A Comparative Study of Calorimetric Methods to Determine the Crosslinking Degree of the Ethylene-Co-Vinyl Acetate Polymer Used as a Photovoltaic Encapsulant
Résumé
EVA copolymer foils are widely used as encapsulants
for photovoltaic (PV) cells in PV modules. These foils
need to be crosslinked during module manufacturing, to
enhance their properties. Accurate and reliable methods for the
determination of their crosslinking degree are thus very important.
In this work, two semi-empirical calorimetric methods are
considered and compared to a scientifically sound rheological
method used as a reference. The main purpose of this work is
to reveal the chemical and physical fundamentals on which the
two calorimetric methods are based, to allow for a scientific
understanding of their advantages, and limitations. For one of
these calorimetric methods, the so-called “Melt-Freeze” method,
we have sought for a deeper understanding of the underlying
crystallization physics through the use of successive selfnucleation
and annealing experiments, which give access to
the crystallite size distribution of EVA, and to the influence of
crosslinking upon it.