The use of polymers in microelectromechanical systems (MEMS) has raised exponentially, due to higher flexibility in comparision to standard inorganic materials and lower cost in terms of materials and processing. Polyvinylidene fluoride (PVDF) is the most commonly used polymer in MEMS. PVDF crystallizes into three different regular conformations. The regular packing of these conformations induces different crystal phases, named alpha, beta, gamma and delta, these last three are polar phases, so with potential application in MEMS. There are several methodologies to obtain these phases from the most stable one, being one of them the heterogeneous nucleation. Carbon nanotubes (CNTs) can act as nucleating agents. CNTs can accelerate the crystallization, and also provide the nucleation of different polymorphs. The challenge to disperse a high concentration of CNT in polymer matrix and to exploit the axial properties of CNTs can be faced by assembling them into a macroscopic fiber, with the tubes aligned parallel with the fiber axis.[1] The formation of polar phases in PVDF can be favored by nucleation on CNT. After isothermal crystallization at high temperatures, a quite different melting peak sequence is observed by DSC melting experiments. The monitoring of these melting processes by a sequence of X-Ray diffractograms every few degrees Celsisus may give a relevant information about the main polymorphs formed. This monitoring can be performed by X-Ray Synchrotron Radiation due to its high intensity,[2] being this study in CNT Fibre/PVDF composites the objective of this work. References. [1] V. Reguero, et al., Chem. Mater. 2014, 26, 3550. [2] J. P. Fernandez-Blazquez et al., Macromolecules 2007, 40, 1775.