ArticlePDF Available

Studies on the Water Absorption Properties of Short Hemp—Glass Fiber Hybrid Polypropylene Composites

Authors:

Abstract and Figures

Hemp fiber is one of the inexpensive and readily available bast natural fibers and hemp-fiber reinforced polymer composite products have gained considerable attraction for automotive interior products. Though extensive research has been made on the performance evaluation of these composite materials, not much data is available on the moisture absorption of the composites, which restricts their use in exterior applications. This study aims to investigate the moisture absorption of short hemp fiber and hemp-glass hybrid reinforced thermoplastic composites to study their suitability in outdoor applications. The water absorption properties and its effect on the tensile properties of hemp and hemp/glass fiber hybrid polypropylene (PP) composites prepared by an injection molding process were investigated. Effect of hybridization on the water uptake and the kinetics of moisture absorption of the hemp fiber composites were evaluated by immersing the hybrid composite samples in distilled water at different temperatures, of 40, 60 and 80°C. The composites showed a Fickian mode of diffusion; however, a deviation was observed at higher temperature and may be attributed to the microcraks developed at the interface and dissolution of the lower molecular weight substances from the natural fibers. Equilibrium moisture content (Mm) showed that water up take of 40 wt% hemp fiber reinforced PP composites was highest and incorporation of glass fiber decreased the water uptake significantly (40%). Equilibrium moisture content was found to be independent of temperature, while diffusion coefficient (D) was increased with temperature. Effect of water absorption on the tensile properties of the composites showed that there is a significant reduction in strength and stiffness. It was observed that hybridization with glass fibers did not have any significant effect on the strength properties of the aged samples. The tensile properties of the re-dried aged samples showed an increased retention of strength properties after drying; however a complete recovery of the properties has not been achieved. This indicated that water absorption is not a physical process and permanent damage occurred to the composite after aging.
Content may be subject to copyright.
Studies on the Water Absorption
Properties of Short Hemp–Glass Fiber
Hybrid Polypropylene Composites
SUHARA PANTHAPULAKKAL AND MOHINI SAIN*
Center for Biocomposites and Biomaterials Processing Faculty of Forestry
University of Toronto, Toronto, Canada M5S 3B3
ABSTRACT: Hemp fiber is one of the inexpensive and readily available bast
natural fibers and hemp-fiber reinforced polymer composite products have gained
considerable attraction for automotive interior products. Though extensive research
has been made on the performance evaluation of these composite materials, not
much data is available on the moisture absorption of the composites, which restricts
their use in exterior applications. This study aims to investigate the moisture
absorption of short hemp fiber and hemp-glass hybrid reinforced thermoplastic
composites to study their suitability in outdoor applications. The water absorption
properties and its effect on the tensile properties of hemp and hemp/glass fiber
hybrid polypropylene (PP) composites prepared by an injection molding process
were investigated. Effect of hybridization on the water uptake and the kinetics
of moisture absorption of the hemp fiber composites were evaluated by immersing
the hybrid composite samples in distilled water at different temperatures, of 40, 60
and 80
C. The composites showed a Fickian mode of diffusion; however, a deviation
was observed at higher temperature and may be attributed to the microcraks
developed at the interface and dissolution of the lower molecular weight substances
from the natural fibers. Equilibrium moisture content (M
m
) showed that water
up take of 40 wt% hemp fiber re inforced PP composites was highest and
incorporation of glass fiber decreased the water uptake significantly (40%).
Equilibrium moisture content was found to be independent of temperature, while
diffusion coefficient (D) was increased with temperature. Effect of water absorption
on the tensile properties of the composites showed that there is a significant
reduction in strength and stiffness. It was observed that hybridization with glass
fibers did not have any significant effect on the strength properties of the aged
samples. The tensile properties of the re-dried aged samples showed an increased
retention of strength properties after drying; however a complete recovery of the
properties has not been achieved. This indicated that water absorption is not a
physical process and permanent damage occurred to the composite after aging.
KEY WORDS: natural fiber composites, hemp, fiber, water absorption, tensile
properties.
*Author to whom correspondence should be addressed. E-mail: m.sain@utoronto.ca
Journal of COMPOSITE MATERIALS, Vol. 41, No. 15/2007 1871
0021-9983/07/15 1871–13 $10.00/0 DOI: 10.1177/0021998307069900
ß 2007 SAGE Publications
INTRODUCTION
R
ECENTLY, NATURAL FIBER reinforced polymer composites have experienced
a tremendous growth in the composite industry because of their eco-friendliness
and cost effectiveness [1–3]. They have already found use in building, construction,
automotive, and packaging applications. Despite the attractiveness and environmental
advantages of the natural fiber composites, their poor hygrothermal resistance compared
to synthetic fiber reinforced plastics or engineering thermoplastics restricts their use
in many structural as well as outdoor applications. The absorbed moisture results in to the
deterioration of mechanical properties since the water not only affects the unfilled
polymer matrices physically and/or chemically but also attacks the hydrophilic natural
fiber as well as the fiber-matrix interface [4–14]. In order to expand the realm of natural
fiber composites, it is required to increase the moisture diffusion resistance and thereby
increase the retention of the properties after aging. Several research works have been
reported on the hygrothermal aging of natural fiber, such as wood fiber, sisal, flax,
pineapple leaf fiber, jute, oil palm, and bamboo fiber, reinforced thermoset resins and
thermoplastics, which shows the relevancy of the subject [4–14].
Most of the studies in this area are mainly focused to improve the inherent weakness of
the natural fiber composites and has been accomplished by increasing the hydrophobicity
of the natural fibers through various physical and chemical pretreatments of the fibers
[5,8–10,12,14]. Incorporation of compatibilizers also enhances the resistance to moisture
through improved interaction between the fibers and the polymer matrix [7,8,11,13,14].
Hybridization with a small amount of moisture resistant and corrosion resistant synthetic
fibers is another technique by which the strength and the stiffness as well as the moisture
resistance of the natural fiber composites can be improved. Hybrid fiber composite
materials can be comprised of a combination of more than one type of fibers in the same
matrix. Though in principle several fibers can be incorporated into the hybrid system,
a combination of only two types of fiber would be the most beneficial. By hybridization,
it is possible to achieve a balance between performance properties and cost of the
composites, which would not be obtained with a single kind of reinforcement. In other
words, by careful selection of reinforcements it is possible to engineer the material to better
suit various practical requirements with economic benefits. Researchers have reported that
incorporation of glass fibers with natural fibers like sisal, bamboo, and oil palm empty
fruit bunch (OPEB) fibers, in thermoset as well as thermoplastic matrix resulted
in improved performance [15–18].
