Fight the wood rot

Some people believe that firmly embracing a live tree for several minutes suffices to restore one’s vital activity. And who would not like to live in a wooden house? The more so since wood is inexpensive, available and easy to process material. However, wood has a drawback: microorganisms can damage it causing staining and rot. Fungi, mould, and bacteria are the deadliest enemies of wood. They both ruin the ornamental properties and cause softening of wood thus damaging irreparably the load-bearing constructions. Modern biocidal chemicals can help to prevent this.

Whence the firewood?

Wood is still one of the most widely used construction materials due to its availability, variety of wood types with different properties, low cost, and ease of processing. However, wood has a major drawback: without proper protection from the weather impact it can soon lose its mechanical and ornamental properties.

Wood-staining and mould fungi can damage lumber during air-drying, storage and transport, especially in warm and damp season. The vital activity of wood-staining fungi results in accumulation of the exuded pigments in wood cells. This becomes apparent in form of blue-grey colouring of the wooden surface called blue stain.

Mould fungi developing on the wood surface form green, blue-green, blue, black, or rose-coloured stains that consist of spores, sporiferous organs, and mycelium. Blue stain and mould fungi inhabit all types of wood, but prefer wood of coniferous trees, especially pine sapwood. Two types of staining are discriminated, depending on the fungi types and the depth of their penetration into the wood. Surface staining penetrates wood to the depth of up to 2 mm.

The other type is bulk staining, which can with time completely permeate the alburnum. There are two more types of staining: substrate and spacing-board staining. Spacing-board blue stain (sometimes mould) in the form of transversal stripes appears when wet spacing boards contaminated with fungi are used in lumber storage.

Wood-staining and mould fungi increase water permeability of wood and thus provide favourable conditions for the development of more dangerous wood fungi, which cause decomposition of this material.

Blue stain and mould fungi propagate with spores, which put forth growth as soon as they get on a wet or slowly drying wood. Provided favourable conditions, the spore needs only several hours to send the growing tube deep into the bulk of green lumber. A similar process can develop during wood sawing for construction and reconditioning of wooden buildings.

Wood contaminated with staining and mould fungi does not lose its mechanical properties. However, if no measures are taken to counter the action of these fungi, water permeability of wood increases (even if it is covered with paint or varnish).

This provides favourable conditions for propagation of more dangerous wood-destructing fungi that decompose lignin and cellulose. The latter type of fungi causes rapid degradation of the mechanical properties of wood.

Moreover, the mould fungi and bacteria inhabiting wood endanger human health by increasing the risk of mycogenic allergic diseases: asthmatic bronchitis, bronchial asthma, nettle rash, etc.

The way out

Once the bulk damage of wood appears, there is no way to reverse the process: the rotten fragments should be removed. Reliable protection of construction materials should be planed in advance to prevent such grave consequences.

Treating green lumber with a suitable antiseptic within 3-4 hours after sawing can prevent damage caused by staining and mould fungi.

The antiseptics recommended for wood protection should have the following characteristics. They should be highly toxic towards fungi, but harmless for humans and animals, have high permeability into wood, and high stability. Besides, they should have no specific odour, should not degrade the mechanical properties of wood and its appearance, and should cause no corrosion of metal bracing of the wooden structures.

Note that most antiseptics penetrate wood to the depth of 10 mm, and provide the maximum efficiency only when wood is impregnated under pressure or in vacuum that requires special equipment. Some of the antiseptics cause unwanted colouration of wood and reduce the adhesion of paints and varnishes applied later. This essentially reduces the field of application of such chemicals.

Chemicals based on polyalkylene guanidines (PAGs) – Biopag, Phosphopag, and Septopag – developed by the Institute of Ecotechnologies can be successfully applied for protection of lumber, wooden constructions, and woodwork.

The tests of the novel chemicals performed by the Senega Lab for Wood Protection have shown that PAGs successfully suppress up to 30 types of mould, staining, and destructive fungi. The first group includes Penicillium ochrochloron, Aspergillus terreus, Fusarium moniliforme, Penicillium brevicompactum, Fusarium poae, Aspergillus niger, Penicillium chrysogenum, Alternaria humicola, Phialophora fastigiata.

The 2nd group includes Fusarium javanicum, Fusarium merismoides, Doecylomices variotte (???), Sporodesmium cladosporioides, Trichosporium heteromorphum, Aspergillus hennebergii, Disula peni-cola, Cladosporium forlarum, Verticilium marqvandi, The 3rd group includes Aspergillus amstelodami, Penicillium cyclopium, Alternaria tenuis, Pullularia pullulans, Fusarium culmorum, Penicillium purpurogenum, Aspergillus flavus, Leptographium lundbergii, Trichosporium harzianum.

PAGs comply with the strictest requirements for antiseptics for wood protection. Their biocidal properties are in no way inferior to those of the currently used antiseptics. However, they have an obvious advantage due to their low toxicity and environmental friendliness.

Whereas most of antiseptics are highly toxic, cancerogenic, and hazardous for the environment, PAGs have low toxicity for any way of exposure of human organism (3rd – 4th class of toxicity). PAGs have no odour, cause no allergy and irritation of mucous tunics, and inhibit corrosion of metals.

PAGs are environment-friendly due to their polymeric structure. They contain no heavy metals or strong oxidants. Biocidal action of PAGs is due to the guanidine groups attached to the macromolecule. Such groups are active parts of many natural compounds and pharmaceutical substances. Warm-blooded organisms, as well as activated sludge in water basins always contain ferments that can decompose PAGs.

PAGs are solids that are stable in long term storage without loss of biocidal properties (monitoring term was 15 years). They are well soluble in water, and water solutions retain biocidal activity for at least 2 years.

Water-soluble chemicals Biopag and Phosphopag are recommended for protection of lumber from blue stain and mould fungi in timber and woodworking industry, as well as in construction and maintenance of buildings. The technology of wood treatment with PAG biocides does not require any complex equipment.

Spraying the wooden surface with biocide or applying PAG with a paintbrush is sufficient to ensure protection of lumber from staining and mould fungi. Short soaking of wooden material in a bath filled with a water solution of PAG is also possible. Water solutions of PAGs do not colour wood.

Organosoluble biocide Septopag can be also used for protection of wood and woodwork. This biocidal varnish contains Biopag chemically bound to the polymeric film-forming base, so that the biocidal component can not be washed away by water.

After evaporation of the organic solvent Septopag forms a thin waterproof polymeric film on the wooden surface. This film prevents fungi growth both on the surface and in the bulk, and the wood acquires a natural yellowish tint. The tests have shown that a single treatment of wood effectively protects it against wood fungi for at least several months.

Irina VOINTSEVA,

Dr.Sci. (chemistry)

Stanislav KOZEL,

Deputy Director of the

Institute of Ecotechnologies

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