Fibre
Development
of Eri silk
and polyester
blended yarn
In India Eri silk is
produced in large quantities and
possesses tremendous blending
possibilities with other natural
fibres like wool, cotton and jute.
The scientists at Dharwad, Tamil
Nadu and Mumbai made an
attempt to develop two varieties
of Eri silk polyester blended yarn
on short staple spinning system
to diversify the Eri silk. This
work was carried out to develop
the process to cut the Eri fibres
of required length from the Eri
cocoons. The Eri fibres were
blended with polyester in 50:50
and 30:70 blend ratio and to
develop a suitable process
parameter for yarn on short
staple spinning system.
The developed yarns
were tested for physical
properties and comparisons
were made on the performance
of different blend ratio. The
results show that the 30:70 Eri
polyester yarn exhibit better
performance than that of 50:50
blend [Sreenivasa, Itagi MR, Vijay
Kumar HL and Nadiger GS, Development
and study of the properties of Eri silk
and polyester blended yarn,
Man-made Text India, 2005,
48(1), 15-18].
Vol 5(6) November-December 2006
Degummed
silkworm
silk fibres
Technology for
animal fibre
identification
The scientists at China performed
tensile tests on silkworm cocoon silk. Fibres
were degummed using five different methods:
distilled water, boracic acid-sodium borate
buffer, sodium carbonate, urea and succinic
acid. Using an electronic single-fibre tensile
instron, the force-displacement curves were
obtained for each condition. Effects of
degumming on silk include a decrease in the
initial elastic modulus and a decrease in the
proportional limit (i.e., yield point). The results
revealed that degumming weakens at least one
type of non-covalent interaction of core fibrion,
such as hydrogen bonds and Van der Waal’s
bonds. The stress-strain curve determined from
a force-displacement curve as rescaled by the
corresponding sample cross-sectional area failed
to reproduce the actual mechanical properties
of two fibroin core fibres because of variable
degradation of the sericin coating. Following
two important factors associated with
degumming could affect the tensile properties
of silkworm silk: (i) the change in the
microstructure of two core fibroin and (ii) the
degumming ratio. SEM was used to observe
visually the morphology and fractography of
differently degummed cocoon silk fibres. Effects
of different degumming treatments on the
tensile behaviour, mechanical properties,
morphology and fractography of cocoon silk are
clearly visible [Jiang Ping, Liu Huifen, Wang Changhe,
Applications of animal fibres
in various highly valuable industrial
products have increased their demand
but due to no precise method available
to identify and differentiate the fibres
they are often adulterated during
marketing. The researchers at
Department of Biotechnology, PSG
College of Technology, Coimbatore,
India used a PCR-RFLP ( Polymerase
Chain Rection-Restriction Fragment
Length Polymorphism) technique to
differentiate cashmere and wool fibres
derived from goat and sheep,
respectively. The presence of DNA in
animal hair shafts has enabled the
isolation of DNA from scoured
cashmere and wool fibres. The
mitochondrial cytochrome b
sequences of both species were
amplified by PCR using primers
designed from conserved regions.
The polymorphism observed
between the two species was detected
by restricting the amplified product
by endonucleases viz., BamH1 and
Ssp1. The RFLP profile clearly
distinguishes the cashmere and wool
fibres and this technique can also be
exploited to test adulteration in
animal fibres qualitatively [Subramanian
Wu Lingzhi, Huang Jianguo and Guo Cong, Tensile behavior
and morphology of differently degummed silkworm
(Bombyx mori) cocoon silk fibres, 2006, 60(7),
919-925].
S, Karthik T and Vijayaraaghavan NN, Single
nucleotide polymorphism for animal fibre
identification, J Biotechnol, 2005, 116(2),
153-158].
437
Fibre
Biodegradable polymers/bamboo fibre biocomposite
In recent years, the development
of biocomposites from biodegradable
polymers and natural fibres have attracted
great interests in the composite science,
because they could allow complete
degradation in soil or by composting
process and do not emit any toxic or
noxious components. Thus, researchers at
USA conducted studies to develop the
biocomposites with designable interfacial
properties from biodegradable polymers,
poly (lactic acid) (PLA) and poly (butylene
succinate) (PBS), and bamboo fibre (BF)
by using lysine-diisocyanate (LDI) as a biobased coupling agent.
