Propriedades acústicas de materiais compostos de borracha reciclada e fibras de poliéster oco de sete furos

Prévia do material em texto

JOURNAL OF
C O M P O S I T E
M AT E R I A L SArticle
Damping acoustic properties of reclaimed
rubber/seven-hole hollow polyester fibers
composite materials
Xiaoou Zhou1,2, Sheng Jang1, Xiong Yan1, Xueting Liu1 and
Li Li1
Abstract
A series of thin, low-cost and environment-friendly elastomeric composites consisting of reclaimed rubber, which is a
waste product of roller processing of textile mill and seven-hole hollow polyester fibers, were fabricated. In this study,
the damping property of the reclaimed rubber composites was tested in the dynamic mechanical thermal analyzer, the
sound absorption property was investigated using the impedance tube method, the morphology was characterized by
scanning electron micrographs and the mechanical property was measured by strength tester. The study concluded that
reclaimed rubber/seven-hole hollow polyester fibers elastomeric composites exhibited an exceptional damping perform-
ance with a broad temperature range, and that acoustical absorption of materials increased significantly with increasing
seven-hole hollow polyester fibers content. Meanwhile, reclaimed rubber/seven-hole hollow polyester fibers demon-
strated an acoustic property of 1 mm thickness and a mass ratio of 100/25, giving a sound absorption coefficient peak,
0.407 at 2500 Hz. The analysis also revealed that the mechanical properties of the composites improved significantly with
the increase of fibers. As an acoustical absorption material with high damping performance and a broad temperature
range, reclaimed rubber/seven-hole hollow polyester fibers composites have potential applications in fields of
engineering.
Keywords
Textile reclaimed rubber, seven-hole hollow polyester fibers, sound absorption property, damping property
Introduction
As a large producing country of rubber products,
which, at the same time, is in serious shortage of
rubber resources, China consumes most of the rubber
materials, creating a large number of rubber wastes
every year. The wastes may pose a serious threat to
the environment as they have stable three-dimensional
chemical network structure, which makes their melt-
down and dissolution almost impossible. It is therefore
necessary to improve or to develop a certain process or
applications for waste rubber. The common processing
of waste rubber mainly involves landfill, combustion
heat utilization and recycling. Due to their potential
threat to the environment, the first two processing
methods are prohibited in many countries.1,2 Only recy-
cling can reduce the pollution as well as make up for the
shortage of rubber resources. As a big country of
textile, China is very rich in textile waste resources.
The recycling of textile waste cannot only realize the
repetitive use of the resources but also reduce pollution.
As a newly emerging industry that features low cost and
high efficiency, it boasts broadprospects for development.
Every year a large number of old roller and leather
collars are to be scrapped in the textile factory. The
main components of those raw materials are nitrile
butadiene rubber (NBR) and polyvinyl chloride
(PVC). There are several ways to make use of recycling
particles. The most familiar method is to introduce a
small amount of recycling particles into the NBR and
1Key Laboratory of Textile Science and Technology, Ministry of Education,
College of Textiles, Donghua University, Shanghai, China
2Library of Donghua University, Shanghai, China
Corresponding author:
Xiong Yan, Key Laboratory of Textile Science and Technology, Ministry of
Education, College of Textiles, Donghua University, Shanghai, China.
Email: yaxi@dhu.edu.cn
Journal of Composite Materials
2014, Vol. 48(30) 3719–3726
! The Author(s) 2013
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DOI: 10.1177/0021998313513047
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PVC before they are made into rollers. But even a tiny
amount will affect the quality. Some people verified that
the mixing of recycling particles with a certain ratio of
concrete contributes to the improvement of the tenacity
and impact resistance of concrete materials, as well as
achievement of sound insulation properties.3–9
However it decreases the tensile strength yet and the
viscoelastic properties of rubber are invalid just as the
filler.10 In order to take full advantage of the reclaimed
rubber (R-Rubber) and make full use of its character-
istic, it is necessary to find a new way to treat and to
reuse it. Turning waste into treasure while endowing
the waste material with new features is a new highlight
of the textile R-Rubber application.
Recently, we have conducted an intensive study on
Chlorinated Polyethylene (CPE)/seven-hole hollow
polyester fibers (SHPF) composites and found that
the sound absorption performance and mechanical
properties of the material with mixed fiber is
improved.11 Based on previous research, a series of
new composites with the regenerative powder of textile
recycling rubber as the matrix filled with the SHPF
have been produced. This paper reports on their
damping properties, effective sound absorbing charac-
teristics as well as their strong mechanical properties
so as to illustrate the possibility of expanding the
application of textile R-Rubber to other fields.
