Lignin-based Adhesives Research Articles

Do green wooden composites using lignin-based binder have environmentally benign alternatives? A preliminary LCA case study in China

Nowadays, formaldehyde emissions from petroleum-based adhesives contribute considerably to environmental problems and are a constraint to the development of forest-based industries. Although many efforts are being made to develop new lignin-based adhesives for panels, very few studies were carried out via life cycle assessment (LCA). This study aims to assess the life cycle of green wooden composites by using hybrid-modified ammonium lignosulfonate (HMAL) as the binder and investigate the possibility of lignin-based binder to be a good alternative. This study is a step further of the previous work conducted on HMAL as an alternative binder for medium-density fiberboard (MDF) or, in other words, the wooden composite made from HMAL and wood fiber (WF). LCA was carried out to assess the environmental impacts during the life cycle of the new manufacturing process of HMAL/WF production using ReCiPe 1.08 Endpoint and IPCC global warming potential (GWP) method built into the GaBi version 6.0 software. The production system involved two subsystems: raw material supply and board manufacture. Meanwhile, a comparative LCA of conventional MDF, with three main damage categories and GWP, was also carried out. The hydrogen peroxide (H2O2) production, electricity, and the HMAL/WF manufacturing stages had the greatest environmental impact. The comparative results pointed out that HMAL/WF production is environmentally superior to conventional MDF in general. Due to the environmental impacts associated with the HMAL binder, a sensitivity analysis was carried out. Suggestions were made for a cleaner production, in which the H2O2 dose was reduced to 24 wt%. H2O2 use, energy, and electricity consumption are main contributors to most impact categories, which help us to find the potential improvements of sustainability, choose the appropriate HMAL technology, and optimize the HMAL/WF system. Feasible production processes and life cycle costs are factors that still need to be studied.

Isolation and characterization of lignin from the oak wood bioethanol production residue for adhesives

Lignin was isolated from the residue of bioethanol production with oak wood via alkaline and catalyzed organosolv treatments at ambient temperature to improve the purity of lignin for the materials application. The isolated lignins were analyzed for their chemical composition by nitrobenzene oxidation method and their functionality was characterized via wet chemistry method, element analysis, 1H NMR, GPC and FTIR-ATR. The isolated lignin by acid catalyzed organosolv treatment (Acid-OSL) contained a higher lignin content, aromatic proton, phenolic hydroxyl group and a lower nitrogen content that is more reactive towards chemical modification. The lignin-based adhesives were prepared and the bond strength was measured to evaluate the enhanced reactivity of lignin by the isolation. Two steps of phenolation and methylolation were applied for the modification of the isolated lignins and their tensile strengths were evaluated for the use as an adhesive. The acid catalyzed organosolv lignin-based adhesives had comparable bond strength to phenol-formaldehyde adhesives. The analysis of lignin-based adhesives by FTIR-ATR and TGA showed structural similarity to phenol adhesive. The results demonstrate that the reactivity of lignin was enhanced by isolation from hardwood bioethanol production residues at ambient temperature and it could be used in a value-added application to produce lignin-based adhesives.

Lignin‐based polycondensation resins for wood adhesives

AbstractLignin‐based wood adhesives are obtained that satisfy the requirements of relevant international standards for the manufacture of exterior‐grade wood particleboard. Formulations based on low molecular mass lignin and presenting an increase in the relative proportion of reactive points yield better results than the higher molecular mass lignin used in the past. These lignins allow a higher proportion of hydroxymethylation during preparation of methylolated lignins. These lignin‐based adhesives also yield acceptable results at particleboard pressing times that are sufficiently low to be of industrial significance. Lignin‐based wood adhesives, in which a nonvolatile nontoxic aldehyde (glyoxal) is substituted for formaldehyde in their preparation, are prepared and tested for application to wood panels such as particleboard. The adhesives yield good internal bond strength results for the panels, which are good enough to comfortably pass relevant international standard specifications for exterior‐grade panels. The adhesives also show sufficient reactivity to yield panels in press times comparable to that of formaldehyde‐based commercial adhesives. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1690–1699, 2007

Biorefining of softwoods using ethanol organosolv pulping: Preliminary evaluation of process streams for manufacture of fuel-grade ethanol and co-products

