Meaning
Standard test methods established by international standardization bodies define the protocols for determining transition temperatures and enthalpies of polymers by differential scanning calorimetry. Within the plastics compounding and molding sectors, astm d3418 is the primary reference used to measure the melting temperature and crystallization temperature of thermoplastic resins. The procedure determines these critical thermal benchmarks by monitoring heat flow changes while heating and cooling a specimen under a controlled atmosphere.
The standard does not apply to materials that decompose within the transition temperature range.
Test Procedure
Specimen preparation requires cutting a small sample of five to ten milligrams from the polymer. This sample sits in an aluminum pan while an empty pan serves as the reference. The heating cycle runs at a constant rate of ten or twenty degrees Celsius per minute.
Nitrogen gas flows through the cell to prevent oxidation during the run.
Thermal Transition
Different polymer grades display distinct heat flow curves that reveal their baseline properties. Thermal history is removed during a first heating run before the cooling cycle records the crystallization peak. A second heating run yields the true melting profile of the resin.
Process Utilization
Molding parameters are adjusted based on the reported transition points. Processors use these temperatures to set safe extrusion barrel profiles. Parts printed or molded from regrind can be compared against virgin baseline curves to detect degradation.
