There exist only few studies on the possibility to use the in-situ microfibrillar technology in HDPE/PA blends notwithstanding the good knowledge on the structure and properties of these blends. The main objective of this chapter is to summarize these studies in the field of the preparation, mechanical and structural characterization of HDPE/PA6 and HDPE/PA12 MFC materials. Along this presentation, the relationship between the mechanical properties and the structure of the MFCs on various length scales studied by various techniques will be discussed, as well.FCT grant SFRH/BPD/45252/2008 - to Nadya DenchevaFCT sabbatical grant SFRH/BSAB/812/2008 - to Zlatan DenchevHASYLAB at DESY , Hamburg,, Germany,Grant Number II-07-011 E
