**Abstract**

This chapter summarizes the study of the filler (ie copper) effect on LDPE phasic composition in LDPE/Cu composites prepared in solution. During this research work, a particular effort is focused on the use of DSC under non-standard conditions. Therewith, the presence of copper microparticles has a great effect on the network phase than on the crystalline long-range-order phase of LDPE structure. Furthermore, LDPE phasic composition in absence and presence of copper microparticles is investigated by FTIR spectroscopy followed by a spectral simulation of the band that appeared at 720 cm−1 corresponding to the CH2. Anywise, the two-phase model confirmed that no variation is observed of LDPE phase composition for all copper contents into LDPE/Cu films. However, with the three-phase model the orthorhombic phase fraction was found to be constant compared to the fraction of amorphous and that of network phase were found to increase and decrease respectively with increase in the copper particle load in the film. Overall, the thermal and structural behavior of LDPE in presence of copper particles allows this type to be used as phase change materials (PCMs) by adding a paraffin fraction in the LDPE/Cu composite. An update of the most relevant work carried out in the field of phasic characterization of polyethylene is presented in this chapter.

**Keywords:** LDPE/Cu composite films, LDPE crystallinity, LDPE Network phase, thermal stability
