What Tests Are Conducted on Composite Films (Part 3)

Today, we’ll continue explaining the relevant tests related to the physical and chemical properties of composite molds: water vapor transmission rate, oxygen permeability, residual solvent levels, microbial contamination, evaporation residue, toluene diamine, potassium permanganate, and heavy metals.

Water vapor transmission rate

The amount of water vapor that passes through a 1 m² sample over 24 hours under specified conditions: a defined temperature, relative humidity, a fixed vapor pressure difference, and a particular material thickness.

Xiaomin on Testing: Barrier performance against water vapor is one of the key factors affecting a product’s shelf life quality—and also serves as an important reference for shelf-life analysis. By conducting tests and analyses on this specific parameter, companies can proactively address issues like moisture-related spoilage that arise when products are sensitive to water vapor. For instance, a high water vapor transmission rate indicates poor moisture resistance in the composite film packaging, making potato chips particularly prone to becoming damp and stale.

Oxygen Permeability

Oxygen transmission rate is the volume of oxygen that passes through a unit area of plastic films, aluminum foil, vacuum-aluminized films, and other materials per unit time under steady-state conditions, at a constant temperature and with a fixed pressure difference. It is expressed as a volume value measured under standard temperature and pressure conditions, with units of cm³/m²·d·Pa.

Xiaomin on Testing: Oxygen is a critical factor affecting the shelf life and quality of products like food and pharmaceuticals—and it also serves as an important reference for shelf-life analysis. By testing for oxygen levels, manufacturers can proactively identify and address quality issues such as oxidative spoilage, which often occur due to sensitivity to oxygen. For instance, to extend the shelf life of powdered milk and prevent oxidation-induced spoilage or clumping caused by exposure to air, high-barrier packaging materials are essential for effective protection.

Solvent Residue Level

Solvent residues in plastic composite film packaging typically arise from inks, solvents, and the production process itself, which may involve the extensive use of organic solvents. As per standard requirements, the levels of these organic solvents—such as toluene, xylene, ethyl acetate, methyl ethyl ketone, butyl acetate, ethanol, and isopropyl alcohol—are rigorously tested.

Xiaomin on Testing: During the printing process, composite films typically contain varying amounts of solvents such as alcohols, ethyl acetate, and benzene-based compounds in the ink or adhesive. Each solvent has a different molecular weight and boiling point, leading to distinct evaporation rates—and consequently, differing levels of residual solvent contamination. According to the national standard GB/T 10004-2008, the total residual solvent content must be ≤5 mg/㎡, with benzene-based solvents required to be completely absent. This testing method allows manufacturers to promptly identify whether the composite film still contains residual solvents, which is crucial for ensuring product safety.

Microorganisms

Microbial testing is a method that applies microbiological principles and techniques to examine the types, quantities, and characteristics of microorganisms present in composite membranes, as well as their potential impact on human health, thereby determining whether the composite membrane meets quality standards.

Xiaomin on Testing: Microorganisms adhering to plastic composite films used in packaging can cause "secondary contamination" of even compliant products, leading to issues like bag swelling and product spoilage. This test allows you to assess the total colony count of the composite film, as well as detect coliforms, molds, and specific pathogenic bacteria—including Shigella, Salmonella, and Staphylococcus aureus.

Residue from evaporation

The evaporation residue (total migration) is a test procedure that simulates the contact between food and a composite film, allowing migratable substances from the film to transfer into a food simulant. The total amount of these migrants is then determined by an evaporation-drying-weighing process.

Xiaomin on Testing: Evaporation residue represents the total amount of soluble and insoluble substances that may migrate from the product into food, potentially posing adverse health effects on humans and directly impacting product quality. It also indicates the likelihood of residual particles leaching out when plastic composite film packaging comes into contact with liquids like alcohol, oil, or vinegar during use.

Toluene diamine

Toluene diamine It is a chemical substance with toxicity, primarily used as one of the raw materials for organic synthesis. 。

Xiaomin on Testing: Since toluene diamine can irritate the respiratory tract, mucous membranes, and skin—and is highly toxic—China’s national standard GB 9683-1988 sets the migration limit for toluene diamine in food simulants contained within composite food packaging bags at 0.004 mg/L.

Potassium permanganate

The potassium permanganate consumption refers to the amount of substances in the composite membrane material that can be oxidized by potassium permanganate when they migrate into the soaking solution. Most of the substances oxidized by potassium permanganate are organic compounds that have migrated out, including polymer monomers, olefins, and other similar materials.

Xiaomin on Testing: This test determines whether the composite film material contains soluble organic substances, such as low-molecular-weight polymers like olefins, dimers, and trimers. Since these soluble organic compounds can enter the human body through liquids and potentially pose health risks to consumers, China has established strict regulatory limits for food-contact materials, mandating that their content must not exceed 10 mg/kg.

Heavy metals

Heavy metals pose certain risks to human health and the environment. Standards require the detection of metals such as mercury, cadmium, lead, chromium, and arsenic—also referring to commonly toxic heavy metals in general.

Xiaomin on Testing: This test helps determine whether heavy metals were added to the composite film's raw materials during production, and whether the heavy metal content exceeds the relevant standards.