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The purpose of this work is to present the results of preparing a polymeric composite with enhanced properties based on natural rubber and hemp. Amounts of 10 and 20 phr hemp were used to obtain the composites. The samples have been processed by sulfur vulcanization and characterized by several methods. The mechanical characteristics, gel fraction, cross-link density, rubber-fiber interactions and water uptake have been investigated depending on the hemp content. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) techniques were also employed for characterization. The values of hardness, tensile strength and tearing strength have increased with the fiber content increasing due to the interaction between the fibers and natural rubber. Also, good adhesion between hemp fibers and rubber matrix was observed in SEM micrographs. The gel fraction value was over 95 % for all composites and increased with the increasing of hemp content. The cross-link density was determined on the basis of equilibrium solvent-swelling measurements applying the modified Flory-Rehner equation. It was observed that cross-linking density of composites increased slightly with the increase of amount of hemp but still was lower than that of the natural rubber without hemp. The extent of interaction between rubber and fiber was determined using the Kraus equation. Results of water absorption tests showed that water uptake increased with the increase of fiber content and temperature. The physical and chemical investigations have shown the reinforcing effect of hemp on sulfur vulcanized natural rubber, as well.
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Iranian Polymer Journal
ISSN 1026-1265
Volume 24
Number 2
Iran Polym J (2015) 24:135-148
DOI 10.1007/s13726-015-0307-6
Polymeric composites based on natural
rubber and hemp fibers
Elena Manaila, Maria Daniela Stelescu &
Florica Doroftei
1 23
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Iran Polym J (2015) 24:135–148
DOI 10.1007/s13726-015-0307-6
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Iran Polymer and
Petrochemical Institute
ORIGINAL PAPER
Polymeric composites based on natural rubber and hemp fibers
Elena Manaila · Maria Daniela Stelescu ·
Florica Doroftei
Received: 19 June 2014 / Accepted: 5 January 2015 / Published online: 18 January 2015
© Iran Polymer and Petrochemical Institute 2015
equation. It was observed that cross-linking density of
composites increased slightly with the increase of amount
of hemp but still was lower than that of the natural rub-
ber without hemp. The extent of interaction between rub-
ber and fiber was determined using the Kraus equation.
Results of water absorption tests showed that water uptake
increased with the increase of fiber content and tempera-
ture. The physical and chemical investigations have shown
the reinforcing effect of hemp on sulfur vulcanized natural
rubber, as well.
Keywords Polymeric composites · Natural rubber ·
Hemp · Physical–mechanical characteristics · Cross-link
density · FTIR
Introduction
The reinforcement of rubber compounds with fibers has
become necessary in many products, especially in the tire,
hose and belt industries [1]. Currently, the most viable way
toward eco-friendly composites is the use of natural fibers
as reinforcement. Natural fibers represent a traditional class
of renewable materials which, nowadays, are experiencing
a great revival [2]. On the other hand, natural fibers exhibit
many advantageous properties which promote the replace-
ment of synthetic fibers in polymer composites. They are
low-density materials yielding relatively lightweight com-
posites with high-specific properties, therefore, natural fib-
ers offer a high potential for an outstanding reinforcement
in lightweight structures.
Natural fibers are derived from renewable resources and
do not require a large amount of energy to process them
and are biodegradable, as well [3, 4].These fibers also offer
significant cost advantages and therefore the utilization
Abstract The purpose of this work is to present the
results of preparing a polymeric composite with enhanced
properties based on natural rubber and hemp. Amounts of
10 and 20 phr hemp were used to obtain the composites.
The samples have been processed by sulfur vulcanization
and characterized by several methods. The mechanical
characteristics, gel fraction, cross-link density, rubber-
fiber interactions and water uptake have been investigated
depending on the hemp content. Fourier transform infrared
spectroscopy (FTIR) and scanning electron microscopy
(SEM) techniques were also employed for characteriza-
tion. The values of hardness, tensile strength and tearing
strength have increased with the fiber content increasing
due to the interaction between the fibers and natural rub-
ber. Also, good adhesion between hemp fibers and rubber
matrix was observed in SEM micrographs. The gel frac-
tion value was over 95 % for all composites and increased
with the increasing of hemp content. The cross-link density
was determined on the basis of equilibrium solvent-swell-
ing measurements applying the modified Flory–Rehner
E. Manaila
National Institute for Laser, Plasma and Radiation Physics,
Electron Accelerators Laboratory, 409 Atomistilor St.,
077125 Magurele, Romania
e-mail: elena.manaila@inflpr.ro
M. D. Stelescu (*)
National R&D Institute for Textile and Leather, Leather
and Footwear Research Institute, 93 Ion Minulescu St, Bucharest,
Romania
e-mail: dmstelescu@yahoo.com
F. Doroftei
Department Of Scanning Electron Microscopy, Petru Poni
Institute of Macromolecular Chemistry, Physical Characterization
of Polymers, Aleea Grigore Ghica Voda, 41A, Iasi 700487,
Romania
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of lightweight, lower cost natural fibers such as jute, flax,
hemp, sisal, abaca, coir offer the potential to replace a large
segment of the synthetic fibers in numerous applications
[5, 6]. Production of natural fibers causes less severe envi-
ronmental impacts as compared to those of synthetic fibers.
Natural fibers cultivation depends mainly on solar energy
and for the fiber production, processing and extractions, a
relatively small amount of fossil fuel energy is required. On
the other hand, the production of synthetic fiber depends
mainly on fossil fuels and needs nearly ten times more
energy as compared to natural fiber. As a result, the pollut-
ant gas emissions to the environment from synthetic fiber
production are significantly higher than those from the nat-
ural fiber production [3, 7].
In our work, hemp fibers obtained from the bast of the
Cannabis sativa L. were used for natural rubber reinforce-
ment. Hemp has been cultivated for at least 6,000 years
and it may be one of the oldest non-food crops. Growing
practice shows that biomass yield of hemp is high, and
hemp improves the soil structure, the tall plant stems of
hemp suppress weeds effectively, and diseases and pests
are rarely recorded. Thereby, addition of pesticides is not
needed. It has also been reported that hemp produces sev-
eral times more of the important cellulose source, fiber
component, than other crops such as corn, kenaf, and cot-
ton. Therefore, it is of interest to determine the potential
for hemp fibers to find appropriate solutions and sustain-
able systems. The most usual purpose of hemp cultivation
is to isolate the fibers present in the bark on the hemp stem
surface, for production of ropes, textiles and paper. Some
newer industrial uses of plant cellulose have been devel-
oped and are found to be promising; one of them is cel-
lulose nanoparticles usage as fillers to improve mechanical
and barrier properties of biocomposites that are a rapidly
developing branch of biotechnology [4, 8].
In this work, some composites based on natural rubber
and hemp were analyzed in which the elastomer was cross-
linked using accelerator and sulfur. The sulfur vulcaniza-
tion process requires the presence of carbon–carbon double
bonds in the polymer chains which leads to a three-dimen-
sional rubber network, where the polymer chains are linked
to each other by sulfur bridges. As a result, sulfur-cured
articles have good tensile and tear strength, good dynamic
properties, but poor high-temperature properties like aging,
for instance [9, 10]. Sulfur vulcanization reactions can be
broadly classified into two types: unaccelerated and accel-
erated ones [11, 12]. Unaccelerated sulfur formulation
consists of rubber and sulfur while the accelerated systems
contain rubber, sulfur, accelerators and activators (ZnO,
PbO, MgO etc.) [11]. Zinc oxide is the most important acti-
vator. Usually an activator system, a combination of zinc
oxide and a long-chain fatty acid such as stearic acid is
used. Fatty acids, e.g., stearic acid, are used to solubilize
zinc ions into the system and set them free to form com-
plexes with accelerators [12]. Generally, it can be stated
that increasing the pH leads to activation of the vulcani-
zation. The basic activators mentioned lead to improved
strength properties of the vulcanizates and reduced vulcani-
zation time [11]. In our experiments, we used two accelera-
tors, zinc oxide and stearic acid (Table 1).
