Concept of Tercet Molecular Nanocomposites and Preliminary Studies on [PPTA/(PA-6/PA-66)] System of Miscible Blend of
Polyamide-6/Polyamide-6,6 Molecularly Reinforced at Nano Level by Poly(p-phenylene-terephthalamide)
Concept of Tercet Molecular Nanocomposites and Preliminary Studies
on [PPTA/(PA-6/PA-66)] System of Miscible Blend of Polyamide-6/
Polyamide-6,6 Molecularly Reinforced at Nano Level by Poly(pphenylene-terephthalamide)
Sanjay Palsule*, Anuja Baijal, and Sampat Singh Bhati
Department of Polymer & Process Engineering, Indian Institute of Technology, IIT-R SRE Campus, Paper Mill Road,
Saharanpur 247001 India
Received: 21 July 2014, Accepted: 11 August 2014
SUMMARY
A tercet molecular nanocomposite is a ternary miscible polymer system in which a miscible blend of two flexible
polymers is molecularly reinforced at nanometre level by a rigid-rod macromolecule and the tercet molecular
nanocomposite demonstrates properties better than those of the constituent flexible polymers and their blend. A
tercet molecular nanocomposite of a blend of flexible polyamide-6 (PA6) and polyamide-6,6 (PA6,6) molecularly
reinforced at the nanometre level by a rigid-rod poly-p-phenylene-terephthalamide (PPTA) has been processed
by coagulating a sulfuric acid solution of the components in water. This study reports miscibility, structure
and properties of PPTA/[PA6/PA6,6] tercet molecular nanocomposites. Miscibility has been established by
recording single intermediate glass transition temperatures by differential scanning calorimetry. Homogeneous
morphology and dispersion of PPTA in [PA-6/PA-6,6] below 5 nanometre level has been established by scanning
electron microscopy. Intermolecular interactions dispersing PPTA in [PA-6/PA-6,6] below the 5 nm level by
imparting miscible homogeneous morphology and have been identified by Fourier transform infra red (FTIR)
spectroscopy. Improved tensile mechanical properties of the tercet molecular nanocomposite, compared to those
of the constituent flexible polymer blend, have been established by universal testing machine.
Keywords: Tercet molecular nanocomposite, Miscible ternary polymer blend, Nano morphology,
Mechanical properties, Rigid-rod polymer, PPTA, PA-6, PA-66
1. Concept of
Tercet Molecular
Nanocomposite
Polymeric materials have been
classified 1 into four generations.
Homopolymer and copolymer
thermoplastics, thermosets and
elastomers have been classified as the
first generation polymers; particulate
and fibre reinforced polymer
composites and polymer blends, as
the second generation polymers;
and molecularly reinforced polymer
blends as third generation polymers.
Nano polymers and nano polymeric
composites have been classified as the
fourth generation polymers.
Helminiak presented the concept
of a molecular composite2-3 as a
miscible blend of a flexible polymer
molecularly reinforced by the rigidrod polymer. The concept was further
developed by Takayanagi 4-5; and
Fukai et al. developed a miscible
molecular composite6. The subject
has been reviewed7-8. Palsule1,9 has
described the basic principles of a
molecular composite. Young and
Eichhorn10, and Green et al.11 have
established that when the rigid-rod
polymer is thermodynamically
miscible with a flexible polymer
in a molecular composite, then the
rigid-rod macromolecule gets fully
extended and gets dispersed at
*e-mail: [email protected], [email protected]. *Telephone no: (+91) 97 206 77 999
Smithers Information Ltd., 2015
©
Polymers & Polymer Composites, Vol. 23, No. 6, 2015
nanometre level acting like a single
walled nanotube (SWNT) (Figure 1).
A molecular composite functions like
a nanocomposite, and has been termed
a molecular nanocomposite10,11.
As an extension of the concept of a
molecular nanocomposite, the concept
of a tercet molecular nanocomposite
is herewith presented as a ternary
miscible polymer system, in which
a miscible blend of two flexible
polymers is molecularly reinforced
at the nanometre level by a rigidrod macromolecule. The resultant
tercet molecular nanocomposite
demonstrates properties better than
those of the constituent flexible
polymers and their blend due to its
miscible nature and reinforcement at
the nanometre level by the rigid-rod
macromolecule.
