Efficiency of High-Frequency Pressing of Spruce Laminated Timber Bonded with Casein Adhesives

This study identifies the importance of reducing press times by employing high-frequency pressing of spruce-laminated timber bound with sustainable casein adhesives. Spruce lamellas with dimensions of 12 × 10 × 75 cm were bonded into five-layered laminated timber and then separated into single-layer solid wood panels. Three types of casein (acid casein from two sources and rennin) were used. To compare the effectiveness of the casein formulation, two control samples bonded with polyvinyl acetate (PVAc) adhesive were pressed at room temperature (20 °C) and also with high-frequency equipment. The tests included compression shear strength, modulus of rupture, modulus of elasticity and screw withdrawal resistance on the wood panel surface and in the glue line. The average values of casein-bonded samples compression strengths ranged from 1.16 N/mm2 and 2.28 N/mm2, for modulus of rupture (MOR) were measured 85 N/mm2 to 101 N/mm2 and for modulus of elasticity (MOE) 12,200 N/mm2 to 14,300 N/mm2. The screw withdrawal resistance (SWR) on the surface of the wood panels ranged from 91 N/mm to 117 N/mm and in the adhesive line from 91 N/mm to 118 N/mm. Control samples bonded with PVAc adhesive did not perform better for compression shear strength, MOR and MOE, but for SWR in the adhesive line with 114 N/mm. Casein-bonded spruce timber pressed with HF equipment represents a sustainable new product with reduced press times, hazardous emissions and improved workability.

The effect of oil palm trunk particles and composite density on the physical and mechanical properties of rigid polyurethane foam composite

The oil palm trunk (OPT) particle was used as a filler for the manufacture of rigid polyurethane foam composites (RPUFC). The purpose of this research is to investigate the effect of OPT particle content and variation of composite density on the physical and mechanical properties of RPUFC. The RPUFC was created with five different volume fractions of OPT particles (0, 2.5, 5, 7.5, 10 wt%) and three different composite densities (40, 50, 60 kg/m3). The OPT particles, polyols, and isocyanate were mixed, poured and formed in a closed mold. The moisture content (MC), water absorption (WA), compressive strength (CS), screw withdrawal (SW), and internal bonding strength (IB) properties were determined according to JIS A 5908-2003. The flexural strength (FS) properties were determined according to ASTM D790. The physical properties (MC, WA) were increased with increasing OPT particles in the RPUFC. The RPUFC with 2.5% OPT particle was higher in modulus of rupture, modulus of young and CS values compared to RPUFC control. The IB and SW values were increased when 2.5% OPT particles were added to RPUFC. The best PURFCs were produced with the addition of 2.5% particles at a density of 50 and 60 kg/m3.

Influence of Adhesive Systems on the Mechanical and Physical Properties of Flax Fiber Reinforced Beech Plywood

In order to improve the acceptance of broader industrial application of flax fiber reinforced beech (Fagus sylvatica L.) plywood, five different industrial applicated adhesive systems were tested. Epoxy resin, urea-formaldehyde, melamine-urea formaldehyde, isocyanate MDI prepolymer, and polyurethane displayed a divergent picture in improving the mechanical properties—modulus of elasticity, modulus of rupture, tensile strength, shear strength and screw withdrawal resistance—of flax fiber-reinforced plywood. Epoxy resin is well suited for flax fiber reinforcement, whereas urea-formaldehyde, melamine urea-formaldehyde, and isocyanate prepolymer improved modulus of elasticity, modulus of rupture, shear strength, and screw withdrawal resistance, but lowered tensile strength. Polyurethane lowered the mechanical properties of flax fiber reinforced plywood. Flax fiber reinforced epoxy resin bonded plywood exceeded glass fiber reinforced plywood in terms of shear strength, modulus of elasticity, and modulus of rupture.

Comparison of the Effects of Two Different Hollow Nails in the Treatment of the Young Pauwels Type Ⅲ Femoral Neck Fractures

Background: At present, there is a higher complication rate after treatment of femoral neck fractures with three parallel hollow nails (PHN) in the young Pauwels type Ⅲ femoral neck fractures.For better effect,F-shape hollow nails(FHN) is used to treat femoral neck fractures.The purpose of this study is to compare the clinical efficacy of FHN and PHN and provide reference for clinical application.Methods: Thirty-eight consecutive patients admitted from January 2017 to January 2020 were selected for the study. According to random number table method, the patients were divided into two groups:group A (FHN) and group B (PHN). The gender, age, BMI, comorbidities, time from injury to operation and other general preoperative demographics were not statistically different (P>0.05). The data of the two groups can be comparable.The occurrence of avascular osteonecrosis of the femoral head (AVN), femoral neck shortening, hollow screw withdrawal was recorded in follow-up.Then, Harris hip score (HHS), pain visual analog score (VAS) of two group were obtained at the last follow-up. Results: The mean follow-up period after surgery was 21.4±10.1 (range, 14–29) months. There were 18 cases(mean age, 47.5±9.6) in group A, 20 cases (mean age, 48.6±10.1) in group B. There was no significant difference between the two groups in AVN, femoral neck shortening (P>0.05), the two groups had statistically significant differences in screw withdrawal (F=4.416, P<0.05). There was no significant difference in HHS and VAS between the two groups at the last follow-up (P>0.05).Conclusion: Three parallel hollow nails (PHN) and F-shape hollow nails (FHN) have similar short-term effects in the young Pauwels type Ⅲ femoral neck fractures, but the nail withdrawal rate of FNH is lower.