Hemp fiber is one of the inexpensive and readily available bast natural fibers and has
attracted considerable attention of researchers and auto-parts manufacturers in Europe
and North America. Several researchers exploited the reinforcing potential of hemp fibers
in developing thermoplastic and thermoset composites using different forms of hemp
fibers and various processing techniques [19–26]. However, most of the studies
concentrated on the performance properties and not many data are available on the
durability of hemp fiber composites [27–29]. Misra and Naik studied water absorption
of various natural fiber filled novolac resin and reported that hemp fiber–filled composites
showed highest water absorption [27]. Recently, Rouison et al. from our group have
studied the durability of resin transfer molded hemp fiber–polyester resin with the help
of magnetic resonance imaging technique [29]. We have already reported that short
hemp/glass fiber hybrid composites have enough potential to be used for structural
applications where high stiffness is required [30]. In this study the effect of hybridization
1872 S. P
ANTHAPULAKKAL AND M. SAIN
of hemp fibers with glass fibers on the water absorption properties of the hemp fiber
reinforced polypropylene composites were studied in order to study suitability of these
composites in outdoor applications. Special emphasis was given to the study of the
mechanism of water absorption from the kinetic characteristics and the effect of aging
on the tensile properties of the composites.
EXPERIMENTAL
Materials
Polypropylene PP 6331 obtained from Himont was used as the polymer matrix for the
composites. Hemp fibers with a fiber length of 12 mm used in the study was native hemp
grown in Ontario and was obtained from Hempline Inc., Ontario. E-glass fibers with 6 mm
length were used together with hemp fibers for making hybrid composites and were
obtained from Plastic World, Canada. The compatibilizer used in the preparation of
composites was Orevac-CA 100, which is a maleated polypropylene supplied by Arkema,
Canada.
Processing
Formulation of the composites prepared for this study is given in Table 1. Total weight
percentage of the fibers in the composites was fixed at 40. The ingredients were melt
blended using a Brabender Plasticorder at 170
C and at 60 r.p.m. for 5 min. The melt-
blended materials were allowed to cool to room temperature and then granulated using
a C.W. granulator. Granulates prepared were then injection molded into standard ASTM
test specimens for tensile, flexural and impact strength determination. Injection molding
conditions used were: injection, temperature, 200
C; injection time, 8 s; cooling time, 25 s;
and mold opening time, 2 s.
Water Absorption Studies
Water absorption studies were performed following the ASTM D570-98 method.
In order to study the kinetics of water absorption, six injection molded impact specimens
of every sample were submerged in distilled water at different temperatures, 40, 60, and
80
C. The samples were taken out periodically and weighed immediately, after wiping out
the water on the surface of the sample, using a precise four-digit balance to find out the
Table 1. Formulation of composites.
Designation of samples PP (wt%) Glass fiber (wt%) Hemp fiber (wt%) Compatibilizer (wt%)
A 55 0 40 5
B 55 5 35 5
C5510305
D5515255
Short Hemp–Glass Fiber Hybrid PP Composites 1873
content of water absorbed. All the samples were dried until constant weight with the
four-digit balance, previously to be immersed in water. The percentage of water absorption
at any time, t, M
t
, was calculated by the equation:
W
ðtÞ
W
ð0Þ
W
ð0Þ
100 ¼ water absorption, M
t
ð%Þ
where W
(t)
is the weight of the sample at time t, and W
(0)
is the initial weight of the sample
(at t ¼ 0). The percentage equilibrium moisture absorption, M
m
, was calculated as an
average value of several constitutive measurements that showed no appreciable additional
absorption.
To study the effect of water absorption on the mechanical properties, six tensile test
specimens of every sample were immersed in distilled water at room temperature and
determined the water content periodically as explained before until the content of water
remained invariable or remained more or less the same.
Tensile Test
Tensile properties were measured with a standard computerized testing machine
(Sintech Model 20) in accordance with the ASTM D-638 procedure at a crosshead rate
of 12.5 mm/min. Tensile tests were performed on the dry samples before aging, wet
samples after the samples reached the saturation limit and on re-dried aged samples in
order to investigate the mechanism and extent of deterioration of properties after aging.
Drying of the wet samples was carried out at 60
o
C for 5 days in an air oven.
RESULTS AND DISCUSSION
Water Uptake
Water absorption curves of injection molded PP, hemp/glass fiber hybrid composites
(A–D) at 40
C is shown in Figure 1, where percentage of water absorbed is plotted against
the square root of the soaking time. Each data point represents the average of six samples.
In all the samples, except PP, percentage moisture absorption, M
t,
increases steadily with
t
1/2
in the initial stage and then tends to level off following the saturation point, indicating
a Fickian mode of diffusion. The equilibrium moisture content at the saturation level (M
m
)
of PP and the composites are summarized in Table 2. Water absorption of polypropylene
is 0.40% and upon reinforcing with 40 wt% of hemp fiber a large increase in water uptake
(M
m
¼ 8.5) was observed. This is attributed to the hydrophilic character of natural fibers
since the matrix had little effect on the amount of water absorbed. A high amount
of natural fiber in the composite showed a high uptake of water. The variation in the water
uptake of the hemp-glass hybrid PP composites as a function of glass fiber content at 40
C
is also evident in Figure 1. Incorporation of glass fiber in the hemp fiber PP composites
decreased the equilibrium moisture content significantly and is attributed to the removal
of hydrophilic natural fiber with the glass fiber in the composite. Incorporation of 5 wt%
of glass fiber decreased the maximum moisture content in the composite by 10% and
1874 S. P
ANTHAPULAKKAL AND M. SAIN
shows a steady decrease with further addition of glass fiber. Equilibrium moisture
content of the composites is decreased by 40% with the addition of 15 wt% glass fiber
content.
Effect of temperature on the water absorption behavior can be understood from the
water absorption curves of PP and composites at different temperatures, 40, 60, and 80
C
(Figures 1–3). At all temperatures PP shows the lowest water absorption, whereas hemp
fiber composites exhibited the maximum water uptake. Though there is an increase in the
initial uptake of water with increase in temperature, it is evident that in all the cases,
equilibrium moisture content remains more or less the same indicating that M
m
is
independent of temperature (Table 3). The higher uptake of water may be due to the
micro cracks developed on the surface and inside the material and/or natural fiber
swelling due to moisture and the resulting fiber debonding from the matrix due to the
moist and high temperature environment. As a result of the enhanced initial uptake
of water, increase in the immersion temperature has considerably shortened the
time required to reach equilibrium. For example, by increasing the temperature
from 40
Cto60
C the time required to reach equilibrium is decreased by about 170 h
(Figures 1 and 2) and further decrease was observed when the temperature increased
0
2
4
6
8
10
010203040
Time
1/2
(h)
Water absorption (%)
Pol
y
mer 0%
g
lass 5%
g
lass 10%
g
lass 15%
g
lass
Figure 1. Water absorption curves of hemp fiber composites with different glass fiber content at 40
C.
Table 2. Equilibrium moisture content of composites.
Content of glass fiber,
Equilibrium moisture content, %
wt% 40
C60
C80
C
PP 0.49 0.49 0.50
0 8.55 8.57 8.39
5 7.67 7.66 7.41
10 6.25 6.38 6.20
15 5.07 5.20 5.06
Short Hemp–Glass Fiber Hybrid PP Composites 1875
from 60
Cto80
C (Figures 2 and 3). Another important observation noticed is that
at 80
C, moisture uptake reaches a maximum and then decreases thereafter. This may
be due to the enhanced leaching of low molecular weight soluble materials from
natural fiber at high temperature that leads to material loss after prolonged period
of water immersion [31].
