Research and Analysis on air permeability test of

2022-07-31
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Research and Analysis on permeability test of flexible packaging materials

[Abstract]: This paper briefly introduces the measurement methods and relevant test standards of gas permeability through the description of gas permeability process. The influence of gas (excluding organic gas) penetration into packaging materials on the contents of flexible packaging was also introduced

Keywords: permeability, testing, packaging, materials

gas penetration testing of wrapper

abstract:gas penetration, information about test methods, reference standards, and some representative equipment 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: penetration, testing, wrapper, packaging

as we all know, in the food, medicine, precision electronic components and other industries, the gas barrier performance of product packaging materials is a very important indicator, which can directly affect the storage life, storage environment and sales environment of products. The influence of gas on food and drugs was first widely concerned by the flexible packaging industry. The penetration of oxygen may lead to food deterioration and drug failure. Now, for food and drug packaging, the industry standard has given a preliminary description of the packaging film with the promulgation of the national oil consumption limit regulations and further upgrading, tightening the air permeability and testing. This paper introduces the gas permeability mechanism of the film, the influence of gas transmission on the contents, and the widely used gas barrier test method. This article only introduces the test of common gases, not organic gases

1. gas permeation process

in a broad sense, the permeability of packaging materials is through material or material transfer between materials and contents. From the thermodynamic point of view, the permeation of small molecular substances into packaging materials is a single molecule diffusion process, and the speed of the whole process is determined by two factors: solubility parameter and diffusion coefficient. Without discussing the package leakage, the barrier of the film to gas is the penetration of gas into the film: gas molecules enter the material surface from the high concentration area, diffuse to the material, and desorb from the other surface of the low concentration area

1.1 diffusion phenomenon

diffusion phenomenon is caused by mass transfer and mass flow caused by uneven distribution of component density. From the microscopic point of view, the diffusion phenomenon in gas is directly related to the thermal motion of gas molecules

1.2 influence of penetrating gas on contents

the barrier performance of product packaging materials is a very important index for industries such as food, medicine and precision electronic fixtures to separate and stretch sample components at a fixed speed. For example, for fruit preservation, the oxygen resistance and moisture resistance of the packaging film (that is, the barrier of the film to oxygen and water vapor) are the determinants of the fruit preservation period. Another example is Shangshi Zhitong ointment, which is a drug that especially needs oxygen barrier packaging. If PVDC film packaging with good gas barrier and humidity barrier is selected, the odor will not be lost and the curative effect will not be affected

oxygen in the air has a certain destructive effect on the nutritional components in food: oxygen oxidizes the oil in food, even at low temperature; Peroxide produced by oil oxidation can make food lose its edible value, and produce strange odor and toxic substances; Oxygen can make vitamins and various amino acids in food lose their nutritional value; Oxygen can also aggravate the reaction of oxidative browning of food; For food microorganisms, most of the bacteria propagate and grow due to the existence of oxygen, resulting in the corruption and deterioration of food. For the preservation of fruits and vegetables, fresh fruits and vegetables still breathe to maintain their normal metabolism during storage, transportation and circulation, absorb a certain amount of oxygen and release a certain amount of CO2 and water, and consume some nutrients. The low oxygen permeability of the film can reduce the released water and consumed nutrients, and prolong the preservation period of fruits. In the packaging of carbonated soft drinks, pet plastic containers account for 40% of the total carbonated soft drink packaging, replacing some glass bottles and metal cans, due to its good transparency, strength and impermeability to CO2

as for drug packaging, it is mainly active in the lubricant industry, and the packaging materials can play an important role in the quality, validity, packaging form, sales, cost, etc. of drugs. Generally, each glass fiber is uniformly coated with plastic materials for drug production. Whether it is tablets, granules, injections, liquids, powders, ointments, etc., it is in a situation of less quantity and more varieties. Moreover, it takes more complicated ways from the drug leaving the factory to reaching the patients. Drug packaging materials shall have stability, barrier performance, structural performance and good processability. Oxygen has the greatest impact on drugs in the air. Oxygen can oxidize and deteriorate many drugs, such as vitamin C, a, D, adrenaline, phenol, etc., thus reducing the content of their main components, weakening or ineffective efficacy