Vulcanization with sulfur and accelerators of NR is done
generally by ionic mechanism and leads to the formation of
sulfur bridges between (C–Sx–C) macromolecules or cyclic
combination of sulfur. At high temperatures, desulphura-
tion takes place, determining the formation of shorter sulfur
bridges. The initial step in vulcanization (Scheme 1) seems to
be the reaction of sulfur with the zinc salt of the accelerator
to give a perthio-salt, XSxZnSxX where X is a group derived
from the accelerator. This salt reacts with the rubber hydrocar-
bon RH, to give a rubber-bound intermediate and a perthio-
accelerator group which, with further zinc oxide will form a
zinc perthio-salt of lower sulfur content; this may again be an
active sulfurating agent, forming intermediates XSx1R. In
this way, each molecule of accelerator gives rise to a series of
intermediates of varying degrees of polysulfidity [13].
The intermediate XSxR then reacts with a molecule of
rubber hydrocarbon RH to give a cross-link, and more
accelerator is regenerated (Scheme 2).
Scheme 3 shows the reaction route which may be written
for sulfur vulcanization. In the reaction, intramolecular bridges
(cyclic structure) can be formed as showed in Scheme 4.
The objective of this research is to obtain a new elasto-
meric material based on NR with good characteristics and
compatibility with environment, by replacing active fillers
of rubber blends such as carbon black or silica (which has
serious harmful effects on health) with natural fibers. Silica
is known to have adverse effects on health, causing silico-
sis, cancer (Group 1 according to IARC—the International
Agency for Research on Cancer) tuberculosis, autoim-
mune and kidney diseases. In 1995, the IARC rated carbon
black as IARC classification 2B—possibly carcinogenic
to humans and definitely carcinogenic to animals [1416].
The novelty of the present work consisted in the use of
hemp fibers as organic fillers in the natural rubber mixtures
to obtain composites with enhanced properties. There are
many research works in which composites were obtained
based on synthetic rubber and natural fibers [1719], but
only a few composite materials were based on natural rub-
ber and hemp fibers that were analyzed [2022]. Two of
these studies were conducted by us, where the cross-link-
ing has been achieved with benzoyl peroxide or by electron
beam irradiation [21, 22]. Studies on the use of natural fib-
ers to replace inorganic fillers in rubber mixtures started to
grow during the last 10 years due to their advantages and
for these reasons, this research can contribute to developing
and consolidating new knowledge in the rubber field.
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Experimental
Materials
The following materials were used to prepare the above
polymer composites: natural rubber (NR) Crep 1X (74
ML1 + 4 Mooney viscosity at 100 °C, 0.32 % volatile mate-
rials, 0.38 % nitrogen, 0.22 % ash, 0.021 % impurities) from
Almar Trading Co (Pte) Ltd, Sri Lanka and ground hemp
(thread length of max 3 mm). Cross-linking was done using:
2.5 phr sulfur, 0.5 phr 2-mercaptanobenzothiazole (MBT)
and 1 phr tetramethylthiuram disulphides (TMTD) (assay
97 %, autoignition temperature 316 F), Sigma-Aldrich,
as accelerators, the 5 phr zinc oxide (97.1 % active ingre-
dient) Werco Metal, Zlatna Romania and 1 phr stearic acid
(0.025 % of ask) Cevo Industry Co., China as activator. The
main properties and chemical structure of the reactants used
(accelerators and activators) are presented in Table 1.
Table 1 Chemical structure
and properties of reactants
(accelerators and activators)
used
Scheme 1 Initial step in sulfur
vulcanization
Scheme 2 Reaction between
intermediate XSxR and rubber
molecule
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Sample preparation
The blends were prepared on an electrically heated laboratory
roller mill. For preparation of the polymeric composites, the
blend constituents were added in the following sequences:
natural rubber (NR) roll binding (2 min), embedding ZnO and
stearic acid (1 min), adding ground hemp (2–3 min), cooling
the mixture and adding sulfur and vulcanization accelerators
(1 min), homogenization of blends and removing from the
roll in the form of sheet (4 min). The process variables were:
temperature 25-50 ± 5 °C, ratio 1/1.1 and total blending time
9–10 min. The plates required for physico-mechanical tests
with sizes of 150 × 150 × 2 mm were obtained by pressing
in a hydraulic press at 160 °C and 150 MPa; the curing time
was 19 min. The recipe according to which the rubber sam-
ples have been prepared is shown in Table 2.
Mechanical characteristics
Tensile strength tests were carried out with a Schopper
strength tester with testing speed of 460 mm/min, using
dumb-bell shaped specimens according to ISO 37/2012.
Residual elongation is the elongation of a specimen and
was calculated using the following equation:
where, L0 is the initial length between two marks and L is
the length between the marks 1 min after the sample broke
in a tensile test.
The hardness was measured using a hardener tester
according to ISO 7619-1/2011 on samples having the
thickness of 6 mm. The elasticity (rebound resilience) was
evaluated with a Schob type test machine also on samples
of 6 mm thick, according to ISO 4662/2009.
The sol–gel analysis was performed on cross-linked
NR rubber (with and without hemp) to determine the mass
fraction of insoluble NR (the network material resulting
from network-forming cross-linking process) from sam-
ples (gel fraction). The samples were swollen in toluene
and extracted after 72 h to remove any scissioned frag-
ments and unreacted materials. The networks thus treated
were dried in air for 6 days, after that in a laboratory oven
at 80 °C for 3 h and finally were reweighed. The gel frac-
tion was calculated as follows:
(1)
Residual elongation
(%)=
LL
0
L0
×
100
Scheme 3 Possible reactions by sulfur vulcanization
Scheme 4 Formation of intramolecular bridges
Table 2 The recipe for the preparation of rubber samples
Ingredients Parts per hundred
Natural rubber 100.0
Stearic acid 1.0
Zinc oxide 5.0
Sulfur 2.5
MBT 0.5
TMTD 1.0
Hemp Variable (0, 10 and 20)
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Where, ms and mi are the weight of the dried sample after
extraction and the weight of the sample before extraction,
respectively [23, 24].
