Marie-France Thévenon

Non-toxic albumin and soja protein borates as ground-contact wood preservatives

Wood preservatives based on protein borates, both obtained by just mixed water solutions of protein and boric acid, as well as in the case of premanufactured protein borates salts are shown to be a good method to greatly retard the leaching of boron from treated timber. Hence just premixed albumin + boric acid, premanufactured albumin borate and soja protein + boric acid all showed good preservative performance and much retarded leaching of boron. Accelerated biological tests indicated that boric acid partially fixed to timber by formation of a salt with albumin and other proteins which are then insolubilised by heat-induced coagulation can yield durability performances comparable to those obtained with CCA wood preservatives. The results of the biological tests show that protein borates, and particularly albumin borate, can be classified as long-term, wide-spectrum, ground-contact, heavy-duty wood preservatives, and are only composed of boric acid, a non-toxic to mammals biocide and of a non-toxic, natural, sometimes waste material, namely a protein. The mechanism is one of partially reversible rather than totally irreversible fixation of boron, leaving at all times small amounts of boron free to exercise its antifungal activity, but drastically diminishing its tendency to leach and greatly retarding its leaching. Boric acid leaching as a function of exposure time appears to tend to an equilibrium value. The timber is treated by just single stage, water-borne vacuum/pressure treating cycles as for traditional wood preservatives.ZusammenfassungHolzschutzmittel auf der Basis von Proteinboraten wurden entweder einfach durch Verrühren der wässrigen Lösungen von Protein und Borsäure hergestellt oder als vorgefertigte Protein-Borsäuresalze verwendet. Die Proteinsalze erwiesen sich als sehr wirkungsvoll gegen das Auswaschen von Bor(säure) aus behandeltem Holz. Borsäuresalze mit Albumin und Sojaprotein zeigtem zudem gute Schutzwirkung gegen Pilzbefall. Die Borsäure ist dabei teilweise fixiert durch Ausbilden von Salzbindungen an die Proteine, welche ihrerseits durch Wärmebehandlung, d.h. Koagulation unlöslich gemacht werden. Diese salze erreichen im beschleunigten biologischen Test ähnliche Schutzwirkungen wie CCA-Holzschutzmittel. Die biologischen Test zeigion, daß die Proteinborate, insbesondere Albuminborat als Holzschutzmittel für folgende Anwendungen charakterisiert werden kann: Langzeitwirkung, breites Spektrum, für Bodenkontakt und hochwirksam. Sie bestehen nur aus der für Säuger ungiftigen Borsäure und aus nicht toxischen, natürlichen, zuweilen auch als Abfallprodukte vorkommenden Proteinen. Die Wirkungsweise beruht auf der teilweise reversibelen Fixierung der Borsäure, wodurch einerseits jederzeit geringe Mengen freier Borsäure als pilzhemmender Stoff zur Verfügung steht, andererseits aber das übliche Auswaschen der Borsäure drastisch verlangsamt wird. Der Verlauf der Borsäure-Auswaschung scheint einem Gleichgewicht zuzustreben. Die Holzbehandlung geschieht in einem Schritt mit der für wässrige Holzschutzmittel üblichen Vakuum/Druck-Imprägnierung.

Protein borates as non-toxic, long-term, wide-spectrum, ground-contact wood preservatives

Wood preservatives based on protein borates and in particular albumin borate greatly retarded the leaching of boron from treated timber. Accelerated biological tests indicated that boric acid partially fixed to timber by formation of a salt with albumin and other proteins which are then insolubilised by heat-induced coagulation can yield durability comparable to that obtained with CCA wood preservatives. The results of the biological tests show that protein borates, and particularly albumin borate, can be classified as long-term, wide-spectrum, ground-contact, heavy-duty wood preservatives, and are only composed of boric acid. a non-toxic to mammals biocide and of a non-toxic, natural, sometimes waste material, namely a protein. Investigation of the chemical mechanisms of boric acid fixation by the protein indicated that both acid-base salt formation occurs, as well as the further formation at increasing boric acid proportions of additional boric acid/protein complexes. The mechanism is hence only one of partially reversible rather than totally irreversible fixation of boron, leaving at all times small amounts of boron free to exercise its antifungal activity, but drastically diminishing its tendency to leach and greatly retarding its leaching. Boric acid leaching as a function of exposure time appears to tend to an equilibrium value which is different for each type of protein used and differs in the case of treated timber from that obtained by just leaching of the protein borate coagulum.

Impregnation of Scots pine and beech with tannin solutions: effect of viscosity and wood anatomy in wood infiltration.

