Technical method for determining the melting peak temperature of fibers using differential scanning calorimetry (DSC)

Differential Scanning Calorimeter (DSC) analyzes the phase transition behavior of materials by measuring the changes in heat flux during programmed temperature control. For fiber materials such as synthetic fibers, natural fibers, or composite fibers, the melting peak temperature is an important parameter for characterizing their thermal stability and crystallization properties. The melting peak corresponds to the process of disrupting the ordered structure of the crystalline region in the fiber, and the peak temperature can directly reflect the heat resistance and processing applicability of the material.

　1、 Experimental steps

1. Measuring instruments

　　DZ-DSC300 Differential Scanning Calorimeter

　　2. Sample preparation

2.1 Sampling requirements: Take about 10-20 mg of fiber sample to ensure uniformity and no contamination.

2.2 Preprocessing

If the fibers are in the form of long filaments or bundles, they need to be cut into powder or short fiber segments to avoid uneven heat conduction.

If it is necessary to eliminate thermal history (such as residual stress during processing), a heating and cooling cycle treatment can be carried out (such as cooling after raising to 200 ° C at 10 ° C/min).

　3. Instrument calibration

3.1 Use standard substances (such as indium and tin) to calibrate the temperature and heat flux signals of DSC.

3.2 Ensure nitrogen or inert gas protection (flow rate 50-100 mL/min) to avoid interference from oxidation reactions.

　　4. Test parameter settings

4.1 Temperature range: Set the heating range according to the fiber type (such as 30 ° C to 300 ° C).

4.2 Heating rate: Usually choose 10-20 ° C/min (commonly 10 ° C/min). Excessive heating rate can cause peak temperature shift, which needs to be adjusted in conjunction with literature or standard methods.

4.3 Repeat testing: Each group of samples should undergo at least 2 to 3 parallel experiments to verify data reproducibility.

　5. Experimental operation

5.1 Spread the sample evenly in an aluminum crucible.

5.2 Set a blank crucible as a reference and place it in the DSC furnace body simultaneously with the sample crucible.

5.3 Start the program to heat up and record the heat flow curve in real-time.

　　2、 Data analysis

1. Identification of melting peaks

Analyze the DSC curve through software to locate the endothermic peak (melting peak).

Determine the following characteristic temperatures (Figure 1, PA66 schematic)

　　Figure 1 PA66

　Figure 2 PET

Starting point: The starting point of the curve baseline deviation. Peak: The peak temperature of the endothermic peak.

Termination point: The end point of the melting process.

　　3、 Common Problems and Solutions

　　1. Baseline drift or high noise

Reason: Excessive sample size, inadequate crucible sealing, or unstable gas flow rate.

Solution: Reduce the sample size to below 5 mg, check the sealing of the crucible, and calibrate the gas flow rate.

　2. Melting peak splitting or multi peak phenomenon

Reason: The sample contains impurities or is not dried (due to interference from water evaporation).

Uneven crystalline structures are formed during the processing.

Solution:

2.1 Improve resolution by adjusting the heating rate (such as reducing it to 5 ° C/min).

2.2 Conduct annealing treatment on the sample (constant temperature followed by cooling at a specific temperature) to eliminate metastable crystals.

2.3 Dry the fibers thoroughly before testing (place them in a dryer or vacuum oven for processing).

3. The test results have a large deviation from the literature values

Reason: Differences in fiber batches, effects of additives (such as flame retardants, plasticizers) or blending modifications.

Inaccurate calibration or abnormal instrument status.

Solution:

3.1 Compare literature data of samples from the same source to confirm the consistency of material composition.

3.2 Re calibrate the instrument, check the sensitivity of the sensor and the sealing of the furnace body.

　　4. Sample thermal decomposition interferes with melting peak

Reason: Some fibers (such as natural fibers or synthetic fibers containing thermosensitive groups) undergo degradation before melting.

Solution:

4.1 Use inert gas (such as nitrogen) protection to reduce the risk of oxidative degradation.

4.2 Use rapid heating (such as 20 ° C/min) to shorten the high-temperature residence time.

　4、 Experimental precautions　

1. Sample representativeness: Fiber samples should be taken from the same batch to avoid data deviation caused by production process fluctuations.

2. Avoid contamination: Use tweezers to pick up and place samples and crucibles to prevent hand oil contamination.

3. Data comparability: The melting peak temperatures at different heating rates cannot be directly compared, and the testing conditions should be specified.

4. Instrument maintenance: Regularly clean the DSC furnace body to avoid residue affecting heat conduction.

　　5、 Application examples

5.1 Case: Analysis of Melting Behavior of Recycled Polyester Fibers

Background: Due to the complex processing history of recycled PET fibers, the melting peak may exhibit broadening or shifting.

5.2 Measurement parameter settings

Heating rate: 10 ° C/min, nitrogen protection (50 mL/min)

Temperature range: 30~300 ° C

5.3 Result Analysis

The melting peak temperature is reduced by about 3-5 ° C compared to native PET, indicating damage to crystal integrity.

The decrease of 30% in melting enthalpy confirms the decrease in crystallinity during the recovery process.

　6、 Experimental conclusion　

Differential scanning calorimetry provides an efficient and sensitive means for characterizing the melting behavior of fibers. By standardizing the sample preparation process, optimizing testing parameters, and analyzing data reasonably, key thermodynamic parameters such as melting peak temperature can be accurately obtained, providing theoretical support for the design, processing, and recycling of fiber materials.