Synthesis of Hybrid Cellulose Acetate Membranes and Application of the Flynn-Wall-Ozawa Isoconversional Method

Abstract

The synthesis of hybrid materials is a promising alternative in the production of materials with optimized properties. In this context, the classic cellulose acetate membranes are being modified. It is worth mentioning that knowing the thermal stability of cellulosic materials is an essential factor in their use since organic polymers have low thermal resistance, limiting their applicability. This work evaluates the synthesis and the study of the thermal degradation kinetics of hybrid cellulose acetate membranes. The synthesis was carried out using the sol-gel process, with the phase inversion technique, through the reaction of cellulose acetate with organometallic precursors: tetraethyl orthosilicate, TEOS; 3-aminopropyl triethoxysilane, APTES, and titanium isopropoxide, TiPOT, in fixed composition. Thermal characterization was performed with thermogravimetric analysis at different heating rates under a nitrogen atmosphere. The kinetic parameter of thermal decomposition activation energy, Ea, was estimated with the isoconversional method proposed by Flynn-Wall-Ozawa (FWO). The degradation kinetics shows that the change in the chemical composition of the samples directly interferes with their thermal properties. Thus, it is possible to observe that the activation energy found for the reference sample, AC-Pure, in the first and second batches was 233.5 and 219.05 kJ/mol, respectively. The composition modification results in an increase in activation energy, in which sample B0//100-30 recorded 310.31 and 226.05 kJ/mol in the first and second batches; and sample B100//0-30 reached 452.73 and 424.74 kJ/mol. It is clear that the increase in the thermal resistance of the samples is associated with the change in the chemical composition and must be attributed to the increase in the TEOS content in the composition due to the formation and increase in the presence of siloxane groups in the material.