Oxygen permeability testing is a critical quality control procedure for evaluating the gas barrier performance of plastic films and sheets used in food, pharmaceutical, and industrial packaging. This technical article explains the principles, standard test methods (ASTM D3985, ISO 15105, GB/T 19789), sample requirements, and typical applications of oxygen transmission rate (OTR) determination for plastic sheeting materials.
Technical Overview
Oxygen permeability determination measures the rate at which oxygen molecules migrate through plastic films and sheeting under controlled conditions of temperature, humidity, and partial pressure difference. This property, commonly expressed as the Oxygen Transmission Rate (OTR), is a fundamental barrier characteristic that directly determines the shelf life of oxygen-sensitive products, the protective performance of packaging structures, and the suitability of materials for modified atmosphere packaging (MAP) and other advanced packaging technologies.
Plastic sheeting materials exhibit oxygen transmission rates spanning several orders of magnitude. Non-polar polyolefins such as low-density polyethylene (LDPE) typically show OTR values in the range of 2,000–8,000 cm³/(m²·24h), while high-barrier materials such as ethylene-vinyl alcohol copolymer (EVOH) and polyvinylidene chloride (PVDC) coatings can achieve values below 1 cm³/(m²·24h). Aluminum foil laminates and metallized films can reach even lower values approaching virtual oxygen impermeability. Quantifying these differences with precision requires standardized instrumental methods performed under strictly controlled environmental conditions.
The most widely referenced standards for this determination include ASTM D3985 (coulometric sensor method), ISO 15105-1 (differential-pressure method), ISO 15105-2 (equal-pressure method), GB/T 19789 (Chinese national standard, coulometric method), and JIS K 7126. Selection of the appropriate method depends on the material type, expected transmission range, and the influence of humidity on the polymer matrix.
Testing Samples
Monolayer Plastic Films and Sheets
Single-layer materials such as LDPE, LLDPE, HDPE, PP (polypropylene), PET (polyethylene terephthalate), PVC, PA (polyamide/nylon), PS, and PLA sheeting represent the most common sample category. Samples should be flat, free of creases, pinholes, inclusions, and thickness variations, with a minimum testing area typically defined by the instrument's diffusion cell geometry (commonly 5 cm² to 50 cm²). A minimum of three specimens per material is recommended for statistical validity.
Multilayer and Laminated Structures
Coextruded films, adhesive laminates, and coated structures (for example, PET/EVOH/PE, OPP/PVDC, BOPP/metallized layers) are tested to verify the barrier contribution of each functional layer in the composite structure. Specimen preparation must avoid delamination at the edges, and cut edges should be cleanly sealed during mounting to prevent lateral oxygen ingress between layers.
Coated and Treated Materials
Silicon oxide (SiOx) and aluminum oxide (AlOx) coated films, metallized films, and films with organic barrier coatings require careful handling to prevent abrasion or cracking of the thin inorganic coating. The coated side orientation should be documented, as asymmetric structures may exhibit direction-dependent transmission behavior.
Sample Conditioning Requirements
Prior to testing, specimens must be conditioned in a controlled environment, typically 23°C ± 2°C and 50% ± 5% relative humidity for a minimum of 48 hours, unless otherwise specified by the relevant standard or material specification. Conditioned samples should be handled with gloves to prevent contamination of the test area by skin oils.
Testing Items
The core measurable parameters in oxygen permeability determination include:
- Oxygen Transmission Rate (OTR): the volume of oxygen passing through a unit area of the specimen per unit time, expressed in cm³/(m²·24h) under specified test conditions.
- Oxygen Permeability Coefficient (P): a material-intrinsic property normalized for thickness, expressed in cm³·cm/(m²·24h·cmHg) or cm³·mm/(m²·24h·atm), used to compare materials independently of gauge.
- Oxygen Permeance: the OTR normalized by the oxygen partial pressure difference across the specimen, expressed in cm³/(m²·24h·atm).
- Temperature dependence characteristics: OTR values at multiple temperatures for activation energy analysis using Arrhenius relationships.
- Humidity dependence characteristics: OTR values at controlled relative humidity levels (typically 0%, 50%, 85%, and 100% RH) to characterize moisture-sensitive barrier polymers such as EVOH and polyamide.
Testing Methods
Coulometric Sensor Method (Equal-Pressure Method) — ASTM D3985 / ISO 15105-2 / GB/T 19789
In the coulometric method, the specimen is mounted as a sealed barrier between two chambers. One side is swept with pure oxygen (test gas, ≥99.5% purity), while the opposite side is swept by oxygen-free carrier gas (typically a nitrogen-hydrogen mixture). Oxygen that permeates through the specimen is entrained by the carrier gas and delivered to a coulometric sensor, where it is electrochemically reduced. The electrical current generated is directly proportional to the mass of oxygen reaching the sensor, following Faraday's law. Because both sides of the specimen are at essentially equal total pressure, this method eliminates the risk of leakage-driven errors and pressure-induced deformation, making it the globally preferred method for flexible packaging materials.
