Abstract
Raman and Fourier Transform Infrared (FT-IR) spectroscopy was used for assessment of structural differences of celluloses of various origins. Investigated celluloses were: bacterial celluloses cultured in presence of pectin and/or xyloglucan, as well as commercial celluloses and cellulose extracted from apple parenchyma. FT-IR spectra were used to estimate of the Iβ content, whereas Raman spectra were used to evaluate the degree of crystallinity of the cellulose. The crystallinity index (XCRAMAN%) varied from −25% for apple cellulose to 53% for microcrystalline commercial cellulose. Considering bacterial cellulose, addition of xyloglucan has an impact on the percentage content of cellulose Iβ. However, addition of only xyloglucan or only pectins to pure bacterial cellulose both resulted in a slight decrease of crystallinity. However, culturing bacterial cellulose in the presence of mixtures of xyloglucan and pectins results in an increase of crystallinity. The results confirmed that the higher degree of crystallinity, the broader the peak around 913 cm−1. Among all bacterial celluloses the bacterial cellulose cultured in presence of xyloglucan and pectin (BCPX) has the most similar structure to those observed in natural primary cell walls.
Highlights
Cellulose is the most abundant natural polymer
We have proposed that Raman and infrared spectroscopy would complete the knowledge on cellulose structure and polymer interaction of the model materials
The aim of this study was twofold: (i) to assess the structural differences between cellulose of various sources of origin, i.e., commercial celluloses, bacterial cellulose and cellulose from apple cell walls with Raman and Fourier Transform Infrared (FT-IR) spectroscopy; (ii) To investigate whether bacterial cellulose reflects the structure of natural cellulose from apple parenchyma
Summary
Cellulose is the most abundant natural polymer. Each cellulose molecule is an unbranched polymer containing from 1,000 to 1 million D-glucose units, linked together with β-1,4 glycosidic bonds [1].Celluloses from various sources are all the same at the molecular level, but they differ in their crystalline structures and the way that other biopolymers bind to them. Cellulose is the most abundant natural polymer. Each cellulose molecule is an unbranched polymer containing from 1,000 to 1 million D-glucose units, linked together with β-1,4 glycosidic bonds [1]. Celluloses from various sources are all the same at the molecular level, but they differ in their crystalline structures and the way that other biopolymers bind to them. Native cellulose is a mixture composed of two distinct crystalline phases, cellulose Iα and Iβ, which have the same conformations, but differ in crystal structure, having triclinic (Iα) and monoclinic unit cells (Iβ). Celluloses Iα and Iβ possess the same molecular building and O3-H–O5 intra-chain hydrogen bonding, but they have different O2-H–O6 inter-chain hydrogen bonding. Cellulose Iβ contains two chains in each monoclinic unit cell, while Iα contains one chain in the triclinic unit cell [4,5]. Cellulose Iα is interconverted into Iβ by bending during fibril formation [9]
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