Thermo Gravimetric Analysis (TGA) is commonly used to determine the volatile, polymeric and filler components of rubber materials. Tests conducted with various copolymers, terpolymers and base resistant polymers under nitrogen purge showed that polymer degradation was complete by 6000C. However, when such polymers were incorporated into a typical rubber matrix a thermally resistant residue was seen to form at 600 9C. This resulted in under determination of the elastomer content as well as inaccuracies in filler determination.
Given the multivariate complexity of the rubber compound it was decided to first investigate the thermal degradation phenomenon using a (simple) mixture of polymer based on Vinylidene fluoride/Hexafluoropropylene, N990 and (< 1 wt %) carnauba wax. The error associated with polymer determination was 2.0 wt. %. Using a design of experiment methodology the effects of metal oxides /hydroxides that are commonly used in FKM rubbers were investigated. The error increased to 4 wt.% in the individual and combined presence of MgO and Ca(OH)2. Fe2O3 and ZnO were seen to have marginal effects (1.0 wt.%). The effect of TiO2 was most dramatic. At 3.0 wt. % TiO2 the fluoroelastomer content was underestimated by 16.0 wt.%. TiO2 caused a lowering of the degradation onset temperature and this effect increased with increases in concentration.

The investigations established that non isothermal oxidizing conditions (air purge) can be used to eliminate or significantly minimize the formation of residual fluoro organics. For the materials tested the temperature requirements did not significantly overlap with temperature requirements for carbon black oxidation, hence it was possible to determine polymer and filler component from a single test. This technique did not work for materials containing Fe2O3, In this case the better condition was to increase test temperatures to over 9000C in nitrogen. Generally an initial analysis of the rubber via FTIR and WDXRF were useful for determining test conditions for thermal analysis.

A combination of FTIR, XPS and modulated TGA were used to understand the mechanism(s) that affect the thermal degradation of polymer mixtures containing TiO2.