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Infrared and Raman spectroscopy of polypropylene

Authors:
  • SINTEF and University of South-Eastern Norway

Abstract

Vibrational spectroscopy is one of the most versatile methods of polymer characterization [1]. Other methods may be better in a certain area, but the advantage of vibrational spectroscopy is that it supplies several types of information, while being a rapid and inexpensive method. Infrared (IR) and Raman spectroscopy probe the vibrational spectrum by absorption and inelastic scattering, respectively. In many cases these two techniques are complementary. For a noncentrosymmetric molecule, such as isotactic PP (iPP) in a 31 helix, bands which are strong with one technique are often weak with the other. From a practical point of view, the requirements for sample preparation are different. IR spectroscopy, being an absorption method, is mostly performed on thin films in transmission mode. However, reflection methods or photoacoustic detection can be utilized to analyze thick or opaque samples, with a range of penetration depths. In principle, no sample preparation is required for Raman spectroscopy. Fluorescence has been a problem when analyzing polymers with this technique. However, this problem is almost eliminated with Fourier transform (FT) Raman instruments, which excite in the near infrared (NIR) range (∼4000-11000 cm-1) and analyze the scattered light in a modified FT-IR instrument.
Infrared and Raman spectrosc0py
of
polypropylene
Erik
Andreassen
GENERAL
Vibrational spectroscopy is one of the most versatile methods of polymer
characterization
[1].
Other methods
may
be
better
in
a certain area,
but
the advantage of vibrational spectroscopy is
that
it
supplies several types
of information, while being a
rapid
and
inexpensive method. Infrared
(IR)
and
Raman spectroscopy probe the vibrational spectrum
by
absorp-
tion
and
inelastic scattering, respectively.
In
many
cases these two
techniques are complementary. For a noncentrosymmetric molecule,
such as isotactic PP (iPP)
in
a 31 helix,
bands
which are strong
with
one
technique are often
weak
with
the other. From a practical point of view,
the requirements for sample preparation are different.
IR
spectroscopy,
being
an
absorption method, is mostly performed
on
thin films in
transmission mode. However, reflection methods
or
photoacoustic detec-
tion can
be
utilized to analyze thick
or
opaque samples,
with
a range of
penetration depths. In principle,
no
sample preparation is required for
Raman spectroscopy. Fluorescence has been a problem
when
analyzing
polymers
with
this technique. However, this problem is almost elimin-
ated
with
Fourier transform (Ff) Raman instruments, which excite
in
the
near infrared (NIR) range (
~
4000--11000
em -1)
and
analyze the scattered
light
in
a modified Ff-IR instrument.
The literature
on
IR
and
Raman spectroscopy applied to PP is
vast
[2].
It
goes from fundamental studies
in
polymer chemistry
and
physics to
applications, such ·as forensic analysis
and
identification systems for
Polypropylene:
An
A-Z
Reference
Edited
by
J.
Karger-Kocsis
Published
in
1999
by
Kl'lwer Publishers, Dordrecht. ISBN 0
412
80200 7
Configurations,
conformations,
chain
packing
and
structure 321
recycling processes. A range of specialties,
such
as surface analysis,
microspectroscopy, on-line analysis
and
diffusion studies, are repre-
sented. The following sections summarize the basic elements
in
spectro-
scopic characterization of
PP.
These methods extract information from
the vibrational spectra regarding molecular configurations, conforma-
tions
and
orientations, as well as deformation
and
degradation mech-
anisms.
CONFIGURATIONS, CONFORMATIONS,
CHAIN
PACKING
AND
LAMELLAR STRUCTURE
Vibrations
in
a polymer crystal can
be
excited
at
widely different levels,
ranging from dimensions corresponding to a
bond
length
up
to the
thickness of a lamella. There are
two
types of modes
in
a polymer
crystal: Lattice
modes
and
internal modes.
In
the former, whole chains
move relative to each other. However,
apart
from a few special cases,
vibrational spectroscopy only utilizes the internal modes,
with
molecular-level information. Internal modes can further be divided into
modes
with
h.igh
and
low
degrees of intramolecular coupling. The latter
type is
not
sensitive to the chemical environment of the active group.
Hence, the frequencies associated
with
such
'localized'
modes
(often
referred to as
group
frequencies) are roughly the same for different
molecules containing the same group.
The spectra of atactic
PP
(aPP)
and
iPP melts contain some well-
known
group
frequencies (involving
CH
2
and
CH
3 groups), while other
bands are
due
to coupled modes.
