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 you heat up a specific type of plastic that doesn’t have a clear shape, it turns into a sticky liquid or feels like rubber at a certain temperature. This specific temperature is called the Glass Transition Temperature, or Tg for short. If you cool it back down, that’s the temperature where the plastic starts to get hard, stiff, and more likely to break.

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 a 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.

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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 only apply 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 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 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 

The glass transition temperature is the temperature when a hard state of plastic is converted into a sticky or rubbery state
Melting temperature is the 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 polymers with a straight-chain structure, an augmentation in molecular weight causes a proportional reduction in chain end concentration. This reduction subsequently decreases the free volume at the end group regions, elevating the material’s glass transition temperature (Tg).

Polar Groups – The presence of polar groups within the polymer increases the intermolecular forces as well as the interaction between different polymer chains. This heightened cohesion level reduces the material’s free volume, which in turn results in an increase in its Tg.

Molecular Structure – Introducing a large, rigid side group into the polymer’s structure increases the Tg. This is mainly because the cumbersome, inflexible side group curtails the overall mobility of the polymer molecules.

Chemical cross-linking – An increment in the level of chemical cross-linking within the polymer hampers molecular movement. This restricted mobility leads to a corresponding decrease in free volume, culminating in a higher Tg for the material.

Water and Moisture Content

When there’s more water or moisture in the material, it forms hydrogen bonds with the long molecules in the polymer. These bonds push the molecules further apart, creating more open space or “free volume” in the material.

Because of this, the temperature at which the material becomes glass-like, called the glass transition temperature (Tg), goes down. For example, HDPE (High-Density Polyethylene) has a Tg of -110 degrees, while for PVC (Polyvinyl Chloride), the Tg is 60 degrees in a hard form.

Addition of Plasticizers

When you add substances called plasticizers to the material, it creates more free volume between the polymer chains. This makes it easier for these long molecules to move around and slide past each other. Because they can move more easily, the Tg of the material becomes lower, meaning it turns glass-like at a lower temperature.

Entropy and Enthalpy Effects

In materials that have a more random, or “amorphous,” structure, the level of disorder—known as entropy—is usually higher than in materials with a neat, “crystalline” structure. If there’s a high level of entropy, the glass transition temperature (Tg) of the material will also be higher.

Pressure and Free Volume

If there’s more pressure around the material, the free volume within it decreases. Less free volume means that the polymer molecules have less room to move. Because they’re more tightly packed, the Tg, or the temperature at which the material becomes glass-like, will go down.

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Glass Transition Temperature of Mainstream Polymers

