Madera y Bosques vol. 21, núm. especial: 63-76 2015 Wood preservation using natural products Preservación de la madera usando productos naturales Rubén Francisco González-Laredo1,2*, Martha Rosales-Castro3, Nuria Elizabeth Rocha-Guzmán2, José Alberto GallegosInfante2, Martha Rocío Moreno-Jiménez2 and Joseph J. Karchesy4 1 Instituto Tecnológico de Durango. Depto. Ingenierías Química y Bioquímica. Felipe Pescador 1830 Ote., 34080 Durango, Dgo. México * Corresponding author. gonzalezlaredo@yahoo.com 2 Facultad de Ciencias Forestales. Universidad Juárez del Estado de Durango. Durango, Dgo. México 3 CIIDIR-IPN Durango. Biotechnology Group. Sigma 119 Fracc. 20 de Noviembre, 34220 Durango, Dgo. México 4 Oregon State University. College of Forestry. Department of Wood Science & Engineering. Corvallis OR, USA 997331 AbstrAct It is a current concern in the wood preservation ield to avoid the use of toxic chemicals and develop new technologies based on low environmental impact agents and sustainable principles. Under this expectation, an intended state-of-the-art is introduced on the application of natural products such as traditional tar and wood oils as well as tannins and plant extracts. A particular revision to heartwood chemical components is offered. The combined methods of using natural and chemical components are reviewed, considering as outstanding the mixtures of natural organic constituents with cooper and boron salts that seem to be under encouraging experimentation. Fungicides and anti-termite applications are commented as well the leaching problem of inorganic salts. Chemical modiication of wood structure through the formation of adducts and the treatment with nanomaterials are promising tools that will change the actual view and performance of wood preservation techniques. Keywords: bark, biocides, extract, fungicide, oil, phenolics, tannins, termites. resumen Una de las prioridades actuales en el campo de la preservación de madera es evitar el uso de materiales tóxicos, desarrollando nuevas tecnologías fundamentadas en principios sustentables y empleando agentes de bajo impacto ambiental. Con esta expectativa se plantea una revisión del estado del arte sobre la aplicación de productos naturales, tales como taninos, alquitrán, aceites y extractos vegetales. Se presenta en particular una revisión sobre los componentes químicos contenidos en el duramen de maderas naturalmente resistentes. Se analizan los métodos combinados de ingredientes naturales y químicos, resaltando las mezclas de componentes naturales orgánicos con sales de cobre y boro que parecen representar una opción experimental coniable. Se comentan también las aplicaciones fungicidas y anti termitas, así como los problemas de lixiviación de sales inorgánicas. Opciones como la modiicación química de la madera vía la formación de aductos y por tratamiento con nanomateriales son procesos promisorios que cambiaran eventualmente la manera de ver y aplicar la tecnología actual de preservación de maderas. Palabras clave: corteza, biocidas, extracto, fungicidas, aceite, compuestos fenólicos, taninos, termitas. IntroductIon chemical preservatives containing metals for wood treat- Wood as a natural renewable resource plays an important ment and their disposal problems have urged the search role in the world economy, particularly in the construc- for more ecologically friendly technologies. The current tion and furniture ields. The expectation for better progress and implementation of new technologies has options in preserving wood from biodegradation during been limited due to variability between the laboratory and storage, transportation, manufacturing, and in service is the ield performances of natural products alternatives, actual. Environmental issues from the conventional toxic and legal problems derived from the lack of globally 63 González-Laredo et al. Wood preservation deined quality standards. Plant extracts, biological con- spans and performances. These non-structural chemical trol agents, and combination of chemical and natural pro- components play a major role in the susceptibility of wood cesses are emerging as partial solutions to control wood against wood decay organisms. Using a wide selection of deteriorating organisms such as fungi, bacteria and ter- extraction methods, extractives from naturally durable mites. wood species have been used to inhibit a wide range of Any wood protection plan may involve a systematic organisms from human pathogens to insects, wood decay approach, starting with moisture control as most wood fungi, and mould fungi (Kirker et al., 2013). The attack of attacking organisms require a water source. Finishes, these organisms in general can be prevented with syn- including water repellents, can help to protect wood in thetic organic and inorganic preservatives. Although most slight deterioration environments, as above ground condi- of them are harmful to human health and the environ- tions. Durable wood, including heartwood from naturally ment, it has been shown that it is encouraging the applica- resistant species and chemically treated wood, can be used tion of wood extractives as natural preservatives. to replace deteriorated wood in moderate to extreme locations such as ground contact (Loferski, 1999). It is known that the heartwood is the naturally resistant part of tree woods, while sapwood in almost all spe- Since a previous review on tannins as wood protec- cies has no natural durability. The extractive compounds tion agents (González-Laredo, 1996) some important are produced as the living ray cells in the inner sapwood advances have been made in the exploration of new zone die, forming the non-living heartwood. As the sap- organic and natural biocides for the development and wood dies in wood species with durable heartwood, a innovation of sustainable processes to be applied for wood series of reactions in the storage or parenchyma cells of preservation. Since then several interesting reviews have the wood rays converts the stored sugars and starch into a been published (Singh and Singh, 2012; Verma et al., diverse group of biocides that constitutes the new heart- 2009; Yang, 2009; Mai et al., 2004). Also a dozen of wood chemicals (Scheffer and Morrell, 1998). The leading related patents intended to extend service life of wood and components of wood extractives are tannins, obtained wood products using some natural bioactive components typically from tree barks; lavonoids, exhibiting antifun- have been conceded (USPTO, 2013). It continues to be gical and feeding deterrent activities against subterranean imperative developing sustainable technologies for pro- termites (Carrillo-Parra et al., 2011; Reyes-Chilpa et al., tecting wood and wood products from biodegradation 1995; Reyes Chilpa et al., 1997; Reyes-Chilpa et al., 1998; with a minimum environmental impact. It is expected Sundararaj et al., 2015); quinones, with natural repellent that at some point the totally organic systems will be and toxic properties, mainly against termites; and stil- required for wood products in residential uses. benes imparting natural heartwood durability, mainly for its resistance to fungal (Nascimento et al., 2013). nAturAl durAbIlIty - wood protectIon The role of extractives in durability of eight wood from trees species compared to a nondurable control was evaluated The wood protection against biodeterioration is closely in laboratory for resistance to termite attack and decay by linked to the accumulation of extractives typically in the brown-rot and white-rot decay fungi (Kirker et al., 2013). heartwood. They are often produced by the standing tree Nearly all of the wood species displayed higher weight as defensive compounds to environmental stresses, con- loss due to termite or fungi when extractives were ferring natural resistance. However, extractive content is removed, which was comparable to the nondurable con- highly variable not only from tree to tree but also within trols. It has been suggested that micro-distribution of an individual tree. Therefore, it is a big challenge trying to extractives within the wood may be more important than standardize these materials and recommend service life incidence of bulk extractive in the heartwood, although 64 Madera y Bosques vol. 21, núm. especial: 63-76 2015 in-situ studies of extractives are extremely dificult. Both against common wood decay fungi for indoor applica- quantity and particularly quality of extractives have a key tions. Similarly, these extracts have shown termiticidal role, but their relative contribution varies considerably action against Reticulitermes grasei at relative high reten- from substrate to substrate. Moreover, Morrell (2011) tions above 90 kg/m3 on pine and 85 kg/m3 for beech sam- conirmed in western juniper that the presence of heart- ples, suggesting their use as environmentally sound wood had no effect on durability of adjacent sapwood. alternatives for wood protection (Tascioglu et al., 2012). This was observed while testing two Hawaiian heart- In the tropical rain forest, the pressure from insects woods with exceptionally resistance to termite and fungal and fungi has prompted the development of highly resis- attack in non-soil contact, where juniper heartwood was tant and long living species. As a consequence, some shown slightly less resistant to attack. woody plants are appreciated for their resistance to decay, Stirling et al. (2007) have evaluated individual com- which may be explained by the relatively high levels of ponents of western red cedar extracts and determined extractives, mainly in their heartwood. Such is the case of their role as biocidal, metal chelators, or radical scaven- seven woody species (Bagassa guianensis, Manilkara ger. They found that thujaplicins, β-thujaplicinol, and pli- huberi, Sextonia rubra, Vouacapoua americana, Andira catic acid were toxic to decay fungi and good metal surinamensis, Handroanthus serratifolius, and Qualea chelators. Plicatic acid and β-thujaplicinol showed also rosea) studied by Rodrigues et al. (2012) with varying nat- excellent radical scavenging activity. According to Morris ural durability against soft-rot, brown rot, and white rot and Stirling (2012), some of the protective compounds in degradations. From the seven wood extracts, the one from the cedars remain under typical ield exposure (UV, rain), H. serratifolius was the most effective even compared but are removed through solvent exposure. Thus, leach- with commercial standards. ability