Advances in High Barrier Film Materials Research

Advances in High Barrier Film Materials Research

In recent years, high barrier film materials have been widely used in the packaging of food, pharmaceuticals, chemicals, electronic device encapsulation, and fuel cell membranes, owing to their excellent barrier properties, low cost, ease of use, good transparency, strong print adaptability, and good mechanical performance. These materials have experienced rapid development. The superior barrier properties of high barrier film materials are a key characteristic, encompassing excellent gas barrier properties, moisture resistance, oil resistance, and fragrance retention.
Early barrier film materials were represented by ethylene-vinyl alcohol copolymer (EVOH), polyamide (PA), polyvinylidene chloride (PVDC), and polyvinyl alcohol (PVA) films. With the robust demand for products in the food and beverage, medical, and chemical industries driving stricter requirements for packaging barrier properties, various high-performance barrier film materials have now been developed. These include multilayer polymer composite films, vacuum metallized composite films, and polymer/layered nanocomposite films. This article summarizes and shares insights on the barrier performance, production technologies, and applications of various high barrier film materials.
1. Multilayer Polymer Composite Films
Due to the varying advantages and weaknesses in the performance of different polymers, single polymer film materials find it challenging to meet the multifunctional requirements of numerous products. Therefore, multilayer film composite technology, which combines two or more single polymer films to form multilayer polymer composite films, is used to complement the performance advantages of various polymers. This not only enhances the barrier properties of the film materials but also improves other properties such as heat sealability, thermal resistance, mechanical properties, and UV resistance. Currently, the development of multilayer film composite technology includes co-extrusion, coating, and layer-by-layer assembly techniques.

1.1 Co-Extrusion Composite Films

Co-extrusion composite films are produced by heating and melting various polymers using multiple extruders, which are then co-extruded through a multi-channel die to form multilayer composite films. This technology is primarily used for thermoplastic polymer composites that are compatible, and it does not use solvents, thus reducing environmental pollution. The production process is streamlined, and the cost is low, making it widely used in film production companies. Recent research has achieved new progress in co-extrusion composite film materials. For instance, Wang Ruobing et al. [1] used polyethylene (PE), polypropylene (PP), nylon 6 (PA), and ethylene-vinyl alcohol copolymer (EVOH) to prepare a five-layer composite film. EVOH and PA6 serve as the barrier layers, while PE acts as the heat seal layer. This five-layer co-extrusion composite film exhibits high barrier properties and excellent mechanical performance, making it an ideal high barrier packaging material. Similarly, Liang Xiaohong et al. [2] blended and modified EVOH with PE and PA to prepare a PE/PA/EVOH/PA tough high barrier composite film, which boasts excellent comprehensive performance and promising application prospects.

1.2 Coating Composite Films

Coating composite films are made by dissolving barrier polymers in a solvent to form a coating solution, which is then applied to the surface of a base film using coating equipment. After drying and curing, a multilayer composite film is formed. This technology is suitable for polymers that are difficult to process into films independently, such as PVDC and PVA. It is a simple process with low production cost and good barrier properties, though it may leave organic solvent residues that cause environmental pollution. Recent research has also made significant advancements in coating composite films. For example, Sang Lijun et al. [3] applied a 2-4 µm PVDC coating on PP, PE, CPP (cast polypropylene), and PET (polyester) films, significantly reducing their gas and moisture permeability, which is used in manufacturing pharmaceutical composite packaging bags. Shu Xin et al. [4] employed biaxially oriented PP, biaxially oriented PET, biaxially oriented PA, or PE films as base films, treated them with corona discharge, and then applied a modified acrylate polymer BARILAYER high barrier coating solution. After thorough drying and curing at 40-50°C for 5-6 hours, the coated surface was printed and laminated with a polyolefin film. The resulting new high oxygen barrier plastic flexible packaging film has readily available raw materials, low cost, superior barrier properties compared to PVDC, and is unaffected by relative humidity. BARILAYER is biodegradable and burns to produce only CO2 and H2O, highlighting its environmental innovation.

1.3 Layer-by-Layer (LbL) Composite Films

Layer-by-layer composite films are made by alternately depositing specific polymers, quantum dots, nanoparticles, and biomolecules under complementary interactions (such as electrostatic interactions, hydrogen bonding, coordination bonding, and covalent bonding) to form multilayer composite films. By altering deposition cycles, pH, temperature, molecular weight, and ionic strength, high-performance composite film materials can be obtained, which are widely used for flame retardancy, antibacterial properties, and gas barriers. Current research has also seen new developments in layer-by-layer composite films. For instance, by hydrogen bonding poly(acrylic acid) (PAA) and polyethylene oxide (PEO), a tough gas barrier composite film was prepared. When the pH was adjusted to 3, a 20-layer self-assembled PAA/PEO bilayer was formed, significantly reducing the oxygen permeability of a 1.58 mm thick natural rubber sheet by 89.6%. The resulting film has excellent oxygen barrier properties and some toughness due to weaker hydrogen bonding compared to ionic bonding, making it suitable for high-strain applications. Similarly, by layer-by-layer assembling polyetherimide (PEI), PAA, and PEO through PEI/PAA ionic bonding and PAA/PEO hydrogen bonding, a PEI/PAA/PEO/PAA composite film was formed. When the pH was adjusted to 3, a 20-layer self-assembled four-molecule layer was created, significantly reducing the oxygen permeability of a 1 mm thick polyurethane rubber sheet by 93.3%, making it suitable for gas barrier applications in inflatable products such as tires.

