Permeability test and permeability test of the hot

Permeability test and permeability test of materials

Abstract: according to the testing requirements of materials for gas permeability, this paper introduces two methods of permeability test and permeability test, and describes in detail the applicable materials, the similarities and differences of the two methods

key words: permeability, permeability, permeability, film, non-metallic

permeability of gas to materials is one of the important items of material physical property testing. Materials with low permeability are called to have certain operation stability to gas; Among these materials, the materials with extremely low gas permeability are also called barrier materials, which are widely used as functional materials (such as commodity packaging); Materials with high permeability are relative to materials with certain barrier properties. Their gas permeability is very large, there are many kinds, and they are also widely used

1. Permeability test

we often say that permeability test refers to the detection of specific gas permeability for materials with certain gas barrier. Most of these materials are high molecular polymers or multilayer composites made of high polymers, which are widely used in product packaging in food, medicine, chemical industry, electronics, military industry and other fields. Among them, materials with excellent barrier property (extremely low gas permeability) can be used for the packaging of goods sensitive to oxygen and water vapor, which is the focus of the development of plastic packaging industry in recent years, and also the basis for the development of new packaging such as inflatable packaging, vacuum packaging, sterile packaging and so on

the permeability test methods of materials mainly include differential pressure method and isobaric method, of which the differential pressure method is the most widely used (see the article "permeability test methods and equipment" of Languang Laboratory Forum on October 10 and 17, 2005). The pressure difference method is a purely physical detection method, with clear test principle, which is consistent with the principle of the later mentioned permeability test equipment. It is the fundamental method in permeability test. Differential pressure method is divided into vacuum differential pressure method and positive differential pressure method. According to the detection standard, vacuum gauge or gauge pressure sensor with very high resolution is required, and small pressure changes in the detection process need to be accurately collected

permeability test has the following characteristics:

first, for the permeability test equipment of vacuum differential pressure method, the vacuum degree of the test chamber is the most important index. ASTM D (2003) requires that the low-pressure side of the vacuum differential pressure method is at 26pa. The visible hand of the government undoubtedly plays a decisive role in reducing production capacity this year. Both ISO 2556:2001 and gb/t require that the low-pressure side pressure is not greater than 27 Pa. The permeability tester needs to be equipped with a vacuum pump with high vacuum pumping capacity. Since the vacuum degree is directly related to the state of the sample, whether the vacuum degree can meet the standard requirements will have a certain impact on the test data

secondly, the accuracy of vacuum gauge directly affects the accuracy of test results, and the choice of accuracy will have certain restrictions on the range of vacuum gauge. Due to the low permeability of gas to such materials, the pressure change rate of the lower chamber during the test is also very small, so the range of the vacuum gauge does not need to be too large. Table 1 lists the measured data of oxygen permeability test of five high barrier materials. In this group of tests, the maximum pressure change from the end of the test is not greater than 20Pa

third, the change of temperature can directly affect the barrier property of the sample. The permeability coefficient, solubility coefficient and diffusion coefficient of the material are affected by temperature changes and follow Arrhenius equation

at present, professional permeability testing equipment for such materials with low gas permeability is developing rapidly. Labthink vac-v1 gas permeability instrument can fully meet the national standards and ISO standards, and its function is very powerful

2. Permeability test

for plastic foam, leather, textiles, cardboard, paper, porous ceramics and other materials with high permeability, when used in some specific fields, it is necessary to quantify the permeability of gas to these materials. For example, whether the permeability of cigarette paper is properly selected can directly affect the appearance of cigarettes, the taste of cigarettes and the content of smoke components, The control of textile permeability is the key factor that directly affects the comfort of clothing. The test of gas permeability of this kind of material is called permeability test, which requires professional permeability tester

the permeability test methods of this kind of materials can be generally divided into two types: constant flow pressure difference and constant pressure difference flow measurement (for details, please refer to "technology and materials for automotive industry with experimental speed up to 0.001mm/min ~ 1000mm/min" and "permeability test of automotive non-metallic materials" in September and October 2005). The constant flow pressure difference method is mainly used to test polyurethane foams and soft or semi-rigid porous elastic materials; Constant pressure differential flow measurement method is mainly used in textiles, non-woven fabrics, leather, geotextiles, etc; The permeability test of paper, leather and other materials needs to test the time of passing through a certain volume of air in the sample under a certain pressure difference, which can be classified as the flow measurement under constant pressure difference, and then it can be calculated through the measured flow

compared with the previously introduced permeability test, the permeability test has the following characteristics:

first, the test objects are different. The permeability test is mainly used to detect films, while the permeability test is mainly used to detect porous materials, non-woven fabrics, etc

secondly, permeability test can detect the permeability of oxygen, nitrogen, carbon dioxide, air and other gases to materials, while permeability test mainly detects the permeability of air to materials

third, there is a great difference in the length of the test time. The permeability test time is long, and the permeability test time is much shorter, mainly because the permeability of the two test materials is very different

fourth, because the permeability test mainly detects materials with high permeability, the equipment does not need to use a highly sensitive vacuum gauge or pressure sensor, and the requirements for the vacuum pumping capacity of the vacuum pump are relatively low, but the pressure sensor is required to have a wide range to meet the needs of different permeability tests

fifth, the key components of the permeability test equipment are not only pressure sensors and vacuum pumps, but also the accuracy and range of the flowmeter

sixth, due to the differences in testing standards and methods, the units of test data vary greatly for different materials: for example, the final test result of textiles is air permeability (mm/s), while the final test result of leather is air permeability (ml/cm2 · h). With special operation software, the same permeability tester can complete the conversion of the above test data

at present, the development of air permeability testing equipment is very uneven. For example, there are many kinds of air permeability testers for textile, paper and other materials in the market, while there are few air permeability testing equipment for polyurethane foam and porous elastic materials. This year, the tqd-g1 air permeability tester developed by Labthink blue light is a testing device with both constant flow pressure difference and constant pressure difference flow measurement modes. With professional software, it can basically meet the needs of air permeability testing of most non-metallic materials. Moreover, Labthink blue light can customize the air permeability tester with specified testing range and accuracy according to the testing needs of customers, which is more practical

3. Summary

it is the same to detect the permeability of gas to materials. The difference of material properties causes obvious changes in the detection equipment. Selecting the corresponding equipment according to the detection needs is the best way to obtain the practical test range and accuracy. Although special testing equipment has been sold on the market for flexible packaging materials, cigarette paper, textiles and other materials, the introduction of tqd-g1 air permeability tester is undoubtedly a beneficial promotion for the control of air permeability of materials for polyurethane foams, porous elastomers and so on

source; Jinan Languang Electromechanical Technology Co., Ltd