0
2
4
6
8
10
0
5
10 15 20 25 30 35 40
Time
1/2
(h)
Water absorption (%)
Polymer 0% glass 5% glass 10% glass 15% glass
Figure 2. Water absorption curves of hemp fiber composites with different glass fiber content at 60
C.
0
2
4
6
8
10
0
10 20 30 40
Time
1/2
(h)
Water absorption (%)
Polymer 0% glass 5% glass 10% glass 15% glass
Figure 3. Water absorption curves of hemp fiber composites with different glass fiber content at 80
C.
1876 S. PANTHAPULAKKAL AND M. SAIN
Kinetics of Water Absorption
Moisture absorption into the composite materials is considered by three major
mechanisms and they include. (i) diffusion of water molecules inside the microgaps
between polymer chains; (ii) capillary transport of water molecules into the gaps and flaws
at the interface between fibers and the polymer due to the incomplete wettability and
impregnation; and (iii) transport of water molecules by micro cracks in the matrix, formed
during the compounding process [13,16,32]. Though all three mechanisms are active,
the overall effect can be modeled conveniently considering the diffusion mechanism.
There are three different kinds of diffusion behavior and they include Case I or
Fickian diffusion, Case II and non-Fickian or anomalous diffusion [13,33,34]. The three
cases of diffusion can be distinguished theoretically by the shape of the sorption curve,
which is represented by the empirical equation:
M
t
M
m
¼ kt
n
where M
t
is the moisture content at time t, M
m
is the moisture content at the equilibrium
and k and n are constants. The value of coefficient n shows different behavior between the
three cases. For Fickian diffusion n ¼ 1/2, while for Case II n ¼ 1 and for anomalous
diffusion n shows an intermediate value (1/2<n<1). The value of k provides an idea about
the interaction of moisture with the material.
The mechanism of water uptake and hence the study of the kinetic parameters n and k,
the data were analyzed by adjusting the experimental values to the following equation,
which is derived from the Equation 1.
log
M
t
M
m

¼ logðkÞþn logðtÞ
The values of the parameters n and k obtained from the fitting curves of the water
absorption of hemp fiber and hemp/glass fiber hybrid composites are summarized in
Table 3. At all temperatures, values of the parameter n for hemp fiber composites and
hybrid composites are very close to each other and close to that of the value of n ¼ 0.5,
which indicates the Fickian diffusion mechanism in the composites. However, the values
are less than 0.5 at 80
C, which indicate a deviation from Fickian diffusion. The deviation
Table 3. Moisture sorption constants of composites with different glass fiber
content at different temperatures.
Temperature
Content of glass fibre,
40
C60
C80
C
wt% n knkn k
0 0.5163 0.233 0.4902 0.265 0.475 0.337
5 0.5174 0.231 0.4851 0.266 0.466 0.336
10 0.5174 0.231 0.4682 0.277 0.4678 0.334
15 0.5061 0.238 0.4814 0.267 0.4723 0.338
Short Hemp–Glass Fiber Hybrid PP Composites 1877
observed may be due to the additional mechanism observed as a result of the fiber
swelling, fiber matrix interface weakening, micro cracking, and leaching. The higher
uptake of water after 80–90 h may be due to the micro cracks developed on the surface and
inside the material and/or natural fiber swelling due to moisture and the resulting fiber
debonding from the matrix due to the moist and high temperature environment. Also
dissolution of low molecular weight soluble materials from natural fiber such as short
chain hemicellulose, pectin, and other soluble sugars may enhance at high temperature,
which leads to material loss after prolonged period of water immersion. As long as the
moisture gain is greater than material loss, the weight of the specimen increases. Because of
the water absorbed at the micro cracks and at the weak interface, the sorbed water content
increase and therefore the weight change profile is greater than the Fickain curve for
a certain period of time. Similar results were reported in the case of graphite epoxy
composites, where material loss is due to the dissolution of epoxy resin [31]. The k values
remain more or less constant for all the composites at each temperature while there is an
increase with increase in temperature indicating that as the temperature increases the
moisture interaction with the composite material also increases.
Diffusion coefficient (D), which shows the ability of the water molecules to penetrate
inside the composites, was calculated using the following equation from the initial slope
of the plot of M
t
/M
m
against (time)
1/2
[33,34]:
M
t
M
m
¼
4
h
D

1=2
t
1=2
An example of such a plot for composites at 40
C is shown in Figure 4 and the values
obtained at different temperatures for all composites are summarized in Table 4.
The values obtained for diffusion coefficients are in agreement with the range of values
reported by other authors [6,13,29]. According to these reports the values for diffusion
0
0.2
0.4
0.6
0.8
1
1.2
0 500 1000 1500 2000 2500
Time
1/2
, (S
1/2
)
M
t
/M
m
0%
g
lass 5%
g
lass 10%
g
lass 15%
g
lass
Figure 4. Diffusion curve fitting plots for hemp fiber and hybrid composites at 40
C.
1878 S. PANTHAPULAKKAL AND M. SAIN
coefficient for natural fiber reinforced composites fall in the order of 10
8
–10
9
cm
2
/s.
Increase in immersion temperature increase the diffusion coefficient significantly and is as
expected for a process involving mobility of solvent molecules. This also indicated faster
diffusion rate and faster attainment of equilibrium water uptake with increase in
temperature. It was observed that at each temperature, though the incorporation of 5 wt%
glass fiber did not change the diffusion coefficient, further inclusion of glass fiber content
decreased the diffusion coefficient. However, at high temperature, 80
C, there is no change
in the diffusion coefficient even with a high amount of glass fiber content. At high
temperatures, the temperature dependant diffusion is more significant and may overcome
the moisture resistance offered by glass fiber.
Effect of Water Absorption on the Tensile Properties
To study the effect of water absorption on the tensile properties, tensile tests were
performed on wet samples after the saturation level (3624 h) is reached. Tensile strength
and modulus of PP, hemp/glass fiber hybrid composite before and after aging, as a
function of glass fiber content is shown in Figures 5 and 6. Tensile strength and stiffness of
virgin PP remain unaltered even after prolonged immersion in water, whereas aging
resulted in a considerable reduction of the strength and the stiffness of all the composite
samples. The percentage reduction in the strength and the stiffness of PP and composites
A–D is given in Table 5. The reduction in the strength and the stiffness is attributed to the
changes occurring in the fibers, and the interface between the matrix and the fiber, as there
is no significant effect on the properties of PP matrix after aging. Swelling of natural fiber
as a result of prolonged exposure to water leads to the reduction in the stiffness of the
fibers and also resulted in the development of shear stress at the interface that causes
debonding of the fibers from the matrix. The loss in the strength (35%) and the modulus
(57%) values of the hemp fiber composites after aging are believed to be the inability of the
swelled natural fiber to carry the stress transferred from the matrix through the disrupted
interface as a result of water absorption. Despite the reduction in the equilibrium moisture
content in hybrid composites, glass fibers did not alter the degradation of the hemp fiber
composites. The percentage reduction in the strength and modulus of the hybrid
composites is found to be 40% and 47% respectively. The observed percentage retention
in the modulus of the hybrid composites is higher than that of natural fiber composites.
