"WOOD PRESERVATIONA Literature Review of a Survey on Usage of Treated Wood in aLocality (Eldoret, Kenya)ByTable of ContentsIntroduction ............................................................................................................................... 3Biological Degradation ............................................................................................................. 3Physical Degradation ................................................................................................................ 4Chemical Degradation .............................................................................................................. 4Natural Durability Wood .......................................................................................................... 4Economic Impact of Wood Deterioration ................................................................................. 5Wood Preservation .................................................................................................................... 5History of Wood Preservation .................................................................................................. 5Wood Preservation Methods ..................................................................................................... 7Performance of Preservatives ................................................................................................... 8Economic Aspect of Wood Preservation .................................................................................. 8Kenyan Case ............................................................................................................................. 9An overview of forest status ..................................................................................................... 9Bibliography ........................................................................................................................... 11 WOOD PRESERVATION: A Literature Review of a Survey on Usage of Treated Woodin a Locality (Eldoret, Kenya)IntroductionWood due to its anatomical properties is susceptible to many deleterious factors that lead toits deterioration especially when exposed to them in service. The principle causes ofdeterioration of wood in service include fungal infection, termites and other insects, marineborers, mechanical failure and fire (Wilkinson, 1979). An obvious omission here is theseasoning defects that are deleterious too to the wood. Degradation or deterioration of woodis thus categorised into three processes namely: Physical, Biological and Chemicaldegradation.Biological DegradationHere, insects, fungi and marine borers fall. Most of these biological degraders target woodcomplex substances such as cellulose and lignin. Cellulose for instance is broken down intosimple materials. Insects attack wood at any state of its existence. Many kinds of insects dopredate wood but prominent predators are the termites.Termites’ attack on wood mainly focuses on cellulose. This deprives wood of stabilitymaking it inapplicable for many uses. Termites are of four main types that include:subterranean (living in soil), dry wood termites, damp wood and harvester termites. The magnitude of attack of wood by termites is most prevalent in the tropics as these are theareas with conditions necessary for their survival. In addition, with most woods in these areasbeing hardwoods which have cellulose in high proportions, termites are a real threat.Fungal decay is another biological wood deteriogen. Fungi mainly infect standing trees, logsin transit and storage as well as converted timber in seasoning sheds or in structures. Attackof fungi on wood produces rots and this is the basis of categorisation of the various fungi.The groups include: brown rot, white rot, soft rot and moulds and stains. Brown rots attackcellulose leaving lignin and hence the brown colour. White rot feed on lignin leavingcellulose and hence the white colour while soft rots mainly thrive in wet conditions. Mouldsand stains on the other hand cause surface mould growth and stain without attacking wood. Marine borers attack wood used in marine environment. The borers mainly bore woodmaking it more porous and hence weak for structural use.The above are the main causes of biological degradation. However agents include bacteria,beetles and locusts among many others.Physical DegradationThis has its main agents as fire and mechanical weathering. Fire has the most rapid degradingeffect as opposed to other agents. Wood is burnt and reduced to ash at temperatures as highº as 500 C. Mechanical weathering is mainly as a result of environmental factors like sunlight,humidity, wind and rain. Wood surface thus becomes roughened, fibres separate and are thenwashed away rain in much the same way as the earth’s surface is altered by the weather.Chemical DegradationWhen wood comes into contact with strong acids and alkalis, it undergoes chemicaldegradation. The initial effect is discolouration of wood but on continued exposure itweakens for most of its applications.According to Irving, S.G. and Wesley, E.L (1973), the structural components of wood cellwall