Plastic packaging is used widely in various industries. There are multiple reasons behind preferring them for your product. It allows us to consume products in ways that would be very difficult, without it. It safeguards vulnerable products from damage during transit and from contamination or moisture damage. It preserve products for longer time period by sealing it completely. These features of plastic film define its quality. And the quality is further defined by the molecular elasticity of the polymers due to which it can yield the strength required. This elasticity or strength is also known as the impact strength. To maintain the plastic film strength, manufacturers must conduct an impact resistance test using a proficient instrument such as Dart impact tester.

Purpose of testing Impact resistance

The purpose of an impact test is to evaluate the ability of a material to absorb energy during a collision. This energy may be used to determine the toughness, impact strength, fracture resistance, impact resistance of the material depending on the test performed. These values are important for the selection of materials for packaging which will be subjected to applications that require undergoing very rapid loading processes.

It is widely used in plastic industry, as one of the biggest challenges for plastic bag producers is developing high-quality material with increased impact resistance.

The Testing Standard-ASTM D1709

The Dart impact tester is a conventional instrument used for evaluating the impact strength or toughness of a plastic film. It complies with the testing standards of ASTM D1709. According to this standard, the test utilizes a single dart apparatus and a single drop height, while modifying the dart weight. Test results can be used either as a quality control evaluation or for end use comparisons. 

Depending upon the expected impact strength of the test sample, either Method A or Method B is chosen. These methods differs in the dart size and the drop height for the dart chosen.

For example:

Test Method ‘A’ uses a dart with a 38.0 ± 1-mm diameter and a hemispherical head dropped from a height of 0.66 ± 0.01 m. It may be used for films whose impact resistances require masses of about 50 g or less to about 2 kg to fracture them.

Test Method ‘B’ uses a dart with a 50 ± 1-mm diameter hemispherical head dropped from a height of 1.50 ± 0.03 m. Its range of applicability is from about 0.3 kg to about 2 kg.

(Above values are just an example to explain the difference between Method A & B, it can vary for other standards or instruments.)

A number of test samples are impacted to determine an appropriate starting point for the weight of the dart. The testing sample is clamped tightly and fully stretched in a ring at the base of the drop tower. The mounting bracket is adjusted to the appropriate drop height as per the requirement, and the dart is inserted into the bracket. The dart is released to drop into the center of the testing sample. The drop weight and the test result are then recorded which is usually based on the pass/fail criteria. 

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