The Barrier Function of Organic Nanomontmorillonite in Single-Material Plastic Packaging

The Barrier Function of Organic Nanomontmorillonite in Single-Material Plastic Packaging

I. Single-Material Barriers Are More Environmentally Friendly and Recyclable

The European Soft Packaging Circular Economy Organization (CEFLEX) explicitly states in its Circular Economy Design Guidelines that plastic packaging materials should be produced using single materials as much as possible to improve recycling efficiency and recyclability. Nestlé and Coca-Cola have both clearly indicated their commitment to achieving 100% recyclable or reusable packaging. This implies a transition from multi-material structures to single-material structures, which not only complies with future environmental regulations but also enhances recycling efficiency.

Compared to multi-layer composite packaging, single-material structures often exhibit weaker barrier properties. Therefore, ensuring that packaging maintains good performance while meeting environmental requirements has become a critical issue. To address this challenge, plastic packaging often employs several different barrier methods to enhance barrier performance.

II. Current Barrier Methods in Plastic Packaging

1. Coating Methods (e.g., aluminum coating, SiO₂ coating, etc.)

By depositing a layer of metal or inorganic material on the plastic surface, a barrier layer is formed. Aluminum-coated layers possess excellent gas and moisture barrier properties and are commonly used in food packaging to extend shelf life. Inorganic coatings such as SiO₂ provide additional oxygen and moisture barrier properties. This coating method can only be applied to intermediate layers, with inner layers requiring heat-sealable layers and outer layers requiring composite printing layers. Each layer uses different materials, making recycling and reuse difficult.

2. Composite Co-Extrusion Method (e.g., PVDC, EVOH, PA, PVA, etc.)

This method involves co-extruding different materials in a molten state to form a multi-layer structure. EVOH (ethylene-vinyl acetate copolymer) is a commonly used high oxygen barrier material widely applied in food packaging. PA (nylon) has good oil barrier properties and is often used in packaging for high-fat foods. PVDC and PVA also provide excellent gas and moisture barrier properties. Such barrier packaging typically consists of 3–9 layers of different materials co-extruded to achieve barrier and packaging functions. However, due to the different materials, recycling and reuse are challenging.

3. Blending Method (addition of inorganic materials)

This method offers an excellent alternative. By incorporating inorganic materials such as montmorillonite, silicates, and nanomaterials into the plastic matrix, both the material's rigidity and heat resistance are enhanced, while also improving its barrier properties. These nanoscale inorganic materials blend well with the plastic matrix and are easily recyclable.

III. Barrier Function of Organic Nano Montmorillonite in Packaging

Montmorillonite (MMT) is a natural layered hydrated silicoaluminate mineral, with each plate having a thickness of approximately 1 nm and a size range of 1–1,000 nm. Its structural formula is (Al,Mg)₂SiO₁₀₂·nH₂O. Due to the instability of aluminum in the aluminum oxide octahedron, it is easily replaced by lower-valent atoms, resulting in a certain negative charge between adjacent layers. To maintain the stability of the interlayer structure, the negative charge attracts surrounding cations such as Na+, Ca2+, Mg2+, Al3+, and K+, thereby conferring cation exchange capacity and strong adsorption ability on montmorillonite.

After blending with polymers, its crystal structure easily peels off, resulting in a dense layered structure with a high aspect ratio. This increases the path length for gas penetration through high-molecular-weight polymers and extends the gas penetration time. A 1 nm thick layered structure forces gas and moisture to “take 300 detours,” simultaneously, its nano-effects restrict the movement of polymer chains, enhance intermolecular interactions, strengthen the polymer's cohesive force, increase molecular chain packing density, and significantly improve the material's barrier properties.

IV. Processing and Application Methods for Organic Nano-Montmorillonite

Montmorillonite must undergo two processes to achieve nano-scale dispersion within polymers. Only thoroughly dispersed and uniformly distributed nano-silicate layers can achieve optimal performance.

1. Purified montmorillonite undergoes intercalation reactions to form organic nano-montmorillonite

Inorganic montmorilonite has interlayer spacings of approximately 1–1.5 nm, and its layers are stacked in piles of dozens due to electrostatic forces, making it impossible to disperse each nano-layer individually. Only through intercalation reactions (typically requiring 30–40% intercalation agent) can the interlayer spacing of montmorillonite be increased to 2–4 nm, transforming it into organic nano-montmorillonite. This reduces the material's surface free energy and changes its hydrophilicity to lipophilicity, enabling better dispersion within polymers.

2. Intercalated montmorillonite must undergo shear processing using a twin-screw extruder to achieve complete nano-dispersion

To achieve optimal dispersion and exfoliation of organic montmorillonite, it is recommended to use a co-rotating twin-screw extruder or BUSS kneader when mixing thermoplastic composites. During extrusion mixing, it is advisable to select screw combinations with the largest possible length-to-diameter ratio (>40L/D) and thread modules capable of achieving high dispersion. To avoid compaction, it is best to add it to the melted polymer via a side feed device.

When dispersing in a twin-screw extruder, care should be taken not to “over-shear” the organic montmorillonite to prevent agglomeration. It is best to use dispersion mixing screw elements. Overheating can lead to reduced product performance and the formation of odors. Excessive heating may cause smoke at the die, and extremely high shear rates in the extruder can also lead to re-agglomeration and performance degradation.

It is recommended to first process the montmorillonite into masterbatch before using it for cast film or blown film applications: 30%–50% montmorillonite masterbatch pre-mix (first batch-processed then dispersed in a twin-screw extruder, or produced via side-feed dispersion, with appropriate addition of grafting compatibilizers and dispersing aids).

V. Applications of Organic Nano-Montmorillonite in the Packaging Industry

1. Electronic Packaging

2. Industry Inflatable

Packaging Industry As a new type of functional material, organic nano-montmorillonite has demonstrated strong barrier potential in the plastic packaging industry. With ongoing technological advancements, montmorillonite is poised to become an important component of high-performance packaging materials, meeting the growing market demand.

It should be noted that YINSU Flame Retardant specializes in the development and production of environmentally friendly flame retardants. Its product K100 is an organic nanomontmorillonite flame retardant with excellent performance. K100 not only enhances the flame retardancy of plastic packaging materials but also maintains the mechanical properties and processability of the materials. It is an ideal choice for achieving both flame retardancy and barrier functionality in single-material plastic packaging. With the continuous development of green packaging concepts, YINSU Flame Retardant's K100 product is expected to play a more significant role in the packaging field.