1064 nm FT-Raman spectroscopy for investigations of plant cell walls and other biomass materials

Abstract

Raman spectroscopy with its various special techniques and methods has been applied to study plant biomass for about 30 years. Such investigations have been performed at both macro- and micro-levels. However, with the availability of the Near Infrared (NIR) (1064 nm) Fourier Transform (FT)-Raman instruments where, in most materials, successful fluorescence suppression can be achieved, the utility of the Raman investigations has increased significantly. Moreover, the development of several new capabilities such as estimation of cellulose-crystallinity, ability to analyze changes in cellulose conformation at the local and molecular level, and examination of water-cellulose interactions have made this technique essential for research in the field of plant science. The FT-Raman method has also been applied to research studies in the arenas of biofuels and nanocelluloses. Moreover, the ability to investigate plant lignins has been further refined with the availability of near-IR Raman. In this paper, we present 1064-nm FT-Raman spectroscopy methodology to investigate various compositional and structural properties of plant material. It is hoped that the described studies will motivate the research community in the plant biomass field to adapt this technique to investigate their specific research needs.

Keywords: Raman spectroscopy; biomass; cell walls; cellulose; crystallinity; lignin; near-IR; plants.

Figure 1

SEMs of normal (A) and compression wood (B).

Figure 2

Average Raman spectra, in the region 250–1850 cm⁻¹, comparing normal and compression wood of black spruce.

Figure 3

Correlation between 18-Segal-WAXS and univariate Raman crystallinities.

Figure 4

380 cm⁻¹ region of Raman spectra of a number of cellulose samples.

Figure 5

Correlations of lignin's 1600 cm⁻¹ band intensity with Klason and total lignin for various lignocellulosic materials. Klason lignin (%) is listed in parentheses. Black spruce MWEL (48.4), 2 samples of southern pine (28.9), black spruce (27.3), white oak (25.2), aspen (18.3), corn stalk (13.8), partially delignified black spruce (8.1), and unbleached kraft pulp (4.9).

Figure 6

Spectra sets of never-dried and dried aspen woodcellulose; (A) 2650–3100 cm⁻¹, (B) 250–1550 cm⁻¹.

Figure 7

Cellulose I, cellulose II, and cellulose III_I compared in various spectral regions; (A) 50–750 cm⁻¹, (B) 850–1550 cm⁻¹, (C) 2600–3600 cm⁻¹.

Figure 8

Conformations of CH₂OH group—gt, gg, and tg.

Figure 9

Effect of water removal on 2890 cm⁻¹ band intensity. (A) BNSWKP, (B) cellulose I, cellulose II, and amorphous cellulose.

Figure 10

Raman spectra of Jack pine holocellulose in never-dried, dried, and dried-then-rewet states; (A) 850–1850 cm⁻¹, (B) 250–650 cm⁻¹.

Figure 11

Low frequency (50–250 cm⁻¹) Raman spectra of various celluloses in dried state.