The cross-link density (ν) of the samples was determined
on the basis of equilibrium solvent-swelling measurements
(in toluene and xylene at 2325 °C) by applying the well-
known modified Flory–Rehner equation for tetrafunctional
networks. The samples (2 mm thick) were initially weighed
(mi) and immersed in solvent for 72 h. The swollen samples
were removed and cautiously dried to remove the excess
solvent before being weighed (mg) and, during this opera-
tion, the samples were covered to avoid solvent evaporation
during weighing. The solvent traces and other small mole-
cules were then eliminated by drying in air for 6 days and in
a laboratory oven at 80 °C for 3 h. Finally, the samples were
weighed for the last time (ms) and volume fractions of poly-
mer in the samples at equilibrium swelling ν2m were deter-
mined from swelling ratio G as follows:
where,
and ρr and ρs are the densities of rubber samples and sol-
vent (0.942, 0.865 and 0.864 g/cm3 for rubber, toluene and
xylene, respectively). The densities of elastomer samples
were determined by hydrostatic weighing method, accord-
ing to SR ISO 2781/2010. By this method, the volume of
a solid sample is determined by comparing the weight of
the sample in air with the weight of the sample immersed
in a liquid of a known density. The volume of the sample
is equal to the difference in the two weights divided by the
density of the liquid. The cross-link densities of the sam-
ples, ν, were determined from measurements in a solvent,
using the Flory–Rehner relationship as follows
where, V1 is the molar volume of solvent (106.52 and
122.88 cm3/mol for toluene and xylene, respectively), ν2m is
the volume fraction of polymer in the sample at equilibrium
swelling, and χ12 is the Flory–Huggins polymer–solvent
interaction term.
Rubber–fiber interactions
The extent of interaction between rubber and fiber can
be analyzed using Kraus equation. The Kraus theory and
(2)
Gel fraction (%
)=
m
s
mi
×
100
(3)
ν
2m=
1
1+G
(4)
=
g
s
×
r
(5)
ν
=−
Ln(1ν2m)+ν2m+χ12ν
2
2m
V1
ν1/3
2mν2m
2
Kraus equation [25] have been successfully used by some
researchers to assess the interfacial interaction in fiber-rein-
forced rubber composites [2628]. The Kraus equation is
as follows:
where, Vro and Vrf are the volume fractions of rubber in the
vulcanized gum and in fiber-filled swollen sample, respec-
tively, f is the volume fraction of fiber and m is the fiber
polymer interaction parameter. The volume fraction of rub-
ber in the swollen sample, Vrf, was calculated by the fol-
lowing expression:
where, ρr and ρs are the densities of rubber samples and
solvent (0.94 g/cm3 for natural rubber and 0.866 g/cm3 for
toluene), respectively, D is the deswollen weight of the test
specimen (dry weight), F is the weight fraction of the insol-
uble components, T is the weight of the specimen and A0 is
the weight of the absorbed solvent at swelling equilibrium.
Water uptake test
Effect of water absorption on fiber reinforced natural rubber
composites are investigated in accordance with SR EN ISO
20344/2004. The samples were dried in an oven at 80 °C
for 2 h and then were allowed to cool at room temperature
in desiccators before weighing. Water absorption tests were
conducted by immersing the samples in distilled water in
bottles and keeping at room temperature 23 ± 2 °C and in a
laboratory oven at 70 ± 1 °C. Samples were removed from
the bottles at periodic intervals and the wet surfaces were
quickly wiped using a clean dry cloth or tissue paper and
weights of the specimen after swelling were determined at
regular intervals until no further increase in solvent uptake
was detected. The moisture absorption was calculated
by the weight difference. The percentage weight gain of
the samples was measured at different time intervals. The
water uptake was calculated as follows:
where, mS is the weight of the sample saturated with water,
determined at periodic intervals and m1 is the initial weight
of the oven-dried sample [29, 30].
FTIR spectroscopy
Changes of the chemical structure of natural rubber/
hemp fibre composites were highlighted using a FTIR
(6)
V
ro
Vrf =1m
f
1
f
(7)
V
rf =
(DFT)
ρr
(DFT)
ρ
r
+
A0
ρr
(8)
Water uptake
(%)=
m
S
m
1
m1
×
100
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spectrophotometer—JASCO FT/IR 4200, by ATR measure-
ment method. Samples spectra are the average of 30 scans
realized in absorption in the range of 4,000–600 cm1, with
a resolution of 4 cm1.
SEM
The surface texture of the rubber/hemp composites was
examined using the Quanta 200 scanning electron micro-
scope (FEI Co., USA). All the surfaces were examined
after sputter coating with gold to avoid electrostatic charg-
ing and a poor image resolution.
Results and discussion
Mechanical characteristics
The variations of mechanical properties are shown in
Table 3. It can be seen from Table 3 that mechanical proper-
ties of the NR/hemp composites vulcanizates were affected
by increasing the fiber concentration, compared with NR
sample. The results illustrate that the properties, except-
ing the elasticity, are improved by the addition of hemp.
The elasticity decreased with the increase of fiber amount
in blends. According to Morton [31], elasticity (rebound
resilience) is the ratio of energy given up on recovery from
deformation to the energy required to produce the defor-
mation [32]. The decrease in resilience is explained by
the hemp particles that introduce a mechanism by which
the strain energy diminishes. Since rebound resilience is
directly proportional to the degree of elasticity and segment
mobility, the presence of hemp reduces elasticity and seg-
ment mobility of the cured NR composites. The increase of
the amounts of filler leads to the increase of hardness and
decreased resilience [3133].
The mobility of hemp particles and slippage of chains
attributed to applied stresses on cured composite increases
the hysteretic behavior of the cured composite [33, 34].
Therefore, the resilience decreased with increasing load
of hemp. This decrease may be due to the change in the
morphology of the sample by vulcanization. The hardness
exhibited an increase of about 40 % for 10 phr hemp and
47 % for 20 phr hemp while the tensile strength exhibited
an increase of 92 and 200 % with the same fiber loading.
Therefore, this can be attributed to a strong interface as
well as a close packing arrangement in the composite.
As expected, incorporation of hemp in matrix has
improved tensile strength. This improvement is due to the
adequate interaction between natural rubber and fiber [28].
The increase in tensile strength is due to the good adhesion
of the filler in matrix and to the agglomeration of filler par-
ticles. The elongation-at-break decreased with the increase
of fiber content in composites. The decrease of elongation-
at-break with the increasing of fiber content in the compos-
ite is the result of the high cross-linking. On the other hand,
its reduction indicates that ductility became worse when
hemp was added to NR composites. Thus, the hemp addi-
tion to composites restricts the molecular chains movement
[35]. The decrease in the elongation-at-break is also due to
the striking forces between the filler and the polymer mol-
ecules leading to the development of a cross-linked struc-
ture which limited the free mobility of the polymer chains,
hence increased the resistance to accelerate upon the
execution of tension [8, 35]. The elongation-at-break val-
ues showed a decrease of 28 % for both concentrations of
hemp. The tearing strength has followed the same trends as
the hardness and tensile strength: it has increased with the
increase of fiber content in composite. The tearing strength
has shown an increase of about 75 % for 10 phr hemp and
with 287 % for 20 phr hemp content in composite. The val-
ues of hardness, tensile strength and tearing strength have
increased with the fiber content increasing in the composite
due to a better interaction of fiber with NR. These results
indicate that the hemp has a reinforcing effect on natural
rubber.
Gel fraction and cross-link density of blends
To determine the cross-linking density, it is necessary to
know the parameter χ, that is the Flory–Huggins interac-
tion parameter between solvent and polymer, which can be
determined according to Blanks and Prausnitz [36, 37] by
applying Eq. (3).
where:χS is the entropic contribution of this parameter
(usually beings 0.34, according to Blanks and Prausnitz);χH
is the enthalpic contribution, obtained from the molar vol-
ume of a solvent, VmS,, universal gas constant R, absolute
temperature T (K), the Hildebrand solubility parameters of
the polymer (δP) and solvent (δS).
