Structure and morphology of cellulose fibers in garlic skin

Abstract

The knowledge of the texture and morphology of cellulose is essential for reliable modelling of cell growth and mechanical resistance of vegetal systems. Microscopic observations on thin layers of the skin of Allium sativum have shown elongated structures (i.e. cellulose fibers) imbedded in a matrix of more or less rounded cells. Examination by an optical polarizing microscope (OPM) has shown an intermittent high and low birefringence along fibers. Transversal regions with a reduced brightness along fibers are expected to contain a higher amount of amorphous lignin, hemicelluloses and waxes, some of which might also be birefringent, but at a much lower degree than cellulose. Scanning electron microscopy (SEM) has also evidenced an alternating growth of the fibers. Moreover, the negative sign of birefringence suggests a parallel orientation of cellulose nanofibrils transversally to the fiber axis. The characteristic modulation of intensity along lignocellulosic fibers can be due to variation of the cellulose concentration or orientation, perhaps caused by circadian cycles of temperature and light during growth. Indeed, imperfect orthogonal light can be totally reflected at the interface between regions with different values of the refractive index, contributing to the optical effect of banding.

Processing and properties of jute (Corchorus olitorius L.) fibres and their sustainable composite materials: a review

“…Jute bres contain large sub-categories of substances including cellulose, hemicelluloses, lignin, pectin, polyuronide, acetyl matter, fat, ash, nitrogen (N 2 ) and some other components such as aqueous extracts and mineral substances. [302][303][304] Jute bres composed of lignocelluloses have been observed to possess strongly polarized hydroxyl groups. 58,305,306 Details of the composition of the jute bres are presented in Table 3.…”

“…14,165,168,169,352,[396][397][398] However, plant bres have some disadvantages, including hydrophilic behavior, poor thermal stability, and in particular poor adhesion with a hydrophobic resin, which results in poor interfacial bonding and low mechanical strengths. 235,399 In this case, surface modication 173,278,303,[400][401][402][403][404][405][406] has the ability to solve most of these drawbacks. The limitations of PFRCs can be strengthened through the use of chemical or physical methods, treatment of bres, or use of coupling agents.…”

“…In composites, their dielectric properties depend on the polarization of their constituents and mainly inuenced by interlaminar, dipolar, and atomic polarization. 303,[576][577][578][579][580] The polarization of the interfaces at very low frequencies has a greater effect on the dielectric properties. Interfacial polarization occurs when charge carriers are trapped at the intersection of heterogeneous systems, primarily by dipoles in the case of NFRCs.…”

“…In plant bres, the availability of -OH groups contributes to their polarization. 303 The dielectric constant is calculated using eqn (3), as follows:…”

“…In plant fibres, the availability of –OH groups contributes to their polarization. 303 The dielectric constant is calculated using eqn (3), as follows:where C is the parallel capacitance, t is the width, A is the cross-sectional area, and ε 0 is the free space permittivity (8.85 × 10 −12 F m −1 ). The resistivity and conductivity of the sample can be calculated using the following equations:Conductivity = 1/ ρ where R is the parallel resistance and ρ is the resistivity.…”