Viscoelastic and dielectric properties of composites of poly(vinyl butyral) and alumina particles with a high filling degree


Filler-filler and filler-matrix interactions in polymer composites increase with filler concentration and strongly influence the mechanical and rheological properties of polymer composites. By means of the spouted bed spray granulation process polymer composites with an extremely high concentration of inorganic fillers can be prepared. In this work, the viscoelastic properties of highly filled composites of poly(vinyl butyral) (PVB) and alumina particles are studied in the glassy, entanglement and terminal flow regime of poly(vinyl butyral). Ceramic-polymer composites with a volume concentration of inorganic particles between 61 vol% and 77 vol% were prepared. Such large filler fractions imply a strong effect of filler-filler interactions on the viscoelastic properties of the composite. Dynamic-mechanical thermal analysis reveals that the composites are characterized by a predominantly elastic behaviour below and above the glass transition temperature of the polymer phase because of strongly pronounced filler-filler and polymer-filler interactions. A phenomenological equation is proposed in order to describe the reinforcement effect which implies an increase of storage modulus by a factor of up to four orders of magnitude. The results of frequency and strain sweeps in the oscillatory mode show that the polymer phase strongly influences the deformation of the contact network of inorganic particles. Differential scanning calorimetry and broadband dielectric spectroscopy indicate that the glass transition temperature of poly(vinyl butyral) does not significantly differ within experimental resolution for pristine PVB and the PVB phase in the composites.
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