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Glass Transition Temperature
The following is a summary table of the glass transition temperature (Tg), covering key parameters, material comparisons, processing influences, and solutions for your reference
Glass Transition Temperature (Tg) Summary Table
| Category | Content | Examples/Notes |
|---|---|---|
| Definition | Critical temperature where amorphous polymers transition from glassy to rubbery state | No phase change, only segmental mobility change |
| Difference from Tm | Tg: Amorphous materials; Tm: Crystalline materials | PC (Tg≈147°C, no clear Tm); PP (Tm≈160°C, Tg≈-10°C) |
| Testing Methods | – DSC (Differential Scanning Calorimetry) – DMA (Dynamic Mechanical Analysis) – TMA (Thermomechanical Analysis) |
DMA detects storage modulus (E’) and tanδ peaks |
| Influencing Factors | – Chain rigidity↑→Tg↑ – Plasticizers↑→Tg↓ – Crosslinking↑→Tg↑ – Molecular weight↑→Tg slightly increases |
PVC (Tg≈80°C) with DOP drops below room temp |
| Typical Material Tg | – ABS: 105°C – PC: 147°C – PMMA: 105°C – Natural rubber: -70°C |
High-Tg materials (e.g. PEEK, Tg=143°C) for high-temp applications |
| Injection Molding | – Barrel temp > Tg (amorphous) or > Tm (crystalline) – Mold temp < Tg-20°C for fast solidification |
PC molding: Barrel 280-320°C, Mold 80-120°C |
| Defect Correlation | – Stress cracking (demolding near Tg) – Dimensional instability (storage near Tg) |
ABS part warping in summer (Tg=105°C but stress relaxation occurs) |
| Mold Design | – High-Tg: Enhanced cooling (beryllium copper/contour channels) – Low-Tg: Moderate mold heating |
POM (Tg≈-85°C) requires prevention of premature freezing |
| CNC Machining | – Cutting temp < Tg (prevent sticking) – Fiber-reinforced: Carbide tools + cooling |
Carbon PA6 (Tg=50°C): Diamond drills + air cooling |
| Industry Cases | – Medical PMMA covers: Annealing at 80°C (Tg-25°C) – Drone frames: Low-temp machining prevents delamination |
Annealing time: 2hrs (thickness-dependent) |
Quick Reference Guide
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High-Tg Materials: PC, PEEK, PSU (high-temp components)
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Low-Tg Materials: TPE, rubber (flexible seals)
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Critical Controls: Injection cooling rate, CNC heat management
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