The Hildebrand solubility parameters of the solvents (δS)
are 18.3 (MPa)1/2 and 18.2 (MPa)1/2 for toluene and xylene,
respectively [38].
(9)
χ
=χSχH=χS+
V
mS
RT
(δSδP)
2
Table 3 Mechanical properties of the NR/hemp composites
Properties NR NR/10 phr hemp NR/20 phr hemp
Elasticity (%) 64… 52 42
Hardness (oShA) 53 74 78
Tensile strength (N/mm2) 1.3 2.5 3.9
Elongation at break (%) 140 100 100
Tearing strength (N/mm) 8 14 31
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The solubility parameter of a polymer can be estimated
by use of one of several group-contribution methods, such
as those given by Small, Hoy and Van Krevelen [37]. Cal-
culation of δP by a group-contribution method requires the
value of a molar attraction constant Fi, for each chemical
group in the polymer repeating unit. The solubility param-
eter of a polymer is then calculated from molar attrac-
tion constants and the molar volume of the polymer, V
(cm3 mol1), as follows:
The molar volume of the natural rubber is of
72.468 cm3 mol1. A listing of the molar attraction con-
stants, Fi for chemical group in natural rubber repeating-
unit and the molar attraction constant for the repeating
unit of NR,
Fi
, by Small, Hoy and Krevelen is given in
Table 4.
In Table 5 are given the results obtained for the solubil-
ity parameter (by Small, Hoy and Krevelen) and for the
Flory–Huggins interaction parameter between solvent and
polymer, χ.
Table 6 shows the gel fraction (mass fraction of the
network material resulting from a network-forming
polymerization or cross-linking process; the gel fraction
comprises a single molecule spanning the entire volume
of the material sample) and cross-link density (number of
cross-links per unit volume in a polymer network) of the
samples vulcanized as a function of the hemp content.
The cross-link density was calculated using the values of
χ12 as being 0.3900 and 0.3875 for toluene and xylene,
respectively.
The gel fraction values are over 95 % for all blends and
this increase depended on the amount of hemp in the com-
posites. The cross-link density (ν) of the samples changed
slightly as the amount of hemp in blends increased. Our
experimental results, confirmed by others [3941], show
that with the increase in cross-link density, the hardness
and tensile strength have increased, whereas the elonga-
tion-at-break decreased. Thus, it can be considered once
again that hemp acted as filler in natural rubber blends and
leads to reinforcement of them.
(10)
δ
P=
Fi
V
Rubber-fiber interactions
The extent of interaction between rubber and fiber was
analyzed using Kraus equation and the results are listed
in Table 7. Samples of NR with 10 and 20 phr content of
hemp fiber were swollen in toluene and xylene for 72 h.
From the results it is observed that for both solvents, the
equilibrium solvent uptake of the samples has increased
when the fiber content increased, fact which caused a
decrease in Vrf. The ratio Vro/Vrf increased because Vr0 is
constant. This is due to the decreased hindrance exerted by
the hemp fibers at higher loadings.
The diffusion mechanism in the composite in strongly con-
nected with the ability of rubber to provide pathways for the
solvent to progress in the form of randomly generated voids.
As the void formation increased with fiber content, the solvent
uptake also increased. The ratio Vro/Vrf is the degree of restric-
tion of swelling of the rubber matrix due to the presence of
fibers [28]. The ratio Vro/Vrf for composites with 10 phr and
20 phr hemp was found to be 1.0881 and 1.0952 in toluene,
respectively. Similar values of 1.0779 and 1.0865 were also
obtained in xylene for composites with 10 and 20 phr hemp,
respectively. Because the increases up to 1 % (0.65 and 0.79 %
in the case of toluene and xylene, respectively) for composites
having 20 phr hemp compared with those having 10 phr hemp
are extremely small, we can say that we have a good adhesion
between natural rubber and hemp fibers.
Interactions between fillers and rubbers have a sig-
nificant effect on reinforcement properties of a filled rub-
ber. Chemical and physical properties of rubber and filler
as well as their amount in a compound affected on these
interactions [42]. Rubber–rubber interactions mainly
occur when blends of rubber are used in compounds and
Table 4 Molar attraction
constants Fi at 25 °C and
Fi
,
for the repeating unit of NR
Group Number of groups By Small By Hoy By Van Krev-
elen
F FiF FiF Fi
–CH31 438 438 303 303 420 420
–CH2 2 272 544 269 538 280 560
>C=CH– 1 266 266 422 422 304 304
F
i
1.248 1.263 1.284
Table 5 Values of the solubility parameter (by Small, Hoy and Krev-
elen) and interaction parameter χ12
Method δPχ12 (toluene) χ12 (xylene)
By Small 17.2,215 0.3900 0.3875
By Hoy 17.4285 0.3727 0.3695
By Van Krevelen 17.7183 0.3545 0.3515
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are considered to be not as significant as filler–rubber
and filler–filler interactions. Filler–rubber interactions are
described by the compatibility of the filler with the rub-
ber, while filler–filler interactions are described by the
attraction of filler to itself and the ability to form a net-
work. Filler–filler interactions are a primary mechanism
in reinforcement, especially at high-filler loading. These
attractions depend on chemical interactions between the
filler particle surfaces (filler–filler, filler–rubber), physi-
cal interactions (van der Waals forces, hydrogen bonding),
morphology of the filler network, and filler volume fraction
[42, 43].The mechanism proposed was that sulfur forms
bond between NR–NR rubber. From this perspective it was
quite expected that the presented results indicate a rather
poor adhesion between NR–hemp filler and sulfur cure. In
another study [6, 21, 22], elastomer cross-linking was per-
formed using benzoyl peroxide or electron beam irradiation
to obtain also a natural rubber/fiber composite. In addition
to elastomer cross-linking, peroxide and electron beam can
perform chemical surface modification of fibers [6, 21, 22].
Water uptake
The water uptake of samples is presented in Fig. 1 depend-
ing on immersion time (in hours): (Fig. 1a) at 23 ± 2 °C
and (Fig. 1b) at 70 ± 1 °C. It can be observed that water
uptake increased with the increase of fiber content and
temperature. Thus: (a) after 24 h in water at room tem-
perature, water uptake values were: 0.38 % for the sample
without hemp, 2.15 % for samples having 10 phr hemp and
2.57 % for samples having 20 phr hemp; (b) after 24 h in
water at 70 °C water uptake values were: 2.78 % for the
sample without hemp, 7.38 % for samples having 10 phr
hemp and 8.38 % for samples having 20 phr hemp; (c)
after 192 h in water at room temperature water uptake val-
ues were: 3.12 % for the sample without hemp, 9.63 % for
samples having 10 phr hemp and 11.29 % for samples hav-
ing 20 phr hemp; (d) after 192 h in water at 70 °C water
uptake values were: 6.43 % for the sample without hemp,
14.15 % for samples having 10 phr hemp and 15.16 % for
samples having 20 phr hemp.
