Hemicelluloses, spectra

To be cost effective, the process must use organisms capable of fermenting the full spectrum of five- and six-carbon sugars released from cellulose and hemicellulose. The advent of efficient genetically engineered organisms equipped with metabolic pathways to handle both types of sugars is an important... 

Pyrolysis in inert atmosphere between 400 and yOO C produces water vapour, CO2, combustible gases CO, H2, CH and a multitude of organic vapours from the biopolymers cellulose (C6(H 0)s), hemicellulose (Cj(H20)4) and lignin. An impression of the complex product spectrum especially of the condensable organic vapours is given in Fig. 6. The remainder is a black char, mainly consisting of carbon and inorganic ash oxides. 

The spectrum of aspen wood (Figure 7.1) shows the presence of the three fundamental wood constituents. A band for cellulose is at 895 cm (g-anomer in pyranose ring) <22). xhe band at 1740 cm" is due to uronic acid and acetyl groups in hemicellulose. The bands from 1235 to 1605 cm, specially the one at 1505 cm", are representative of lignin while those from 950-1100 cm" are due, in part, to carbohydrates (C-0 bonds in alcohols). 

To a weighed amount of 1 mg corn cobs hemicellulose, 200 mg of potassium bromide was added. The mixture was ground to a homogeneous form and then analyzed the vibration in the range of wave number 500-4000 cm . Infrared spectra recorded the fingerprint spectrum and the spectrum of functional groups resulting from the hemicelluloses [5]. The results can be seen in Table 8.1. 

Fibrillar fines obtained from cellulosic fibres are known for their unique structure, material characteristics, and potential applications (Hubbe et al. 2008). An amorphous lignin and hemicellulose matrix separates the elementary nanofibrils in natural vegetable fibres. Based on raw material sources, pretreatment and subsequent defibrillation procedures will produce a broad spectrum of fibril structures as well as nomenclatures used to describe them. Thus, we find various terms adopted in the field, such as nanoscale-fibrillated cellulose, cellulosic fibrillar fines, cellulose aggregate fibrils, and microfibrillar cellulose. 

Figure 7 The spectrum of biomass pretreated with 1% H2SO4 contains signals from both native cellulose and lignin (hemicellulose has been removed). Subtraction of a lignin spectrum provides a spectrum of native cellulose which can provide the crystalline index by focusing on the crystalline signal at 88 ppm and on the amorphous signal at 84 ppm. Data were acquired at 9.4 T using a 14 kHz spinning frequency. Reproduced from Bemardinelli et al. [114] published under the CC-BY license.

In this study, MALDI-TOF-MS was employed to determine die structure and amount of side chains as die presence of uronic acid is known to have effects on the molecular properdes of xylan (25). The MALDI-TOF-MS spectrum of an acid-insoluble hemicellulose fraction isolated from the press lye, which was methylated (17,18) prior to measurement, is shown in Figure 2. 

Figure 1. CP/MAS C-NMR spectra recorded at 7.05 T on cellulose / isolated from different sources and one hr aft pulp. From bottom to top the sources are Valonia, Cladophora, Halocynthia, and cotton linters. The top spectrum is bleached birch krcft pulp that contains hemicelluloses. (Reproduced with permission from reference 16. Copyright 1999).

Isolated cellulose I and xylan extracted finm bleached birch pulp was mixed in order to study the process opposite to the removal of hemicelluloses fiom bleached kraft pulp by acid hydrolysis (16). The spectrum of hydrated tylan is shown in Figure 6. 

Figure 3. NMR spectrum (45°C, 500 MHz, OMSO d ) of reactive mixture composed of hemicellulose (0.08 M with respect to the repeating unit), Hema-Im (0.1 M) and triethylamine (0.02 M) after 0 h. (Reproduced from reference I, with permission from WILEY-VCH.)...

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