Return list

How to test the seal performance of black and white PE packaging for liquid milk?

Jun 15,2020

Source: Link Testing Instruments Co., Ltd

Liquid milk is an important part of many people’s diet. Since a large amount of fat and protein are contained in milk, it is easily oxidized, as a result, the quality of the milk can be compromised within its shelf life. Therefore the packaging materials used for liquid milk are required to have sufficient oxygen barrier property. Moreover, the seal performance of the packaging should meet requirements for extending the shelf life of liquid milk.

Currently coextruded black and white film made of PE is widely used in package for liquid milk. Such material features opaque, low cost, portability and environment-friendly characteristics, for which it is popular in packaging for liquid milk. The barrier property of some black and white film is quite ordinary and the shelf life of the milk using such material is usually about 30 days. In contrast, when a material with ultra-barrier property is used as the packaging material for liquid milk, the shelf life can be extended to 90 days. Therefore, it is recommended that milk manufacturers to select suitable packaging materials with high oxygen barrier property.

Meanwhile the manufacturer should pay more attention to the seal performance of the packaging for liquid milk. If the seal performance of the black and white PE packaging is not good enough, the packaging bag may be broken during the process of product filling, transportation or storage within its shelf life.

This article provides a test method of seal performance of black and white PE packaging bag for your reference. The test specimens are black and white PE bags for fresh milk. The testing instrument is Link Testing’s LTY-01 Leak Tester.

In the tests, the specimen is submerged in the water within the vacuum chamber, and then the vacuum chamber is evacuated to form differential pressure between the inside and outside of specimen. The leakage property could be obtained by observing the steady progression of bubbles from the specimen and how the specimen expands and restores to its original shape after vacuum release.

Figure 1. LTY-01 Leak Tester

The tests should be performed according to the following procedures.

Add certain amount of distilled water into the vacuum chamber. Then submerge the specimen into the distilled water. The top of the specimen should be at least 25mm away from the surface of the distilled water.

Turn off the vacuum pump and close the sealing cover of vacuum chamber.

Set pressure and start evacuating the vacuum chamber with vacuum pump.

Stop evacuation after the preset pressure is reached and maintain the pressure for a certain period.

Observe whether there are successive air bubbles coming out when evacuating the vacuum chamber and maintaining the vacuum degree.

Turn off the vacuum pump. Open the sealing cover and remove the specimen. Wipe off the water on the surface of the specimen. Check if there is distilled water enter the inside of the specimen if necessary.

Switch off the instrument.

With the test results, the manufacturer of black and white PE bags can adjust their production process to improve the seal performance of the packaging bags. As well the users of those bags can select packaging bags with proper seal performance for their products.

For more details about LTY-01 Leak Tester, please visit

About Link Testing Instruments Co., Ltd:

Link Testing Instruments Co., Ltd is one leading supplier of packaging testing instruments, which is headquartered in Jinan, China

Live Chat