consist of cellulose in a matrix of hemicelluloses and lignin. Cellulose andhemicelluloses are carbohydrates polymers that are easily hydrolysed to shorter chainpolymers and sugars by dilute mineral acids. This embrittles wood severely depriving it oftensile and impact strength and toughness.Alkalis attack the hemicelluloses and lignin, removing them by solubilisation and therebyreducing stiffness, bending strength and crushing resistance of the wood. Natural Durability WoodCertain woods exhibit ability to resist attacks by foreign organisms merely by havingirritating extractives and other toxic chemical substances in their anatomy basically in theircell wall constituents. This ability is what is termed natural durability and which can be longlasting or temporary. Wide extremes of exposure to degradation conditions of the wood canlead to downward fluctuation of the resistance. Species like Juniperus procera (Africanpencil cedar) are known for this attribute and is widely utilised for fencing poles among otherstructures where a higher measure of permanence is required. However, it is worth notingthat due to uncertainty of natural phenomena, treatment of such woods though perceived resistant should not be an exception. Furthermore, preservation of wood not only focuses onbiological attack prevention but also such factors as fire mechanical weathering andchemicals that equally degrade wood.Economic Impact of Wood DeteriorationWood deterioration by above agents not only causes large monetary losses but also results inindirect losses that have heavy impact on the national economy of any country.There are less tangible losses for instance, represented in wasted timber and in rejection ofwood items in favour of alternatives that are by far less suitable and unlike wood are in thelong run an irreplaceable resource.Cutting of forest stands to replace unserviceable wood entails a costly commitment of labourand of timber provenance being exhausted. Direct and indirect losses will continue to beeconomic while elephant until wood is totally protected from these deterioration factors.The brief overview above depicts wood as a rather susceptible material whose service lifecan be greatly jeopardised by the many of its degrading agents. In this regard ways andmeasures to minimise its susceptibility come into playWood PreservationWood preservation is broadly defined as the practice carried out aimed at extending orprolonging wood working life. This is either by application of natural or artificial barriers? thereby protecting it from agents of degradation (Kihia, 1994) . In the first place, woodpreservation by extending the service life of wood lowers demand that emanates from lack ofdurability of untreated wood. It is actually a conservation oriented practice whose long termbenefits are sustainability of wood provenance that form paramount component ofbiodiversity.History of Wood PreservationWood preservation is an old practice whose origin can be traced historically to the ancientcivilisations in Egypt and Mesopotamia. In these ages, wood preservation methods usedseldom employed chemicals as these had not been discovered. Main method then was by? stWood Science and Technology Department, Proceedings of 1 Biennial Research & Extension Symposiumth st (29 September – 1 October 1994) charring which was effective since up to date some of such woods exist in structures. The artof treatment has been perfected over the years with the advent of methods such as use of oils,salt and plant extracts among other traditional methods. Evolution of modern treatmentmethods of wood started in the era of European industrial revolution (1630 – 1830 AD).During these times, the world exploration took centre stage. As a result there was dominanceof sea transport by most of the then world powers like Britain. Most of the ships had theirstructures made of wood. This was found to be susceptible to marine borer attack hencearousing the need to look for ways and means of preserving wood to reduce susceptibility.During the same period of industrial revolution, wood was also utilised highly fortransmission poles of power to the new industries, telegraphic lines and railway sleepers.Such needs also required a measure of durability and hence the need for preservationmeasures.Britain is the first country in which a treatment plant was first set up in 1838 by Bethel. In theUnited States and Canada, this happened in 1895 and 1911 respectively. From then on, woodtreatment has evolved and up to modern times most of the initial methods have beenperfected to the more modern ones used today.In Kenya, it was determined by 1994 through a study by East African Tanning and ExtractCompany (EATEC) that the supply of power and telegraphic poles required 80,000 maturetrees every year to replace fallen lines without preservation (Kihia, 1994). This was3approximately 150 hectares with a total volume of 30,000m .However, through preservation, the volume was drastically reduced and could be saved forother uses.The same study concluded that wood preservation industry played a crucial role in woodresource conservation. However, it reckoned that the magnitude of this role