This indicates that reduction in the strength of the composites may be mainly due to the
interfacial degradation of the fibers and the matrix. This is contrary to the earlier studies
Table 4. Diffusion coefficients of hemp fiber composites with different glass
fiber content at different temperatures.
Content of glass fiber,
Diffusion coefficient at different temperatures, DT10
8
cm
2
/s
wt% 40
C60
C80
C
0 1.11 2.27 4.45
5 1.12 2.28 5.12
10 0.87 2.24 4.39
15 0.79 1.78 4.32
Short Hemp–Glass Fiber Hybrid PP Composites 1879
reported where incorporation of glass fiber decrease the degradation of natural fiber
composites [16,18]. Thwe and Liao [16] found that water absorption of 30% bamboo fiber
reinforced composites resulted in a strength reduction of 6.84% and 11.55% respectively
after 520 and 1200 h where that of a composite with 20% bamboo and 10% glass fiber
showed only 5.62 and 8.9% reduction in strength for the same period of time.
The plausible explanation for the observed deviation of the results may be the degradation
20
40
60
PPABCD
Glass fiber content (%)
Tensile strength (MPa)
Before aging Wet samples Redried samples
Figure 5. Tensile strength of PP and hemp/glass fiber hybrid composites before and after aging.
0
1
2
3
4
5
PP A DCB
Glass fiber content (%)
Tensile modulus (GPa)
Before aging Wet samples Re-dried samples
Figure 6. Tensile modulus of PP and hemp/glass fiber hybrid composites before and after aging.
1880 S. PANTHAPULAKKAL AND M. SAIN
of natural fiber coupled with the stress corrosion of glass fiber even in the absence of stress
(it has been reported that stress corrosion of glass fibers results in the strength
degradation [35]) and the associated degradation of the fiber–matrix interface as a result of
a prolonged period (3624 h) of immersion of composites in water. The moisture absorption
and the degradation of mechanical properties depend on the amount of fiber content and
period of immersion, and hence the resultant changes in the properties also differ from
earlier reports.
In order to investigate the extent of deterioration in the strength properties, the wet
samples that have been subjected to water absorption were re-dried and tensile tests
performed. The strength and the modulus values (Figures 5 and 6) showed that the tensile
properties were not fully recovered; however, the percentage retention in the re-dried state
is relatively much higher compared to wet samples. This indicates that aging in natural
fiber and its hybrid composites cannot be considered as a physical process where
water acts as a plasticizer and removal of water leads to almost complete recovery of the
properties [36]. In natural fiber composites, prolonged interaction with water may result
in an irreversible or permanent damage to the fiber and the fiber matrix interface and
hence to the composites.
CONCLUSIONS
Investigation in to the water absorption properties of hemp/glass fiber hybrid PP
composites as a function of glass fiber content showed that resistance to moisture diffusion
to the composites was increased with hybridization with glass fibers. Under the present
conditions, all the composites followed the predictions of Fick’s law, where the amount
of water absorbed increases linearly with square root of time and gradually levels off after
saturation level is reached; however there is a small deviation at high temperature.
Maximum moisture content in the composite decreased with the incorporation of glass
fibers and remained more or less the same with the temperature. The calculated diffusion
coefficient of the composites was found to be dependant on the temperature and glass fiber
content. Nevertheless, at high temperatures, diffusion coefficient is almost independent
of the glass fiber content. Water absorbed by the composite had a detrimental effect
on the tensile strength and the modulus of both hemp fiber and hybrid fiber composites.
Tensile strength of the re-dried aged samples indicated a permanent damage to the fiber
and/or interface and hence to the composites. The results indicated that long term aging
in water decrease the strength properties of the composites, irrespective of the hybrid
nature of the composites.
Table 5. Percentage retention in tensile strength and modulus of PP and composites A-D
after aging and re-drying.
Retention of tensile strength (%) Retention of tensile modulus, (%)
Sample designation Wet sample Re-dried sample Wet sample Re-dried sample
PP 99.3 99.3 92.3 97.8
A 64.8 77.8 43.5 65.8
B 64.8 77.4 43.4 70.6
C 60.3 70.0 48 71.5
D 59.7 65.4 52.7 77.5
Short Hemp–Glass Fiber Hybrid PP Composites 1881
ACKNOWLEDGMENTS
The Authors would like to acknowledge NCE Auto 21, Arkema, Canada and Hempline
Canada for the financial and in-kind assistance of this project. Technical help from Shiang
Law is also greatly acknowledged.
REFERENCES
1. Woodhams, R.T, Thomas, G. and Rodgers, D.K. (1984). Wood Fibres as Reinforcing Fillers
for Polyoefins, Poly. Eng. Sci., 24: 1166–1171.
2. Bledzki, A.K, and Gassan, J. (1999). Composites Reinforced with Cellulose Based Fibers,
Prog. Polym. Sci., 24(2): 221–274.
3. Sain, M., Law, S., Suhara, F. and Boullioux, A. (2005). Interface Modification and
Mechanical Properties of Natural Fibre Polyolefin Composite Products, J. Reinf. Plast.
Comp., 24(2): 121–130.
4. Balatinecz, J.J. and Park, B.D. (1997). The Effects of Temperature and Moisture
on the Properties of Wood Fiber Thermoplastic Composites, J. Thermoplast. Comp. Mater.,
10: 476–487.
5. George, J., Bhagawan, S.S. and Thomas, S. (1998). Effect of Environment on the Properties
of Low-density Polyethylene Composites Reinforced with Pineapple Leaf Fiber, Comp. Sci.
Technol., 58: 1471–1485.
6. Marcovich, N.E., Reboredo, M.M. and Aranguren, M.I. (1999). Moisture Diffusion in Polyester
Wood Fiber Composites, Polymer, 40: 7313–7320.
7. Singh, B., Gupta, M. and Verma. A. (2000). The Durability of Jute Fiber Reinforced Phenolic
Composites, Comp. Sci. Technol., 60(4): 581–589.
8. Stamboulis, A., Baillie, C.A., Garkhail, S.K., Van Melick, H.G.H, and Peijs, T. (2000).
Environmental Durability of Flax Fibers and their Composites Based on PP Matrix, Appl.
Comp. Mater., 7: 273–294.
9. Joseph, P.V., Rabello, M.S., Mattoso, L.H.C., Joseph, K. and Thomas, S. (2002).
Environmental Effects on the Degradation Behaviour of Sisal Fiber Reinforced
Polypropylene Composites, Comp. Sci. Techol., 62: 1357–1372.
