Why is PEG not stable in air during heating?
Polyethylene glycol (PEG) has been used since the 60's for the preservation of wood. However, catabolism it has been found that by heating the material becomes fluid. What is the mechanism behind - and it poses problems catabolism for future preservation? Read the original article here
PEG is a very useful art waxes, which are available in a wide range of materials. This is prepared from ethylene oxide, using catalysts can polymerize catabolism to form homologous compounds of the general formula HO (CH2CH2O) nH. The products are usually referred catabolism to as such. PEG 400, which discloses the number average molecular weight of the epoxy resin consisting of the product. PEG 400 is made up of homologues catabolism with n = 2 and up to n = 15. [1] PEG is liquid at room temperature up to an (average) molecular weight catabolism of approx. 800, which in the case of solids. The higher catabolism the molecular weight, the more wax-like character. PEG is used in industry, pharmaceuticals, cosmetics, temporary binder in ceramic materials, lubricants, catabolism metalworking, etc.
Preservation of archaeological wood Our interest in PEG is due to a more specific use. Archaeological excavation wood is usually so degraded that it can not tolerate direct drying. The cracks and crevices, and the tree is very degraded (most usually of wood from the Viking Age and even older) shrinks strongly by drying and loses its original form. This is because most of the pulp is disintegrated, and in some cases, only midtlamellen back. Sometimes as much as 90% of the wood (cellulose) broken down, and it looks more like a soft sponge. PEG is water-soluble. Very degraded wood may be impregnated by adding PEG to water in increasing concentrations. It is a process that takes years and you end up with a sluggish condition, consisting primarily of wax, but still retains its original appearance. Since the shape is maintained, one can use treated wood for the reconstruction of example. a ship's hull.
Ships impregnated with PEG PEG has since the 60s been the most widely used preservative. catabolism The probably best known impregnation is "Regalskeppet Vasa ', which sank in the Stockholm catabolism archipelago in 1628 [2]. At home we have for example. catabolism Viking ships from Skuldelev [3,4], which is on display at the Viking Ship Hall in Roskilde and Hjortspringbåden (see front page) located at the National Museum. It's not small amounts used. During impregnation of the Vasa was the amount absorbed almost 15 tons. In Denmark it is reckoned that 1 tonne of wood demands - incl. the remaining volume of impregnating cut clean - 2 ton PEG [5]. Kilo price of PEG are large supplies approx. 20 billion, catabolism and average estimated that its preservation rate of approx. 800 per. kg wood. There is therefore bound substantial funding for preservation of wood-based antiquities. PEG can be decomposed into liquid Our studies of PEG due to a problem, we were made aware of in the late eighties. Large pieces of Hjortspringbåden was left in solid PEG blocks in a former canning, and should now udpræpareres and genudstilles (Figures 1 and 2). We were approached by conservation staff, as it turned out, PEG, after being melted catabolism overnight at approx. 100 C and subsequently cooled to room temperature, would solidify again. It was reproduced in the lab and we were able to demonstrate that by blowing of PEG with air at 80 C, however, PEG 4000 of up to 16 hours is broken down into a liquid. The average molecular weight of residualvæsken was below 1000 [6]. It was obviously of great concern and we decided to investigate the mechanism further.
Since commercial PEG mechanism consists of many homologues of high molecular weight, and our equipment was limited to a few gas chromatographs with associated mass spectrometers, it was decided to focus on one of the less homologous, tetraethylene glycol (TEG). TEG contains the ether and hydroxy groups we assumed in advance may be sensitive to oxidation which may be involved. It has traditionally been assumed that this oxidation is the same as that in mainstream ethers [7), and there have been presented several 'evidence' for the oxidation of the ether group [8-11]. When we exposed TEG for a controlled aging, bubbling purified air at 70 C, dark and a humidity of approx. 5%, then, an analysis of the degradation products that TEG was degraded to very small number of components (Figure 3), and that they all could be related to TEG, triethylene glycol (TriEG) and their formic acid esters [12]. It thus seems as if the primary degradation product is formic acid, which agrees very well with an attack on the three ether groups in the TEG. An attack catabolism on the hydroxyl groups at the ends on the other hand a bid likely to the formation of formic acid and thus to the esters that are subsequently formed. This is consistent with a report from 1966, when Dulog and Storck [8] reported that the only oxidation product was water, while the IR spectrum showed a clear carbonyltop, given
Polyethylene glycol (PEG) has been used since the 60's for the preservation of wood. However, catabolism it has been found that by heating the material becomes fluid. What is the mechanism behind - and it poses problems catabolism for future preservation? Read the original article here
PEG is a very useful art waxes, which are available in a wide range of materials. This is prepared from ethylene oxide, using catalysts can polymerize catabolism to form homologous compounds of the general formula HO (CH2CH2O) nH. The products are usually referred catabolism to as such. PEG 400, which discloses the number average molecular weight of the epoxy resin consisting of the product. PEG 400 is made up of homologues catabolism with n = 2 and up to n = 15. [1] PEG is liquid at room temperature up to an (average) molecular weight catabolism of approx. 800, which in the case of solids. The higher catabolism the molecular weight, the more wax-like character. PEG is used in industry, pharmaceuticals, cosmetics, temporary binder in ceramic materials, lubricants, catabolism metalworking, etc.
