Latest Advancements in the Development of High-Performance Lignin- and Tannin-Based Non-Isocyanate Polyurethane Adhesive for Wood Composites

Abstract

The depletion of natural resources and increasing environmental apprehension regarding the reduction of harmful isocyanates employed in manufacturing polyurethanes (PUs) have generated significant attention from both industrial and academic sectors. This attention is focused on advancing bio-based non-isocyanate polyurethane (NIPU) resins as viable and sustainable substitutes, possessing satisfactory properties. This review presents a comprehensive analysis of the progress made in developing bio-based NIPU polymers for wood adhesive applications. The main aim of this paper is to conduct a comprehensive analysis of the latest advancements in the production of high-performance bio-based NIPU resins derived from lignin and tannin for wood composites. A comprehensive evaluation was conducted on scholarly publications retrieved from the Scopus database, encompassing the period from January 2010 to April 2023. In NIPU adhesive manufacturing, the exploration of substitute materials for isocyanates is imperative, due to their inherent toxicity, high cost, and limited availability. The process of demethylation and carbonation of lignin and tannin has the potential to produce polyphenolic compounds that possess hydroxyl and carbonyl functional groups. Bio-based NIPUs can be synthesized through the reaction involving diamine molecules. Previous studies have provided evidence indicating that NIPUs derived from lignin and tannin exhibit enhanced mechanical properties, decreased curing temperatures and shortened pressing durations, and are devoid of isocyanates. The characterization of NIPU adhesives based on lignin and tannin was conducted using various analytical techniques, including Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), matrix-assisted laser desorption/ionization with time-of-flight (MALDI-TOF) mass spectrometry, and gel permeation chromatography (GPC). The adhesive performance of tannin-based NIPU resins was shown to be superior to that of lignin-based NIPUs. This paper elucidates the potential of lignin and tannin as alternate sources for polyols in the manufacturing of NIPUs, specifically for their application as wood adhesives.

Eco-Friendly and High-Performance Bio-Polyurethane Adhesives from Vegetable Oils: A Review

“…The market is dominated by a wide variety of adhesives, many of which are synthetic and fossil-fuel-based. However, the dwindling fossil fuel resources and the focus on sustainable materials have led to increased interest in an eco-friendly alternative: vegetable oil-based adhesives [ 9 , 18 , 19 , 21 , 26 , 27 , 29 , 30 , 32 , 33 , 34 , 35 , 36 , 37 , 39 , 40 , 41 , 42 , 73 , 74 ], lignin-based adhesives [ 75 , 76 ], tannin-based adhesives [ 76 , 77 ], protein-based adhesives [ 78 , 79 ], and starch-based adhesives [ 80 , 81 , 82 ].…”

“…Lignin and tannin from various renewable materials are currently also being developed as raw materials for making PU [ 75 , 76 ]. However, lignin-based PUs exhibit higher brittleness due to the rigid and complex aromatic structure of lignin, which limits the flexibility and ductility of the resulting polymer matrix [ 75 ].…”

“…Vegetable oil-based PUs can potentially overcome brittleness due to their aliphatic structure, which provides greater flexibility and elasticity compared to the aromatic structure of lignin, resulting in a more ductile and less brittle polymer matrix [ 83 , 84 ]. Lignin and tannin-based PUs often suffer from poor water resistance due to the hydrophilic nature of lignin’s hydroxyl groups, which can limit their application in environments with high moisture exposure [ 76 ]. Vegetable oil-based PUs, on the other hand, generally exhibit better hydrophobicity and water resistance compared to lignin, making them more suitable for applications requiring moisture barrier properties [ 84 , 85 ].…”

Performance of Particleboard Made of Agroforestry Residues Bonded with Thermosetting Adhesive Derived from Waste Styrofoam

“…Wood adhesives represent a key element in the production of wood-based composites [ 5 , 6 , 7 , 8 ]. Currently, approximately 95% of wood adhesives used worldwide for manufacturing wood composites are based on formaldehyde.…”

Emissions of Volatile Organic Compounds (VOCs) as Safety Indicators in the Development of Wood-Based Binderless Boards

“…Over the last decades, numerous studies have been carried out to replace these petroleum-based binders with biobased binders [15][16][17] or even to produce binderless boards, based on the self-adhesive properties of the various raw materials used, due to their chemical composition [18][19][20][21]. These boards show great promise, particularly in terms of mechanical properties.…”