Experimental
Material and sample preparation
The materials used for fiber reinforced rubber produc-
tion were reclaimed rubber (R-Rubber), which is a
waste product of roller processing of textile mill, with
the main components NBR and PVC, and SHPF, fine-
ness 10dtex and length 60mm, as the filler (Sinopec
Yizheng Chemical Fiber Company Limited, China).
After R-Rubber was kneaded with two-roller mill at
65�C for 20min, SHPF were added and mixed with
R-Rubber according to the different proportions. To
enhance the composite homogeneity, the mixture was
kneaded again. The sheeted mixtures were molten for
10min and then pressed at 140�C for 15min under
10MPa. Finally, samples were cooled at room tempera-
ture to obtain films with different thickness of 0.5mm,
1mm and 2mm.
Performance testing
Sound absorption properties of the composites were
assessed using a two-microphone transfer-function
method, according to ISO 10534-2 standards. The test-
ing apparatus was a part of a complete acoustic system
SW260 (BSWA Technique Company, China). A
middle-tube setup was employed to measure different
acoustical parameters in the range of 100–2500Hz
(Figure 1). At one end of the tube, a loudspeaker was
placed as a sound source and the test material was
placed at the opposite end to measure sound absorption
properties. Samples were placed into a measurement
tube using a machined aluminum rod (length 20mm
and diameter 60mm). Each set of the experiment was
repeated three times in order to have average
measurements.
Morphology studies of the composites were con-
ducted by using a JEOL JSM-5600LV series scanning
electron microscope (SEM). All the samples were
immersed in liquid nitrogen for 5min and then
broken. The fractured surfaces were sputter-coated
with gold before examination.
The mechanical properties of R-Rubber composites
were based on tensile testing for rubber, according
to GB/T528-92 using the fabric electronic strength instru-
ment HD026NE (Hongda Experimental Instrument,
China). Samples were cut into dog-bone shape.
Figure 1. Assembled diagram of measured sound absorption coefficient with an impedance tube.
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The sample length was 115mm and width 25mm, the
width of the narrow section being 6mm and the gage
length 25mm. The instrument was set at a speed of
500mm/min for testing.
Dynamic mechanical thermal analysis (DMA) of the
composites was conducted by using DMA 7 e analyzer
(Perkin Elmer company, America); 12mm� 4mm�
1.0mm dimension specimens wereused. The loss
factor of the composites was tested under the tensile
mode, with the heating rate 10/min, the frequency 1Hz.
Results and discussion
The dynamic mechanical properties of composites
Loss factor (tand) is the ratio of loss modulus (E’’) and
storage modulus (E’) for materials. It is one of the
important parameters to evaluate damping properties
and vibration energy dissipation ability.12 Figure 2
shows the temperature dependence of tand, storage
modulus (E’) and loss modulus (E’’) for R-Rubber/
SHPF composites with different SHPF content. As
shown in Figure 2(a), tand was going down gradually
with the fiber content increasing, the general trend was
moving toward the direction of high temperature. The
temperature at the tand peak of R-Rubber/SHPF with
the mass ratio 100/5 and 100/10 are the same as that of
the matrix, whereas the temperature with the mass
radio of 100/15, 100/20 and 100/25 remains much the
same, all higher than that the matrix. The tand �0.3
corresponding to the temperature range is the effective
damping area of the polymer damping material, and
high damping materials with wide temperature range
requires effective damping temperature range of at
least 60–80�C, such as R-Rubber, whose effective
damping area is from the 10�C to 90�C with the tand
peak of 0.641 at 34�C. With increasing SHPF content,
the temperature range of the material became gradually
narrower. Especially at higher concentration, the effect-
ive damping area of the composite with a mass ratio of
100/25 was from 18�C to 88�C while the tand was 0.42
to the peak at 50�C. It is also a kind of damping mater-
ial with wide effective functional area.
The damping performance of fiber reinforced com-
posites is mainly affected by the matrix. The addition of
the SHPF as a filling material diminishes the free
Figure 2. Temperature dependence on tand, storage modulus and loss modulus for R-Rubber/SHPF composites with different SHPF
content: (a) tand; (b) storage modulus and (c) loss modulus.
SHPF: hollow polyester fibers; R-Rubber: reclaimed rubber.