A low concentration of LDI as
bio-based coupling agent was added to
environment friendly biocomposite during
kneading process. Particularly, tensile
properties and water resistance were
appreciably improved by this mechanochemical reactive processing, which will
be of merit for industrial applications.
These improvements were due to the
enhanced interfacial adhesion between the
polymer matrix and BF. Furthermore, the
Bamboos
results of enzymatic degradation showed
that biodegradability could be adjusted by
controlling the degree of interfacial
adhesion using LDI. In areas, where
biocompatibility and environmentally
responsible design and construction are
required, these biocomposites have
potential for dramatic growth with a green
concept. Primary applications for
biocomposites include toys for children,
furniture, flooring, hardware for
electronic products, especially one-way
disposable products and so on [Lee SeungHwan and Wang Siqun, Biodegradable polymers/
bamboo fibre biocomposite with bio-based
coupling agent, Composites Part A: Appl Sci
Manuf, 2006, 37 (1), 80-91].
High impact polystyrene reinforced with sisal fibres
The growing use of natural fibres
as reinforcements of thermoplastic
polymers is mainly driven by ecological
reasons and specially as an alternative to
the use of glass fibres due to the good
mechanical properties, easy processing
and low cost of the composites obtained.
The mechanical behaviour of high impact
polystyrene (HIPS) reinforced with short
sisal (Agave sisalana Perr.) fibres was
investigated by researchers at Argentina
and Spain. The incorporation of sisal fibres
to HIPS led to an increasing trend of
stiffness with fibre content, while tensile
strength and deformation at break were
found to decrease. It was attributed to the
poor adhesion between fibre and matrix
and to the restriction to matrix yielding
438
imposed by sisal fibres, respectively. All
composites displayed ductile behaviour
under both quasi-static and impact
loading conditions. Hence, the
Normalization method and the essential
work of fracture were adopted based on
their experimental simplicity to
characterize fracture behaviour under
Agave leaves
quasi-static and impact conditions,
respectively.
The composites exhibited a
maximum in fracture toughness with fibre
content probably due to a competition
between fibre-related toughening and
rubber-related toughening. The essential
work of fracture methodology was also
proved to be a useful tool to characterize
fracture behaviour for natural fibre
composites under impact loading. A
significant decrease of impact fracture
toughness was found for the composites
in comparison to the plain matrix [Antich
P, Vázquez A, Mondragon I and Bernal C, Mechanical
behavior of high impact polystyrene reinforced with
short sisal fibres, Composites Part A: Appl
Sci Manuf, 2006, 37(1), 139-150].
Natural Product Radiance
Fibre
Coconut fibre-based soilñcement block
In Thailand, the Building
Scientific Research Center (BSRC) started
research work on the use of natural fibres
as an admixture on composite materials.
Thus, new lightweight composite concrete
and particle boards were developed using
young coconut (Cocos nucifera Linn.),
durian peel (Durio zibethinus Linn.)
and coconut coir. The manufactured
specimens have good thermo-physical
properties and more especially, they have
low thermal conductivity. Now-a-days,
there are some on-going studies on the
durability and long-term performance of
these materials so that commercial
development might start.
The researchers at Thailand
carried out studies to develop a new type
of soil-cement block using coconut coir
with low thermal conductivity. Various
mixture ratios were considered and five
specimens per sample were fabricated
using local hand-made manufacturing
process widely used in the country.
Investigation was limited to the specimens’
thermal conductivity, compressive
strength, weight and bulk density. It was
concluded that the use of coconut fibre
as an admixture can reduce the block
t h e r m a l
conductivity
and weight. The
optimum
volume ratio of
soil : cement :
sand
to
Green coconut
produce good properties is 5.75 : 1.25 :
2. The ratio of coconut coir is 20% of
cement corresponding to 0.8 kg/block.
The average specimen properties are as
follows: thermal conductivity of 0.6510
W/m K, compressive strength of 39.55 kg/
cm2, weight of 4.85 kg and bulk density
of 1586.77 kg/m3. When compared to
commercial soil-cement block, the
corresponding decrease of thermal
conductivity and weight are fairly
significant, 54% and 750 g, respectively.
