Heat of Fusion /
Crystallization / Melting
Point / Glass Transition by DSC (Differential
Scanning Calorimeter)
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ASTM D3418
/ E1356
ISO
11357
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Scope:
Using a DSC (differential scanning calorimeter) the following are commonly determined:
Tg = Glass Transition Temperature = Temperature (°C) at which an amorphous polymer or an amorphous part of a crystalline polymer goes from a hard brittle state to a soft rubbery state.
Tm = melting point = Temperature (°C) at which a crystalline polymer melts.
Δ Hm = the amount of energy (joules/gram) which a sample absorbs while melting.
Tc = crystallization point = Temperature at which a polymer crystallizes upon heating or cooling.
Δ Hc = the amount of energy (joules/gram) a sample releases while crystallizing.
Combined with an FTIR analysis, a DSC thermal scan can be used to help further identify certain types of materials by their melting points and is a useful tool for checking plastic parts or resins for contamination not seen by FTIR. It is also used to characterize materials for their thermal performance.
Test Procedure:
The DSC head area contains equivalent sample and reference compartments located adjacent to each other. The reference compartment contains an empty aluminum pan and cover equivalent to those used to encapsulate a test sample. The sample compartment is where an encapsulated sample of about 10 to 15 milligrams is placed for testing.
The sample is heated at a controlled rate and a plot of heat flow versus temperature is produced. The resulting thermal scan is then analyzed. The ASTM Heating Rate is 10°C/minute for melting point (Tm), 20°C for glass transition (Tg). The ISO Heating Rate is 20°C/minute.
Specimen size:
A sample weight of 10 to 15 mg is required.
Data:
A thermal scan, depending upon the material type, can provide a Tg, Tm, ΔHm and or ΔHc.
Typical DSC Thermal Scan of a PEEK Material
Showing a Tg a Tc and a Tm
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