10. Lin, Q., Zhou, X. and Dai G. (2002). Effect of Hydrothermal Aging and Environment on
Moisture Absorption and Mechanical Properties of Wood Flour Filled Polypropylene
Composites, J Appl. Polym. Sci., 85(14): 2824–2832.
11. Manikandan Nair, K.C. and Thomas, S. (2003). Effect of Aging on the Mechanical
Properties of Short Sisal Fiber Reinforced Polystyrene Composites, J. Thermoplast. Comp.
Mater., 15: 249–271.
12. Tajvidi, M. and Ebrahimi, G. (2003). Water Uptake and Mechanical Characteristics of Natural
Filler Polypropylene Composites, J. Appl. Polym. Sci., 88: 941–946.
13. Espert, A., Vilaplana, F. and Karlsson, S. (2004). Comparison of Water Absorption in
Natural Cellulosic Fibers from Wood and One Year Crops in Polypropylene Composites and
its Influence on their Mechanical Properties, Comp. Part A, 35: 1267–1276.
14. Arbelaiz, A., Fernandez, B., Ramos, J.A., Retegi, A., Liano-Ponte, R. and Mondragon, I.
(2005). Mechanical Properties of Short Flax Fiber Bundle Polypropylene Composites: Influence
of Fiber Matrix Modification, Fiber Content, Water Uptake and Recycling, Comp. Sci.
Technol., 65: 1582–1592.
15. Rozman, H.D., Tay, G.S., Kumar, R.N., Abusamah, A., Ismail, H. and Mohd.Ishak, Z.A.
(2001). Polypropylene Oil Palm Empty Fruit Bunch Glass Fiber Hybrid Composites:
a Preliminary Study on the Flexural and Tensile Properties, Europ. Polym. J., 37: 1283–1291.
16. Thwe, M.M. and Liao, K. (2002). Effects of Environmental Aging on the Mechanical
Properties of Bamboo–Glass Fiber Reinforced Polymer Matrix Hybrid Composites, Comp.
Part. A, 33: 43–52.
1882 S. PANTHAPULAKKAL AND M. SAIN
17. Sreekala, M.S., George, J., Kumaran, M.G. and Thomas, S. (2002). The Mechanical
Performance of Hybrid Phenol–Formaldehyde Based Composites Reinforced with Glass and
Oil Palm Fibers, Comp. Sci. Technol., 62: 339–353.
18. Mishra, S., Mohanty, A.K., Drzal, L.T., Misra, M., Parija, S., Nayak, S.K. and Tripathy, S.S.
(2003). Studies on Mechanical Performance of Biofiber/Glass Reinforced Polyester Hybrid
Composites, Comp. Sci. Technol., 63: 1377–1385.
19. Williams, G.I. and Wool, R.P. (2000). Composites from Natural Fibers and Soy Oil Resins,
Appl. Comp. Mater., 7: 421–432.
20. Se
`
be, G., Cetin, N.S., Hill, C.A.S. and Hughes, M. (2000). RTM Hemp Fibre-reinforced
Polyester Composites, Appl. Comp. Mater., 7: 341–349.
21. Pervaiz, M. and Sain, M.M. (2003). Sheet Molded Polyolefin Natural Fiber Composites
for Automotive Applications, Macromol. Mater. Eng., 288 : 553–557.
22. Bledzki, A.K., Fink, H.P. and Speecht, K. (2004). Unidirectional Hemp and Flax EP- and
PP-Composites: Influence of Defined Fiber Treatments, J. Appl. Polym. Sci., 93: 2150–2156.
23. Rouison, D., Sain, M. and Couturier, M. (2004). The Effect of Surface Modification on the
Mechanical Properties of Hemp Fiber/Polyester Composites, SAE World Congress and
Exposition, SAE Paper No. 2004-01-0728.
24. Mohanty, A.K., Wibowo, A., Misra, M. and Drzal, L.T. (2004). Effect of Process Engineering
on the Performance of Natural Fiber reinforced cellulose acetate biocomposites, Comp. Part A,
35: 363–370.
25. Behzad, T. and Sain, M. (2005). Cure Simulation of Hemp Fiber Acrylic Based Composites
During Sheet Molding Process, Polym. Polym. Comp., 13(3): 235–244.
26. Mehta, G., Drzal, L.T., Mohanty, A.K. and Misra, M. (2006). Effect of Fiber Surface
Treatment on the Properties of Biocomposites from Nonwoven Industrial Hemp Fiber Mats and
Unsaturated Polyester Resin, J. Appl. Polym. Sci., 99: 1055–1068.
27. Mishra, S. and Naik, J.B. (1998). Absorption of Water at Ambient Temperature and Steam
in Wood–Polymer Composites Prepared from Agrowaste and Polystyrene, J. Appl. Polym. Sci.,
68: 681–686.
28. Mishra, S., Naik, J.B. and Patil, Y.P. (2004). Studies on Swelling Properties of Wood/Polymer
Composites Based on Agro-waste and Novolac, Advances in Polym. Technol., 23: 46–50.
29. Rouison, D., Couturier, M., Sain, M., MacMillan, B. and Balcom, B.J. (2005). Water
Absorption of Hemp Fiber/Unsaturated Polyester Composites, Polym. Comp., 26: 509–525.
30. Panthapulakkal, S. and Sain, M. (In Press). Injection Molded Short Hemp Fiber/Glass
Fiber Reinforced Polypropylene Composites–Mechanical, Water Absorption, and Thermal
Properties, J. Appl. Polym. Sci.
31. Zhou, J. and Lucas, J.P. (1995). The Effects of Water Environment on Anomalous Absorption
Behaviour in Graphite/Epoxy Composites, Comp. Sci. Technol., 53: 57–64.
32. Loos, A.C. and Springer, G.S. (1981). Moisture Absorption of Polyester E –glass Composites,
Environmental Effects on Composite Materials. 51–62, Technomic Publishing Co. Inc., CT, USA.
33. Crank, J. (1956). Mathematics of Diffusion, p-347, Oxford University Press, Oxford.
34. Comyn, J. (1985). Polymer Permeability, p-383, Elsevier Applied Science Publishers.
35. Metcalfe, AG. and Schmitz, G.K. (1972). Mechanism of Stress Corrosion in E-glass Filaments,
Glass Technol., 12(1): 15–23.
36. Mohd Ishak, Z.A. and Lim, N.C. (1994). Effect of Moisture Absorption on Tensile Properties
of Short Glass Fiber Reinforced (Polybutylene Terephthalate), Polym. Eng. Sci., 34: 1645–1655.
Short Hemp–Glass Fiber Hybrid PP Composites
1883
... It was reported by Mard et al. [82] that higher the fiber loading, greater was the % moisture absorbed by the composites for a wood particle reinforced high density PE matrix system. Panthapullakal and Sain et al. fabricated 40 wt.% hemp/glass fiber reinforced PP hybrid composites and reported that hybridization of glass fiber to the composite system reduced the water absorption behavior significantly [83]. Also, Akil et al. [84] used three different mediums such as distilled water, sea water and acidic mediums for studying the moisture absorption behavior of the jute reinforced polyester composites. ...