1.4 Other Composite Films
In addition to the multilayer film composite technologies mentioned earlier, innovative methods such as layer-by-layer casting, chemical grafting, and blend extrusion are also employed to create high-performance multilayer polymer composite films with superior barrier properties.
Layer-by-Layer Casting: This method involves preparing a three-layer biodegradable poly(L-lactic acid) (PLLA)/polyvinyl alcohol (PVA)/PLLA composite film, where the PVA middle layer acts as the barrier layer and the hydrophobic PLLA layers on both sides serve as protective layers. The PVA barrier layer significantly enhances the barrier properties of PLLA. When the PVA content accounts for 20% of the composite film, its oxygen barrier property improves by 272 times compared to a single PLLA film, while also enhancing mechanical properties. The PLLA/PVA/PLLA composite film demonstrates strong practical applicability and aligns with the trend of developing environmentally friendly composite films.
Chemical Grafting: Chitosan (CS) is grafted onto an oxidized cellulose (OC) matrix, altering the microstructure of the base material during the chemical grafting process. The resulting OC/CS composite film combines the advantages of both polymers, offering excellent water and oxygen barrier properties, antibacterial characteristics, high transparency, and good mechanical performance. It is a safe, biodegradable, and high-performance packaging material.
Blend Extrusion: Ethylene-vinyl alcohol copolymer (EVOH) and nylon 6 (PA6) are blended and extruded to prepare ethylhexyl acrylate (EHA) films, which are then laminated with polyethylene (PE) films to create EHA/PE composite films. Research confirms that EHA films have high oxygen barrier properties, and the EHA/PE composite films exhibit better water and oxygen barrier properties than PA films, EVOH films, and PA6/PE composite films, making them suitable for refrigerated fresh packaging.
2. Vacuum Metallized Composite Films
Vacuum metallized composite films are produced by depositing metals (such as aluminum) or inorganic oxides (such as silicon dioxide, aluminum oxide, or titanium dioxide) onto plastic film surfaces using vacuum coating technology. These films, including vacuum metallized aluminum films or vacuum metallized ceramic films, offer excellent barrier properties, high production efficiency, low cost, and ease of use. They are widely used in food packaging and even in the encapsulation of electronic products. Ceramic films are particularly noted for their high transparency and eco-friendliness, making them a current research hotspot. For example, plasma-enhanced chemical vapor deposition (PECVD) can deposit SiOx layers on polycaprolactone (PCL) film substrates, improving barrier properties without being affected by temperature and humidity, aligning with the development of environmentally friendly materials. Deposition of SiOx on PLLA films using PECVD followed by coating a PVA layer on the SiOx layer via solution coating results in new PLLA/SiOx/PVA composite films. These films have barrier properties similar to PA/PE composite films and improved flexibility, along with biodegradable advantages, making them a promising replacement for PA/PE composite films in food packaging.
3. Polymer/Layered Inorganic Nanocomposite Films
Polymer/layered inorganic nanocomposite films are created by dispersing layered inorganic fillers that form nanoscale microstructures into polymers, resulting in nanocomposite films. The nanoplatelet structure of the filler can block gas infiltration, significantly improving the barrier properties of the material. Current popular layered nanofillers include montmorillonite (MMT), layered double hydroxides (LDHs), and graphene nanosheets (GNSs), which are at the forefront of research due to their unique structures and excellent properties. For instance, using the principle of entropy increase, highly ordered organic/inorganic nanocomposite films are self-assembled. By printing a 0.1-0.2% volume fraction of polyvinylpyrrolidone (PVP) aqueous solution as a polymer film layer and a 0.2 wt% volume fraction of MMT dispersion as a nano layer using an inkjet printer, a PVP/MMT bilayer is self-assembled via ionic bonding. Printing five layers of PVP/MMT bilayers on a PET substrate results in oxygen barrier properties superior to high-barrier metalized PET, with high transparency, safety, and environmental friendliness, indicating broad applications in food packaging.
Oxidative cleavage of multi-walled carbon nanotubes yields graphene oxide nanoribbons (GONRs), which are chemically modified using isophorone diisocyanate (IPDI) to produce functional graphene oxide nanoribbons (IP-GONRs). These are then used to prepare IP-GONRs/thermoplastic polyurethane (TPU) composite films via solution casting. With a 3.0 wt% IP-GONRs content, the oxygen permeability of TPU decreases by 67%, significantly enhancing its barrier properties, making it suitable for food packaging and lightweight gas storage applications.
Using a simple vacuum filtration method, flexible, transparent PVA/layered double hydroxide (LDH) composite self-supporting films are prepared. The ordered two-dimensional structure of the composite film effectively inhibits oxygen diffusion, enhancing its oxygen barrier properties, making it promising for applications in electronic device encapsulation and fuel cell membranes, where high barrier properties are critical.
Summary
Currently, driven by the strong market demand for food, pharmaceuticals, and chemicals, packaging film materials are developing rapidly. The requirements for film materials are becoming higher, necessitating the development of multifunctional films with high barrier properties, freshness preservation, thermal resistance, and antibacterial properties. High barrier film materials are developing rapidly. Meanwhile, with the increasing scarcity of resources and growing environmental awareness, developing environmentally friendly high barrier film materials has also become a hot topic. In the coming years, we should continue to focus on the research and development of high barrier film materials, aiming to bridge the gap with foreign high barrier film technologies and meet the growing market demand.