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volume of the polymer molecular chain, which, in
return, reduces the latter’s vitality. Besides, owing to
the alternating stress existing between fiber and
matrix surface, the composite consumes energy based
on shear mechanism of stress transmission mode,13,14
so the damping performance of the composite is smaller
than the matrix. In addition, the glass transition tem-
perature of the composite is related to the performance
of fiber. There are little changes in the microstructure of
the matrix as well as small influence on the molecular
chain motion when the fiber content is low, which
causes the glass transition temperature to be changed
scarcely. When the content of the fiber is increasing, the
free volume of the matrix is decreasing continually, and
the contact surface of the fiber and the matrix is
increased, which blocks the motion of the molecular
chain, so the glass transition temperature of the com-
posites with high content of fiber is higher than that of
the matrix.
As shown in Figure 2(b), the storage modulus of
composite material increased slightly with the fiber con-
tent increasing. The fibers act as the role of the filler in
materials. Moreover, it is noted that with increasing the
fiber content up to 100/20, the material remained at
higher storage modulus in the viscous flow state. The
main reason is that when the fiber content reaches crit-
ical value, fiber is cut through the process of mixing by
shear force of roller. At the same time, fiber networks
have been formed in matrix, which will be confirmed at
the section of composites’ micro morphology, there-
fore, the storage modulus is improved.
As shown in Figure 2(c), the loss modulus of
R-Rubber/SHPF composites increased slightly with
the fiber content increasing. The curve shape and vari-
ation trend of the composite was the same as pure
R-Rubber’s. The result demonstrates that the compos-
ite possesses better capability of energy dissipation, and
the fiber content has very little effect on the damping
temperature range. Meanwhile, the damping capacity
of material has been improved. In addition, it seems
to be contradicted with variation of the loss factor.
This is because tand is the ratio of loss modulus and
storage modulus. So when the loss modulus’ increase is
less than that of the storage modulus, although the
energy dissipation capacity has improved, the loss
factor expresses in falling.
Analysis of the composites’ micro morphology
As shown from SEM of micrographic surface (Figure
3(a)), the fiber was limited in the intersecting surface of
composites with mass ratio 100/5. There was less fiber
entanglements state in the composite fracture. The
result demonstrates that fiber networks have not
formed at lower levels of SHPF. However, it is obvious
that fibers were entangled in composite with mass ratio
100/25 (Figure 3(b)).This implies that there is a consid-
erable number of fiber network structures in the com-
posite. Besides, in the intersecting surface of the
composites with mass ratio 100/25 are noted many
holes formed due to fibers pulled out from the matrix.
It could be concluded that when the fiber content is
high, the viscosity of fiber and matrix is declining and
the damping values decrease. That is why tand lowers
gradually with the increasing fiber content, which is
consistent with the above analysis.
The acoustic performance of composites
As seen in Figure 4, neither the matrix nor the
R-Rubber/SHPF (100/5) was sound-absorbing due to
the fact that the sound absorption coefficient was below
0.2 at the frequency range from 100 to 2500Hz.
However, with increasing SHPF content, a remarkable
shift to the high-frequency direction in sound absorp-
tion properties could be observed. The sound
Figure 3. SEM of micrographic surface of R-Rubber/SHPF composites: (a) SEM of R-Rubber/SHPF (100/5) and (b) SEM of R-Rubber/
SHPF (100/25).
SHPF: hollow polyester fibers; R-Rubber: reclaimed rubber.
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absorption coefficient of the R-Rubber/SHPF compos-
ites with mass ratio 100/0, 100/5, 100/10, 100/15, 100/20
and 100/25 at 1800Hz was 0.095, 0.104, 0.145, 0.13,
0.146 and 0.138 and the sound absorption coefficient
at 2500Hz was 0.212, 0.23, 0.254, 0.3, 0.365 and 0.407.
The sound absorption property is positively corre-
lated with the damping property and the air content,
especially the flowing air content. As shown in Figure 2,
the tand peak was gradually descending with the fiber
increasing; on the other hand, the temperature corres-
ponding to tand peak was shifted to higher temperature
slightly. In theory, the sound absorption property
decreases together with the damping property. But in
practice, the reverse is true. This aberration indicates
that there are some other factors that influence acous-
tical absorption of R-Rubber/SHPF. Air was injected
into the composite by SHPF adding, which affected a
part of sound waves reflecting back. It also affected
another part of sound waves being refracted into the
interior of the composites as stress wave through dis-
turbing the inner particle, which made air compression
with the head conduction through the pore walls, and
finally the incident sound energy was consumed as heat.