of natural wood extractives presents a major obsta- During heartwood formation, many tree species pro- cle for wood use in ground exposure. Extractive content is duce higher quality resistant wood by inserting mainly primarily responsible but not directly correlated with phenolic substances in the formed cell walls as in the case durability. Therefore, it is probable that individual com- of black locust (Robinia pseudoacacia). This has inspired ponents of extractives confer durability rather than bulk the modiication of wood properties by a chemical treat- presence of extractives. An additional factor that may also ment with commercially available hydrophobic lavonoids confer resistance to leaching and decay is the physical bar- (Ermeydan et al., 2012). Inserting hydrophobic molecules rier from the peculiar wood cell anatomy. It may provide into wood cell walls following a tosylation pretreatment additional protection against fungal colonization or resist has provided an alternative and well-suited way to signii- any severe extraction from removing the chemicals pres- cantly reduce the water uptake of cell walls. The resultant ent in the heartwood. artiicial heartwood improved its dimensional stability Bark extract from mimosa (Acacia mollissima) and and wood performance applying the basic principles of quebracho heartwood extract (Schinopsis lorentzii) have chemical and physical polymer interactions among the lig- shown antifungal resistance, while pine bark (Pinus bru- nocellulose cell wall and simple or polycyclic phenolic tia) was innefective, when tested against white rot fungi compounds and brown rot fungi (Tascioglu et al., 2013). These plant extracts are known for their high condensed tannin con- plAnt extrActs tents. When extract retentions in wood samples increased, Traditionally, natural extracts has been explored through- the resulting mass losses of all tested species decreased. out history to protect wood. Oils, tars and extracts were Commercial mimosa and quebracho extracts may be used used to impregnate wood structures, but their availability at concentration levels of 9% - 12% as wood preservatives and economic feasibility have not promoted their exten65 González-Laredo et al. Wood preservation sive use. Steam distillation for oils, water soluble and nique is one way of providing high water-repellence efi- selective extraction with organic solvents for extracts, and ciency at low oil retention levels (Hyvönen et al., 2006). pyrolysis for tars have been the processes used to produce This has environmental beneits as it uses water as a thin- raw wood preservatives. The natural sources have been ner, instead of the common organic solvents. Another almost any part of select wooden and herbaceous plants: option is to promote the oxidation and polymerization of bark, heartwood, fruit, seeds, and leaves. Among sources the crude tall oil, which can be accelerated by iron cata- of plant oils (either vegetal oils or essential oils), lax seeds lysts, thus preventing the oil from exuding out of the wood (Lyon et al., 2007a), cinnamon (Lin et al., 2007), citrus and keeping the water repellent eficiency (Hyvönen et al., peels (Macias et al., 2005), and tung seeds have been 2007a). Limiting to some extent the water uptake by the experimented as potential wood protectors, showing emulsion technique will allow the tall oil to dry, and pro- diverse activities as antibacterial, antifungal, antitermite, moting the in situ iron oxidation will keep it into the wood and antinematode agents. The list continues with exotic (Hyvönen et al., 2007b). This may be performed in one sources such as the oil from the nut of kukui plant (Aleu- single step in existing wood preservation plants. rites moluccana), which is being used to protect canoes Vegetable oils may be potential preservatives when against marine borer damage according to native folklore applied as a layer into wood surface by decreasing water (Nakayama and Osbrink, 2010). However the results absorption and actually performing as water repellents indicated that this oil acts as a feeding deterrent rather (Tomak and Yildiz, 2012). Still, impregnation with vege- than a toxic agent. Parallel interest has incited to explore table oils is not enough to impart tolerable biological the major active components present in such oils and resistance against decomposition factors (i.e., decay or extracts, by example cinnamaldehyde in the case of cinna- insect attack), but actually easing wood to burning. In mon, and turpentine and volatiles in orange peels. fact the need of high oil absorption level required for good It has thought that toxicity and antioxidant proper- protection make the process impractical. However, the ties of bark extracts such as mangrove plant (Rhizophora concept can be improved adding biocides and optimizing apiculata) may impart natural resistance to termite action the retention of oil needed. By example, drying oils are (Khalil et al., 2009). Dewaxed bark was extracted with commonly used for preserving solid wood or wood com- methanol and successively partitioned with chloroform, posites in combination of metals to form a copper ammo- ethyl acetate (EA), and butanol. A chromatographical nium acetate complex wood