Phosphorus-Containing Attapulgite/Liquefied Cellulose-Based Epoxy Composites: Enhancement of the Flame Retardancy and the Mechanical Properties

A promising route is established to produce a liquefied cellulose-based epoxy resin via phenol-catalyzed liquefaction, glyoxal cross-linking, and epoxidation. To simultaneously enhance flame retardancy and mechanical strength, attapulgite (ATP) was organically engineered with a phosphorus–silicon coupling agent (KH560–DOPO) to create a hybrid filler (AKD). The incorporation of 6 wt% AKD enabled the composite to achieve a UL-94 V-0 rating and a high limiting oxygen index (33.1%), while tensile strength and elongation at break increased by 36.7% and 24.1%, respectively. The analysis confirmed the successful liquefaction of cellulose and the covalent grafting of phosphorus and silicon onto ATP. The AKD/LCP composite material has a synergistic flame retardant mechanism of condensed phase and gas phase. The synergistic P–Si–C framework effectively promoted char formation and reinforced the polymer network. This work demonstrates a scalable route to stabilize renewable cellulose into high-performance epoxy resins, combining bio-based chemistry with advanced flame-retardant nanotechnology and providing new ideas for the development of fire-resistant polymeric materials.