Peyman Ahmadi

Formaldehyde-free starch adhesives offer a renewable alternative to conventional binders used in medium-density fiberboard (MDF), but their application remains limited by poor moisture resistance and insufficient mechanical performance. The aim of this research work was to investigate and evaluate the combined effects of sorbitol and glycerol plasticizers, citric acid modification, and urea addition on the properties of starch-based adhesives and the resulting MDF panels. Five adhesive formulations were prepared and characterized using Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Laboratory MDF panels were manufactured and evaluated for thickness swelling (TS), water absorption (WA), internal bond strength (IB), modulus of rupture (MOR), and modulus of elasticity (MOE). Among the tested formulations, the hybrid adhesive system, composed of sorbitol/starch/glycerol/urea/citric acid (SSGUC), provided the best overall performance. Panels bonded with SSGUC exhibited the lowest TS and WA after both 2 and 24 h of water immersion, with TS₂ values of 22.74 to 24.54% and WA₂ and WA₂₄ values of 91.16–101.43% and 132.11–141.29%, respectively. The same panels achieved IB, MOR, and MOE values of 0.59–0.86 MPa, 24.95–26.17 MPa, and 2413–2632 MPa, respectively. FTIR spectral changes were consistent with citric-acid-mediated esterification and modified hydrogen-bonding interactions in the urea-containing formulations, while DSC revealed formulation-dependent differences in thermal behavior. The FTIR interpretation was based primarily on comparative band development and intensity changes rather than on marginal peak-position shifts. Overall, the results indicate that combining sorbitol and glycerol with citric acid and urea can improve the moisture resistance and mechanical performance of starch-bonded MDF. Further optimization, including rheological characterization and comparison with commercial binders, is required to assess industrial applicability.

Poplar wood (Populus deltoides), a fast-growing and abundant species, holds promise for sustainable material use, but its low density, poor dimensional stability, and weak strength restrict high-value applications. This study examined property enhancement through resin impregnation with phenol-formaldehyde (PF), melamine-urea-formaldehyde (MUF), and polyethylene glycol (PEG) at 5%, 10%, and 15% concentrations. Modified specimens were tested for weight percent gain, bulking, water absorption, dimensional swelling, modulus of rupture, modulus of elasticity (MOE), impact strength, and surface hardness, as well as machinability and carving performance using expert evaluation and Computer Numerical Control (CNC) surface quality. Given the laboratory-scale dimensions of the specimens, the resins achieved satisfactory penetration, as also reflected in the WPG values. The 15% PF treatment produced the greatest improvements, yielding a WPG of 26.3%, MOE above 10,000 MPa, and reduced surface roughness to 2.90 µm. Compared with untreated samples, PF-modified wood showed superior dimensional stability, machining resistance, and carving clarity, approaching the properties of hardwoods such as walnut and beech. MUF led to moderate benefits, whereas PEG mainly caused bulk increase without significant strength or moisture resistance improvements. Overall, PF impregnation effectively upgraded poplar wood, indicating its potential as a cost-effective alternative for decorative and structural applications.

This study investigates the enhancement of the physical and mechanical properties of date palm wood ( Phoenix dactylifera ) through a two-stage treatment process. This process involves impregnation with low-viscosity melamine–formaldehyde (MF) resin, followed by densification. The goal is to address the inherent weaknesses of palm wood and explore its potential for high-value applications. Wood samples were treated with different resin concentrations 5, 10, and 25% (wt. %) and subjected to a 50% compression ratio. Physical properties such as density, water absorption, and thickness swelling were evaluated, while mechanical tests included bending strength (MOR), stiffness (MOE), impact resistance, and screw-holding capacity (SHC). Additionally, formaldehyde emissions were measured to assess environmental impact. Key findings revealed significant improvements in both physical and mechanical properties. Density increased nearly fourfold in the most intensively treated samples, while water absorption and thickness swelling were significantly reduced, indicating improved dimensional stability. Mechanical properties showed substantial enhancements, with MOR improving by 241%, MOE by 136.36%, and SHC by 114%. Notably, formaldehyde emissions were low, thus meeting the emission limits specified in the Chinese National Standard GB/T 17657. The combination of impregnation and densification demonstrated synergistic effects, often outperforming single treatments. These findings suggest that the proposed treatment method offers a promising approach to valorizing date palm waste, potentially addressing environmental concerns while creating high-performance, environmentally friendly wood products suitable for various applications. This study contributes valuable insights to the field of wood modification, opening new possibilities for utilizing date palm wood in industries requiring materials with enhanced strength and dimensional stability. Graphical Abstract

Sugarcane bagasse is an agro-waste that could replace timber resources for the production of bio-composites. Composite boards such as particleboard offer an issue for the use and recycling of poor quality timber, and these engineered products can overcome some solid wood limitations such as heterogeneity and dimension. Bagasse offers an alternative to wood chips for particleboard production but present some disadvantages as well, such as poor physico-mechanical properties. To address these issues, bagasse fibers were treated with an innovative natural resin formulated with tannin and furfural. Impregnated particles with different concentrations of resin (5%, 10%, and 15% m/m) were exposed to temperatures of 40°C, 60°C, 80°C, and 100°C for resin curing. Various types of tannin-based adhesives, including tannin formaldehyde, tannin/formaldehyde-furfural, and tannin hexamine, were utilized for bonding the treated bagasse particles. The resultant panels were assessed for their physical and mechanical properties and compared to those produced using Melamine-Urea-Formaldehyde (MUF) adhesive. The density of the panels varied from 650 to 730 kg/m³ depending on the resin concentration. The values for both modulus of elasticity and modulus of rupture increased as the resin concentration increased. The internal bonding values exhibited an increase with resin concentration up to a critical point, after which a decreasing trend was observed. The water absorption and thickness swelling were significantly reduced with an increase in resin concentration. However, the panels produced using MUF adhesive yielded the most favorable physico-mechanical properties. Additionally, the panels made with tannin-based adhesives met the minimum requirements specified in the standard EN 312 (specifications for uncoated resin-bonded particleboards) for application in dry conditions. The analysis of formaldehyde emissions indicated that panels produced with tannin-based adhesives exhibited significantly lower emissions compared to those made with MUF. The tannin/furfural resin showed great potential for improving the quality of bagasse particleboard using tannin-based adhesives.