Significance of wood extractives for wood bonding

Abstract

Wood contains primary extractives, which are present in all woods, and secondary extractives, which are confined in certain wood species. Extractives in wood play a major role in wood-bonding processes, as they can contribute to or determine the bonding relevant properties of wood such as acidity and wettability. Therefore, extractives play an immanent role in bonding of wood chips and wood fibres with common synthetic adhesives such as urea-formaldehyde-resins (UF-resins) and phenol-formaldehyde-resins (PF-resins). Extractives of high acidity accelerate the curing of acid curing UF-resins and decelerate bonding with alkaline hardening PF-resins. Water-soluble extractives like free sugars are detrimental for bonding of wood with cement. Polyphenolic extractives (tannins) can be used as a binder in the wood-based industry. Additionally, extractives in wood can react with formaldehyde and reduce the formaldehyde emission of wood-based panels. Moreover, some wood extractives are volatile organic compounds (VOC) and insofar also relevant to the emission of VOC from wood and wood-based panels.

Low-Molecular-Weight Phenols Recovery by Eco-Friendly Extraction from Quercus Spp. Wastes: An Analytical and Biomass-Sustainability Evaluation

“…Therefore, such species are subject of increasing interest in various fields such as pharmaceuticals, leather tanning, cosmetics, and the food industry [7][8][9][10][11]. Low-molecular-weight hydroxybenzoic acids and some of their derivatives can be obtained from wood extractives and via induced lignin degradation [12,13]. Lignin is a phenolic high-molecular-mass biopolymer, composed of a highly branched phenylpropanoid framework based on the three monomers coumaryl, coniferyl, and sinapyl alcohol.…”

Comparison of Methodologies for Acid Buffering Capacity Determination—Empirical Verification of Models

“…In P3, where the hardener amount was beyond the optimum, a loose structure in the cross-section also occurred. This phenomenon results from the rapid curing of the adhesive with an excess of acidic hardener and subsequent deterioration of the bond line by acid upon storage [1,5]. In the case of the oak panels (Table 4), it was difficult to observe any significant differences in the structure or thickness of the three boards, regardless of the hardener amount.…”

“…The chemical properties of wood and wood extractives, such as pH value and buffering capacity, are considered prime factors in bonding [5]. The gel time of a urea-formaldehyde (UF) resin strongly depends on the acidity of the wood substrate which is associated with the content of the wood extractives [6,7].…”

Comparison on Reduction of VOCs Emissions from Radiata Pine (Pinus Radiata D. Don) between Sodium Bicarbonate and Ozone Treatments

“…However, the energy consumption of heat treatment in the wood industry is high, and it can cause other drawbacks including the change of surface color and decrease of mechanical strength [10]. As another effective method, extraction is often used to modify wood chemical properties, and affects wood thermal stability [11], cementing [12,13], and antibacterial properties [14]. Studies have shown that wood VOCs mainly originate from their extraction [15].…”