... To develop an excellent interfacial adhesion, the surface of the NF must be chemically active and interact with the other functional groups of the polymer matrix.In this regard, Ti3C2 Mxene nano sheet bounded to aromatic polyamide (AF) were reinforced in the PP matrix to fabricate composites. Both Ti3C2 and AF were etched with hydrofluoric acid and phosphoric acid before bounding to each other[83]. In another study, Maity et al.[84] used fluorinated AF for reinforcing PP and reported increased mechanical and thermalproperties of the composites after using fluorinated AF as reinforcement. ...
Thesis
In almost every industrial sector, advances in processing and applications of composite materials have grown significantly in the last decade. Conventionally, polymer composites are reinforced with synthetic carbon and glass fibers and often used in making structural and semi-structural components. Although, lower density and high strength to weight ratio of carbon fiber always offers an edge over glass fibers as a reinforcing material, but at the same time production of these carbon fibers creates huge amount of carbon footprint and green house gaseous emissions. Additionally, most of the carbon fiber is reinforced with the thermoset epoxy matrix which is hard to recycle, and hence, makes thermoplastics such as polypropylene (PP) as a matrix of choice. The Paris agreement in 2016, and many directives such as the EU end of-life-vehicle directives, are directed towards reducing vehicle weight and introducing recyclability in vehicles. Composite fabrication techniques and tailoring of their various properties has paved a long way in the last few decades. However, most significant advancement lately in the composite industry has been the reinforcement of the polymeric matrix with environment friendly natural fibers for the fabrication of composites. These composites offer high strength-to-weight ratio, easy processability and multi functionality over the traditional glass, carbon or aramid fiber reinforced polymeric composites. Presently, these composites are employed in automotive, aircraft, defence sector, sports packaging, etc. However, with the evolution of emerging sector like EVs (electrical vehicles) and various rules and regulation imposed by government to reduce carbon emissions, these composites may become a game changer in automotive industry. These composites offer strength, reduced weight and sustainability due to the presence of natural fibers. Another possible approach towards the sustainable development is the use of reinforcements such as recycled aramid and nylon fiber into the polymeric matrix. To meet the aforementioned sustainability and product performance objectives, use of naturally occurring sisal fiber reinforced PP composites could be best suited for this task. Property issues like moisture absorption and low impact strength can be tailored further in a sustainable way through hybridization with particulate fillers such as fly ash. To add to the variety of the development of performance composites that are sustainable, basalt fiber apart from natural fiber, which is an inorganic fiber with glass-like chemical composition and also of natural origin, can be considered as another suitable option. Likewise, recycled nylon/aramid fibers can also be used for the reinforcement purpose, since these are used in abundant amounts in the packaging industry. The presented thesis is thus an attempt to develop PP based sustainable hybrid composites with novel formulations and tailored properties using sisal, basalt and recycled nylon fibers that would excellently meet the industrial requirements. The thesis is organised in a way to lead to a step-by-step development of a sustainable composite with improved tensile, flexural, and impact properties by hybridizing fly ash (waste from power plants) with sisal fiber reinforced PP. As a first step, impact strength of the PP was first optimized by blending it with PP-g-MA, SEBS and SEBS-g-MA in an appropriate formulation content. Then, the optimal blend consisting of PP, SEBS and SEBS-g-MA with demonstrated superior impact strength was selected as the base matrix for the reinforcement of various filler/reinforcements. In the later stage, alkali-treated sisal fiber was reinforced into the base matrix and the one with optimum mechanical properties was selected for the hybridization with the silane treated fly ash. A positive hybridization of the silane treated fly ash was observed from an evident enhancement in the impact property of the composites. Though, a very insignificant increment in the tensile and flexural properties of the composites was observed, the hybrid composites with 5 wt.% fly ash and 25 wt.% sisal fiber in base matrix demonstrated the highest tensile and flexural properties among all formulated composites. Since interfacial interactions play an important role in transferring the load from matrix to reinforcement, another dedicated chapter focuses on this aspect through description of the various treatment/hybridization techniques for the fly ash. Fly ash, under high energy ball milling and treatment with cetylammonium bromide, reported excellent interactions with the base matrix compared to silane treated fly ash. Hence, another chapter shares the investigation expressing benefits of CTAB treatment of fly ash and hybridization with sisal fiber to achieve excellent mechanical properties. Likewise, for stronger structural and other high temperature applications, replacement of sisal fiber with the basalt fiber is proposed in the subsequent chapter and the evaluated performance properties like mechanical, thermal, and thermomechanical presented. A step towards a greener composite was examined further by reinforcing NaOH, CaCl2, silane treated and recycled nylon fiber in the base matrix and evaluating the properties of recycled composite. Most importantly, all the composites fabricated in the current study used micro/nano- structured fly ash as a hybridizing filler with pre-treated sisal, basalt and nylon fibers separately. Finally, the thesis concludes on a positive note of accomplishing the major objectives of the thesis and also recommends the potential use of such formulated hybrid composites and surface modification techniques to a broader field and applied areas of composite science and technology.
... It is determined by the filler dispersion in the polymer matrix, fiber distribution, fiber adherence to the matrix, fiber contact area, reinforcement high load-bearing behavior, fiber origin, surface treatment (physical or chemical), and stacking sequence. Through experimental studies, most researchers reported that strength enhancement depends on fiber loading, treatment, aspect ratio, and contact area [151][152][153]. Due to hybrid composites' enhanced strength and land-bearing capacity, they are used in many automotive applications such as car interior components and door panels. ...
... Panthapulakkal and Sain [153] analyzed the impact of the water absorption of hemp fiber composites on tensile strength. They found that the inclusion of glass fiber in the hemp composite increased the tensile properties. ...
... It is determined by the filler dispersion in the polymer matrix, fiber distribution, fiber adherence to the matrix, fiber contact area, reinforcement high load-bearing behavior, fiber origin, surface treatment (physical or chemical), and stacking sequence. Through experimental studies, most researchers reported that strength enhancement depends on fiber loading, treatment, aspect ratio, and contact area [151][152][153]. Due to hybrid composites' enhanced strength and land-bearing capacity, they are used in many automotive applications such as car interior components and door panels. ...
... Panthapulakkal and Sain [153] analyzed the impact of the water absorption of hemp fiber composites on tensile strength. They found that the inclusion of glass fiber in the hemp composite increased the tensile properties. ...
