What is the Glass Transition Temperature of Plastics?

Hello people; the physical properties of any polymer have a direct impact on its applicability. Let’s take a look at the Tg of plastic materials.

What is the Glass Transition Temperature of Plastics

When an amorphous polymer is heated, the temperature at which the polymer structure turns “Sticky liquid or rubbery” is known as Glass Transition Temperature or Tg. It is also stated as a temperature at which amorphous polymer starts showing glassy-state properties such as stiffness, rigidness, and brittleness after cooling.

The temperature at which the polymers are heated depends on their chemical structure and thus can be used to identify polymers. For example, a Tg is only exhibited by an amorphous polymer. On the other hand, crystalline polymer shows both Tm and Tg since they contain an amorphous fragment.

The value of glass transition temperature depends on the mobility of the polymer chain, and most synthetic polymer ranges between 170,000 to 500,000.

The transition from glass to the rubber-like state is an integral feature of the polymer attribute, signifying a region of drastic changes in the physical properties such as elasticity and hardness.

The most notable changes in Tg are volume, hardness, elongation to break, and Young Modulus of solids.

Hard and rigid plastics like polystyrene and poly(methyl methacrylate) are used below their glass transition temperatures, meaning that when they are in their glassy state, their Tg values are around 100 °C (212 °F).

On the contrary, Rubber elastomers like polyisobutylene and polyisoprene are used above their Tg when they are in their rubbery state. This is because they’re soft and flexible in that state, and crosslinking intercepts are accessible for their molecules, thus providing rubber with a fixed shape at room temperature.

Quality control, research, and development are The prime applications of determining a polymer’s Tg. Apart from that, it is also used as an integral tool for modifying plastic materials’ physical properties.

The glass transition temp. For the most mainstream thermoplastics is as follows:

The Tg of polypropylene is -20 and -10.

The Tg of polyethylene is -110 as both minimum and maximum values.

Interesting Read – What is the Density of Plastics? | The Complete Guide 

How to Measure Glass Transition Temperature?

The most common test method to determine the glass transition temperature of plastics is ASTM E1356. The test method assesses the Tg of materials using differential thermal analysis or scanning calorimetry.

The test methods are only applicable for amorphous and crystalline materials with stable partial amorphous regions that are stable and do through decomposition in the glass transition region. For both ways, DTA and DSC, their peaks are related to endothermic and exothermic transitions with thermal input and show phase changes.

  • Regarding DTA, the difference between the sample and referenced material is observed against temperature or time. While the rise or fall in temperature of the sample in the particular atmosphere is programmed.
  • In DSC, the difference in heat flow to a sample and reference material is observed against time or temperature. Thus, the rise or fall in temperature is programmed in a specific atmosphere.

Apart from DTA and DSC, there are several other methods to determine the glass transition temperature of plastic material, such as:

  • Thermomechanical analysis 
  • Thermal expansion measurement 
  • Micro-heat transfer measurement 
  • Heat capacity 
  • Isothermal compressibility 
  • Specific heat measurements

The Difference Between Amorphous and Crystalline Polymers 

Polymers (plastics, elastomers, and rubber) are large macromolecules formed by combining many smaller units called monomers. The molecules can be both amorphous and crystalline.

Amorphous Crystalline
Amorphous polymers are polymers that are comprised of amorphous regions where molecules are randomly arranged.
Crystalline or semi-crystalline have a highly ordered or sequenced structure. They are called semi-crystalline as all crystalline plastics have some amount of amorphous material.
Do not have a sharo melkting
Do you have a sharp melting point
Amorphous polymers are transparent
Crystalline polymers are opaque/Translucent
Have low shrinkage
Have high shrinkage
Poor chemcial reisatcne
Good chemical resistance
High gas permeability
Low gas permeability

Glass Transition Temperature Vs. Melting Temperature 

Tg Tm
The glass transition temperature is the temperature when a hard state of plastic is converted into a sticky or rubbery state
Melting temperature is a temperature at which solid material is converted into its liquid form
Marks out the transition of glass state into rubber state
marks out the transition of a solid phase into a liquid phase
It can be observed in amorphous and semi-crystalline compounds
It can be observed in crystalline compounds
Depends on the chemical structure of the substance
It depends on the chemical bonding of molecules in the substance and the external pressure

The Factors Affecting Tg 

Chemical Structure

Molecular Weight – In straight-chain polymers, if there is an increase in molecule weight, it leads to a decrease in chain-end concentration, thereby decreasing free volume at the end group region and increase in Tg.

