Sustainable Polyurethane–Lignin Aqueous Dispersions and Thin Films: Rheological Behavior and Thermomechanical Properties

Abstract

Sustainable aqueous polyurethane (PU) dispersions derived from castor oil and lignosulfonate (LS) have been successfully synthesized with stable nanoscale morphology and average particle sizes as small as 35 nm with no organic solvent. Incorporation of a rigid structure of LS into the castor oil-based PU reinforces the resulting cast films of the PU−LS nanocomposites and increases the cross-link density, as determined by dynamic mechanical analysis measurements and the theory of rubber elasticity. In addition, the LS plays a significant role in enhancing the ultimate mechanical and thermal properties of the resulting nanocomposite films. The TEM morphologies of the PU−LS dispersions confirmed that the average particle sizes are constant (approximately 35 nm) for all different LS concentrations. The effect of LS on the dynamic viscosity of PU−LS aqueous dispersions at different angular frequencies in the linear viscoelastic regime has also been investigated, and the experimental data were analyzed based on the Cross model. The dynamic viscosity increases significantly with increasing LS content while holding a constant 15 wt % of the solid content in all dispersions. The nature of LS as a water-soluble material suggests that PU−LS nanoparticles adsorb more water onto the particle surface with increasing LS content, which leads to a considerable decrease in the concentration of free water in the dispersion, and consequently, the viscosity increases dramatically. The influence of different concentrations of LS on the reduced viscosity of the dispersions was investigated using the Krieger−Dougherty viscosity model with a critical concentration of LS (ϕ c = 0.08) above which the viscosity of the dispersions increased strongly. The current study provides an effective and promising approach to synthesize high-performance, biorenewable nanocomposites for coatings and adhesives.

Multiple Structure Reconstruction by Dual Dynamic Crosslinking Strategy Inducing Self‐Reinforcing and Toughening the Polyurethane/Nanocellulose Elastomers

“…PU elastomers on the market mainly come from nonrenewable petroleum resources. [5] Accordingly, it has become particularly important to synthesize PUs from environmental friendly biodegradable resources or attempt to include other bio-based resources (cellulose, [6] lignin, [7,8] chitosan [9] ) to realize high-strength composite materials. [10] However, the stable covalent cross-linking network in these elastomers is irreversible, and conditions such as aging, wear and spontaneous fracture occur in service.…”

Waterborne Polyurethane Dispersions and Thin Films: Biodegradation and Antimicrobial Behaviors

“…For anionic PUDs, a DMPA is one of the most common internal emulsifiers that can be reacted with diisocyanate and polyols to produce prepolymer. After that, a triethylamine (TEA) is typically used to neutralize the carboxylic acid groups to form the ionic function groups required for the production of PUDs that are stable in water [ 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ].…”

Composite waterborne polyurethane reinforced with silane modified lignin as an adhesive between polypropylene decorative films and wood‐based panels

“…[29][30][31][32] However, the incorporation of lignin into polymers is difficult due to poor dispersion, which may be improved though by adding appropriate additives. In previous studies, several techniques have been reported to pre-treated lignin such as esterification, [33] monomer polymerization, [34] quaternary ammonium grafting, [35] and nano-lignin particle preparation. [36] As mentioned above, the lignin with appropriate modification may be used as reinforcement in WPU adhesives.…”