Therefore, commercial development is
highly promising [Khedari Joseph,
Watsanasathaporn Pornnapa and Hirunlabh
Jongjit, Development of fibre-based soil-cement
block with low thermal conductivity, Cement
Concr Comp, 2005, 27 (1), 111-116].
Alginate/carboxymethyl chitosan blend fibres
Alginate fibres have been
extensively used in wound dressing
applications due to their excellent
biocompatibility, non-toxicity and
potential bioactivity, which can offer many
advantages over traditional cotton and
viscose gauzes. Another type of natural
polysaccharide used in wound
management products is chitin and its
partially deacetylated derivative, chitosan.
It is well known that blending is an
effective and convenient method to
improve the performance of polymer
materials. Thus, researchers at China and
UK conducted studies to prepare novel
bicomponent fibres from alginate and CMchitosan.
Vol 5(6) November-December 2006
Alginate and CM-chitosan blend
fibre can be obtained by spinning their
solution through a viscose-type spinet into
a coagulation bath containing aqueous
CaCl2. A strong intermolecular interaction
between alginate and CM-chitosan
molecule occurred in the blend fibres, this
being due to good miscibility between
alginate and CM-chitosan molecules. The
optimal tensile strength and breaking
elongation in dry state were obtained when
the CM-chitosan contents were 30 and 10
wt%, respectively. The wet tensile strength
and breaking elongation decreased with
increase of CM-chitosan content. The
introduction of CM-chitosan in the blend
fibre improved water-retention properties
of the blend fibre compared to that of
pure alginate fibre. The fibres treated with
aqueous solutions of silver nitrate and
HTCC, respectively, possessed good
antibacterial activity to Staphylococcus
aureus and these treatments had not
changed the mechanical and waterretention properties of the fibres
significantly. This novel alginate and CMchitosan blend fibre would seem to hold
potential for wound dressings [Fan Lihong,
Du Yumin, Zhang Baozhong, Yang Jianhong, Zhou
Jinping and Kennedy John F, Preparation and
properties of alginate/carboxymethyl chitosan blend
fibres, Carbohydr Polym, 2006, 65(4),
447-452].
439
Fibre
Application of sisal fibre reinforced soil
with cement or cactus pulp in bahareque technique
Among the different building
techniques that use unbaked soil, one that
is used widely in tropical countries is the
so-called ‘bahareque’ technique, which is
similar to the ‘wattle and daub’
technique, that consists of applying by
hand to a wooden or bamboo truss a
mixture of soil reinforced with vegetal
fibres and possibly stabilizing agents. The
bond between the soil and the support is
not very strong, but stability is ensured by
the mechanical connection that is created
between the soil and the truss.
In order to improve bahareque
technique, sisal fibre reinforced soils were
stabilized with cement or cactus pulp by
researchers at Italy. Bending, abrasion
resistance, water absorption and erosion
tests were performed and the results were
compared with those obtained on the
traditional plasters used in soil
technologies. The tests confirmed the
effectiveness of fibres in improving the
tensile behaviour of unbaked soil as a
building material. The addition of fibres
appears to be particularly advantageous
for use in connection with the bahareque
technique, since it makes it possible to
reduce the brittleness of the soil mortar
applied to the wooden supporting frame;
furthermore, the presence of fibres,
combined with that of stabilizing agents
such as cement or cactus pulp, can greatly
improve the durability of buildings. The
performance capabilities of sisal fibre
reinforced soil stabilized with cement are
better than those of cactus pulp stabilized
soil. The use of cactus pulp as a stabilizing
agent to improve the behaviour of the soil,
however, is very interesting because this
is a natural, ecological material [Mattone
Roberto, Sisal fibre reinforced soil with cement or
cactus pulp in bahareque technique, Cement
Concr Comp, 2005, 27(5), 611-616].
Elastic modulus of natural fibre reinforced
thermoplastics
Natural fibre reinforced
thermoplastics (NFRT) are increasingly
used in a variety of commercial
applications, but there has been little
theoretical modeling of structure/property
relationships in these materials. In a study
conducted by researchers at Canada,
micromechanical models available in the
short fibre composites literature were used
to predict the stiffness of some
commercially important natural fibre
composite formulations. Also included are
equations that correct the Young’s
modulus of natural fibres for changes in
moisture content and density that occur
as a result of processing.
