Materials Sciences and Applicatio ns, 2010, 1, 336-342
doi:10.4236/msa.2010.16049 Published Online December 2010 (http://www.scirp.org/journal/msa)
Characteristic and Performance of Elementary
Hemp Fibre
Dasong Dai, Mizi Fan
Civil Engineering Department, School of Engineering and Design, Brunel University, London, UK.
Received September 6th, 2010; revised November 16th, 2010; accepted November 20th, 2010.
ABSTRACT
This paper presents systematic and improved methodologies to characterize the surface and fracture of elementary
hemp fibres by Field Emission Scanning Microscope (FE-SEM), determine the Microfibril Angles (MFA) by an ad-
vanced microscopy technology and examine the crystallinity by X-Ray Diffraction (XRD) and Fourier Transform Infra-
red (FTIR). The results showed that 1) There existed various deformations/defects in elementary hemp fibres, showing
four types of deformations, namely kink bands, dislocations, nodes and slip planes. The crack on the surface of elemen-
tary fibres was the initial breaking point under stress; 2) Under tension the primary wall and secondary wall of hemp
fibres showed different deformation and breaking behaviour. The crack initiated in a weak point of primary wall and
subsequently propagated along radial direction from S1 to S2 layers; 3) The average MFA for the broken regions of S2
layer was 6.16˚ compared to 2.65˚ for the normal hemp fibres and the breaking of hemp fibres occurred at the points
where had the biggest MFA; 4) The average MFA was 2.65˚ for S2 layer and 80.35˚ for S1 layer; 5) The Crystallinity
Index (CI) determined by XRD and FTIR was very similar, showing the lattice parameters of the hemp fibres tested a =
6.97 Å, b = 6.26 Å, c = 11.88 Å and γ = 97.21˚, and the ratio of 1423 to 896 cm-1 was found more suitable for CI
evaluation for hemp fibres.
Keywords: Natural Fibres, Fracture, Crack, X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy
(FTIR)
1. Introduction
Hemp fibre has widely been used in many civilizations.
It has been reported that the earliest use of hemp was
over 6000 years ago [1-3]. The increasing environmental
awareness, growing global waste problems and continu-
ously rising high crude oil prices have motivated gov-
ernments all over the world to increase the legislative
pressure. This in turn promotes researchers, industries
and farmers to develop the concepts of environmental
sustainability and reconsider renewable resources. Re-
newable resources from agricultural or forestry products
form a basis for new industrial products or alternative
energy sources, such as hemp fibre [4]. Hemp fibres have
long been valued for their high strength and long fibre
length, and used extensively in the fabrication of ropes
and sails, as well as for paper and textiles. Hemp fibres
consist of different hierarchical microstructures, whereby
microfibrils serve as basic units. The microfibrils are
embedded in a matrix of hemicelluloses and form the
different cell wall layers of an elementary fibre, which
generally has a large average diameter ranging from 10
to 50 m [5]. The elementary fibres are bonded together
with pectin’s and small amounts of lignin framing the
next level of microstructure, i.e. technical fibres, with a
diameters ranging from 50 to 100 m [6]. These filaments
are fixed together with a pectin-lignin matrix to form
fibre bundles in the cortex of plant stems. Thus, bast fi-
bres are bundles of individual strands of fibres held to-
gether by a pectin-lignin interface [7].
The fibres of never dried hemp contain numerous de-
formations. All these deformations appear where there is
a change in microfibril direction and a distorsion of the
fibrils. The deformations can be seen under polarized
light [8-14], but the largest of them also could be dis-
cerned without polarisers [15] (e.g. SEM [16-18], Raman
spectroscopy [19-22]). The deformation of fibres can
affect the strain distribution in elementary fibre, leading
to localized strain concentrations [23], and hence reduce
both compressive strength and tensile strength [24],
which was also proved by a finite element (FE) modeling

Characteristic and Performance of Elementary Hemp Fibre 337
of the tensile behaviour of single flax and hemp fibre
[25]. The fibres in the matrix may break at the point with
deformations [26], and the concentration of stresses
around the deformation could act as the site of initiation
of fibre-matrix debonding as well as for the formation of
micro-cracks in the matrix which contribute to global
fracture of composite [27]. Limited work conducted on
the breaking behaviour of wood pulp [28], cotton [29],
and flax [30] also indicated that the break behaviour of
the primary and secondary cell wall of the flax fibres was
different from that of wood and cotton [17]. The primary
cell wall generally breaks in a brittle manner, whereas
the secondary cell wall, bridged by fibrils, splits rela-
tively easily along the length direction.
