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

• Dielectric and thermal properties of hollow Zn2SiO4/iPP composites were investigated.
• The lower ɛr 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 TCɛ of composites are improved by addition of HW filler.

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 (ɛr) 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 ɛr values of the composites were lower than those predicted by the Bruggeman model when using ɛf = 6.6 (Zn2SiO4) and ɛm = 2.4 (iPP). However, the data could be made to fit the Bruggeman model when ɛf was assumed to be 4.8, suggesting that the air included in the HW filler suppressed the ɛr 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.

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