preservative (Roos and Acher, guided puriication by a termite bioassay gave the EA frac- 2004). The preservative is applied effectively into the tion as the more active with a distinctive composition of wood to improve its decay and termite resistance. The bioactive constituents based on aromatic carboxylic acids drying oil in the wood reduces water absorption and and phenolics. These results suggest that the astringency swelling, increasing its mechanical strength; even in a of polyphenols and their antioxidant activity may play a wood composite it may require less binding resin than role in preventing termite attack. normal. Also, the copper ammonium acetate-oil complex may be added to green wood either in solid or laked form. oIls And moIsture control Bio-oil produced by pyrolysis of non-conventional Controlling moisture content is a very effective way of pro- raw materials like palm fruit shells was characterized and tecting timber because treating with biodegradable tall oil, positively tested as wood preservative agent (Sunarta et reduces the capillary water uptake of pine sapwood. How- al., 2011). The pyrolytic liquid yielded at a ratio of 35% - ever, there are two problems that limit the extensive use of 37% by weight of the waste material was effective against tall oil for wood protection, the amount of oil needed and drywood termites (Cryptotermes spp.) and particularly its tendency to exude from the wood. The emulsion tech- against the blue stain fungi (Ceratocystis spp.). 66 Madera y Bosques vol. 21, núm. especial: 63-76 2015 Forest residues such as wood and barks from oaks wood with smoke, moisture content is reduced and PAH s and pines were subjected to thermal degradation to pro- are condensed and diffused inside wood structure. PAH s duce bio-oils, and subsequently fractionated to obtain lig- have shown to provide some resistance to biological dete- nin-rich fractions, consisting mainly of phenols and rioration driven by termite attack (Hadi et al., 2010), and neutrals fractions. Whole bio-oils and their lignin-rich microorganisms Aeromonas hydrophila and Listeria fractions were studied as potential environmentally monocytogenes (Sunen et al., 2003). benign wood preservatives with antifungal properties to replace metal-based chromated copper arsenate (CCA) and combIned metAls And bIocIdes copper systems. At relatively high loading level (25%), the Combined use of certain metals acting as chelators with raw bio-oils showed excellent wood preservation proper- organic biocides might enhance their eficacy. Some met- ties. However, prevention of leaching is very critical to als are key components on fungal enzymes because they provide decay resistance (Mohan et al., 2008). Other function as co-factors, and metal chelation may reduce organic residues may have potential use as raw material the wood decay by fungi. Therefore, it is important to ind for producing oils and vinegars as wood preservatives, the right combination of metal chelators and biocides that fungicides, herbicides, repellents and insecticides (Tiilik- promotes the required synergistic action. Another kala et al., 2010). approach is to increase the eficacy of organic biocides Adding linseed oil increases boric acid retention; it with antioxidant additives that synergically can scavenge also reduces leachability and improves eficacy against the free radicals action of wood degrading microorgan- termites (Lyon et al., 2007a). The ammonium borate isms. In doing so the fungal activity may be successfully oleate (ABO), a complex product from the reaction between slowed down. Paradoxically, organic preservatives may be boric acid, ammonia and oleic acid, was positively tested unstable with time. Thus, we need to understand the as a wood preservative treatment against white and brown impact of different environmental conditions on the via- rot fungi (Lyon et al., 2009), and also resulted effective bility of the active ingredients, which may be susceptible against termites (Lyon et al., 2007b). Eficiency of the ABO to degradation by the same wood decay action or parallel salt is based on the repellence provided by fatty acids, mechanisms. These may include evaporation, water leach- which deters boron leaching and penetration of water and ing, chemical or biological degradation of either the bio- fungi. This may be considered a dual treatment from the cide successful combination of coating and biocide products. photodegradation. Consequently, a protection additive In this case, the vacuum leaching procedure is inappropri- has to be considered (Ruddick, 2008). or the formed biocide-wood complex, and ate to place specimens in real exposure conditions because it forces penetration of water. This observation has tAnnIn-metAl complexes reminded the lack of standardized procedure of testing for One of the original classical patents was iled by Laks combined coating and biocide treatments. (1991) afirming that complexes of sulphated tannin A traditional method to preserve wood in Asian extracts and copper (II) ions effectively protect wood countries such as Indonesia is by smoking samples, which against fungal attack. The complex can be impregnated is an indirect way to apply wood condensates into the into wood in a single step