The Use of TOPEM to Analyze the First Heating Run of Biodegradable Disposable Cups - METTLER TOLEDO

The Use of TOPEM to Analyze the First Heating Run of Biodegradable Disposable Cups

TOPEM® measurements of semicrystalline polylactide (PLA) show how overlapping effects in the first heating run can be separated and interpreted. This allows the correct enthalpy of melting of the original sample to be determined.


Introduction

Several different thermal processes occur in the first DSC heating run of a material such as reorganization, the relaxation of internal stress, and changes in the thermal contact between the sample and crucible.

Conventional DSC curves are sometimes difficult to interpret if these processes produce effects that overlap thermal events in the sample such as the glass transition, cold crystallization, and melting. A second heating run after controlled cooling does not always help you to understand the effects observed in the first heating curve.

The problem can be solved by performing temperature-modulated measurements using TOPEM®. This technique allows non-reversing effects such as reorganization and stress relaxation to be separated from reversing effects such as the glass transition.

The small temperature modulation hardly influences non-reversing effects, but with reversing effects gives rise to a corresponding modulation of the heat flow.

This work describes the analysis of biodegradable polylactide (PLA) disposable cups used for serving cold drinks [1]. The cups were manufactured using a deep drawing process at temperatures around the glass transition. In the production process, the PLA material experiences high and very localized cooling rates. The article discusses the conclusions can be drawn about the material from the first heating run using TOPEM®.


Experimental details
Sample Preparation

The samples were taken from the middle part of the wall of the cup where the material is stretched and is least thick. Square samples of 3 to 4 mg were cut from the wall and measured in 40-μL standard aluminum crucibles...



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Conclusions

TOPEM® allows us to understand the effects measured in the first heating run and permits conclusions to be drawn about the morphology of the sample. Contrary to the initial results obtained from the evaluation of the first heating run using conventional DSC, the degree of crystallinity turns out to be significantly smaller.

Cold crystallization begins immediately at the glass transition. The mobility of the polymer chains increases and mechanical stresses produced in the deep drawing production process of the cup decrease.

The sample crystallizes during the heating run, reorganizes and melts. The total heat flow curve, which shows the behavior of the sample at the underlying heating rate von 2 K / min, agrees very well with a conventional DSC measurement at 2 K / min (not shown).



The Use of TOPEM® to Analyze the First Heating Run of Biodegradable Disposable Cups | Thermal Analysis Application No. UC384 | Application published in METTLER TOLEDO Thermal Analysis UserCom 38