Article
Full-text available
The main objective of this study is to examine the impact of reinforcements on the strength of natural fiber composites. Recent advancements in natural fiber composites have minimized the usage of man-made fibers, especially in the field of structural applications such as aircraft stiffeners and rotor blades. However, large variations in the strength and modulus of natural fiber degrade the properties of the composites and lower the safety level of the structures under dynamic load. Without compromising the safety of the composite structure, it is significant to enrich the strength and modulus of natural fiber reinforcement for real-time applications. The strength and durability of natural fiber can be enriched by reinforcing natural fiber. The reinforcement effect on natural fiber in their woven, braided, and knit forms enhances their structural properties. It improves the properties of natural fiber composites related to reinforcement with short and random-orientation fibers. The article also reviews the effect of the hybridization of natural fiber with cellulosic fiber, synthetic fiber, and intra-ply hybridization on its mechanical properties, dynamic mechanical properties, and free vibration characteristics, which are important for predicting the life and performance of natural fiber composites for weight-sensitive applications under dynamic load. Keywords: natural fiber composite; woven natural fiber; orientation; mechanical; dynamic mechanical; vibration
... The composites showed similar water absorption curves for the entire immersion period. Therefore, the water absorption percentages were considered to be consistent with Fickian diffusion [94][95][96]. Moreover, it shows that SD played a profound role on the water absorption behaviour of samples, that is, the water absorption increased with the increase of SD content, which is also consistent with the studies reported by other researchers [6,[97][98][99][100][101][102]. ...
Article
Full-text available
In recent years, composites consisting of polymers and cellulosic materials have attracted increasing research attention. Polypropylene (PP) is among the most common polymer types found in excavated waste from landfills. Moreover, wood waste generated from wood products manufacturing such as sawdust (SD) offers a good potential for the fabrication of composite materials, and it is readily available in the environment. In this paper, wood polymer composites (WPC) consisting of recycled PP (rPP) and (SD) were prepared and characterised. A range of mechanical properties, including tensile strength, flexural properties, creep and hardness were studied, along with morphology, thermal properties, water degradation and contact angle. The results showed that the mechanical and thermal properties of rPP increased with an increase in 40 wt% of the SD content. Furthermore, the SD content significantly influenced the water uptake of the composites. Time–temperature superposition (TTS) was applied to predict the long-term mechanical performance from short-term accelerated creep tests at a range of elevated temperatures. The short-term creep test showed efficient homogeneity between the fillers and matrix with increasing temperature. The produced wood polymer composites displayed a comparable physical property to virgin polymer and wood and could potentially be used for various structural materials.
... The water absorption curves of RPW-RWW composites are shown in Figure 8a. Figure 8b shows the images of WPCs immersed in water. It can be observed that the water absorption rate increased rapidly in the first few days and it slowed down after 8 days [52][53][54]. The water absorption process continued with the prolonged immersion until the specimen reached saturation after 20 days. ...
Article
Full-text available
The depletion of natural resources due to the aggressive industrialization in the last decades has brought considerable attention to research aimed at developing green and sustainable products using eco-friendly materials. The purpose of the current study was to develop wood polymer composites (WPCs) using recycled plastic waste (RPW) generated from university laboratories and recycled wood waste (RWW) from construction and demolition (C&D) activities by melt-blending technique. The WPCs were characterised for their mechanical and thermal properties, as well as water uptake and morphology. The SEM micrograph indicated good interaction between RWW and RPW matrix. The mechanical strength of the WPCs was found to increase from 26.59 to 34.30 MPa, with an increase of the RWW content in the matrix. The thermal stability was higher in the composite with a higher percentage of RWW in the matrix. The wettability results indicated that the composite with a higher RWW (20%) had a higher water uptake. These results suggest that the produced WPCs can be a promising environmental-friendly material, while maintaining good mechanical, thermal, and wettability properties.
Article
This paper evaluated the effect of water adsorption on the tensile characteristics of hybrid aramid/glass/epoxy composites. The composite samples ([G6]S, [A6]S, [G3A3]S, [A3G3]S immersed in hydrothermal aging conditions (distilled water at 25°C, distilled water at 70°C, seawater at 25°C, seawater at 70°C) for 1000 h. The kinetic diffusion parameters of hybrid and plain specimens were evaluated experimentally and theoretically. Further, the effects of the stacking sequence of fabrics, seawater/distilled water aging, and temperature on the tensile behavior of dry, wet, and re-dried specimens were systematically discussed. At the end of the test, SEM images were obtained from the surfaces of the broken samples. Water gain plots for various conditions displayed that the samples absorbed more water when the aramid fabrics were on the outer surface of the hybrid composites. The hydrothermal aging significantly decreased the tensile strength of hybrid aramid/glass/epoxy and plain glass/epoxy composites. The tensile strength decrease rate of samples immersed in distilled water was higher than in seawater. Besides, the re-drying process induced more tensile strength degradation for both water types. SEM results showed that delaminations increased with aging and increasing temperature.
Article
The building sector is one of the most dynamic in terms of energy consumption, consuming about 40% of the world’s energy. This same sector is also responsible for about 1/3 of the world’s greenhouse gas emissions. In recent years, the adoption of composite materials, particularly those strengthened through the use of natural fibers is growing in all areas. This increase is the direct result of the important performances offered by these materials and that includes lightness, thermal, and acoustic insulation along with respect for the environment. This led to the integration of materials, such as bio composites or bio sandwiches, into various building structures constructions relating to civil engineering. However, numerous researches related to bio composites showed the need to explore them further particularly concerning the issue of moisture absorption as the presence of water affects the behavior of plant fibers both in terms of swelling and degradation. It is within this context that the present study focuses on modeling the water absorption behavior of bio sandwich materials having an agglomerated cork core associated with fibers extracted from the plant Quercussuber L. Fick’s law and Artificial Neural Network (ANN) are applied to model the experimental results pertaining to this absorption behavior. The experimental investigation starts by placing the original samples in tank filled with distilled water at an ambient temperature of 25°C. Mass samples are later and periodically taken on specimen with cork core having different thicknesses (5, 10, and 20 mm) as well as on laminated skin sandwiches made of short flax fibers until saturation that lasted around 25 days. The two Fick’s diffusion characteristic parameters represented by the mass gain at saturation (Mm) and the diffusion coefficient (D) were determined analytically and water absorption kinetics behavior was recorded and later compared to the curves predicted by Fick’s laws. Statistical processing of the results was carried out through the application of the analysis of variance ANOVA.
Article
Natural fibres as reinforcement for composite materials have witnessed a resurgence of interest in the past few years, largely due to ecological concerns, legislative directives and technological advancements. Hemp is one of the most popular natural fibres used as reinforcement in polymers owing to its superior mechanical properties. At present, hemp fibres have attracted the global interest of design engineers for developing composites having extensive applications in automobiles, electrical, construction and packaging industries. Although several literatures explore different aspects of hemp fibre reinforced composites, there is no proper literature that summarizes the surface treatment, processing techniques, mechanical performance and hybridization of hemp fibre composites. This review is envisioned to put forth a comprehensive summary of the research work published in the field of hemp fibre reinforced composites with special reference to the structure of hemp fibres, different methods for surface modification and processing techniques to fabricate the composites based on thermoplastic, thermoset and biopolymers. The paper also focuses on the effects of surface treatment on the mechanical performance of the composites.
