Determination of In Situ Esterification Parameters of Citric Acid-Glycerol Based Polymers for Wood Impregnation
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The development of wood treatments is of increasing industrial importance. A novel technique for improving the properties of lodgepole pine and white pine through modification of the microstructure is described. The present investigation is devoted to the synthesis and determination of in situ parameters of citric acid and glycerol based polymers for wood impregnation. This solvent free approach is environmentally friendly and achieved through an esterification condensation reaction under acidic conditions. Crude glycerol and citric acid reactants were cross-linked via a curing process at 160 °C creating a polymer with only water as the byproduct. The ester bonds and crosslinking levels were controlled using different catalysts and citric acid contents and related to the reaction time and temperature. The nature of bonding within the polymers and at the wood cell walls was determined by FT-IR analysis. The thermal properties such as glass transition temperature (Tg) were studied using TGA/DSC and the effect of citric acid content and catalyst type determined. Dimensional stability of impregnated wood samples improved above 50% for each sample with HCl and p-TSA catalysts compared to control samples. FTIR spectra were studied to show the presence of the ester linkages of the polymer in situ at the wood cell walls. Bonding between the polymer and wood macromolecules were observed by scanning electron microscopy and interpreted as evidence of chemical bonds at the wood cells. When prepared using a catalyst, the polymer was intimately incorporated into wood structure significantly improving the substrate dimensional stability. Enhanced stability makes this approach of particular interest for exterior wood products especially as a green renewable option for the wood industry.
KeywordsCrude glycerol Citric acid Polymerisation Wood impregnation Wood dimensional stability
The authors are grateful to Natural Sciences and Engineering Research Council of Canada for the financial support through its IRC and CRD programs (IRCPJ 461745-12 and RDCPJ 445200-12) (MSc CRD 14) as well as the industrial partners of the NSERC industrial chair on eco-responsible wood construction (CIRCERB). Thanks are also due to Ursula Potter and Dr Philip Fletcher from the Microscopy and Analyse Suite, University of Bath for help given for scanning electron microscopy and Dr Martin Ansell, Department of Architecture and Civil Engineering, University of Bath for helpful discussions. Acknowledgement is also due to the Canadian Queen Elizabeth II Diamond Jubilee scholarship scheme and the Ministry of Economy, Science and Innovation of the Province of Quebec in its Research Support Program PSR-SIIRI.
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