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. 2025 May 5;30(9):2056.
doi: 10.3390/molecules30092056.

Foaming of Bio-Based PLA/PBS/PBAT Ternary Blends with Added Nanohydroxyapatite Using Supercritical CO2: Effect of Operating Strategies on Cell Structure

Pei-Hua Chen  1   2 , Chin-Wen Chen  3 , Tzu-Hsien Chan  3 , Hsin-Ying Lin  3 , Ke-Ling Tuan  3 , Chie-Shaan Su  4 , Jung-Chin Tsai  5 , Feng-Huei Lin  1
Affiliations

Foaming of Bio-Based PLA/PBS/PBAT Ternary Blends with Added Nanohydroxyapatite Using Supercritical CO2: Effect of Operating Strategies on Cell Structure

Pei-Hua Chen et al. Molecules. .

Abstract

This study explored the innovative foaming behavior of a novel biodegradable polymer blend consisting of polylactic acid/poly(butylene succinate)/poly(butylene adipate-co-terephthalate) (PLA/PBS/PBAT) enhanced with nanohydroxyapatite (nHA), using supercritical carbon dioxide (SCCO2) as an environmentally friendly physical foaming agent. The aim was to investigate the effects of various foaming strategies on the resulting cell structure, aiming for potential applications in tissue engineering. Eight foaming strategies were examined, starting with a basic saturation process at high temperature and pressure, followed by rapid decompression to ambient conditions, referred to as the (1T-1P) strategy. Intermediate temperature and pressure variations were introduced before the final decompression to evaluate the impact of operating parameters further. These strategies included intermediate-temperature cooling (2T-1P), intermediate-temperature cooling with rapid intermediate decompression (2T-2P), and intermediate-temperature cooling with gradual intermediate decompression (2T-2P, stepwise ΔP). SEM imaging revealed that the (2T-2P, stepwise ΔP) strategy produced a bimodal cell structure featuring small cells ranging from 105 to 164 μm and large cells between 476 and 889 μm. This study demonstrated that cell size was influenced by the regulation of intermediate pressure reduction and the change in intermediate temperature. The results were interpreted based on classical nucleation theory, the gas solubility principle, and the effect of polymer melt strength. Foaming results of average cell size, cell density, expansion ratio, porosity, and opening cell content are reported. The hydrophilicity of various foamed polymer blends was evaluated by measuring the water contact angle. Typical compressive stress-strain curves obtained using DMA showed a consistent trend reflecting the effect of foam stiffness.

Keywords: PLA/PBS/PBAT/nHA polymer blend; bimodal cell structure; foaming strategy; supercritical CO2.

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Conflict of interest statement

The authors declare that they have no conflicts of interest. The authors declare no competing financial interests.

Figures

Figure 1
Figure 1
Operating conditions and SEM images for foaming strategies: (A) Strategy A with one-step (1T-1P) process, (B) Strategy B with two temperature levels (2T-1P) process, with intermediate cooling to 110 °C, and (C) Strategy C with two temperature levels and two pressure levels (2T-2P) process, with intermediate cooling to 110 °C and intermediate rapid pressure reduction to 100 bar.
Figure 2
Figure 2
Plots of the relative frequencies of cell size distribution results for foaming strategies: (A) Strategy A with one-step (1T-1P) process, (B) Strategy B with two temperature levels (2T-1P) process, with intermediate cooling to 110 °C, and (C) Strategy C with two temperature levels and two pressure levels (2T-2P) process, with intermediate cooling to 110 °C and intermediate rapid pressure reduction to 100 bar.
Figure 3
Figure 3
The schematic diagram for operating conditions of the (2T-2P, stepwise ΔP) foaming strategy.
Figure 4
Figure 4
The SEM images and relative frequencies of cell size distribution results for (2T-2P, stepwise ΔP) foaming strategies: (D) Strategy D with stepwise pressure drop to 120 bar and with a holding time of 3 min, (E) Strategy E with stepwise pressure drop to 100 bar and with a holding time of 5 min, and (F) Strategy F with stepwise pressure drop to 80 bar and with a holding time of 7 min.
Figure 5
Figure 5
Effect of the foaming pressure on the large cell size obtained from foaming strategies D, E, and F.
Figure 6
Figure 6
The SEM images and relative frequencies of cell size distribution results for (2T-2P, stepwise ΔP) foaming strategies: (G) Strategy G with intermediate temperature at 100 °C, (E) Strategy E with intermediate temperature at 110 °C, and (H) Strategy H with intermediate temperature at 120 °C.
Figure 7
Figure 7
Effect of the foaming temperature on the large cell size obtained from (2T-2P, stepwise ΔP) foaming strategies G, E, and H.
Figure 8
Figure 8
The experimental results of (a) cell size, (b) cell density, (c) expansion ratio and porosity, and (d) opening ratio of the foamed polymer blend in this study using various foaming strategies from A to H.
Figure 9
Figure 9
The water contact angle of the foamed polymer blend using foaming strategy E.
Figure 10
Figure 10
The decreasing trend of water contact angle for the foamed polymer blends from (a) foaming strategies D, E, and F; (b) foaming strategies G, E, and H.
Figure 11
Figure 11
The compressive stress–strain curves for the foamed polymer blends from (a) foaming strategies D, E, and F; (b) foaming strategies G, E, and H.
Figure 12
Figure 12
Schematic diagram of the experimental foaming process.
See this image and copyright information in PMC

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