A non-solvent extraction method for measuring gel content of ethylene vinyl acetate

Uncured ethylene vinyl acetate (EVA) is a thermoplastics polymer that has a low glass transition temperature and melting point. To be suited for photovoltaic (PV) module application, EVA has to be cross-linked or cured into a thermoset polymer through the application of peroxide during the module fabrication process, e.g. lamination for crystalline silicon PV modules. A key means of monitoring the degree of cross-linking (or gel content) of EVA is through solvent extraction. Some of the commonly used solvents include toluene, tetrahydrofuran and xylene. These chemical extraction methods pose several drawbacks including HSE issues in dealing with chemicals, long turnaround time, high variation, and sometimes inaccurate gel measurements. Thus it is of great interest to the industry to develop an alternative EVA gel content method that can overcome the aforementioned shortcomings. In this paper, we report using differential scanning calorimetry (DSC) to measure the gel content of EVA. The result show that DSC is not only viable but also a fast and reliable method of measuring EVA gel content. Further, the method can also be used to monitor the peroxide level, type and curing kinetics in different EVAs. A comparison between DSC and solvent extraction method has been made.