Two approaches for introduction of wheat straw lignin into rigid polyurethane foams

Dispersion Methodology for Technical Lignin into Polyester Polyol for High-Performance Polyurethane Insulation Foam

“…Despite this interest, the maximum reduction in thermal conductivity observed in KL-incorporated RPUF within acceptable densities (<50 kg m –3 ) was only up to ∼4% (with 5 wt % in polyol) . Incorporated at low loadings (reportedly ∼1.8–5 wt % in polyol), ,− the lignin particles act as nucleating agents which reduce the average cell size ,, and therefore reduce the thermal conductivity of the RPUF . However, regardless of loading levels, the observed reduction of thermal conductivity is negligible ,, and/or often reportedly accompanied by the reduction in physical and mechanical properties of RPUF. ,,,− …”

“…The inconsistencies in the properties of lignin-incorporated RPUF are attributed to the heterogeneous structure and high polydispersity of lignin, which challenges the dispersion of lignin in polyether polyols that are commonly used for the production of RPUF . While the level of dispersion is influenced by the incorporation approach and the loading levels, ,,, KL tends to agglomerate and forms heterogeneous dispersions of micro- and nanoparticles in polyether polyols. ,, Such agglomerates and/or high loading levels can increase the viscosity of the polyol dispersion, resulting in RPUF with inhomogeneous properties. , To improve the reactivity and dispersion, lignin has been reportedly transformed into reactive lignin polyols, through chemical modification (oxypropylation, depolymerization, or functionalization). ,,− However, such approaches increase the cost of production and result in less-sustainable lignin-based polyols due to the use of large amounts of nonrenewable chemicals and solvents. , …”

Synthesis and characterization of bio-polyols through the oxypropylation of bark and alkaline extracts of bark

“…The combination of a higher molecular weight, less degradation, and a higher bark fraction due to a higher biomass conversion yield, have all led to a polyurethane network that was superior to that made from a liquefied bark-based polyol. Furthermore, the oxypropylated bark showed improved mechanical properties over oxypropylated lignin PUFs with the highest reported elastic modulus of 3.41 MPa (Cateto et al, 2014); oxypropylated kraft lignin PUFs with a highest reported strength value of 140 kPa and modulus of 3.41 MPa (Li and Ragauskas, 2012); and a lower modulus, but comparable strength to PUFs made from oxypropylated organo-solv lignin (Arshanitsa et al, 2013). The oxypropylated bark PUF however had a lower elastic modulus and strength than foams made from liquefied starch that was then oxypropylated (Yoshioka et al, 2013).…”

Studies of polyurethane foams prepared with hybrid silicon and hydroxymethylated lignin

“…As such, high-value utilization of lignin can partially replace petroleum products to prepare rigid polyurethane foam, which is degradable and eco-friendly. 4,5 The cross-linked mesh structure and the rigid structure of benzene ring of lignin can enhance the mechanical properties of polyurethane foam, and the rigid polyurethane foam made of lignin also has higher thermal stability. The hydroxyl-rich lignin can be used as a charcoal source, and the char layer formed during combustion can enhance the flame-retardant properties of the foam.…”

“…The alkali lignin extracted from papermaking waste liquid currently is not well‐utilized, making it a waste and lost resources while also increasing the pollution of the environment. As such, high‐value utilization of lignin can partially replace petroleum products to prepare rigid polyurethane foam, which is degradable and eco‐friendly 4,5 . The cross‐linked mesh structure and the rigid structure of benzene ring of lignin can enhance the mechanical properties of polyurethane foam, and the rigid polyurethane foam made of lignin also has higher thermal stability.…”