Influence of thermoplastic spacer on the mechanical, electrical, and thermal properties of carbon black filled epoxy adhesives

A new approach of mimicking the selective localization mechanism of conductive filler into one phase of immiscible polymer blend system is proposed here, where a moderate fine of polymethylmethacrylate (PMMA) powder is prepared and used as the spacer in the carbon black (CB) filled epoxy adhesives system that can be applied at room temperature. The main purpose of PMMA-spacer is to promote the formation of conductive networks via aiding the 3D self-assembly of CB filler, selectively in the continuous phase of epoxy. PMMA-spacer content ranged from 10, 20, 30, 40, and 50 vol.% were investigated under electrical, mechanical, and thermal properties for both unfilled and 15 vol.% CB filled system. With the incorporation of 10 vol.% PMMA-spacer, the filled system shows promising improvement in electrical conductivity, with three order of magnitude increment at 15 vol.% CB loading. Toughening mechanism of epoxy was observed, where crack deflection upon the PMMA-spacer is observed under scanning electron microscopy characterization and agreed by fracture toughness calculation. Thermal stability and coefficient of thermal expansion were improved at the minimum addition of PMMA-spacer content, at 10 vol.%, while a small reduction in flexural strength is observed because of the poor interface interaction between the PMMA-spacer and epoxy matrix. Interestingly, a limited interaction between the PMMA-spacer with epoxy at the curing temperature of 100°C is observed, indicating the solubility of PMMA-spacer in epoxy before crosslinking process occurred. Copyright © 2016 John Wiley & Sons, Ltd.