Lignin as a Partial Polyol Replacement in Polyurethane Flexible Foam

Abstract

This study was focused on evaluating the suitability of a wide range of lignins, a natural polymer isolated from different plant sources and chemical extractions, in replacing 20 wt.% of petroleum-based polyol in the formulation of PU flexible foams. The main goal was to investigate the effect of unmodified lignin incorporation on the foam’s structural, mechanical, and thermal properties. The hydroxyl contents of the commercial lignins were measured using phosphorus nuclear magnetic resonance (31P NMR) spectroscopy, molar mass distributions with gel permeation chromatography (GPC), and thermal properties with differential scanning calorimetry (DSC) techniques. The results showed that incorporating 20 wt.% lignin increased tensile, compression, tear propagation strengths, thermal stability, and the support factor of the developed PU flexible foams. Additionally, statistical analysis of the results showed that foam properties such as density and compression force deflection were positively correlated with lignin’s total hydroxyl content. Studying correlations between lignin properties and the performance of the developed lignin-based PU foams showed that lignins with low hydroxyl content, high flexibility (low Tg), and high solubility in the co-polyol are better candidates for partially substituting petroleum-based polyols in the formulation of flexible PU foams intended for the automotive applications.

Kraft Lignin with Improved Homogeneity Recovered Directly from Black Liquor and Its Application in Flexible Polyurethane Foams

“…A previous study demonstrated that the lignin macromolecules comprised higher content of hydroxyl groups than the polyether-based polyols. 31 Hence, lignin may react with more diisocyanate to form more urethane linkages, increasing the density of PU foams. The density of Lignin-1 and -2-based PU foams indicated that the Kraft lignin recovered at pH = 7 was more suitable than the Kraft lignin recovered at pH = 12 to produce the lower-density PU foams.…”

“…Such a difference between the lignin-based PU foams and control PU foams in the ultimate elongation was statistically significant ( P < 0.05), and it might be related to the rigid aromatic rings in the lignin macromolecules. 31 Moreover, the ultimate elongation of lignin-based PU foams was observed to rely on the lignin categories, indicating that the flexibility and elasticity of lignin-based PU foams were indirectly affected by the lignin recovery processes.…”

“…The weight loading capacity of PU foams is often considered in the application of floor carpets, and the effect of adding the lignin into the PU foams on the support factor was evaluated in this study. 31 Generally, a higher value of support factor indicates a better ability of PU foams to support the weight. 31 As shown in Figure 7 a, the average support factor value of control PU foams was 3.0, and that of lignin-based PU foams ranged from 2.6 to 5.1.…”

Polyurethane-Nanolignin Composite Foam Coated with Propolis as a Platform for Wound Dressing: Synthesis and Characterization

“…The SEM was used to evaluate the morphology and microstructure of the surface and cross-section of PU-NL foam and PU-NL/EEP wound dressing ( Figure 3 ). This characteristic is important as the mechanical performance of the foam is highly influenced by the average cell size and the thickness of cell walls [ 48 ].…”

“…A range below 100 nm is evident for lignin as nanoparticles. Generally, lignin-based polyurethane foams produce smaller cell sizes and thicker cell walls than the pure PU, which might be due to the nucleating agent role of NL, explaining the higher density values and mechanical properties [ 48 ].…”