Addition of Rigid Particulate Fillers

It is well known that to achieve good impact strength in mineral-filled thermoplastics composites, effective dispersion of the filler is of overriding importance. 

For a linearly elastic material the fracture stress (Op) for a plate containing a sharp crack of length a is given by [67]  

From this analysis, it is clear that high aspect ratio filler particles, which are needed to achieve stiffness in a composite will inevitably cause increased stresses in the polymer matrix near the particle edges, which will facilitate failure under impact loads. 

In cases where elimination of agglomerates is essential to ensure that optimum compound properties are achieved, melt filtration can be used. This is important in pigment masterbatch production or in coloured compounds to be spun into fibres, where agglomerates can lead to fibre breakage. Removal of impurities or large defect particles by melt filtration can also increase the fatigue life of FIDPE pipe and the resistance to breakdown of polymer subjected to an electrical stress [71, 72]. 

Properties of a compound, made on the twin-screw extruder showed some sensitivity to screw speed, screw profile (shear intensity) and mass output rate, with the best results obtained using a high screw speed and low material throughput. Blend homogeneity and impact resistance were closely related to the energy input through the compounder drive. 

---