Volume 20 Issue 2

Paper and paperboard are highly regarded for their recyclability and sustainability, but their inherent inhomogeneity presents challenges for material characterization and modeling. Despite being pressed during production, they remain compressible in the thickness direction, making density a key factor in determining mechanical properties. This study examines the effect of density and thickness compression on the in-plane mechanical behavior of paper and paperboard through uniaxial tensile tests on both laboratory paper with different refining energies and commercial paperboard with anisotropy. The results confirm that density significantly affects stress-strain response, elasticity, and plastic deformation. To capture this effect systematically, an efficiency factor is introduced that provides a quantitative measure of the density-dependent mechanical behavior to model the influence of density using a linear function. Incorporating efficiency factors refines the material modeling approach and improves predictions of stiffness and plastic stress. Higher refining energies result in a more homogeneous structure, reducing density-related variations, while commercial paperboard is less affected by fiber orientation and surface coatings. The proposed efficiency factor provides a new framework for optimizing and modelling the influence of the pressure and density on material parameters of fiber-based materials.

Presently, structural grade cross-laminated timber (CLT) panels are manufactured for interior applications. To expand the use of CLT to exterior applications, there is a need to protect the panels from biodegrading agents such as fungi and termites. Pressure treatments are effective methods of increasing the durability of wood and wood-based products. There are limited studies on the influence of micronized copper azole (MCA) treatment on the rolling shear modulus and rolling shear strength of a commercially produced 3-ply southern yellow pine CLT panel Grade V3. It was found that MCA treatment didn’t have a significant effect on the rolling shear strength of the CLT panels, with the rolling shear strength being 2.19 and 2.31 MPa for the untreated and treated CLT panels, respectively. The bonding durability of the CLT panels had mixed results, with the control specimens measuring a significantly lower wood failure percentage (WFP) of 32% as compared to approximately 75% for the MCA treated specimen. The measured block shear strength (BSS) was approximately the same for the treated and the untreated shear block specimen except for one manufacturing group. The average delamination for the treated specimens was 11% while the average delamination for the untreated specimens was 13.2%.

The rapid development of the manufacturing industry has increased the demand for sustainable and efficient logistics solutions. Chip block pallets (CBPs) made from mixed forest group sawdust offer a promising alternative to traditional pallets due to their reliance on lower-cost, renewable materials. This study aims to evaluate the effects of different adhesives, phenol-formaldehyde (PF), urea-formaldehyde (UF), and poly-urea-formaldehyde (PUF), and varying pressing times on the physical and mechanical properties of CBPs. The CBPs were produced using 30, 60, and 90 min pressing times at 180 °C. The results showed that PF demonstrated the highest compressive strength (6.93 MPa) and screw-holding strength (343 N), making it suitable for applications requiring high mechanical performance. The PUF exhibited lower mechanical strength but provided significant environmental advantages with reduced formaldehyde emissions. Meanwhile, UF displayed adequate performance at shorter pressing durations but decreased efficiency with prolonged pressing. Optimal results were achieved at a pressing time of 60 min, which improved physical and mechanical properties while minimizing water absorption. These findings highlight the potential of CBPs as an eco-friendly and effective alternative, with adhesive and pressing parameters tailored to meet specific application requirements.

A flame-retardant treatment for cellulosic paper was applied by spraying the paper with combinations of lignin, phytic acid, and sodium silicate. Lignin enhanced the flame retardancy in the condensed phase, while phytic acid provided dual-phase flame resistance. Sodium silicate further improved thermal stability by forming silica gel through its reaction with phytic acid. The limiting oxygen index increased from 16.8% to 22.0%, and in vertical flame tests, treated paper self-extinguished within 1.5 s, whereas untreated paper burned completely in 12.0 s. Thermogravimetric analysis revealed enhanced thermal stability, with treated paper retaining 36.5% residual char at 900 °C compared to 0% in untreated paper. Despite the relatively low coating coverage from the spray deposition method, the synergistic interaction of phytic acid, lignin, and silica gel effectively compensated by promoting dense char formation and thermal insulation. Fire retardancy was attributed to phytic acid-catalyzed lignin and silica composite formation in the char layer, enhancing structural stability and shielding efficiency. Raman spectroscopy confirmed improved graphitization (I_D/I_G = 1.20), while scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and Fourier transform infrared spectroscopy (FT-IR) verified phosphorus and silica retention. This treatment showed potential for high-performance flame-retardant cellulose materials in packaging, construction, and other industries.

The mechanical and free vibration behaviors of unsaturated polyester matrix composites reinforced with 10-, 50-, and 150-mm-long palmyra palm leaf stalk fibers were examined. The fibers were alkali-treated before being used as reinforcement, which improved fiber-matrix interfacial strength, while reducing their hydrophilic character. The hand layup process followed by compression molding technique were used to produce the composites. Experiments were conducted to determine the tensile, flexural, impact, and vibration characteristics following the required ASTM standards. The results demonstrated that the most effective adhesion with the matrix was achieved with 50-mm-long fibers. To identify the properties of free vibration, a fast Fourier transform analyzer was used. Longer fibers offered slightly higher natural frequencies in the composites. To understand the mechanism of fracture, specimens that had been subjected to tensile testing were analyzed using scanning electron microscopy. Developing engineering applications with effective vibration-damping capabilities for a sound absorption potential compared to other lignocellulosic fiber composites may be achieved using palmyra palm leaf stalk fibers-reinforced composites.

