Las estructuras laminares reticulares de madera deformadas elásticamente (elastic timber gridshells) destacan por su eficiencia material y sostenibilidad al emplear tiras inicialmente rectas de madera de pequeña sección que se curvan en flexión activa. No obstante, su desarrollo ha estado condicionado por una laboriosa puesta en obra, dependiente de medios auxiliares y de un intensivo trabajo manual in situ. El presente trabajo plantea una nueva metodología de diseño y fabricación que integra la eficiencia propia de la flexión elástica con técnicas de fabricación digital mediante maquinaria por control numérico de tres ejes y el uso de uniones carpinteras para fomentar la prefabricación de este tipo de estructuras. Se explora la capacidad de patrones con trayectorias biaxiales para generar mallados perpendiculares, se analizan las ventajas constructivas derivadas y se propone un novedoso concepto de sistema de conexión nodal basado en uniones carpinteras ortogonales integradas en la geometría de las láminas. Esto permite el mecanizado de la estructura empleando tableros estructurales. Los principios del sistema se integran en un flujo de trabajo paramétrico que abarca desde el diseño hasta la fabricación, validado mediante diversos prototipos a escala y un demostrador a escala real de 7,5 m de luz. Los resultados muestran la viabilidad del enfoque propuesto para integrar procesos de fabricación digital y prefabricación off-site, favoreciendo la reducción de las operaciones manuales durante el ensamblaje. Finalmente, se identifican las limitaciones del sistema y los principales desarrollos necesarios para su escalabilidad.
The influence of pilot-hole geometry on screw holding strength in solid softwood furniture elements remains insufficiently understood, particularly when wood species, pilot-hole dimensions, and grain direction are considered simultaneously. This study aimed to investigate the effects of pilot-hole diameter and depth on the screw holding strength of selected softwood species commonly used in furniture manufacturing and to identify the best-performing pilot-hole configurations among the tested levels for different grain directions. The materials examined were Larix decidua Mill. (larch), Pinus sylvestris L. (Scotch pine), Abies sp. (fir), Picea orientalis L. (spruce) and Cedrus libani A.Rich (cedar). A total of 900 specimens were prepared, comprising 5 wood species, 9 pilot hole configurations (3 diameter by 3 depth), and 10 replications for each condition. Screw withdrawal tests were conducted under static tensile loading, with 450 specimens tested parallel to the grain and 450 perpendicular to the grain. The results indicated that, for the withdrawal tests parallel to the grain, the highest mean screw holding strength was obtained with a pilot-hole diameter corresponding to 50 % of the screw diameter, while pilot-hole depth had no significant main effect. In case of the withdrawal tests perpendicular to the grain, highest mean screw holding strength was obtained with a pilot-hole diameter corresponding to 75 % of the screw diameter, whereas pilot-hole depth again showed no significant main effect. Wood species and pilot-hole diameter significantly affected screw holding strength, and all two-way and three-way interactions were significant. Cedar exhibited the highest mean screw holding strength in both loading orientations. These findings highlight the importance of considering pilot-hole diameter in relation to wood species and grain direction for screw connections in solid softwoods.
The intensive utilization of agricultural residues, particularly wheat straw (WS), in particleboard production as an environmentally sustainable alternative to wood-based panels remains limited due to their poor bonding performance with conventional adhesives. Citric acid (CA) has recently gained increasing attention as a bio-based adhesive and appears to be a promising solution to overcome the bonding challenges associated with wheat straw However, there is limited information available on the combined effects of the moisture content (MC) of the mat and the adhesive dosage on the behavior of WS particleboard bonded with citric acid. Therefore, the objective of this study was to determine the optimal moisture content (MC) and the optimal CA content required to achieve satisfactory physical and mechanical properties without pretreating the straw particles. To this end, the resinized straw particles were oven-dried at different times intervals (2 h to 14 h) and temperatures (80 degrees C and 100 degrees C) to obtain mat with various moisture content (0,5 %- 20 %). The effects of adhesive content of 15 %, 20 %, 25 %, and 30 % (based on the dry mass of the straw) on the properties of the panels were also studied. The optimum moisture content of the mat before hot pressing was about 11%, and the corresponding panel exhibited flexural strength, modulus of elasticity and internal bond of about 12 MPa, 3700 MPa and 0,26 MPa, respectively, while the thickness swelling and water absorption after 24-hour immersion were 6,5% and 46 %, respectively. Increasing the adhesive content from 15 % to 30 % led to an increase in flexural strength from 9 MPa to 13 MPa and 117% in internal bond. However, a further increase in the adhesive content above 20 % did not lead to any statistically significant differences in the physical properties. In general, the results showed that due to the acidic nature of citric acid, it is possible to produce particleboard from wheat straw without pretreating the straw particles before use.
