Deterioration mechanism on flame retardancy of aliphatic waterborne polyurethane-based hybrid coatings under ultraviolet radiation: Experiment and pyrolysis kinetics

Abstract

Organic-inorganic hybrid intumescent flame retardant coating (IFRC) has been manifested as a promising solution to prevent fire spread of the plywood for indoor decoration. The aliphatic waterborne polyurethane (AWP)-based IFRC is prepared using the silicon-based aerogel, β-cyclodextrin, and nano-ZnO as the functional filler, and its ultraviolet-aging deterioration mechanism on flame retardancy is investigated through microstructure characterizations and pyrolysis kinetic calculation. The results show that the flame-retarding and smoke-suppressing properties of the IFRC gradually deteriorate with the prolonged ultraviolet exposure from 6 to 60 cycles, evidenced by the reduced flame retardancy index of 0.19 (drops from 1.00), the rising fire growth index from 0.87 to 1.45 kW m −2 s −1 , the increased average effective heat of combustion from 3.45 to 5.65 MJ·kg −1 , and the rising total smoke production from 91 to 153 m 2 . Because the ultraviolet radiation favors the chain scission of AWP and cleavage of –HN-CO-, crystallization of Zn 3 (PO 4 ) 2 , ZnP 4 O 11 , and SiP 2 O 7 for the IFRC during burning, leading to the reduced E α of 330–150 ℃ (decreases by 20%) approximately, presenting a reduced water contact angle and a fluffy char. It preliminary seeks the ultraviolet-aging flame-retarding mechanism with quantitative techniques and explores the condensed flame-retarding mechanism further. • Ultraviolet-aging deterioration mechanism of hybrid IFRCs is quantitatively investigated. • The ultraviolet radiation favors the crystallization of Zn 3 (PO 4 ) 2 , ZnP 4 O 11 , and SiP 2 O 7 . • The ultraviolet radiation contributes to the E α of 330–150 ℃ decreased by 20% approximately.