Focus on resins: Chimar Hellas | 31
Similarly, within the national project BIORESCOM, new adhesive bio-resins and composite materials were developed using phenolic and furan monomers/oligomers from lignocellulosic biomass (olive and grape pruning and peach stones).
Phenolic type resins were synthesised with
(a) partial replacement of formaldehyde by furfural at levels up to 80% w/w, (b) phenol replacement by lignin phenolic fractions at levels up to 50% w/w and (c) simultaneous substitution of phenol by lignin and its phenolic fractions (up to 30% w/w) and formaldehyde by furfural (up to 60% w/w). All resins gave successful 3-layer plywood panels in laboratory scale production with performance close to the reference panels. Furthermore, Urea-formaldehyde (UF) resins were also produced using the acidic liquids from the hydrothermal treatment of different agricultural biomasses as acidifying agents during resin synthesis. Their adhesive strength was evaluated through their application in the production of typical particleboards and all the boards produced with them had lower formaldehyde content (as per EN-ISO 12460-05:2015) than the reference board produced with a typical UF resin. As part of the Cell Suc national project, Chimar produced new particle boards and plywood panels on a laboratory scale using innovative alkyd resins based on human- friendly monomers derived from renewable sources.
The resins were prepared in collaboration with the Aristotle University of Thessaloniki and their synthesis involved the reaction of succinic acid (SA) with a) ethylene glycol (EG) and b) polyethylene glycol (PEG). The particleboards produced with the experimental resins had internal bond strength similar to the reference panels and an improvement was observed in the moisture resistance performance. In the framework of the EU project
Liberate, Chimar studied the synthesis of phenol-formaldehyde based resins by replacing phenol up to 50% w/w with phenolics obtained from a) electrochemical depolymerisation of kraft and organosolv lignin b) solvent-based fractionation of organosolv FABIOLA lignin. These resins successfully produced
3-layer plywood panels on a laboratory scale. Although the quality of the panels was somewhat lower than the reference panels made with a typical PF resin, this work has shown that the use of lignin fractions obtained by electrochemical or solvent treatment is possible and promising in such an application. Moreover, in the framework of the EU project Selectiveli, CHIMAR used magnesium lignosulphonate (MgLS) and a mixture of phenolics resulting from its electrochemical
treatment as phenol substitutes during the synthesis of phenol-formaldehyde resins (PF) at levels up to 80% w/w. Although all resins were successfully used in 3-ply plywood panels on a laboratory scale, a phenol substitution level of up to 50% w/w is considered to be optimal for panels with properties comparable to a reference plywood panel.
Chimar in-house research led also to
the development of phenol-formaldehyde (PF) resins in which the phenol has been partially replaced by proteins from various sources (e.g. soy), at levels up to 50%w/w. The properties of these resins were close to those of the reference PF resins while laboratory tests showed that they are suitable for the production of a variety of panels such as particleboards, and plywood panels.
Chimar has also improved the bonding performance of urea-formaldehyde resins by adding low levels of untreated whey protein, either during the synthesis of the resin or in the glue mixture during the production of particleboard. Whey protein is a by-product of the dairy industry and its use in UF resins provides a solution for its further use in value-added applications. This work was part of the national project 19SMEs2009 and the results showed that even at low addition level whey protein addition provided boards with improved mechanical and water resistance. Furthermore, plant proteins derived from the residual biomass from oilseed plants such as rapeseed, were successfully used to replace up to 40% of the phenol needed during the synthesis of phenolic type resins (EU Pro-Enrich project). Chimar is pursuing this further using more protein samples and expanding the work to other oilseed biomass residues (e.g. sunflower, cotton).
Proteins extracted from municipal solid
waste such as spent coffee ground were tested by Chimar as phenol substitute in the synthesis of phenolic type resins and results so far have been promising for replacement levels up to 40%. This research is ongoing.
Within the framework of national project BREW2BIO, pectin in urea-formaldehyde resins (UF) has been introduced for the production of particleboards. Both commercial and experimental pectin samples (the latter extracted from orange peel residues) were added during the resin’s synthesis as well as in the glue mixture, which was later applied by spraying onto the wood particles for particleboard production. The testing of panel properties showed a positive effect on the panels’ tensile strength (Internal Bond, IB), providing promising evidence for the potential to reduce the carbon footprint of wood-based panels by incorporating in them renewable materials extracted from food waste. Cellulose, the most abundant biopolymer in nature, was used in its several nano types (crystalline, micro-/nano-fibrillated, bacterial) in adhesive systems for manufacturing wood-based panels and panels’ surfaces. The objective was to determine the cellulose effect on the product properties and performance, while trying to modulate the cellulose application either during resin synthesis or in the glue mixture preparation. The results obtained were quite promising, with some types of cellulose showing improvements in either resin or panel properties, depending on the approach used. This research is transversal and still ongoing. All the above applications pave the way for the adoption of sustainable solutions in the industrial fields of adhesives and composite wood products. ●
Above: Chimar is involved in R&D for a number of alternative bio-based resin systems
www.wbpionline.com | April/May 2024 | WBPI
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