Liquefied wood (LW) is a naturally based product which has the potential to be used as an adhesive. It can be used as a part of a polymer formulation, as a part of an adhesive mixture with commercial adhesives, or as an independent material for wood bonding. In this study, wood was liquefied at 180 °C using ethylene glycol as the solvent and sulphuric acid as a catalyst. In the first part of research, LW with different pH values was used for the bonding of solid wood at 200 °C for 15 min. In the second part, LW with an optimal pH value was used for bonding at different press temperatures for 15 min. In the third part, the minimum pressing time at the optimal pH value and at the optimal press temperature was determined. Unmodified LW with a negative pH value, a press temperature of 180 °C, and a pressing time of 12 min was determined to be optimal (based on highest shear strength) for the bonding of 5 mm thick wood lamellas with the LW used in this study. At these conditions bonds exhibited shear strength of around 7 N/mm2 which was too low to attain standard requirements. Despite this, high wood failure (100 %) was observed as a consequence of low pH value and high press temperature which caused damage of the part of beech lamellas where LW was applied.
COBISS.SI-ID: 2034057
The bonding of beech (Fagus sylvatica L.) with liquefied wood (LW) causes deterioration of the wood surface, resulting in a high percentage of wood failure at a relatively low bond shear strength. Light microscopy, scanning electron microscopy, FT-IR micro-spectroscopy and elemental carbon, nitrogen and sulphur (CNS) analysis techniques were used to investigate the formation of such bonds. It was assumed that the degradation of lignin, hemicelluloses and parts of the cellulose occurred in the cells of the wood surface where the LW had been applied. At the elevated temperatures occurring during the bonding process, the deteriorated cells were carbonised to some extent. The weak boundary layer of the bond was determined to be a layer of delignified cells located between the zone of partly carbonised cells on the one side and the cells of the undamaged wood of the adherend on the other side. The bonds which formed during the bonding of wood with LW were found to be very untypical compared to bonds formed by synthetic wood adhesives. No adhesive film was formed, the adhesive-adherend interface was not clear and the cells of the adherend subsurface were damaged.
COBISS.SI-ID: 2058889
The influence of viscoelastic thermal compression (VTC) on surface wettability and bonding performance of wood was evaluated. Low quality beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) were densified with the VTC process to different degrees of densification. Control and densified strips were bonded with phenol–formaldehyde (PF) adhesive and liquefied wood (LW). Shear strength of bonded assemblies was determined after 1 week of conditioning at 20 °C and relative humidity of 65 %. Wettability was determined on the basis of the contact angle of water, PF adhesive, and LW using the Wilhelmy method. Results showed that densification of beech and spruce wood did not significantly affect the shear strength of specimens bonded with PF adhesive. In beech assemblies bonded with LW shear strength decreased significantly with increased density, whereas in bonded spruce specimens decrease of shear strength was not significant. It was found that degree of densification and bonding process used in the study were not appropriately chosen for spruce wood specimens, since major deformations after the bonding process occurred. Wettability changed significantly after densification. Contact angle of water and LW increased after densification, whereas contact angle of PF showed inverse trend and decreased after VTC process. Furthermore, the degree of densification had a minor effect on the wettability.
COBISS.SI-ID: 1024488788
The aim of this study was to increase the durability of adhesive bonds containing liquefied wood (LW). LW was obtained with liquefaction of black poplar wood in ethylene glycol (EG) as the solvent and sulphuric acid (SA) as the catalyst. An optimal time of 120 minutes and a wood:EG mass ratio of 1:3 was defined for liquefaction at 180 °C. After liquefaction, the EG was evaporated in order to achieve a low solvent content LW with a final mass ratio of 1:1. Four different adhesive mixtures were prepared: LW with a mass ratio of 1:1 (LW1:1), LW with a mass ratio of 1:3 (LW1:3), LW with a mass ratio of 1:1 and added condensed tannin (CT) (LW1:1/CT), and LW with a mass ratio of 1:3 and added CT (LW1:3/CT). The solid beech wood lamellas which were bonded with these adhesive mixtures were tested directly after bonding, and later on, after 7, 30 and 50 days. The test results indicated greater bonding shear strength in the case of LW1:1 compared to LW1:3. The addition of CT did not contribute to essentially higher shear strength values.
COBISS.SI-ID: 1935753
Black poplar wood, diethylene glycol (DEG), and sulphuric acid as a catalyst were used as starting reactants for liquefaction. Optimal conditions for liquefaction were established: reaction temperature 150 °C, reaction time 95 min, ratio of wood:DEG = 1:5 and 3% of sulphuric acid addition. The liquid mixture obtained by the liquefaction was composed of the real product of the reaction (the so called excess solvent free liquefied wood (ESFLW)) and of the remaining unreacted DEG. The unreacted DEG was successfully separated from the ESFLW and analysed with HPLC for levulinic acid content. Theoretical weight ratio between the wood and DEG required for the reaction was estimated. OH number investigation showed that the ESFLW in the liquid mixture contributes to maximally 60% of the free OH groups. The crosslinking of the ESFLW without any curing agents or additives was performed for the first time, and the drying stages investigated. FT-IR investigations demonstrated that the obtained crosslinked polymer film could be an ether and/or ester network.
COBISS.SI-ID: 1703049