PLA Glass Transition Temperature
Glass transition temperature, also known as Tg, is a critical temperature in the behavior of amorphous polymers. It is the temperature at which the polymer transitions from a hard and brittle state to a more rubbery and flexible form, much like the behavior of glass as it is heated.
PLA glass transition temp is 60-65 °C.
What is Glass Transition Temperature?
The glass transition temperature (Tg) is the point at which a substance transitions from a rigid and solid state to a more flexible and rubbery state due to increased molecular mobility.
How is Tg of PLA Plastic is Calculated
The primary method used to determine the glass transition temperature (Tg) of plastics, including PLA, is ASTM E1356. This method utilizes differential thermal analysis (DTA) or differential scanning calorimetry (DSC) to evaluate the Tg of materials.
It is important to note that these techniques only apply to amorphous materials or crystalline substances with stable partial amorphous areas that do not decompose in the glass transition region.
In DTA and DSC, thermal input initiates peaks corresponding to endothermic and exothermic transitions, indicating phase changes. DTA works by measuring the difference in temperature or time between the sample and reference materials while observing the changes in temperature of the sample in a specific atmosphere.
On the other hand, DSC measures the discrepancy in heat flow to a sample and reference material while monitoring the temperature changes programmed in a specific atmosphere.
In addition to DTA and DSC, other techniques can determine the glass transition temperature of ABS plastic, including:
- Thermomechanical analysis,
- Thermal expansion measurement,
- Micro-heat transfer measurement,
- Heat capacity
- Isothermal compressibility,
- Specific heat measurements.
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Factors Affecting PLA Glass Transition Temperature
Various factors can influence the Tg of PLA. Below are the most significant ones:
PLA’s glass transition temperature (Tg) is significantly affected by its molecular weight, as higher molecular weight PLA has longer chain segments that can interact with each other through entanglement, resulting in a higher degree of chain packing.
As a result, the intermolecular interactions require more energy to break and transition the material from a glassy to a rubbery state, increasing Tg. Conversely, lower molecular weight PLA has shorter chain segments and less chain entanglement, decreasing Tg.
The Tg of PLA is also significantly influenced by its crystallinity. Being a semi-crystalline polymer, PLA has both amorphous and crystalline regions, and the quantity of crystallinity in the material can dramatically impact its Tg.
When the material has crystalline regions, it results in a higher Tg due to the restriction of chain mobility and increases material rigidity. Conversely, when the amount of crystallinity decreases, the Tg of the material reduces, resulting in a more flexible material due to the increased chain mobility.
The conditions, including the processing temperature, pressure, and cooling rate, can all influence the Tg of the final product. For instance, high temperatures and pressure during extrusion can increase chain mobility and, therefore, a lower Tg.
The addition of various additives can also impact the Tg of PLA. For instance, adding plasticizers or impact modifiers can lower the Tg of the material by increasing chain mobility and reducing the intermolecular forces between the chains.
Additionally, adding fillers such as glass fibers or carbon nanotubes can increase the overall rigidity of the material and result in a higher Tg.
Comprehending the determinants influencing the PLA glass transition temperature is vital for refining its properties to suit diverse applications. PLA’s Tg can be substantially impacted by its molecular weight, crystallinity, processing temperature, and additives, allowing for the customization of its material properties.
By tailoring these factors, PLA can be developed to suit specific applications such as packaging, 3D printing, and medical devices.