Meaning
Thermal analysis parameters mark the onset temperature of glass transition during initial differential scanning calorimetry heating runs on polymer samples. In resin qualification and injection moulding quality control, TG1 identifies the point where an amorphous or semi-crystalline polymer shifts from a rigid glassy state into a flexible rubbery regime during first heating. This measured onset value captures the physical state of the as-moulded plastic part, reflecting residual stress and cooling history imparted during processing.
The parameter governs material thermal characterization, applying to solid polymers and stopping where thermal degradation or chemical cross-linking overwrites baseline glass transition behavior.
Thermal Characterization
Differential scanning calorimetry measures heat flow differences between a polymer sample and an inert reference as temperature increases at controlled rates. Evaluating the TG1 value on raw resin pellets provides a baseline transition threshold prior to thermal processing. Deviations between raw resin values and moulded part values indicate molecular weight degradation or physical aging during extrusion.
Processing History
First heating runs retain structural relaxation effects caused by rapid cavity cooling. Fast chilling rates in thin-wall injection moulds suppress crystallization and trap non-equilibrium chain conformations within the polymer matrix.
Relaxation Behavior
Reheating the sample past its onset transition releases trapped internal energy, causing an endothermic enthalpy relaxation peak near glass transition. Moulding facilities monitor this thermal signature to optimize mould surface temperature and cooling time settings. Maintaining consistent thermal history across moulding runs prevents dimensional warping and premature mechanical failure of molded components during elevated ambient exposure.
