• Rural Digital Europe
• Publications close
• KR close
• European Journal of Wood and Wood P... close

Abstract The mechanical properties of four ply-lam cross-laminated timbers (CLTs) containing a plywood layer were compared with those of glued laminated timber (GLT) and CLT. The bending, out-of-plane shear, compression strengths were highest in the GLT, which was followed by the ply-lam CLTs and CLT. The modulus of elasticity values for three studied ply-lam CLT samples were 1–2.5 GPa higher than GLT; however, the bending strength of all ply-lam CLTs was 7.3–18.8 MPa lower than GLT. The length of the plywood product is 2,440 mm, and longitudinal bonding is required to manufacture ply-lam CLTs of length > 3m. The prediction of bending capabilities by shear analogy was compared with the bending properties when joints were included. The performances of all the pilot-scale ply-lam CLT samples exceeded the predicted bending performance standards for MOE (10 GPa) and modulus of rupture (30 MPa) All samples exceeded 10 GPa and 30 MPa, based on projected and experimental data.

The aim of this study was to investigate the effect of the knife-incising pretreatment on the surface checks occurrence of red pine heavy timber after drying. The effect of knife-incising was evaluated by comparison with surface checks which occurred in the control and kerfed material. The results revealed that the knife-incising treatment was effective compared with control in the prevention of surface checks, and the effect is similar to that of the kerfing treatment. In addition, the combination of incising and kerfing was most effective in preventing surface checks.

Formaldehyde emissions from wood particleboards bonded with pine and wattle tannin-based adhesives, using hardeners paraformaldehyde, hexamethylenetetramine and TN (tris(hydroxyl)nitromethan), were measured by the perforator method (DIN EN 120—European Committee For Standardization 1991). All particleboards made using the wattle tannin systems with the three different hardeners were satisfied grade E1, while in the case of pine tannin only the use of the hexamine hardener led to grade E1 being satisfied. This tendency was attributed to the curing mechanism of the hardener, the reactivity of the tannin molecule toward formaldehyde and the fast reactivity toward formaldehyde of pine tannin, due to the inclusion of phloroglucinolic A-rings within its molecular structure. Hexamine was effective at reducing formaldehyde emission in tannin-based adhesives when used as the hardener. Being a more sensitive and advanced method, it was also used. The samples used for gas chromatography were gathered during the perforator method. The formaldehyde emission levels obtained from gas chromatography were similar to those obtained from the perforator method.

This study was performed to investigate a radial distribution of moistures and tangential strains within a 30 mm thick log cross section of larch by a circumferential slicing-method during radio-frequency/vacuum (RF/V) drying. Before the RF/V drying, the moisture contents (MC) at the heartwood zone remained nearly constant in the range of about 42 percent MC to 53 percent MC, while from around 0.80 diameters away from the pith toward bark they abruptly raised to maximum 149.4 percent MC and then decreased slightly. From 79 hours of the drying times to end of the drying the moisture distribution along the radial direction remained almost uniform. When the log cross section fell below fiber saturation point at 79 hours of drying, most of the slices represented the maximum tensile strains, and from that time the tangential strains in tension steadily increased toward the bark side, and reached the maximum value at the border zone between heartwood and sapwood. Most of log cross sections of larch could be dried without formation of checks and V-shaped cracks during the RF/V drying process.