Discussion of the Conversion Curve
Purpose
To show how the conversion curve can be obtained from the reaction peak.
Sample
Sample Unvulcanized NBR with 50% polymer content
Conditions
Measuring cell: DSC822e with IntraCooler cooling option
Pan: Aluminum 40 Pl, with pierced lid Sample preparation: Cube weighing 27.4 mg cut from the starting material immediately before the measurement.
DSC measurement: From 60 °C to 220 °C at 10 K/min.
Atmosphere: Nitrogen, 50 ml/min
The conversion was calculated as a function of temperature from the reaction peak of the NBR rubber curve (from Section 3.1.3. Comparison of DSC measurements of vulcanization reaction).
Evaluation
The evaluation was performed using the DSC Conversion evaluation program.
The percent conversion, α(T), is calculated from the heat flow curve Φ(T)
where T0 is the lower temperature limit of the peak evaluation and T1 is the upper temperature limit. The partial area of the peak from the temperature T0 to the actual temperature is ΔHpart. The total area of the peak is ΔHtot.
Interpretation
The course of the reaction can be estimated from the conversion curve. The reaction begins relatively slowly and reaches a maximum reaction rate between 150 °C and 160 °C.
The reaction rates in the individual stages of the reaction can be selectively influenced by varying the content of vulcanizing agents, accelerators, retarders and activators in the vulcanization system.
Conclusions
The cross-linking system can be optimized with the aid of conversion curves. The curves can also be used for kinetic analysis (e.g. with Model Free Kinetics).
Discussion of the Conversion Curve | Thermal Analysis Handbook No.HB408 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 1
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