⁷²

2.3 Dip coating method

The dip coating procedure offers the benefit of being able to cover both sides of the substrate with a high-quality layer. This technique has the benefit of being less costly than the others. Drainage, deposition, and immersion are the three phases. Solvent evaporation comes after solvent removal. In order to give adequate time for coating, the substrate is dipped in the solution at a standard rate during the first phase. Drainage and deposition are the following stages. They are retained in the solvent after the substrate forms. By using the previously indicated method, a thin layer is formed on the substrate and is gradually removed. The process of extracting the product from the crude extract ends with solvent evaporation. Subsequently, the solvent-containing substrate is baked by heating it to a certain temperature. ^{73 , 74 , 75}

2.4 Electrochemical method

Electrochemical synthesis is a straightforward chemical preparation technique carried out with the use of an electrochemical workstation. An electrochemical reaction requires the use of three electrodes: a counter electrode, a reference electrode, and a working electrode. With this synthesis approach, polymer nanocomposite films that may be directly created on an electrode surface for electrocatalytic applications are produced in the most efficient manner. The amount of product produced can also be determined by the integrated charges used, and an electrochemical synthesis could be impacted by an applied potential or current density alone. Many advantages are generally provided by this technology, such as fast reaction times, ease of control, simplicity in operation, and environmental friendliness. Furthermore, by removing the use of an oxidant, the electrochemical method produces a product with higher purity. Unfortunately, the limited surface area of the working electrode has limited the use of electrochemical technologies for large-scale manufacturing. ^{76 , 77 , 78 , 79}

In order to create a layered graphene nanosheet/polyaniline (GNS/PANI) multilayer composite, Gao et al. coated reduced graphene oxide sheets (GNS) using a dip-coating process before electrostatically depositing PANI nanofibers. Using Hummer’s approach, synthetic graphite oxide (GO) was created from natural graphite. The dispersion was sonicated by the researchers in an ultrasonic bath to exfoliate the GO. Then, utilizing glucose as a reductant, GNS was created. The GNS/PANI nanocomposite was created by electropolymerizing PANI nanofibers onto the surface of the GNS film using a three-electrode electrochemical cell that included platinum foil and a saturated calomel electrode (SCE). The GNS layer was created by partially dipping stainless steel sheets into the suspension and letting them dry uniformly. Afterwards, the stainless-steel sheet coated with GNS film served as a functional electrode for the PANI deposition. The electrolyte was a mixture of aniline (0.1 M) and sulfuric acid (1 M). By applying a voltage between 0.2 V and 1.2 V against SCE for two cycles of cyclic voltammetry at a scan rate of 5 mV/s, aniline monomers were In situ electropolymerized on GNS. The creation of the GNS/PANI nanocomposite was aided by the electrostatic interaction between positively charged aniline monomer ions and negatively charged GNS nanosheets. A multilayered GNS/PANI composite was produced after both components were placed on the substrate. In order to produce the multilayered composite, the electro-polymerization procedure was repeated. Afterwards, ethanol was used to rinse the coated samples before they were burnt to dried. ⁸⁰

2.5 Melt intercalation technique

The melt intercalation method is an economical, solvent-free, and eco-friendly process. Its main benefit is that it produces a dispersion of nanoparticles that is uniformly dispersed, optimizing the material’s thermal properties. Nevertheless, the high temperatures required could change or deteriorate the nanoparticles’ surface characteristics. The polymer matrix is initially heated to a high temperature in this method. Then, after adding the nanoparticles, the mixture is agitated vigorously for a certain amount of time to guarantee even dispersion. Processing conditions, host polymer compatibility, and nanofiller surface modification can all be managed during the dispersion process. ⁸¹

2.6 In-situ polymerization

Polymer nanocomposites are often synthesized using this method. In this procedure, the monomer and nanoparticles are combined using an appropriate solvent. In essence, monomers are contacted with nanoparticles to create a polymer nanocomposite, which is subsequently polymerized with the aid of a suitable reagent or free radical initiator. This strategy has a bottom-up methodology. This method can be used to create multidimensional, clearly defined structures that have completely different attributes from their original ancestors. It is frequently difficult to achieve homogeneous dispersion inside a polymeric matrix. A metal precursor is employed in the polymer matrix to create metal or metal oxide particles from nanoparticles. The In situ technique provides for precise control over particle size and form. The sol–gel procedure is the most popular way to chemically transform metal nanoparticles into an organic phase. ^{26 , 82}

