Understanding OTR and WVTR in Flexible Packaging Bags
Mar 22, 2024
Flexible packaging bags have become ubiquitous in various industries due to their convenience, versatility, and cost-effectiveness. However, ensuring the preservation of the packaged contents requires understanding and controlling two critical parameters: Oxygen Transmission Rate (OTR) and Water Vapor Transmission Rate (WVTR). These parameters are crucial in determining the shelf life and quality of perishable goods. In this article, we delve into the significance of OTR and WVTR in flexible packaging bags, explore the ASTM F-1249 test method for measurement, discuss calculation methods, and provide data references for common packaging materials.
Significance of OTR and WVTR
OTR measures the rate at which oxygen permeates through a material, while WVTR measures the rate of water vapor transmission. For products sensitive to oxygen or moisture, such as food, pharmaceuticals, and electronics, controlling OTR and WVTR is vital to prevent spoilage, degradation, or loss of efficacy.
Flexible packaging materials, typically composed of multiple layers laminated together, offer various barrier properties to oxygen and moisture. Common structures include PET/AL/PE (Polyethylene), PET/PE, and PET/VMPET/PE. Understanding the transmission rates of these materials is essential for designing packaging that meets specific product requirements.
ASTM F-1249 Test Method
ASTM F-1249 provides a standardized method for measuring OTR and WVTR of flexible barrier materials. The test involves sealing a sample of the material between a controlled atmosphere and a known concentration of oxygen or water vapor. The transmission rate is then determined by monitoring the change in gas concentration over time using appropriate instrumentation, such as gas chromatography or coulometric sensors.
Calculation Methods
Once the transmission rates are measured, they are typically expressed in units such as cc/m2/day for OTR and g/m2/day for WVTR. These values indicate the volume or mass of gas or moisture that passes through one square meter of the material per day under specific test conditions. Calculating the transmission rates allows packaging engineers to compare different materials and optimize packaging designs for specific applications.
Data References
For PET/AL/PE, PET/PE, and PET/VMPET/PE structures, the following approximate transmission rate ranges can be considered:
PET/AL/PE: OTR: 0.01-0.1 cc/m2/day, WVTR: 0.1-1 g/m2/day
PET/PE: OTR: 1-10 cc/m2/day, WVTR: 1-10 g/m2/day
PET/VMPET/PE: OTR: 0.1-1 cc/m2/day, WVTR: 0.5-5 g/m2/day
These values can vary depending on factors such as material thickness, temperature, humidity, and sealing conditions. It’s essential to conduct specific tests on the actual packaging material to obtain accurate transmission rate data for a particular application.
In conclusion, understanding and controlling OTR and WVTR in flexible packaging bags are crucial for ensuring product quality and shelf life. The ASTM F-1249 test method provides a standardized approach for measuring transmission rates, and accurate data on transmission rates for different packaging materials enable informed decision-making in packaging design and selection.
By employing suitable barrier materials and optimizing packaging structures, manufacturers can enhance product protection, reduce spoilage, and meet consumer expectations for quality and freshness.