Determination of Oxygen Transmission Rate of Plastic Cling Film: Test Methods, Standards, and Applic

Oxygen transmission rate (OTR) determination is a critical quality control test for plastic cling film used in food packaging, as oxygen permeability directly affects product freshness, shelf life, and packaging performance. This technical article explains the principles, testing standards (ASTM D3985, ASTM D1434, ISO 15105, GB/T 1038, GB/T 19789), specimen preparation, and practical applications of oxygen transmission rate measurement for cling films. It serves as a professional reference for packaging manufacturers, food processors, and accredited third-party laboratories performing barrier property evaluations.

Technical Overview

Plastic cling film (food wrap) is a thin, flexible packaging material widely used for wrapping fresh produce, meat, seafood, cheese, and prepared foods. Because cling film is not a complete oxygen barrier, molecular oxygen continuously permeates through the polymer matrix and interacts with the packaged food. The rate at which oxygen passes through the film under defined conditions of temperature, humidity, and partial pressure difference is defined as the oxygen transmission rate (OTR), commonly expressed in units of cm³/(m²·24h) under standard test conditions.

Oxygen transmission through cling film has a direct impact on food quality and safety. Excessive oxygen ingress accelerates oxidation of fats and oils, causes color fading in fresh-cut produce, enables growth of aerobic spoilage microorganisms, and leads to rancidity. Conversely, for products such as fresh red meat, a sufficiently high oxygen transmission rate is actually required to maintain the bright red oxymyoglobin color. Therefore, accurate determination of oxygen transmission rate is essential for material selection, shelf-life estimation, and modified atmosphere packaging (MAP) design.

Cling films are typically manufactured from polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), or multilayer composite structures. These materials exhibit dramatically different oxygen barrier properties, with PVDC providing a high barrier and PE providing a relatively high transmission rate. Standardized test methods established by ISO, ASTM, and GB standardization organizations allow laboratories to measure and compare these properties reproducibly.

Testing Samples

Polyethylene (PE) Cling Film

Low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) cling films, typically 8–15 μm thick, are the most common household and commercial wraps. They exhibit relatively high oxygen transmission rates, generally on the order of several thousand cm³/(m²·24h), making them suitable for products such as fresh vegetables and bread that require some gas exchange.

PVC Cling Film

Plasticized polyvinyl chloride cling film offers excellent clarity, stretch, and self-adhesion, and is widely used in supermarkets for meat and produce wrapping. Its oxygen transmission rate falls in an intermediate-to-high range and can be influenced by plasticizer content and ambient relative humidity.

PVDC Cling Film

Polyvinylidene chloride cling film provides outstanding oxygen and aroma barrier properties, with OTR values typically below 40 cm³/(m²·24h). It is used for high-fat foods, cured meats, and premium packaging applications where oxidation must be minimized.

Multilayer and Coated Composite Films

Laminated structures such as PE/PVDC, PE/EVOH/PE, or silicon-oxide-coated films combine cling properties with enhanced oxygen barrier performance. These samples are tested to verify that lamination, coating, and converting processes have not degraded barrier performance.

Biodegradable Cling Film

Compostable films based on PLA, PBAT, and starch blends are increasingly tested for oxygen transmission rate, as their barrier properties are often strongly dependent on relative humidity and must be characterized before commercial use.

Testing Items

The core testing items for oxygen barrier evaluation of cling film include:

• Oxygen transmission rate (OTR), reported in cm³/(m²·24h) or cm³/(m²·day·atm)
• Oxygen permeance, normalized to the oxygen partial pressure difference across the specimen
• Oxygen permeability coefficient, normalized for film thickness, used for material comparison
• OTR at controlled relative humidity (e.g., 0%, 50%, 85% RH) to evaluate humidity sensitivity
• OTR at elevated temperatures to assess temperature dependence and accelerated storage behavior
• Specimen thickness measurement at multiple positions, required for calculating permeability coefficients

Testing Methods

Coulometric Sensor Method (Equal-Pressure Method)

The coulometric method described in ASTM D3985, ISO 15105-2, and GB/T 19789 is the most widely used technique for measuring the oxygen transmission rate of cling film. The specimen is clamped as a barrier between two chambers. High-purity oxygen or oxygen-enriched gas flows through one chamber, while an oxygen-free carrier gas (nitrogen with a trace of hydrogen) flows through the other at equal pressure. Oxygen molecules that permeate the film are swept by the carrier gas to a coulometric sensor, where they are electrochemically reduced. According to Faraday's law, the sensor current is directly proportional to the quantity of transmitted oxygen, allowing precise quantification of the transmission rate.