Evaluation of cement-bonded particleboards produced from mixed sawmill residues

This study evaluates the application feasibility and properties of cement-bonded particleboards produced from mixed tropical hardwood species. Wood residues from a typical sawmill were collected, dried and used in the manufacturing of the cement composites. The wood residues used were from Ceiba pentandra and Gmelina arborea timber species. The residues were mixed in seven ratios in the production of the composite samples. Two control experimental samples containing unmixed residues of each species were also produced. The test carried out on the boards were flexural strength, water uptake properties and wet and dry screw withdrawal resistance. The effect of the wood mix ratio on the board properties was evaluated. The result showed that all properties except the screw withdrawal resistance were significantly influenced by the mix ratios (p < 0.05). The wet and dry screw withdrawal resistance ranged from 1170 to 1770 N and 1360 to 1830 N, respectively. The optimum wood mix ratio for enhancing mechanical performance of the boards was 1:4 of C. pentandra/G. arborea wood residues. Based on the result of this study, the particleboards produced can be used as wood composite ceiling tiles in building applications.

Assessment of Wooden Foundation Piles after 125 Years of Service

Buildings on piles have been constructed in Ljubljana since the Bronze Age. The piles were made of different types of wood. In the present study, piles that were erected about 125 years ago were investigated. Investors tend to renovate a building; therefore, the piles were analysed to assess the structural condition of the building. The building showed no signs of damage. To gain access to the piles, a 2 m thick layer of soil was removed. On-site, the following analyses were carried out: drilling resistance with a resistograph and a screw withdrawal test. Part of the piles was isolated and light microscopy, scanning electron microscopy, infrared spectroscopy, dynamic vapour sorption, density analysis, and chemical analysis were performed. Microscopic analysis revealed that the piles were made from the wood of Scots pine (Pinus sylvestris). The results indicate that the wood was severely degraded, mainly by soft-rot fungi and bacteria, resulting in a significant deterioration of its mechanical properties.

Effects of the Face/Core Layer Ratio on the Mechanical Properties of 3D Printed Wood/Polylactic Acid (PLA) Green Biocomposite Panels with a Gyroid Core

Gyroid structured green biocomposites with different thickness face layers (0.5, 1, 2 and 2.5 mm) were additively manufactured from wood/ polylactic acid (PLA) filaments using a 3D printer. The mechanical properties of the composite panels, bending properties, compressive strength (parallel to the surface), Brinell hardness, and face screw withdrawal resistance, were determined. The surface layer thickness significantly affects the mechanical properties of the composite materials. As the surface layer thickness was increased from 0.5 to 2.5 mm, all the mechanical properties significantly improved. In particular, the Brinell hardness and face screw withdrawal resistance of the specimens improved sharply when the skin thickness was higher than 2 mm. The bending strength, bending modulus, compressive strength (parallel to the surface), Brinell hardness, and face screw withdrawal resistance of the specimens with a skin of 0.5 mm were found to be 8.10, 847.5, 3.52, 2.12 and 445 N, respectively, while they were found to be 65.8, 11.82, 2492.2, 14.62, 26 and 1475 N for the specimens with a 2.5 mm skin. Based on the findings from the present study, gyroid structured composites with a thickness of 2 mm or higher are recommended due to their better mechanical properties as compared to the composites with skins that are thinner.

Influence of cooling rate on the physical properties, chemical composition, and mechanical properties of heat-treated rubberwood

This study aimed to reduce the loss of mechanical strength in heat-treated rubberwood by rapid cooling. Heat-treated rubberwood specimens were prepared by controlling their cooling rate during the cooling phase of the heat treatment. The effects of cooling rate on the physical properties, chemical composition, and mechanical properties of heat-treated rubberwood were evaluated. Results indicated that cooling rate significantly influenced mass loss (ML). ML in heat-treated rubberwood cooled at 6 °C min−1 decreased by 23% relative to that in heat-treated rubberwood subjected to natural cooling. Compared with the heat-treated rubberwood subjected to natural cooling, the heat-treated rubberwood that was cooled at 4.5 °C min−1 increased in modulus of rupture (MOR), surface hardness, and screw withdrawal strength (tangential section) by 26, 8, and 16%, respectively. The cool rates exerted less effects on the dimensional stability, surface color, modulus of elasticity (MOE), compressive strength parallel to grain (CS), and screw withdrawal strength (radial section) of the heat-treated rubberwood. The application of rapid cooling to wood heat treatment could efficiently shortened the heat treatment period, thus increasing productivity.

Steatite Powder Additives in Wood-Cement Drywall Particleboards

The objective of this study was to develop a new drywall wood-based particleboard as an alternative to gypsum board. Various development iterations have led to the use of wood particles, steatite powder and Portland cement. The resulting outcome shows that screw withdrawal resistance was improved by 37% and bending properties by 69% compared to gypsum board of a similar density (0.68–0.70). The raw surface of the boards is of good quality and comparable to the paper-faced surface of gypsum board. Furthermore, the reaction to fire was evaluated through bench-scale test with a cone calorimeter. The investigated particleboard did not reveal visual signs of combustion after 20 min when exposed to a radiant heat of 50 kW/m2, while burning of the overlay paper of gypsum board occurred at about 57 s, suggesting that wood-cement-steatite powder particleboard could be classified as a quasi non-combustible material.