Microfoamed Strands by 3D Foam Printing.

We report the design, production, and characterization of microfoamed strands by means of a green and sustainable technology that makes use of CO to create ad-hoc innovative bubble morphologies. 3D foam-printing technology has been recently developed; thus, the foaming mechanism in the printer nozzle is not yet fully understood and controlled. We study the effects of the operating parameters of the 3D foam-printing process to control and optimize CO utilization through a maximization of the foaming efficiency. The strands' mechanical properties were measured as a function of the foam density and explained by means of an innovative model that takes into consideration the polymer's crystallinity content. The innovative microfoamed morphologies were produced using a bio-based and compostable polymer as well as polylactic acid and were then blown with CO. The results of the extensive experimental campaigns show insightful maps of the bubble size, density, and crystallinity as a function of the process parameters, i.e., the CO concentration and temperature. A CO content of 15 wt% enables the acquirement of an incredibly low foam density of 40 kg/m and porosities from the macro-scale (100-900 μm) to the micro-scale (1-10 μm), depending on the temperature. The foam crystallinity content varied from 5% (using a low concentration of CO) to 45% (using a high concentration of CO). Indeed, we determined that the crystallinity content changes linearly with the CO concentration. In turn, the foamed strand's elastic modulus is strongly affected by the crystallinity content. Hence, a corrected Egli's equation was proposed to fit the strand mechanical properties as a function of foam density.