Preservation of archaeological wood Our interest in PEG is due to a more specific use. Archaeological excavation wood is usually so degraded that it can not tolerate direct drying. The cracks and crevices, and the tree is very degraded (most usually of wood from the Viking Age and even older) shrinks strongly by drying and loses its original form. This is because most of the pulp is disintegrated, and in some cases, only midtlamellen back. Sometimes as much as 90% of the wood (cellulose) broken down, and it looks more like a soft sponge. PEG is water-soluble. Very degraded wood may be impregnated by adding PEG to water in increasing concentrations. It is a process that takes years and you end up with a sluggish condition, consisting primarily of wax, but still retains its original appearance. Since the shape is maintained, one can use treated wood for the reconstruction of example. a ship's hull.
Ships impregnated with PEG PEG has since the 60s been the most widely used preservative. catabolism The probably best known impregnation is "Regalskeppet Vasa ', which sank in the Stockholm catabolism archipelago in 1628 [2]. At home we have for example. catabolism Viking ships from Skuldelev [3,4], which is on display at the Viking Ship Hall in Roskilde and Hjortspringbåden (see front page) located at the National Museum. It's not small amounts used. During impregnation of the Vasa was the amount absorbed almost 15 tons. In Denmark it is reckoned that 1 tonne of wood demands - incl. the remaining volume of impregnating cut clean - 2 ton PEG [5]. Kilo price of PEG are large supplies approx. 20 billion, catabolism and average estimated that its preservation rate of approx. 800 per. kg wood. There is therefore bound substantial funding for preservation of wood-based antiquities. PEG can be decomposed into liquid Our studies of PEG due to a problem, we were made aware of in the late eighties. Large pieces of Hjortspringbåden was left in solid PEG blocks in a former canning, and should now udpræpareres and genudstilles (Figures 1 and 2). We were approached by conservation staff, as it turned out, PEG, after being melted catabolism overnight at approx. 100 C and subsequently cooled to room temperature, would solidify again. It was reproduced in the lab and we were able to demonstrate that by blowing of PEG with air at 80 C, however, PEG 4000 of up to 16 hours is broken down into a liquid. The average molecular weight of residualvæsken was below 1000 [6]. It was obviously of great concern and we decided to investigate the mechanism further.
Since commercial PEG mechanism consists of many homologues of high molecular weight, and our equipment was limited to a few gas chromatographs with associated mass spectrometers, it was decided to focus on one of the less homologous, tetraethylene glycol (TEG). TEG contains the ether and hydroxy groups we assumed in advance may be sensitive to oxidation which may be involved. It has traditionally been assumed that this oxidation is the same as that in mainstream ethers [7), and there have been presented several 'evidence' for the oxidation of the ether group [8-11]. When we exposed TEG for a controlled aging, bubbling purified air at 70 C, dark and a humidity of approx. 5%, then, an analysis of the degradation products that TEG was degraded to very small number of components (Figure 3), and that they all could be related to TEG, triethylene glycol (TriEG) and their formic acid esters [12]. It thus seems as if the primary degradation product is formic acid, which agrees very well with an attack on the three ether groups in the TEG. An attack catabolism on the hydroxyl groups at the ends on the other hand a bid likely to the formation of formic acid and thus to the esters that are subsequently formed. This is consistent with a report from 1966, when Dulog and Storck [8] reported that the only oxidation product was water, while the IR spectrum showed a clear carbonyltop, given
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