407
Sanjay Palsule, Anuja Baijal, and Sampat Singh Bhati
Figure 1. Schematic representation of macromolecules of PPTA as single walled
nanotube 2. PPTA/[PA-6/PA-6,6]
Tercet Molecular
NanoComposite System
According to Flory19, it is difficult to
achieve thermodynamic miscibility
in a binary blend of a flexible and
a rigid-rod polymer due to low
combinatorial entropy of mixing and
high tendency for self-alignment of the
rigid-rod macromolecule. However,
miscible molecular composite systems
consisting of PPTA and PA have been
developed4,5; for example, PPTA/PA-6
and PPTA/PA-6,6; and specific studies
on establishment of miscibility 20
in PPTA/PA-6 and PPTA/PA-6
molecular composites by differential
scanning calorimetry and Fourier
transform infra red spectroscopy have
been reported.
Although several ternary polymer
blend systems have been developed12-18
and even reinforcement has been
observed in some of these ternary
blend systems containing a rigid
polymer or a thermotropic liquid
crystalline polymer, no miscible
ternary system of a rigid polymer /
flexible polymer / flexible polymer
with molecular reinforcement at
nanometre scale has been reported.
This study aims to develop the first
ternary miscible polymer system of
two flexible polymers and a rigid-rod
macromolecule in the form of a tercet
molecular nanocomposite of PPTA/
[PA6/PA66] of a miscible polyamide-6/
polyamide-6,6 blend molecularly
reinforced at the nanometre level
by a rigid-rod poly(p-phenylene
terephthalamide).
A tercet molecular nanocomposite
is analogous to a fibre reinforced
408
polymeric composite in which
a miscible blend of two flexible
polymers acts as the polymeric matrix
reinforced at nanometre level by single
extended rigid-rod macromolecule
that acts analogous to the reinforcing
fibre of the fibre reinforced polymeric
composite. Properties of a fibre
reinforced polymer composite are
governed by properties of the matrix
polymer, properties and the aspect
ratio of the reinforcing fibre, and
fibre/matrix interfacial adhesion. In
an analogous manner, properties of
a tercet molecular nanocomposite
are governed by properties of the
flexible polymer blend forming
the matrix, properties and aspect
ratio of the single extended rigidrod macromolecule reinforcing the
material at nanometre level, and the
miscibility between the miscible
flexible polymer blend and the
reinforcing rigid-rod macromolecule.
Consequently, efforts are being
made in this study to develop
PPTA/[PA6/PA66] tercet molecular
nanocomposite, anticipating the
possibility of miscibility due to
similar solubility parameters of PA6, and PA-6,6 and hydrogen-bonding
between all its three constituent
polymers- PA-6, PA-6,6 and PPTA.
Miscibility, the essential condition
for processing the tercet molecular
nanocomposite, has been established in
this study by recording glass transition
temperatures by differential scanning
calorimetry, and by establishing the
intermolecular interactions imparting
miscible single phase morphology by
Fourier transform infrared (FTIR)
spectroscopy. The homogeneous
morphology of PPTA/[PA6/PA66]
with less than 5 nanometre level
dispersion of reinforcing PPTA
macromolecules has been examined
by scanning electron microscope. The
composite nature of the system has
been demonstrated by establishing
that the mechanical properties of
all the compositions of the tercet
molecular nanocomposites of PPTA/
[PA-6/PA-6,6] are better than those
of the constituent flexible blend of
PA-6/PA-6,6.
Polymers & Polymer Composites, Vol. 23, No. 6, 2015
Concept of Tercet Molecular Nanocomposites and Preliminary Studies on [PPTA/(PA-6/PA-66)] System of Miscible Blend of
Polyamide-6/Polyamide-6,6 Molecularly Reinforced at Nano Level by Poly(p-phenylene-terephthalamide)
3. Experimental
3.1 Materials
Polyamide-6 (PA-6) [Figure 2a] used
was Gujlon obtained from GSFC,
(India). Polyamide-6,6 (PA-6,6)
[Figure 2b] was DuPont’s Zytel.