treatment using a water/organic samples. Wood burning produce smoke that contains a solvent system, or formed in situ by treating the wood variety of toxic polycyclic aromatic hydrocarbons (PAHs), with an aqueous solution containing the extract and sub- as well as phenols, aldehydes, ketones, organic acids, alco- sequently treating the wood with an aqueous solution of a hols, esters, hydrocarbons and several heterocyclic com- copper (II) salt. This was based on sulphide derivatives of pounds (Stołyhwo and Sikorski 2005). When treating catechins from condensed tannins that have shown a 67 González-Laredo et al. Wood preservation broad biocidal spectrum. Particularly, epicatechin-4-al- an agro-industrial waste, were tested satisfactorily along kylsulides and cupric complexes containing up to 20, and with copper salts addition against Trametes versicolor. preferably 5 to 15 carbon atoms, were particularly effec- The bioassays showed poor fungal inhibition for the wood tive against wood rotting fungi and gram-positive bacte- samples impregnated only with the tannin extract. How- ria. Such sulphides were prepared by reacting condensed ever, the tannin–copper complex mixture showed greater tannin, either in the form of puriied tannin extracts or fungal inhibition due mainly to the retention values and pulverized plant tissues, with an appropriate thiol reagent the phenolic nature of solutions. under mild acidic conditions (Laks, 1990). Currently, the tendency seems to develop processes that Later, Lotz (1993) proposed the use of impregnating incorporate biocides into wood or wood products, but the agents such as halogenated tannin extracts from plant biocide is presented as a nanoparticle. The biocide as a species, which are relatively more resistant to fungi, nanoparticle is applied into the wood or wood particles weathering, rotting, and insect attack. The tannin extracts applying suficient pressure to force it to penetrate into the were converted to their halogenated products and wooden material (Laks and Heiden, 2004). Nanotechnol- absorbed by the treated wood samples. The halogenated ogy is promising for wood preservation; as well nano-metal tannin material may be used with other treatment agents treatment may be totally different from the traditional ele- such as ixatives or metal salts. In this case, Bromine was mental metals treatment and perform in a different way. suggested as the preferred halogen material, with opti- Nano-metals have characteristic size and charge that may mum treatment occurring at bromine concentrations improve their performance in wood protection applications. above 2%, but preferably around 4% - 5%. If their particle size is smaller than the diameter of pores in The mechanism of preservation by chemically modiied tannin and tannin-ammonia-copper agents was exam- the bordered pits or in the wood cells, complete penetration and uniform distribution in wood can be reached. ined by Yamaguchi and Yoshino (2005). Wood decay by Fomitopsis palustris was markedly suppressed by treating fungIcIdes used for wood protectIon wood with the modiied tannins agents, although the Fungicides are organic or inorganic substances, natural or mycelial growth and the protein generated slightly synthetic agents, acting against fungi. Their toxicant or increased. The preservative effects of the chemically modi- retardant mechanism of action depends on their chemical ied tannins were attributed to inhibition of the enzymatic structure and bioactive functional groups from which all breakdown of wood components by xylanases, mannases important biocidal properties are derived. Some fungi- and cellulases. No pH drop was observed in the culture cides may present combined bactericidal, insecticidal or medium, where the treated wood powder was set, imply- other biocidal effects, as boric acid does (Lloyd et al., ing negative production of oxalic acid, which is distinc- 1990). In searching for natural fungicides, they should tively produced by F. palustris. The mechanism proposed fulil the mentioned properties as shown in table 1. was the chelation of copper, an essential trace element for Fungicide eficacy is not a constant parameter because wood decay by the brown rot fungi, by the tannin, and the is inluenced by more biological and environmental fac- neutralization or suppression of oxalic acid production by tors inside and outside of the fungal cells. Also it depends the ammonia-copper involved in the chemical preparation. on its ability to impair fungal cells, suppress growth, and Synergic effect of natural product with an inorganic inhibit enzymatic or other actions from rotting-fungi on fungicide, and waste product upgrading were conceptual- wooden substrates. The reference for ield and lab tests is ized by Lomelí-Ramírez et al. (2012) in the use of pheno- the critical minimal concentration (%) or the minimal lics from coconut tree residuals for wood protection. critical retention in wood (kg/m3) (Reinprecht, 2008). Dis- Tannins extracted from the ibrous mesocarp of coconut, tinctive parameters to consider are shown in table 2. 