3.1 Mechanical properties

The study of mechanical properties of PNCs for packaging applications is crucial for ensuring the durability, reliability, and effectiveness of packaging materials. PNCs are increasingly used in packaging due to their enhanced mechanical properties. ^{50 , 59 , 84 , 85 , 86 , 87} These materials consist of a polymer matrix reinforced with nanoscale particles like clay, silica, or carbon nanotubes. The incorporation of nanofillers significantly enhances mechanical properties, including tensile strength, impact strength, Young’s modulus, stress at yield, strain at break, and elongation at break, making PNCs ideal for packaging. ^{85 , 86 , 87}

Notably, PNCs exhibit increased tensile strength. Abbas et al. (2017) demonstrated that adding nano-silica to polypropylene enhances tensile strength and modulus, crucial for packaging durability during transportation and handling. ⁴⁹ Roberto Pantani et al. (2023) found that PLA-ZnO nanocomposite films showed a slight increase in Young’s modulus and reduced elongation at break. Adding a plasticizer potentially improves mechanical strength. ZnO/PHBV nano-bio composites exhibited a 57 % increase in Young’s modulus with 4 wt% ZnO NPs loading, attributed to increased PHBV crystallinity, homogeneous nanoparticle distribution, and strong interfacial adhesion. However, the strain at break decreased by 30 % with higher ZnO NPs content due to filler reinforcement. ⁸⁸ In PP/ZnO nanocomposites, elongation at break and tensile strength values decreased due to agglomeration and poor interfacial adhesion. ⁸⁹ Singh et al. (2024) incorporated CdSe nanoparticles into the polymer matrix using solvent casting technique. Also, the effect of morphology of CdSe nanoparticles and different concentrations resulted in the enhanced mechanical, optical and physico-chemical properties at minimal concentration of nanofiller. ^{90 , 91}

Increase the mechanical properties of polymer matrices, such as brittleness, strength, flexural strength, elasticity, and ductility, inorganic particles are frequently added. The enhanced mechanical properties are dictated by the interplay between the polymer matrix and nanofiller chemistry, the loading of the nanofiller, and the surface interactions between the two. Numerous studies have revealed that even at low filler loadings, polymer nanocomposites containing nanoparticles like SiO₂, TiO₂, ZnO, ZrO₂, and clay have mechanical strength. Nonetheless, certain limitations might arise from the formation of aggregations at interfacial contacts. ^{92 , 93 , 94} The mechanical characteristics of a polyvinyl alcohol/silica nanocomposite (SiO₂/PVA) were investigated by Nakane et al. They found that when the filler amount was increased to 30 wt%, the brittle composite was produced, and while mechanical strength increased significantly, the percentage of elongation at break decreased. ⁹⁵ Sengupta et al. studied the mechanical properties of polymer nanocomposites made of polyamide-6.6/SiO₂, poly (trimethylhexamethylene terephthalamide)/SiO₂, and polystyrene (PS)/ZnO. Adding 5 wt% SiO₂ nanoparticles improved the matrix’s tensile strength and Young’s modulus made of polyamide-6.6. More than 10 % of the weight of the nanocomposite was loaded with silica, increasing its strength. On the other hand, elongation at break and ductility were also decreased. The nanocomposite becomes more brittle as the nanofiller loading surpassed 25 wt%. Tensile modulus was significantly increased while elongation at break was decreased when 5 wt% ZnO particles were added to the polystyrene matrix. Surface adhesion was unable to manage significant mechanical stresses in a satisfactory manner. ⁹⁶

3.2 Optical properties

Inorganic particles have been employed for some of the earliest known uses because of their optical characteristics. Over the past 20 years, there has been a lot of interest in the development of transparent polymer nanocomposites with unique optical properties such light absorption, a high refractive index, and photoluminescence. The optical characteristics of nanocomposites are influenced by the distribution, size, shape, and concentration of nanoparticles. The size and shape of inorganic nanoparticles directly affect their intrinsic optical properties, including refractive index, color absorption, and emission. When the size of the nanoparticles decreases to less than 10 nm, a quantum confinement effect is seen, which modifies the optical properties of the nanoparticles relative to their bulk counterparts. ^{97 , 98}

Optical properties such as absorbance, transparency, reflectance, UV-blocking tendency, optical clarity, and opacity are crucial for packaging applications. Mallakpour et al. (2017) used surface-modified TiO₂ nanoparticles (30 nm–50 nm) to fabricate PVA/TiO₂ nanocomposites via solution casting. These nanocomposites showed significant UV absorbance compared to pure PVA, indicating enhanced UV-blocking capabilities, making them ideal for UV-protective packaging. ⁹⁹