Extended rigid-rod macromolecules
of poly(p-phenylene terephthalamide)
(PPTA) [Figure 2c] were obtained by
dissolving DuPont’s Kevlar® fibre in
sulfuric acid (SA). Commercial grade
sulfuric acid (SA) was used.
3.2 Processing of the PPTA/
[PA-6/PA-6,6] Tercet Molecular
Nanocomposite
PPTA/[PA-6/PA-6,6] tercet molecular
nanocomposites have been processed
with compositions [5/(47.5/47.5)],
[10/(45/45)] and [15/(42.5/42.5)]. The
processed compositions thus contained
5, 10 and 15% rigid-rod PPTA
macromolecules and the remaining 95,
90 and 85% of the PA-6/PA-66 blend
contained equal amounts (50%) each
of PA-6 and PA-6,6.
Prior to processing PPTA/PA6-PA66
tercet molecular nano composite, it
is necessary to establish miscibility
in the constituent flexible polymer
blend of PA-6/PA-6,6, consequently,
a flexible blend of 50/50 PA-6/PA6,6 was processed and miscibility in
the blend was also established. To
process 50/50 PA-6/PA-6,6 blend,
equal amounts of PA-6 and PA-6,6 were
separately dissolved in SA by stirring
the solutions continuously for 50 h at
room temperature, until clear solutions
were obtained. Equal amounts of clear
solutions of PA-6/SA and PA-6,6/SA
were mixed to obtain PA-6/PA-6,6/
SA ternary solution that was stirred
and mixed for 50 h until completely
mixed clear transparent solution was
obtained. 50/50 PA-6/PA-6,6 flexible
blend was obtained in the form of flakes
by co-precipitating the ternary PA-6/
PA-6,6/SA solution in distilled water
and further by washing the flakes with
distilled water and acetone and drying
the flakes in air oven and vacuum oven
for 24 hours each.
Difficulties in processing a ternary
PPTA/[PA-6/PA-6,6] blend by directly
mixing PA-6, PA-6,6 and PPTA in
SA had been anticipated. To process
10(45/45) PPTA(PA-6/PA-66) tercet
molecular nanocomposite, first a blend
of 5/45 PPTA/PA-6 in sulfuric acid
was processed; and another blend of
5/45 PPTA/PA-6,6 in sulfuric acid
was separately processed. These two
solutions were finally mixed to obtain
a blend of 10/45/45 PPTA/(PA-6/
PA-66) in sulfuric acid that was coprecipitated in distilled water, and
the obtained flakes were washed with
acetone and distilled water, and dried.
For this, appropriate amounts of PA-6
(45) and PPTA (5) were separately
dissolved in SA by stirring the solutions
continuously for 50 hours at room
temperature, until clear solutions
were obtained. Clear solutions of
PA-6/SA and PPTA/SA were mixed to
obtain 5/45 PPTA/PA-6,6/SA ternary
solution that was stirred and mixed for
50 hours until completely mixed clear
transparent solution was obtained. 5/45
PPTA/PA-6 blend was thus obtained in
sulfuric acid solution. Similarly, 5/45
PPTA/PA-66 blend was also separately
obtained in sulfuric acid solution. The
5/45 PPTA/PA-6 in SA and 5/45 PPTA/
PA-6, 6 in SA were mixed to obtain 10/
(45/45) PPTA(PA-6/PA-66) solution.
This solution was stirred for 50 hours
until clear solution was obtained.
10/(45/45) PPTA/(PA-6/PA-6,6)
tercet molecular nanocomposite
was obtained in the form of flakes
by co precipitating the PPTA/PA-6/
PA-6,6/SA solution in distilled water.
The precipitated flakes were washed
thoroughly with distilled water and
acetone to remove traces of sulfuric
acid, and dried in air oven and then
vacuum oven for 24 hours each to
remove water and acetone and to obtain
dry 10/[45/45] PPTA/[PA6/PA6,6]
tercet molecular nanocomposite flakes.