By
applying various theoretical
and
experimental methods, the distribution of conformations can
be
deduced
from these bands. Several additional
bands
appear
in
the spectrum of
iPP
in
the
solid state, especially
in
the 800--1200cm-1 range (Table 1).
These
bands
are attributed to the 31 helix, which is the regular conforma-
tion
in
all iPP polymorphs, as well as in the mesomorphic phase. Two
commonly
used
'helix
bands',
at
998
and
841
cm-1, only
appear
for helix
segments
with
at
least~
11
and
-14
repeat units, respectively. The
band
at
973cm-
1 is attributed to shorter helix segments,
and
is also observed
with iPP melts,
althoug!
with
reduced intensity
and
a small frequency
shift. For solid samples, it is sometimes resolved into
two
peaks, attrib-
uted to
amorphous
and
crystalline domains, respectively. With aPP, this
peak is usually only a shoulder.
Because the ability to form regular helices
depends
on
the degree of
isotacticity, the latter can
be
estimated indirectly using the helix bands.
Among the various
band
combinations
used
as isotacticity indices, the
peak area ratio A(998cm-1
)/A(973cm-
1) is
one
of the
most
common.
Raman
and
IR measures of
isotacti~_~ty
have been
shown
to correlate well
with direct measurements,
such
as
nuclear magnetic; resonance (NMR),
erik.andreassen@sintef.no
322
Infrared
and
Raman
spectroscopy
of
polypropylene
Table 1 The most
used
bands
in
the
vibrational
spectrum
of semicrystalline iPP
(based
on
[2]
with
some
modifications).
Note
that
the
actual frequencies
depend
on
factors such as
instrument
type, analysis
method
and
sample type.
Raman
Infrared
Main
active
group
vibrations
frequency
(cm-
1)
frequency
(cm-
1)
2956vvs vCH3 asym.
2952m 2953vvs
vCH
3 asym.
2920m 2921vvs
vCH
2 asym.
2905m 2907sh
vCH
2883s 2877vs
vCH
3 sym.
287lw
2869vs
vCH
2sym.
2840m 2840vs vCH2 sym.
1458vs 1460s
8C~
asym.,
8CH
2
1435w 1434m
8CH
3 asym.
1371sh 1370s
8CH
3 sym.,
mCH
2, 8CH,
vCCb
1360s 1357m 8CH3
sym
.,
8CH
1330vs 1326vw 8CH, -rCH2
1306vw 1305w
mCH
2
,TCH
2
1296vw 1296vw
mCH
2, 8CH, -rCH2
1257w 1255w 8CH,
TC~,
pCH3
1219s 1220vw
-rCH
2, 8CH,
vCCb
1167sh 1164m
vCCbl
pCH
31
8CH
1152vs 1154w
vCCb,
vC-CH3, 8CH, pCH3
1102w
llOlvw
vCCbl
pCH3
mCH
2, -rCH,
8CH
1040s 1045vw vC-CH3,
vCCb,
8CH
998m 998m pCH3, 8CH,
mCH
2
973s 973m pCH3,
vCCb
94lm
940vw pCH3,
vCCb
900m 900w pCH3, pCH2,
8CH
84lvs
841m pCH2,
vCCb,
vC-CH3, pCH3
809vs 809w pCH2,
vCCbJ
vC-CH3
530m 528w
mCH
2, vC-CH3, pCH2
458m 456vw
mCH
2
398s 396vvw
mCH
2
,8CH
321m 320vvw
mCH
2
252m 248vvw
mCH
2
,8CH
Abbreviations: b = backbone, m = medium, s = strong,
sh
= shoulder, v = very, w -
weak, 8 = bending, v = stretching, p = rocking, T = twisting, w = wagging.
and
calibration curves have been constructed.
It
is
important
that
the
samples have experienced the same solidification conditions,
and
anneal-
ing procedures
may
be
necessary
in
some cases.
On
the other
hand,
the
same
band
combinations can also
be
used
to estimate the degree of
crystallinity as a function of
both
material
and
processing parameters.
Although these measurements are only based
on
one-dimensional order,
Molecular
orientation
and
deformation
·
323
they are highly correlated
with
crystallinity
data
from other sources, as
well as density measurements. Bands corresponding
to
irregular con-
formations can be
used
to characterize the
amorphous
phase. However,
few
pure
'amorphous'
bands
have
been
identified.
It
has
been
suggested
that the
band
at
1154cm-1 mainly originates from the amorphous phase
in
iPP.
Similar correlations exist for syndiotactic PP (sPP),
but
the picture is
complicated
by
the fact
that
at
least three different regular conformations
have
been
observed
in
crystalline
sPP.
