PVAC, Glass Transition Temperature and Plasticizer Content

Sample

Polyvinylacetate films with 0 to 12.5% plasticizer

Conditions

Measuring cells: DSC821^e with liquid nitrogen cooling

Pan: Aluminum standard 40 µl, hermetically sealed

Sample preparation: Punched disks of approx. 5-mm diameter

DSC measurement: Heating from 25 °C to 100 °C at 10 K/min to eliminate thermal history. Uncontrolled fast cooling to -100 °C.

                                    Actual measurement from -100 °C to 80 °C at 10 K/min

Atmosphere: Nitrogen, 50 cm³/min

Interpretation

For clarity, the DSC curves show only the regions in which the glass transition occurs. As expected, the presence of the plasticizer lowers the T_g. The glass transitions become broader with increasing plasticizer content

The measured value of T_g of the PVAC without plasticizer of 18.3 °C does not agree with the value usually reported of 30 °C. It is known that the T_g of PVAC depends strongly on the moisture content. A moisture content of 1% lowers the T_g by about 7 K. Moisture is therefore an efficient plasticizer, but it is volatile. Hence with some materials it is possible for water, absorbed as moisture from the air, to act as a plasticizer. Solvent residues originating from the manufacture or processing of the material can also behave as (unwelcome) plasticizers.

Conclusions

The influence of plasticizers on the glass transition of a polymer can be determined by performing a few simple DSC measurements with samples of different plasticizer content. Care should be taken to eliminate interferences due to different thermal history and the presence of moisture.

_{PVAC, glass transition temperature and plasticizer content | Thermal Analysis Application No. HB255 | Application published in METTLER TOLEDO TA Application Handbook Thermoplastics}