Influence of Urea-formaldehyde Adhesive Modification with Beech Bark on Chosen Properties of Plywood

Abstract

The influence of beech bark concentrations as filler in urea-formaldehyde (UF) adhesives was investigated relative to the composite forming process and selected properties of final 5-layer beech plywood. Beech bark was used as filler to lower the wood processing waste production and decrease formaldehyde emissions. A combination of UF adhesives filled with different beech bark concentrations as the adhesive was used. Three different concentrations of beech bark, 15 wt.%, 20 wt.%, and 25 wt.% were used in the experiment. Urea-formaldehyde adhesive filled with 20 wt.% technical flour was used as a reference sample. The effect of the filler was studied via its temperature profile during pressing, mechanical properties in bending, water absorption, thickness swelling, and formaldehyde emissions after pressing. The time needed to reach the temperature between the beech veneers, at least 105 °C, which was equal to the final temperature filler-adhesive-wood matrix cross-linking, was also investigated during the pressing process. The measurements of the free formaldehyde emissions showed that for samples with non-zero bark concentrations there was a decrease of formaldehyde emissions by at least 46%.

Bonding strength of benuang and duabanga glulams using their barks as phenol formaldehyde-filler

“…The differences characteristic of barks may affect the suitability of bark as PF-filler. Filler are generally used as additives in glue mixtures to increase viscosity and provide better gap filling properties and lower formulation costs [7,29]. Depending on these functions, the choice of filler is based on its effect on the adhesive's viscosity.…”

“…Organic fillers generally are biomass waste, such as walnut shell, pinenut shell, ginkgonut shell, coconut shell, periwinkle shell, palm kernel, wood flour, waste rubber, corncob residue, and wood waste ash [5,6,9,[13][14][15][16][17]. Furthermore, bark flour, such as southern yellow pine bark [18], walnut, chestnut, fir, and spruce barks [19,20], alder bark [5,6], beech bark [7], and western red cedar bark [21] are organic filler which are widely used for adhesive. The bark is mainly produced as byproducts in wood industry.…”

“…In the process of gluing, filler serves to fill the porous part of wood, such as vessel and other voids [7]. Generally, addition of filler into wood adhesive can improve gluing properties such as bonding strength, thermal stability, viscosity, and glue spreading.…”

“…The high availability of bark and high phenolic content are an advantages in the utilization of bark as filler [19]. The previous studies of bark fillers in the manufacture of wood composite was mainly originated from softwood species [7,18,19,21], which was probably due to the high abundance of softwood species in the temperate area. However, utilization of bark as filler from tropical hardwoods species is not investigated completely yet.…”

Bending Forces at the Proportionality Limit and the Maximum – Technological Innovations for Better Performance in Wood Processing Companies

“…During bending, the wood is forced to deform in a preselected direction, i.e. the character of the deformation will be forced (Wagenführ 2000;Blomberg et al 2005;Gaff et al 2015aGaff et al , 2016Gaff et al , 2017Ružiak et al 2017).…”