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#106 Glass Transition Temperature Tg of Plastics

Category : Mold Materials
December16, 2011

Thermoplastic resins melt when its temperature becomes higher than its melting point and becomes liquid, but as it is gradually cooled from the liquid state its viscosity gradually increases, and it goes into a rubbery state and it finally solidifies. The temperature at the border from the rubbery state to the solid state (called the glass state) is called its "glass transition temperature". The glass transition temperature is generally indicated as Tg.

Tg is a physical quantity that is determined by the type of plastic. By knowing the value of Tg, it is possible to estimate the time required for the molded item to cool inside the cavity and the molded item temperature at which it can be ejected from the mold.

The values of Tg are given below for the major plastics.

Name of plastic Tg
Polyethylene -125°C
Polypropylene 0°C
Polyvinyl chloride 87°C
Polystyrene 100°C
ABS 80 to 125°C
Polymethyl methacrylate 90°C
Polyamide 6 50°C
Polyamide 66 50°C
Polyacetal -50°C
Polycarbonate 150°C
Polyphenylene sulfide 126°C
Polyurethane -20°C
Polyether sulfone 230°C
Polyphenylene oxide 104 to 120°C
Polyamide imide 275°C
Polylactic acid 57°C
Polytetrafluoroethylene 126°C
EVA -42°C
Polyacrylonitrile 104°C
Polyfluoro vinylidene 35°C
Polypropylene terephthalate 50°C
Polyethylene terephthalate 69°C

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