Effects of hollow Zn₂SiO₄ particles addition on dielectric properties of isotactic polypropylene-HW composites

Highlights: • Dielectric and thermal properties of hollow Zn₂SiO₄/iPP composites were investigated. • The lower ε_r of composites is obtained by addition of hollow-structured filler. • The dielectric loss of composites is on the order of 10⁻⁴ for all weight fraction. • The CTE and TCε of composites are improved by addition of HW filler. - Abstract: Hollow willemite (Zn₂SiO₄) filler particles (HW) were synthesized via a spray pyrolysis method and used to make composites with isotactic polypropylene (iPP). The dielectric constant (ε_r) of iPP/HW composites exhibited slight variations with the addition of the filler having the high crystallinity, while the dielectric loss (tan δ) value decreased significantly, from 20.1 × 10⁻⁴ to 1.78 × 10⁻⁴. As the weight fraction of the HW filler was increased, though the tan δ values of the composites slightly increased but these values maintained on the order of 10⁻⁴ because of the highly crystalline filler. The measured ε_r values of the composites were lower than those predicted by the Bruggeman model when using ε_f = 6.6 (Zn₂SiO₄) and ε_m = 2.4 (iPP). However, the data could be made to fit the Bruggeman model when ε_f was assumed to be 4.8, suggesting that the air included in the HW filler suppressed the ε_r of the composite. It was also established that the coefficients of thermal expansion and temperature coefficients of dielectric constant of the iPP/HW composites were significantly improved with increasing HW filler concentrations.