These are all different from the
regular conformation
in
iPP, which makes
it
easy to distinguish between
iPP
and
sPP.
The
two
most common regular sPP conformations, the 21
helix (tggttg'g't)
and
the
planar
zig-zag, can
be
identified
by
character-
istic
bands
at
977
and
962
cm-
1, respectively. A
band
at
867
cm-
1 exists
for
both
conformations
and
is often
used
as a syndiotacticity index,
in
various combinations.
In
addition
to
tacticity, the molecular configuration is also affected
by
chemical defects. Head-to-head addition gives rise to peaks
at
755cm-
1
(-(CH
2)2
-)
and
1030cm-
1
(-cH(CH
3
)-CH(CH
3
}-).
Although iPJ' does
not
have
a.Q.y
bands
representing three-dimensional
crystalline order, intermolecular coupling
may
lead to
band
splitting,
due
to
phase
differences between internal
modes
in adjacent chains,
and
non-equivalent molecular sites
in
the
unit
cell. With iPP, this usually
appears as
peak
broadening, because the splitting cannot
be
resolved.
However, some multiplets have
been
resolved
in
low-temperature
studies. Differences
in
the spectra of the
a,
~'
'Y
and
mesomorphic phases
of iPP have
been
attributed to differences
in
chain
packing, i.e. different
unit cells
and
packing defects. The positions
and
intensities of the
CH
3
stretching
bands
are especially sensitive to chain packing. These
bands
have, for instance,
been
used
to
study
the
~-a
transition.
At
the extreme low-frequency
end
of the Raman spectrum, the so-
called longitudinal acoustic
modes
(LAM), probe the lamellar structure,
including the fold surfaces. These lattice
modes
correspond to accordion-
like deformations of the chain. The lamella thickness is related to the
frequency of these modes. A quantitative expression has
not
been
found
for helical
PP,
but
an
in~!-se
relation has
been
proved. LAM
bands
in
the
range 10-20
cm-
1 h,ave been
used
to compare
PP
samples
in
terms of
lamella thicknesses. A similar
mode
exists
in
the amorphous phase; the
so-called disoriented LAM (DLAM). A DLAM doublet observed
near
220cm-1
in
iPP melts
has
been
associated
with
31 helix segments.
MOLECULAR ORIENTATION
AND
DEFORMATION
Molecular orientation is a key
par.~r,neter
when
studying relationships
between processing parameters
and
mechanical properties.
It
can
be
324
Infrared
and
Raman
spectroscopy
of
polypropylene
measured
by
both
IR
and
Raman spectroscopy. The
magnitude
of the IR
absorption
depends
on
the angle between
the
incident electrical field
and
the transition moment. Using polarized incident light, this so-called
dichroic effect can
be
used
to assess the molecular orientation. The
orientation parameter obtained
by
IR dichroism is essentially the average
of cos2
e,
where e is the angle between a reference axis (usually the
main
axis of deformation)
and
the chain axis. The Raman scattering process is
more complicated
than
IR absorption. This leads
to
some problems,
but
also extended possibilities. As
an
example, Raman scattering gives a
more detailed description of the orientation
by
assessing the average of
both
cos2 e
and
cos4
e.
The angle between the transition
moment
vector
and
the helix axis
must
be
known
in
order to quantify the IR orientation data. Transition
moment
angles for PP
bands
are usually assumed to
be
0 or
'IT
/2,
but
this
is probably
not
correct. The large variation
in
orientation factors calcu-
lated from different
bands
is partly
due
to different transition
moment
angles (not taken into account)
and
partly
due
to actual differences
in
orientation (since different
bands
may
represent different structural
states). As mentioned above, the
bands
in
IR
and
Raman spectra of PP
are unresolved multiplets. Most multiplets have the same transition
moment angle,
but
for the Raman scattering the picture is more compli-
cated. This reduces the
number
of Raman
bands
which can
be
used
for
orientation measurements.
A large
number
of IR bands have been
used
in
orientation studies.
Bands
at
809, 841, 973
and
1154cm-1 have been
used
in
both
IR
and
Raman studies,
with
various
phase
assignments. IR
and
Raman orienta-
tion factors are correlated with
data
from other methods,
such
as
wide-angle X-ray scattering
(WAXS)
(orientation of crystallites)
and
birefringence (average of all phases).
TheIR
orientation factors have
in
some cases been calibrated
by
adjusting the transition
moment
angle.
The 1460cm-1 IR
band
has been reported to
be
insensitive to orientation,
because
it
is
due
to
two
overlapping
bands
with
opposite transition
moments. Hence, this
peak
may
be
used
as a reference.
