Analysis of Permeability Test of Flexible Packaging Materials

[Abstract]: This article briefly describes the method of gas permeation measurement and related test standards by describing the gas permeation process. The impact of gas (not including organic gases) on the packaging material was also described.

Keywords: breathability, testing, packaging, materials

Gas Permeation Testing of Wrapper
Abstract:Gas permeation, information about test methods, reference standards, and some representative equipments are introduced. Effects of gas (such as oxygen, air, nitrogen, carbon dioxide etc. not include the organically gas) penetration to the content are shown.
Key words: Permeation, Testing, Wrapper, Packaging

As we all know, in the food, medicine, precision electronic components and other industries, the gas barrier properties of product packaging materials is a very important indicator, it can directly affect the product's shelf life, preservation environment, sales environment. The impact of gas on food and medicine is the earliest cause for the soft packaging industry's widespread concern. Oxygen infiltration may lead to food deterioration, drug failure, etc. Now, for food and pharmaceutical packaging, industry standards have been preliminary to the permeability and testing of packaging films. Instructions. This article describes the gas-permeable mechanism of the film, details the effect of gas permeation on the contents, and the widely used gas barrier test methods. This article only describes the tests of commonly used gases and does not involve organic gases.

1. Gas infiltration process
The permeability of the packaging material is broadly defined as the material or material transfer between the material and the content. From the thermodynamic point of view, the penetration of small molecules into the packaging material is a single molecule diffusion process. The speed of the entire process is determined by the solubility parameter and the diffusion coefficient. Without discussing the leakage of the package, the barrier property of the film to the gas is the penetration of gas into the film: the gas molecules enter the surface of the material from the high-concentration region, and then they desorb from the other surface of the low-concentration region through the diffusion into the material. .

1.1 Diffusion phenomenon
The phenomenon of diffusion is due to the uneven distribution of component density and the resulting mass transfer resulting in mass flow. Microscopically speaking, the diffusion phenomenon in gas is directly related to the thermal motion of gas molecules.
1.2 The effect of gas on the contents
For food, medicine, precision electronic components and other industries, the barrier properties of product packaging materials is a very important indicator. For example, the preservation of fresh fruit, the oxygen barrier property and moisture resistance of the packaging film (ie, the barrier property of the film to oxygen and water vapor) are the decisive factors for the fruit preservation period. Another example is a wound-injury and analgesic cream, which is a drug that requires oxygen-blocking packaging. If you choose a PVDC film that is good in gas barrier and moisture resistance, the odor will not be lost, and it will not affect the efficacy.

Oxygen in the air has a destructive effect on the nutrients in foods: Oxygen oxidizes the fats and oils in foods, even under low temperature conditions; peroxides produced by the oxidation of oils can make foods lose food value, and Odor occurs, producing toxic substances; oxygen can cause vitamins and various amino acids in foods to lose their nutritional value; oxygen can also increase the oxidative browning of foods; for food microorganisms, most bacteria reproduce and grow due to the presence of oxygen. Causes food spoilage. For fresh fruits and vegetables, fresh fruits and vegetables are still breathing during their storage and transportation to maintain their normal metabolism. They absorb a certain amount of oxygen and release a certain amount of CO2 and water, and consume part of the nutrients. The oxygen permeability of the film is low. Can reduce the release of water and nutrients consumed to extend the fruit's shelf life. In carbonated beverage packaging, because PET has good transparency and strength and impermeability to CO2, PET plastic containers currently account for 40% of the whole carbonated soft drink packaging, replacing some glass bottles and metal cans.

For pharmaceutical packaging, packaging materials can play an important role in the quality, validity, packaging, sales, and cost of pharmaceuticals. General pharmaceutical production, whether it is tablets, granules, injections, liquids, powders, ointments, etc., is in a situation of less quantity and more, and it takes a more complicated route from the time the medicine is delivered until it reaches the patient. Drug packaging materials should have stability, barrier properties, structural properties and good processability. The most important oxygen in the air is oxygen. Oxygen can make many drugs, such as vitamins C, A, D and epinephrine, phenol and other oxidative deterioration, so that their main component content decreased, curative effect weakened or ineffective.

