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The effects of surface hydroxyl groups in polyethylene-silica nanocomposites

Logically, the surface chemistry of filler particles must be a key factor that governs how they interact with a polymer matrix, determining for example, how strongly the particles are bound into the matrix and how easy or difficult it is to achieve a homogenous dispersion of filler particles. This second point is surely one of the most basic challenges when producing a nanocomposite (poor dispersion is frequently stated as the cause of undesirable results). Many attempts have been made to modify the surface chemistry of filler particles through surface functionalization. Typically, this is achieved by chemically attaching polymer chains to the surface of the filler particles. In this paper we try a more direct approach; the surface chemistry of silica nanoparticles is modified by processing them at high temperature. This procedure removes hydroxyl groups from the surface of the filler particles, leaving siloxane groups which are stable at room temperature. Polyethylene composites were produced using both “as delivered” and high temperature processed nanosilica. After heat treatment the particles become hydrophobic which reduces the propensity for water uptake in the resulting nanocomposite and significantly modifies the dielectric response of the material.