Detection of tropical wood in paper - Chemotaxonomy and anatomy to identify Mixed Tropical Hardwood (MTH III) Controls to protect forests
How do you recognize the types of wood used in paper products?
The progressive deforestation of our planet reduces biodiversity and accelerates global warming. In order to counter the trade in illegally harvested wood, the wood used must be identified. This already works very well for solid wood and plywood, but how do you determine which woods were used to make paper? A lot of the worldwide wood use consists of these pulp and paper materials. In this project, funded by the DBU, methods for the identification of wood species are developed and established in a cooperation between the University of Hamburg (UHH) and the Thünen Institute for Wood Research. The UHH follows the chemotaxonomic approach, while the TI follows the approach via morphological features.
Paper goods are subject to the European Timber Regulation (EUTR) - importers must be able to name the types of wood used and their legal origin as part of their duty of care. To check the manufacturer's information, the woods contained in the paper are determined using their characteristic structural features. In the case of hardwoods, the anatomical references of the particularly distinctive vascular elements are compared. Therefore, detailed descriptions of the cell types are required. So far, these have existed almost exclusively for woods in Europe and North America. As part of the project funded by the DBU, references for many Asian woods were recorded for the first time and published in the form of an atlas. Test laboratories all over the world can now use it to identify important commercial timber and protected timber from Asia.
01.08.2018 - 31.01.2021
Project number: 34295/01
In general, the chemotaxonomy tries to classify plants based on their phytochemicals. In this part of the project, we are tracking the woods used in the paper through the slightest remains of their characteristic chemical ingredients (biochemical composition). A completely new method has been developed for identifying wood species in paper. In the chemotaxonomic approach, bleached fibers are extracted and characterized by GC / MS.
For this, on a laboratory scale but close to industry parameters, pure pulp needs to be produced first as references: The anatomically identified solid wood is shredded into wood chips. In the sulfate (Kraft) process and in several bleaching stages, the lignin is largely removed from the wood while maintaining the carbohydrates. Between the production steps the pulp is being washed with water. The aim of these process steps is to produce pulp fibers that are as white as possible. Many wood components, especially water-soluble wood components, are lost during the production of pulp.
Figure 1: From solid wood to paper the material goes through many process steps. Nevertheless, the chromatograms of the extracts show a high density of information
Although a large part of the extract substances is washed out during production, a little less than 0.1% remains in the pulp. These leftover substances can be various substances such as fats, resins, sterols or tannins. Figure 2 shows schematically the extraction of these substances from the pulp. A successive extraction with solvents of different polarity should, if possible, remove all remaining ingredients. The extracts obtained in this way are analyzed with gas chromatography - mass spectrometry.
Figure 2: Extraction: solvent evaporates, condenses in the cold trap, drips into the sample and flows off
Figure 3 shows the chromatograms of the extracts of Bangkirai and White Meranti pulp inverted. The chromatogram section in Figure 3 (RT 48-120 min) illustrates both the similarities and the differences of the chromatograms. Both species belong to the genus Shorea. A database for comparing unknown samples is created from the measurement data of the references.
Figure 3: Chromatograms of the extracts of Bangkirai and White Meranti pulp (inverted representation) in comparison - similarities and differences
In this cooperation project, the anatomists of wood research at the Thünen Institute provide a morphological approach with which wood species can be identified in charcoal, paper and fiber products. The woods are recognized by their anatomical features under the microscope.
For more information, visit Thünen Institute.
Figure 4: Measurement of a vascular element. From: ATLAS OF VESSEL ELEMENTS, Helmling S. et al., 2018, Iawa Journal 39