Effects of compound coupling agents on the properties of PTFE/SiO_2 microwave composites

摘要

PTFE-based microwave composites filled with SiO_2 dielectric ceramic (PTFE/SiO_2) were prepared by powder processing technique followed by hot pressing. The effects of compound coupling agent on the contact angle and surface energy of SiO_2 filler, as well as moisture absorption, dielectric properties, temperature coefficient of dielectric constant (τ_ε) and coefficient of thermal expansion (CTE) of the PTFE/SiO_2 composites were investigated. The content of SiO_2 in PTFE/SiO_2 composites was maintained as 57 wt%. SiO_2 powders were pre-treated by the mixture of phenyltrimethoxysilane (Z6124) and amino-propyltriethoxysilane (KH550) coupling agents before mixing and reacting with PTFE. The compositions of the coupling agents mixture are x% KH550 + (1.5 — x)% Z6124 (x: mass ratio to SiO_2, x = 0, 0.15, 0.3, 0.45, 0.6, 0.75, 1.5). The results show that as the content of KH550 and Z6124 is 0.3 and 1.2 wt%, respectively, the modified SiO_2 filler has a maximum value of contact angle, at the same time the composites achieve a most compact structure with a maximum density of 2.031 g/cm~3. Moreover, improved properties, including dielectric constant (ε_r) of 2.83, dielectric loss (tan 8) of 7.4 x 10~(-4), CTE of 28.81 ppm/℃ and temperature coefficient of dielectric constant (τ_ε) of 22.8, are obtained. The ratio of experimental and theoretical dielectric constant values is 96.97%. It has been found that the compound coupling agent (KH550 and Z6124 are 0.3 and 1.2 wt%, respectively) results in improved performance of the composites than that of previous reported work.