The standard “TAPPI T 464 Water vapor transmission rate of paper and paperboard at high temperature and humidity” developed by the Technical Association of the Pulp, Paper and Converting Industries (TAPPI) describes a procedure for the gravimetric determination of the water vapor transmission rate (WVTR) of sheet materials at 90 degrees with a 37,8 percent relative humidity atmosphere on one side and a dryer on the other. This method is generally suitable for all materials up to 3 mm thick, but can be used with caution for thicker materials if the edges of the sample are completely sealed. In other conditions, the standard “TAPPI T 448 Water vapor transmission rate of paper and paperboard at 23 degrees and 50 percent relative humidity” is valid for the test. This test can be used for both wrinkled and non-wrinkled samples.
The test method described in the TAPPI T 464 standard provides a means of measuring the ability of a material to protect its contents from undesirable changes resulting from the transmission of water vapor to or from the surrounding medium. The effect of temperature and humidity on the water vapor transmission rate of paper or paperboard is rarely linear, so test results obtained at lower temperatures and humidities cannot be safely generalized to apply to warmer, more humid conditions.
If the sheet materials are not homogeneous, there can be a significant difference in transmission rate depending on the side facing the higher humidity. Often this test is performed to simulate the practical use of the material, for example, a material for sealing a dry product is tested by exposing the product facing surface in the package to the dry atmosphere.
Three sheets of material are required for testing. These tests are carried out over a period of 5 days, with readings taken twice a day, unless the client specifies an alternative time frame. The client must specify which surface is exposed to moisture.
Water vapor transmission rate (WVTR) is the steady-state rate at which water vapor passes through a film under specified temperature and relative humidity conditions. Conditions can vary, but the most common conditions are standardized to 37,8 degrees Celsius and 90 percent relative humidity.
Water vapor transmission rate is considered important, especially for packaging performance. A critical function of flexible packaging is to keep dry products (potato chips, bagels, etc.) or dry and moist products (cheese, cake, etc.) moist. Without protective packaging, products rapidly gain or lose moisture until they reach equilibrium with the surrounding environmental relative humidity, at which point crispy products become soggy and chewy products become hard and dry.
Water vapor transmission rate is the standard measurement by which films are compared for their ability to resist moisture transmission, with lower values indicating better moisture protection. Only values reported at the same temperature and humidity can be compared, as transmission rates are directly affected by both of these parameters.
The most obvious factor affecting the water vapor transmission rate is thickness. The water vapor transmission rate of a thicker film is half that of a thinner one. The water vapor transmission rate of different products may be different. The primary factors that cause these differences are:
Among the numerous tests, measurements, analyses and evaluation studies that our organization has carried out for businesses in various sectors, it also provides testing services defined in the “TAPPI T 464 Water vapor transmission rate of paper and cardboard at high temperature and humidity” standard with its trained and expert staff and advanced technological equipment.
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