Development of Poly (Lactide Acid) Foams with Thermally Expandable Microspheres.

Ákos Kmetty,Katalin Litauszki

doi:10.3390/polym12020463

Ákos Kmetty, Katalin Litauszki

Open Access

https://doi.org/10.3390/polym12020463

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Journal: Polymers	Publication Date: Feb 17, 2020
Citations: 41	License type: CC BY 4.0

Affiliation: Budapest University of Technology and Economics

Abstract

This study presents the investigation of different content of thermally expandable microsphere (EMS) type of a physical blowing agent added to polylactic acid (PLA). The effects of the different doses of EMS, processing temperatures, and d-lactide content of the polylactic acid were analyzed for foam properties and structures. We characterized the different PLAs and the physical blowing agent with different testing methods (gel permeation chromatography, rotational rheometry, isothermal thermogravimetric analysis, and thermomechanical analysis). The amounts of the foaming agent were 0.5, 1, 2, 4, 8 wt%, and processing temperatures were 190 °C, 210 °C, and 230 °C. The foam structures were produced by twin-screw extrusion. We used scanning electron microscopy to examine the cell structure of the foams produced, and carried out morphological and mechanical tests as well. The result of extrusion foaming of PLA using different amounts of EMS shows that an exponentially decreasing tendency of density reduction can be achieved, described by the following equation, ρ(x (R2 = 0.947) at 190 °C. With increasing processing temperature, density decreases at a lower rate, due to the effect that the microspheres are unable to hold the pentane gas within the polymer shell structure. The d-lactide content of the PLAs does not have a significant effect on the density of the produced foam structures.

Highlights

The foaming of polymers is possible mechanically, physically, and chemically [1,2,3]
The foam density achieved with the use of chemical foaming agents (CBA) during extrusion is higher than 0.5 g/cm3
We used thermally expandable microsphere (EMS) physical blowing agent (PBA) with different amounts (0.5, 1, 2, 4, 8 wt%) for the extrusion foaming of polylactic acid (PLA)

Summary

Introduction

The foaming of polymers is possible mechanically (air dispersion), physically (gas injection, bead foaming, expandable microspheres), and chemically (foaming agents that generate effective gases through thermal decomposition, e.g., in the case of during polyurethane foaming) [1,2,3]. Due to PLA’s low melt elasticity [12], melt strength [13], and slow crystallization kinetics [14], PLA extrusion foaming is challenging and has its limitations. The foam density achieved with the use of chemical foaming agents (CBA) during extrusion is higher than 0.5 g/cm. For extrusion foaming of PLA with a physical blowing agent, density reduction can be made most successfully with CO2 [15]. The resulting density range is lower than 0.1 g/cm , for this, both the PLA raw material (e.g., with a chain-extender [16], a nucleating agent [17], or by post-production heat-treatment [18]) and the processing equipment need to be modified [19]

Objectives

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Results