Effects of moderate temperatures: Artificial ageing of softwood and its effects on mechanical properties and chemistry

Abstract

During thermal impact on wood the properties and chemistry of the biopolymer composite are changed. The effect of ageing processes at moderate temperatures on tensile strength perpendicular to grain of Norway spruce wood [Picea abies (L.) Karst.] was studied, along with chemical changes. Test specimens were exposed to a three-step ageing cycle lasting for 7 days [50°C/95% relative humidity (RH), –20°C/65–70% RH and 75°C/15% RH], which was repeated 24 times. A significant decrease in tensile strength in the tangential direction was observed. Chemical changes in the wood matrix resulting from the artificial ageing cycle were assessed by attenuated total reflection Fourier transform infrared spectroscopy, solid-state [¹³C]cross-polarized magic angle spinning nuclear magnetic resonance spectroscopy, and detection of the volatile and semivolatile organic compounds by headspace solid-phase microextraction gas chromatography coupled to mass spectrometry. The sugar composition of hemicelluloses was analysed by acid methanolysis. During artificial ageing chemical changes influencing the mechanical properties mainly occurred in the polysaccharide matrix, whereas the lignin remained unaltered.

Keywords:

• Ageing
• hemicellulose
• Picea abies (L.) Karst.
• tensile strength
• VOC

Acknowledgements

The authors gratefully acknowledge the financial support by the Berger Solutions Group. Furthermore, the authors wish to thank Manfred Schwanninger for his guidance and help during infrared interpretation.