The water absorption at 23 ± 2 °C stops after 456 h for
the sample without hemp and after 600 h for sample with
hemp (Fig. 1a). Temperature of 70 °C seems to accelerate
Table 6 Gel fraction and cross-
link density of samples Sample Toluene Xylene
Gel fraction (%) ν (104 mol/cm3) Gel fraction (%) ν (104 mol/cm3)
NR 96.22 ± 0.22 3.1304 ± 0.95 96.95 ± 0.41 3.2095 ± 1.56
NR/10 phr hemp 97.94 ± 0.16 2.8334 ± 1.06 97.97 ± 0.16 2.9415 ± 2.06
NR/20 phr hemp 98.07 ± 0.49 2.8965 ± 2.07 98.47 ± 1.12 3.0243 ± 0.99
Table 7 Values of Vrf and Vro/Vrf of NR/hemp fiber composites in
toluene and xylene
Samples Toluene Xylene
Vrf Vro/Vrf Vrf Vro/Vrf
NR/10 phr hemp 0.2563 1.0881 0.2595 1.0779
NR/20 phr hemp 0.2546 1.0952 0.2574 1.0865
Fig. 1 Water uptake according to the amount of hemp in composites
at: a 23 ± 2 °C and b 70 ± 1 °C
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the moisture water uptake behavior. At this temperature the
water absorption stops after 216 h for the sample without
hemp and after 264 h for sample with hemp (Fig. 1b). It
can be seen that the composites absorb water very fast ini-
tially (in the first 24 h) but after that the amount of water
absorbed increased slower (after 192 h). In these compos-
ites, water is absorbed mainly by the hemp. By increas-
ing the amount of hemp in composite, the water absorption
increased, as well. This can be explained by the fact that
the diffusion of water in elastomers is not straight forward
by presence of hydrophilic materials (such as the hemp).
When the NR/hemp composite is exposed to moisture, the
hemp fibers undergo swelling. The high cellulose content
in hemp fiber (approximately 75 %) further contributes to
more water penetrating into the interface of composites
materials [30].The natural rubber is a hydrophobic mate-
rial and its water absorbability can be neglected [17]. For
the same absorption time, composites having high-fiber
content exhibit high-water absorption because one of the
properties of these natural fibers (hemp) is hydrophilic
characteristic.
FTIR analysis
The natural rubber/hemp fiber composites were analyzed
by FTIR in order to know their various chemicals con-
stituents. The main component of NR is cis-1,4-polyiso-
prene with a high degree of long chain branching gener-
ally associated with the presence of non-hydrocarbon
groups distributed along the chains. The natural rubber
is composed of hydrocarbons 89.3–92.4 wt%, protein
2.5–3.5 wt% and other ingredients (fatty acids, resins, and
inorganic materials) 4.1–8.2 wt%). Natural fibers can be
considered as naturally occurring composites consisting
mainly of cellulose fibrils embedded in lignin matrix. The
cellulose fibrils are aligned along the length of the fiber,
which render maximum tensile and flexural strengths, in
addition to providing rigidity. The reinforcing efficiency
of natural fiber is related to the nature of cellulose and its
crystallinity. The main components of natural fibers are
cellulose (α-cellulose), hemicellulose, lignin, pectins and
waxes [44].
Figures 2, 3, 4 and 5 shows the infrared spectra and the
characteristic bands of natural rubber, hemp fibers and
natural rubber/hemp fiber composites vulcanized with
sulfur, in the range of 4,000–650 cm1. The broad band
in the region of 3,300–3,265 cm1, which can be due to
the OH-stretching vibration, gives information concern-
ing the hydrogen bonds from the amorphous celluloses
[45], but at the same time the absorption bands at 3,280–
3,290 cm1 were identified to be attributed to the proteins
and both monopeptides and dipeptides present in natural
rubber [46]. This band is specific for NR and cellulose,
lignin and hemicellulose from the hemp fibers existing
into the mixture [47]. Absorption bands with maxima at
3,040–3,033 cm1 corresponding to CH stretching in the
–CH=CH2 group, are observed. Vulcanization of the pol-
ymeric compositions results in consumption of the dou-
ble bonds in NR molecules, thus the intensities of these
absorption bands decreased. The characteristic bands of
the saturated aliphatic sp3 C–H bonds are observed in the
region 2,970–2,850 cm1 which are assigned to νas (CH3),
νas (CH2), and νs (CH2), respectively (as three correspond-
ing bends) [48].
On the other hand, the presence of amorphous cellu-
losic samples can be further confirmed by the band from
2,925 to 2,917 cm1, corresponding to the C–H stretch-
ing vibration [45]. The absorption located in the region
Fig. 2 FTIR spectrum for NR in the range of 650–1,400 cm1
Fig. 3 FTIR spectrum for hemp in the range of 650–1,400 cm1
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1,742–1,734 cm1 corresponds to the C=O stretch in non-
conjugated ketones, carbonyls and in ester groups [49] and
the absorption bands in the region of 1,635–1,623 cm1
were due to absorbed water in cellulose [50] or are caused
by lignin (aromatic skeletal vibrations) [49]. Still in the
1,740–1,727 cm1 range, the absorption band was identi-
fied to the fatty acid ester groups of NR [51] and the pres-
ence of absorption bands in the spectral region located
between 1,664 and 1,658 cm1, is due to valence vibration
of homogeneous double bonds (C=C) in the NR structure.
Their intensity decreased for vulcanized samples compared
with non-vulcanized samples.
In addition, strong bands were observed for all vulcani-
zates at 1,450–1,375 cm1 and can be attributed to chain scis-
sion of the C–H groups or to amide groups (–NH2) produced
by the accelerated sulfur curing systems. The bands in the
range of 1,100–950 cm1 indicated the formation of a high
content of C–S stretches in this system [52]. Natural rubber
cis-isomer configurations can be observed at 850–740 cm1
[52]. At the same time absorption bands in this region can
be due to the hemp presence in the composite material.
Thus, the absorption band in the region 1,450–1,430 cm1,
is assigned to a symmetric CH2 bending vibration and this
band is also known as the “crystallinity band” [45]. The
band which appeared in the range of 1,320–1,305 cm1 is
assigned to the cellulose component: bending vibration of
C–H and C–O groups of aromatic rings [49, 50]. The absorp-
tion located in the region 1,165–1,150 cm1 corresponds to
the anti-symmetrical deformation of the C–O–C bond and
the absorption located in the region 1,070–1,020 cm1 is due
to the C–O, alcohol, O–H or aliphatic ethers [49, 50].
SEM analysis
To correlate the influence of fibers hemp content on the
mechanical properties and rubber–fiber interactions, the
morphological aspect of the natural rubber/hemp compos-
ites was necessary to be evaluated by SEM technique. For
SEM analysis, the samples were initially immersed in sol-
vent (toluene and xylene) for 72 h to remove unvulcanized
natural rubber. SEM micrographs of the natural rubber and
natural rubber/hemp composites with 10 and 20 phr hemp
content are shown in Figs. 6, 7 and 8.
Fiber alignment factors play a crucial role in the overall
properties of composites. There is always a chance of fiber
entanglement with randomly oriented fibers reinforced
composites. The random orientation of fibers produces
lower mechanical properties compared to long unidirec-
tionally oriented fibrers. This fiber entanglement can create
elastomeric rich areas, which can contribute to the forma-
tion of voids and porosity. Voids and porosity can act as
stress concentrators leading to failure of composite samples
[53]. The SEM micrographs obtained showed fibers disper-
sion within the matrix.
Figures 7 and 8 indicate that the hemp fibers present
striations, parallel to the fiber axis. The SEM micrographs
also revealed that the hemp fibers are uniformly distrib-
uted in the natural rubber matrix. This distribution plays a
positive role in improving the properties of the composite,
especially the tensile strength, as observed in this study.
