Non-Furanic Humins-Based Non-Isocyanate Polyurethane (NIPU) Thermoset Wood Adhesives

Abstract

Predominantly non-furanic commercial humins were used to prepare humin-based non-isocyanate polyurethane (NIPU) resins for wood panel adhesives. Pure humin-based NIPU resins and tannin–humin NIPU resins were prepared, the latter to upgrade the humins’ performance. Species in the raw humins and species formed in the NIPU resins were identified by Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI ToF) spectrometry and Fourier Transform Infrared (FTIR). Humins, fulvic acid and derivatives, humic acid and its fragments, some lignans present and furanic oligomers present formed NIPU linkages. Thermomechanical analysis (TMA) showed that as with other biomaterials-based NIPU resins, all these resins also showed two temperature peaks of curing, the first around 130 °C and the second around 220 °C. A decrease in the Modulus of Elasticity (MOE) between the two indicated that the first curing period corresponded to linear growth of the oligomers forming a physical entanglement network. This then disentangled, and the second corresponded to the formation of a chemical cross-linked network. This second peak was more evident for the tannin–humin NIPU resins. All the laboratory particleboard made and tested either bonded with pure humins or with tannin–humin NIPU adhesives satisfied well the internal bond strength requirements of the relevant standard for interior grade panels. The tannin–humin adhesives performed clearly better than the pure humins one.

Furanic Humins from Biorefinery as Biobased Binder for Bitumen

“…Industrial humins as heterogenous macromolecular compounds can be considered furanic lignins and therefore should find sustainable pathways of valorization. This is already the case for so-called non-furanic humins (composed of humic and fulvic substances in soil) that can be processed with tannins to prepare non-isiocyanate wood adhesives [ 18 ]. Recent examples have demonstrated that furanic humins can be employed in substantial amounts to prepare durable wood panels [ 19 ], biobased composites [ 20 ], or foams [ 21 , 22 ] or as a UV shielding agent for thin PVA films [ 23 ].…”

Feasibility Study of the Synthesis of Isocyanate-Free Polyurethanes from Catechin

“…The chemical modification of bio-sourced polyphenol is interesting because of its environmentally friendly traits [8,9]. These syntheses have been conducted by replacing bisphenol A and isocyanate by natural polyphenol or sugar [10][11][12][13][14]. Recently, different studies reported modification of polyphenolic compounds such as catechin and tannins, two flavonoid-type polyphenol compounds, for the synthesis of different polymers [15][16][17][18] presenting antioxidant properties [19].…”

Non-Isocyanate Aliphatic–Aromatic Poly(carbonate-urethane)s—An Insight into Transurethanization Reactions and Structure–Property Relationships

“…Diisocyanate vapors and their residuals in the final product can cause some health problems during manufacturing and use [ 8 ], which is why the transition toward a more sustainable synthesis method of PUs is desired. This is evidenced by the extensive range of PU applications (e.g., foams, coatings, adhesives, and varnishes) [ 9 , 10 , 11 , 12 , 13 , 14 ] and their constantly growing global market, which is valued at around EUR 53 billion [ 15 ].…”