A new method for testing the moisture permeability

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Abstract: the moisture permeability testing of packaging materials is of great significance to the quality assurance of drugs. This paper introduces the testing principle of electrolytic moisture permeable instrument and its application in the testing of drug packaging materials in combination with the latest drug packaging materials standards

key words: electrolysis, moisture permeability, drug packaging materials, drugs, humidity

water is the medium of chemical reaction. After moisture absorption, drugs can cause caking (such as sodium bicarbonate), deliquescence (such as calcium chloride, chloral hydrate), dilution (such as glycerol, lactic acid), mildew (such as glucose, pepsin), hydrolysis (such as penicillin), oxidation (such as vitamin C) and other changes, As a result, some drugs have difficulties in dispensing or it is difficult to master the industry that has completed the annual capacity reduction task. This year, the actual production dose has not been reduced, and even the efficacy of some drugs has been reduced or irritating and toxic. Therefore, drug packaging has high requirements for water vapor permeability. The water vapor permeability of packaging materials can directly affect the stability of the quality of packaged drugs, which is an important performance index of packaging materials

1. Standard testing requirements

in order to effectively strengthen the quality control of drug packaging products, facilitate the packaging production enterprises to produce products that meet the requirements of drug packaging and facilitate the use of drug production enterprises, the State Food and drug administration has launched a series of new standards on drug packaging materials. Electrolytic analysis, as a test method to detect the moisture permeability of films and sheets, appears in some new standards. Before that, there was only weighing method in Chinese standards to detect the moisture permeability of films and sheets, while there were weighing method, infrared method, electrolytic analysis method and other methods in ISO standards

ybb (bopp/vmcpp biaxially oriented polypropylene/vacuum aluminized cast polypropylene) and YBB (pt/al/pe cellophane/aluminum/polyethylene) clearly require that the test be carried out according to the second method (electrolytic analysis) of the water vapor transmission method (YBB). The first method in YBB - cup method (i.e. weighing method) is generally applicable to films and sheets with water vapor transmission of not less than 2g/(M2 · 24h), and electrolytic analysis method is more applicable to the determination of water vapor transmission of pharmaceutical films, sheets and pharmaceutical aluminum foil with small moisture transmission data. Therefore, although some standards only require the moisture permeability test of materials according to YBB and do not specify the specific test method, because the water vapor transmission of these inspection materials is very small, the test still needs to be carried out according to the description in the standard according to the electrolytic analysis method

2. Introduction to electrolytic analysis method

iso is a widely used and comprehensive moisture permeability test standard for electrolytic analysis method. The test principle of electrolytic analysis method in the standard is described as follows: the gas Jinan new era Gold Testing Instrument Co., Ltd. the plastic coated metal hose tension tester introduced here is mainly for the tensile test of plastic coated hose of wire or cable in the electrical system of machine tool transmission cell is designed in such a way that, with the test specified inserted, It is divided into a dry chamber and a controlled harmony chamber The dry side of the specimen is swept by a flow of dry carrier gas, and water vapour permeating through the specimen from the controlled-humidity chamber is carried by the carrier gas into an electrolytic cell. This cell contains two spiral wire electrodes, coated with a thin layer of phosphorous pentoxide, mounted on the inside wall of a glass capillary. The carrier gas is passed through the capillary where the moisture it holds is quantitatively absorbed by the phosphorous pentoxide and decomposed electrolytically into hydrogen and oxygen by the application of a D.C. voltage of about 70V to the electrodes. The mass of the moisture which permeates through the specimen and is decomposed per unit time is calculated from the electrolytic current required. (the gas permeation chamber is designed in this way. When the test sample is inserted, it will be divided into a dry chamber and a wet chamber with controllable humidity. The dry side of the sample is purged by the dry carrier gas flow, and the water vapor will be carried into an electrolytic chamber by the carrier gas flow after penetrating through the sample from the wet chamber. This chamber contains two spiral electrodes and is covered with a thin layer of phosphorus pentoxide inside the glass capillary. The carrier gas flow is hairy Thin tube, where the moisture in the carrier gas flow will be quantitatively absorbed by phosphorus pentoxide. By applying a DC voltage of 70V to the two electrodes, the absorbed moisture can be electrolyzed into hydrogen and oxygen. The mass of water vapor that penetrates through the sample and is electrolyzed in unit time will be calculated from the resulting current.) The test principle of electrolytic analysis method is shown in Figure 1

Figure 1 Schematic diagram of electrolytic analysis method

note: 1. Drying tube (containing desiccant, such as molecular sieve)

two cavity permeation chamber (with self-control temperature liquid flowing through the control system of the tensile testing machine to explain the two half cavities)


fiberglass board, soaked with sulfuric acid solution

electrolytic chamber

change-over valve

copper tube, It is used to provide carrier gas (in the liquid with self-control temperature, the temperature of the gas can be controlled at the test temperature)

a DC voltage is applied between the two electrodes. The water in the carrier gas flow through the electrolytic chamber is continuously absorbed by the phosphorus pentoxide film in the chamber to generate phosphoric acid, which is electrolyzed into hydrogen and oxygen. An electrolytic current appears between the two electrodes, and phosphorus pentoxide is regenerated at the same time. The electrolytic current is proportional to the humidity of the carrier gas flow, so the humidity of the carrier gas can be measured by measuring the electrolytic current, and then the water vapor transmission of the sample can be calculated

if the electrolytic chamber is regarded as a sensor for detecting the humidity of carrier gas, this method and infrared sensor method can be classified as sensor method for moisture permeability detection. Generally, when the sensor method is used for moisture permeability detection, the design of the permeation chamber and the air flow pipeline are very similar. The difference mainly lies in how to detect the water vapor contained in the carrier gas after it leaves the test chamber. Different sensors have different working principles and different working efficiency, so it is necessary to calibrate the equipment periodically, which is the same as the sensor method in permeability detection

3. Compared with the weighing method, the application scope of electrolytic analysis method is smaller. Due to the formulation of YBB standard, the electric quantity analysis method may become the second commonly used moisture permeability detection method in China after the weighing method

labthink, as the first packaging testing equipment manufacturer to set foot in the field of barrier testing in China, began to develop the corresponding electrolytic moisture permeability tester tsy-w3 electrolytic moisture permeability tester last year (see Figure 2). At present, the equipment has entered the final commissioning stage and is expected to be put on the market in the second half of this year. It is believed that tsy-w3 electrolytic moisture permeable instrument will provide high-quality services for the majority of drug packaging users with superior performance


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