The experience has highlighted that it is not possible
to use or appropriate to compare data available from
different investigations reported in the literatures.
Measuring natural fibres proves to be a great challenge.
Microstructural defects, fibre abstraction (e.g. single
fibre) and processing are all yet to be studied. This pa-
per is an attempt to characterize the surface and reveal
the failure mechanism of elementary hemp fibres. Sys-
tematic and improved methodologies and advanced
technologies have been developed to investigate the
microfibril angles of elementary hemp fibres and the
crystallinity of hemp fibres. The surface of hemp fibres
after tensile loading and fracture of fibres after breaking
were also observed carefully to characterize the surface
and reveal the failure mechanism of elementary hemp
fibres. This paper is the first of a series of papers from
an intensive research programme aiming at a better un-
derstanding of natural fibre resources and the develop-
ment of their high strength composites for applications
in various industrial sectors.
2. Materials and Methods
2.1. Materials
Hemp fibres were supplied by a Hemp Farm & Fibre
Company Ltd, UK. The fibres arrived in a form of fibre
bundles. Salt products, namely, copper (II) nitrate (30 wt
%) and cobalt (II) chloride (≥ 98.0%) were obtained
from Sigma-Aldrich Company Ltd, UK.
2.2. Microfibril Angle (MFA) Measurement
Hemp fibres (0.1 g) were placed into a beaker contained
100 ml salt solution (5%, wt/vol), whether copper nitrate
or cobalt chloride, and heated at 80˚C for 2 hours. The
beaker container was placed into ultrasonic bath and
treated at 80˚C for 2 hours. The treated hemp fibres were
finally washed with distill water. Photomicrographs were
taken using BX51 Reflected Light Microscope equipped
with a CAM-XC50-5MP cooled CCD camera, then using
UTHSCSA ImageTool to measure the microfibril angle
of S1 and S2 layers. 50 test pieces were used.
2.3. Deformation of Hemp Fibres
Optical microscopy was employed to examine the de-
formation of hemp fibres. The BX51 Reflected Light
Microscope equips with 5 ×, 20 ×, 50 ×, 100 × objectives,
a CAM-XC50-5MP cooled CCD camera and 100 W
Halogen for transmitted or reflected light. The fibres
were positioned on a slide using cyanacrylate glue and
covered with a cover slip. Images were analysed and
captured as 2576 × 1932 RGB jpeg files. The experi-
ments were performed at room temperature and 1000 test
pieces were examined.
2.4. Fracture Characterization
Surface and fracture characterization of hemp fibres were
conducted within a Zeiss Supra 35 VP field emission
scanning electron microscope (FE-SEM). Individual fi-
bres were randomly and gently isolated from fibre bun-
dles. The isolated fibres were conditioned at 20 ± 2˚C
and 65 ± 2% relative humidity before temporarily fixed
on the mounting card (Figure 1) with adhesive tape. A
droplet of glue was applied on the centre of both sides of
the hole along the length of card. The testing was then
carried out as fellows:
1) Subject the prepared samples to SEM and charac-
terize the surface of the test pieces;
2) Subject the samples to tensile strength test by using
Instron 5566 at a crosshead speed of 0.1 mm/min and
with 10 mm gauge length. The test results of mechanical
performance of the elementary fibres are presented in a
separate paper (Dai, et al. 2010);
3) Re-sample the test pieces for fracture characterization
from the broken test pieces after tensile tests and
subject them to oven-drying at 105˚C. The test pieces
were then coated with a thin layer of platinum in an
Figure 1. Set-up of single fibre testing: a = specimen mount,
b = test specimen mounted on the mount.

Characteristic and Performance of Elementary Hemp Fibre 338
Edwards S150B sputter coater (BOC Edwards,
Wilmington, MA) to provide electrical conductivity.
The fracture surface of the coated test pieces were
observed by using the secondary electron mode
images (digitally). 50 test pieces were used.
