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, 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 or is only exhibited by an amorphous polymer. On the other hand, crystalline polymer shows both Tm (melt temperature) 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.
Talking about Tg, the most notable changes 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, when they are in their glassy state, their Tg values are both at 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 free for their molecules, thus providing rubber with a fixed shape at room temperature.
The prime application of determining a polymer’s Tg is quality control and research and development. Apart from that, it is also used as an integral tool for modifying plastic materials’ physical properties.
Interesting Read – What is Hardness in Plastics? An In-Depth 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 Tg of materials using differential thermal analysis or differential scanning calorimetry.
The test methods are only applicable for amorphous material and crystalline materials that have partial amorphous regions that are stable and do through decomposition in the glass transition region. For both methods, DTA and DSC, their peaks are related to endothermic and exothermic transitions with thermal input and show phase changes.
- Talking about DTA, the difference between the sample and referenced material is observed against temperature or time. While the rise or fall in temprature 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 the amorphous regions where molecules are randomly arranged.||
Crystalline or semi-crystalline have a highly ordered or sequenced structure. They are called semi-crystalline as ll crystalline plastics have some amount of amorphous material.
|Do not have a sharo melkting||
Do 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 a temperature when a hard state of plastic is converted into a sticky or rubbery state||
Melting temperature is a temprature where 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
|Can be observed in amorphous and semi-crystalline compounds||
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 –
Molecular Weight – In straight chains 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 increasing Tg.
Molecular Structure – Placing a large, inflexible side group increases Tg of the material due to increased mobility.
Chemical cross-linking – increase in the cross-linking decreases the mobility leading to a decrease in free volume and an increase in Tg.
Water and Moisture Content:
An increase in moisture content leads to the creation of hydrogen bonds with polymeric chains increasing the distance between them. And thus, increase the free volume and decreases Tg.
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 resulting in a decrease in the Tg of a polymer.
Entropy and Enthalpy Effects:
Usually, the value of entropy is higher in amorphous material compared to crystalline material. Therefore, if the value of entropy is high, then the value of Tg is also high.
Pressure and Free Volume:
As the pressure increase in the surroundings, it will lead to a decrease in free volume and ultimately high Tg.
Engaging Read – What is Shore Hardness Scale? | The Complete Guide
Glass Transition Temperature of Mainstream Plastics –
|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|
|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|
|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, 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, 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 Filled||-50||-5|
|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.
1. How does cooling affect glass transition temperature?
Ans. The glass transition temperature will increase or lower viscosities as the cooling rate increases.
2. What is the meaning of transition temperature?
Ans. The temperature at which there is 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.
3. Do metals have glass transition temperatures?
Ans. Like plastics and glasses, metals also have glass transition temperatures, but unlike glasses and plastics, may metal crystallize almost immediately after the glass transition temperature is passed.
4. What is a rule of thumb relating Tg to TM?
Ans. The connection between melting and glass transition is already implied by the well-established rule of thumb that Tg ≈ (2/3)Tm.
5. Why does polyethylene has a lower Tg than polystyrene?
Ans. 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 –
That was all I had to say about the glass transition temperature of polymers. Always have a keen eye on the difference between Tg and Tm because it’s crucial. Talking about the testing methods, whether it’s DTA or DSC choose wisely to have the best results in the quality control department.
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