The chemical and surface changes induced by heat treatment can affect wood-adhesive interactions; however, limited attention has been given to the role of silane-based surface modification in enhancing the bonding and mechanical performance of heat-treated cross-laminated timber (CLT). Heat-treated Pinus sylvestris (Scots pine) and Abies bornm & uuml;lleriana (Uluda & gbreve; fir) were used as outer layers in the manufacture of three-layer CLT panels, and their mechanical properties were evaluated in this study. Heat treatment (HT) was carried out at 200 degrees C for 4 hours according to the Thermo-wood method. Layers were joined using one-component polyurethane-based adhesive. Some samples were treated with a silane-based coupling agent before bonding to improve bonding performance, and the effects of silane on bonding and mechanical properties were studied. Within this frame, tensile shear strength (TSS), bending shear strength (BSS), modulus of elasticity in bending (MOE), and tensile strength perpendicular to the surface (PTS) were measured. According to the results, silane modification generally improved mechanical performance, leading to a significant 74 % increase in PTS in Scots pine, while also affecting BSS (13 %) and MOE (7 %) in fir. In contrast, HT mainly altered bending-related behavior, most notably in Uluda & gbreve; fir (BSS approximate to 10 %). Uluda & gbreve; fir samples showed a higher BSS performance when compared to Scots pine ones. Overall, this study emphasizes that HT and silane modification can improve the mechanical performance of CLT, with effects varying by wood species and mechanical properties, providing valuable insights for the enhancement of low-durability wood.
This study investigates sustainable wood-plastic composites produced from heterogeneous furniture-factory waste sawdust and recycled polypropylene, with maleic anhydride-grafted polypropylene as a compatibilizer. Composites containing 0-40 wt% furniture-factory waste sawdust and 0 or 3 wt% maleic anhydride-grafted polypropylene were melt compounded and injection molded. Mechanical, physical, thermal, morphological, and biological performances were systematically evaluated. Increasing furniture-factory waste sawdust content significantly increased tensile and flexural moduli, while tensile strength, elongation at break, and impact strength decreased in the absence of maleic anhydride-grafted polypropylene due to weak interfacial adhesion. The addition of 3 wt% maleic anhydride-grafted polypropylene markedly enhanced mechanical performance, increasing tensile strength to 22,80 MPa and flexural strength to 43,58 MPa at 40 wt% furniture-factory waste sawdust (improvements of up to 42,9 % and 35,7 % respectively, relative to the uncompatibilized counterparts). Scanning electron microscopy analysis confirmed improved fiber encapsulation and reduced interfacial defects. Water absorption increased with furniture-factory waste sawdust content, while fungal mass losses remained below 2 % for all formulations. Thermal analysis revealed reduced initial degradation temperatures with furniture-factory waste sawdust and a broader decomposition range in the presence of maleic anhydride-grafted polypropylene. These results demonstrate that heterogeneous furniture-factory waste sawdust can be successfully incorporated into recycled polypropylene-based wood-plastic composites and that MAPP compatibilization significantly enhances composite performance. The findings provide valuable insights into the mechanical, physical, thermal, morphological, and biological characteristics of FFWS/rPP composites produced from real industrial waste streams.