The benefits of hydrothermal carbonization (HTC) for carbon sequestration, energy, and soil remediation are widely recognized. Up to the present, there has been much research on hydrochar from terrestrial biomass residues, but there is little research on hydrochar based on aquatic plants. In this study, the physical and chemical properties of water hyacinth (representative of aquatic plants) and corn stalk (representative of terrestrial plants) were systematically analyzed under the condition of single hydrothermal carbonization. The results showed that water hyacinth-based hydrochar (WHHC) had well-developed pores, rich functional groups, and high nitrogen content. Among them, the nitrogen content of WHHC was 3.83%, which was more than three times the nitrogen content of corn straw-based hydrothermal carbon (CSHC) (1.11%), and the number of micropores, mesoporous pores, and macropores were also higher than that of CSHC. These differences were attributed to the contrasting growing environments and main components of water hyacinth and corn stalk. These differences revealed their potential application directions: WHHC can be used as an adsorbent and soil amendment; CSHC is more suitable as a supplementary energy source because of its higher carbon content and stability.

Robinia wood has a high technical and economic potential due to its future availability, its mechanical properties, and its durability. This also applies to its use in structural timber construction. Such applications require the manufacture of bonded construction products from this type of wood in order to compensate for dimensional shortcomings. In an application-oriented research project, tests were carried out for manufacturing technologies and resulting properties of glued laminated timber made from the hardwood species Robinia for structural purposes. Based on adapted visual grading rules, the strength and stiffness profiles of Robinia laminations were evaluated. The influence of different adhesive types and of production parameters on the strength and durability properties of glued finger joints and glulam bond-lines were characterised. By means of a simulation model based on X-FEM methods in combination with Monte Carlo simulations, the property potential of glued Robinia laminated timber was calculated. The model was calibrated by means of input parameters from the empirical lamination and finger joint test data and verified by a small series of full-scale glulam tests. The investigations showed the great potential of Robinia glulam, especially in highly loaded and heavily weathered applications.

Effects of adding wollastonite (W, at 5% and 10%) and palm leaf residues(at 10%), based on the dry weight of wood fibers, were evaluated relative to selected properties of medium-density fiberboards (MDF), bonded with two adhesive systems, i.e., urea-formaldehyde (UF, at 10%) and isocyanate (IC, at 5%) resins. The results indicated a general improvement in screw withdrawal resistance in the UF-bonded panels due to the addition of wollastonite. This enhancement is attributed to the reinforcing effect of wollastonite. In the IC-bonded panels, the addition of wollastonite had an improving effect when W-content was 5%. The addition of defibrated palm leaves generally decreased the screw withdrawal resistance of the MDF panels due to the soft nature of the palm fibers. The fire properties of the IC-bonded panels tended to be more favorable or at least comparable to those of the UF-bonded panels, which was attributed to the formation of bubbles in the cured resin. The addition of wollastonite generally improved fire properties in both resins. It was concluded that wollastonite and defibrated palm leaves can be recommended for MDF production when the contents of wollastonite and palm leaves do not exceed 5% and 10%, respectively.

The main objective of this study was to manufacture and test environmentally friendly composite materials using biomass residues as reinforcement: pine needles and recovered paper. A mixed matrix was also used, with natural dammar resin as the predominant component, in order to favor the eco-friendly nature of the resulting material. The manufacturing process employed was the lay-up hand technique. Another objective was to investigate how dammar resin influences the mechanical properties as its mass percentage increases in the mixed resin composition. To investigate the influence of dammar resin on the mechanical properties of the composites, additional materials were fabricated for comparison, using the same reinforcements but with two types of synthetic matrices: epoxy and acrylic. The samples were tested for tensile strength, compression, bending, Shore D hardness, and vibrations.The results indicated that as the percentage of dammar in the matrix increased, a decrease in the strength and rigidity of the material occurred, accompanied by an increase in elasticity and ductility. Water absorption tests showed that the saturation process occurred much faster, as pine needles tend not to absorb a significant amount of water due to the presence of lignin, wax, resins, and pectin, which act as a natural water-repellent barrier.

Thermoplastic starch (TPS) was evaluated as a filler in a poly(butylene adipate-co-terephthalate) (PBAT) matrix. The effect of different levels of TPS (0%, 10%, 30%, 50%) on the composite was studied. The TPS/PBAT composites were prepared by melt blending modification and high temperature moulding. The mechanical properties, hygroscopicity, water absorption, thermal stability, and micromorphology of the PBAT-based composites were tested. The results showed that the tensile strength of TPS/PBAT composites decreased from 13.7 to 3.83 MPa when the TPS content was increased from 0 wt% to 50 wt%; the flexural and tensile strengths of the composites with the addition of 10 wt% TPS were increased by 14.9% and 16.3%, respectively, compared to those of pure PBAT. The water absorption, moisture absorption balance and contact angle of the composites were improved and the contact angle of the 30 wt% TPS/PBAT composites reached 108 deg. The addition of TPS reduced the coefficient of linear expansion of the composites, which showed better thermal stability. The results are important for the development of new biodegradable composites.