Geopolymerization of halloysite clay nanotubes mixed with hydroxypropyl cellulose for development of composite films with flame resistance properties

The growing demand for sustainable and high-performant materials has driven interest in geopolymers, which are known for their outstanding thermal stability and fire resistance. This study focuses on the conversion of hydroxypropyl cellulose/halloysite composite film (containing 70 wt% of clay nanofiller) to geopolymer with flame retardant action and high thermal stability. The effects of the geopolymerization on the structural, mechanical and thermal properties of the film have been investigated. The geopolymeric material possesses superior tensile resistance and higher thermal stability as compared with those of the composite film. According to non-isothermal thermogravimetric analysis, the presence of clay nanotubes and their consequent geopolymerization reduce the activation energy of hydroxypropyl cellulose degradation, while wettability experiments highlighted that both composite film and geopolymer are hydrophilic materials as evidenced by their initial water contact angle (ca.15°). Remarkably, the composite geopolymer immediately stops the flame propagation due to the presence of heat barrier layers. On the other hand, the addition of halloysite within hydroxypropyl cellulose film generates a reduction of the burning rate (from 0.5 to 0.08 cm 2 /s) evidencing that clay nanotubes (before geopolymerization) act as flame retardant fillers. This work demonstrates that the combination of hydroxylpropylcellulose and halloysite clay nanotubes is promising to obtain sustainable geopolymeric materials with specific functionalities, such as fire resistance, useful for various technological and engineering applications.