Pulps with residual lignin ranging from 6.4-27.4% (w/w) were prepared from mixed softwoods using a proprietary biorefining technology (the Lignol process) based on aqueous ethanol organosolv extraction. The pulps were evaluated for bioconversion using enzymatic hydrolysis of the cellulose fraction to glucose and subsequent fermentation to ethanol. All pulps were readily hydrolyzed without further delignification. More than 90% of the cellulose in low lignin pulps (< or =18.4% residual lignin) was hydrolyzed to glucose in 48 h using an enzyme loading of 20 filter paper units/g cellulose. Cellulose in a high lignin pulp (27.4% residual lignin) was hydrolyzed to >90% conversion within 48 h using 40 filter paper units/g. The pulps performed well in both sequential and simultaneous saccharification and fermentation trials indicating an absence of metabolic inhibitors. Chemical and physical analyses showed that lignin extracted during organosolv pulping of softwood is a suitable feedstock for production of lignin-based adhesives and other products due to its high purity, low molecular weight, and abundance of reactive groups. Additional co-products may be derived from the hemicellulose sugars and furfural recovered from the water-soluble stream.

Fundamental studies on the development of lignin-based adhesives, I. Catalytic demethylation of anisole with molecular oxygen

In the presence of a catalyst consisting of metal-porphyrin complex and a reductant, anisole was converted into phenol by molecular oxygen at room temperature with a total turnover of the catalyst of about 70 times in 24 h.

クラフトリグニン樹脂接着剤の製造

The preparation of kraft lignin-based wood adhesives with high tensile shear strength and water resistance was investigated. Softwood and hardwood kraft lignins (NKPL and LKPL) were isolated from industrial concentrated waste liquors in yields of 15.8% and 15.0% based on solids, respectively. A mixture of lignin and phenol (85 : 1570 : 30) was hydroxymethylated by reacting with formaldehyde in an alkaline aqueous methanol for 2 hours at 80°C. The reaction products. hydroxymethylated was named a lignin-phenol resin (LP). Walnut powder was added to LP for a lignin-based adhesive (LPA). LPAs produced from NKPL or LKPL containing over 20% of phenol had high dry tensile shear strength bonds when hot-pressed for 615 minutes at 140°C, but their wet strengths after 48-hour boil deteriorated strikingly. Alternative lignin-based adhesives (LPRA) which consisted of 8070% LP, 2030% resorcinol and so forth developed satisfactory bonds in either dry or wet strength when hot-pressed for 615 minutes at only 75100°C. All of 3-ply shinanoki plywoods bonded with LPRAs provided higher wood failure in the wet test than in the dry test. Ether soluble fractions (LP-2) from acidified LP contained hydroxymethylated phenols such as 2, 4, 6-trihydroxymethylphenol, so the resorcinol together with paraformaldehyde was found to be used as crosslinking agents between ether insolubles (LP-1) such as hydroxymethylated lignin-phenol copolymers and LP-2 to form water-insoluble macromolecule for adhesion. LPRA required less energy for bonding and yielded high-quality bonds, indicating that it may be useful as wood adhesives for various kinds of wood products.

Studies on lignin‐based adhesives for plywood panels

AbstractLignin, a naturally occurring polymer, was isolated from sawdust and used as a substitute in phenol formaldehyde resins. Thus lignin‐phenol formaldehyde adhesives for plywood with lignin‐phenol ratios of 50:50, 60:40, 70:30, 80:20 and 90:10 were prepared. Glue shear strength for these adhesives was tested by preparing three‐ply plywood panels. The adhesives showed a dry bond strength varying from 0.57 to 0.82 MPa. The glue shear strength for cold water resistance tests varied from 0.16 to 0.25 MPa, indicating that even 80% replacement of phenol with lignin is capable of producing a bond quality acceptable for cold water resistant grade plywood.

Jute stick lignin-based adhesives for particle boards

Soda lignin isolated from spent soda liquor of jute stick pulp was used for the preparation of lignin phenol formaldehyde resins. The adhesives were used to prepare jute stick particle boards. It was observed that phenol in phenol formaldehyde resin could be replaced up to a maximum of 50% by jute stick soda lignin.