Polar Groups – Attendance of polar groups increases intermolecular forces, interchain interaction, and cohesion, decreasing the free volume and increasing Tg.

Molecular Structure – Placing a large, inflexible side group increases the Tg of the material due to increased mobility.

Chemical cross-linking – an increase in the cross-linking decreases mobility leading to a decrease in free volume and an increase in Tg.

Water and Moisture Content

Increasing moisture content leads to hydrogen bonds with polymeric chains increasing their distance. And thus, increasing the free volume and decreasing Tg. Therefore HDPE glass transition temperature is -110, whereas PVC glass transition temperature is 60 in its rigid form.

Addition of Plasticizers

Adding plasticizers will increase the free volume in the polymer structure. That makes it easier for the polymer chains to slide past each other, resulting in polymer chains moving around at lower temperatures, decreasing the Tg of a polymer.

Entropy and Enthalpy Effects

Usually, the entropy value is higher in amorphous material than in crystalline material. Therefore, if the entropy value is high, then the value of Tg is also high.

Pressure and Free Volume

As the pressure increases in the surroundings, it will decrease free volume and, ultimately, high Tg.

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Glass Transition Temperature of Mainstream Polymers

Polymer Name Minimum Value (°C) Maximum Value (°C)
ABS – Acrylonitrile Butadiene Styrene 90 102
ABS Flame Retardant 105 115
ABS High Heat 105 115
ABS High Impact 95 110
Amorphous TPI, Moderate Heat, Transparent 247 247
Amorphous TPI, Moderate Heat, Transparent (Food Contact Approved) 247 247
Amorphous TPI, Moderate Heat, Transparent (Mold Release grade) 247 247
Amorphous TPI, Moderate Heat, Transparent (Powder form) 247 247
CA – Cellulose Acetate 100 130
CAB – Cellulose Acetate Butyrate 80 120
Cellulose Diacetate-Pearlescent Films 120 120
Cellulose Diacetate-Gloss Film 120 120
Cellulose Diacetate-Integuard Films 113 113
Cellulose Diacetate-Matt Film 120 120
Cellulose Diacetate-Window Patch Film (Food Grade) 120 120
Cellulose Diacetate-Clareflect metalized film 120 120
Cellulose Diacetate-Colored Films 120 120
Cellulose Diacetate-Flame retardant Film 162 162
Cellulose Diacetate-High Slip Film 120 120
Cellulose Diacetate-Semitone Films 120 120
CP – Cellulose Proprionate 80 120
COC – Cyclic Olefin Copolymer 136 180
CPVC – Chlorinated Polyvinyl Chloride 100 110
EVOH – Ethylene Vinyl Alcohol 15 70
HDPE – High-Density Polyethylene -110 -110
HIPS – High Impact Polystyrene 88 92
HIPS Flame Retardant V0 90 90
LCP Glass Fiber-reinforced 120 120
LCP Mineral-filled 120 120
LDPE – Low-Density Polyethylene -110 -110
LLDPE – Linear Low-Density Polyethylene -110 -110
PA 11 – (Polyamide 11) 30% Glass fiber reinforced 35 45
PA 11, Conductive 35 45
PA 11, Flexible 35 45
PA 11, Rigid 35 45
PA 12 (Polyamide 12), Conductive 35 45
PA 12, Fiber-reinforced 35 45
PA 12, Flexible 35 45
PA 12, Glass Filled 35 45
PA 12, Rigid 35 45
PA 46, 30% Glass Fiber 75 77
PA 6 – Polyamide 6 60 60
PA 66 – Polyamide 6-6 55 58
PA 66, 30% Glass Fiber 50 60
PA 66, 30% Mineral filled 50 60
PA 66, Impact Modified, 15-30% Glass Fiber 50 60
Polyamide semi-aromatic 115 170
PAI – Polyamide-Imide 275 275
PAI, 30% Glass Fiber 275 275
PAI, Low Friction 275 275
PAR – Polyarylate 190 190
PBT – Polybutylene Terephthalate 55 65
PC (Polycarbonate) 20-40% Glass Fiber 150 150
PC (Polycarbonate) 20-40% Glass Fiber Flame Retardant 150 150
PC – Polycarbonate, high heat 160 200
PCL – Polycaprolactone -60 -60
PE – Polyethylene 30% Glass Fiber -110 -110
PEEK – Polyetheretherketone 140 145
PEEK 30% Carbon Fiber-reinforced 140 143
PEEK 30% Glass Fiber-reinforced 143 143
PEI, Mineral Filled 215 215
PEI, 30% Glass Fiber-reinforced 215 215
PEI, Mineral Filled 215 215
PESU – Polyethersulfone 210 230
PESU 10-30% glass fiber 210 230
PET – Polyethylene Terephthalate 73 78
PET, 30% Glass Fiber-reinforced 56 56
PETG – Polyethylene Terephthalate Glycol 79 80
PFA – Perfluoroalkoxy 90 90
PGA – Polyglycolides 35 40
PHB-V (5% valerate) – Poly(hydroxybutyrate – co-valerate) 3 5
PI – Polyimide 250 340
PLA, Fiber Melt Spinning 55 65
PLA, Heat Seal Layer 52 58
PLA, Injection molding 55 60
PLA, Spunbond 55 60
PLA, Stretch blow-molded bottles 50 60
PMMA – Polymethylmethacrylate/Acrylic 90 110
PMMA (Acrylic) High Heat 100 168
PMMA (Acrylic) Impact Modified 90 110
PMP – Polymethylpentene 20 30
PMP 30% Glass Fiber-reinforced 20 30
PMP Mineral Filled 20 30
POM – Polyoxymethylene (Acetal) -60 -50
PP – Polypropylene 10-20% Glass Fiber -20 -10
PP, 10-40% Mineral Filled -20 -10
PP, 10-40% Talc Filled -20 -10
PP, 30-40% Glass Fiber-reinforced -20 -10
PP (Polypropylene) Copolymer -20 -20
PP (Polypropylene) Homopolymer -10 -10
PP, Impact Modified -20 -20
PPE – Polyphenylene Ether 100 210
PPE, 30% Glass Fiber-reinforced 100 150
PPE, Impact Modified 128 150
PPE, Mineral Filled 100 150
PPS – Polyphenylene Sulfide 88 93
PPS, 20-30% Glass Fiber-reinforced 88 93
PPS, 40% Glass Fiber-reinforced 88 93
PPS, Conductive 88 93
PPS, Glass fiber & Mineral-filled 88 93
PPSU – Polyphenylene Sulfone 220 220
PS (Polystyrene) 30% glass fiber 90 120
PS (Polystyrene) Crystal 90 90
PS, High Heat 90 90
PSU – Polysulfone 187 190
PSU, 30% Glass fiber-reinforced 187 190
PSU Mineral Filled 187 190
PVC (Polyvinyl Chloride), 20% Glass Fiber-reinforced 60 100
PVC, Plasticized -50 -5
PVC, Plasticized Filled -50 -5
PVC Rigid 60 100
PVDC – Polyvinylidene Chloride -15 -15
PVDF – Polyvinylidene Fluoride -42 -25
SAN – Styrene Acrylonitrile 100 115
SAN, 20% Glass Fiber-reinforced 100 115
SMA – Styrene Maleic Anhydride 110 115
SMA, 20% Glass Fiber-reinforced 110 115
SMA, Flame Retardant V0 110 115
SRP – Self-reinforced Polyphenylene 150 168

