100B-20 |
Determination of surface energy, wettability and oil-resistance of packaging materials using a digital-image-processing system |
J. H. HAN, Department of Food Science, University of Manitoba, Winnipeg, MB R3T 2N2, Canada Surface energy, wettability and oil-resistance are very important surface characteristics of materials which affect the performance of packaging materials. All these characteristics can be determined by measuring contact angles of standard liquid drops on the material surfaces. The objective of this study is to verify the benefit of a digital-image-processing-system to measure the contact angles of liquid drops on sample solid materials accurately, conveniently and cost-effectively. A digital microscope was connected to a personal computer. The packaging materials were glued on a well-leveled platform and the microscope was positioned horizontally for capturing the side-view image. At the lens position of 10X, the side-view image was acquired and converted into a binomial edge-enhancing picture using conventional photo editing software. The contact angle of the digital image was measured by hand in the case of a small number of samples or using a line-slope calculation software in the case of large samples. The surface energy was calculated from a Fox-Zisman plot. The same system was used for wettability and oil-resistance determination by measuring the contact angles of water and oil drops with time, respectively. The dynamic changes in the contact angle due to water and oil absorption was recorded by the system using a camcorder option. For the water and oil absorption tests, the cosine of contact angles showed very accurate linear relationship with time. Water absorptiveness and oil-resistance were calculated from the slope of the cosine contact angle and time. Surface energies of sample plastic films (PVC and PP) obtained from the Fox-Zisman plot ranged from 32 – 33 mJ/m2. The digital-image-processing system was very convenient and accurate to measure the contact angles of standard liquid drops on the packaging materials, especially for the measurement of dynamic changes of the contact angles with time to determine the water/oil absorption.
Session 100B, Food Packaging
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