Thinker X400
LCD 3D Printer L10
Hyper Speed TPU
Standard TPU 90A Filament
Standard TPU 95A Filament
TPU Rainbow-95A
Ultra Silk PLA
Standard PLA
Silk Tri-color PLA
More
Standard PETG
PETG-GF
PETG-CF
Hyper Speed PETG
PA6/12-GF
Standard ASA
Hyper Speed ASA
ASA Glass Fiber
ASA Carbon Fiber
ABS Glass Fiber
ABS Carbon Fiber
Hpyer Speed ABS Filament
Water Washable Resin
Low Odor Resin
ABS Like Resin
Temperature and Polymers: Thermal Properties and DSC Characterization
2026-01-15
Having clarified the structure of polymer materials, we will next focus on their thermal properties to explore the laws governing the variation of polymer behavior with temperature. To achieve this goal, it is first necessary to introduce a testing method that can accurately characterize the thermal properties of polymers—Differential Scanning Calorimetry (DSC).
1. Definition of Differential Scanning Calorimetry (DSC)
Differential Scanning Calorimetry (DSC) is a core thermal analysis technique. Its principle is to place a polymer sample in a closed test chamber and capture the thermal response of the sample by measuring the heat change required to maintain a constant rate of temperature increase in the chamber. The core purpose of this method is to locate the characteristic temperatures at which polymers undergo various state transitions (such as glass transition, crystallization, melting, etc.). Essentially, it achieves the quantitative characterization of their thermal properties by tracking the energy absorption and release behavior of polymers during the gradual heating process.
2. Key Thermal Transition Temperatures of Polymers
1. Glass Transition Temperature (Tg)
The glass transition temperature is a core thermal characteristic possessed by all polymers, referring to the critical temperature at which the physical state of the polymer transitions from a hard and brittle glassy state to a soft and elastic rubbery state. For amorphous polymers, Tg is a key indicator defining their maximum service temperature—exceeding this temperature, the mechanical properties of the material will deteriorate significantly, making it unable to maintain its original service functions.
2. Crystallization Temperature (Tc)
The crystallization process only occurs in the temperature range between the glass transition temperature (Tg) and the melting temperature (Tm), which is the process by which polymer molecular chains arrange regularly from a disordered state to form an ordered crystalline structure. The crystallization temperature (Tc) is not the only temperature at which crystallization occurs, but rather the temperature point at which the polymer crystallization rate reaches its maximum. At this point, the mobility of the molecular chains and the thermodynamic driving force for regular arrangement reach an optimal balance.
3. Melting Temperature (Tm)
The melting temperature is a unique thermal transition temperature of semicrystalline polymers, corresponding to the temperature at which the ordered crystalline regions inside them begin to melt and the lattice structure collapses. It should be noted that amorphous polymers do not have a clear melting temperature due to the absence of regular crystalline regions, and will only soften continuously as the temperature increases.
4. Decomposition Temperature (Td)
The decomposition temperature is the critical temperature at which the polymer begins to undergo thermal degradation. At this point, the covalent bonds in the main chain skeleton of the polymer will break, and the chemical structure and macroscopic properties of the material will be irreversibly damaged. This temperature is an important indicator defining the thermal stability range of the polymer—exceeding Td, the material will completely lose its service value.
3. DSC Testing Principle and Thermal Transition Process Analysis
To understand the correlation between the DSC curve and the thermal transition of polymers, the core lies in clarifying the heat distribution logic: the heat injected into the test chamber is originally intended to maintain a constant rate of temperature increase in the chamber. However, if the polymer sample absorbs or releases energy due to internal structural rearrangement, the system needs to additionally supplement or reduce heat input to keep the heating rate constant—this heat change will be recorded by the DSC instrument to form a characteristic curve. Combined with a typical DSC heating curve, the energy change laws of each thermal transition stage can be analyzed as follows:
In the initial stage of the test, the system applies a constant amount of heat to make the temperature of the chamber rise at a constant rate. When the temperature reaches Tg (glass transition temperature), the instrument will detect a significant increase in the heat required to maintain the constant heating rate. This is because the polymer needs to absorb a large amount of thermal energy at this stage to break the non-covalent bonds between molecules (such as van der Waals forces and hydrogen bonds), enabling the originally frozen molecular chains to gain mobility, which is macroscopically manifested as the material transitioning from a hard and brittle state to a soft and elastic state. After the glass transition is completed, the specific heat capacity of the polymer will rise to a new stable level. At this point, the system needs to continuously input a constant high amount of heat to maintain the original heating rate.
As the temperature continues to rise, the mobility of the polymer molecular chains further increases. When the temperature reaches Tc (crystallization temperature), the molecular chains have gained sufficient mobility to spontaneously arrange regularly to form an ordered crystalline structure. Since the transition from a disordered state to an ordered crystalline structure is an exothermic process, the sample will release energy to the environment. Therefore, the system does not need to input too much heat to maintain the constant heating rate, corresponding to an exothermic peak in the DSC curve.
After the crystals are fully formed, the sample no longer releases energy, and the system returns to a stable heat input state. However, when the temperature rises to Tm (melting temperature), the situation reverses again: the lattice structure of the polymer's crystalline regions needs to absorb a large amount of thermal energy to collapse, and the molecular chains return to a disordered state of motion, making the sample exhibit strong endothermic behavior. At this point, the system needs to significantly increase heat input to maintain the heating rate, corresponding to an endothermic peak in the DSC curve. After all crystalline regions are completely melted, the endothermic process of the sample terminates, and the heat input returns to stability.
When the temperature continues to rise to Td (decomposition temperature), the covalent bonds in the main chain of the polymer molecules begin to break, and the material undergoes thermal decomposition. At this point, the specific heat capacity of the sample drops sharply, and it no longer requires a large amount of heat to increase the temperature, corresponding to an obvious baseline shift in the DSC curve, indicating that the material has entered the stage of thermal degradation.
In summary, the baseline shift corresponding to Tg, the exothermic peak corresponding to Tc, the endothermic peak corresponding to Tm, and the baseline mutation corresponding to Td in the DSC curve together constitute the complete thermal characteristic spectrum of the polymer. This provides a core basis for accurately characterizing its thermal properties and defining the service temperature range.