Polymer NameMinimum Value (°C)Maximum Value (°C)
ABS – Acrylonitrile Butadiene Styrene90102
ABS Flame Retardant105115
ABS High Heat105115
ABS High Impact95110
Amorphous TPI, Moderate Heat, Transparent247247
Amorphous TPI, Moderate Heat, Transparent (Food Contact Approved)247247
Amorphous TPI, Moderate Heat, Transparent (Mold Release grade)247247
Amorphous TPI, Moderate Heat, Transparent (Powder form)247247
CA – Cellulose Acetate100130
CAB – Cellulose Acetate Butyrate80120
Cellulose Diacetate-Pearlescent Films120120
Cellulose Diacetate-Gloss Film120120
Cellulose Diacetate-Integuard Films113113
Cellulose Diacetate-Matt Film120120
Cellulose Diacetate-Window Patch Film (Food Grade)120120
Cellulose Diacetate-Clareflect metalized film120120
Cellulose Diacetate-Colored Films120120
Cellulose Diacetate-Flame retardant Film162162
Cellulose Diacetate-High Slip Film120120
Cellulose Diacetate-Semitone Films120120
CP – Cellulose Proprionate80120
COC – Cyclic Olefin Copolymer136180
CPVC – Chlorinated Polyvinyl Chloride100110
EVOH – Ethylene Vinyl Alcohol1570
HDPE – High-Density Polyethylene-110-110
HIPS – High Impact Polystyrene8892
HIPS Flame Retardant V09090
LCP Glass Fiber-reinforced120120
LCP Mineral-filled120120
LDPE – Low-Density Polyethylene-110-110
LLDPE – Linear Low-Density Polyethylene-110-110
PA 11 – (Polyamide 11) 30% Glass fiber reinforced3545
PA 11, Conductive3545
PA 11, Flexible3545
PA 11, Rigid3545
PA 12 (Polyamide 12), Conductive3545
PA 12, Fiber-reinforced3545
PA 12, Flexible3545
PA 12, Glass Filled3545
PA 12, Rigid3545
PA 46, 30% Glass Fiber7577
PA 6 – Polyamide 66060
PA 66 – Polyamide 6-65558
PA 66, 30% Glass Fiber5060
PA 66, 30% Mineral filled5060
PA 66, Impact Modified, 15-30% Glass Fiber5060
Polyamide semi-aromatic115170
PAI – Polyamide-Imide275275
PAI, 30% Glass Fiber275275
PAI, Low Friction275275
PAR – Polyarylate190190
PBT – Polybutylene Terephthalate5565
PC (Polycarbonate) 20-40% Glass Fiber150150
PC (Polycarbonate) 20-40% Glass Fiber Flame Retardant150150
PC – Polycarbonate, high heat160200
PCL – Polycaprolactone-60-60
PE – Polyethylene 30% Glass Fiber-110-110
PEEK – Polyetheretherketone140145
PEEK 30% Carbon Fiber-reinforced140143
PEEK 30% Glass Fiber-reinforced143143
PEI, Mineral Filled215215
PEI, 30% Glass Fiber-reinforced215215
PEI, Mineral Filled215215
PESU – Polyethersulfone210230
PESU 10-30% glass fiber210230
PET – Polyethylene Terephthalate7378
PET, 30% Glass Fiber-reinforced5656
PETG – Polyethylene Terephthalate Glycol7980
PFA – Perfluoroalkoxy9090
PGA – Polyglycolides3540
PHB-V (5% valerate) – Poly(hydroxybutyrate – co-valerate)35
PI – Polyimide250340
PLA, Fiber Melt Spinning5565
PLA, Heat Seal Layer5258
PLA, Injection molding5560
PLA, Spunbond5560
PLA, Stretch blow-molded bottles5060
PMMA – Polymethylmethacrylate/Acrylic90110
PMMA (Acrylic) High Heat100168
PMMA (Acrylic) Impact Modified90110
PMP – Polymethylpentene2030
PMP 30% Glass Fiber-reinforced2030
PMP Mineral Filled2030
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 Ether100210
PPE, 30% Glass Fiber-reinforced100150
PPE, Impact Modified128150
PPE, Mineral Filled100150
PPS – Polyphenylene Sulfide8893
PPS, 20-30% Glass Fiber-reinforced8893
PPS, 40% Glass Fiber-reinforced8893
PPS, Conductive8893
PPS, Glass fiber & Mineral-filled8893
PPSU – Polyphenylene Sulfone220220
PS (Polystyrene) 30% glass fiber90120
PS (Polystyrene) Crystal9090
PS, High Heat9090
PSU – Polysulfone187190
PSU, 30% Glass fiber-reinforced187190
PSU Mineral Filled187190
PVC (Polyvinyl Chloride), 20% Glass Fiber-reinforced60100
PVC, Plasticized-50-5
PVC, Plasticized Filled-50-5
PVC Rigid60100
PVDC – Polyvinylidene Chloride-15-15
PVDF – Polyvinylidene Fluoride-42-25
SAN – Styrene Acrylonitrile100115
SAN, 20% Glass Fiber-reinforced100115
SMA – Styrene Maleic Anhydride110115
SMA, 20% Glass Fiber-reinforced110115
SMA, Flame Retardant V0110115
SRP – Self-reinforced Polyphenylene150168

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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