For a
syst~m
with uniaxial orientation, only
one
orientation factor is
needed. However, a bimodal orientation (autoepitaxy)
may
develop
in
iPP solidified
under
high
stress in a uniaxial stress field.
Due
to this
effect, some IR studies, e.g. of melt
spun
fibers, are flawed
by
assuming a
uniaxial orientation for all samples. The orientation along three ortho-
gonal axes have been measured for films (uniaxially
and
biaxially
oriented)
and
injection-molded samples, using reflection
and
tilting
methods. A simple IR transmission
method
without
tilting
has
also
been
demonstrated for iPP, based
on
the
841
and
809cm-
1 peaks. These
bands
originate from viprations of the same regular helix conformation,
and
the
transition moments are close to 0
and
'IT
/2.
The orientation along the
Molecular
orientation and
deformation
325
three orthogonal axes can be calculated from three measurements
of
the ratio A(841cm-1
)/A(809cm-
1
),
with
polarization parallel
and
per-
pendicular to a reference direction in the plane,
and
no
polarization,
respectively. This
method
is also well suited for samples with a very high
degree of uniaxial orientation.
Orientation measurements have also been implemented for in-situ
analyses of
PP.
The orientation
and
relaxation kinetics of melts
in
shear
flows have been
studied
by
IR spectroscopy
in
a rheometer. In another
example, the orientation
in
the transition front of the neck
during
tensile
deformation has been analyzed
by
Raman microspectroscopy. This last
example is a natural link to studies of samples subjected to mechanical
stress.
Several
IR
and
Raman
bands
are sensitive to stress, i.e. molecular
deformation. Stress generally affects
both
the position
and
the profile
of
the peaks. The latter effect is taken as evidence of
an
uneven
stress
distribution,
but
usually only the former effect (a frequency shift) is
utilized. The
bands
with
the highest stress sensitivity are those with large
contributions from axial stretching of C
-c
bonds
along the backbone.
The shift
of
the
band
at
1164c~-I
is usually reported to be the
most
sensitive probe,
with
a stress sensitivity factor
on
the
order
of
-20cm-
1/
GPa. The sensitivity factors
of
vibrational
bands
vary
with
temperature,
morphology
and
stress level. Most factors are negative,
but
a few
positive shifts have also been reported for
PP.
Observed sensitivity
factors have been confirmed
by
calculations.
Raman
and
IR spectroscopy have been
used
in
a
number
of studies
of
molecular load distributions
and
deformation mechanisms
in
PP,
usually
in combination with a mechanical loading device (tension
or
compres-
sion). The topics
studied
include true loads
on
atomic bonds, chain
scission
under
stress, stress relaxation
and
creep, residual stresses,
and
stresses along
aramid
fibers
in
a
PP
matrix
during
pull-out testing.
A
number
of
new
analysis techniques have
been
developed recently,
combining polarized IR spectroscopy
and
periodic mechanical perturba-
tion.
If
the strain airip)!.tude is small, the spectral response (due to
molecular orientation
an~
deformation) is linear
and
can be analyzed
in
terms of in-phase
and
out-of-phase components. This technique is often
referred to as dynamic IR linear dicroism (DIRLD). DIRLD evolved into
the
20
IR technique,
in
which a
20
spectrum, I(v1, v2
),
is obtained
by
considering the relative
phase
differences between IR absorptions
at
different frequencies, v1
and
v2 With these techniques, species with
different response to the external perturbation can
be
distinguished. As
an example, peaks with contributions from both crystalline
and
amor-
phous domains can be resolved. Some initial studies of PP
with
these
techniques
have
been reported.
326
Infrared
and
Raman
spectroscopy
of
polypropylene
COPOLYMERS
AND
BLENDS
Ethylene-propylene copolymers are of
high
commercial interest,
and
IR
spectroscopy is
an
excellent tool for analyzing these systems
[3].
Isolated
ethylene units
(-(CH
2)3-sequences), typically found
at
low
ethylene
concentrations, give rise to a
band
at
733cm-1.
It
has
been
shown
that
ethylene units can
be
accommodated inside PP crystals
without
reducing
the degree of crystallinity,
but
the average helix length, as measured
by
IR
helix bands, decreases,
due
to the ethylene interruption. A
band
at
721
cm-
1 appears
when
there are two
or
more consecutive ethylene units
between propylene units. PE crystallites can
be
identified
by
a
pure
'crystalline'
band
at
730cm-1.
