Degradation of Wood

Degradation of Wood : 

Degradation of Wood N.KANAGARAJ BSF-06-007 BSC[FORESTRY]

Physical and Chemical degradation : 

Physical and Chemical degradation Weathering Cumulative affects ?air, light, water, Temperature and mechanical factor. Surface phenomenon Light Lignin is photo-degraded by light-quicker. -Decreases water resistance - yellowish to brown color

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Temperature and moisture Alternate wetting and rapid dry ?swell and shrink ?develop case hardening, checking and lifting of the grain . The stress develop b/w surface and deep layers lead to splits and checks . Freezing and thawing- checking? due to expansion of water. Moisture exposes new surfaces

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Air Strong wind containing sand & dirt – mechanical abrasive action known as Sand blasting -Faster degradation –exposure of fresh surface. Advanced weathering may result in warping or cupping of boards

Chemical degradation : 

Chemical degradation Wood is highly stable polymer,does not degrade its own Certain metals coming in contact corrode and cause chemical rot This rot is more due to presence of certain extractive like tannins Due to two or more metals when galvanic cells sets up in wet wood-lead to electrochemical degradation-Nail Sickening Gases like So2, No2, and O3 -causes depolymerisation

Biological degradation : 

Biological degradation Wood being of organic origin- suitable food for many organism Till the tree is alive- own resistance (produces certain chemicals) After felling- undergo deterioration.

Bacteria degradation : 

Bacteria degradation Very slow degradation Only few cellulytic bacteria can degrade wood Contact with soil or water saturated conditions – Favourable Causes softening of surface layers Excessive shrinkage on drying

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Attack- mostly in Heart wood Wood is called- Wet wood Lower density, toughness, compression strength But have higher permeability to preservatives Bacteria- play a dominant role in rapid decomposition of fungus attacked wood

Fungal degradation : 

Fungal degradation Optimum temp(16-32o c) MC b/w 35-50% Adequate supply of air

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Ascomycetes & fungi imperfecti –developes stain –E.g blue stain. Confined to sapwood. At higher MC Consumes only stored material- no significant affect on strength properties-reduces aesthetic value Stain or Moulds Fungi

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Stained wood- consume more bleach to get desired pulp Increases the permeability of wood

Wood Rot or Decay fungi : 

Wood Rot or Decay fungi Favourable condition – the fungal spores in the air germinate on wood- produces filament –Hyphae Hypae penetrate deep-consuming the cell wall & cell content. Heartwood is resistant- Toxic chemicals

Whit rot : 

Whit rot Attacks all component Wood becomes spongy or fibrous with whit pocket or streaks E.g – Polyporous versiclor, -Polystrictus sanguineusetc The fungus has decayed the sapwood and dark heartwood turning it white. This white rot fungus attacked all cell wall components

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Mottled white rot in wood decayed by Ganoderma applanatum Combination of delignification and a simultaneous white rot attack in the wood

Brown rot : 

Brown rot Consumes only carohydrate Lignin is not much affected Wood changes to brownish residue E.G Lenzitus trabea, poria monticola In advanced stages of decay the wood cracks and checks into cubicle pieces. Little to no integrity remains in this decayed wood.

Soft rot : 

Soft rot Lower fungi Require high moisture Action is similar to brown rot Hypae –confined to secondary wall which developes cavities Surface develops checks E.g timber in cooling towers, sea water, pole tops, used in bathroom, ground contact Soft rot in wood often appears brown and can be confused with decay caused by brown rot fungi

Insect degradation : 

Insect degradation Borers & termites accounts for major destruction during storage and use. Degradation varies with Climatic conditions Timber species

Pinhole borers or Shot hole borers : 

Pinhole borers or Shot hole borers Platypodidae & scolytidae? Bark beetles & Ambrosia beetles First to appear and causes severe damage MC < 50%- unable to thrive Bark beetles Mine b/w bark and wood Engraving both

Ambrosia beetles : 

Ambrosia beetles More destructive Tunnels are more extensive & extend deep into the Heartwood Nourish on a mould type fungus –Ambrosia Do not feed on wood- Contact insecticide should be used

Flat headed borers and long horn beetles : 

Flat headed borers and long horn beetles Buprestidae and cerambycidae Simultaneously or succeeded the attack of pin hole borers Lay eggs on or in cervices of bark and wood Larvae excavate tunnels-tightly packed with dust like boring and pellets Prefers- presence of Bark Drying of wood for 4-6 months makes it immune to such attack

Powder post beetle : 

Powder post beetle Term due to– Interior of the attacked wood is reduced to flour Lyctidae and Bostrichidae?E.g Stromatum barbatum, Lyctus sp. Capable of attacking relatively dry timber Attacks both sapwood & heartwood? of both soft wood & hardwood Damage- tunneling activity

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Indication-Piles of powder beneath the infested area & noise of larval activity Damage by lyctus beetle rates second only to termites

Termites : 

Termites Attacks at all stages-tree, logs &wood in service Most severe destroyer of wood and wood product in the world

Subterranean Termites : 

Subterranean Termites Major destroyer Operates from a underground tunnels-protection from sunlight and prevent loss of moisture Eats the wood from inside leaving exterior untouched Heterotermes indicola- severe in india

Dry wood termites : 

Dry wood termites In moist coastal regions and north East india Damages even dry, sound and seasoned wood No contact with ground E.g Cryptotermis bengalensis

Marine organisms : 

Marine organisms

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Pholads & sphaeromids attacks wood mainly for shelter Limnoriids and teredinids feed upon it Heavy attack of sphaeroma – honey combs the timber Limnoria – wood becomes spongy mass E.G of spp. Found in indian harbour Sphaeroma terebrans, Martesia striata, Bankia sp., Tredo fuiifera, Limnoria bombayensis, Lyrodus pedicellatus

Foulers : 

Foulers Marine fouling occurs on moving or stationary structure Foulers- include wide range from plants material to animal group Microscopic form i.e bacteria, diatoms and algae –first settlers on any submerged surface These slimy deposits promote further settlement of living organism

Effects of Decay and discolouration : 

Effects of Decay and discolouration Distinct change in colour Characteristic dour is given off by wood Zonation lines may formed by some fungi Reduces strength, hardness, elasticity of wood Decrease in specific gravity occurs

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Thank u

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