Also, it is observed that with the increase of hemp amount
in composites, fibers appear not individually but form-
ing large bundles. Micrographs also show the effect of the
fracture on the fibers. As expected for efficiently reinforced
Fig. 4 FTIR spectra for NR/hemp composites in the range of 600–
2,000 cm1
Fig. 5 FTIR spectra for NR/hemp composites in the range of 2,600–
4,000 cm1
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composites, during the fracture process fibers suffered
rupture instead of being pulled out. This observation is
indicative of a good adhesion of the fibers to matrix. Mate-
rials with high fiber load presented some small voids in
its matrix structure. The nature of these voids is not clear.
Absence of pulled-out fibers suggests that these voids may
be formed at the conformation of the material [54].
The good adhesion showed in the SEM micrographs,
was transferred to the mechanical properties of the com-
posites prepared, which were considerably enhanced by
the presence of fibers, as can be seen from the data sum-
marized in Table 3. In addition, a good adhesion between
the hemp fibers and the rubber matrix was observed from
the SEM micrographs.
Fig. 6 SEM micrographs of natural rubber: a immersed in toluene and b immersed in xylene
Fig. 7 SEM micrographs of natural rubber with 10 phr hemp: a immersed in toluene and b immersed in xylene
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Conclusion
The objective of this research was to obtain a new elasto-
meric material based on NR, with enhanced properties, by
replacing active fillers from rubber blends such as carbon
black or silica with natural hemp fibers. The values of hard-
ness, tensile strength and tearing strength have increased
with the fiber content increasing in the composite due to
a good interaction of fiber with NR and these results indi-
cate that hemp has a reinforcing effect on natural rubber.
The gel fraction value was over 95 % for all blends and
increased with the amount of hemp in the composites. The
cross-linking density (ν) of samples changed slightly as the
amount of hemp in blends increased. It can be observed
that water uptake increased with increasing fiber content
and temperature because the diffusion of water in elasto-
mers was not straightforward by the presence of hydro-
philic materials (such as the hemp). The water absorption
tests indicate that for the temperature of 23 ± 2 °C the satu-
ration appeared after 456 h for the sample without hemp
and after 600 h for sample containing hemp, while the
high temperature of 70 °C seems to accelerated the water
uptake behavior and the saturation appeared after 216 h
for the sample without hemp and after 264 h for sample
with hemp. To investigate the reinforcement efficiency of
natural fibers, the infrared spectra of natural rubber, hemp
fibers and natural rubber/hemp fiber composites vulcan-
ized with sulfur have been achieved in the 4,000–650 cm1
range. The main components of natural fibers (cellulose,
hemicellulose, and lignin), NR-specific proteins and fatty
acid ester groups and the amide groups produced by the
accelerated sulfur curing systems were identified in the
investigated mixture. Also, to correlate the influence of fib-
ers hemp content on the mechanical properties and rubber-
fiber interaction, the morphological aspect of the natural
rubber/hemp composites was evaluated by SEM technique.
The micrographs obtained showed the fiber dispersion
within the matrix and a good adhesion of fibers with the
matrix. SEM micrographs also revealed that the hemp fib-
ers are uniformly distributed in the natural rubber matrix,
fact which plays a very important role in improving the
properties of the composite, especially the tensile strength.
Our investigations concerning the basic mechanical proper-
ties, some physical and chemical parameters, the infrared
spectroscopy and scanning by electron microscopy depend-
ing on hemp content in NR vulcanized with sulfur proved
the reinforcing effect of the hemp fibers.
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... From the SEM of the material in figure 4, a we can find that the fibers are not continuous. When the material is subjected to external tensile force, the external force is transmitted to the fiber through the fiber matrix interface and the interfacial bonding between the FHHPF and the HXNBR matrix enables the fiber and the substrate to bear the external stress effectively and limit the deformation of the rubber matrix simultaneously [22]. In addition, compared with the pure HXNBR, when the HXNBR/FHHPF composite is under external force, besides the fracture of the original HXNBR matrix, the pull out friction between the fiber and the matrix during the pulling process and some fibers ruptured, under the combine action, the tensile strength of the material is improved. ...
... In addition, compared with the pure HXNBR, when the HXNBR/FHHPF composite is under external force, besides the fracture of the original HXNBR matrix, the pull out friction between the fiber and the matrix during the pulling process and some fibers ruptured, under the combine action, the tensile strength of the material is improved. However, the HXNBR matrix still plays the main role in strength property of material in this situation, so although the elongation at break is lower, but the material deformation is still large [22][23][24]. With the further increasing of FHHPF content, the fibers were evenly distributed in the matrix and a dense fiber web was formed gradually. ...
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A series composite was prepared by adding hydrogenated carboxyl nitrile rubber (abbreviated HXNBR) as the matrix and four-hole hollow polyester (abbreviated FHHPF) as the reinforcement. The sound absorption properties of these composites were studied. The results show that with the increasing of FHHPF quantity, the storage modulus increases and the loss factor decreases gradually. On the contrary, the sound absorption performance of the composite was improved continuously. Composite with 40% FHHPF in 1 mm thickness is the best. The sound absorption coefficient reached to 0.651 at 2500 Hz and the effective frequency range of absorption coefficient above 0.2 was 1750-2500 Hz. When the amount of FHHPF increased to 50%, negative effects of overuse shown up, that led to the decreasing of the sound absorption property. With a constant mass ratio 70/30 of HXNBR/FHHPF composite, the sound absorption performance can be enhanced by changing its thickness. However, the improvement was smaller after the thickness increased to 2 mm. When increasing the thickness above 2 mm, the improvement of sound absorption performance tended to move to the middle and low frequency. In the meantime, the tensile mechanical properties of the composite were significantly improved by adding FHHPF. Tensile tenacity was improved greatly and the breaking elongation is significantly decreased. The deformation of the composite was smaller and more stable, which was beneficial for the actual engineering practice.
... On the other hand, despite the attractive properties and good processability, fillers, especially the reinforcing ones, are used to obtain NR composites suitable for a variety of the commercial applications. As conventional reinforcing fillers in NR processing, nonrenewable inorganic compounds such as carbon black, calcium carbonate, silica and clays are widely used [13][14][15][16][17]. Due to some advantages, e.g., low cost and biodegradability, these nonrenewable fillers are often replaced by renewable organic fillers derived from plants and animals from natural resources [18][19][20]. Raw renewable organic fillers are often sourced from plant or animal wastes, i.e., straw, wood flour, coir fiber, crab and shrimp shells [20][21][22]. Cellulose extracted from plants or agricultural wastes and chitin or chitosan derived from crab and shrimp shells have been reported to be a good reinforcement for NR composites [23][24][25][26]. ...
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In this study, the possibility of using ionic liquids (ILs) as auxiliary substances improving the vulcanization and physicochemical properties of natural rubber (NR) biocomposites filled with nanosized silica was investigated. Hence, the influence of ILs with bromide and chloride anions and various cations, i.e., alkylimidazolium, alkylpyrrolidinium and alkylpiperidinium cation, on the curing characteristics and crosslink density of NR compounds was determined. Furthermore, the effect of nanosized silica and ILs on the functional properties of the obtained vulcanizates, including mechanical properties under static and dynamic conditions, hardness, thermal stability and resistance to thermo-oxidative aging, were explored. Applying nanosized silica improved the processing safety of NR compounds but significantly increased the optimal vulcanization time compared to the unfilled rubber. ILs significantly improved the cure characteristics of NR compounds by increasing the rate of vulcanization and the crosslink density of NR biocomposites. Consequently, the tensile strength and hardness of the vulcanizates significantly increased compared to that without ILs. Moreover, the use of nanosized silica and ILs had a favorable impact on the thermal stability of the vulcanizates and their resistance to prolonged thermo-oxidation.
