TAPPI UM 573

Abstract

<strong>Scope and significance</strong> <br>This method is for the determination of water vapor permeability of paper, paperboard, and flexible packaging materials under storage conditions at -18&#176;C (0&#176;F). It is generally suitable for sheet materials up to 125 &#956;m (5 mils) thick. The method has been developed because of increased emphasis on frozen-food production, and because no existing procedure gives results which correlate with those at -18&#176;C. [TAPPI T 448 "Water Vapor Transmission Rate of Sheet Materials at Standard Temperature and Humidity" is suitable at temperatures of 23&#176;C (73&#176;F) and 50% relative humidity, and TAPPI T 464 " Gravimetric Determination of Water Vapor Transmission Rate of Sheet Materials at High Temperature and Humidity" applies at 38&#176;C (100&#176;F) and 90% RH.] <br>In general, packaging materials used for storage at -18&#176;C should be capable of protection against an appreciable loss of moisture for periods up to 1 or 2 years. The final selection of materials for such storage is probably best done by actual package storage tests for the full length of time required. This method is a simplified and rapid method which has been shown to give results indicative of behavior during long-term storage. Many of the packaging materials are based on cellulose, including paper, paperboard, cellophane, and glassine. The time required for these materials to reach moisture equilibrium when exposed at -18&#176;C may be several weeks or months. The assumption is made in this procedure that equilibrium is reached, for practical purposes, in the 7-day initial conditioning period.