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. 2025 Apr 29;18(9):2006.
doi: 10.3390/ma18092006.

Synthesis and Characterization of Soy Hull Biochar-Based Flexible Polyurethane Foam Composites

Kavya Ganesan  1 , Bethany Guin  1 , Elijah Wilbanks  1 , James Sternberg  1
Affiliations

Synthesis and Characterization of Soy Hull Biochar-Based Flexible Polyurethane Foam Composites

Kavya Ganesan et al. Materials (Basel). .

Abstract

Flexible polyurethane foams are a diverse class of materials encompassing furniture, packaging, automotive, and many other industrial and domestic applications. Polyurethane foams are synthesized by the addition of polyols and isocyanates; however, the petroleum origin and toxic nature of isocyanates have driven many to look for more sustainable routes to production. Renewable fillers have emerged as a biobased resource to decrease the carbon footprint of this widely used polymeric material. In this study, soy hulls, as mass-produced, industrial by-products of soybean production, were used to create a biochar beneficial in the synthesis of flexible polyurethane foam composites. The addition of soy hull biochar was found to maintain the compression properties of foams at a decreasing isocyanate index, reducing the amount of isocyanates needed for production. In addition, the addition of biochar decreased the flammability of foams, important for many applications where consumer safety is important. The results point to the ability to create safer, more sustainable, and even more cost-effective polyurethane foams through the reduction in isocyanate use while maintaining the properties of this important class of polymers.

Keywords: biochar; flammability; flexible polyurethane foams; sustainability.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
(a) FTIR spectra and (b) SEM image of biochar used.
Figure 2
Figure 2
(a) One-way ANOVA boxplot for CFD at different biochar concentrations. (b) Representation of composite foams with biochar content from 0 to 20% at the 100 Iso Index.
Figure 3
Figure 3
Increasing biochar content from 0 to 20 wt.% (0 C–20 C). (a) SEM image of foams; (b) CFD of foams; (c) FTIR of foams.
Figure 4
Figure 4
(a) TGA of foams; (b) DSC of foams from 0 to 20 wt.% biochar (0–20 C) at the 100 Iso Index.
Figure 5
Figure 5
(a) Density for decreasing Iso Index for foams with 0% and 10% biochar; (b) CFD for decreasing Iso Index with 0% and 10% biochar; (c) CFD curve for foam with decreasing Iso Index and 0% biochar content; (d) CFD curve for foam with decreasing Iso Index and 10% biochar content.
Figure 6
Figure 6
SEM images of foam cells for varying isocyanate (a) 0% biochar; (b) 10% biochar.
See this image and copyright information in PMC

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