CO₂TR: What Carbon Dioxide Transmission Rate Is and How It Is Measured

Carbon dioxide transmission rate (CO₂TR) is an important parameter for evaluating the gas barrier properties of films and packaging materials. It describes the amount of carbon dioxide that passes through a material over a defined area and period under specified test conditions.

CO₂TR testing helps laboratories, packaging manufacturers and material developers characterize barrier performance, compare materials and support packaging development and quality control.

Understanding how CO₂TR is measured is essential because carbon dioxide transmission depends on several factors, including material composition, thickness, temperature, pressure conditions and the selected test method.

Why Is CO₂TR Important?

Carbon dioxide can play an important role in the behavior of packaged products. Depending on the application, the ability of a packaging material to limit or allow CO₂ transmission may influence packaging design and material selection.

Packaging Material Selection

Different polymers, coatings and multilayer structures can exhibit different carbon dioxide barrier properties. CO₂TR testing helps compare candidate materials under defined conditions.

Packaging Development

Measurements can support the evaluation of alternative film structures, coatings and material combinations. They can also help assess changes in barrier performance when a packaging material is modified.

Gas Barrier Characterization

CO₂TR provides information about carbon dioxide transmission through a material. When considered alongside other relevant barrier measurements, it can contribute to a broader assessment of packaging performance.

Quality Control

Consistent testing can help laboratories compare samples, investigate differences between material batches and monitor barrier characteristics over time.

CO₂TR is one parameter used to characterize a material. A transmission rate alone does not determine the performance of a complete package or establish product shelf life.

How Is CO₂TR Measured?

CO₂TR is measured by evaluating the transmission of carbon dioxide through a sample under defined test conditions. The precise procedure depends on the selected method and the measurement system.

In a typical film transmission test, the sample is mounted between two chambers. One side is exposed to carbon dioxide or a gas mixture containing CO₂, while the other side is used to detect or measure the gas that passes through the material.

The instrument records the transmission behavior and determines the CO₂TR according to the selected measurement method.

Preparing the Sample

The sample should be representative of the material being evaluated and prepared according to the applicable test procedure.

Its thickness, structure and condition should be documented where relevant. Wrinkles, damage, contamination or inadequate mounting may affect the measurement, so sample preparation should be consistent when comparing different materials.

For coated films and multilayer structures, testing the complete material can help characterize the barrier performance of the finished construction.

Defining Test Conditions

Test conditions influence the interpretation of CO₂TR results. Important parameters may include temperature, gas composition, pressure difference and other method-specific settings.

These conditions should be controlled and recorded according to the selected method. Results obtained under different conditions should not automatically be considered equivalent.

Recording and Interpreting Results

The measurement system records carbon dioxide transmission and reports the result using the units and calculation procedure associated with the selected method.

When comparing materials, confirm that the same parameter is being evaluated and that the units, sample characteristics and test conditions are compatible.

Which Units Are Used for CO₂TR?

CO₂TR is commonly expressed as the volume of carbon dioxide transmitted through a unit area over a specified period.

Examples of commonly used units include:

• cm³/(m²·day) — cubic centimetres per square metre per day.
• cm³/(m²·24 h) — cubic centimetres per square metre over 24 hours.

The notation used may vary depending on the reporting convention and test method.

A CO₂TR value should always be interpreted alongside its units and the relevant test conditions. Values expressed using different units must be converted appropriately before comparison, and the underlying measurement conditions must also be considered.

CO₂TR vs. Carbon Dioxide Permeability

CO₂TR and carbon dioxide permeability are related, but they describe different quantities.

Carbon Dioxide Transmission Rate

CO₂TR measures the amount of carbon dioxide passing through a specified area of material over a defined period under stated conditions.

It is commonly used to characterize the gas barrier performance of films as tested.

Carbon Dioxide Permeability

Carbon dioxide permeability describes the transport of CO₂ through a material as a material-related property. Depending on the method and calculation convention, a permeability coefficient accounts for the driving force for gas transport and material thickness.

Why the Difference Matters

CO₂TR and permeability coefficients are not interchangeable. They represent different quantities and may use different units.

When comparing results, check:

• Whether the reported parameter is CO₂TR or a permeability coefficient.
• The units and calculation method.
• The thickness and structure of the tested material.
• The temperature and pressure conditions.
• Whether the measurements were obtained using comparable methods.

For more information, read CO₂ Permeability and CO₂TR: Measurement and Analysis.

Which Factors Affect CO₂TR Results?

Carbon dioxide transmission depends on both the material being tested and the measurement conditions.

Material Composition

Different polymers and barrier materials have different physical and chemical characteristics that influence carbon dioxide transport.