Differential-Pressure Method (Manometric Method) — ISO 15105-1 / ASTM D1434 / JIS K 7126
In the pressure-difference method, one side of the specimen is exposed to oxygen at a known pressure while the other side is evacuated to a low residual pressure. Oxygen permeating the specimen increases the pressure on the low-pressure side, and this pressure rise is measured over time with high-sensitivity pressure transducers. The transmission rate is calculated from the steady-state rate of pressure change. This method requires no carrier gas and no sensor chemicals, but it imposes a total pressure differential across the sample and demands rigorous leak checking, vacuum integrity, and temperature stability.
Standard Test Conditions
Tests are typically conducted at 23°C ± 1°C (or 23°C ± 2°C depending on the standard) with oxygen at approximately 1 atm test pressure on the high side. Relative humidity conditions may range from 0% RH (dry) to 90% RH or higher for humidity-conditioned evaluations. The instrument chamber temperature must be controlled within ±0.1°C to ±0.5°C, as oxygen permeability of polymers approximately doubles for every 7–10°C temperature increase.
Test Procedure Summary
- Measure and record specimen thickness at multiple points; verify uniformity within ±10%.
- Condition specimens according to the specified atmosphere.
- Mount the specimen securely in the diffusion cell with a hermetic seal (typically using vacuum grease or a gasket system); verify the absence of leaks.
- Purge both chambers with conditioning gases until a stable baseline is established.
- Introduce oxygen to the test side and monitor the sensor signal until steady-state transmission is reached.
- Calibrate the instrument periodically using a reference material (such as NIST-traceable polyester film or certified reference film) with a known OTR value.
- Calculate OTR, permeance, and permeability from the steady-state signal; report all test conditions, specimen thickness statistics, and mean values with standard deviations.
Applications
Oxygen permeability data for plastic sheeting support a wide range of industrial and regulatory applications:
- Food packaging development: selecting barrier structures for oxygen-sensitive foods such as processed meats, dairy products, nuts, coffee, dried foods, and beverages; validating MAP and vacuum packaging performance.
- Pharmaceutical packaging: qualifying blister films, sachets, and laminate structures for tablets, effervescent products, and oxidation-sensitive formulations, in alignment with stability study requirements.
- Medical device packaging: verifying sterile barrier performance of breathable and non-breathable packaging materials per recognized sterilization compatibility frameworks.
- Material R&D and comparison: evaluating EVOH grades, nanocomposite barrier materials, and coated films; ranking candidate structures during development.
- Quality control and supplier verification: incoming material inspection, lot-to-lot consistency monitoring, and process change validation in manufacturing.
- Shelf-life modeling: incorporating OTR values into predictive models that estimate product oxidation over the intended storage period.
- Compliance and certification: accredited third-party laboratories provide test reports accepted by retailers, brand owners, and regulatory submissions worldwide.
FAQ
What is the difference between OTR and oxygen permeability coefficient?
OTR describes the transmission behavior of a specific specimen of a given thickness under defined conditions, expressed as cm³/(m²·24h). The permeability coefficient is a thickness-normalized material property that allows comparison between materials of different gauges. Both values must always be reported together with the test temperature and relative humidity.
Why do EVOH and nylon films show much higher OTR at high humidity?
EVOH and polyamide are hydrophilic barrier polymers. Absorbed water molecules plasticize the polymer matrix, increasing chain mobility and free volume, which dramatically reduces barrier performance. EVOH can lose more than half of its barrier capacity at 100% RH compared with dry conditions. For this reason, EVOH barrier layers are typically sandwiched between polyolefin layers in real packaging structures, and OTR testing must include the relevant humidity condition.
How long does a typical oxygen permeability test take?
Test duration depends on the barrier level. High-transmission films (OTR above 100 cm³/(m²·24h)) may reach steady state within 2–6 hours. High-barrier materials (OTR below 1 cm³/(m²·24h)) may require 24–72 hours or longer to equilibrate, especially for thick or multilayer laminates with long lag times.
Can finished packages be tested instead of flat sheeting?
Yes. Package-level oxygen ingress testing is covered by ASTM F1307 (coulometric determination of oxygen transmission of rigid packages) and related whole-package methods. However, flat-sheet OTR testing per ASTM D3985 remains the standard approach for material characterization and specification.
What sample quality issues can invalidate test results?
Pinholes, creases, edge leaks, poor sealing, contamination, and non-representative thickness variation are the most common causes of erroneous OTR values. Leak verification, careful specimen cutting, and clean handling procedures are essential for reproducible results.
How often should the instrument be calibrated?
Best practice is to verify instrument calibration with a certified reference film before and after critical test campaigns, and to perform full calibration on a scheduled basis per the manufacturer's recommendations and laboratory quality system requirements (for example, ISO/IEC 17025-aligned procedures).