could even beincreased if the consumers and producers were to be well informed about the best ways ofpreserving wood and benefits of wood preservation. The consumer part could be improvedby emancipating them from ignorance that led to usage of poorly treated wood throughcarrying out vigorous informative campaigns while the producers could be informed ofimproved methods in a bid to raise quality of their products for increased durability.Years down the line, there has been a pronounced decline in forest cover in Kenya. Thisnecessitated a governmental ban on logging in 1998 to facilitate conservation of theremaining volume along with raising more trees for insured future sustainability. This greatly affected supply and usage of wood in the country. Wood treatment plants besides others werethe mostly affected as there was nolonger availability of raw materials for treatment. In thesame line, it is worth mentioning that usage of treated wood was a rather low note, asrealisation had not come to many wood utilisers that sustainability of forest for wood wasjeopardised.Wood Preservation MethodsThe term wood preservation is generally used to imply use of some chemical or a mixture ofchemicals that are poisonous to the wood destroying organisms. Preservation method caneither employ pressure or non-pressure methods.Wood treating methods fall into three major groups employing sap displacement, capillaryabsorption and diffusion and pressure methods (Kollmann, 1984).? Sap displacement is basically for sapwood treatment due to its permeability. Green poles areused and the process generally involves displacement of voidal sap by the preservativeapplied under high pressure. This method is best suited for green softwood poles such as pinepoles that re freshly cut.Capillary absorption or diffusion encompasses brushing, spraying, dipping and soakingmethods. It is mainly done to air-dried wood. Capillary absorption takes place first duringtake up of solution to the void structure. Then follows diffusion in the cell walls.Preservatives make wood toxic to organisms that use it for food or shelter, fire retardantsreduce flame spread and prevent from supporting its own combustion, water repellent slowmoisture changes in wood while other chemicals make wood resistant to acids or alkalis ormodify its characteristics for spread applications. All these practices are geared towardsincreasing durability of wood. However, it should be noted that nothing lasts forever and it isrudimental to heed to the philosophy that constant motion is the essence of this life as Clark,? 1868 (18) puts it “Though sometimes in ignorance, the perishable character of allsurrounding things may be lamented, yet on the other hand, it must notbe forgotten that perpetual destruction and perpetual renewal are inreality essential cause of all life, beauty and harmony”?Refers to freshly felled wood that has not undergone any of the moisture expulsion processes?Robert D. Graham, Wood Preservation History and Purpose, 1973 (pp 2) Pressure methods are the most effective means of treating solid wood. In this case, a pressureas high as 500 pounds per square inch (psi) or more is needed. Such pressure mainly causespenetration of preservative (usually liquid) through the pits of resistant woods. A nearlyconventional set up of a cylinder where woods are put and then injection of pressure andpreservative for a given duration is used.Three broad categories of wood preservatives are recognised (H.E. Desch, 1996). Theseinclude the following.Tar oil preservative such as creosote, water born preservatives which are salts or mixtures ofsalts in water with the commonly used being CCA (Copper Chrome Arsenate) and finallyorganic solvent preservatives, in which the active ingredients are dissolved in petroleumdistillates such as PCP (pentachlorophenol)Performance of PreservativesPreservative systems must perform their function throughout the service life of the productunder a variety of exposure conditions. Thus, marine piling preservatives must resistleaching, erosion from tides and marine organisms for several decades. Poles and land pilingmust be treated with systems that protect both the aerial and below ground proportions for aconsiderably long time (30 – 60 years) in a variety of climatic conditions, soils and leachingconditions (Robert, 1973).Hence, any effective wood preservative must be; able to be retained by wood, less leachable,highly penetrable to the wood and highly toxic to the target organisms.Economic Aspect of Wood PreservationThe economic merits that are derived from wood preservation in contact with ground havelong been recognised by many sectors of economy from railways, power transmitters, postalauthorities and building and construction companies especially in developed countries.It is however only recently that the value of treatment has come to limelight of fullrecognition by individuals utilising timbers for building, garden, fencing, green houses andother wooden structures.According to W.P.K. Findlay (1985), the annual cost of an item or unit depends on the firstcost (in place) divided by the number of years that the item lasts. Precisely, that annual cost "