Cu-Modified ZSM Zeolite Has Synergistic Flame Retardance, Smoke Suppression, and Catalytic Conversion Effects on Pulp Fiber After Ammonium Polyphosphate Flame-Retardant Treatment

After the flame-retardant treatment, a pulp fiber has the problems of high smoke production and high smoke toxicity. To solve the above problems, a ZSM zeolite after copper modification was added to the ammonium polyphosphate (APP) flame-retardant pulp, and the effects of the modified ZSM zeolite on flame retardance, smoke suppression, and toxicity reduction were investigated. The content of Cu in the ZSM zeolite modified by ion exchange and calcination (500Cu-Z) was 1.73%, and its existing forms were free Cu2+, combined Cu2+, and Cu+. After modification, the strength of the weak and medium strong acids in the zeolite decreased, and the total acid content decreased by 10.90%. However, in the high-temperature range, a new strong acid site appeared. Compared with the APP-treated pulp fiber, the addition of 500Cu-Z could reduce the carbonization length, and the amount of smoke released decreased by 63.28% at the same time. The analysis of the gas composition indicates that the 500Cu-Z zeolite can reduce the relative concentration of CO to decrease the toxicity of smoke in the combustion process. A stronger flame-retardant layer was formed on the surface of the pulp fiber after adding zeolite and APP. There were chemical bonds such as P═O, C═C, C–O, Si–O–Si on the surface of the flame-retardant layer of 500Cu-Z/A/Pulp2.0. The 500Cu-Z zeolite had a synergistic flame-retardant effect with APP on the pulp fiber. After combustion, it was shown that a phosphoric acid layer existed on the surface of the fiber. The addition of zeolites can form a mosaic mechanism between the zeolite and the phosphoric acid layer to strengthen the flame-retardant layer. To conclude, the flame-retardant layer may reduce the generation of smoke and 500Cu-Z zeolites in layer catalytic CO to CO2 in smoke to reduce toxicity.