Comment about "The measurement of the micro-fibril angle in soft-wood" by K. M. Entwistle and N. J. Terrill

Abstract

In a recent paper “The measurement of the micro-fibril angle in soft-wood,” Entwistle and Terrill [1] describe the use of wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) for measuring the tilt angle of the cellulose fibrils with respect to the longitudinal cell axis (microfibril angle, MFA) of soft wood. The authors present a consistent and detailed mathematical description of the method and experimental results that illustrate the theoretical description. They report their findings as an “improvement to Cave’s method” [2] and cite a total of four papers, where those two being concerned with X-ray scattering date from the 1960s. It must be pointed out that since the pioneering X-ray studies of Cave and Meylan [2, 3] a great number of papers on the use of WAXD and SAXS for determining the MFA have been published. In this comment, we first refer to work which clearly shows that WAXD and SAXS are, in the meanwhile, well-established methods for the determination of MFA’s in wood. Second, we show how to evaluate WAXD and SAXS patterns from rectangular wood cells, which Entwistle and Terrill termed as “not capable of yielding microfibril angles.” Already in the 1960s, Kantola et al. [4, 5] used both WAXD and SAXS for determining the MFA in wood. They investigated the influence of the sample orientation on the scattering pattern and derived Equation 2 in Entwistle and Terrill [1]. Further studies using X-ray diffraction from the 002 as well as the 040 planes of cellulose in wood were carried out for example by Nomura and Yamada [6], Paakari and Serimaa [7] and Sahlberg et al. [8]. In a recent paper by Evans [9], it was shown that the asymmetric positions of two poles of one reflection on the detector as they are described by Entwistle and Terrill (see their Equation 1a and 1b) can lead to asymmetric scattering patterns at some sample orientations. Lichtenegger et al. [10], took advantage of this asymmetry to determine the fibril orientation in single cell walls in cross sec-