Compressive viscoelastic properties of softwood kraft lignin-based flexible polyurethane foams

Abstract

Softwood kraft lignin (SKL)-based water-blown flexible polyurethane foams were prepared using SKL as a crosslinking agent and a hard segment polyol. Polyethylene glycol (PEG) as a soft segment diol and 2,4-toluene diisocyanate (TDI) were used. While increasing hard segment content caused the increase in crosslink density in foams, the foams became more and more viscous with increasing hard segment content due to the distinctive phase heterogeneity in foams. In this case, the contributiveness of the filler-like behaviors of separated hard segments always overtook the crosslinking effects derived from SKL in terms of overall viscoelasticity, thus the resultant viscometric properties such as tanδ max and hysteresis loss increased as hard segment content increased. Furthermore, increasing M n,PEG caused the severer microphase separation and intensified the filler effects in foams, thus the foams became more viscous with increasing M n,PEG . The 25 % and 65 % CFD values and Young's moduli of foams increased with increasing hard segment content due to the increase in crosslink density for foams, and the properties also increased with increasing foam density. Most of foams showed the support factors in the range of 2-3, which are suitable values for cushioning use. Even though the microscopic deformation behaviors in foams are irrelevant to foam density, the cyclic compressive tests showed that the higher foam density possess the better shape recovery performances.

Lignin-Based Polyurethanes: Opportunities for Bio-Based Foams, Elastomers, Coatings and Adhesives

“…Oxypropylated lignins have been incorporated into rigid PU foams at 5–100 wt % loading with “comparable performance” to control foams [15,70,94,102]. The incorporation of modified lignins into rigid PU foams has been reported to improve biodegradation [103], compressive strength [104,105,106], tensile strength [107], thermal conductivity [108], thermal degradation [109], and anti-flaming properties [110] compared to control foams. In some cases it is also reported to increase density [106], cell size [84], and cell irregularity [88] of the foams.…”

“…Lignin incorporated into flexible PU foams can act as both a filler [119] and crosslinking agent (by reacting with an isocyanate) [106]. Previous studies have used either unmodified lignins [95,106] or chemically modified lignins [120,121,122] to partially replace (6–30 wt %) the polyol portion of flexible PU foams. The thermal stability and mechanical properties foams prepared using modified lignins were reported to increase by increasing lignin content [120,121,123].…”

“…Kraft softwood lignin has been used to replace 10–30% (by weight) of the polyol in flexible foam formulations and reported that the developed foam had viscoelastic behavior similar to the control foams [106]. The foam produced with 100% replacement of the polyol with sodium lignosulfonate lignin was dense, brittle, and mechanically weak and was more like a rigid foam than flexible foam [123].…”

A Study of the Effect of Kosmotropic and Chaotropic Ions on the Release Characteristics of Lignin Microcapsules under Stimuli-Responsive Conditions

“…Several studies demonstrated that lignins have useful rheological and viscoelastic properties to develop a structural material, 16,24,33 meaningful film forming ability, 31,33,34 and compatibility with a wide range of solvents. 23,24,34 Lignins are multifunctional biopolymers that carry many aliphatic hydroxyl and phenolic groups.…”

Optimization of Pretreatment and Alkaline Cooking of Wheat Straw on its Pulpability Using Response Surface Methodology

“…The lignin macromolecule is mainly composed of phenyl propane structures (Jeong et al 2013). Many chromophoric groups are present the molecule, such as phenolic hydroxyl, quinone structures, and carbonyl (Fjellström et al 2008).…”