| Haimenkou site is located in Jianchuan County, Dali City,Yunnan Province,which is generally considered to be the largest riverine wooden"Stilt house settlement site",, and is listed as one of the top ten archaeological discoveries in 2008,and has very important archaeological value. Haimenkou sites water archeological wood has degraded seriously because of age-old and Inadequate protection after excavation, which needs to be reinforcement timely.The Project "key technology research and application of Haimenkou sites water archeological wood reinforcing protection" started in December 1,2012. the task force members did the exploratory trials with the Haimenkou sites water archeological wood small specimens(the size:2cm×2cm×2cm).and they identified eventually 3 programs:natural resin reinforcement method,chitosan reinforcement method, Phenolic resin reinforcement method. This paper analyzed the decayed degree and mechanism of Haimenkou sites water archeological wood,and then reinforced 143 water archeological woods with the 3 programs which has been adjusted according to the actual situation between June 2013 to December 2014. The reinforcing archeological wood are expected to be showed in Jian Folk Museum from May 2015. This paper describes and analyzes all the work between June 2013 to December 2014.this paper evaluate the decayed degree of water archeological wood by the ways of basic density, drying shrinkage and swelling rate, compressive strength parallel to grain,surface contact angle etc.,and analyze the decayed mechanism by the ways of conventional chemical analysis, solid state NMR, the degree of crystallinity analysis, SEM and TEM microscopic structure, fourier transform infrared spectroscopy etc.Then,143 water archeological woods are reinforced with 3 methods. Since that the volume of Haimenkou sites water archeological wood is much larger than small specimens in exploratory trials,and that decayed degree has a great difference between individuals,so based on data of preliminary exploratory trials, combined with previous analysis of decayed degree and decayed mechanism, we Finalized 3 reinforcing applications after adjustment:　reinforce 62 archeological woods with natural resins, reinforce 21 archeological woods with chitosan, reinforce 60 archeological woods with phenolic resin. Evaluating reinforcement effect by ways of basic density, compressive strength parallel to grain, anti-loss properties, resistance to rot bacteria etc..and analyzing reinforcement mechanism after reinforcement. The final test results are summarized as follows:(1) The degradation of Haimenkou sites water archeological wood is very serious. Most of the archeological wood’s surface color is black or brown-black, the serious degrading archeological wood is very soft,which is Pressed gently to obvious indentations.By analyzeing a moderately degrading archeological wood,we find that:the basic density of archeological wood is only 0.16g/cm3,the compressive strength parallel to grain shen the moisture content 12% is only 3.67 Mpa, which illustrate that Haimenkou sites water archeological wood has been degraded very seriously. The water archeological wood can’t keep the original shape after dehydration and need to be reinforced.(2) The decay mechanism analysis of water archeological wood: By general chemical analysis,FT-IR, solid state NMR,we kow that: The degradation of hemicellulose is most severe,followed by cellulose,and there is a certain degradation of lignin. The cellulose crystalline regions have been seriously degrading,and the The degree of archeological wood crystallinity is decreased significantly.By SEM and TEM microstructure analysis,we know that:the degradation of water archeological wood mainly due to bacterial decay. We also found a small amount of fungus(mainly discolorating fungal) in archeological wood interior. The decadent parts are honeycomb,and mainly in secondary wall.The pore size made by bacterial decay is between tens to Hundreds of nanometers, can accommodate free water,which lead to The archeological wood can’t be restored to its original size when re-absorbent after dehydration shrinkage.The middle lamella is relatively intact,which allows the water archeological wood keep it’s appearance shape.(3) The color of natural resin reinforcing archeological wood is close to the color of modern health wood. Few more seriously decadent archeological wood are cracking and deformed.Many properties of the reinforcing archeological wood are significantly improved than that which are not reinforcing,such as basic density, compressive strength parallel to grain, dimensional stability, hydrophobic ability, resistant to decay.The resistance to water loss of reinforcing archeological wood is very good. properties of the reinforcing archeological wood meet their transport, storage and exhibition. The rosin and shellac within the archeological wood cell wall can be re-dissolved out under the premise of there is no breakage of the cell wall,which can be meets the artifacts reinforcement reversibility.(4) The reinforcing mechanism analysis shows:The rosin and shellac mainly depositing within the cell wall, filling the pores(Including the large size pores which can accommodate free water) due to bacterial decay.The cell wall of reinforcing archeological wood are very full,and it’s secondary wall and middle lamella have a good combination.The damaged bordered pits are filled with rosin and shellac,which is the main reason of reinforcing archeological wood’s excellent hydrophobic properties. A small amount of reinforcing agent fill in the cell cavity filling in lump form,or attached to cell inner wall in lamellar form. The analytical methods can not prove whether start up the chemical reaction between the reinforcing agents and the chemical composition of the cell wall.(5) The color, basic density etc. of chitosan reinforcing archeological wood are improved significantly. chitosan reinforcing archeological wood are irreversible. The strengthening mechanism of chitosan are similar with natural resins,which are mainly physical filling.(6) The color of phenolic resin reinforcing archeological wood is light reddish-brown. Part of the Reinforcing archeological wood are cracking and deformed after dry.The properties such as basic density ect.are Improved significantly. The resistance to water of phenolic resin reinforcing archeological wood is not as good as natural resin’s.The phenolic resin reinforcing archeological wood can be washed away formaldehyde and resols small molecules in water and which has a certain amount of formaldehyde emission(19.15 mg/100g).So, regardless of dry preservation or wet preservation,we need to isolate the storage space from surroundings.(7) The phenolic resin reinforcing mechanism analysis shows:First,the resols small molecules is deposited in archeological wood’s cell wall mainly.Then, the resols small molecules arise polymerization reaction gradually with impregnation, bleaching and drying.It is mainly B-staged phenol resin in reinforcing archeological wood when we do reinforcing mechanism analysis test. It is possible that the phenolic resin in reinforcing archeological wood cell wall is aggregated into C-staged phenol resin. The the cellulose molecule chain close to each other as the polymerization reaction,which creates new crystalline regions,so the degree of crystallinity of phenolic resin reinforcing archeological wood is improved significantly. The studies can not prove whether the chemical reactions occurs between phenolic resin and chemical composition of the wood cell wall.The appearance and color of reinforcing archeological woods with three methods are very close to modern health wood,which retains the characteristics before burial, such as annual ring and traces of artificial knifed etc. The advantages and disadvantages and occasion for use are different:The mechanical strength of reinforced by phenolic resin are the highest, the process flow is simple, this method is suitable for reinforcing large volumes water archeological wood in the site.The dimensional stability, hydrophobicity and resistance to water loss of natural resin reinforcing archeological wood are vwry well,and the mechanical strength can meet the requirements of reinforcement,and this method is reversible.But the process flow of natural resin is relatively complex,which is suitable for reinforcing large volumes water archeological wood far away from the site. The reinforcingt method of chitosan don’t have distinct advantages,and the costs is relatively high. |
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