ASTM D7138-16

5.1.1 Synthetic fibers may be either amorphous or semi-crystalline thermoplastics or thermosets. Synthetic fibers may change from the solid to a liquid-like state on heating because of the glass transition of amorphous polymers, the melting of crystalline regions of semi-crystalline polymers, or at the onset of degradation. Thermoplastic fibers consist of crystalline and amorphous regions and may be manufactured with a range of molecular weights. The amorphous and crystalline fiber structure and variable molecular weight can lead to a melting temperature range instead of a discreet melting point (see Table X1.1).

5.2.1 If there are differences of practical significance between reported test results for two or more laboratories, perform comparative testing to determine if there is a statistical bias between them, using competent statistical assistance. As a minimum, use the samples for such a comparative test that are as homogeneous as possible, drawn from the same lot of material as the samples that resulted in disparate results during initial testing and randomly assigned in equal numbers to each laboratory. Compare the test results from the laboratories involved using a statistical test for unpaired data, at a probability level chosen prior to the testing series. If bias is found, either its cause must be found and corrected, or future test results for that material must be adjusted in consideration of the known bias.

1.2.1 Method 1, Differential Scanning Calorimetry (DSC), measures changes in heat capacity and will detect the glass transition, the crystalline melting and endothermic thermal degradation.

1.2.2 Method 2, a visual determination of melting, determines any change that visually appears as a transition from a solid to a liquid state.

1.2.3 Due to the differences in what each test method measures, the results from Method 1 and Method 2 cannot be compared.