Company: GÖTTFERT
MFI and moisture
Influence of the moisture content of PET in the melt index test
Polyester PET is strongly influenced by the moisture content during processing and even more so during testing. One of the most common tests is the melt flow index. Here, moisture can lead to a deterioration of the material, which becomes visible through an increase in the melt flow index.
In general, the slope of the moisture dependence increases with increasing moisture content. Incorrect or improper drying leads to a higher measurement uncertainty, as the result is increasingly dependent on changes in humidity.
The correct values for temperature and time can be found in the manufacturer’s data sheet. In the case of PA and PET in particular, drying at excessively high temperatures can lead to recondensation of the materials, resulting in a higher molecular weight or a lower melt index than the original sample.
After drying, the residual moisture should be checked with a suitable measuring device (hygrometry), especially if the data is to be used for comparative measurements.
For PA and PET, the residual moisture must be less than 0.035 %.
A vacuum drying oven achieves very good drying results by forcing the moisture molecules to the surface at a low temperature where they evaporate.
Summary
- For certain samples, the residual moisture has a major influence on the test result
- Correct drying is of great importance here. Vacuum drying ovens have proven to be suitable.
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Rheological testing equipment since 1962
GÖTTFERT Werkstoff-Prüfmaschinen GmbH was founded in 1962 by Prof. Dr. Otto Göttfert. In the second generation, his son Dr Axel Göttfert took over as sole managing director.
On the world market, the medium-sized company is known as one of the leading companies in the niche area of rheological testing equipment. The innovative rheological systems are used worldwide in laboratories as well as in production.
To be closer to many customers, a subsidiary was opened in Rock Hill, South Carolina, USA, in 1989. In 2011, GOETTFERT (China) Limited was founded with headquarters in Beijing and Shanghai.
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