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	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 

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 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 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.

FAQs 

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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