Hemp fibres, hardwood fibres,
rice hulls, and E-glass fibres were blended
440
into high-density polyethylene in mass
fractions of 10-60-wt%. The addition of a
natural fibre component to the
polyethylene resulted in an increase of
stiffness by a factor of between three and
six, while not resulting in a significant
weight increase. It was found that standard
micromechanical models, which have
been used successfully to predict the
stiffness properties of traditional synthetic
fibre composites, can be applied to
natural fibre systems with mixed success.
To apply micromechanical
models to composites containing natural
fibres, the volume fraction of fibres
should be computed and used on a cell
wall basis. It was necessary to use a
correction to the fibres tensile modulus
to reflect the increased cell wall density.
An additional correction was presented to
account for the relationship between the
mechanical properties of wood fibres and
their moisture content.
It was found that although the
density of natural fibres does change, the
three lower aspect ratio natural fibres were
not significantly degraded during
processing. This is regarded as a benefit
of using natural fibres as opposed to
synthetic fibres, which are susceptible to
significant fibre degradation during
processing [Facca Angelo G, Kortschot Mark T
and Yan Ning, Predicting the elastic modulus of
natural fibre reinforced thermoplastics,
Composites Part A: Appl Sci Manuf, 2006,
37 (10), 1660-1671].
Natural Product Radiance
Fibre
Hemp fibre reinforced concrete composites
Natural fibres like jute, coir,
bamboo and sisal have already been used
as reinforcement materials in cement
matrices for many years, especially in
developing countries. Many factors affect
the properties of natural fibre reinforced
concrete (NFRC). They include fibre type,
fibre geometry, fibre form, surface, matrix
properties, mix design, mixing method,
placing method and curing method, etc.
Hemp fibre has high tensile strength and
strong tolerance for an alkali environment.
These properties make hemp fibre a good
reinforcement material. Thus, hemp fibre
reinforced concrete (HFRC) was examined
by researchers at School of Engineering
and Technology, Deakin University,
Geelong, Australia. An experimental
program was developed to evaluate the
properties of HFRC, and data analysis was
based on the statistical method of the
fractional factors design. The variables of
the experimental study were: (1) mixing
methods; (2) fibre content by weight; (3)
aggregate size: and (4) fibre length. Their
effects on the compressive and flexural
performance of HFRC composites were
investigated. The specific gravity and water
absorption ratio of HFRC were also
studied.
Different mixing methods affect
the mechanical and physical performance
of the HFRC composites. Compressive
strength of the HFRC is weaker when
compared to the conventional concrete
regardless of the mixing method used. Wet
mix has a more positive influence on the
composite’s flexural properties (flexural
strength, toughness and toughness index)
than dry mix method, possibly due to the
enhanced bonding between fibre and
matrix. These properties make the HFRC
more suitable for use in such applications
as pavements. Fibre content by weight is
the main factor that affects compressive
and flexural properties of HFRC, regardless
of the mixing method used [Li Zhijian, Wang
Xungai and Wang Lijing, Properties of hemp fibre
reinforced concrete composites, Composites
Part A: Appl Sci Manuf, 2006, 37(3),
497-505].
Durability of natural fibres in cement composites
Recently, considerable effort has
been directed towards using various
vegetable fibres, which are available in
abundance in tropical and sub-tropical
countries, as reinforcement in cement
composites for producing cost-effective
building materials with a view to have a
sustainable development. However, the
long-term durability of natural fibres in
cement composites has been the single
concern, which has come in the way of
wide spread application and acceptance
of the above materials. Hence, an attempt
was made by researchers at Department
of Civil Engineering, Pondicherry
Engineering College, Pondicherry, India to
study the effect of alkaline mediums
(calcium hydroxide and sodium
hydroxide) and fresh water on the
durability of coir, sisal, jute and Hibiscus
Vol 5(6) November-December 2006
cannabinus Linn. The effect of the
above mediums on some of the salient
chemical compositions of fibres, which
are susceptible for dissolution, have also
been studied. The above fibres are
subjected to alternate wetting and drying
and continuous immersion for 60 days in
three mediums (water, saturated lime and
sodium hydroxide). Compressive and
flexural strengths of cement mortar
specimens reinforced with the above fibres
in their natural (dry) condition and with
the ‘corroded fibres’ (i.e. the fibres
subjected to continuous immersion/
alternate wetting and drying in the above
mediums) are determined and compared
with the strengths of ‘control mix’
specimens. The results revealed that there
was substantial reduction in the salient
chemical composition of all the four
fibres, after exposure in the various
mediums. Coir fibres are found to retain
higher percentages of their initial strength
than all other fibres, after the specified
period of exposure in the various
mediums. The compressive and flexural
strengths of all natural fibre reinforced
mortar specimens using corroded fibres
are less than the strength of the reference
mortar (i.e. without fibres) and fibre
reinforced mortar specimens reinforced
with dry natural fibres. Further studies
are required to correlate the fibre strength
and durability in alkaline mediums with
that of the composite exposed to
laboratory/field conditions [Ramakrishna G
and Sundararajan T, Studies on the durability of
natural fibres and the effect of corroded fibres on
the strength of mortar, Cement Concr Comp,
2005, 27(5), 575-582].