2.5. Crystallinity of Hemp Fibr es
The crystallinity of hemp fibres was determined by using
a powder X-Ray Diffraction Method (PXRD). A D8 ad-
vanced Bruker AXS diffractometer, Cu point focus
source, graphite monochromator and 2D-area detector
GADDS system were used. The diffracted intensity of
CuKα radiation (wavelength of 0.1542 nm) was recorded
between 5˚ and 60˚ (2θ angle range) at 40 kV and 40 mA.
Samples were analyzed in transmission mode. The unit
cell of hemp fibre was calculated by DIFFRAC plus soft-
ware, and the Crystallinity Index (CI) was evaluated by
using Segal empirical method [30] as follows:
()
002
002
% 100%
amII
CI
I
−
=×
(1)
where I002 is the maximum intensity of diffraction of the
(002) lattice peak at a 2θ angle of between 22˚ and 23˚,
which represents both crystalline and amorphous materi-
als. And Iam is the intensity of diffraction of the amor-
phous material, which is taken at a 2θ angle between 18˚
and 19˚ where the intensity is at a minimum [31]. It
should be noted that the crystallinity index is useful only
on a comparison basis as it is used to indicate the order
of crystallinity rather than the crystallinity of crystalline
regions. 100 replicates were used.
2.6. Composition of Hemp Fibres
Composition of hemp fibres was examined by using
Fourier Transform Infrared Spectroscopy (FTIR) meas-
urement which uses a Perking-Elmer spectrometer and
the standard KBr pellet technique. A total of 16 scans
were taken for the sample between 650 cm-1 and 4000
cm-1, with a resolution of 2 cm-1. Hemp fibres were
ground and mixed with KBr and then pressed into a pel-
let for FTIR measurement.
3. Results and Discussion
3.1. Microfibril Angle (MFA) of Hemp Fibres
The orientations of hemp fibres treated with both copper
(II) nitrate and cobalt (II) chloride solutions can be de-
tected under light microscope. However, it was found
that the orientations of MFA in the samples treated with
the former solution were much more distinctive than
those with the latter solution treatment. This may result
in more accurate measurements of MFA. An example of
microfibril orientations in S1 and S2 layers observed
under light microscope at 1000 × is given in Figures 2(a)
and 2(b) . It was found that, microfibrils in S2 layer have
a Z-helical orientation, while in S1 layer have S-helical
orientation. The average MFA in S2 inner layer is 2.65˚
(arrange from 1˚ to 3.27˚), which is smaller than 4˚ mea-
sured previously by Fink [32]. This may be due partly to
the different hemp fibres from different geographical
sources. The average MFA in the outer part of S2 layer
ranges from 23˚ to 30˚. The average MFA in S1 layer is
80.35˚ (range from 77.7˚ to 86.2˚), which is in agreement
with the results of previous worker [33] who found the
average angle in S1 layer was 70-90˚.
3.2. Crystal Struc ture of Hemp Fibres
X-ray crystallography was used to investigate the crys-
tallinity of hemp fibres. An example of X-ray powder
diffraction photograph from hemp fibres is given in Fig-
ure 3. It can be seen from Figure 3 that the major crys-
talline peak of the hemp fibres occurred at 2θ = 22.1˚,
which represents the cellulose crystallographic plane
(002, Bragg reflection). The minimum intensity between
002 and 110 peaks (Iam) is at 2θ = 18.6˚. The crystallinity
(a) (b)
Figure 2. Microfibril angle of hemp fibre: MFA in S2 layer
(a); MFA in S1 layer (b).
10 15 20 25 30 35 40
0
500
1000
1500
2000
2500
3000
3500
4000
4500
I004
Iam
I002
I110
I⎯110
Intensity (a.u.)
2θ (°)
Figure 3. X-ray diffractogram of hemp fibres.

Characteristic and Performance of Elementary Hemp Fibre 339
index of hemp fibre is 56%. Other well-defined peaks
present on the X-ray diffractogram are at 2θ = 14.3˚, 2θ
= 16.8˚ and 2θ = 32.3˚, and these reflections correspond
with the (110), (110) and (004) crystallographic planes,
respectively. The lattice parameters of hemp fibres which
were calculated by DIFFRAC plus are: a: 6.97 Å; b: 6.26
Å; c: 11.88 Å; γ: 97.21˚.
