2024 Volume 9 Article ID: 24-0004
Currently, there is no technology that facilitates the nondestructive and contact-free estimation of the peel load of the heat seals of food and other packages in the production line. To address this gap, this study proposed a method using laser photoelasticity. Considering the environmental impact of plastics, biodegradable resin polylactic acid was selected as a sample, and the optical retardations of the sealed section of the specimens were measured by changing the seal temperature in the range of 80–105 ºC. The specimens were then peeled off using a tensile tester, and the loads were recorded. The relationships among the optical retardation, peel load and sealing temperature exhibit dependence on the combination of the machine direction (MD) (direction in which the resin film is stretched during manufacturing) and the direction of the sealing line. This was because the polymer chains were oriented in the MD in advance, and the orientation changed along the sealing line owing to temperature and pressure caused by heat sealing. The MD and sealing temperature at the manufacturing site are known; therefore, it was suggested that it should be possible to obtain a rough estimate of the peel strength using the photoelastic method. However, care would have to be taken, because the estimation accuracy might reduce, further depending on the combination of the MD and seal line.
