Detection of chlorinelabelled chitosan in Scots p

Authors: Erik Larnøy Morten Eikenes Holger Militz

Publish Date: 2010/02/27

Volume: 45, Issue: 1, Pages: 103-110

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Abstract

The aim of this study was to use energydispersive Xray spectroscopy EDX to localize chitosan in the cell wall of chitosanimpregnated Scots pine It was of interest to investigate the concentration of chitosan in wood to gain further knowledge and understanding of the distribution of chitosan in the wooden matrix After deacetylation chitosan was reacetylated with chloroacetic anhydride to achieve a covalent bonding of chloride to the chitosan polymer Chloridelabelled chitosan was measured by EDX using a scanning electron microscope and described as chloride intensity Analysis of free chloride anions was performed by dialysis and inductively coupled plasma atomic emission spectroscopy There was a significant correlation between the molecular weight of chitosan and the intensity of covalentbonded chloride to the chitosan polymer High molecular weight chitosan showed a better interaction with the cell wall structure than low molecular chitosanDue to the enhanced focus from governments environmental organizations and consumers on the use of environmentally benign wood preservatives the use of traditional wood preservatives containing chromium and arsenic is restricted The most common wood preservatives in Europe today are based on copper which is on the reduction list of some European countries including Norway Application of fungicides is by far the most widely used method to control fungal decay in wood However chemical control may induce biocide resistance in fungi and there are also health risks to consider when using fungicides Other wood protection systems based on chemically modified wood products have to some extent become commercially available but there is still a growing need to develop antifungal chemicals that are not toxic to humans and the surrounding environmentChitin a 14 linked polymer of 2acetamido2deoxyβdglucose is the most abundant natural nitrogencontaining polysaccharide and its annual bioproduction is estimated to be higher than 109 tons Tracey 1957 According to Rubin 2003 the global annual production capacity for chitin is 8000 tons Approximately 5000 tons are used to manufacture glucosamine the rest is used for chitin/chitosan applications The major source of chitin is crustacean shells which is a byproduct of the seafood refining industry Chitin is also found in the skeletons of several insects and in the cell walls of several fungi Allan and Hadwiger 1979 Chitosan is deacetylated chitin and is mainly produced from chitin by hydrolysis of the amide C–N bond by strong alkali Mima et al 1983 From earlier work Eikenes et al 2005 it is known that to achieve sufficient protection of the wood against brown rot fungi a certain level 35 kg chitosan/m3 wood and distribution of chitosan in the wood structure is neededThe molecular size of chitosan has a great impact on the properties of chitosantreated wood Larnøy et al 2006 show that a molecular size of 159 kDa gave a 30 better recovery rate than 15 kDa which again agrees with the results found by Eikenes et al 2005 They also found that high molecular chitosan gave a better antifungal effect than low molecular chitosan Larnøy et al 2005 described the limitations in penetration of high molecular weight chitosan in wood and the tradeoff between high uptake and proper fixation was discussed As molecular weight is an important factor when impregnating wood with chitosan it was of interest to study different molecular weights of chitosan in the cell wall of pineTo the knowledge of the authors there has not been any study that confirms the presence localization and quantification of chitosan in the wood matrix This paper describes the detection of chitosan in pine sapwood using scanning electron microscope SEM in conjunction with energydispersive Xray spectroscopy EDX Chitosan consists of carbon hydrogen oxygen and nitrogen and is therefore difficult to detect by EDX partly due to their low energy spectrum and partly because wood has a similar elemental spectral composition and it is thus difficult to distinguish between spectra without deconvolution By reacetylation of the amine of chitosan with chloroacetic anhydride covalentbound chloride is achieved and the chloridemodified chitosan molecules are now detectable by EDXClear samples of Scots pine sapwood Pinus sylvestris L 5 × 10 × 30 mm³ r × t × l were taken from boards vacuum dried at 60°C To remove any free natural chloride atoms in the wood matrix that could interfere with the results the samples were leached according to EN 84 1997 and left to dry in ambient condition before they were impregnated with chitosanThe wood samples were weighed and impregnated using the following processes initially weighed and evacuated for 1 h at 001 N/mm2 followed by 1 h at a pressure of 10 N/mm2 The pressure was then released and the weight of the samples was recorded for control of uptake The impregnated samples were then left to dry in ambient conditions and were not leached after this point

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