Material testing machines for testing tensile properties of materials are used more and more widely, but not all testing machines are suitable for tensile testing of flexible packaging materials. Based on the material testing standards of our country, this paper analyzes the indexes that should be paid special attention to when selecting the tensile testing machines for flexible packaging materials.

The tensile property of plastics and rubber is one of the most important and basic properties of their mechanical properties, which largely determines the use of this kind of plastics and rubber occasions. Tensile properties can be tested by tensile tests.

1. Tensile properties of polymer

The material testing machine requires the polymer to have the necessary mechanical properties when used as material. It can be said that for most applications of polymer, mechanical properties are more important than other physical properties. For example, the elongation at break of PE is between 90% and 950% (among which the elongation of LLDPE is higher). The elongation of some materials can be more than 1000% by special manufacturing process, and the elongation at break of common polymer materials is more than 50% - 100%. Heat shrinkable films and stretching films are usually required for high tensile properties of materials.

2. Tensile test

Tensile test (stress-strain test) usually clamps the two ends of the material specimen on two clamps at a certain distance, and the two clamps separate and stretch the specimen at a certain speed to measure the stress change on the specimen until the specimen is destroyed.

Tensile test is one of the most widely used methods to study the mechanical strength of materials. It is necessary to use a constant speed tensile testing machine. According to the different ways of load measurement, the testing machine can be divided into pendulum type and electronic tensile testing machine. At present, the electronic tensile testing machine is mostly used.

3, selection index of electronic tensile testing machine

Since flexible packaging materials are mainly polymer materials or their related materials, such as the elongation of the polymer materials mentioned above is far superior to the metal, fiber, wood, board and other materials, so the tensile testing machine for polymer and the ordinary material tensile testing machine has a certain difference, especially need to pay attention to. It is the effective travel of the electronic tension machine and the two aspects of the sample fixture.

In the tensile test, the size of the sample used is small, but the elongation of the material is generally high, so the tensile properties of the flexible packaging materials need to be equipped with a large stroke tensile machine, otherwise the clamp operation may exceed the limit of the stroke, causing damage to the equipment.