1.Brief introduction Due to influence of thermal history, various properties of polymers will change, especially thermal properties of crystalline polymers. Thermal history of polymer is affected by various factors such as preparation process, storage conditions, and usage environment. Usually, thermal history of materials is studied by thermal analysis and viscoelasticity measurement. This paper introduces a case, in which PET has different viscoelastic properties due to different thermal history. 2. Experi ment The sample used this time was an extruded 0.5mm-thickness PET sheet. First, the sample was heated up for the first time until the cold crystallization process was completed, then cooled down slowly, and then heated up for the second time until the sample was about to but did not melt. Instruments: SDM 5600H Rheological workstation and DMS 200 dynamic thermomechanical instrument. Deformation mode: stretching. Measurement frequency: 0.5, 1, 2, 5, 10 ...
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