... Use of renewable organic fillers can replace the non-renewable inorganic fillers in the NR composites and it introduced the concept of green NR composites. The organic renewable fillers isolated from the animal or plant wastes including crab shell, coir fibre, straw [37,38], etc. have many advantages such as biodegradability, low cost, non-toxicity, less abrasive nature and lessor specific weight [39,40]. Bio-fillers such as cellulose, chitin, lignin, etc. have been explored as efficient reinforcing candidates in NR matrix. ...
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Natural rubber (NR) is an eminent sustainable material and is the only agricultural product among various rubbers. Use of nanofillers in NR matrix as a reinforcing agent has gained huge attention because they offer excellent matrix-filler interaction upon forming a good dispersion in the NR matrix. Nanoscale dispersion of fillers lead to greater interfacial interactions between NR and fillers compared to microfillers, which in turn lead to a conspicuous reinforcing effect. Addition of various nanofillers into NR matrix improves not only the mechanical properties but also the electrical, thermal and antimicrobial properties to an extreme level. The current review describes the reinforcing ability of various nanofillers such as clay, graphene, carbon nanotube (CNT), titanium dioxide (TiO2), chitin, cellulose, barium titanate (BaTiO3) and lignin in NR matrix. Moreover, reinforcement of various hybrid nanofillers in NR is also discussed in a comprehensive manner. The review also includes the historical trajectory of rubber nanocomposites and a comprehensive account on the factors affecting the properties of the NR nanocomposites.
... Composites developed from sources, such as plant oils and chicken feather fibers, offer both commercial and environmental advantages (Rajkumar, Srinivasan, and Suvitha 2013). The usage of renewable materials also benefits global sustainability and reduction of global warming gases (Asim et al. 2020;Manaila, Stelescu, and Doroftei 2015). Plant oils and chicken feathers make suitable substitute to petroleum-based materials as they are found abundantly all over the world. ...
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For the past few decades environmental concerns had been influencing the researchers to employ natural fibers and polymers from renewable resources as a replacement for petroleum-based resins and synthetic fibers. In this work, materials from renewable resources were used to prepare the composites. Modified epoxidised soybean oil as resin was employed to prepare the composites with chicken feather fibers as the reinforcing agent by compression molding technique. Epoxidised soybean oil (ESO) was modified by reacting with methacrylic acid and methacrylic anhydride to form resin. Rosin acid derivative was synthesized to serve as the crosslinker for replacement of the petroleum based divinylbenzene (DVB). For comparison, divinylbenzene (DVB) was also employed to copolymerize with the same resin. Chemical structure of rosin derivative was verified by ¹H-NMR spectroscopy. FT-IR study showed the interaction between resin, chicken feather fiber (CFF) and rosin derivatives. The morphological features of the composites were evaluated by scanning electron microscopy (SEM), where it indicated a uniform interaction among the components of the composites. Different experimental results showed that the composites with higher amount of rosin acid derivative showed better properties. Results demonstrated that rosin acid derivative can serve as a substitute for petroleum-based rigid compounds for preparing biocomposites.
... The ecological and economic global treats of late have called for the production of natural fibre-reinforced and sustainable composite materials as a suitable alternative for conventional fibre-reinforced polymer composites. Nowadays, the natural fibresbased reinforcement is the most feasible approach towards ecological-friendly composite materials [1]. There is a persistent demand for natural fibres in the automotive [2] and industrial sectors. ...
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Owing to growing environmental awareness in green technology, the whole gamut of engineering sector has started shifting towards natural fibre-oriented materials from synthetic materials. The adequate dynamic stability and damping property are important design necessities in a polymer composite structure. Given this perspective, this paper discusses the formulation of distinct hybrid laminates with various weight ratios of jute- and linen-incorporated epoxy polymer and the influence of their weight ratios on the dynamic attributes. Dynamic mechanical thermal analysis is employed to quantify the viscoelastic attributes of the hybrid laminates. The natural frequency of cantilevered laminate beam is determined experimentally by free vibration analysis and the damping factor of the laminate beam is computed analytically by half power bandwidth technique. The cole–cole mapping analysis is made to understand the interfacial adhesion of the different laminates with hybrid configurations. The hybrid laminate with equal weight proportion of jute and linen is found to be optimal as it has exhibited maximum stiffness property and load bearing capability with high glass transition temperature. The influences of frequency on storage modulus and loss factor of the optimal hybrid laminate with respect to temperature are analysed. Several vibratory responses of the optimal hybrid laminate beam for different natural frequencies and damping factors are elicited and studied.
... In the last two decades, due to upward environmental awareness, there is an increasing demand for the development of natural fiber based green and sustainable rubber composites. Many researchers reported the designing of advanced rubber composites based on different types of natural fiber such as short jute [2,[6][7][8][9], bamboo [10,11], short coir [12][13][14], sisal [15,16], oil palm [15][16][17], kenaf [18], grass [19,20], hemp [21,22], pineapple leaf [23,24], etc. Compared to petroleum based materials, natural fibers have some additional advantages, i.e., availability, biodegradability, light-weight, low-cost, renewability and non-toxic nature [9,25]. ...
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In the present study, the suitability of various chemical treatments to improve the performance of jute fibers (JFs) filled natural rubber (NR) composites was explored. The surface of JFs was modified by three different surface treatments, namely, alkali treatment, combined alkali/stearic acid treatment and combined alkali/silane treatment. Surface modified JFs were characterized by X-ray diffraction (XRD) pattern, Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM). The reinforcing effect of untreated and surface treated JFs in NR composites was comparatively evaluated in terms of cure, mechanical, morphological and thermal properties. Combined alkali/silane treated JFs filled NR composite showed considerably higher torque difference, tensile modulus, hardness and tensile strength as compared to either untreated or other surface treated JFs filled NR systems. A crosslink density measurement suggested effective rubber-fibers interaction in combined alkali/silane treated JFs filled NR composite. Morphological analysis confirmed the improvement in the interfacial bonding between NR matrix and JFs due to combined alkali/silane treatment allowing an efficient “stress-transfer” mechanism. As a whole, combined alkali/silane treatment was found to be most efficient surface treatment method to develop strong interfacial adhesion between NR matrix and JFs.
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This work investigates the effect of different loading of copper alumina nanoparticles (Cu-Al2O3) on the processing characteristics, crystalline, morphological, mechanical, and thermal properties of natural rubber (NR). The effective reinforcement of Cu-Al2O3 nanoparticles into NR was carried out using a simple and efficient two roll mill mixing technique and the structural changes were systematically analyzed by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscope (HR-TEM), differential scanning calorimetry, and thermogravimetric analysis. The FTIR and XRD of NR/Cu-Al2O3 showed the characteristic absorption bands and the crystalline peaks of Cu-Al2O3 in the prepared composites. SEM and HR-TEM showed the uniform distribution of nano Cu-Al2O3 in the NR matrix. The processing time of the nanocomposites was significantly decreased with the addition of metal oxide nanoparticles, which indicated the reduction in the cost of the fabrication of elastomer product using Cu-Al2O3 nanoparticles. Mechanical properties such as modulus, tensile strength, hardness, heat build-up, glass transition temperature, tear properties, abrasion, and thermal stability were greatly enhanced by the reinforcement of Cu-Al2O3 into the NR matrix. The swelling behavior of composite with respect to different loading of nano-filler was also investigated in various aromatic solvents. The addition of nanoparticles reduces the solvent uptake of the composite and the maximum solvent resistance was noted for the composite with 5 phr loading.