3.3. FTIR Analysis
Infrared spectrum of hemp fibres is displayed in Figure
4. The typical functional groups and the IR signal with
the possible sources are listed in Table 1 for a reference.
It could be observed from Table 1 that five components
exist in the hemp fibres after retting pretreatment. Figure
4 shows a weak absorbance around 1729 cm-1 in the
FTIR spectrum of hemp fibre, which might be attributed
to the presence of the carboxylic ester (C=O) in pectin
and waxes. Intensities of some bands in IR spectra have
been found to be sensitive to variations of cellulose
crystallinity and have been used to evaluate Crystallinity
Index (CI) of cellulose. The ratios of peaks at 1423 cm-1
and 896 cm-1, 1368 cm-1 and 2887 cm-1 and 1368 cm-1
and 662 cm-1 are normally used to measure CI e.g.
[34-37]. In this study, the ratio of 1368 cm-1 and 2887
cm-1 is above 1 which seems to be unsuitable for evalua-
tion, while the ratios of 1423 to 896 cm-1 and 1368 to
662 cm-1 are 55.7% and 49.3% respectively. The value
calculated by using Segal empirical method is 56%, in-
dicating that the ratio of 1423 to 896 cm-1 is more suit-
able for CI evaluation.
3.4. Deformation of Hemp Fibres
Optical microscope observation showed that much de-
formation has occurred in hemp fibres and some types of
deformation are difficult to distinguish. In this study, any
defect of fibres which may affect the mechanical properties
3500 3000 2500 2000 1500 1000
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
1506
662
896
995
1048
1019
1155
1246
1317
1368
1423
1623
1729
2887
Absorbance
Wavenumbe
r
(
c
m
-1
)
3336
Figure 4. FTIR spectra of hemp fibres.
Table 1. Main infrared transition for hemp fibre.
Wavenumber
(cm-1) Vibration Sources
3336 OH stretching
Cellulose,
Hemicellulose
2887 C–H symmetrical stretching
Cellulose,
Hemicellulose
1729 C=O stretching vibration Pectin, Waxes
1623 OH bending of absorbed
water Water
1506 C=C aromatic
symmetrical stretching Lignin
1423 HCH and OCH in-plane
bending vibration Cellulose
1368, 1362 In-the-plane CH bending Cellulose,
Hemicellulose
1317 CH2 rocking vibration Cellulose
1246 C=O and G ring
stretching Lignin
1202 C-O-C symmetric
stretching
Cellulose,
Hemicellulose
1155 C-O-C asymmetrical
stretching
Cellulose,
Hemicellulose
1048, 1019,
995
C-C, C-OH, C-H ring and
side group vibrations
Cellulose,
Hemicellulose
896
COC,CCO and CCH
deformation and
stretching
Cellulose
662 C-OH out-of-plane bending Cellulose
of the fibres, especially the tensile strength, was recorded
and called deformation. The results of numerous exami-
nations (1000 test pieces) of hemp fibres can be cata-
loged into four types of deformation of hemp fibres
(Figure 5). The characteristic of each type deformation
are as follows: 1) Kind bands, formed in the fibres as a
result of axial curing stresses; 2) Nodes, formed in the
regions of localized delamination and compressive strain;
3) Dislocations, appeared in untreated natural fibre; and
4) Slip planes, crinkled in the cell wall resulting from a
slight linear displacement of the wall lamellae. It is ap-
parent that these deformations appear when there is a
change in microfibril direction and a distorsion of fibrils.
Nevertheless, whilst it is clear that some of deforma-
tions occur during plant growth, a significant amount of
deformation is resulted from decortication and other
down-line processing. Deformations could be the weak
points which broken at beating, mechanical treatment
and in acidic environments. It is believed that stress
concentrations around deformations can act as sites for
the initiation of fibre matrix debonding as well as for the
formation of micro cracks in the matrix.
