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. 2024 May 29;14(1):12395.
doi: 10.1038/s41598-024-62958-4.

Tuning pore size and density of rigid polylactic acid foams through thermally induced phase separation and optimization using response surface methodology

Morteza Ghorbandoust  1 , Mohammad Fasihi  2 , Reza Norouzbeigi  1
Affiliations

Tuning pore size and density of rigid polylactic acid foams through thermally induced phase separation and optimization using response surface methodology

Morteza Ghorbandoust et al. Sci Rep. .

Abstract

Rigid polylactic acid (PLA) foams fabricated via thermally induced phase separation (TIPS) utilizing a ternary solution of PLA, Tetrahydrofuran (THF), and water. The PLA gels were stabilized mechanically by the substituting of the THF/water solvent mixture with ethanol as non-solvent and subsequently vacuum dried. A comprehensive characterization of PLA foams was achieved by Scanning Electron Microscopy (SEM), X-ray Diffractometry (XRD) and Brunauer-Emmett-Teller (BET) analyses. The BET area obtained in the PLA foam is up to 18.76 m2/g. The Response Surface Methodology (RSM) was utilized to assess the impacts of four independent variables (polymer concentration, solvent composition, quench temperature, and aging time) on the pore size and density of PLA foam. The experimental findings demonstrated that the fabrication parameters could be fine-tuned to govern the morphology of the pores, comprising their size and density. The optimal values of parameters for cell size were identified by RSM to be 8.96 (wt%), 91.60 (w/w), 5.50 °C, and 3.86 h for the optimum cell size of 37.96 µm (37.78 by Genetic Algorithm). Optimum density by RSM 88.88 mgr/cm3 (88.38 mgr/cm3 by Genetic Algorithm) was obtained at 5.00 (wt%), 89.33 (w/w), 14.40 °C and 2.65 h.

Keywords: Foam; Morphology; Phase separation; Polylactic acid; Response surface.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Ternary phase diagram of a polymer/solvent/non-solvent system.
Figure 2
Figure 2
Illustration of the three coarsening mechanisms, (a) coalescence, (b) Ostwald ripening, and (c) hydrodynamic growth.
Figure 3
Figure 3
PLA foam fabrication steps, (a) polymer solution, (b) quench and gelatin, and (c) foam obtained after vacuum drying.
Figure 4
Figure 4
Cross-sections of prepared foams after gold coating.
Figure 5
Figure 5
SEM images of fractured surface of foams: (a) Run 5, (b) Run 9, (c) Run 10, (d) Run 11, (e) Run 12, (f) Run 15, (g) Run 18, (h) Run 24, (i) Run 26, (j) Run 28, (k) Run 29, (l) Run 30.
Figure 6
Figure 6
Cell size distribution of PLA foams: (a) Run 5, (b) Run 9, (c) Run 10, (d) Run 11, (e) Run 12, (f) Run 15, (g) Run 18, (h) Run 24, (i) Run 26, (j) Run 28, (k) Run 29, (l) Run 30.
Figure 7
Figure 7
Plots of (a, c) response surface and (b, d) contour for the effect of PLA concentration and aging time on cell size and density at constant THF/water ratio and quenching temperature in central point.
Figure 8
Figure 8
Plots of (a, c) response surface and (b, d) contour for the effect of quenching temperature and THF/water ratio on cell size and density at constant PLA concentration and aging time in central point.
Figure 9
Figure 9
XRD diffractograms of polylactic acid foam (a) THF/water ratio 86/14 (w/w) and (b) THF/water ratio 90/10 (w/w).
Figure 10
Figure 10
Different residual plots for testing the adequacy of the proposed model (a) cell size and (b) density.
Figure 11
Figure 11
Interaction plot of the (a) cell size and (b) density.
Figure 12
Figure 12
(a) Optimization plot for cell size and (b) Variation of fitness function versus generation.
Figure 13
Figure 13
(a) Optimization plot for density and (b) Variation of fitness function versus generation.
Figure 14
Figure 14
Water absorption capacity of the PLA foams.
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