These tercet molecular nanocomposite
flakes were finally used to establish the
miscibility, interface, morphology and
tensile properties of PPTA/[PA-6/PA66] tercet molecular nanocomposites.
Thus, the [5/(47.5/47.5)], 10[(45/45)]
and [15/(42.5/42.5)] compositions
of [PPTA([PA-6/PA-6,6)] tercet
molecular nanocomposite were also
obtained by following the same
process.
Samples for evaluation of tensile
modulus and tensile strength were
Figure 2. Structure of (a) Polyamide-6 (PA-6), (b) Polyamide-6,6 (PA-6,6) and (c)
poly(p-phenylene terephthalamide) (PPTA)
Polymers & Polymer Composites, Vol. 23, No. 6, 2015
409
Sanjay Palsule, Anuja Baijal, and Sampat Singh Bhati
processed by pressing the flakes of
PA-6, PA-6,6 that were regenerated
from SA, PA-6/PA-6,6 blend and the
PPTA[PA-6/PA-6,6] tercet molecular
nanocomposite compositions
separately in a hot press.
4. Testing and
Characterisation
4.1 Miscibility
A NETZSCH differential scanning
calorimeter (DSC 200 F3 Maia®)
was used to record glass transition
temperatures of component PA-6
and PA-6,6 polymers, blend of 50/50
PA6/PA6,6 and the [5/(47.5/47.5)],
10[(45/45)] and [15/(42.5/42.5)]
compositions of [PPTA/[(PA-6/PA6,6)] tercet molecular nanocomposites
as a function of temperature. All
experiments were carried out under
nitrogen at a heating and cooling rate
of 5 °C/min.
To evaluate true miscibility, the
samples were repeatedly cycled in
the temperature range of 25 °C to
275 °C because Polyamide-6 and
Polyamide-6,6 may degrade at around
300 oC and PPTA does not show any
glass transition temperature even at
500 oC.
4.2 Morphology and
Nanometre-Level Dispersion
Morphology of the gold coated
PPTA/[PA-6/PA-6,6] tercet molecular
nanocomposites of [5/(47.5/47.5)],
10[(45/45)] and [15/(42.5/42.5)]
compositions was investigated with
a Field Emission Scanning Electron
Microscope (FE-SEM), Model Quanta
200F, using an acceleration voltage
of 15kV to establish that rigid-rod
macromolecules were of not more
than 5 nm dimensions to show the
nanometre-level dispersion.
4.3 Mechanical Properties
The tensile properties of PA-6,
PA-6,6, constituent PA-6/PA-6,6
miscible blend and PPTA/[PA-6/PA-
410
6,6] tercet molecular nanocomposites
of [5/(47.5/47.5)], 10[(45/45)] and
[15/(42.5/42.5)] compositions were
evaluated on a Universal Testing
Machine, (Model 3382, INSTRON 25
Ton Capacity). The tensile tests were
performed in accordance with ASTM
standards D 638M with cross head
speed of 50 mm/min. Results of tensile
tests were recorded as an average of five
samples of PA-6, PA-6,6, flexible PA-6/
PA-6,6 blend acting as matrix and of
each of the following tercet molecular
nanocomposites- PPTA/[PA-6/PA-6,6]
- [5/(47.5/47.5)], 10[(45/45)] and [15/
(42.5/42.5)]
5. Results and
Discussion
5.1 Miscibility and Thermal
Reinforcement
5.1.1 Methods and Criteria for
Miscibility
Following the differential scanning
calorimetry studies to establish
miscibility in molecular composites1,4,6,
miscibility in PPTA[PA-6/PA-6,6]
tercet molecular nanocomposites
developed in this study has also been
established by differential scanning
calorimetry, following the criterion
that miscible polymer blends show
a single glass transition temperature
intermediate between those of the
component polymers and phase
separated blends show two glass
transitions corresponding to individual
components21. The change in heat
capacity at the glass transition is
relatively small for blends containing
rigid-rod polymers, like PPTA, and
consequently the magnitude of the
endothermic step is also small. It is
well known that the rigid-rod polymers,
like PPTA, do not have any identifiable
glass transition temperature. However,
this PPTA has been considered an
ideal reinforcing macromolecule for
molecular nanocomposites4,5,20 due
to its high aspect ratio and rigid-rod
chain structure, and for this reason
it has been used to develop the
PPTA/[PA-6/PA-6,6] tercet molecular
nanocomposites of [5/(47.5/47.5)],
10[(45/45)] and [15/(42.5/42.5)]
compositions. In the absence of the
possibility of recording the glass
transition temperature of a rigid-rod
polymer like PPTA, it is now customary
to establish miscibility in blends based
on such rigid-rod like macromolecules
(e.g. molecular nanocomposites) by
assuming1,6 that the presence of a
glass transition temperature [Tg] for
the blend, at a temperature higher
than the glass transition temperature
of the constituent flexible polymer
(flexible polymer blend, in case of
tercet molecular nanocomposite) in
proportion to the amount of the rigid
polymer in the blend, indicates a
miscible single phase system.