Material composition is therefore an important consideration when comparing barrier performance.

Film Thickness

Film thickness can influence the measured transmission rate. Comparisons between materials should account for thickness and distinguish transmission rate from permeability coefficients.

Temperature

Temperature can affect gas transport through a material. Results obtained at different temperatures may therefore differ, even when the same material is tested.

Pressure and Gas Conditions

The driving force for gas transmission depends on the conditions established during testing. Gas composition and pressure conditions should be defined according to the selected method.

Coatings and Multilayer Structures

Coatings, laminates and multilayer films combine materials with different properties. The overall carbon dioxide barrier performance depends on the complete structure and the integrity of its layers.

Sample Preparation and Test Method

Sample damage, inconsistent preparation or inadequate mounting can affect measurement reliability. Different methods may also use different conditions or calculation conventions.

Consistent procedures help laboratories obtain results that can be meaningfully compared.

Which Materials Can Be Tested?

CO₂TR testing may be used to evaluate a range of films and barrier materials, depending on the instrument configuration and selected method.

Examples include:

• Single-layer plastic films.
• Coated films.
• Metallized films.
• Multilayer films and laminates.
• Other barrier materials compatible with the test configuration.

The suitability of a particular material depends on its characteristics, the expected transmission values and the capabilities of the measurement system.

For related applications, explore Permeability Testing of Plastic Films and Permeability Testing of Multilayer Films and Laminates.

CO₂TR Testing in Packaging Applications

Carbon dioxide transmission testing can support material evaluation in applications where gas barrier performance is relevant.

Food Packaging

The transmission of carbon dioxide may be one of the parameters considered when evaluating packaging materials for particular food products and packaging systems.

CO₂TR measurements help characterize material performance under defined conditions.

Explore Permeability Testing for Food Packaging.

Flexible Packaging

Flexible packaging may use coated, laminated or multilayer films to achieve specific barrier characteristics. CO₂TR testing can help compare these structures under consistent conditions.

Explore Permeability Testing of Flexible Packaging.

Packaging Material Development

During material development, CO₂TR measurements can help characterize alternative formulations and film constructions. When combined with other relevant tests, they contribute to a broader evaluation of barrier properties.

The significance of a particular result depends on the application and the requirements of the complete packaging system.

How to Choose a CO₂TR Testing System

Choosing a suitable instrument starts with identifying the required measurement parameter, sample type and test conditions.

Important considerations include:

• Measurement objective: confirm whether CO₂TR or a carbon dioxide permeability coefficient is required.
• Material characteristics: consider composition, thickness, coatings and layer structure.
• Expected transmission values: confirm that the measurement system is suitable for the expected range.
• Test conditions: identify the required temperature, gas and pressure conditions.
• Sample configuration: check compatibility with the instrument and selected method.
• Reporting requirements: establish the units and information needed to compare results.
• Additional parameters: consider whether oxygen or water vapor transmission must also be measured.

For laboratories evaluating multiple gas barrier properties, a system designed for more than one transmission parameter may help consolidate testing requirements.

The final selection should be based on the intended application and confirmed instrument capabilities.

ExtraSolution Instruments for CO₂TR Testing

ExtraSolution offers solutions for measuring carbon dioxide transmission through films and barrier materials. The most suitable instrument depends on the parameters required, the sample characteristics and the intended test conditions.

MultiPerm O2-CO2

Designed for oxygen transmission rate (OTR) and carbon dioxide transmission rate (CO₂TR) measurements.

Explore MultiPerm O2-CO2.

MultiPerm H2O-CO2

Designed for water vapor transmission rate (WVTR) and carbon dioxide transmission rate (CO₂TR) measurements.

Explore MultiPerm H2O-CO2.

TotalPerm

Combines OTR, CO₂TR and WVTR measurement capabilities in one integrated system.

Explore TotalPerm.

Confirm the required measurement parameters and sample compatibility with ExtraSolution when selecting an instrument for a specific application.

Conclusion

Carbon dioxide transmission rate (CO₂TR) is an important parameter for characterizing the gas barrier performance of films and packaging materials. It measures carbon dioxide transmission under defined conditions and supports material comparison, packaging development and quality control.

Reliable interpretation requires attention to material composition, thickness, temperature, gas and pressure conditions, units and the selected test method. CO₂TR should also be distinguished from carbon dioxide permeability, as the two parameters represent different quantities.

ExtraSolution provides solutions for measuring carbon dioxide transmission through films and barrier materials.

Contact ExtraSolution to discuss your CO₂TR testing requirements and identify a suitable measurement system.