Marand et al. synthesized PAI/TiO₂ nanocomposite films using an in situ sol–gel method. At low nanofiller concentrations, these films exhibited transparency due to uniform nanoparticle distribution, but became opaque as the concentration increased. This study concluded that PAI/TiO₂ nanocomposite’s transparency and opacity can be customized by adjusting TiO₂ nanofiller concentrations, making them versatile for packaging applications. ¹⁰⁰ Kim et al. (2011) fabricated composite films of PVA and graphene oxide (GO) using modified Hummer’s methods and solution mixing. These films, cast onto PET substrates, displayed a layered structure with high transparency of 97 % light transmittance for 0.1 wt% GO and 92 % for 0.3 wt% GO at 550 nm wavelength. This indicates that low-concentration graphene oxide can produce highly transparent composite films suitable for clear, visually appealing packaging. ¹⁰¹ Wang et al. (2005) developed PMMA/SiO₂/ZrO₂ nanocomposites using a non-hydrolytic sol–gel technique. The nanocomposite films maintained over 95 % optical transmittance even with 20 % nanoparticle loading. The study concluded that this method effectively produces nanocomposites with excellent optical clarity, and their optical properties can be tailored by varying nanoparticle concentrations, making them suitable for high-performance packaging applications. ¹⁰²

Parlak, Demir, and colleagues created a highly absorbent and transparent nanocomposite to efficiently absorb ultraviolet light. Utilizing a polystyrene (PS) matrix, cerium (IV) oxide (CeO₂) nanoparticles were applied to poly-methyl methacrylate (PMMA) chains in order to precisely match the refractive index. Developing UV-absorbing properties with enough visual transparency has been the subject of a lot of study. CeO₂ nanoparticles were tied to PMMA chains in order to match their refractive index to a PS matrix. According to many research, the UV-blocking properties of transparent nanocomposites with minuscule nanoparticle concentrations are significantly enhanced. ¹⁰³ The amount of UV absorption in composites is mostly determined by their particle size. The absorption edge decreases in particle size as it approaches the blue. Xiong et al. investigated the UV-absorbing properties of a poly (styrene-butyl acrylate) (PS-PnBA) copolymer matrix containing ZnO particles of various sizes, including 60 nm and 100 nm. They observed that when the particle diameter decreased, the UV absorption edge shifted toward the blue. When compared to bulk semiconductor materials, quantum confinement effects cause an increase in the energy band gap and a shift in the UV absorption edge towards the blue side. ¹⁰⁴

3.3 Thermal properties

Polymer nanocomposites (PNCs) are notable for their exceptional thermal properties, which are particularly beneficial for packaging applications. Key thermal properties include thermal conductivity, melting point, heat capacity, glass transition temperature, and thermal degradation, crucial for studying thermal stability. ⁸⁶

Adding copper nanoparticles to LDPE and LLDPE enhances thermal stability due to their higher heat capacity and thermal conductivity. However, exceeding 5 % copper content decreases stability due to energy diffusion from copper nanoparticle clusters. Studies suggest metal ions can accelerate the deterioration of some polymers, such as SAN, when exposed to temperatures above 230 °C for extended periods. ¹⁰⁵ Lee et al. (2014) observed that adding nanofillers to an ethylene vinyl acetate (EVA) matrix improves thermal stability. ¹⁰⁶ Layered double hydroxide (LDH) nanofillers modified with anionic surfactants like sodium dodecyl sulfate (DS), sodium dodecylbenzene sulfonate (DBS), and stearate (SA) showed significant improvements. DS-LDH/EVA nanocomposites exhibited a 19 °C increase in thermal stability, while DBS-LDH/EVA and SA-LDH/EVA nanocomposites showed a 12 °C increase. Research indicates that carbon nanotubes (CNTs) enhance the thermal stability of polyethylene (PE) due to their excellent thermal conductivity. ¹⁰⁷ Li et al. (2005) found that incorporating multi-walled carbon nanotubes (MWCNTs)) into PE via in situ polymerization significantly improves thermal stability and delays the thermal decomposition of the PE matrix. This improvement is attributed to the formation and stabilization of MWCNTs-bonded macroradicals. These findings highlight the importance of PNCs in enhancing thermal properties for packaging applications, ensuring materials can withstand higher temperatures and maintain their integrity during use. ¹⁰⁸

