A simple way to synthesize a nano-scale stable epoxy emulsion for sizing CF/epoxy composites

Abstract

A simple method to prepare an emulsifier was proposed to form a stable nano size emulsion as a sizing agent to enhance the interfacial bonding strength between carbon fiber (CF) and epoxy resin. The toluene diisocyanate (TDI) grafting strategy can effectively introduce hydrophilic polyethylene glycol (PEG) and hydrophobic poly(propylene glycol) (PPG) into the side chain of the epoxy resin without consuming epoxy groups. The PPG chain segment length was controlled to improve the stability of the emulsion. An emulsion prepared with EP–PEG6000–PPG2000 (EE-P20) as the emulsifier had the highest stability, and could be placed for more than 6 months without changes in the droplet size. The wettability of CF modified by this sizing agent was obviously improved, and the interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) of CF(EE-P20) were increased by 42.33% and 17.41%, respectively. It was worth noting that the moisture absorption of CF(EE-P20) was 3.12% at 90% relative humidity. The introduction of the PPG segment not only improved the storage stability of the emulsion, but also improved the moisture resistance of CF after sizing. This simple continuous grafting method provides a new idea for adjusting the structure of the epoxy sizing agent, and the obtained emulsifier has a wide application prospect in the field of the CF sizing agent.