IsoStep Measurements of SBR

Purpose

The IsoStep™ method can be used to separate crystallization from melting processes. This is shown by measuring a sample of emulsion polymerized SBR containing an oil.

Sample

Unvulcanized SBR (Krylene 1721) 

Conditions

Measuring cell: DSC822^e with IntraCooler cooling option

Pan: Aluminum 20 µl Sample preparation: Cube of approx. 4 mg cut from the starting material and cooled rapidly to the start temperature.

DMA measurement: Heating from –65 °C to 75 °C with isothermal segments of 60 s. In the heating segments the temperature was increased by 4 K at 4 K/min. Sapphire was used for calibration.  

Atmosphere: Air, stationary atmosphere, no flow

Evaluation

The measured curves were evaluated with the IsoStep™ software. This generates three new curves, namely the specific heat capacity curve, the reversing curve and the non-reversing curve. The reversing curve corresponds to the heat capacity curve converted into heat flow units. Both curves are calculated from the heating segments. The non-reversing curve allows information to be obtained about the kinetic content of the measurement. It is evaluated from the isothermal segments and is displayed in heat flow units.

Interpretation

In the SBR sample measured, the glass transition of the polymer and the crystallizations and melting processes of the mineral oil overlap to some extent. The conventional DSC curve is shown in Section 4.4.4. Transitions of low molecular weight components in SBR.

Both the specific heat capacity and reversing curves clearly show the SBR glass transition. The glass transition temperature is –36.5 °C and the step height, Δc_p, is 0.41 J/gK. The crystallization of the oil cannot be observed in the reversing curve. Under the experimental conditions used, the melting process is measured as a peak at about 10 °C. The enthalpy of fusion is found to be –1.80 J/gK. The crystallization peak can be seen at about 30 °C in the non-reversing curve. The peak area yields a value of 1.70 J/gK for the enthalpy of crystallization. The values agree well with the results obtained from conventional DSC and ADSC (see Sections 3.1.4 and 4.4.4. Transitions of low molecular weight components in SBR). 

_{IsoStep Measurements of SBR | Thermal Analysis Application No. HB466 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 2}