The impregnation process of Scots pine and beech samples with tannin solutions was investigated. The two materials involved in the process (impregnation solution and wood samples) are studied in depth. Viscosity of mimosa tannin solutions and the anatomical aspect of beech and Scots pine were analysed and correlated. The viscosity of tannin solutions presents a non-newtonian behaviour when its pH level increases, and in the case of addition of hexamine as a hardener, the crosslinking of the flavonoids turns out to be of great importance. During the impregnation of Scots pine (Pinus sylvestris L.) and beech (Fagus sylvatica L.), the liquid and solid uptakes were monitored while taking into consideration the different conditions of the impregnation process. This method allowed to identify the best conditions needed in order to get a successful preservative uptake for each wooden substrate. The penetration mechanism within the wood of both species was revealed with the aid of a microscopic analysis. Scots pine is impregnated through the tracheids in the longitudinal direction and through parenchyma rays in the radial direction, whereas in beech, the penetration occurs almost completely through longitudinal vessels.

One-step tannin fixation of non-toxic protein borates wood preservatives

Materials and methods Ten specimens for each case of Pinus sylvestris sapwood of dimensions 50 • 15 x 5 mm were treated under 15 minutes vacuum (-1 bar) and 30 minutes at atmospheric pressure with solutions of (1) boric acid (5% weight/volume) + Pinus radiata tannin extract (1% w/v) + egg albumin (1% w(v), (2) boric acid (5% w/v) + Pinus radiata tannin extract (1% w/v) + collagen (animal glue AT 400, 1% w/v), and (3) boric acid (5% w/v) + Pinus radiata tannin extract (1% w/v). Untreated specimens were also prepared. The specimens were dried at 103 ~ for 4 hours. Half of the untreated and treated specimens were leached for 5 days in 20~ water using lots of 50 ml water for each specimen, changed each day with a fresh 50 ml volume of water. The leaching waters were analysed for leached proteins (Li; Tanner; Larkin) (no proteins leached), leached boric acid (Li; Tanner; Larkin) and leached tannin (Thevenon; Pizzi; Haluk); [all of the tannin was still in the wood after 5 days leaching for cases (1) and (2), while 97.2% of the tannin remained in the wood for case (3)]. Leached and unleached specimens were incubated for I month at 25 ~ on agar medium in Petri dishes inoculated with Coniophera puteana, Gloeophyllurn trabeum and Poria placenta. On each plate a leached or unleached untreated control specimen was also evaluated for % mass loss.

Effect of an oil heat treatment on the leachability and biological resistance of boric acid impregnated wood

Vegetable oils provide boron retention of about 30% of initial amount depending on oil drying properties. Linseed oil is the most efficient, followed by soybean oil and rapeseed oil. Durability of C. japonica and F. crenata wood specimens has been enhanced by application of linseed oil alone but not enough to reduce termite’s attack of Coptotermes formosanus. Treating wood with a 1.0% w/w boric acid solution prior to oil treatment protects C. japonica from termite and fungi degradations. Efficiency against termites is mainly due to boron retention by oil but hydrophobic oil also forms a barrier decreasing fungi penetration. Boron efficacy threshold around 0.7 kg/m3BAE, lower than classical boron treatments thresholds indicates that oil water-repellence reinforces boron biostatic effect.RésuméLa recherche en préservation du bois se tourne à présent vers des produits à faibles impacts environnementaux. Nous avons étudié l’opportunité d’associer borates et huiles végétales pour accroître la rétention du bore ainsi que la résistance du bois aux termites et aux champignons xylophages. Les huiles végétales permettent de retenir environ 30 % du bore initial selon leurs propriétés de séchage. Ainsi, l’huile de lin est plus efficace que les huiles de soja et de colza. La durabilité d’éprouvettes d’aubier de C. japonica et F. crenata est améliorée par l’ajout d’huile de lin mais trop peu pour éviter les attaques de termites Coptotermes formosanus. En revanche, la combinaison d’une imprégnation par une solution d’acide borique à 1.0 % m/m suivi d’une traitement à l’huile protège efficacement C. japonica contre les termites et les champignons. Alors que son efficacité contre les termites semble principalement due à la rétention du bore, l’huile semble former une barrière efficace contre la pénétration des champignons xylophages. Les seuils d’efficacité d’environ 0.7 kg/m3BAE, plus faible que ceux enregistrés pour les traitements classiques au bore indique que l’huile renforce l’effet biostatique du bore.

FRIENDLY WOOD PRESERVATIVE SYSTEM BASED ON POLYMERIZED TANNIN RESIN-BORIC ACID FOR OUTDOOR APPLICATIONS

Boron compounds are used as wood preservatives as they are both fungicide and insecticide, relatively inexpensive and environmentally acceptable. Nevertheless, in the field of wood protection, borates are only used for indoor non-exposed applications or in association with other biocides, due to their main disadvantage of being readily leachable from treated wood. To overcome this problem, boric acid was fixed into wood with condensed tannins and hexamine through a non-formaldehyde emission polymer network. Treated mixtures were tested with different proportions of mimosa tannins and hexamine, with and without co-added boric acid. The treated beech samples were leached and tested according to European Standard EN 113 against Pycnoporus sanguineus in tropical conditions. The systems had minimal boron depletion and good fungal decay efficacy, meeting the efficacy requirements of EN 113.

