Comparison and Analysis of the Difference in Water Vapor Transmission Rate of Same Packaging Materials

Packaging materials for dry products, powder products, electronic products and other products sensitive to water vapor should have good moisture barrier performance, which is generally characterized by testing the water vapor transmission rate of packaging materials; packaging materials with high water vapor transmission rate have poor moisture barrier performance.

Water vapor permeability refers to the mass of water vapor that permeates a unit area of a material in a specified time period. According to the principle of the dissolution in the similar material structure and the permeation process of gas in the material, polar water molecules have higher water vapor permeability in polar polymer materials and materials with more free volume for molecular diffusion. Therefore, the structure of packaging materials affects its moisture barrier performance. Then the question will be, is the moisture barrier performance of packaging materials of the same material structure the same or at the same level? In this paper, the water vapor transmission rate of two packaging materials with the same material structure was tested and analyzed.

Test sample

In this test, two KPET/PE composite films with the same application and material were used as test samples to compare their moisture barrier performance.

Test standard

The test methods for water vapor transmission of flex plastic packaging materials include cup method, electrolytic sensor method, infrared sensor method and humidity sensor method. This test is conducted based on the principle of cup method. The test process is in accordance with ASTM E96 Standard Test Methods for Water Vapor Transmission of Materials

Test instrument

To improve the test efficiency and the comparability of the results, C360M Water Vapor Transmission Test System which can test six samples simultaneously is used as the test instrument. C360M is developed and produced independently by Jinan Labthink Instruments Co., Ltd.

Test principle

The cup method, also known as the gravimetric method, is to obtain the water vapor transmission rate of the material according to the change of the mass of the test dish in the test process. The principle can be divided into two ways: dry cup method and wet cup method. A certain amount of desiccant is put into the test dish of dry cup method, and a certain amount of distilled water is contained in the test dish of wet cup method. After the sample is sealed to the test dish, the inside of the test dish is separated from the external environment. Control the humidity of the external environment, the external environment of the dry cup method is with high humidity, and the external environment of the wet cup method is with low humidity. The water vapor permeates from the high humidity side to the low humidity side through the sample, resulting in the increase (dry cup method) or decrease (wet cup method) of the mass of the test dish. By weighing the change of the mass of the test dish with the infiltration time, the water vapor transmission rate of the sample can be calculated.

Figure 1 C360M Water Vapor Transmission Test System

Instrument specification

Supports both dry cup method and wet cup method, the test range of dry cup method is 0.01 ~ 1,200 g/(m2·24h), the test range of wet cup method is 0.01 ~ 10,000 g/(m2·24h). 6 samples can be tested at the same time, improves the efficiency. The test chamber is precisely temperature controlled and remains stable at a range of (15~55)℃ ± 0.2℃.Equipt with High-efficiency and mist-free automatic humidity regulator which controls the humidity at a range of (10%~90%)RH ± 1%RH . It is unnecessary to replace the inner core of the desiccator, which can continuously work for 20,000 hours. The sample size is Φ 74 mm, and the test area is 33 cm2. air velocity is automatically adjusted. Patented test chamber and test dishes with advanced fluid dynamics and thermodynamic designs. Unique, DataShieldTM system (optional) facilitates centralized management of user data. It supports a variety of formats of exported data. Reliable security algorithms are used to prevent data leakage. It supports universal wired and wireless LAN, optional private wireless network and third-party software.

Application

(1) This instrument is applicable to the test of water vapor transmission of film, sheet, paper and paperboard, textile and non-woven cloth and other packaging materials. Films including various plastic films, plastic composite films, paper plastic composite films, geomembranes, coextrusion films, waterproof and breathable films, aluminized films, aluminum foil, aluminum plastic composite films and other film materials; sheets including various engineering plastics, rubber, building materials (waterproof materials for construction), thermal insulation materials, such as PP, PVC, PVDC, nylon and other sheets. It is applicable to test the water vapor transmission of building materials, aseptic wound protective films, medical plaster patches and other materials.

(2) The instrument conforms to a number of national and international standards, such as GB 1037, GB / T 16928, ybb00092003, ISO 2528, ASTM e66, ASTM D1653, TAPPI t464, DIN 53122-1, etc.

Test procedure

Test in this paper adopt the wet cup method.

(1) Cut three specimens with a diameter of 74 mm from two samples with sample cutter.

(2) Add a certain amount of distilled water to each of the six test dishes, clamp the specimens to the test dishes, place the test dishes on the test dish holder in the instrument test chamber, and close the chamber cover.

(3) Set the sample name, test temperature, humidity, test interval, test mode and other parameter on the control software of the instrument and start the test. The instrument weights the test dishes automatically according to the set parameters, and displays the test results of each test dish after the test.

Test result

Take the arithmetic mean of the test results of three samples as the water vapor transmission rate of each sample. The water vapor transmission rate of two types KPET/PE samples was 0.7981 g/(m²·24h) and 3.4162 g/(m²·24h) respectively.

Conclusion

The moisture barrier performance of packaging materials is different due to different material structures. However, for the packaging materials with the same structure, the water vapor transmission rate is also different due to the influence of production process, barrier layer thickness and other factors. The fact that the water vapor transmission rate of the two samples with the same structure tested in this paper is quite different confirms the above conclusion. Therefore, it is important to test the moisture barrier performance of packaging materials to ensure product quality. The test process is simple, six samples being tested at the same time increases the test efficiency, same test conditions such as wind velocity and other factors is guaranteed so as to ensure the comparability of the two samples, the test results are accurate and reliable.