The721/730cm
-1
pair
is a doublet
due
to
intermolecular coupling. The
band
at
730
cm-1
may
be
confused
with
the
band
at
733cm-
I,
but
the former is sharper
and
changes
with
tem-
perature. At
low
propylene concentrations (or
with
special catalysts),
isolated propylene units can
be
identified
by
a
band
at
935
cm-
1. Sequen-
ces of more
than
about three units give rise to a
band
at
973cm-I, which
was discussed above.
Various
band
combinations have been
used
to characterize the ethyl-
ene
and
propylene distributions
in
copolymers, depending
on
the
copolymer type (statistical
or
block)
and
the ethylene content.
It
must
be
noted that additives often contain methylene sequences comparable to
those incorporated
in
the copolymer chain. Copolymers can also be
analyzed
in
the NIR range, which is well suited for on-line implementa-
tion
and
nondestructive analysis. The analysis
and
identification of
copolymers have gained
much
in
sensitivity
and
reliability
by
applying
statistical methods to large parts of the spectrum. Studies of size exclu-
sion chromatography
(SEC)
fractions have given detailed information
on
the performance of catalyst systems. Comonomer distributions obtained
with
IR
spectroscopy agree well
with
NMR
data
.
Several other propylene-based copolymers
and
blends have been
analyzed
by
vibrational spectroscopy. The EPDM (ethylene-propylene-
diene-monomer) content in PP
/EPDM
(low temperature impact) blends
is a linear function of the ratio A(2850cm-1
)/A(2920cm-
1)
up
to
80%
EPDM. Functionalized PP (compatibilizer) for use
in
PP blends is often
characterized
by
IR spectroscopy. These compatibilizers typically consist
of PP grafted
with
anhydrides or acids,
and
may
be
analyzed
in
terms of
chemical details
and
graft content. Intermolecular interaction between
groups
on
the grafted side chain
and
the non-PP component
in
the blend
has been characterized
by
band
shifts
and
band
broadening.
Vibrational spectroscopy makes it possible to assess morphological
parameters (e.g. order
and
orientation) of the blend constituents separat-
ely.
This has, for instance, been demonstrated
with
PP
/polyamide
melt
spun
fibers. The composition
and
morphology of microdomains
in
PP
Degradation
327
based blends have been analyzed
by
IR
and
Raman microspectroscopy.
The micro-Raman imaging technique, which is based
on
confocal laser
line scanning, offers the best spatial resolution (typically 1
J.Lm
laterally
and
3
J,Lm
in
depth).
DEGRADATION
IR
spectroscopy is one of the
most
common methods for studying the
degradation
and
stabilization of
PP
under
various conditions
[4].
It
is a
versatile tool for identifying the chemical species formed
in
the degrada-
tion process
and
obtaining kinetic parameters.
IR
spectroscopy also
offers some special possibilities: orientation, stress
and
degradation can
be measured simultaneously,
in
order to
study
the complicated relation-
ship between degradation kinetics
and
molecular orientation
and
stress,
The difference between
bulk
and
surface degradation can
be
assessed.
Microspectroscopy can reveal local variations
in
degradation, e.g.
due
to
inhomogeneous distributions of antioxidants.
IR
emission spectroscopy
has
been
demonstrated as a tool for studying the thermal degradation of
PP.
. .
The exact degradation mechanism
depends
on
the conditions (tem-
perature, stress, UV light,
'Y
irradiation, plasma treatment, electrical field,
etc.), the type of
PP
and
the morphology. However, the same chemical
species are involved, containing hydroxyl (OH) groups, carbonyl
(C=O)
groups
and
unsaturated
(C=C)
groups (Raman spectroscopy is more
sensitive to unsaturated groups
than
IR spectroscopy). Hydrogen-
bonded hydroxyl groups give rise to a broad
peak
around
3400 cm-1,
while multiple overlapping carbonyl peaks
appear
somewhat
later,
typically centered
around
1720
cm-
1. The degree of degradation is often
characterized
by
a carbonyl index, which is the area of the major
carbonyl
peak
relative to
an
internal standard, such as the 1166cm-1
band. From the hydroxyl
and
carbonyl groups, degradation products
such as peroxides, alcohols, carboxylic acids, ketones, aldehydes, esters
and -y-lactones can
be
identified
by
performing derivatization reactions
and consulting
handb~ks
on
group
frequencies of organic molecules.
An
analysis based.on carbonyl peaks is the most reliable.
Bands
due
to unsaturated groups are less studied.
