Yogurt is a milk product that made by fresh milk. After pasteurization, beneficial bacteria (starter) are added to the milk. After fermentation, it is then cooled and filled. The fermentation process makes the sugar and protein in the milk richer. About 20% is hydrolyzed into small molecules. After fermentation, the fatty acids in milk can increase twice as much as raw milk. These changes make yogurt easier to digest and absorb. The high protein and fat content of yogurt determines that it is sensitive to oxygen. Therefore, in order to ensure the shelf life of yogurt, yogurt in plastic cups is usually sealed with a composite film added with metal materials such as aluminum foil as a cover film. If composite fastness between the single-layer films of the cover film is low, that is, the peeling strength of each single-layer film is low when peeling off. When the cover film is torn off, it is easy to see that the cover film and the cup body are not separated but are in the cover film. The separation of the pasting points of each single-layer film not only brings inconvenience to consumers, but also causes a decline in the corporate image and impact the shelf time of yogurt. Therefore, all food companies should strengthen the composite fastness testing of cover film materials. Test methods and instruments The testing process of composite film peel strength is carried out in accordance with the standard GB 8808 "Peel Test Method for Soft Composite Plastic Materials". The testing equipment used in the peel strength test is a tensile testing machine. The testing equipment used in this article is the LTS-05S intelligent electronic tensile testing machine independently developed and produced by Link Testing Instruments Co.,Ltd. Test samples and test process Test sample: A certain brand of composite film material for cup yogurt cover. Experimental procedure: (1) Use a sampler to cut 5 samples each of 15 mm wide and 200 mm long from the horizontal and vertical directions of the cover film sample. (2) Manually peel off one end of each of the 10 specimens by approximately 50 mm. (3) Clamp the two ends of the peeled part of the sample with the upper and lower clamps of the equipment respectively, so that the long axis direction of the sample coincides with the center line of the two clamps. (4) Set the test parameters such as displacement and test speed, and click the test start option to start the test. (5) The equipment automatically tests and records the force value during the sample peeling process, and reports the final test results after the test is completed. Test results and analysis The average transverse peel strength of the samples tested in this article is 4.412 N/15mm, and the average longitudinal peel strength is 5.944 N/15mm. The LTS-05S intelligent electronic tensile testing machine is used to test the composite fastness of the cover film for yogurt cups. It has the characteristics of simple operation, high repeatability and accuracy of test results, and can truly reflect the composite fastness of the cover film.
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