Waterborne Glass Fiber Sizing Agents: Soft–Hard Janus Particles

Interface modification via a sizing agent is a crucial strategy for improving mechanical properties of a glass fiber (GF) reinforced polypropylene (PP) composite. In this work, soft-hard Janus particles (JPs) were designed and synthesized by polymerization-induced phase separation of seeded emulsion and incorporated into a waterborne GF sizing agent for interface modification. The JPs-sized GF exhibited enhanced surface roughness (Ra) from 6.3 to 23.1 nm and reduced polar surface energy from 30.20 mJ/m² to 25.48 mJ/m². The soft-hard segmented structure of JPs formed a gradient modulus interphase layer with a thickness of about 244 nm that dissipated fracture energy through microdeformation. The JPs modification can enhance the interfacial adhesion with their amphiphilicity, introduce nanoscale roughness at the interface, and construct a gradient modulus interphase layer synergistically, which resulted in strengthening and toughening the short GF reinforced PP composite simultaneously. It reveals the promising application of JPs in advanced composite interfacial engineering.