Abstract
The potential of ammonium lignosulfonate (ALS) as an eco-friendly additive to urea–formaldehyde (UF) resin for manufacturing high-density fiberboard (HDF) panels with acceptable properties and low free formaldehyde emission was investigated in this work. The HDF panels were manufactured in the laboratory with very low UF resin content (4%) and ALS addition levels varying from 4% to 8% based on the mass of the dry wood fibers. The press factor applied was 15 s·mm−1. The physical properties (water absorption and thickness swelling), mechanical properties (bending strength, modulus of elasticity, and internal bond strength), and free formaldehyde emission were evaluated in accordance with the European standards. In general, the developed HDF panels exhibited acceptable physical and mechanical properties, fulfilling the standard requirements for HDF panels for use in load-bearing applications. Markedly, the laboratory-produced panels had low free formaldehyde emission ranging from 2.0 to 1.4 mg/100 g, thus fulfilling the requirements of the E0 and super E0 emission grades and confirming the positive effect of ALS as a formaldehyde scavenger. The thermal analyses performed, i.e., differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and derivative thermogravimetry (DTG), also confirmed the main findings of the research. It was concluded that ALS as a bio-based, formaldehyde-free adhesive can be efficiently utilized as an eco-friendly additive to UF adhesive formulations for manufacturing wood-based panels under industrial conditions.
Highlights
Due to recent technological and material developments, the wood-based panel industry has become one of the fastest growing industries worldwide [1,2] with an estimated annual production of approximately 357 million m3 in 2019, which represents a 100% increase compared to 2000 [3]
The transition to circular, low-carbon bioeconomy, growing environmental concerns, and strict legislation related to emission of harmful volatile organic compounds (VOCs), such as free formaldehyde from wood-based panels, have posed new requirements related to the development of environmentally friendly wood-based panels [4,5,6,7,8,9], optimization of lignocellulosic resources [10,11,12,13], and use of alternative raw materials [14,15,16,17,18,19]
Due to their numerous advantages, such as short press times, low press temperatures, high reactivity, water solubility, good adhesion performance, and low price [23,24,25,26], urea– formaldehyde (UF) resins have become the most important type of resins used in the production of wood-based panels with an estimated global annual consumption of approximately 11 million tons of resin solids [25,26,27]
Summary
Due to recent technological and material developments, the wood-based panel industry has become one of the fastest growing industries worldwide [1,2] with an estimated annual production of approximately 357 million m3 in 2019, which represents a 100% increase compared to 2000 [3]. [20,21,22,23] Due to their numerous advantages, such as short press times, low press temperatures, high reactivity, water solubility, good adhesion performance, and low price [23,24,25,26], urea– formaldehyde (UF) resins have become the most important type of resins used in the production of wood-based panels with an estimated global annual consumption of approximately 11 million tons of resin solids [25,26,27]. Harmful formaldehyde emissions can be reduced by adding various inorganic, organic, and mineral compounds as formaldehyde scavengers to conventional wood adhesives, such as phosphates, salts, urea, nanoparticles, bark, tannins, etc. [34,35,36,37,38,39,40,41,42,43], by surface treatment of finished wood-based panels [34] or by using eco-friendly, formaldehyde-free adhesive formulations [44,45,46,47,48,49,50,51,52,53,54]
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