Differential-Pressure Method (Manometric Method)

The differential-pressure method specified in ASTM D1434, ISO 15105-1, and GB/T 1038 clamps the specimen between two evacuated chambers. Oxygen at a known pressure is then introduced into one chamber while the other chamber remains under vacuum. Oxygen permeating through the film increases the pressure in the lower chamber, and this pressure rise is monitored over time with high-sensitivity transducers. The steady-state pressure change rate is used to calculate the gas transmission rate and permeability coefficient. This method does not require carrier gas and can measure multiple gases using the same instrument.

Specimen Preparation and Conditioning

Specimens should be free of wrinkles, pinholes, folds, and contamination. Test pieces are cut to match the test cell exposure area, and film thickness is measured at a minimum of five to ten positions using a calibrated micrometer. Prior to testing, specimens are conditioned in a standard atmosphere (typically 23°C ± 2°C and 50% ± 5% RH) for at least 40 hours in accordance with GB/T 2918 or the equivalent ISO 291 procedure. Sealing is achieved using vacuum grease or elastomeric gaskets to eliminate edge leakage, and at least three replicate specimens are recommended.

Test Conditions and Calculation

Standard test conditions are 23°C ± 0.5°C with 0% RH or controlled relative humidity, using 99.9% purity oxygen. Testing continues until a steady-state transmission value is reached. The oxygen transmission rate is calculated as the volume of oxygen transmitted per unit area per unit time, normalized to a unit oxygen partial pressure difference. For material characterization, the permeability coefficient is derived by multiplying the transmission rate by the film thickness and dividing by the partial pressure difference. All test reports must state the temperature, relative humidity, specimen thickness, exposure area, and the standard method applied, since OTR results are only comparable under identical conditions.

Applications

Oxygen transmission rate determination of cling film supports numerous industrial and regulatory applications:

• Shelf-life estimation and validation for perishable foods, dairy products, and high-fat items susceptible to oxidation
• Design and optimization of modified atmosphere packaging (MAP) for fresh-cut produce and processed meats
• Selection of wrap films for fresh red meat, where high oxygen transmission preserves bloom color
• Incoming material inspection and batch-to-batch quality control in film manufacturing
• Research and development of new resin formulations, thickness reduction, and coating technologies
• Verification of barrier performance after sterilization, storage, or converting processes
• Compliance demonstration for food contact material specifications and customer technical agreements

FAQ

What is the difference between oxygen transmission rate and oxygen permeability coefficient?

Oxygen transmission rate (OTR) describes the amount of oxygen passing through a specific film specimen of defined thickness under specified conditions, expressed per unit area and time. The permeability coefficient is a material property obtained by normalizing the transmission rate for thickness and pressure difference, allowing comparison between different materials.

Which testing standard should be selected?

ASTM D3985, ISO 15105-2, and GB/T 19789 (coulometric methods) are preferred for low-to-medium barrier films such as cling film because of their high sensitivity. ASTM D1434, ISO 15105-1, and GB/T 1038 (differential-pressure methods) are suitable when carrier gas is unavailable or multi-gas testing is required. The chosen standard should always be stated in the test report.

Does relative humidity affect the test result?

Yes. Hydrophilic materials, biodegradable films, and plasticized PVC show significantly increased oxygen transmission at elevated humidity, so testing at the humidity matching actual use conditions is recommended.

How long does a typical test take?

High-barrier films such as PVDC may require 24 hours or longer to reach steady state, while high-transmission PE wraps may stabilize within several hours. Test duration depends on barrier level, temperature, and instrument sensitivity.

What are typical OTR values for common cling films?

Indicative ranges at 23°C include approximately 10–40 cm³/(m²·24h) for PVDC film and several thousand cm³/(m²·24h) for PE and PVC wraps. Values vary with thickness, formulation, and humidity, so laboratory measurement under standardized conditions is essential for accurate specification.