For optical and electrical applications, nanocomposites are perfect since they are transparent and thermally stable. ^{109 , 110} Nanoparticles can enhance mechanical strength, optical clarity, and magnetic properties in polymer matrices in addition to thermal stability. For instance, graphene oxide (GO)-polyvinylpyrrolidone (PVP) nanocomposites have exceptional mechanical, thermal, and dielectric properties, rendering them perfect for application in sensors, conductive coatings, and energy storage devices. Comparably, functional nanocomposites such as titanium dioxide, cellulose nanoparticles, and carbon nanotubes have demonstrated notable improvements in mechanical, electrical, and optical properties, hence broadening their prospective uses in the biological, electronic, and structural domains. Zirconia and silica nanoparticles were added by Wang et al. to improve the heat stability of poly (methyl methacrylate) (PMMA). The activation energy needed to break down PMMA polymer chains by heat was quadrupled by the addition of merely 0.5 % of nanoparticles. The mobility of polymer chains inside the composites was restricted by inorganic nanofillers, which also prevented free radicals from harming the PMMA main chains. Due to nanoparticle dispersion, which hampered heat transmission and served as a barrier against oxygen and volatile degradation agents, it was demonstrated that a number of transparent nanocomposites, including PMMA/clay, ethylene-propylene-diene/clay, PVA/TiO₂, and PS/ZnO, had increased thermal stability. Two of the poly-nanocomposites’ enhanced thermal properties include a delayed decline in the coefficient of thermal expansion and a shift in the thermal degradation start peak. ¹¹¹ Zhang et al. synthesized a transparent ZnO/PMMA nanocomposite by In situ polymerization and evaluated its heat stability against a composite prepared by direct physical mixing. Because of the interactions between the polymer matrix and the nanofiller at the interface, the in situ polymerized composite exhibited superior heat stability. ¹¹² In situ polymerization was employed by Demir et al. to create a transparent, thermally stable PMMA/ZnO nanocomposite. Research findings indicate that an increase in filler content leads to a higher glass transition temperature in optically transparent poly-nanocomposites that exhibit enhanced thermal properties. ¹¹³

3.4 Physico-chemical properties

PNCs have superior barrier properties and solvent resistance, with permeability influenced by particle size, shape, and alignment. High surface area and large aspect ratio nanoparticles enhance barrier properties by forming a tortuous path, increasing diffusion path length, and reducing permeability. ^{101 , 114} Non-flammability and high thermal stability make these nanocomposites ideal for protective barrier packaging, as they reduce heat and mass transfer between the flame and the polymer. ¹⁰⁵ The incorporation of nanofillers can also enhance the thermal stability of the composites, making them suitable for packaging applications that require resistance to high temperatures. ^{115 , 116} PNCs can also demonstrate improved chemical and solvent resistance, which is crucial for packaging materials that need to shield contents from deterioration. ^{3 , 45 , 117 , 118} One of PNCs’ greatest benefits is their enhanced gas barrier because nanofillers provide gas molecules a winding route, thus lowering their permeability. ¹¹⁹ PNCs also offer better moisture barrier properties, blocking the passage of water vapor and maintaining the quality and shelf life of packaged goods. Certain nanofillers, like titanium dioxide (TiO₂), can enhance the UV resistance of PNCs, protecting the contents from UV-induced degradation. These enhanced properties make PNCs ideal for various packaging applications, including food, pharmaceutical, and cosmetic packaging, where they help extend the shelf life and maintain the quality of the. ^{3 , 119 , 120} Overall, polymer nanocomposites offer a number of benefits for packaging applications, including enhanced mechanical strength, excellent barrier qualities, thermal stability, and chemical resistance, all of which ensure the quality and lifespan of products. ^{115 , 116 , 121}

Nanofillers, such as layered silicates, are used in the packaging industry as flame retardants. Low water vapor pressure (WVP) is desirable for high-performance food packaging, protective coatings etc. ¹²² Significant barrier efficiency is observed at reduced WVP values. Additionally, nanocomposites possess remarkable tensile strength and modulus properties. A study by Penaloza et al. (2018) uses poly (methyl methacrylate)/nanoclay nanocomposites with 20 wt% nanofiller show a 60 wt% improvement in modulus compared to the base polymer. ¹²³ A study by Kwon et al. (2013) on polymer/graphite nanocomposites found that permeability decreases with low filler loading. ¹²⁴ Jin et al. (2013) demonstrated that graphite and graphene-filled polyamide matrices exhibit optimal permeability properties at low filler loading. In ethylene vinyl alcohol/graphite nanocomposites, initial vapor permeability decreases with 1 wt% graphite content, but increases at 2 wt% due to nanosheet aggregation. ¹²⁵ Similarly, water permeability of polyamide (PA11) and polyamide (PA12) nanocomposites increases with graphene content above 0.1 wt% loading. ¹²⁶ Lai et al. (2015) studied cyclic olefin copolymer filled with graphene, finding that water vapor permeability reduces by 21 % with 0.06 wt% graphene content, but higher loadings increase vapor permeability due to graphene nanosheet agglomeration. These findings highlight the importance of optimizing nanofiller content to achieve desired barrier properties for packaging applications. ¹²⁷

