Ultrahigh molecular weight polyethylene (UHMW-PE) belongs to the specialty polymer grade because of its unique properties. Among other applications, it is used for battery separator membranes elaboration for automotive applications. These PE separators are porous membranes composed of a blend of UHMW-PE, naphthenic oil and precipitated silica. With the aim of understanding the membrane structuring mechanisms, we studied the influence of silica and oil concentrations on the UHMW-PE crystallization during the elaboration process. Results have shown that the high initial thickness of the UHMW-PE crystals is reduced after the process. Moreover, χc (crystallinity) and Tc (crystallization temperature) are both controlled by the volume fraction of oil. The initial high crystallinity of UHMW-PE (χc ≈ 65%) can be increased in the membrane with a high Oil/PE ratio. Furthermore, silica indirectly contributes to enhance the UHMW-PE crystallinity by acting as a reservoir, hence increasing the possible oil content in the blend. Display omitted •Crystallinity of UHMWPE in different blends with Oil and Silica is analyzed.•Melting behavior is successfully analyzed with the Flory-Huggins theory.•Crystallinity of nascent UHMWPE powder is recovered in the presence of oil.•Silica acts as an oil reservoir thus enhancing the UHMW-PE crystallinity.