Determination of Weak Glass Transitions in Semicrystalline Polymers - METTLER TOLEDO

Determination of Weak Glass Transitions in Semicrystalline Polymers

The glass transition of semicrystalline polymers is often weak and difficult to measure by DSC. In this article, we show how a glass transition step of less than 0.1 J/g·K can be reproducibly determined using the DSC. The sample investigated was isotactic polypropylene (iPP) with a degree of crystallinity of 50%.

 

Introduction

Semicrystalline polymers have crystalline and amorphous regions. The glass transition takes place only in the amorphous region. The glass transition step of semicrystalline polymers is therefore appreciably smaller than that of 100% amorphous polymers.

In practice, this makes it more difficult to determine the glass transition of highly crystalline polymers. Whether a weak glass transition step can still be measured and evaluated by DSC also depends on the width of the glass transition. This becomes larger with increasing crystallinity.

Normally, glass transitions in polymers are measured at heating rates of 10 K/min using samples of about 10 mg. In the following experiments, iPP was employed as a test substance. The results show that the DSC 1 is capable of measuring weak glass transitions even with small samples weighing less than 5 mg. This improves the reproducibility of the analysis.

Conclusions

The DSC 1 can determine the glass transition steps and glass transition temperatures even for glass transitions with a Δcp of the order of 0.1 J/g·K and smaller. This was shown using iPP as an example with sample weights of less than 5 mg.

 

Determination of Weak Glass Transitions in Semicrystalline Polymers | Thermal Analysis Application No. UC 432 | Application published in METTLER TOLEDO Thermal Analysis UserCom 43