Measurement of Glass Transition Temperature of Rubber Materials by Differential Scanning Calorimeter

The glass transition temperature (Tg) is an important parameter for polymer materials such as rubber, which characterizes the temperature at which the material transitions from a glassy state to a highly elastic state. This parameter directly affects the low-temperature performance, elastic modulus, and application scenarios of rubber. Differential Scanning Calorimetry (DSC) is a widely used technique for determining Tg, which accurately captures the phase transition temperature by measuring the heat flux changes of materials during heating or cooling.

　　1、 Experimental principle

　　Differential scanning calorimeterBy comparing the difference in heat flux between the sample and the reference material under programmed temperature control, the thermal effect of the material is detected. When rubber undergoes glass transition, its heat capacity (Cp) undergoes a sudden change, manifested as a step like baseline shift on the DSC curve (Figure 1). Tg is usually taken as the midpoint or inflection point of the curve offset.

　　2、 Experimental steps

　1. Sample preparation　

1.1 Sample selection: Take a rubber sample (5-10 mg) to avoid contamination by impurities.

1.2 Pre treatment: If the sample contains plasticizers, fillers, etc., the composition should be recorded; Annealing treatment may be necessary to eliminate thermal history.

1.3 Sealed Sample Assembly: Place the sample in an aluminum crucible and seal it tightly. Use an empty crucible or inert material (such as alumina) as the reference material.

　2. Equipment selection

2.1 Instrument and Equipment: DZ-DSC300L Differential Scanning Calorimeter

　　2.2 Instrument parameter settings

Temperature range: usually set to -100 ℃ to 50 ℃ (adjusted depending on the type of rubber).

Heating rate: Recommended 10-20 ℃/min (too fast a rate may cause Tg shift).

Atmosphere control: Nitrogen atmosphere (flow rate 50-100 mL/min) to prevent oxidation reactions.

Baseline calibration: Use standard substances such as indium and tin to calibrate the instrument.

　2.3 Testing Process

2.3.1 Blank baseline test (empty crucible).

2.3.2 Load the sample and run a heating cooling heating cycle (eliminate thermal history).

2.3.3 Record the second heating curve to analyze Tg.

　　2.4 Measurement reference standards

GB/T 19466.2-2004/IS011357-2:1999 Plastic Differential Scanning Calorimetry Part 2: Determination of Glass Transition Temperature

GB/T 29611-2013 Determination of Glass Transition Temperature of Raw Rubber Differential Scanning Calorimetry Method

　3、 Data analysis　

Tg determination: On the DSC curve, the glass transition exhibits a step like change. According to the GB/T19466.2-2004/IS011357-2:1999 standard, Tg is taken as the temperature at the midpoint of the baseline offset.

Software processing: Use instrument supporting software for tangent analysis to determine the starting point, midpoint, and endpoint.

　　3.1 Factors affecting measurement results　

1. Heating rate: If the rate is too high, it may cause Tg to shift towards higher temperatures. It is recommended to choose 10 ℃/min.

2. Sample uniformity: Uneven distribution of fillers or plasticizers can lead to multiple transition peaks.

3. Heat history elimination: The initial heating should cover the material above its melting point, and then cool to a low temperature to eliminate the processing heat history.

4. Moisture interference: Water absorbing rubber needs to be dried in advance to avoid masking the Tg by the evaporation heat absorption peak.

　3.2 Practical Application Cases　

Natural rubber (NR): The typical Tg is around -70 ℃ to -60 ℃.

Styrene butadiene rubber (SBR): Tg range -50 ℃ to -30 ℃, affected by styrene content.

Fluororubber (FKM): Tg is relatively high (about -20 ℃ to 0 ℃), and the testing range needs to be adjusted to -50 ℃~100 ℃.

A reliable method for determining rubber Tg using differential scanning calorimetry, accurate measurement can provide key data for rubber formulation design, quality control, and low-temperature performance evaluation.