although many drugs have protective films, the gas resistance of drug packaging is still very important. At present, the six general plastics in the world are still used for packaging: PE, PP, PS, PVC, PA and PC. PE, PVC, PP and polyester are mostly used for drug packaging in China. In addition to meeting the general performance of packaging materials, pharmaceutical packaging materials should also meet special requirements such as safety and applicability. For example, pharmaceutical blister packaging materials include pharmaceutical aluminum foil, plastic hard sheet, heat sealing coating and other materials. Pharmaceutical aluminum foil takes hard industrial pure aluminum as the base material, and has the advantages of non-toxic, corrosion-resistant, impermeable, heat resistant, moisture-proof, light resistant, high-temperature sterilization and so on. Because the drugs are very sensitive to moisture, humidity and light transmission, the blister materials used are required to have high resistance to water, light and steam. PVC, PVDC, or composite materials PVC/PVDC, PVC/PE, PVC/PVDC/PE, PVDC/OPP/PE, etc. are mostly used

2. permeability test methods

from the perspective of test principle, there are two kinds of permeability test methods: pressure difference method and sensor method through electric quantity analysis. At present, the pressure difference method is widely used to test the permeability of thin films

2.1 measuring principle of differential pressure method

separate the film test chamber to be tested into two independent spaces, fill one side (high-pressure chamber) with test gas, and form a certain differential pressure on both sides of the sample. The gas in the high-pressure chamber penetrates through the film into the low-pressure chamber. The gas permeability can be obtained by measuring the pressure or volume change of the low-pressure chamber. GB/t1038-2000 adopts the differential pressure method. The existing international standards for testing the permeability of films by pressure difference method include ASTM dl434-1998, iso15105-1, iso2556:2001, etc

the pressure difference method permeability meter has a wide test range and is easy to use. It can test a variety of gases. The test cost is low, and the equipment price is generally lower than that of the electricity analysis sensor method

Jinan Languang is the first manufacturer in the world to launch the atmospheric pressure difference method permeability tester. Its bty-b1 permeability tester uses the air with the test lower chamber (low pressure chamber) of 1 atmospheric pressure, effectively avoiding the possible impact of the lower chamber leakage on the test

2.2 testing principle of the electricity analysis sensor method

the principle of the electricity analysis type oxygen transmittance tester is to use the film to be tested to separate the test chamber into two independent air flow systems, one side is the flowing gas to be tested (but pure oxygen or mixed gas containing oxygen, the relative humidity of the gas can be set), and the other side is the flowing nitrogen. The pressure difference on both sides of the sample is equal but the oxygen partial pressure is different. Under the effect of concentration difference, the oxygen through the film is sent to the electric quantity analysis sensor under the carriage of nitrogen gas flow, so as to calculate the oxygen transmittance of the material

electric quantity analysis equipment has high low-end accuracy. Due to the same pressure on both sides of the sample, it is conducive to reducing the possible leakage during the test. However, this kind of instrument is expensive, and the oxygen sensor is consumable, so the test cost is high. This kind of instrument has high detection accuracy for samples with low oxygen transmission, but it is not suitable to frequently detect samples with high oxygen transmission due to the limitation of the service life of the sensor. In addition, this kind of equipment has certain selectivity to the test gas

3. conclusion

the penetration of gas into packaging materials may cause the contents to deteriorate and fail, which has a great impact on the shelf life of products. In the world, there are two methods to detect gas permeability: pressure difference method and electric quantity analysis sensor method. China's flexible packaging testing industry has developed rapidly in the field of permeability testing

due to the difference between the common inorganic gas test methods and the water vapor and organic gas test methods, the author will introduce the water vapor permeability test of flexible packaging and the organic gas permeability test of flexible packaging in the future

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