In
the absence of
oxygen, these are the only
new
groups
that
appear. Thermal degradation
in
an
inert atmosphere typically leads to the formation of vinylidene
end
groups (with characteristic
bands
at
889
and
1648cm-1)
at
temperatures
above 300°C, followed
by
vinyl
end
groups (910cm-1)
and
trans-
vinylene
(965
cm-
1)
at
higher
_temperatures. After prolonged treatment
at
elevated temperatures all
PP
bands
disappear -only
an
unsaturated
hydrocarbon liquid is left.
r...:;,
328
Infrared
and
Raman
spectroscopy
of
polypropylene
REFERENCES
1.
Bower, D.l.
and
Maddams, W.
F.
(1992),
The
Vibrational
Spectroscopy
of
Polymers,
Cambridge University Press, Cambridge.
2.
Arruebarrena
de
Baez, M., Hendra,
P.J.
and
Judkins, M. (1995) The Raman
spectra of oriented isotactic polypropylene.
>Spectrochim.
Acta, A51, 2117-24.
3.
van
der
Ven,
S.
(1990),
Polypropylene
and
Other
Polyolefins
-
Polymerization
and
Characterization,
Elsevier, Amsterdam.
4.
LaCoste,
J.,
Vaillant,
D.
and
Carlsson,
D.J.
(1993), Gamma-initiated, photo-
initiated,
and
thermally-initiated oxidation of isotactic polypropylene.
f.
Poly-
mer
Sci.
Polymer
Chern.,
31, 715-22.
Keywords: infrared spectroscopy, Raman spectroscopy, vibrational
spectroscopy, conformation, configuration, near infrared (NIR), surface
analysis, on-line analysis, microspectroscopy, forensic analysis, chain
packing, lamellar structure, polymorphism, group frequencies, coupled
vibation modes, isotacticity index, syndiotacticity index, lattice modes,
internal modes, degree of crystallinity, head-to-head addition, longitudi-
nal acoustic
mode
(LAM), molecular orientation, molecular deformation,
stress-induced frequency shifts,
IR
dichroism,
20
IR, ethylene-propylene
copolymers, blends, ethylene-propylene-diene-monomer (EPDM), func-
tionalized
PP,
compatibilizer, degradation, oxidation, carbonyl index,
carbonyl groups, hydroxyl groups, unsaturated groups.
"
~-.
... In the case of the PP_CNT composite Raman spectrum, it can be observed that as the amount of CNTs increases, the Raman intensity for the three bands increases and a small feature (denoted D ) around 1607 cm −1 could be assigned to dispersive phonon modes in structure. In the range 2750-3000 cm −1 the bands corresponding to the γCH 2 and γCH 3 vibration groups of polypropylene polymer (PP) [36] and G + D of CNTs (~2930 cm −1 ) are very well highlighted. At the low frequency, other distinguishable features, pCH 2 and wCH 2 vibration groups of PP, were observed. ...
... These results are in quite good agreement with other previous scientific literature reports [22], but none of these seem to have observed particular structuring of the best performing composite. To our knowledge, previously reported results for EMI attenuations values of sheets of CNT-PP composite materials thicker than 1 mm were usually lower than 40 dBs [22,36,37]. ...
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Graphene nanoplatelets (GNPs) and multiwall carbon nanotubes (CNTs)-polypropylene (PP) composite materials for electromagnetic interference (EMI) shielding applications were fabricated as 1 mm thick panels and their properties were studied. Structural and morphologic characterization indicated that the obtained composite materials are not simple physical mixtures of these components but new materials with particular properties, the filler concentration and nature affecting the nanomaterials’ structure and their conductivity. In the case of GNPs, their characteristics have a dramatic effect of their functionality, since they can lead to composites with lower conductivity and less effective EMI shielding. Regarding CNTs-PP composite panels, these were found to exhibit excellent EMI attenuation of more than 40 dB, for 10% CNTs concentration. The development of PP-based composite materials with added value and particular functionality (i.e., electrical conductivity and EMI shielding) is highly significant since PP is one of the most used polymers, the best for injection molding, and virtually infinitely recyclable.
... The FTIR was adjusted to a 4 cm − 1 resolution with 32 scans and in the band region spectrum range of 650-3000 cm − 1 . According to previous studies (Andreassen, 1999;Crawford and Quinn, 2017;Käppler et al., 2015;Kotha and Shirbhate, 2015;Tagg et al., 2015), polymers were identified by investigating the existence of a significant peak in band regions (Andreassen, 1999;Käppler et al., 2016Käppler et al., , 2015 at 1174-1087 cm − 1 (stretching vibration of CF 2 ), 1400-1480 cm − 1 (bending vibration of CH2), 1670-1760 cm − 1 (stretching vibration of C--O), 1740-1800 cm − 1 (stretching vibration of C--O), and at 2780-2980 cm − 1 (stretching vibrations of CH/CH 2 /CH 3 groups). ...
