Complex application of products obtained by water extraction of tree bark for the formation of a three-dimensional polyurethane matrix with increased thermo-oxidative stability and availability to microbial mediated degradation

Project status


Project execution time

01.01.2022 to 31.12.2024

Project type


Project number


Project manager

Aleksandrs Aršaņica

Involved laboratories

Laboratory of Lignin Chemistry

Call, activity

Latvian Council of Science Fundamental and Applied Research Project 2021/1 (LCS FARP 2021/1)

Project goal

Polyurethanes (PU) are the most versatile plastics with a constantly growing market. Increasing the share of the renewable component, improving the operational characteristics and biodegradability of PU materials, is a defining direction of the modern development of PU chemistry. The aim of the project is to gain knowledge of the complex use of tree bark components in PU materials. Constituents able to dissolve and react in conditions of PU matrix formation will be isolated from bark by microwave-assisted (MW) water extraction. MW-treatment with the controllable promotion of cell wall degradation and transport of hemicellulose derivatives into the solvent will regulate the extract’s composition and functionality. Extractives will be introduced into the PU matrix via the reaction of OH groups, mainly of carbohydrate origin, with isocyanate. The incorporation of phenolic bark antioxidants of glycoside nature into the PU matrix will inhibit their volatilization at heating. The bark residue after extraction introduced as filler in PU foams will act as fire retardant. The effect of bark extraction products on the mechanical properties, thermo-oxidative stability and biodegradation of PU films and rigid foams will be estimated. The regimes of extraction and methods of the introduction of bark fractions in the recipes of biobased PU materials with improved properties will be the main results of the project. It will promote the development of market products based on forestry wastes.

Projekta galvenie rezultāti: Izveidota teorētiskā bāze un tehnoloģiska pieeja mizas komponentu kompleksai izmantošanai biobāzētu poliuretānu, ar uzlabotām īpašībām, iegūšanai. Ir nopublicēti 5 zinātniskie raksti, ir reģistrēts patents.

Project implementation period: 36 months.
otal financing of the project: EUR 299999.70.
Place of project implementation: Latvian State Institute of Wood Chemistry, Riga, Latvia.


Project Implementation:

Third 6-month activity (01.01.2023 - 30.06.2023)

After characterization of the bark extracts and their fractions composition, functionality, reactivity in the urethane-formation reactions and development of the methodology for their introduction in PU materials, their influence on the structural, mechanical and thermal properties of the model PU films was thoroughly studied. PU elastomers containing up to 50% of bark extractives were obtained.

Experimental data confirmed the crosslinking activity of the bark-sourced biopolyol in PU, leading to an increase in glass transition temperature (Tg), a decrease in sol fraction yield upon leaching of cured PU networks in THF, a significant increase in Young's modulus and tensile strength of material. The bark-sourced building blocks promoted char formation under high temperature and oxidative stress, reducing combustible volatiles and limiting heat release during macromolecular network degradation compared to biopolyol free PU. This shift towards char oxidation at higher temperatures suggests a potential decrease in flammability during actual combustion tests of bio-polyol-based PUs.

 According to the project plan, substantial experimental work has been started to study the availability of synthesized materials to microbial-mediated degradation. The susceptibility to biodegradation of bio-based PU elastomers containing 40% and 50% of black alder bark extractives as biopolyol, replacing fossil-based PEG 400, was compared to that of 100% fossil-based PU. The synthesized PUs films were subjected to a degradation period of 2 months in sewage water and compost-enriched soil, serving as media and sources of biodegrading microorganisms. The weight loss data, as well as the Py-GC/MS, FTIR and TG   confirmed the increased susceptibility to biodegradation of PU containing bark-sourced building blocks in comparison with fossil based PU. The abstract titled "Influence of Black Alder Bark Extractives as Integral Building Blocks on the Susceptibility to Biodegradation of Resilient Polyether Polyurethanes" was submitted for presenting the results at the International Conference EcoBalt 2023 "Chemicals & Environment" in Tallinn, Estonia, from 09 to 11 October 2023.

The project's findings have been submitted for publication in two high-impact scientific journals with a citation index of at least 75% of the average in the field:

"Controlling the Reactivity of Hydrophilic Bark Extractives as Biopolyol in Urethane-Formation Reactions Using Various Catalysts" by Alexandr Arshanitsa, Jevgenija Ponomarenko, Matiss Pals, and Lilija Jashina, submitted to the journal "Industrial Crops and Products."

"Impact of Bark-Sourced Building Blocks as Substitutes for Fossil-Derived Polyols on the Structural, Thermal, and Mechanical Properties of Polyurethane Networks" by Alexandr Arshanitsa, Jevgenija Ponomarenko, Matiss Pals, Lilija Jashina, and Maris Lauberts, submitted for publication in the journal "Polymers."

Second 6-month activity (01.07.2022 - 31.12.2022)

Unlike fossil-derived polyol-polyether, which are enriched with aliphatic OH, bark-derived polyols contain both aliphatic OH and phenolic groups. As reactivity of various phenolic groups, including phenolic groups of catechol, pyrogallol and resorcinol moieties in urethane-formation reaction is not characterized so far, it was studied during this project using both obtained bark extracts and several modelling compounds chosen based on the extract’s composition. Kinetic reactions between the polyols under study, including model compounds, and diphenyl methane diisocyanate in a DMSO solution were monitored using FTIR by measuring the absorption intensity at 2273 cm-1, corresponding to the free -NCO groups of the isocyanate. Additionally, isothermal DSC was employed to determine the second-order rate constants and molar enthalpy of the reactions. According to the obtained results, the involvement of aliphatic OH and phenolic groups of the bark extractives in the reaction with isocyanate can be modified by using different catalysts. The high catalytic activity and selectivity of the tertiary amine - 1,4-diazabicyclo [2.2.2] octane (DABCO) catalyst towards reactions of extractives phenolic groups with PMDI was established. But tin organic - dibutyl tin dilaurate (DBTDL) catalyst exhibit higher activity in the reaction of aliphatic OH groups of carbohydrates with isocyanate compared to compared to amine catalyst.

First 6-month activity (01.01.2022 - 30.06.2022)

The microwave assisted water extraction of coniferous and deciduous tree barks was performed at different regimes. The composition and functionality of coniferous and deciduous tree bark extractives were studied, depending on microwave-assisted water extraction conditions. Was shown that black alder bark extractives (Alnus glutinosa) obtained at low (70-90°C) temperature consists mainly on non-lignin polyphenolic diarylheptanoids from which oregonin is enriched with aliphatic and phenolic OH groups. Water extracts of Baltic pine (Pinus sylvestris) bark obtained at the same temperature mainly consist of condensed tannins or proanthocyanidins. Extracts from both black alder and pine barks obtained at different times of isothermal heating between 130-150°C have decreased content of phenolic secondary metabolites and are rich in carbohydrates, including those derived from cell wall components, such as hemicelluloses. Depending on the extraction conditions, the total content of hydroxyl groups varies in the range of 24-30% for black alder bark extracts and in the range of 21-26% for pine bark extracts.

In order to evaluate the potential application of extracted bark residues as fillers for PU foams, with the ability to enhance the properties of polymer composites while reducing the environmental impact associated with their disposal, their composition was analysed using analytical pyrolysis (Py-GC-MS/FID), FTIR and wet chemistry methods. The solid residues obtained after bark extraction exhibit an enrichment of lignin compared to the initial bark. Consequently, we propose that incorporating bark extraction residues as fillers in polyurethane foam formulations will offer natural fire retardancy by forming a protective charcoal layer on the material surface during high-temperature oxidation.