Article
The searching of suitable alternatives to petroleum‐based fillers is an uncompromising challenge in present day rubber research. Recently, natural fibers are the part of great attention of both academic and industrial researchers due to their easy availability, environmental friendliness, and biodegradability. Natural fiber is cellulose‐rich material, which is preferentially used as alternative filler in rubber technology. This article reviews current advances in natural fibers filled rubber composites in terms of mechanical, thermal, and biodegradable properties (2010–2020). The incorporation of unmodified natural fibers as filler is not able to offer desired reinforcement in rubber composites. Several surface modification methods can be introduced to improve the overall performances of natural fibers filled rubber composites. Finally, the review clarifies present status and future prospects of natural fibers based advanced rubber composites in automobile industry. The successful designing of natural fibers based sustainable rubber composites can introduce a new era in green rubber technology.
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Natural rubber (NR) is well-known as renewable bio-based polymer that has been widely used in a wide variety of applications ranging from ordinary household to aerospace products. In order to meet the complete concept of green growth and sustainable development, the uses of non-toxic chemicals and green fillers alternating to conventional fillers are necessary to be concerned. In this article, we provide up-to-date information on the sustainable development of NR including NR latex production with low ammonia/non ammonia system and the usage of effective curing activator and bio-based processing oil. Moreover, the issue of the environmentally friendly green NR composites is described here with using renewable biomass organic fillers derived from plants and animals such as cellulose and chitin.
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There is a global acceleration in the employment of inorganic fiber-reinforced wood–plastic composites in various fields. The durability of composites is challenged by hot and humid environments, where their service life is greatly shortened compared to that in normal environments. Therefore, it is rare to adding basalt fibers (BF) for wood plastic composites, to extend the actual applications; how to better improve the service life is important issue. So, the physical, mechanical, and thermal properties of composites are deeply investigated for durability. In this study, BF, which is a relatively stable fiber, is selected as the research object. The results indicate that the physical, mechanical, and thermal properties of composites improved by BF. The mechanical properties of composites are optimal when the content of BF reached 10%. Water resistance of the impregnated composites improves more than that of non-impregnated composites. The physical and mechanical properties of composites were observed by scanning electron microcopy. Good interfacial adhesion limits the mobility of polymer chains lead to good performance. Additionally, the thermal properties are enhanced owing to the addition of BF, especially the low linear coefficient of thermal expansion and the high thermal decomposition temperature. BF has a positive effect in reinforced composites.
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Natural fibres will take a major role in the emerging 'green economy' based on the energy efficiency in using of polymer products as renewable materials. These fibres are completely renewable, environmental friendly, high specific strength, non abrasive, low cost and bio-degradability. Natural fibres are rich in cellulose and they are cheap and available in abundant for polymer reinforcement and it is also a potential alternative to the fibers of glass, carbon and other synthetics materials used for the manufacturing of composites. This review paper summarizes the hybrid composites of natural fibre reinforced polymer characteristics and its applications.
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Natural fibers offer many advantages in textile reinforced composites. The main purpose of this study was to turn cotton and flax fibers into knitted preforms, then to use these preforms as reinforcement to examine their ecological and environmental advantages that they provided to the knitted preforms. Our aim was to analyze the difference of flax and cotton fabric composites in terms of tensile, compression and impact strength, also to understand the mechanical contribution of fibre and yam inlay in these composites.
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This paper presents our experiments on obtaining and characterizing polymeric composites based on flax flax wastes and natural rubber. Natural rubber was cross-linked both through a conventional method - using benzoyl peroxide, and an unconventional method - electron beam irradiation. Physical-mechanical properties such as hardness, 100% elongation modulus and tensile strength indicate a significant improvement as a result of adding ground flax waste to blends. Better results have been obtained using crosslinking by electron beam irradiation. The crosslinking rates of samples, measured using the Flory-Rehner equation increase as the amount of flax waste in blends increases and as the electron beam irradiation dose increases. The swelling parameters of samples significantly depend on the amount of flax wastes in blends, because the latter have hydrophilic characteristics. The obtained composites can be used in manufacturing products with applications in the automotive industry, furniture industry, constructions etc.
Research
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This paper was published in Journal of Physical Science, Vol 2(22), 1-14, 2011.
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Amorphous cellulose was obtained from different types of celluloses (microcrystalline cellulose, dissolving pulp and cotton cellulose), by regeneration with ethanol from their solutions in an SO2- diethylaminedimethylsulfoxide (SO2-DEA-DMSO) solvent system. Different techniques, X-ray diffraction (XRD), FTlR spectroscopy and differential scanning calorimetry (DSC) were used to estimate the crystallinity degree. The values obtained for amorphous celluloses were compared with those of the initial samples and correlated with their supramolecular structures. Viscosity measurements have shown that little or no depolymerization occurs during dissolution.
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The present work attempts to provide a review on tribological performance of natural fibre-reinforced polymer composites. Topics related to natural fibre, polymer, composites and tribology have been discussed. Composites have unique properties which can only be obtained by the combination of specific fibres and matrix materials. Today these composites are used in many areas such as automotive and construction which require good mechanical and tribological properties. However, shortcomings in the usage of these fibres, led by environmental concerns, have motivated researchers to explore the possibility of using natural fibres as an alternative.
Conference Paper
The chemical modification by esterification of hardwood sawdust and its polymer constituents (cellulose, lignin) using organic anhydrides has been investigated. it was found that the weight percent gain increased with an increment of reaction temperature and time. The characterization of modified hardwood, cellulose and lignin was performed by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetry (TGA) studies. Thermal stability of chemically modified wood and wood polymers was found to be lower by comparison with unmodified samples.
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The effect of filler loading and bonding agent on the dynamic properties and swelling behaviour of bamboo fibre filled natural rubber composites were carried out. Bamboo fibre was used as a filler and the loading range was from 0 to 50 phr. Dynamic properties were determined using a Monsanto moving die rheometer (MDR 2000) at 150°C. Results show that the maximum elastic torque (S″MH) and minimum elastic torque (S′ML) increase with increasing filler loading and the addition of bonding agent. However, the viscous torque (S″MH) and tan δMH decrease with the addition of bonding agent. For swelling behaviour, the water absorption of the composites increases with increasing filler loading but decreases with the addition of bonding agent. The presence of bonding agent is found to improve the adhesion between bamboo fibre and natural rubber matrix as indicated by the tensile fracture surfaces of the composites using scanning electron microscope (SEM).
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As hemp is a renewable resource with the high biomass yield it could be considered as potential abundant local biomass material for a wide range of applications. In this article hemp fibres architecture as a source of high strength cellulose are analysed. In experimental part steam explosion technology is applied to disintegrate technical hemp fibres to elementary fibres with the aim to find out the best way of procedure without usage to environment harmful chemical pre-treatments and looking forward to solve problems on further nano-level environment friendly hemp cellulose disintegration.