... The FTIR was adjusted to a 4 cm − 1 resolution with 32 scans and in the band region spectrum range of 650-3000 cm − 1 . According to previous studies (Andreassen, 1999;Crawford and Quinn, 2017;Käppler et al., 2015;Kotha and Shirbhate, 2015;Tagg et al., 2015), polymers were identified by investigating the existence of a significant peak in band regions (Andreassen, 1999;Käppler et al., 2016Käppler et al., , 2015 at 1174-1087 cm − 1 (stretching vibration of CF 2 ), 1400-1480 cm − 1 (bending vibration of CH2), 1670-1760 cm − 1 (stretching vibration of C--O), 1740-1800 cm − 1 (stretching vibration of C--O), and at 2780-2980 cm − 1 (stretching vibrations of CH/CH 2 /CH 3 groups). ...
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To reduce microplastic contamination in the environment, we need to better understand its sources and transit, especially from land to sea. This study examines microplastic contamination in Jakarta's nine river outlets. Microplastics were found in all sampling intervals and areas, ranging from 4.29 to 23.49 particles m⁻³. The trend of microplastic contamination tends to increase as the anthropogenic activity towards Jakarta Bay from the eastern side of the bay. Our study found a link between rainfall and the abundance of microplastic particles in all river outlets studied. This investigation found polyethylene, polystyrene, and polypropylene in large proportion due to their widespread use in normal daily life and industrial applications. Our research observed an increase in microplastic fibers made of polypropylene over time. We suspect a relationship between COVID-19 PPE waste and microplastic shift in our study area. More research is needed to establish how and where microplastics enter rivers.
... Raman spectrum of pristine respirator exhibits multiple bands due to CH 2 , CH 3 groups frequencies, and their coupled modes corresponding to isotactic polypropylene (iPP). 69 Bands in the 800 to 1200 cm À1 range are attributed to the 3 1 helix, a regular conformation of isotactic polypropylene polymorphs. 69 No modification was observed in the number of peaks and peak positions, confirming that iPP retains its chemical structure even after various sterilizations. ...
... 69 Bands in the 800 to 1200 cm À1 range are attributed to the 3 1 helix, a regular conformation of isotactic polypropylene polymorphs. 69 No modification was observed in the number of peaks and peak positions, confirming that iPP retains its chemical structure even after various sterilizations. In addition, no chemical changes were observed in Raman analysis of gamma-irradiated facemasks up to 25 kGy. ...
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... identical to those of isotactic polypropylene [24,25], which confirmed that all three types of PPE were made of isotactic polypropylene fibers. ...
Article
Medical personal protective equipment (PPE) made from nonwoven thermoplastic fibers has been intensively used, resulting in a large amount of biohazardous waste. Sterilization is indispensable before recycling medical waste. The aim of this work is to evaluate the effects of the decontamination treatments and help properly recycle the PPE materials. The study investigated the effects of three disinfection treatments (NaClO, H 2 O 2 , and autoclave) on chemical composition, molecular weight, thermal properties, crystallinity, crystallization kinetics, and mechanical tension of three types of PPE (Gown #1, Gown #2, and Wrap) made of isotactic polypropylene fibers. The chemical compositions of the materials were not evidently affected by any of the treatments. However, the M w of the polymers decreased about 2-7% after the treatments, although the changes were not statistically significant. The treatments barely affected the melting and crystallization temperatures and the maximum force at break, but they tended to elevate the thermal degradation temperatures. Although the treatments did not notably influence the crystallinities, crystallization rates and crystal growths were altered based on the Avrami model regression. Since the detected changes would not significantly affect polymer processing, the treated materials were suitable for recycling. Meanwhile, evident differences in the three types of raw materials were recorded. Their initial properties fluctuated notably, and they often behaved differently during the treatments, which could affect recycling operation. Recy-clers should test and sort the raw materials to assure product quality. The results in this study provide fundamental data for recycling medical PPE to reduce its environmental footprint.
... The FT-IR spectra of thiophene (TG0) and imidazole (IMG0) grafted products are given in Figure 2a,b, respectively. When comparing the spectra of TG0 with the starting material (Figure 1a), it is obvious that both spectra show several strong absorption bands at 1452-1453 cm −1 (CH 3 asymmetric bending, δCH 3 asym), 1370-1375 cm −1 (CH 3 symmetric bending, δCH 3 sym), 1165-1168 cm −1 (CH 3 rocking, ρCH 3 and CH bending, δCH), 970-972 cm −1 (CH 3 rocking ρCH 3 ) and 807-810 cm −1 (CH 2 rocking, ρCH 2 ) [34,35]. These peaks belong to the chemical group existed in the neat PP. ...
