More accurate method for grease barrier testing

Several standards for grease barrier testing of packaging materials are being used. These include TAPPI, ASTM and ISO standards. Results are expressed either as the time in which grease has penetrated through the structure or as the amount of grease which has penetrated through the test structure in certain time. The amount of penetrated grease is evaluated either visually or by measuring the diameter and calculating the area of the grease stain. Such tests are not accurate but provide mere approximations. There is thus a need for a more accurate and exact method. A method recently developed at VTT integrates two standard methods and combines visual data with a numerical result obtained by image analysis. Dyed oil or grease is applied automatically onto the test specimen having the test side upwards. A weight is placed onto each specimen. The whole test system is then transferred to the scanner. Scanning can be performed after pre-selected time intervals, and an image analysis script is used to analyse the area fraction of penetrated grease/oil. Both visual and numerical results are obtained after each time interval. Test temperature, test grease and test duration can be selected according to the end-use of the packaging material. Benefits of this test method include automated and operator independent application of test oil, pre-selected scanning intervals, more realistic test durations and temperatures approaching actual packaging applications, and availability of both visual and numerical data. In addition, there is no need to touch the test samples during the testing.