Influence of the Addition of a Fluorinated Oligo-Polystyrene Additive on the Rheology and Hydrophobic Properties of...

The objective of this work is to understand the effect of a perfluorinated random copolymer added in a polystyrene (PS) matrix on the rheological properties during an injection molding process, as well as on the functional wettability of the final parts. A synthesized random perfluorinated copolymer, named POISE-a-20, was first physically blended with a PS matrix at a weight content of 2 wt % and processed on a lab scale using an injection molding machine. The rheological properties of the injection-molded parts were investigated using a plate-plate rheometer, and a specific behavior was observed, where the presence of POISE-a-20 led to an increase in viscosity at low shear rates and an enhancement of the shear-thinning behavior at high shear rates. In situ rheological measurements were then performed during the injection molding of PS/POISE-a-20 blends at additive contents of 10^-2, 10^-1, and 1 wt % at an industrial scale. For the same switchover volume, the presence of POISE-a-20 led to an increase in mold cavity pressures and a shift of the pressure curves to a lower time. These results showed a higher flow speed and less energy dissipated with the addition of POISE-a-20, even at contents as low as 10^-2 wt %. However, when combined with microtexture replication, the additive did not improve the replication quality or the hydrophobicity of the final injection-molded part. Two hypotheses were proposed to explain this result: (i) the presence of textures that inhibit additive migration associated with complex flows involved in topological singularities or (ii) the need to optimize the injection parameters since the shearing of the fluorinated nodules is too important in the industrial injection molding process.