Ethyl Cellulose/SiO<sub>2</sub> Composite Microencapsulated Red Phosphorus: An Efficient Flame Retardant for Epoxy Resin

At present, the shell structures of the microencapsulated red phosphorus (RP) are mostly derived from petroleum materials and possess certain toxicity, which may do potential harm to the human beings and environment during preparation process. To solve this problem, the bio-based ethyl cellulose (EC) was selected as the shell material for microencapsulated RP in this work. Meanwhile, combining the anti-solvent and sol-gel methods in one pot, the EC/SiO 2 shell structure was prepared by one step for the first time. The characterization results verified the fabrication of the integrated EC and EC/SiO 2 shell structures. Meanwhile, the thermogravimery analysis indicated that the EC/SiO 2 shell structure significantly improved the thermal stabilty and char-forming ability of pristine RP. The flame retardance of RP, EC coated RP (RP@EC) and EC/SiO 2 coated RP (RP@EC/SiO 2 ) on epoxy resin (EP) was investigated by cone calorimeter tests. The results showed that EP blending with 7 wt% RP@EC/SiO 2 (EP/RP@EC/SiO 2 ) decreased the heat release rate (HRR) and total heat release rate (THR) of neat EP by 55.65% and 30.11%, respectively. The char residuals after cone calorimeter tests were tested by scanning electron microscope and X-ray diffraction. The results showed that EP/RP@EC/SiO2 composites fabricated char residuals with continuous structures during the burning process, and the amorphous SiO 2 in the char residuals was supposed to further improve the thermal insulation property. The compact and thermostable char residuals formed during cone calorimeter tests led to the superior flame retardance of RP@EC/SiO 2 .