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Article

Evaluation of the Zero Shear Viscosity, the D-Content and Processing Conditions as Foam Relevant Parameters for Autoclave Foaming of Standard Polylactide (PLA)

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Department of Polymer Engineering, University Bayreuth, Universitätsstraße 30, 95447 Bayreuth, Germany
2
Bavarian Polymer Institute and Bayreuth Institute of Macromolecular Research, University of Bayreuth, Universitätsstraße 30, 95447 Bayreuth, Germany
3
Institut für Kunststofftechnik, University of Stuttgart, Pfaffenwaldring 32, 70569 Stuttgart, Germany
*
Author to whom correspondence should be addressed.
Materials 2020, 13(6), 1371; https://doi.org/10.3390/ma13061371
Received: 3 March 2020 / Revised: 13 March 2020 / Accepted: 16 March 2020 / Published: 18 March 2020
(This article belongs to the Special Issue Structure, Properties and Applications of Polymeric Foams)

In this comprehensive study, the influence of (i) material specific properties (e.g., molecular weight, zero shear viscosity, D-content) and (ii) process parameters (e.g., saturation temperature, -time, -pressure, and pressure drop rate) on the expansion behavior during the autoclave foaming process were investigated on linear Polylactide (PLA) grades, to identify and evaluate the foam relevant parameters. Its poor rheological behavior is often stated as a drawback of PLA, that limits its foamability. Therefore, nine PLA grades with different melt strength and zero shear viscosity were systematically chosen to identify whether these are the main factors governing the foam expansion and whether there is a critical value for these rheological parameters to be exceeded, to achieve low density foams with fine cells. With pressure drop induced batch foaming experiments, it could be shown that all of the investigated PLA grades could be foamed without the often used chemical modifications, although with different degrees of expansion. Interestingly, PLAs foaming behavior is rather complex and can be influenced by many other factors due to its special nature. A low molecular weight combined with a high ability to crystallize only lead to intermediate density reduction. In contrast, a higher molecular weight (i.e., increased zero shear viscosity) leads to significant increased expandability independent from the D-content. However, the D-content plays a crucial role in terms of foaming temperature and crystallization. Furthermore, the applied process parameters govern foam expansion, cell size and crystallization. View Full-Text
Keywords: polylactide; biofoams; zero shear viscosity; melt strength; batch foaming; pressure drop rate; low density; small cell size polylactide; biofoams; zero shear viscosity; melt strength; batch foaming; pressure drop rate; low density; small cell size
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MDPI and ACS Style

Standau, T.; Long, H.; Murillo Castellón, S.; Brütting, C.; Bonten, C.; Altstädt, V. Evaluation of the Zero Shear Viscosity, the D-Content and Processing Conditions as Foam Relevant Parameters for Autoclave Foaming of Standard Polylactide (PLA). Materials 2020, 13, 1371. https://doi.org/10.3390/ma13061371

AMA Style

Standau T, Long H, Murillo Castellón S, Brütting C, Bonten C, Altstädt V. Evaluation of the Zero Shear Viscosity, the D-Content and Processing Conditions as Foam Relevant Parameters for Autoclave Foaming of Standard Polylactide (PLA). Materials. 2020; 13(6):1371. https://doi.org/10.3390/ma13061371

Chicago/Turabian Style

Standau, Tobias, Huan Long, Svenja Murillo Castellón, Christian Brütting, Christian Bonten, and Volker Altstädt. 2020. "Evaluation of the Zero Shear Viscosity, the D-Content and Processing Conditions as Foam Relevant Parameters for Autoclave Foaming of Standard Polylactide (PLA)" Materials 13, no. 6: 1371. https://doi.org/10.3390/ma13061371

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