Synergistic effect of zinc borate and microencapsulated black phosphorus nanosheets for improved flame retardancy and smoke-suppression performance of epoxy resin

•Preparation of a microencapsulated BPNs via in-situ polymerization of PETA.•Delaying pyrolysis of BPNs realized by the protection of PETA and ZB.•Significant improvement in fire safety of EP/ZB-BPNs@PETA nanocomposites. To improve the air stability and smoke-suppression ability of black phosphorus nanosheets (BPNs), a simple strategy was proposed. Through microencapsulation of BPNs with pentaerythritol triacrylate (PETA), BPNs@PETA was synthesized. The ZB-BPNs@PETA was obtained through combining zinc borate (ZB) with BPNs@PETA at the ratio of 1:1. The ambient and thermal stability of BPNs was improved after modification due to the protection of PETA shell. The maximum rate of thermal degradation of BPNs for BPNs@PETA and ZB-BPNs@PETA was reduced by 36.87% and 72.38%, respectively, compared with that of BPNs. The results confirmed that PETA and ZB can delay the pyrolysis of BPNs greatly. With the addition of 2.0wt% ZB-BPNs@PETA, the fire safety and thermal stability of EP nanocomposite was improved. EP/ZB-BPNs@PETA 2.0 can pass the UL-94 V-0 rating, and the limited oxygen index value was increased to 32.2% from 25.0%. The values of peak of heat release, total heal release, smoke production rate and total smoke production were reduced by 43.53%, 22.05%, 30.17% and 14.14%, respectively. Additionally, the results of TG-IR showed that ZB-BPNs@PETA can reduce the peak value of absorption intensity of CO by 34.11%, compared with that of EP. From the results of XRD, the presence of Zn3(PO4)2, BPO4 and B2O3 verified the synergistic effect of ZB and BPNs@PETA during combustion. In short, the catalytic dehydration carbonization effect of BPNs improved by PETA and ZB, can largely account for the decrease in fire hazard of EP composites. This work offered a new way to simultaneously improve the smoke-suppression ability and flame-retardant efficiency of BPNs.