Mechanism and kinetics of thermal degradation of insulating materials developed from cellulose fiber and fire retardants

Abstract

The mechanism and kinetics of thermal degradation of materials developed from cellulose fiber and synergetic fire retardant or expandable graphite have been investigated using thermogravimetric analysis. The model-free methods such as Kissinger-Akahira-Sunose (KAS), Friedman, and Flynn-Wall-Ozawa (FWO) were applied to measure apparent activation energy (E a). The increased E a indicated a greater thermal stability because of the formation of a thermally stable char, and the decreased E a after the increasing region related to the catalytic reaction of the fire retardants, which revealed that the pyrolysis of fire retardant-containing cellulosic materials through more complex and multi-step kinetics. The Friedman method can be considered as the best method to evaluate the E a of fire-retarded cellulose thermal insulation compared with the KAS and FWO methods. A master-plots method such as the Criado method was used to determine the possible degradation mechanisms. The degradation of cellulose thermal insulation without a fire retardant is governed by a D3 diffusion process when the conversion value is below 0.6, but the materials containing synergetic fire retardant and expandable graphite fire retardant may have a complicated reaction mechanism that fits several proposed theoretical models in different conversion ranges. Gases released during the thermal degradation were identified by pyrolysis-gas chromatography/mass spectrometry. Fire retardants could catalyze the dehydration of cellulosic thermal insulating materials at a lower temperature and facilitate the generation of furfural and levoglucosenone, thus promoting the formation of char. These results provide useful information to understand the pyrolysis and fire retardancy mechanism of fire-retarded cellulose thermal insulation. Keywords Thermal degradation Á Thermal kinetics Á Fire retardant Á Cellulose fiber Á Thermal insulating APP Ammonium polyphosphate ATH Aluminum hydroxide E a Apparent activation energy (kJ mol-1) EGIM Expandable graphite fire-retardant insulating material FWO Flynn-Wall-Ozawa KAS Kissinger-Akahira-Sunose Py-GC/ MS Pyrolysis-gas chromatography-mass spectroscopy R Gas constant (8.314 J K-1 mol-1) SYIM Synergetic fire retardant insulating material T Absolute temperature (K) TG Thermogravimetry

Expandable Graphite as a Fire Retardant for Cellulosic Materials—A Review

“…Similar tests were performed by Zheng et al [27], with a temperature increase of 5 °C/min. The course of EG thermal decomposition is represented by the thermogravimetric (TG) (Figure 4) and derivative thermogravimetric (DTG) (Figure 5) curves.…”

“…The presence of expandable graphite (EG) greatly improves the char formation rate and quality in FR systems. Based on this literature review, it can be assumed that the incrustation of cellulose with expandable graphite may be of particular importance in the context of the thermal resistance of its amorphous areas [27].…”

“…Moreover, during the char formation, void spaces are formed within char, allowing airflow, and this cool down the fire environment (atmosphere), increasing the time to ignition of protected cellulosic material. In general, the kinetics of fire-protected cellulosic materials are still under investigation [27]. The effectiveness of these flame retardants depends on the heat-induced decomposition of the organic components and the creation of a char layer that insulates the substrate from the heat source.…”

Date Palm Surface Fibers for Green Thermal Insulation

“…This type of analysis is helpful for understanding the thermal stability of insulation materials and establishing their aging and fire-retardant characteristics. Zheng et al, [51] produced a thermal insulation material using cellulose pulp, whose fire retardancy was developed using an intumescent fire retardant, and its activation energy 𝐸𝐸 𝑎𝑎 increased due to the formation of thermally stable char. Later, Lie et al, [52] conducted a kinetic analysis of thermal insulator waste in the form of extruded polystyrene to learn more about its fire retardancy and recycling potential.…”

Foam forming of fiber products: a review

“…One challenge is that poor reaction-to-fire properties of foamformed materials need to be improved to meet the fire safety regulations. Zheng et al [160][161][162] showed that foamed cellulose insulation panels with commercial fire retardants (20% expandable graphite or 25% synergetic) passed fire class E according to the standard EN 13501-1. They also tested if coating of foam-formed materials would improve fire retardancy.…”