68 Madera y Bosques vol. 21, núm. especial: 63-76 2015 Table 1. Antifungal activity, mechanisms and uses of fungicides for wood preservation* Actions 1. Inhibition of respiration. Fungal cells have ainity to diferent chemical groups (i.e., thiol groups), resulting in non-speciic denaturation of proteins and enzymes. 2. Inhibitors of polysaccharide biosynthesis Mechanisms Inhibition of Acetyl coenzyme A (CoA). Fungicide applications 2+ Cupric ion Cu from copper sulphate, copper oxide, copper naphthenate, copper-8-hydroxyquinolinate, Cu-HDO. Interruption of respiratory chain Similar inhibitory efects from arsenic compounds, Suppression of high-energy inter- compounds, carboxamides, tributyltin compounds, or phosphorylation. mediate adenosine triphosphate (ATP). Inhibition of carbohydrate, protein, 2-phenylphenol, pentachlorophenol and other phenolic isothiazolones. Polyoxins and antibiotics from streptomycete (Inhibition lipid and nucleic acid biosynthesis. of chitin synthesis in fungi cell walls). Imidazoles, pyrimidines, triazoles (suppression of lipid synthesis). 3. Inhibitors of cell division Inhibition of microtubules synthesis. Benzimidazole derivatives (e.g. carbendazim, benomyl) interfere with microtubule subunit polymerization, preventing mitosis and depressing the DNA synthesis. 4. Disruptors of fungi cell membranes Structure and function of sterols (i.e., Tiazoles (e.g. azaconazole, propiconazole, tebuconazole). ergosterol) play an important role. Inhibition of sterol biosynthesis is connected with disruption of cell membranes. 5. Enzymes inactivation Tar oils disrupt cell membranes dissolving lipids in membranes. Quaternary ammonium compounds (QAC) can rehydrate and damage the semi-permeable membranes of fungi (e.g. didecyl-dimetyl-ammonium chloride-DDAC), combined with leaking of cell constituents. Simultaneous inhibition of metabo- Hg-based fungicides, dicarboximides (reaction with thiol lic activity, enzymatic functions and groups in proteins). growth of fungi Hg2+ and Cu2+ cations (Inhibition of glycolysis). Boric acid and boron compounds form stable complexes with vitamins, coenzymes or biological molecules with poly-OH groups (action as fungistatic rather than fungi- cide) (Lloyd et al. 1990). 6. Retardants of Fenton polysac- Polysaccharides in wood cells che- Tropolon, β-tujaplicin (inhibit activity of brown-rot fungi) charides depolymerisation mically bond Fe3+ ions 7. Retardants of fungal spread in Adaptive nitrogen redistribution wood mechanisms, which are unique in (Gérardin et al. 2002). Non-toxic amino acid analogue “AIB” α-aminoisobutyric acid (Watkinson and Tlalka 2008). rot-fungi * Prepared from Reinprecht (2010). 69 González-Laredo et al. Wood preservation Tabla 2. Parameters of fungicides eficacy in wood treatment* Fungicide adsorption rate on the surface of fungal cells Fungicide accumulation rate into fungal cells Rate of adsorption depends on physicochemical variables such as pH of wood Retention of fungicide by fungal body can be enhanced in presence of conditioners Fungus species Individual fungi commonly show selective resistance to particular chemical fungicides Fungal cells biomass Fungicide retention/concentration and synergistic applications Fungicide may be inactivated when interacting with fungus, thus it has to be applied at higher concentration than for preventive use. Minimal critical retention or critical minimal concentrations are not usually efective for a long time. Fungus can be adapted to the fungicide and other substances may catalyse or retard eicacy of the fungicide. Environmental factors: Temperature, Moisture Content, UV radiation, and others Abiotic factors inluence activity of fungal cells. Extreme temperatures may inhibit or kill cells; warmer and wetter conditions may assist luid difusion of water soluble fungicides. *Prepared from Reinprecht (2010). bIologIcAl control of wood cide signiicantly reduced the weight losses and the enzyme degrAdAtIon activities associated with white-rot fungi (Trametes versi- The main biological pests for wood preservation are fungi color) and brown-rot (Gloeophyllum trabeum), it could not and insects. These biotic factors cause negative effects in completely inhibit their activity. Results suggested that wood quality mainly by decay and staining damages. Deg- these biocontrol organisms might inhibit slowly but not radation may starts when wood is in contact with soil or totally the decay process. Addition of sugars as carbon water and cell wall polymers is attacked by bacteria. Com- source has not enhanced the speciic activity of the biocon- plementary, handling practices and environmental condi- trol fungus. Another example is the dry-rot fungus Serpula tions are inluential factor to be observed. While chemical lacrymans, which is a typical brown-rot basidiomycete protection of wood products is effective in many cases, it found particularly in woods under certain environmental imposes recognized ecological and health risks. Therefore, conditions. Some Trichoderma isolates prevented Serpula strategies for developing biological control agents are wel- colonisation in experimental wood-block tests. However, come as soon they are speciic at targeting biological haz- the biocontrol fungicides could not stop decay of already ards and are readily biodegradable. Though, since they are infected blocks, making the isolates only valid for preven- living materials