https://pubs.rsc.org/en/content/articlepdf/2015/gc/c5gc00282f

Chemical modification of tannins to elaborate aromatic biobased macromolecular architectures

The annual bark yield in Canada is as much as 17 million m3. Currently, more than half of the bark is incinerated or landfilled and the remainder of the bark is mainly used as a cheap source of energy in saw/pulp mills. Both bark incineration and landfilling can lead to environmental problems. Due to the abundance of ash in bark and the lower sintering point of bark ash than that of wood ash, the combustion of bark can lead to fouling which would damage the combustors. Bark contains a large fraction of extractives and lignin (up to 50 wt% on a dry basis), which can be utilized as a renewable source of chemicals, particularly aromatic chemicals. The technical routes and technologies on the valorization of tree barks for chemicals and materials are reviewed in this paper. These include direct utilization of bark for wooden panels, and extraction for extractives (mainly tannin) and their the application in resins and foam materials, as well as conversion of bark via thermochemical technologies, mainly phenolysis, direct liquefaction in alcohols and pyrolysis. Finally, some challenges and perspectives on the production of chemicals and materials from bark are discussed.

Valorization of bark for chemicals and materials: A review

https://hal.univ-lorraine.fr/hal-03140957/document

Condensed tannins from grape pomace: Characterization by FTIR and MALDI TOF and production of environment friendly wood adhesive

Activated carbons prepared by indirect and direct CO2 activation of lignocellulosic biomass for supercapacitor electrodes

The development of natural adhesives derived from nonfossil resources is very important for the future. Besides, it is desirable to be safe adhesives without using harmful chemical substances. In this study, application of citric acid as a natural adhesive was investigated. Citric acid powder and bark powder obtained from Acacia mangium were used as raw materials. Citric acid powder was mixed with the bark powder, and the resulting powder mixture was poured into a metal mold. The mold was hot-pressed at 180°C and 4 MPa for 10 min, and a bark molding was then obtained. The specific modulus of rupture and modulus of elasticity values of the molding containing 20 wt % citric acid were 18.1 MPa and 4.9 GPa, respectively. The molding did not decompose during a repeated boiling treatment. To clarify the effect of tannin on the adhesiveness of molding, bark was separated into tannin and residue. The molding was not obtained while using the tannin due to the marked fluidity, whereas it was obtained while using the residue, the same as while using the bark. It was considered that components other than tannin contributed to the adhesiveness. Based on the results of Fourier transform infrared spectra, the formation of ester linkages between carboxyl groups derived from citric acid and hydroxyl groups in the bark was confirmed. Accordingly, citric acid brought an adhesion by chemical bonding, and it could be used as a safe natural adhesive. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Application of citric acid as natural adhesive for wood

Fortification of sulfited tannin from the bark of Acacia mangium with phenol–formaldehyde for use as plywood adhesive

One of the limitations in using low molecular weight phenol-formaldehyde (LmwPF) resin as a binder for wood-based panels is the amount of the free formaldehyde being emitted during soaking, pressing and sometimes during the earlier stage of application. Tannin from bark extracts is rich in phenolic compounds, and thus may be able to absorb this free formaldehyde and at the same time provide strength to the joint. In this study, tannin–phenol-formaldehyde adhesives were prepared by blending Acacia mangium bark extracts (40% solids) with low molecular weight phenol-formaldehyde (40% solids at 1:1 ratio). The tannin–LmwPF adhesive produced cured within 4 min at 130°C, reduced the free formaldehyde to level E1 of European norm EN-120. The 3-ply plywood had acceptable shear strength (>1.0 MPa) exceeding the minimum requirements of European norms EN-314-1 and EN-314-2:1993 for interior and exterior applications, respectively. The study has shown that Acacia mangium tannin can be used as formaldehyde scavenger in LmwPF resin without compromising the strength of the joints.

/pdf/acacia-mangium-tannin-as-formaldehyde-scavenger-for-low-2vqccyzpqd.pdf

C. A. Luqman

Papers

Fortification of sulfited tannin from the bark of Acacia mangium with phenol–formaldehyde for use as plywood adhesive

Acacia mangium Tannin as Formaldehyde Scavenger for Low Molecular Weight Phenol-Formaldehyde Resin in Bonding Tropical Plywood