4.1 Metal-oxide and semiconductor-based nanofillers

Polymer nanocomposites incorporating metal-based nanofillers have gained significant attention due to their enhanced properties like optical, ¹²⁸ mechanical ¹²⁹ and thermal ²⁶ in diverse fields of applications such as pharmaceuticals, ¹³⁰ packaging ¹³¹ etc. Various metal oxide, including alumina, ¹²⁸ zinc oxide, ¹³² and titanium oxide, ¹³³ that are commonly used as nanofillers in the polymer matrices are listed in Table 1. Metal nanoparticles, such as copper and silver, can be incorporated into polymers like poly (vinyl alcohol) to improve antibacterial properties and electrical conductivity. ^{134 , 135} Metal-polymer nanocomposites, particularly those containing Pt, Ni, Co, and Au, are popular for catalytic applications. ¹³⁴ The preparation methods for these nanocomposites include melt mixing, solution casting, and electrospinning. ³⁵ The growing interest in these materials is driven by their unique properties and potential for improving performance in numerous industrial sectors.

4.2 Carbon-based nanofillers

Carbon-based nanofillers, including carbon nanotubes (CNTs), ¹³⁹ graphene, ¹⁴⁰ fullerenes, and carbon nanofibers, ¹⁴¹ are widely used to enhance the characteristics of polymer nanocomposites. These nanofillers can improve thermal stability, electrical conductivity, and mechanical strength of polymer matrices ¹⁴² are listed in Table 2. However, challenges such as agglomeration and poor solubility often necessitate functionalization of carbon nanoparticles to improve their dispersion and interaction with polymers. Various methods, including In situ polymerization, solution mixing, and melt blending, are employed to incorporate these nanofillers into polymer matrices. ³⁵ The resulting nanocomposites exhibit enhanced characteristics, such as improved bonding strength, fire retardance, and energy storage capacity. ¹⁴³ Optimizing nanofiller loading and ensuring proper interactions at the polymer-filler interface are crucial for maximizing the benefits of these carbon-based nanofillers in polymer nanocomposites. ¹⁴⁴

4.3 Polymer nanofillers

Polymer nanocomposites incorporate various types of polymeric nanofillers to enhance material properties. These nanofillers are the nanoscale particles made from polymers which are used to enhance the properties of polymer nanocomposites. ^{149 , 150} These nanofillers include polyhedral silesquioxanes (POSS), ¹⁵¹ dendrimers, ¹⁵² nanogels ¹⁵³ etc. which can be one-, two-, or three-dimensional, with their high surface area contributing to improved thermal stability, mechanical, optical and barrier properties of the polymer matrix ^{154 , 155} are listed in Table 3. POSS is a nanostructured material which consists of hybrid organic–inorganic material and dendrimers is a highly branched chain polymer with high degree of functionally that have gained particular attention due to their excellent performance even at low filler content. ^{153 , 156} The effectiveness of nanofillers depends on their dispersion within the polymer matrix and the quality of the interface between filler and matrix. Various functionalization techniques are employed to modify nanofillers and improve their interaction with polymers. ^{149 , 150}