5.1.2 Miscibility in PPTA[PA-6/
PA-6,6] Tercet Molecular
Nanocomposites
Table 1 records the glass transition
temperatures of PA-6, PA-6,6, binary
blend of 50/50 PA-6/PA-6,6 and of the
PPTA/[PA-6/PA-6,6] tercet molecular
nanocomposites of [5/(47.5/47.5)],
10[(45/45)] and [15/(42.5/42.5)] as
measured by differential scanning
calorimeter. The glass transition
temperature of PA-6 is 67.5 oC and of
PA-6,6 is 59.9 oC. The glass transition
temperature of 50/50 PA-6/PA-6,6
blend is recorded as 62 oC, which is
slightly below the 63.7 oC expected
form theoretical calculations for this
blend. This could be due to limitations
of experimental and measurement
techniques. While investigating the
glass transition temperature of the
50/50 PA-6/PA-6,6 blend, no glass
transition temperature was observed
at or near 59.9 oC or 67.5 oC (the glass
transition temperatures of PA-6,6 and
PA-6); and only one glass transition
has been observed for the flexible
blend of PA-6/PA-6,6, at 62 oC, that
is intermediate between those of PA-6
(67.5 oC) and of PA-6,6 (59.9 oC). The
presence and reproducibility of single
glass transition temperature at 62 oC for
the PA-6/PA-6,6 blend, intermediate
between those of PA-6 (67.5 oC) and
PA-6,6 (59.9 oC), confirms miscibility
Polymers & Polymer Composites, Vol. 23, No. 6, 2015
Concept of Tercet Molecular Nanocomposites and Preliminary Studies on [PPTA/(PA-6/PA-66)] System of Miscible Blend of
Polyamide-6/Polyamide-6,6 Molecularly Reinforced at Nano Level by Poly(p-phenylene-terephthalamide)
Table 1. Glass transition temperatures of PA6, PA66, binary blend of PA6/PA66
and tercet molecular nanocomposites of PPTA [PA6/PA66] at heating rates of
5K/min
properties as compared to the 50/50
PA6/PA66 flexible blend.
Polymer, Blend or Tercet Molecular Nano
Composite
Several mechanical properties, for
example, tensile modulus, of a
polymeric material are dependent on
its glass transition temperature. Thus
the higher glass transition temperature
of the tercet molecular nanocomposite
compositions, as compared to that
of 50/50 PA-6/PA-6,6 blend also
indicates the potential of the tercet
molecular nanocomposites exhibiting
better mechanical properties than
those of the 50/50 PA6/PA6,6 flexible
blend. The improved mechanical
properties of the tercet molecular
nanocomposite compared to the
constituent flexible PA-6/PA-6,6 blend
have been established, as reported later
in this study.
Polyamide-6 (PA-6)
Glass Transition Temperature
(Tg) (oC)
67.5
Polyamide-6,6 (PA-6,6)
59.9
Blend of Polyamide-6/ Polyamide-6,6
(PA-6/PA-6,6)
62
Super Molecular Composites
PPTA/ [PA-6/PA-6,6] [5/(47.5/47.5)]
PPTA/ [PA-6/PA-6,6] [10/(45/45)]
PPTA/ [PA-6/PA-6,6] [15/(42.5/42.5)]
110
115
145
in the 50/50 PA-6/PA-6,6 blend. Thus,
the first requirement of a flexible
polymer blend constituting the tercet
molecular nanocomposite being
miscible is established.