441
Fibre
Properties of biodegradable composites
reinforced with bagasse fibre
Recently, there has been an
increasing interest in the completely
biodegradable composites reinforced with
natural fibres, because they are renewable,
biodegradable and environmental friendly,
not withstanding their use in low-cost
applications. Many studies have been
focused on alkali treatment of the natural
fibres to improve the bonding between the
fibre and the resin matrix with a
consequence improvement in the
properties. Biodegradable composites
reinforced with bagasse fibre before and
after alkali treatments were prepared and
mechanical properties were investigated
by researchers at Department of
Mechanical Systems Engineering,
University of the Ryukyus, Okinawa, Japan.
Mechanical properties of the composites
made from alkali treated fibres were
superior to the untreated fibres. Both the
tensile and impact strength of the
untreated bagasse fibre composites
increased with increase in fibre content
to an optimum fibre content of 65% only.
SEM micrographs revealed that the
compressed cellulose structure of the
bagasse fibre could have contributed to
the improvement in these properties.
Composites of 1% NaOH solution treated
fibres showed maximum improvement.
Approximately 13% improvement in
tensile strength, 14% in flexural strength
and 30% in impact strength had been
found, respectively. After alkali treatment,
increase in strength and aspect ratio of
the fibre contributed to the enhancement
in the mechanical properties of the
composites. SEM micrographs of the
fracture surface indicated that the fibres
after the alkali treatment became finer due
to the dissolution of the hemicellulose and
increased aspect ratio, which resulted in
a better fibre-matrix adhesion [Cao Y, Shibata
S and Fukumoto I, Mechanical properties of
biodegradable composites reinforced with bagasse
fibre before and after alkali treatments,
Composites Part A: Appl Sci Manuf, 2006,
37(3), 423-429].
Impact strength of a few natural fibre
reinforced cement mortar slabs
Natural fibres have the potential
to be used as reinforcement to overcome
the inherent deficiencies in cementitious
materials. In recent years, there has been
sustained interest in utilizing natural fibres
in cement composites and in
manufacturing products based on them
with a view to have alternate building
materials, which are energy-efficient,
economical and eco-friendly. Researchers
at Department of Civil Engineering,
Pondicherry Engineering College,
Pondicherry, India conducted experiments
442
to investigate the resistance to impact
loading of cement mortar slabs (1:3, size:
300 mm × 300 mm × 20 mm) reinforced
with four natural fibres, coir, sisal, jute
and Hibiscus cannabinus Linn. and
subjected to impact loading using a
simple projectile test. Four different fibre
contents (0.5%, 1.0%, 1.5% and 2.5%
by weight of cement) and three fibre
lengths (20 mm, 30 mm and 40 mm)
were considered. The results obtained
have shown that the addition of the above
natural fibres has increased the impact
resistance by 3-18 times than that of the
reference (i.e. plain) mortar slab. Of the
four fibres, coir fibre reinforced mortar
slab specimens have shown the best
performance based on the set of chosen
indicators, i.e. the impact resistance (Ru),
residual impact strength ratio (Irs), impact
crack-resistance ratio (C r) and the
condition of fibre at ultimate failure
[Ramakrishna G and Sundararajan T, Impact
strength of a few natural fibre reinforced cement
mortar slabs: a comparative study, Cement Concr
Comp, 2005, 27(5), 547-553].
Natural Product Radiance