Moisture vapour transmission
There are many industries where this property is critical. Moisture sensitive foods and pharmaceuticals are put in packaging with controlled Moisture Vapour Transmission (MVTR) to achieve the required quality, safety, and shelf life. In clothing, MVTR as a measure of breath ability has contributed to greater comfort for wearers of clothing for outdoor activity. The building materials industry also manages the moisture barrier properties in architectural components to ensure the correct moisture levels in the internal spaces of buildings.There are various techniques to measure MVTR, ranging from gravimetric techniques that measure the gain or loss of moisture by mass, to highly sophisticated instrumental techniques that in some designs can measure extremely low transmission rates. There are numerous standard methods described in ISO, ASTM, BS, DIN etc, quite often industry specific.
The conditions under which the measurement is made has a considerable influence on the result. Both temperature of and humidity gradient across the sample need to be measured, controlled and recorded with the result. An MVTR result without specifying these conditions is almost meaningless. Certainly no two results should be compared unless the conditions are known. The most common international unit for the MVTR is g/m²/day. In the USA, g/100in²/day is also in use, which is 1/15 of the value of g/m²/day units.
CurTec uses the ASTM E96 – 2000 method to determine the MVTR of its packaging products. The actual tests are done with desiccant where containers are filled with small lumps of anhydrous calcium chloride and then closed according to manual. The closed container is conditioned three days at 40°C and 90% relative humidity, before the weighing starts. The weight of the container is controlled on a weekly basis.
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