DSC Investigations on Crystallinity - METTLER TOLEDO

DSC Investigations on Crystallinity

Purpose

To show the influence of crystallinity on DSC curves using different types of chloroprene as an example.

 

Sample

Unvulcanized CR types: CR 110, CR 112, and CR 210 (Bayer AG)

 

Conditions

Measuring Cell: DSC822e with IntraCooler cooling option

Pan: Aluminum 40 µl with pierced lid

Sample preparation: Cubes of approx. 15 mg were cut from the starting material

DSC measurement: Heating from -60°C  to 100°C at 10 K/min

Atmosphere: Nitrogen, 50 ml/min

 

Evaluation

All the CR samples show a melting peak with a peak maximum at about 42 °C. No information can be gained on the relative perfection and size of the crystallites from the small differences in the peak temperature range. However the large difference in peak areas shows that the proportion of crystallites is very different. The evaluation of the peak area gave the following results:


For CR 210, both the clearly defined glass transition and the relatively small peak area of 6 J/g indicate that the degree of crystallinity is low. A comparison of the peak areas, however, shows that the degree of crystallinity of CR 210 is about 86 times greater than that of CR 110, and that of CR 112 about 2.5 times greater than that of CR 110

 

Interpretation

All three chloroprene curves show a glass transition at approx. 40 °C and an endothermic peak at about 40 °C that is due to the melting of the polymer crystallites. The ability of the CR types to crystallize differs because the structure of the polymer chains are different. This is why the peak areas are different. CR 210 has a relatively large tendency to crystallize. The relatively small melting peak of CR 112 shows that the tendency of this material to crystallize is appreciably less. Hardly any crystallites at all could be detected in CR 110. A melting peak was only visible after 50-fold scale expansion (see upper left diagram).

The absolute degree of crystallinity cannot be determined without knowledge of the specific enthalpy of fusion of the 100% crystalline material. This is, however, not needed for comparative measurements. 

 

Conclusion

An evaluation of the peak area of melting peaks yields information on the degree of crystallinity of elastomers. 

 

DSC Investigations on Crystallinity | Thermal Analysis Handbook No.HB403 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 1.