Glass transition is an inherent property of amorphous polymer materials (ie, amorphous polymers). It is a macroscopic manifestation of the transformation of polymer motion. It directly affects the performance and process properties of materials, so it has been high for a long time. The main content of molecular physics research.
Most polymer materials are usually in the following four physical states (or mechanical states): glassy state, viscoelastic state, high elastic state (rubbery state), and viscous flow state. The glass transition is a transition between the high elastic state and the glass state. From the molecular structure, the glass transition temperature is a relaxation phenomenon in which the amorphous portion of the polymer is frozen from the frozen state to the thawed state.
Taking DSC as an example, when the temperature is gradually increased and the glass transition temperature of the polymer is passed, the baseline on the DSC curve moves toward the endothermic direction (see figure). Point A in the figure is the point at which the deviation starts from the baseline. Extend the baseline before and after the transition. The vertical distance between the two lines is the step ΔJ. The point C can be found at ΔJ/2. The tangent from point C intersects the front baseline at point B. The temperature corresponding to point B is the temperature. It is the glass transition temperature Tg.
Common crystalline plastics are: polyethylene PE, polypropylene PP, polyoxymethylene POM, polyamide PA6, polyamide PA66, PET, PBT, etc.
Non-crystalline plastics are: polycarbon, ABS, benzene, vinyl chloride, etc. (such as plastic case, TV casing, etc.)
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