Although many medicines have a protective film, the gas barrier properties of pharmaceutical packaging are still crucial. At present, the plastics used for packaging still use the six general plastics in the world: PE, PP, PS, PVC, PA, and PC. The domestic pharmaceutical packaging uses PE, PVC, PP, and polyester. In addition to satisfying the general performance of packaging materials, pharmaceutical packaging materials also meet special requirements such as safety and suitability. For example, pharmaceutical blister packaging materials include medicinal aluminum foils, plastic hard sheets, heat-sealable coatings and other materials. Aluminum foil is based on hard industrial pure aluminum. It has the advantages of non-toxicity, corrosion resistance, impermeability, heat resistance, moisture resistance, light blocking, and high temperature sterilization. Because medicines are very sensitive to moisture, moisture, and light penetration, the blisters used require high barrier properties to water, light, and steam. They are mostly made of PVC, PVDC, or composite materials PVC/PVDC, PVC/PE, PVC/ PVDC/PE, PVDC/OPP/PE, etc.

2. Breathability test method

Divided from the test principle, there are two types of breathability test methods: differential pressure method and coulometric sensor method. At present, the differential pressure method is widely used to test the permeability of the film.

2.1 The principle of differential pressure measurement

Measured with the film test chamber into two separate spaces, one side (high pressure chamber) is filled with test gas, a certain pressure difference is formed on both sides of the sample, the gas in the high pressure chamber permeates through the film to the low pressure chamber, The gas permeability can be determined by measuring the pressure or volume change in the low pressure chamber. GB/T 1038-2000 is a differential pressure method. Internationally available pressure differential film gas permeability test standards are ASTM Dl434-1998, ISO15105-1, ISO2556:2001 and so on.

The differential pressure method air permeability meter has a wide test range and is easy to use, and can be used for testing a variety of gases. The test cost is low, and the equipment price is generally lower than the power analysis sensor method.

Jinan Languang is the first manufacturer in the world to introduce an atmospheric pressure differential method breather. The BTY-B1 breathability tester produced by the company uses the air in the lower chamber (low pressure chamber) at 1 atmosphere to effectively avoid the possible appearance of air. Due to the impact of the leakage of the lower chamber on the test.

2.2 Coulometric Analysis Sensor Test Principle
The principle of the coulometric oxygen permeability tester is to divide the test chamber into two independent gas flow systems with a film to be tested, and one side is a flowing test gas (but pure oxygen or a mixed gas containing oxygen, which can be set The relative humidity of the gas) and the flowing nitrogen on the other side. The pressure difference on both sides of the sample is the same but the oxygen partial pressure is different. Under the effect of the concentration difference, the oxygen passing through the film is sent to the electricity analysis sensor under the nitrogen gas flow, so as to calculate the oxygen permeability of the material.

The coulometric equipment has a low end precision, because the pressure on both sides of the sample is the same, which helps to reduce the leakage that may occur during the test. However, such instruments are expensive, and the oxygen sensor is a consumable type, and the test cost is high. This type of instrument has high detection accuracy for samples with low oxygen transmission, but it is not suitable to constantly detect samples with high oxygen transmission due to the limitation of sensor life. In addition, this type of equipment has a certain selectivity for the test gas.

3. in conclusion
The penetration of gas into the packaging material may cause the contents to deteriorate and fail, which has a great influence on the shelf life of the product. Internationally, two methods, differential pressure method and coulometric sensor method, are used to detect gas permeability. The flexible packaging testing industry in China has developed rapidly in the area of ​​air permeability testing.

Since there are certain differences between common inorganic gas test methods and water vapor and organic gas test methods, the author will introduce water vapor permeability testing for flexible packaging and organic gas permeability testing for flexible packaging in the future.