FTIR Measurement of Cellulose Microfibril Angle in Historic Scots Pine Wood and Its Use to Detect Fungal Decay

ABSTRACT

Microfibril angle (MFA) – the orientation of cellulose fibres in the S2 layer of the secondary cell wall – is a key determinant of the stiffness and strength of timber. The microfibril angle depends on the way in which the timber was grown and its position within the tree. Microfibril angle can be measured by X-ray diffraction and other methods, but the methods in current use are slow or require advanced instrumentation. The aim of this study was to explore the use of polarised Fourier transform infrared (FTIR) microscopy as a relatively fast and inexpensive method for measuring MFA in historic Scots pine (Pinus sylvestris L.). The FTIR measurements were calibrated against X-ray measurements of MFA in modern Scots pine. We observed a wide range in MFA values and a radial pattern of MFA similar to modern Scots pine in undecayed Scots pine heartwood from sixteenth and seventeenth century beams in Scottish secular buildings. The density of the heartwood was also similar to modern plantation-grown Scots pine despite the much slower growth rate recorded in the ring widths of the historic timber. The sapwood, which had been attacked by both insect pests and fungi, showed an erratic reduction in density and a large increase in MFA compared to the modern material. The increased sapwood MFA was attributed to selective destruction of the S2 layer of the wood cell walls by fungal decay. Using MFA measurements in conjunction with density offers the possibility to estimate the mechanical properties of sound historic pine timber, to detect fungal decay more sensitively than by density alone, and to distinguish between pest and fungal attack in a way that relates directly to the remaining mechanical performance of the timber.

KEYWORDS:

• Wood
• infrared spectroscopy
• brown rot
• cell wall

Acknowledgements

Dr Craig Kennedy (then at Historic Scotland) and Dr Anne Crone (AOC Archaeology) are thanked for their inputs in the planning of the experiments on historic pine.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Kate Hudson-McAulay http://orcid.org/0000-0002-2389-6503

David Auty http://orcid.org/0000-0002-5146-4476

Michael C Jarvis http://orcid.org/0000-0001-9558-8203

Additional information

Funding

The research described here was funded through a PhD studentship awarded to the University of Glasgow by Historic Scotland. The authors thank Historic Scotland for funding this work and for providing access to the historic wood material. The X-ray diffraction measurements on modern wood were funded by the Scottish Forestry Trust, the Forestry Commission and EC COST Actions EC50 and FP0802.