In this blog, we’ll go through the meaning of Glass Transition, the temperature needed for filaments to reach Glass transition state and melting point, how to increase the glass transition values of a 3D Printed model, which is printed with low glass transition temperature filament (PLA) and more.
What is the glass transition temperature?
Glass transition temperature (Tg), in chemistry, is defined as the temperature at which the material transitions from crystalline state(rigid) to amorphous glassy state. The glass transition temperature, also known as the “rubbery state”, is the temperature at which the physical properties of a solid changes fromhard, crystallized solid to amorphous, solid. (Rubber like state)
When glass transition temperature is achieved, the molecular motion gets frozen. It happens because of intermolecular attractive forces between molecules which are called Van der Waal’s forces.
Van der Waal’s forces can be attributed to the accumulation of electrons within molecules. Too much heat energy can destroy the attraction forces that exist between molecules, resulting in glass transition temperature.
If you don’t know “Chemistry”, the glass transition temperature is defined as the point at which the material changes from a hard or a brittle solid to a softer/rubbery/gooey material. I don’t refer to “gooey” in the sense that gum or syrup. It’s something that you could squeeze without any crack or break.
|Filament||Glass Transition Temp Tg (C)||Nozzle Temperature||Heated Bed Temp||Melting Temp Tm (C)||Warping Risk||Ease of Use||Cost|
|ABS||105°C||230°C – 250°C||Approx. 100°C||Amorphous||Moderate||Intermediate||$15 – $25|
|Polycarbonate||147°C||270°C – 310°C||90°C – 110°C||260°C||High||Difficult||$30 – $60|
|Nylon||70-80°C||230°C – 260°C||80°C – 100°C||217°C||Moderate||Intermediate||$50 – $65|
|PLA||60-65°C||180°C – 230°C||60°C but not required)||155°C||Low||Easy||$10 – $25|
|PETG||80-82°C||230°C – 250°C||Approx. 100°C||210°C||Low||Easy||$15 – $20|
|HIPS||88-92°C||230°C – 250°C||Approx. 100°C||180 – 270°C||Low||Intermediate||$20 – $60|
|TPE||60-130°C||210°C – 230°C||Not required||150–210°C||Low||Easy||$80 – $100|
|ASA||100°C||220°C – 250°C||Approx. 100°C||250-260°C||Low||Intermediate||$30 – $50|
What is the difference between Glass Transition-and Melting Temperature for a filament?
Surprisingly, Glass Transition Temperature, (Tg), and Melting Temperature, (Tm), may sound similar relative to their physical properties, they are not so. Although both terms refer to a change of state, the two terms are quite different.
The phenomenon of glass transition, which is related to viscosity, is not necessarily the crossing point between solids and liquids. It is instead the crossing point between a rigid solid and rubbery solid. Explicitly speaking, the difference is that the melting temperature is the point at which the solid starts melting into liquid; the Glass Transition temperature is the point at which the solid turns to rubbery but is totally liquid.
Let’s consider an example of pizza cheese. The cheese slices are hard when they come out of the freezer. However, after being at room temperature for a while, they soften and become rubbery. This is the Glass Transition Temperature (Tg).
You can spread the cheese on the pizza, bake it in the oven and it will melt. This is the Melting Temperature (Tm), the temperature at which the cheese melts from a rubbery like solid to a viscous liquid.back to menu ↑
What is the meaning of higher temperature glass transition temperature?
A material with a higher glass transition temperature (Tg), means it takes longer for it to change from a solid to a rubbery like soft material after being heated up. If you heat something that has a Tg of 200 C it will soften at 200 C.
Let’s say a material with a Tg of 390 C is heated up, it is subjected to become soft at 390 C heat. This is because it loses its rigidity, stiffness and tensile strength. If the object is heated to temperatures higher than its Tg (glass transition temperature), it may deform too.back to menu ↑
What happens to filament if it is higher than its glass transition temperature
If a filament is at or above its glass transition temperature(Tg) it is thermodynamically unstable and will start showing all the properties of liquid.
Refer to the earlier table about the Glass Transition temperature for your particular filament type. However, I would always recommend that you check the specifications of any filament you purchased as the manufacturer will provide more detailed instructions on how to use it.back to menu ↑
What is the significance of this when setting the temperature for the heated bed?
Two main problems that could arise are related to the bed temperature (rate at which plastic is allowed to cool) and the temperature of extruded filament. These problems are Elephant’s foot and Warping.
Warping occurs when the bottom layers of a printed part are printed onto a cold print bed because of which they contract when they solidify than the top layers.
As a result, the top layers of the part will begin to bend outwards as they cool.
Manufacturers have introduced heated beds to reduce warping of the part being 3D printed. This heated bed prevents the fast cooling of the bottom layers.
Now, the bottom layers are extruded on the heated bed. This heated bed is heated to a temperature that corresponds to the filament used. This limits the Warping of the bottom layers as compared to the top layers. Thus warping can be reduced, if not eliminated entirely.
This is why knowing the glass temperature of the filament is so important. Instead of heating the bed to a random temperature to create warping, heat the bed until it reaches the glass temperature of filament. The printed part will stick better to the bed and eliminated Warping.
Elephant’s foot is caused when the initial extruded layers(usually first layers) are not cooled because of bed temperature being too high or insufficient cooling leading to Elephant’s foot.
