Abstract
Liquefi ed wood (LW) is a promising natural material that can be used as a part of the adhesive formulation. However, adhesive bonds made of LW only, have low durability. The aim of this study was, therefore, to increase the durability of adhesive bonds containing 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 defi ned for liquefaction at 180 °C. After liquefaction, the EG was evaporated in order to achieve a low solvent content LW with a fi nal mass ratio of 1:1. A hydroxyl number for 1:3 and 1:1 LW was determined in order to examine the reduction of hydroxyl groups. 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. The adhesive mixtures LW1:1 and LW1:1 /CT (uncured and cured) were analyzed using FT-IR spectroscopy. No signifi cant differences were observed between the cured LW1:1 and the LW1:1 /CT samples.
Highlights
IntroductionAdhesives are an indispensable part of wood-based composites
ethylene glycol (EG) u iznosu 1:1 i osušen (LW1:1), utekućenog drva s masenim omjerom drvo:EG u iznosu 1:1, dodanim kondenziranim taninom i osušen (LW /condensed tannin (CT) (85/15)) 1:1 ratio between the solvent and wood of 1:3 during liquefaction for 120 minutes at 180 °C was optimal in terms of the highest liquefaction yield achieved
The preparation of this low solvent liquefied wood was performed with ethylene glycol evaporation at 120 °C and at reduced pressure
Summary
Adhesives are an indispensable part of wood-based composites. They are mainly composed of oil-based derivatives, which make them dependent on an ever-increasing oil price. One of the basic constituents of a large number of synthetic wood adhesives is formaldehyde, which is, potentially carcinogenic (IARC, 2004). Due to the free formaldehyde emission, the increasing prices of oil-based derivatives, strict environmental requirements, and increasing ecological awareness, there have been many attempts to produce wood adhesives based on natural and renewable sources. Liquefied wood is one of the naturally-based products that has been developed in recent years.
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