Preparation of cellulose-PCC fibre hybrids: Use as filler in polypropylene (PP) composites

Polymer composite materials find application in various life sectors such as packaging, lightweight construction and the fabrication of medical devices. Functional fillers like mineral colloids, synthetic and natural fibres enable a precise tailoring of the mechanical properties of the resulting compounds. Precipitated calcium carbonate (CaCO 3 , PCC) has proven to be a special popular mineral polymer filler. From economic and ecologic reasons, it is desirable to increase filler contents in polymers while maintaining material strength. To achieve this, the present work has developed a hybrid filler system which is based on carboxymethylated, fibrillated cellulose fibres. CaCO 3 is precipitated onto the fibres in a single step twin-screw extrusion process by the co-precipitation method. This process ensures a strong, permanent interaction between the fibres and the mineral particles, which enables CaCO 3 contents in the filler of up to 68 wt.-%. The resulting hybrid fillers were compounded with polypropylene (PP) in a powder or paste state with filler contents between 5 wt.-% and 20 wt.-%. The resulting composites show an increase in the zero-shear viscosity and, in the event of sufficient network formation, a marked increase in stiffness was observed.