Mechanical properties of cellulose fibres and wood. Orientational aspects<i>in situ</i>investigated with synchrotron radiation

Kölln, Klaas; Grotkopp, Ingo; Burghammer, Manfred; Roth, Stephan V.; Funari, Sérgio S.; Dommach, M.; Müller, Martin

doi:10.1107/s0909049505011714

Cited by 52 publications

(47 citation statements)

References 17 publications

(20 reference statements)

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“…However, the relationship between strain and f c observed for these highly oriented fibres (f c > 0.98) showed a slight deviation from linearity (Ko¨lln et al 2005).…”

Section: Resultsmentioning

confidence: 96%

Orientation of cellulose crystallites in regenerated cellulose fibres under tensile and bending loads

et al. 2006

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The degree of orientation in regenerated cellulose fibres with a diameter of 36lm was determined using position-resolved synchrotron X-ray microbeam diffraction. The fibres were characterized in unstrained condition, under tensile strain, and in bending. A homogeneous distribution of the degree of crystalline orientation (Herman's orientation factor f c = 0.85) across the fibre thickness was found in the unstrained fibre. The degree of orientation of cellulose crystallites increased in a linear manner with increasing tensile strain applied to the fibre. Also in bending, a linear relationship between applied strain and the degree of crystalline orientation was found, where f c increased in tension and decreased in compression. This linear relationship was found to be valid for both the tensile and the compressive zone of the bent fibre.

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“…However, the relationship between strain and f c observed for these highly oriented fibres (f c > 0.98) showed a slight deviation from linearity (Ko¨lln et al 2005).…”

Section: Resultsmentioning

confidence: 96%

Orientation of cellulose crystallites in regenerated cellulose fibres under tensile and bending loads

et al. 2006

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“…Many advanced techniques have been used to follow the local micromechanics of natural cellulose fibres and composites, including Raman spectroscopy, synchrotron X-ray diffraction and half fringe photo-elasticity (Eichhorn et al 2001a, b;Kölln et al 2005;Martinschitz et al 2008;Hughes et al 2000). In this study however, the micromechanical deformation of coir and celery fibres will be investigated using Raman spectroscopy.…”

Section: Introductionmentioning

confidence: 97%

Elastic coils: deformation micromechanics of coir and celery fibres

Bakri

Eichhorn

2009

Cellulose

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Natural fibres, such as flax and hemp, are typically chosen as reinforcing elements in composites to replace traditional glass fibres due to their high stiffness, strength and low strain to failure. Some plant fibres such as coir and celery however possess high strains to failure, which could be utilised in a composite to enhance toughness. This paper reports on the use of Raman spectroscopy to follow the molecular deformation of single fibres of coir and celery. The technique is also used to characterise the orientation of the cellulose structure within the fibres. It is shown by mechanical testing of fibres that both celery and coir possess a non-linear stress-strain curve. Coir fibres however exhibit high strain to failure, whereas celery fibres are shown to have a much lower value of this parameter, despite having a similar coiled fibrillar structure. It is shown by using polarised Raman spectroscopy, and rotating the specimens with respect to the polarisation axis of the laser and measuring the intensity of the 1095 cm -1 Raman band, that both celery and coir fibres combine both axial and transverse orientation, due to their coiled structures. This is also confirmed by birefringence measurements. By following the shift in the central position of this Raman band as a function of cyclic deformation of the fibres, it is shown that the coir fibres recover their molecular deformation, whereas the celery does not show the same level of recovery. This difference between the fibres is postulated to be due to the fact that coir possesses an interlaced fibrillar structure, which remains intact, whereas the celery sub-fibrils unravel and orient towards the fibre axis during deformation.

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“…This difference between the two fibre types might be explained by the previous finding that the highly-processed Cottonized fibres have many more defects than the low-processed Green fibres [18] (see Figure 13), which possibly is caused by the stable growth of distributed damage. In other studies, it has been found that the microfibril angle is higher in defect regions than in non-defect regions [19][20][21], and this will lead to the hypothesis that more defective fibres will show more frequently a nonlinear stress-strain behaviour. This hypothesis is supported by the findings in the present study.…”

Section: Stress-strain Behaviourmentioning

confidence: 99%

Strength variability of single flax fibres

et al. 2011

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Due to the typical large variability in the measured mechanical properties of flax fibres, they are often employed only in low graded composite applications. The present work aims to investigate the reasons for the variability in tensile properties of flax fibres. It is found that the inaccuracy in the determination of the cross sectional area of the fibres is one major reason for the variability in properties. By applying the typical circular fibre area assumption, a considerable error is introduced into the calculated mechanical properties. Experimental data, together with a simple analytical model, are presented to show that the error is increased when the aspect ratio of the fibre cross sectional shape is increased. The variability in properties due to the flax fibres themselves is found to originate from the distribution of defects along the fibres. Two distinctive types of stress-strain behaviour (linear and nonlinear) of the fibres are found to be correlated with the amount of defects. The linear stress-strain curves tend to show higher tensile strength, higher Young's modulus, and lower strain to failure than the nonlinear curves. Finally, the fibres are found to fracture by a complex microscale failure mechanism. Large fracture zones are governed by both surface and internal defects; and these cause cracks to propagate in the transverse and longitudinal directions. Revision of manuscript submitted to Journal of Materials ScienceReference Number JMSC22209 "Strength Variability of Single Flax Fibres" by Aslan et al. Dear EditorThe authors would like to thank the two referees for their constructive comments. The authors have now carefully considered each of the referees' reports which are shown in italic and have taken them into account as described below. Reviewer #1 This is a well-written paper which presents important results with clarity. It complements two papers I have recently seen in refereeing:(1) We have modified the fibre information accordingly at page 3, line 9-13. (1) Thomason et al on 'fibre cross section determination and variability in sisal and flax and its effect on fibre performance characterization' (Composites Science and Technology CSTE-D-11- Response to Reviewer Comments (3) Reference 8 should be Virk AS, Hall W, Summerscales J (not Amandeep, Wayne and Summerscales).This has been changed. (4)There are a few phrases which would benefit from sub-editing by a native English speaker.The manuscript has been corrected by a native English speaker, resulting in a number of grammatical corrections. Reviewer #2 This is a useful contribution to this subject area. There is little doubt that there are issues surrounding the variability in fibre properties and this study is a useful contribution to the debate.(1) It is for this reason that studies of textile fibres use the linear density method of measurement rather than relying upon the dubious notion of a regular (and circular) cross section. This needs to be mentioned in the text.The authors believe that the linear density method whi...

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Mechanical properties of cellulose fibres and wood. Orientational aspectsin situinvestigated with synchrotron radiation

Cited by 52 publications

References 17 publications

Orientation of cellulose crystallites in regenerated cellulose fibres under tensile and bending loads

Orientation of cellulose crystallites in regenerated cellulose fibres under tensile and bending loads

Elastic coils: deformation micromechanics of coir and celery fibres

Strength variability of single flax fibres

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