Test Method for Moisture Barrier Property of EVOH Copolymer Sheeting

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Ethylene vinyl alcohol (EVOH) is a formal copolymer of ethylene and vinyl alcohol, which is one new type of material with good barrier property. EVOH copolymer is defined by the mole% ethylene content: lower ethylene content grades have higher barrier properties; higher ethylene content grades have lower temperatures for extrusion.

EVOH is commonly used as an oxygen barrier in food packaging such as aseptic package, hot-filled package and retort pouch, etc., which are mainly used for dairy products, meat, juice, canned food and seasonings. It is better than other plastics at keeping air out and flavors in, is highly transparent, weather resistant, oil and solvent resistant, flexible, moldable, recyclable, and even printable. Its drawback is that it is difficult to make and therefore more expensive than other food packaging. Instead of making an entire package out of EVOH, manufacturers keep costs down by coextruding or laminating it as a thin layer between cardboard, foil, or other plastics.

The moisture barrier property of EVOH may be compromised when it is placed in high humidity environment. In order to guarantee the food quality within its shelf life, the food manufacturers shall inspect the moisture resistance of their product package made of EVOH regularly.

This article provides a simplified test method for moisture barrier property of EVOH sheeting for your reference. The test specimens are PP/EVOH/PP copolymer sheeting. The testing instrument used to measure the moisture permeability of the test specimens is Labthink’s W3/330 Water Vapor Transmission Rate Test System.

Figure 1. EVOH Copolymer Sheeting and Finished Package made of EVOH

The tests can be performed according to the following testing procedures.

(1)    Before tests, cut 3 pieces of specimens with sample cutter. The size of the specimen should be 108mm by 108mm.

(2)    Mount the 3 pieces of specimens in the test cells of the instrument respectively.

(3)    Set specimen name, specimen thickness, test temperature, test humidity and other parameters. Then start the test by clicking Start Test button.

(4)    Turn on the gas supply. Adjust the nitrogen gas flow rate and the pressure until the humidity inside the test chamber and the nitrogen flow rate reach specified values.

(5)    The system will calculate and display the test results automatically after tests.

For more details about Labthink’s W3/330 Water Vapor Transmission Rate Test System, please visit www.labthink.com

About Labthink Instruments Co., Ltd:

Labthink Instruments Co., Ltd is one leading supplier of packaging testing instruments, which is headquartered in Jinan, China and operated in Boston, U.S.A.