ASTM D4591-22

4.1.1?To measure transition temperatures to aid in the identification of the various fluoropolymers, individually or in mixtures;

4.1.2?To compare the relative levels of crystalline content of two or more specimens of a sample of a fluoropolymer relative to another sample by measuring the heat of fusion;

4.1.3?The heat of crystallization of pure PTFE homopolymer is depending on the relative molecular weight of the specimen. Some PTFE resins are modified with small amounts of comonomers. These modifications have profound effects on crystallization behavior and shall be considered when evaluating the results.

4.1.4?To characterize PTFE (DSC thermal curves determined on powders or products of PTFE that have never been melted convey appreciable information about details of morphology and molecular structure);4.1.5?To supplement the test for standard specific gravity (SSG) described in Specifications D4894 and D4895 by using the heat of crystallization of pure PTFE homopolymer, depending on the relative molecular weight of the specimen. The scopes of these specifications, however, include PTFE resins modified with small amounts of comonomers, and many commercial PTFE resins are modified in this manner. These modifications can have profound effects on crystallization behavior. Published relationships4 between heat of crystallization and molecular weight refer to pure PTFE homopolymers and, therefore, cannot be applied to the modified resins.