This problem is more common in larger prints. It is due to the object’s weight pushing down on the first layers. This weight can cause the first layer to bulge if it isn’t properly cooled.
Because the bed temperature exceeds the filament’s glass transition temperature, the bottom layer does not cool down properly and will start bulging outwards.
Hence, it is important to set the bed temperature after knowing the glass transition temperature of the filament. The bed temperature should always be slightly lesser than glass transition temperature.back to menu ↑
When is it important to have a higher glass transition temperature?
The glass transition temperature is a useful indicator of the temperature at which 3D-printed parts will change from being solid, useful objects to being soft, useless rubber objects. It can even be used to calculate how heavy an object may deform under its own weight.
That’s why it is vital to know the glass transition temperature of the filament used to 3D print the part. This makes us be mindful while using the printed part and about its glass transition temperature. Some plastics such as PLA will deform very quickly even if they are subjected to sun or in a car.back to menu ↑
Filaments for outdoor Applications
While 3D Printing an object intended for outdoor use, it might be better to use ABS like filament. This is because the glass transition temperature of ABS is 105C, which is higher than outdoor hot summer temperatures. PLA can easily deform if exposed to sunlight. .
There are many other filaments that can withstand outside temperatures. These include PETG, ASA and many others.back to menu ↑
Uses that demand Higher Material Withstanding Temperatures
You should use the filament with higher glass transition temperatures while printing the objects that are exposed to higher temperatures. Otherwise, it may deform.
Let’s suppose that you use PETG T (82C), to 3D-print a part that will be exposed to high temperatures of 85C-95C. It will fail and waste your time.
PLA has a low Glass Transition temperature. This is why PLA should not be used for any application where temperature goes beyond that plastic can withstand.
There are many filaments that can be used at high temperatures such as ABS, Polycarbonate and ASA. Refer to the table at end of post for more information.back to menu ↑
Does PLA melt in car?
PLA is a type of thermoplastic that is made out of biodegradable products such as sugarcane and corn. PLA is a 3D printing material that exhibits excellent print quality, good layer adhesion, and moderate strength. My favorite filament is PLA for gears rather than Nylon.
Even soy and corn based PLA filaments are available that are biodegradable
PLA is not suitable for 3D printing car parts. Its Tg is (60-60C) and car parts printed from PLA can deform on hot sunny days.
If you are looking to print some engine replacement parts using PLA, then forget it!
Instead, ABS is used to make car parts. It’s a stronger plastic with a significantly higher Tg of 105C.back to menu ↑
Is it possible to increase the glass transition temperature of PLA part?
The glass transition temperature of PLA prints can be increased by adding additives. However, it may bring down strength or infusibility. So be aware of it.
PLA derivatives such as TPLA and HTPLA have the same advantages as standard PLA, they can withstand higher temperatures than the standard PLA.
An increase in the glass transition temperature will make the part harder and more rigid. The best way to increase the glass temperature of 3D parts printed using standard PLA is to anneal them (heating them upto their glass transition temperature and below their melting point).back to menu ↑
What are some of the benefits of annealing?
Thermal treatment is what’s called “annealing” for 3D prints.
An atmosphere furnace, an oven or indirect heating sources are the most common methods for annealing 3D-printed objects.
This will help to reorganize the internal crystal structure and create larger grains. It will also make objects stronger and less susceptible to layer separation. Tests have shown that 3D printing parts can be annealed to increase strength and overall resistance by up to 40%.
This has the downside that the model can become warped and shrink in XY direction when expanding in Z direction if it is not done correctly.
It is important to remember that annealing objects should be printed with 100% infill. A 20% or 30% infill part when annealed, will cause it to shrink in unpredicted ways, which almost always leads to poor results.
Infill is mandatory for the parts that undergo annealing. Otherwise, a part with 20% or 30% infill may contract unevenly and deform yielding bad results.
Infill support is needed during this process, in order to prevent irrgular or random empty spaces inside the object.
Line infill is the most appropriate, cheapest, and fastest infill type for the annealing process.back to menu ↑
3D printing is a cost-efficient method used to create complex structures and parts with intricate details. Some 3D-printed objects, however, may not have the same structural integrity as objects made from injection molding, especially when they are subject to high stress conditions.
An annealing process is another way to boost up the physical properties of 3D-printed parts. It makes them stronger because the layers fuse more strongly together.back to menu ↑
It increases the glass transition temperature
The process of annealing increases the temperature resistance of 3D-printed objects. This is because 3D-printed objects are random in their molecular structure. They don’t have any melting points. Instead, they gradually soften as they heat up before they melt completely. When the 3D objects are heated, they undergo an annealing process where their molecules reorganize themselves into a semi-crystalline structure.
This leads to stronger intermolecular links and boosts up the glass transition temperatures.
I conducted an experiment to determine what happens to the glass temperature of an object printed using a PLA filament (Tg60C), after it has been annealed to 90C. I found that the glass transition temperature of the object printed from PLA filament (Tg 60C) had reached 110C.
This represents a nearly 100% increase, and it eliminates the greatest challenge of 3D printing objects printed using standard PLA.back to menu ↑
Easier post processing
FDM 3D printing creates a rough outer surface for the printed object. The model will not be smooth and will make it more difficult for later works such as painting and lacquering.
An annealing process is used to smoothen the print surfaces and fill in any missing holes. It also gives models a professional look.
Annealing reduces the time required to finish your print, and also makes it stronger.