and have limited shelf-life, their design and tion (Score et al., 1998). The antagonism mode of action formulation must be improved (Mai et al., 2004). appears to be the inhibitory volatile organic compounds Attemps of biocontrol of wood deterioration with fun- produced by the Trichoderma isolates (Humphries et al., gus such as Trichoderma harzianum, was evaluated by 2002). The production of volatiles by Trichoderma is deter- Canessa and Morell (1997) on ponderosa pine sapwood mined by cultural age and medium composition, and wafers at small-scale tests. Although this ascomycete fungi- mainly by the amino acids available (Bruce et al., 2000). It 70 Madera y Bosques vol. 21, núm. especial: 63-76 2015 is known that aldehydes and ketones of seven to ten car- losses were signiicantly lower compared to the controls, bons such as heptanal, octanal, nonanal and decanal and providing an increase of 6–7 times on the life span. There- related ketones inhibit growth of a wide range of brown fore, these are promising treatments for tropical woods and white-rot fungi. Extended protection by Trichoderma preservation. Similar studies have concluded on the efi- or other fungal antagonists is likely not achievable, but at cacy of cashew nut shell liquid against termites in the ter- least a certain prolongation of the life-time of wood prod- mite mound compared to the conventional creosote ucts is feasible. Experiments to protect wood against decay treatment (Jain et al., 1989). fungi by antagonist action of other microorganisms are still under exploration and evaluation. Another tree with potential phytochemicals is Camphor (Cinnamomum camphor), which is rich in camphor, eucalyptol, terpineol, linalool, and 4-terineol, active com- Insect bIocontrol pounds already used in medicines and insecticides (Liu et Some novel methods for coating, penetrating, treating, and al., 2006). Particularly, camphor leaves extract, which is curing wood, wood composites or cellulosic materials are thermally unstable and volatile but has strong insecticidal inspired in the addition of natural biocides such as aza- and antifungal activity, is mixed with ixing agents to dirachtin from seeds of the Neem tree (Azadirachta indica), facilitate the protection action in bamboo. Some polymers where is present at 0.2% - 0.8% (Subbaraman and Brucker, have been used as modiiers to improve the durability of 2001). This component disrupts the feeding behavior and treated wood. As an example, Melamine-modiied Urea growth cycle of termites, wood-borers and other biologi- Formaldehyde resin prepolymers (MUF) have improved the cally important insects. The water resistant formulation mechanical strength and decay and insect resistance of contains the Neem seed oil plus binding and bittering agents, treated wood and bamboo samples compared to controls which enhance the long active effectiveness of the extract. (Xu et al., 2013). These resins are eficient ixative materi- The composition is non-reactive, non-toxic to vertebrates, als for plant-based preservatives, keeping their activity and non-polluting of surrounding soils. Also, the prepara- and improving their thermal stability. tion may be resistant to oxidation, and photo degradation, when applied in non-aerobic conditions, such as subterra- combIned processes nean use. Azadirachtin as well other speciic insecticidal The co-addition of the synthetic antioxidant and fungicidal compounds are found also in the leaves and ated hydroxytoluene) increased the eficacy of wood sam- bark of the neem tree. Therefore the plant becomes an avail- ples treated with the commercial fungicides Propiconazole/ able source of biocides and a compatible biological control tebuconazole or option against other pest insects (Nathan et al., 2005). (Schultz and Nicholas, 2011). Parallelly, the natural anti- DCOI BHT (butyl- in an accelerated soil-contact test In other paper, Neem extracts alone or mixed with oxidant and metal chelator propyl gallate improved the copper sulphate and boric acid conirmed their antifungal response of above ground samples treated with propi- activity protecting mango (Mangifera indica) and rain conazole and wax. These experiments highlight the anti- tree (Albizia saman) woods (Islam et al., 2009). The Neem oxidant and metal complexing properties of organic extract treatment has been extended with relative success phenolic extracts that protect wood from decay when against beetles and termites because these woods are combined with biocides. widely used in Bangladesh and are very susceptible to The addition of heartwood extractives such as walnut them, as well to decay and wood-staining fungi. The tree has being explored with relative success in combined growth of white rot fungus (Schizophyllum commune) systems based of acid copper chromate, and boric acid was fully inhibited on ield samples containing 1.8% of tested on beech sapwood for white rot fungus resistance the extract or 5% from the mixture. The average weight (Feraydoni and Hosseinihashemi, 2012). Substances such 71 González-Laredo et al. Wood preservation as juglone, 2,7-dimethyl phenanthrene, and gallic acid envIronmentAl concerns And from walnut heartwood lour have been reported with bIotechnology antifungal activity (Hosseinihashemi and Latibari, 2011). Environmental concerns have stimulated the search for In cooper based preservatives, the use of rosin has friendly substitutes to replace toxic chromium and arsenic being proved as good ixing agent. Rosin is a paper sizing in chromated copper arsenate (CCA) systems by soy prod- agent from softwoods that has a suitable hydrophobic ucts in wood preservative formulations (Yanga et al., character and afinity for the wood structure. This feature 2006). Soy is intended as chelating and ixative agent in is appropriate to maintain a low moisture absorbing ten- preservative solutions containing anhydrous cooper sul- dency and help to keep cooper from being leached out phate and hydrated borax. Despite the molecular sizes of (Hien et al., 2012). the copper–protein and copper–boron–protein complexes, Boron compounds are recognized as good wood pre- pine samples were treatable, leached and exposed success- servatives, acting as both fungicide and insecticide, rela- fully to brown rot fungi. Although wood samples needed tively acceptable higher retentions, soy-based formulations should be still (Caldeira, 2010). However, in the ield, borates are used evaluated by long-term ground-contact testing to consider only for indoor and non-exposed applications or in com- them as an optional wood preservative from fungal attack bination with other biocides, because they are easily and replace of CCA . inexpensive and environmentally leachable from treated wood (Thevenon et al., 2009). The Another original approach for ecological preserva- fact is that boron is not ixed chemically to wood, and it tion of wood materials is the copolymerization of phenolic will be leached out if wood in service if subjected to any extracts from pine barks with acrylic monomers into the wet environment, even at moisture contents below 20% cell wall structure (Dumitrescu et al., 2008). Besides the (Peylo and Willeitner, 1995).This boron leaching, which is biocide effect there is a plus regarding the emulsifying a major drawback, has being markedly reduced in wood capacity from the bark extract, which improves the emul- preservatives based on the cross-linking and hardening of sion stability. condensed tannins with hexamine, where boric acid was Traditionally, Biotechnology has found little atten- added and formed a composite. Boron can be covalently tion in the forest products industries, and particularly in ixed to the tannin-hexamine network (Tondi et al., the wood preservation ield. Now, the situation is chang- 2012a). As a desired output, the wood treated with this ing due to legal restrictions on conventional processes det- system has shown a signiicantly enhancement of wood onated by growing environmental concerns and a durability before and even after leaching once tested favourable scientiic background. Current biotechnologi- towards basidiomycetes (Thevenon et al., 2010). The cal approaches for wood protection are targeting to the mechanical and ire-prooing attributes of pine and beech treatment of wood with natural and ecological friendly specimens preserved with these formulations were preservatives and replacing conventional chemicals with improved. Treated samples under compression, bending, biological control agents. hardness, and gluing tests showed average improvements Complementary, Biotechnology is playing an import- of 20%. The treatment with tannins has enhanced the ire ant role in the remediation of wastes from chemically resistance of samples, which was also upgraded with the treated wood. Developing of low environmental impact addition of boron and phosphorous (Tondi et al., 2012b). technologies to remove any biological damage is still one Eventually more work on this concept such as impregna- of the major goals of wood protection industry. An exam- tion, agent diffusion, and wood anatomy considerations ple in this sense may be the experimentation for potential (Tondi et al., 2013), may lead to effective, more environ- recycling of old creosote-treated woods through a pyroly- mental and friendly wood protection systems. sis process to produce tar oils for treating new wood ele- 72 Madera y Bosques vol. 21, núm. especial: 63-76 2015 ments. Wood tar obtained this way may have potential as products. The nanotechnological applications have great a sustainable preservative for wood protection or as a potential to improve treatability of commercially import- component of preservatives (Mazela, 2007). ant wood species, designing engineered composites and delivery systems for speciic targeted applications such as conclusIon developing of slow-release of combined metal and bio- At present time, several types of inorganic and organic cides models. At the end is clear that the goal is offering to fungicides are commonly used for protection of wood the market only safe, stable and effective products, i.e., products against termites, moulds, staining and rotting with economic and environmental sustainability. fungi. However, in the near future the wood preservation industry is required for sustainable processes based on references environmentally more friendly additives. Among the most Bruce, A., R.E. Wheatley, S.N. Humphries, C.A. 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