Note – All the data mentioned above in the table is well researched by our team and comes from reliable sources. However, the information is shared strictly for knowledge purposes. Before working with any material, manufacturers should contact their material suppliers for detailed and accurate information about ht material they’re going to work with.



Below are the frequently asked questions on polypropylene glass transition temperature, PVC glass transition temperature, and HDPE glass transition temperature.

How does cooling affect glass transition temperature?

The glass transition temperature will increase or lower viscosities as the cooling rate increases.

What is the meaning of transition temperature?

The temperature at which a sudden change of physical properties, such as a change of phase or crystalline structure, or at which a substance becomes superconducting, is called transition temperature.

Do metals have glass transition temperatures?

Like plastics and glasses, metals also have glass transition temperatures, but unlike glasses and plastics, many metals crystallize almost immediately after the glass transition temperature is passed.

What is a rule of thumb relating Tg to TM?

The well-established rule of thumb that Tg ≈ (2/3)Tm already implies the connection between melting and glass transition.

Why does polyethylene have a lower Tg than polystyrene?

Polyethylene has TG because of its high flexibility and absence of side groups. In addition, PE is semi-crystalline due to its relatively simple and consistent structure.

The Conclusion 

In conclusion, plastics’ glass transition temperature (Tg) is a vital characteristic that significantly impacts the material’s performance and durability. It influences how the plastic responds to temperature changes, affecting its mechanical properties, such as hardness, strength, and flexibility.

Understanding Tg allows for an informed selection of plastics, tailoring their use to various applications, from everyday products to advanced technologies, ensuring safety, efficiency, and longevity. Mastery of this thermal property is fundamental to advancements in the plastic industry.

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