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Rapid quality assessment of wood-based materials through spectroscopy

Periodic Reporting for period 1 - WoodSpec (Rapid quality assessment of wood-based materials through spectroscopy)

Reporting period: 2019-12-01 to 2021-11-30

The wood sector has a high potential for contributing to mitigate climate change. One way is through more efficient utilization of waste wood. The big challenge is to make sure to treat them as a secondary resource instead of a waste to dispose of. It is important to consider that the recycling potential of waste wood is still low because of the presence of contaminants in wood products, which limits considerably its recycling or reuse. The correct identification of the waste wood category will result in a proper cascading use of the material with benefits in term of reduced energy (use of renewable resources instead of fossil fuels) and economic losses (less material sent to the disposal). For waste wood entering the energy market it can translate in reduced emissions since non-compliant or low-quality material could be removed before entering the stream.

The most appropriate application of the wood-based materials will surely lead to environmental and economic advantages for society. Primarily, the need to ensure that waste wood is correctly separated and consequently properly managed is related to limit risks both for human health and the environment. Secondly, the most appropriate sorting of waste wood avoids losses in terms of material, energy and economic resources. The development of sorting technologies will help in moving in this direction and will increase the added value of the waste wood.
The authorities and traders can use the project results for fast and inexpensive quality classification of wood-based materials. In particular, concerning the biofuels sector, the developed tool will guarantee the traceability and the quality of the product entering the market, which will reduce the emissions caused by the combustion of non-compliant or low-quality materials as well as reduction of the overall costs of quality control. Similarly, wood industries and wood recovery sites can use the results to develop a new approach to wood management which promotes the sustainable exploitation of the material and its best-suited recycling or reuse. The development of a rapid and economic tool based on spectroscopy will lead to an improvement of the quality assurance and simplify monitoring of the wood products with benefits for all stakeholders.

As a consequence, the main objective of this project is to apply spectroscopy, a rapid and economic technique, to classify different wood-based materials and assess the chemical-physical characteristics of the wood materials selected as suitable to be used as biofuel in power plants. The overall aim is to increase green energy production and cascade use of wood materials and decrease landfill and greenhouse gas emissions.
I focused on two different specific objectives to reach this aim:
1) Classification models based on spectroscopic data for the rapid and economic discrimination among different categories of wood-based materials (i.e. glued wood, virgin wood, painted wood, etc.).
2) Rapid determination of quality parameters of wood-based materials selected as suitable for energy production (moisture content and calorific value).
The project has achieved most of its objectives and milestones for the period. Indications for how to perform a sampling procedure in terms of the number of subsamples, replicates and scans are now available. The definition of the most appropriate sampling procedure is essential for improving waste wood management and moving Near Infrared Spectroscopy (NIRS) into real industrial applications. In fact, the determination of waste wood composition and variability translates into reliable analytical results and accurate regression and classification models for sorting the material based on the best reuse, especially when dealing with heterogeneous material (as waste wood is).
Based on the conclusions from the sampling study, a classification model was developed for classifying the samples according to the appropriate reuse of the material: energy production, panel board production or disposal. The obtained results suggest the possibility to discriminate the waste wood material according to the most suitable end-users. In addition, regression models were developed for the rapid evaluation of waste wood parameters for energy applications: moisture content and net calorific value.
Spectroscopy has been widely used in several sectors, such as the food, pharmaceutical and agricultural industries, for its potential to simultaneously predict a broad variety of attributes. Only a limited number of studies has also investigated the application of spectroscopy to the field of wood-based material discrimination. Infrared spectroscopy and chemometrics have already been used to get qualitative information about wood. However, no studies have been carried out on the discrimination between the different categories of waste wood (e.g. untreated wood, glued or painted wood, wood with preservatives, contaminated wood) with the aim to choose the proper application. In addition, it is important to consider that currently spectroscopic techniques are already used in other recycling processes, but not for waste wood, and even the number of studies is limited. Nonetheless, the potential use of spectroscopy for online applications of waste wood is huge and will enable real-time sorting during the recycling process.
For the material selected as suitable for energy application, the identification and characterization of the chemical composition is crucial for its optimal application as biofuel. This composition characterizes the properties, quality, application perspectives and environmental problems related to any fuel. Various studies have been carried out with the aim to predict some of the most important energy parameters (i.e. moisture, ash, nitrogen and carbon contents as well as calorific value) of several biofuel samples. But it is still missing studies related to the investigation of moisture content, ash content and calorific value of different wood-based materials. This information is fundamental to choose the more appropriate combustion system reducing emission and increasing sustainability.
The results of this project represent the first steps for the real-time quality monitoring of wood-based materials using spectroscopy and chemometrics. Indeed, this project demonstrated the possibility to sort waste wood material based on its characteristics and set the stage for improving the waste wood management and moving NIRS in to real industrial applications. In addition, the results generated by this project could be used as a basis for similar problems, but on different fields of application. In fact, it was demonstrated that a good quality control and the accuracy of the results are directly linked to the sampling process, especially when dealing with heterogeneous samples. Obtaining information about the number of samples and replicates to be performed is fundamental to guarantee the reliability of the results. The scientific innovation achieved through the project is deep and the results could boost the stakeholder to optimize the industrial process and support the recycling and reuse of wood-based materials.