4.4 Ceramic-based nanofillers

Ceramic nanofillers are nanoscale particles made from ceramic materials that are used to enhance the properties of polymer nanocomposites (PNCs). ¹⁵⁹ These nanofillers can significantly improve the mechanical, thermal, electrical, and dielectric properties of the composites. Types of ceramic nanofillers include silica (SiO₂) nanoparticles, ¹³⁰ known for their high surface area and chemical stability, alumina (Al₂O₃) nanoparticles, ¹³⁰ which enhance wear resistance and thermal conductivity, and titanium dioxide (TiO₂) nanoparticles, valued for their photocatalytic properties and UV resistance ¹⁶⁰ are listed in Table 4. Additionally, barium titanate (BaTiO₃) nanoparticles are used for their ferroelectric properties, enhancing the dielectric properties of PNCs, while zinc oxide (ZnO) nanoparticles offer antibacterial properties and improve mechanical and thermal properties. ¹³² The advantages of ceramic nanofillers include enhanced mechanical properties, such as increased tensile strength and hardness, improved thermal stability and conductivity, better dielectric properties, and the introduction of specific functional properties like UV resistance and antibacterial activity ^{160 , 161 , 162} Overall, ceramic nanofillers play a crucial role in advancing the capabilities of polymer nanocomposites, making them suitable for a wide range of advanced applications. Proper functionalization and dispersion of nanofillers in the polymer matrix are essential for achieving optimal performance in nanocomposites. ^{158 , 163}

4.5 Composite nanofillers

Hybrid nanofillers, combining different types of nanoparticles, have emerged as a promising approach to enhance the properties of polymer nanocomposites (PNCs). ¹⁶⁸ Two-dimensional (2D) nanosheet-constructed hybrid fillers can improve dispersion and multifunctionality in PNCs. ¹⁶⁹ The integration of carbon nanotubes with insulating clay layers has been shown to significantly increase lithium-ion conductivity and mechanical strength in polymer electrolytes. ¹⁷⁰ Hybrid nanofillers can also enhance mechanical properties, electromagnetic shielding efficiency, and thermal conductivity of polymer. ^{170 , 171} Various combination of polymers and nanofillers are listed in Table 5. Specifically, the combination of montmorillonite and carbon nanotubes as hybrid fillers in thermoplastic-based nanocomposites has demonstrated improvements in rheology, morphology, thermal stability, flame retardancy, electrical properties, mechanical strength, and tribology. ¹⁷² The synergistic effects of hybrid nanofillers facilitate efficient dispersion and optimize the overall functionality of the resulting nanocomposites.

4.6 Critical summary of nanofiller properties and nanocomposite characteristics

Nanofillers significantly influence the properties of nanocomposites, enhancing their performance for various applications. Like metal oxides, such as TiO₂ and SiO₂, improve transparency, thermal stability, and antimicrobial properties. Carbon-based fillers, including r-GO, GO, and CNT, offer superior mechanical strength, thermal stability, and electrical conductivity. Table 6 provides a comparison of the properties of different nanofillers below. This table provides salient properties of nanofillers and composites. The table highlights how specific nanofiller properties contribute to the overall improvements in the polymer nanocomposites.

5.1 Critical analysis

The review identifies several key advancements and remaining gaps in the field of polymer nanocomposites (PNCs) for packaging applications. Studies have highlighted the superior mechanical, thermal, and barrier properties of PNCs, with nanofillers significantly enhancing the overall performance. However, scalability of production remains a challenge, as most research is limited to laboratory-scale synthesis. Additionally, concerns about nanofiller migration into food products and the recyclability of PNCs require further investigation. While biodegradable polymers have been explored, more research is needed on developing high-performing, recyclable PNCs. Some studies may overstate the benefits of PNCs without adequately addressing cost and environmental impacts. Future research should focus on scalable, sustainable production methods, ensuring safety and regulatory compliance, and developing recyclable materials to fully realize the potential of PNCs for sustainable.

5.2 Conclusions

In conclusion, polymer nanocomposites (PNCs) represent a transformative advancement in materials science, particularly within the packaging industry. Their unique combination of enhanced mechanical properties, superior barrier performance, and reduced environmental impact positions them as a highly effective solution for modern packaging needs. The ongoing development of eco-friendly and biodegradable PNCs aligns with the increasing market demand for sustainable packaging options, addressing the urgent need for industries to reduce their carbon footprints and comply with stringent environmental regulations. The synergistic effects between the polymer matrix and the nanofillers lead to improved characteristics, such as increased surface area, enhanced magnetic behavior, superior catalytic activity, and better optical, mechanical, thermal, and barrier properties. This customization potential allows PNCs to be tailored for specific applications, enhancing their versatility in different fields. Moreover, the lightweight and cost-effective nature of PNCs further contributes to their effectiveness in both environmental and industrial contexts, as they help reduce transportation costs and energy consumption. Various fabrication techniques, including in situ synthesis, solution mixing, melt blending, and dip coating etc., provide the flexibility needed to design PNCs that meet specific performance requirements. As research and development in polymer nanocomposites continue to advance, these materials are expected to play an essential role in shaping the future of sustainable packaging, ultimately contributing to a greener and more sustainable world.