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... All these peaks indicate the presence of the methyl group in the polypropylene. The peaks correspond to -CH 2 -symmetric bending, -CH 2 -symmetric stretching, and -CH 2 -asymmetric stretching in polypropylene were observed at 1455, 2838, and 2917 cm −1 , respectively [22][23][24][25]. As an increasing amount of WUF was mixed into the PP, a broad band of increasing intensity began to appear at 1640 cm −1 correspond to the C=O stretching, and at 3330 cm −1 correspond to the hydroxyl (-OH) stretching of the methylol group. ...
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... As any sustainable initiative on recycling and proper handling resides on the materials structural properties, we expect that the newly designed dedicated products will have a strong basis in the scientific results obtained with highly sensitive analytical techniques. In this study, with the help of Raman Spectroscopy, the most appropriate among the highly sensitive analytical techniques in terms of time-consuming signal detection and selectivity (da Silva and Wiebeck, 2019), (Larkin, 2011), (Andreassen, 1999), (Caggiani et al., 2016), (Fremout and Saverwyns, 2012) we investigate a large set of plastic waste samples aged for years, either in aquatic or in terrestrial environments aiming to i) identify the molecular changes in the Raman signal associated with long term aged plastic waste; ii) evaluate the intrinsic or extrinsic factors influencing the common plastics Raman signal and iii) assess the Raman signature usefulness in recognizing a typical signal without ambiguity and building up a logic Raman gate for an efficient waste sorting algorithm. ...
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We investigated the effects of polymer blend variation on the physical, mechanical, and thermal properties of wood-polymer composites (WPC). We used high-density polyethylene (HDPE) and polypropylene (PP) and a combination of 80% PP, 20% HDPE, and 80% HDPE, 20% PP as polymer blends for WPC formulations to simulate recycled plastics. We used black spruce (Picea mariana Mill.) hammer milled fibers (75–250 μm) at 35 wt% as a filler for all the formulations. A two-step process was used for WPC manufacturing; pellet extrusion followed by test samples injection. Tensile and three bending tests characterized the WPC mechanical properties. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) characterized the WPCs’ thermal properties. Water absorption and contact angle measurements assessed the composite dimensional stability. Infrared spectroscopy (FTIR) and electron scanning microscopy (SEM) investigated the WPCs’ surface chemistry and microstructure. Mechanical properties and dimensional stability varied according to polymer composition, with better performance for WPC containing higher PP proportions. Thermal properties varied with the polymer composition in the WPC, with better thermal stability for the formulation containing higher HDPE proportions. Surface chemistry analysis did not reveal any chemical changes on the WPCs surface. Scanning electron microscopy analysis revealed distinct phases in all WPCs without evidence of interfacial adhesion.
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Describes the theory and practice of infrared and Raman spectroscopy as applied to the study of the physical and chemical characteristics of polymers. Its purpose is to give the beginning researcher in the field a firm foundation and a starting point for the study of more advanced literature. To this end the book concentrates on the fundamentals of the theory and nomenclature, and on the discussion of well-documented illustrations of these fundamental principles, including many now-classic studies in the subject. No previous knowledge of either polymers or vibrational spectroscopy is assumed.
Measurements of the relative band intensity changes with orientation can be made in the FT Raman spectrometer on a wide range of isotactic polypropylene specimens. The usefulness of these changes in estimating orientation at the sampled point is considered. It is concluded that the method can be applied with caution.
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The detailed oxidation products have been identified and compared from the γ-, photo-, and thermally-initiated oxidation of unstabilized polypropylene films. Products were identified and quantified by a combination of iodometric analysis and infrared spectroscopy. Spectral resolution was enhanced by derivatization reactions which allow the quantification of primary, secondary, and tertiary hydroperoxide and alcohol groups as well as more reliable analysis of carbonyl species. In contrast to polyethylene oxidation which yields predominantly ketone with lesser amounts of secondary hydroperoxide and carboxylic acid, polypropylene oxidizes to give predominantly tertiary hydroperoxide and lesser quantities of secondary hydroperoxide and ketone. In addition carboxylic acid groups are a minor product except at high degrees of thermal and photoinitiated oxidation. © 1993 John Wiley & Sons, Inc.