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. 2024 Jan 11;29(2):363.
doi: 10.3390/molecules29020363.

The Application of Box-Behnken Design for Investigating the Supercritical CO2 Foaming Process: A Case Study of Thermoplastic Polyurethane 85A

Salal Hasan Khudaida  1 , Shih-Kuo Yen  1 , Chie-Shaan Su  1
Affiliations

The Application of Box-Behnken Design for Investigating the Supercritical CO2 Foaming Process: A Case Study of Thermoplastic Polyurethane 85A

Salal Hasan Khudaida et al. Molecules. .

Abstract

Thermoplastic polyurethane (TPU) is a versatile polymer with unique characteristics such as flexibility, rigidity, elasticity, and adjustable properties by controlling its soft and hard segments. To properly design and understand the TPU foaming process through supercritical CO2, a design of experiments approach, the Box-Behnken design (BBD) was adopted using commercial TPU 85A as the model compound. The effect of saturation pressure, saturation temperature, and immersion time on the mean pore size and expansion ratio were investigated. The design space for the production of TPU foam was shown, and the significance of process parameters was confirmed using the analysis of variance (ANOVA). In addition, extrapolation foaming experiments were designed and validated the feasibility of the response surface model developed via BBD. It was found that the pore size of TPU 85A foam could be controlled within 13 to 60 μm, and a stable expansion ratio could be designed up to six.

Keywords: Box–Behnken design; supercritical CO2 foaming; thermoplastic polyurethane.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Comparison of the pore morphology of TPU foam obtained from (a) Exp. A1, (b) Exp. A2, (c) Exp. A3, (d) Exp. A4, (e) Exp. A5, (f) Exp. A6, (g) Exp. A7, (h) Exp. A8, (i) Exp. A9, (j) Exp. A10, (k) Exp. A11, and (l) Exp. A12.
Figure 2
Figure 2
SEM images for TPU foam obtained from (a) Exp. C1 and (b) Exp. C2.
Figure 3
Figure 3
SEM images for TPU foam obtained from (a) Exp. B9, (b) Exp. B4, (c) Exp. B6, (d) Exp. B10, (e) Exp. B11, (f) Exp. B15, (g) Exp. B7, and (h) Exp. B13.
Figure 3
Figure 3
SEM images for TPU foam obtained from (a) Exp. B9, (b) Exp. B4, (c) Exp. B6, (d) Exp. B10, (e) Exp. B11, (f) Exp. B15, (g) Exp. B7, and (h) Exp. B13.
Figure 4
Figure 4
Effect of saturation temperature on the expansion ratio of TPU foam at saturation pressure of 100 bar and immersion time of 4 h.
Figure 5
Figure 5
Effect of saturation pressure on the mean pore size of TPU foam at a saturation temperature of 120 °C and immersion time of 4 h.
Figure 6
Figure 6
Effect of saturation temperature on the mean pore size of TPU foam at saturation pressure of 100 bar and immersion time of 4 h.
Figure 7
Figure 7
Graphical presentation of the interaction effect of saturation pressure and saturation temperature (AB) on the mean pore size of TPU foam.
Figure 8
Figure 8
TGA results for unprocessed TPU 85A.
Figure 9
Figure 9
DSC thermograms for unprocessed TPU 85A.
Figure 10
Figure 10
Experimental apparatus of supercritical CO2 foaming (1: CO2 cylinder, 2: syringe pump system, 3: thermostatic oil bath, 4: circulating chiller, V: high-pressure vessel, F: filter, A: two-way needle valve, B: three-way ball valve).
See this image and copyright information in PMC

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