Control of wood thermal treatment and its effects on decay resistance: a review

Key messageAn efficient use of thermal treatment of wood requires a depth understanding of the chemical modifications induced. This is a prerequisite to avoid problems of process control, and to provide high quality treated wood with accurately assessed properties to the market. Properties and structural anatomy of thermally modified woods are slightly different than un-processed woods from a same wood species. So it is necessary to create or adapt new analytical methods to control their quality.ContextHeat treatment as a wood modification process is based on chemical degradation of wood polymer by heat transfer. It improves mainly the resistance of wood to decay and provides dimensional stability. These improvements, which come at the expense of a weakening of mechanical properties, have been extensively studied. Since a decade, researches focused mainly on the understanding of wood thermal degradation, on modelling, on quality prediction and quality control.AimsWe aimed at reviewing the recent advances about (i) the analytical methods used to control thermal treatment; (ii) the effects on wood decay resistance and (iii) the advantages and drawbacks of a potential industrial use of wood heating.MethodsWe carried out a literature review of the main industrial methods used to evaluate the conferred wood properties, by thermal treatment. We used papers and reports published between 1970 and 2015, identified in the web of science data base..ResultsApproximately 100 papers mostly published after 2000 were retrieved. They concentrated on: (i) wood mass loss due to thermal degradation determination, (ii) spectroscopic analyses of wood properties, (iii) colour measurements, (iv) chemical composition, (v) non-destructive mechanical assessments and (vi) use of industrial data.ConclusionsOne of most interesting property of heat-treated wood remains its decay resistance. Durability test with modified wood in laboratory are expensive and time-consuming. This review displays data from different analytical methods, such as spectroscopy, thermogravimetry, chemical analyses or mechanical tests that have the potential to be valuable indicators to assess the durability of heat treated wood at industrial scale. However, each method has its limits and drawbacks, such as the required investment for the equipment, reliability and accuracy of the results and ease of use at industrial scale.

Normalised biological tests of protein borates wood preservatives

Materials and Methods Water solutions of albumin borate composed by a solution of 5% boric acid and 1% albumin solution both in water, applied premixed but not reacted to have still a single treatment were used to treat the wood specimens. 10 replicate Pinus syIvestris sapwood specimens for each test of dimensions 50 x 25 x 15 mm were treated under 15 minutes vacuum at I Bar followed by 120 minutes at atmospheric pressure. The treated specimens were then dried at 103~ for 8 hours to cause gelation of the proteins within the timber. The durability of these specimens against fungal attack was evaluated according to European Norm EN 350-1 for a period of 16 weeks and evaluated by average mass loss of the specimens. Twenty of the same type of treated specimens were also tested for 6 months for resistance to termite attack according to European Norm EN 117: while this norm prescribes insects of the Reticulitermes santonensis species we used the more aggressive Heterotermes indicola species. A value rating between 0 ( = no attack) and 4 ( = complete destruction of the specimen) is then assigned to the specimens after 6 months exposure to termites. The results are shown in the table 1.

Effect of extractions on dynamic mechanical properties of white mulberry (Morus alba)

Vibrational properties of wood are affected by several parameters, of which extractives can be one of the most important ones. Wood for European musical instruments has been often studied, but traditional Middle Eastern ones had been left unnoticed. In this study white mulberry (Morus alba L.), the main material for long-necked lutes in Iran, was extracted by five solvents of various polarities (water included). Free-free bar forced vibrations were used to measure longitudinal (L) loss tangent (tanδ), storage (elastic) modulus (E′) and specific modulus (E′/γ) in the acoustic range. Their anisotropy between the 3 axes of orthotropy was determined by dynamic mechanical analysis. Native wood had a quite low EL′/γ but its tanδ was smaller than expected, and the anisotropy of tanδ and E′/γ was very low. Removal of extractives caused tanδ to increase and moduli to decrease. Acetone, the most effective solvent on damping despite a moderate extraction yield, increased tanδL by at least 20% but did not modify E′/γ as much. When used successively, its effects masked those of solvents used afterwards. Anisotropy of E′/γ was nearly unchanged after extraction in methanol or hot water, while tanδ was much more increased in R than in T direction. Results suggest that in white mulberry, damping is governed more by nature and localization of extractives rather than by their crud abundance.

TOXICITY POTENTIAL IN THE EXTRANEOUS COMPOUNDS OF WHITE MULBERRY WOOD (Morus alba)

The health problems amongst musical instrument makers working on the White mulberry (Morus alba), lead to investigate the toxicity potential of wood extractives. Five solvents of different polarity and two methods of extractions were used to ensure a thorough, clear and classified compound removal. The compounds were identified using qualitative GC-mass and the toxicity were determined by studying their effect on termite survival (Reticulitermes flavipes). The results indicated the presence of different compound categories like phenols, higher hydrocarbons, fatty acids, sterols and aromatic components in the extractives. These compounds were not removable by just one solvent and the order of removal was polarity related. The extractives were found toxic towards termites. Resorcinol, which corresponded to the highest proportion of peaks in the GC-mass spectra, has been assigned as the possible compound responsible for the allergic reactions by the artisans.