Study On Polymer PTC Composite Consisting Of Novel Conductive Filler

In this paper, high conductive copper plated with silver is prepared by chemical replacement reaction, and needle-like wollastonite plated with nickel is firstly synthesized by means of electroless plating. Three types of composites with low resistivity and high PTC intensity are fabricated by HDPE incorporation with MCMB, Cu-Ag powder and plated wollastonite, respectively. The prepared novel conductive fillers and their composites are characterized with XRD, SEM. The conductivity of novel fillers are evaluated with self-established piston-cylinder system, and PTC curves are determined by the temperature-resistance measurement device. The percolation threshold of the composite contained porous MCMB and HDPE is near 40%wt. The composite with 65% filler content has room resistivity of 5.6?·cm, PTC intensity of 4.7 orders of magnitude, and middle NTC effect. The simulated results from percolation formula accord with SEM graphs, and demonstrated that particles of MCMB are formed a complex conductive network in the composite. Cu powders plated with 15% Ag are synthesized by means of replacement reaction for the sake of higher conductivity, which are covered by silver nano-particles incompletely. It's HDPE composite contained Cu-Ag 82%wt has room resistivity of 4.61?·cm, PTC intensity of 8.4 orders of magnitude, and NTC intensity of 5.44 orders of magnitude. However, Cu-Ag composite with low room resistivity requires 15%wt higher content of filler than that of MCMB, and its PTC intensity do not tend to decrease with an increase in conductive filler content, but appears serious NTC effect. In order to obtain cheap and high conductive powder, electroless plating is performed on needle-like wollastonite. Nickel alloy is plated on the surface of superfine wollastonite with keeping original neel-like shape by controlling pH value. The HDPE/plated wollastonite composite with 85%wt conductive filler has room resistivity of 3.30?·cm, PTC intensity of 13.57 orders of magnitude, and NTC intensity of 1.1 order of magnitude. It is found that plated wollastonite/HDPE composite, in which filler has a ratio of length, possesses very high PTC intensity and nearly zero NTC effect, as well as low room resistivity. It is also found that conductive powder prepared by electroless plating may has a tendency of delaminating conductive film from particle's surface during processing, which may cause imcomplete exertion of its high conductivity of powder in composites.