Thermochemical Approach for Screening of Alternative Metal Oxides as a Flame Retardant of Modacrylic Fiber

In the view of the exploring novel flame retardants for polymers, modacrylic fibers, which consist of acrylonitrile and vinylidene dichloride, containing metal oxide have been investigated by thermogravimetric–mass spectrometry (TG-MS) analysis. It was found that, among the examined oxides, germanium and antimony oxides formed the corresponding volatile chlorides through the reactions of oxides with hydrogen chloride formed during thermal decomposition of the polymer. The results have been discussed in the framework of thermochemistry. Based on the equilibrium calculation of the polymer–oxide mixture, the predominance diagrams of the M-O-Cl systems (M = Sb and Ge) show that the chlorides are the most stable phases at 573 K, at which temperature the major decomposition of the polymer starts. These results suggest that GeO2 would be a possible candidate of a flame retardant for chlorinated polymers. However, combustion experiments revealed an insufficient performance of the oxide. The inductively coupled plasma with atomic emission spectroscopy (ICP-AES) analysis showed the reactivity of GeO2 for HCl was inferior to that of Sb2O3, and X-ray fluorescence spectrometer (XRF) analysis of the solid thermal decomposition products showed that the evaporation of germanium was less intense than that of the conventional antimony system. This result is presumably due to the smaller rate of the chlorination of GeO2 than that of Sb2O3.

Solid Pyrolysis Modelling by a Lagrangian and Dimensionless Approach--Application to Cellulose Fast Pyrolysis

Many kinds of solids (e.g., biomass, thermoplastic and coal) thermally decompose according to similar types of kinetic pathways. They usually include a first step giving rise to more or less stable solid or liquid species followed by competitive reactions with formation of the final products (solids, vapours, and/or gases). In order to be extended to several types of solids, the present pyrolysis model relies on an original dimensionless Lagrangian approach. Mathematical equations of mass and heat balances are written in the assumptions that non-volatiles products form distinct layers which are separated by each other by moving interfaces that propagate towards the inner parts of the sample. The conditions required to apply this Lagrangian approach to solid thermal decomposition are discussed. The time evolution of pyrolysis products and sample internal temperature profiles are obtained by numerical solving of equations written in a reduced form. The first results of simulations performed in a large range of dimensionless parameters values (thermal Thiele, Biot and thermicity criteria) are reported. It is pointed out that variations of reduced masses as a function of reduced time significantly depend on operating conditions (particularly thermal Thiele and Biot numbers). The results of the model are finally compared to experimental data reported in the literature for cellulose fast pyrolysis. The agreement is quite good considering the uncertainties with which the physicochemical parameters are known from the literature.