As shown in Figure 5, the absorption curve was
directly correlated with SHPF content in the compos-
ites. The sound absorption peak was raised slowly as
the SHPF content was low. The result clearly demon-
strates that additional hollow structure units are
required for sound absorption. But the hollow struc-
ture units are limited, independent and closed, which
results in slow heat consumption, so that the increase
in the sound absorption properties of composites is
not significant. When thefiber content is increased
continually, especially R-Rubber/SHPF (100/25), the
critical number of hollow structure units affects
absorption property, with an incomplete network of
the hollow fibers in the composite. Fiber network
structure contributes to transfer and consumes heat
converted from the sound power. So the sound
absorption property of the composites is improved
in wide frequency domain.
As shown in Figure 6, sound absorption property
was improved by increasing thickness of the compos-
ites. The sound absorption property did not show sig-
nificant difference within the range of 100–1000Hz for
0.5mm, 1mm and 2mm slices. A possible explanation
is that little sound energy was converted into heat to
achieve energy consumption at low incident wave fre-
quency due to small vibration amplitude of interior air
and skeleton for the porous materials with certain rigid-
ity. As noted, the effect of thickness of the composites
on absorption coefficient is apparent when the fre-
quency was in the 1000–2500Hz range. According to
the model Rayleigh of the sound absorption mechan-
ism, material thickness enhances acoustical impedance
while the increase of the sound wave propagation dis-
tance in the materials improves the sound absorption
property.15 In addition, with the increase in sample
thickness, there are more hollow structure units and
fiber network structure elements, which play a positive
role in improving sound absorption property in med-
ium�high frequency.
Figure 4. Effect of SHPF content on the sound absorption performance of R-Rubber/SHPF composites.
SHPF: hollow polyester fibers; R-Rubber: reclaimed rubber.
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The mechanical property of the composites
In the view of the foregoing analysis about the sound
absorption property of composites R-Rubber/SHPF,
the composites with the mass ratio of R-Rubber/
SHPH 100/25 presented good sound absorption prop-
erty in each frequency range. At this time, the mechan-
ical property of the material has become one of the
main factors affecting the application of composite
material in engineering. As shown in Figure 7, the
mechanical property changed sharply with mixing
SHPF compared with the untreated R-Rubber com-
posed of pure elastomers. With increasing SHPF con-
tent, maximum tensile stress increased from 5.97 to
11MPa, while breaking strain reduced from 138.08%
to 44.12%. These observations demonstrated that the
rigidity and strength of the composites were signifi-
cantly enhanced by adding SHPF into the matrix,
Figure 6. Effect of thickness of R-Rubber/SHPF composites with 20% SHPF on the sound absorption property.
SHPF: hollow polyester fibers; R-Rubber: reclaimed rubber.
Figure 5. Effect of SHPF content on the sound absorption peak of composites.
SHPF: hollow polyester fibers; R-Rubber: reclaimed rubber.
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which laid the foundation for the applications of R-
Rubber/SHPF in acoustic field.
Conclusions
A series of thin, low-cost and environment-friendly
elastomeric composites consisting of R-Rubber was
produced and evaluated in terms of their damping prop-
erty, acoustic property as well as mechanical property.
The results show that R-Rubber/SHPF elastomeric
composites exhibited an exceptional damping perform-
ance with a broad temperature range. Meanwhile, the
SHPF content, thickness and cavity of R-Rubber/SHPF
composites had a significant influence on acoustic prop-
erties. The composite with mass ratio of R-Rubber/
SHPF (100/25) and 1mm thickness was noted, giving
a sound absorption coefficient peak, 0.407 at 2500Hz.
When the thickness of the composite including mass
ratio 100/20 was increased (0.5mm to 2mm), R-
Rubber/SHPF presented better sound absorption per-
formance at intermediate�low frequency.
The fiber content in R-Rubber/SHPF had significant
effects on the mechanical property of the composite.
The results show that maximum tensile strength of 1-
mm thick pure rubber was 5.97MPa, while the break-
ing elongation was 138.08%. In contrast, maximum
tensile strength increased to 11MPa with a breaking
elongation of 44.2% in R-Rubber/SHPF composite
with mass radio 25/100. Finally, based on the results
of this study, we believe that R-Rubber/SHPF compos-
ites are developed as a new high-damping acoustic
absorbing film material suitable for a wide temperature
range with additional effective mechanical properties.
Funding
This research received no specific grant from any funding
agency in the public, commercial, or not-for-profit sectors.
Conflict of Interest
None declared.
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