Control of Structure of Filled Polymer Blends

Doctoral thesis, 1997

This thesis deals with the control and analysis of the structure of filled immiscible polypropylene (PP) blends. The intention has also been to implement the knowledge gained in respect of commercially interesting systems as filled PP/(ethylene propylene copolymer (EP)) blends. In PP/(poly(styrene-co-acrylonitrile) (SAN) or poly(methylmethacrylate) (PMMA))/BaSO4 systems, the filler particles are present in the SAN or PMMA phase, but will gradually be occluded in the PP matrix with increasing concentration of maleic anhydride-grafted polypropylene (PP-g-MAH). In PP/polystyrene (PS) blends the filler is situated at the polymer phase boundaries, reducing the domain size drastically. Addition of PP-g-MAH to the different filled systems results in the presence of the BaSO4 in the PP, while styrene maleic anhydride copolymer (SMA) leads to a situation with all the filler particles in the PS phase in the PP/PS system. The mechanism behind the phenomenon of structure control exercised in this work is probably specific interactions between the maleic anhydride units and the Ba2+ atoms at the filler surface. The results are applicable to BaSO4 -filled PP/EP blends, which were processed with standard equipment, extrusion and injection molding, thus showing direct relevance for possible applications. The main analytical tools were scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) in the solid and melt state, Fourier Transform Infrared Spectroscopy (FTIR), and theoretical calculations of the dynamic mechanical properties, using the measured properties of the pure polymer constituents, with an interlayer model. The effects of a filler-polymer interlayer in BaSO4-filled SAN were also investigated as an extension of work performed on compatibilized polymer blends. The most important result hereof is that a dynamic shear loss modulus maximum can be due to specific relative material properties in a blend system and not to a transition in any of the components.