3.5. Breaki ng Pr oces s
Figures 6(a-c) illustrate the initial and final fracture of
an elementary hemp fibre. It was found that the

Characteristic and Performance of Elementary Hemp Fibre 340
(a) (b)
(c) (d)
Figure 5. Deformation of he mp fibre: a = kink band (× 500
magnification), b = node (× 500 magnification), c = disloca-
tion (× 200 magnification), d = slip plane (× 200 magnifica-
tion).
initial crack of hemp fibres starts from primary wall
(Figure 6(a)). This may be due partly to the fact that the
primary cell wall could contain a large fraction of amor-
phous pectin, hemicelluloses, cross-linked lignin and
randomly oriented cellulose as reported previously
[38-40]. The crack then proceeds into the secondary cell
wall (S2) which forms the major part of hemp fibre.
While the S2 layer has been reported containing several
layers [41], this study showed that it at least contains the
outer and inner parts of S2 layers and the MFA of which
gradually decreases. The S2 layer consists of highly
(a) (c)
Figure 6. Breaking process under tension: Initial crack (a,
b), fracture (c) of hemp fibre.
crystalline (CI 60%) cellulose microfibrils (Figure 4)
bounded together by lignin and hemicellulose. The mi-
crofibrils are oriented spirally around the fibre axis. In
this study, the microfibrils in the inner part of S2 layer
have an MFA of about 2.65˚ with respect to the fibre axis,
which explains the stiffness and strength of the fibre in
the axial direction. The MFA in the outer part of S2 layer
ranges from 23˚ to 30˚. The microfibril angle can
strongly influence mechanical properties of fibres, such
as tensile strength and modulus [42], which decrease
with MFA increases. This means that the strength of in-
ner part of S2 layer shall be higher than that of the outer
part of S2 layers. Therefore, the breaking process in
secondary wall of hemp fibres is from S1 layer to outer
part of S2 layer to inner part of S2 layer (Figures 6(b,c)).
3.6. Fracture of Hemp Fibres
Figure 7 shows the fractography of hemp fibres. The
macrofibril can be observed clearly in the fracture sur-
face of hemp fibres. The MFA in the S2 layer at fracture
point was measured and their mean value is 6.16˚ with
respect to the fibre axis. As discussed in the previous
sections, the average MFA in the S2 layer of non-defect
hemp fibre is 2.65˚, indicating that the microfibril direc-
tion changes in the fracture regions of fibre. According
to Mohlin et al. [43], the deformations, which change the
direction of the fibre axis, have a negative influence on
mechanical properties of fibre. Baley [14] reported that
cracks in the flax fibre firstly happened in the area of
kind band. However, the different strength between the
different types of deformation as defined in this study
have not been observed, although it was evident that the
deformation is the main cause for the break of hemp fi-
bres, that is, deformation is the weak link in hemp fibres.
4. Conclusions
A systematic and comprehensive study on the character-
istic and behaviour of elementary hemp fibres presented
in the paper concluded that:
(a) (b)
Figure 7. Fractography of hemp fibre: a = overall view, b =
detail of single fiber fracture.

Characteristic and Performance of Elementary Hemp Fibre 341
1) An improved, accurate method of measure Microfi-
bril Angle (MFA) of elementary hemp fibres could be
developed (in this study): The average MFA was 2.65˚
for S2 layer and 80.35˚ for S1 layer. It was observed that
the type of solutions had an influence on the effective-
ness of pre-treatment which may had an implication of
accuracy of measurement. The solution of Cu(NO3)2 was
found more effective than CoCl2.
2) The lattice parameters of hemp fibre studied were a
= 6.97Å, b = 6.26 Å, c = 11.88 Å and γ = 97.21˚. The
Crystallinity Index (CI) determined by XRD and FTIR
was very similar, and the ratio of 1423 to 896 cm-1 was
found more suitable for CI evaluation for hemp fibres.
3) The characterization on the surface of hemp fibres
after tensile testing and the fracture of the broken fibres
showed that there existed various deformations in ele-
mentary hemp fibres. However, the deformation of hemp
fibres could be cataloged into four types, namely kink
bands, dislocations, nodes and slip planes.
4) Under tensile stress, the initial crack was mainly
from the primary wall and the crack proceeded into the
secondary wall of hemp fibre, giving a breaking order of
S1 layer to out part of S2 layer to inner layer of S2 layer.
The average MFA (6.16˚) at the fracture points of the S2
layer was much higher than that of normal fibres (2.65˚).
5. Acknowledgements
This research programme is funded by the Technology
Strategy Board, Department for Business, Innovation and
Skills, UK.
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