Table 1 also records the glass transition
temperature of the PPTA/[PA6/PA6,6]
tercet molecular nanocomposite of
compositions [5/(47.5/47.5)], [10/
(45/45)] and [15/(42.5/42.5)], and as
110 oC, 115 oC and 145 oC respectively.
While investigating the glass transition
temperatures of all these compositions
of PPTA/[PA-6/PA-6,6], only one glass
transition temperature, much higher
than that of the PA-6/PA-6,6 blend, has
been observed for each of the PPTA/
[PA-6/PA-6,6] compositions, and
no glass transition temperature was
observed at or near 67.5 oC, or 59.9 oC
or 62 oC - that are respectively the glass
transition temperatures of PA-6, PA6-6 and the 50/50 PA-6/PA-6,6 blend.
Reproducibility of the single Tg values
for 50/50 PA-6/PA-6,6 and for various
PPTA/[PA6/PA66] tercet molecular
nanocomposite compositions in
repeated DSC scans, and significant
increase in glass transition temperature
of the tercet molecular nanocomposite
compositions, as compared to that
of the flexible blend of 50/50 PA6/
PA66 in proportion to the amount of
PPTA in the system, establishes true
miscibility in the PPTA/[PA6/PA6,6]
tercet molecular nanocomposite of
compositions [5/(47.5/47.5)], [10/
(45/45)] and [15/(42.5/42.5)].
The role of specific interactions and
similar solubility parameter in polymer
blend miscibility is well documented21.
It may be concluded that miscibility
observed in the PPTA/[PA6/PA6,6]
tercet molecular nanocomposites of
[5/(47.5/47.5)], [10/(45/45)] and [15/
(42.5/42.5)] compositions results from
intermolecular H-bonding between the
C=O and N-H groups of the component
polymers and by some role of the
similar solubility parameters of PA-6
and PA-6,6.
Flory19 has stated that a blend of rigidrod polymer and a flexible polymer
phase separates; however, it may
be noted that the Flory’s theory19 is
based on athermal systems without
any specific interactions. This study
establishes that the specific interactions
and similar solubility parameters
overcome the phase separating forces
and impart miscibility even to a
ternary polymer blend consisting of
two flexible polymers and a rigid-rod
polymer.
The much higher glass transition
temperatures of tercet molecular
nanocomposite compositions
compared to that of flexible PA6/
PA66 blend (62 oC), and increase
in glass transition temperatures of
tercet molecular nanocomposite
compositions, with increasing PPTA
amounts in them; establish that the
tercet molecular nanocomposites
certainly have much-improved thermal
Polymers & Polymer Composites, Vol. 23, No. 6, 2015
5.2 Morphology and Nano
Dispersion
The morphology of [5/(47.5/47.5)],
10[(45/45)] and [15/(42.5/42.5)]
compositions of [PPTA([PA-6/PA6,6)] tercet molecular nanocomposites
investigated by FE-SEM is shown in
Figure 3a, b and c respectively. The
micrographs show uniform structure
with well dispersed intermingled
constituent rigid-rod macromolecules
and the flexible polymers in all
compositions of the tercet molecular
nanocomposites. All the compositions
of the tercet molecular nanocomposites
show a single phase with no phase–
separation, confirming the absence
of a segregated second or third phase
and also indicating that all the three
polymers have mixed at molecular
level forming homogeneous phase
system. No separate segregated rods
or fibrils of PPTA are seen and SEM
confirms that the reinforcing rigid-rod
PPTA macromolecules, intermingled
with the flexible PA-6/PA-6,6 polymer
blend, are dispersed at least below 5
nm, which is the resolution limit of
the SEM.
