Measurement of Crosslinking Degree of Photovoltaic EVA Adhesive Film Layer by Differential Scanning Calorimeter

Differential Scanning Calorimetry (DSC) achieves quantitative analysis of crosslinking degree by monitoring the enthalpy changes of polymer materials during the programmed heating process. The basic principle is based on the thermal effect characteristics of crosslinking reactions: uncrosslinked linear polymer chains release specific reaction heat (Δ H) during the curing process, while fully crosslinked materials do not have this exothermic peak. By comparing the total reaction heat (Δ H ₁) of uncrosslinked samples with the remaining reaction heat (Δ H ₂) of partially crosslinked samples, the degree of crosslinking (G) can be accurately calculated using the following formula: G=(Δ H ₁ - Δ H ₂)/Δ H ₁ × 100%.

1、 Operation steps of the experiment

1. Measuring instruments:DZ-DSC400C Differential Scanning Calorimeter

2. Sample preparation requirements: Cut 10-20mg of uniform sample from the sample, with a thickness not exceeding 0.5mm, to ensure uniform heat conduction. Thin film samples such as photovoltaic adhesive film need to be cut into square pieces with a clean blade to avoid contamination from finger contact.

3. Pre treatment conditions: The sample needs to be dried in a drying vessel for more than 6 hours (temperature 60 ± 2 ℃) to remove moisture and volatile impurities. Rubber samples need to be extracted with solvents (such as toluene) to eliminate plasticizer interference.

4. Experimental parameter settings:

Note: The first heating is used to eliminate thermal history, and the second heating is used to determine the remaining reaction heat Δ H ₂.

5. Graph analysis:

5.1 Heat flow curve analysis: Calculate the enthalpy change value by integrating the DSC curve, and the integration interval should cover the complete heat release peak. For example, the cross-linking exothermic peak of adhesive film usually occurs in the range of 30-60 ℃.

5.2 Example of Crosslinking Degree Calculation: The photovoltaic film sample was tested and found to have Δ H ₁=5.822J/g (uncrosslinked) and Δ H ₂=3.045J/g (crosslinked). Therefore, the crosslinking degree G=(5.822-3.045)/5.822 × 100%=47.69%.