Scope:

ASTM D3418 and ASTM D1356 tests thermal analysis by Differential Scanning Calorimetry (DSC) are required to ensure quality control during product/process development and other applications in polymer and plastic research and development establishments. DSC is an analytical method that gives characteristic thermal transitions of a material by measuring heat absorbed (endotherm) or evolved (exotherm) as a sample is heated. These endotherms and exotherms can provide information about the material, such as melting point (T_M), glass transition temperature (T_G), and heat of fusion (∆H_m). It helps to characterize the thermal behavior and transitions at the same time. DSC analysis is available for material development, quality control, failure analysis, and process development involving various materials, such as polymers, elastomers, and plastics.

Plastic parts and resins are checked for any contamination present in them by FTIR analysis. Sometimes FTIR alone is not sufficient for this purpose, and FTIR is combined with DSC thermal scan to check the contamination present and identify specific types of materials.

Test Procedure:

For ASTM D3418 and ASTM D1356 test methods, there are two adjacent compartments in the DSC head pan, one each for reference and sample. In the sample compartment, an encapsulated sample of about 10 to 15 mg is kept for testing. For testing polymers, no reference material is used, and the reference compartment contains only the empty aluminum pan and a similar encapsulating cover as used in the test sample. The polymer sample is then heated at a controlled rate of 10 °C or 20 °C per minute to a temperature beyond the transition in question. For melting point (T_M), the ASTM Heating Rate is 10 °C/minute, and for glass transition (Tg) it is 20 °C/minute. The ISO Heating Rate is fixed at 20 °C/minute.

A heat flow versus temperature graph is plotted, and the plot is then analyzed to get the melting point (T_M), glass transition temperature (T_G), and heat of fusion (∆H). Glass transition temperature (T_G) is typical to an amorphous material such as amorphous thermoplastic resin. Melting point is critical for a semi-crystalline material such as semi-crystalline thermoplastic resin.

Specimen size:

The test uses a sample weighing 10 to 15 mg.

Data:

The following data is obtained through a thermal scan using a Differential Scanning Calorimeter depending upon the material type and requirement.

T_g = Glass Transition Temperature [this is the temperature (°C) at which an amorphous polymer or an amorphous part of a crystalline polymer converts from a hard, brittle state to a soft rubbery state]

T_M = Melting point [this is the temperature (°C) at which a crystalline polymer melts]

ΔH_m = The amount of energy in joules/gram absorbed by a sample while melting.

T_c = Crystallization point [this is the temperature at which a polymer crystallizes upon heating or cooling]ΔH_c = The amount of energy in joules/gram released by a sample while crystallizing.

Conclusion:

ASTM D3418, ASTM E1356 is a standard test method for heat of fusion, crystallization, melting point and glass transition.