Article
Full-text available
In the present study, a new environmentally friendly thermoset resin was used to manufacture hemp fiber acrylic composites by sheet molding process for automotive applications. A finite difference method was applied to predict the cure behavior and temperature variation of hemp fiber acrylic based composites during the process. Dynamic Differential Scanning Calorimetry (DSC) was employed to determine the kinetic parameters for the curing reaction at different heating rates. It was found the experimental and predicted values are in good agreement at the lower heating rate. The thermophysical properties of the resin, fiber and composite were obtained to use in the model. The temperature profile and the degree of cure of the composite with 40% resin and 60% fiber were simulated and a comparison of numerical results with known experimental data confirms the approximate validity of the model.
Article
Eco-friendly green/biocomposites were fabricated from chopped hemp fiber and cellulose ester biodegradable plastic through two process engineering approaches: powder impregnation through compression molding (process I) and extrusion followed by injection molding (process II). Cellulose ester, e.g. cellulose acetate (CA) plasticized with 30 wt% citrate plasticizer (CAP) was used as the matrix polymer for biocomposite fabrication. Intimate mixing due to shear forces experienced in process II produced superior strength biocomposites over their counterparts made using process I. Biocomposite fabricated through process II containing 30 wt% hemp natural fiber showed an improvement of storage modulus by 150% over the virgin matrix polymer. The coefficient of thermal expansion of the said biocomposite decreased from the CAP polymer by 60% whereas the heat deflection temperature improved by 30% versus the virgin bioplastic, indicating superior thermal behavior of the biocomposite. Plasticized cellulose acetate is proved to be much better matrix than non-polar polypropylene (PP) for hemp fiber (HF) reinforcements because of the better interaction of polar cellulose ester with the polar natural fiber. Fabricated through process II and with same content of hemp (30 wt%) the CAP-HF based biocomposite exhibited flexural strength of 78 MPa and modulus of elasticity of 5.6 GPa as contrast to 55 MPa and 3.7 GPa for the corresponding PP-HF based composite. The experimental findings of tensile modulus of the biocomposites are compared with the theoretical modulus using the rule of mixture. The fiber-matrix adhesion is evaluated through environmental scanning electron microscopy studies.
Conference Paper
In this work hemp fibers were chemically treated in order to improve the fiber/matrix interaction in hemp fiber/unsaturated polyester composites prepared by a Resin Transfer Molding (RTM) process. Chemicals used for paper sizing (AKD, ASA, Rosin Acid and SMA) as well as a silane compound and sodium hydroxide were used to modify the fibers' surface. The tensile, flexural and impact properties of the resulting materials were measured. A slight improvement in mechanical properties was observed for the SMA, silane and alkali treated specimens. However close analysis of these tests and of the fracture surface of the samples showed that there was no amelioration of the fiber/matrix adhesion. It was found that predicted tensile strengths using the rule of mixture were very close to the experimental values obtained in this work. Finally the properties of an hybrid glass fiber/hemp fiber composite were found to be very promising
Article
Wood-fiber thermoplastic composites were prepared with polypropylene (PP) and high-density polyethylene (HDPE) matrix resins employing high shear thermokinetic compounding for fiber dispersion. Wood fibers obtained from recycled newspapers were mixed with the matrix polymers at a level of 30% by weight. In one experiment, sets of six samples were immersed in boiling water for up to 48 hours and subsequently tested for mechanical properties and water absorption. In another experiment, samples were exposed to -40'C, -20'C, 00C, 230C, 40'C and 60'C for two hours and then tested at the same temperatures for tensile and flexural properties. Results showed that immersion in boiling water resulted in water absorption of between 3 and 5%, a decrease in tensile and flexural properties, and an increase in impact strength. When the composites were exposed to various temperatures, both strength and modulus decreased significantly with increasing temperatures above ambient (23°C) level for both PPand HDPE-based composites. The opposite trend was evidenced below freezing.
Article
Natural fibers are potentially a high-performance and non-abrasive reinforcing fiber source. In this study, mechanical properties of polypropylene (PP) composites with various natural fibers such as old newsprint, kraft pulp and hemp were studied. The effect of a low-molecular weight, maleated type coupling agent, on the mechanical properties of these natural fiber-filled PP composites was also investigated and the results showed that this can be used as a good interface modifier for improving the strength properties of the PP-filled composites and the optimum level of the coupling agent was found to be around 3-4 percentage by weight of the composite. Kraft pulp and hemp fiber-filled composites showed better tensile, flexural and un-notched impact strength compared to the glass fiber-filled composites at the same fiber loading. Hybrid composite produced using 10 wt% of glass fiber and 30 wt% of hemp fiber showed only a marginal improvement in the mechanical properties.
Article
The water absorption behaviour and the effects of ageing on the mechanical properties of short sisal fibre reinforced polystyrene composites have been studied with special reference to fibre loading and fibre-matrix interface modification. The composites were subjected to different ageing conditions viz., immersion in boiling water for 24 h, immersion in cold water for 15 days and exposure to hot air at 80°C for five days. The interface modifications were performed by benzoylation, polystyrene maleic anhydride (PSMA) treatment, toluene diisocyanate treatment and silane treatment. The tensile properties and dimensions of the aged samples were measured and compared with unaged samples. The water uptake was found to increase with fibre loading and decrease with fibre modifications. However, PSMA treatment and silane treatment do not produce much variation in water uptake. The mechanical properties and dimensional stability of the treated fibre composites were found to be superior to those of untreated composites under identical ageing conditions. However, it is interesting to note that on water ageing, untreated fibre composites show minimum decrease in tensile strength compared to treated fibre composites and can be explained based on the thermal shrinkage of the polystyrene matrix. The superior properties of the treated composites were associated with the better interfacial interactions in treated fibre composites.
Article
The physical and mechanical properties of jute composites have been studied under various humidity, hydrothermal and weathering conditions. The aging-induced deteriorative effect of these conditions on the dimensional stability, surface topography and mechanical properties of the composites was observed. The severity of aging was more detrimental in an accelerated water test as compared to the other exposure conditions. SEM observation reveals the fibre accentuation along with fibre breakage/splitting and surface discoloration in both natural and accelerated weathering of UV exposure. Some biological defacement in the form of fungal infestation appeared at the cut edges of weathered composites while extensive disfigurement was noticed on all surfaces under high humidity/water-immersion. These results could be useful as an indicator for assessing the suitability of jute composites in damp and dry conditions.
Article
Environmentally beneficial composites can be made by replacing glass fibres with various types of cellulose fibres. Fibres from pine or eucalyptus wood and also one-year crops such as coir, sisal, etc. are all good candidates. The poor resistance towards water absorption is one of the drawbacks of natural fibres/polypropylene composites. New natural fibres/polypropylene composites were made and the water absorption in them was studied by immersion of the composites in water at three different temperatures, 23, 50 and 70 °C. The process of absorption of water was found to follow the kinetics and mechanisms described by Fick's theory. In addition, the diffusivity coefficient was dependent on the temperature as estimated by means of Arrhenius law. A decrease in tensile properties of the composites was demonstrated, showing a great loss in mechanical properties of the water-saturated samples compared to the dry samples. The morphology change was monitored by scanning electron microscopy studies of the samples before and after exposure to water and the devastating effect of water on the fibre structure was shown.