Rheological Behaviour of Highly Filled Materials for Injection Moulding and Additive Manufacturing: Effect of Particle Material and Loading

Within this paper, we are dealing with a mixture of thermoplastic polymer that is filled with inorganic fillers at high concentrations up to 60 vol.%. A high number of particles in the compound can substantially change the rheological behaviour of the composite and can lead to problems during processing in the molten state. The rheological behaviour of highly filled materials is complex and influenced by many interrelated factors. In the present investigation, we considered four different spherical materials: steel, aluminium alloy, titanium alloy and glass. Particles with similar particle size distribution were mixed with a binder system at different filling grades (30–60 vol.%). We showed that the rheological behaviour of highly filled materials is significantly dependent on the chemical interactions between the filler and matrix material. Moreover, it was shown that the changes of the particle shape and size during processing lead to unexpected rheological behaviour of composite materials as it was observed in the composites filled with glass beads that broke at high contents during processing.

Effect of hexafluoropropylene oxide plasma polymer particle coatings on the rheological properties of boron nitride/poly(dimethylsiloxane) composites

This work explores the use of conformal nanoscale plasma coatings on the surface of boron nitride (BN) powders to control the rheological properties of BN/poly(dimethylsiloxane) (PDMS) composites. BN particles are conformally coated with hexafluoropropylene oxide (HFPO) in a tumbling RF-plasma reactor. Following the HFPO plasma treatment, XPS evidence indicates the presence of thin coating on the surface of the particles having a F:C ratio of 1.77. Filled BN/PDMS composites are investigated using oscillatory shear rheometry in the concentration range of 0.09-0.41 vol% (varphi). The addition of the plasma treated BN particles to the PDMS matrix reduces the complex viscosity by 40-60% when compared with equally loaded control samples across a broad concentration range. The frequency dependence of the maximum packing fraction (varphi(m)=0.38-0.42) is also observed for both treated and untreated particles. The maximum packing fraction does not appear to be significantly affected by the conformal plasma polymer treatment. The investigation has shown that the relative dynamic viscosity of the BN/PDMS can be described by the modified Mooney equation.