Testing and Evaluation of Films

A variety of tests are available for determining film quality. Many are based on ASTM standards. For example, tests for permeation of oxygen, water vapor, or other substances may be carried out, and will be discussed in Chapter 14. Tests for impact strength, tensile strength, tear strength, and other mechanical properties are important for many applications. Tests particularly related to quality control in the film production process include those that relate in some fashion to the appearance of the film. 

ASTM D3351 describes the gel count test. Gels are imperfections found in the film, often related to thermally induced cross-linking. In the standard test, a 640 in area of film is examined and the number and size of gels are counted. 

Thermal shrinkage of films can be determined by following ASTM D2732 and immersing a sample in a temperature-controlled liquid for a defined time, or by making measurements at a series of temperatures in the range of interest. 

Name and describe the functions of the three main sections of an extruder screw. 

Discuss the differences in properties you might expect between cast film and blown film produced from the same resin. What are the major reasons for these differences  

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