411
Sanjay Palsule, Anuja Baijal, and Sampat Singh Bhati
5.3 Intermolecular Interactions
FTIR spectra of 50/50 PA6/PA6,6 and of PPTA[(PA6/PA-6,6)]
5/[(47.5/47.5)], 10/[(45/45)], 15/
[(42.5/42.5)], tercet molecular
nanocomposites in the range between
wavenumber 2000cm-1 to 500 cm-1; and
4000 cm-1 to 2500 cm-1 are recorded
in Figures 4 and 5 respectively. C=O,
N-H, C-H and hydrogen bonds are
present in all the polymers constituting
the tercet molecular nanocomposite:
PPTA, PA-6, PA-6,6.
In the FTIR spectra, (Figure 4) the
band around 1640cm-1 is attributed
to C=O stretching vibrations (amide
I mode) and the band around 1544
cm-1 is for the combined vibrations
of N-H and C=O groups (amide II
mode). This feature is present in all
the four samples i.e.; in 50/50 PA6/
PA-6,6 and also in PPTA[(PA6/PA6,6)] 5/[(47.5/47.5)], 10/[(45/45)],
15/[(42.5/42.5)] tercet molecular
nanocomposites. As shown in Figure
4, the FTIR spectra assigned to C=O
stretching vibrations (amide I mode) is
present exactly at 1640 cm-1 for 50/50
PA6/PA-6,6 and PPTA[(PA6/PA6,6)] - 5/[(47.5/47.5)], 10/[(45/45)],
and 15/[(42.5/42.5)]. The combined
vibrations of N-H and C=O groups
(amide II mode) are present at
1543 cm-1 for 50/50 PA6/PA-6,6, and
at 1544 cm-1 for the PPTA[(PA6/PA6,6)]-5/[(47.5/47.5)], 10/[(45/45)],
and 15/[(42.5/42.5)].
In the FTIR spectra (Figure 5), the bands
at or near 3305 cm-1 are assigned to
stretching vibrations of H-bonded N-H
groups. As shown in Figure 5, the band
for stretching vibrations of H-bonded
N-H groups for 50/50 PA6/PA-6,6
is present exactly at 3304 cm-1; for
PPTA[(PA6/PA-6,6)] - 5/[(47.5/47.5)]
at 3306 cm-1, for PPTA[(PA6/PA-6,6)]
- 10/[(45/45)] at 3306 cm-1, and for
PPTA[(PA6/PA-6,6)] - 15/[(42.5/42.5)]
at 3308 cm-1. These hydrogen bonds
Figure 3. SEM images of [PPTA[(PA-6/PA-6,6)] tercet molecular nanocomposites
of composition (a) [5/(47.5/47.5)], (b) 10[(45/45)] and (c) [15/(42.5/42.5)]
(b)
(a)
(c)
Figure 4. FTIR spectra in the range 2000 cm-1 – 500 cm-1
The FTIR spectrum (Figure 5) for
stretching vibrations of C-H bonds
is assigned to the bands around 2865
cm-1 and 2940 cm-1. As shown in
Figure 5, stretching vibrations of
C-H bonds for 50/50 PA6/PA-6,6 are
present at 2863 cm-1 and 2937 cm-1.
Similarly for PPTA[(PA6/PA-6,6)]-5/
[(47.5/47.5)], the bands are present
at 2865 cm -1 and 2939 cm -1; for
PPTA[(PA6/PA-6,6)] - 10/[(45/45)],
the bands are at 2866 cm -1 and
2940 cm-1; for PPTA[(PA6/PA-6,6)]
– 15/[(42.5/42.5)] at 2866 cm-1 and
2940 cm-1, showing the presence of
C-H bonds.
412
Polymers & Polymer Composites, Vol. 23, No. 6, 2015
Concept of Tercet Molecular Nanocomposites and Preliminary Studies on [PPTA/(PA-6/PA-66)] System of Miscible Blend of
Polyamide-6/Polyamide-6,6 Molecularly Reinforced at Nano Level by Poly(p-phenylene-terephthalamide)
are formed between the H atom
of N-H group and O atom of C=O
group present in the PA6, PA-6,6 and
PPTA. These hydrogen bonds, along
with similar solubility parameters of
PA-6 and PA-6,6 impart miscibility
and homogeneous interface, leading
to nano-level dispersion of PPTA
and forming the tercet molecular
nanocomposites.
5.4 Mechanical Properties
Table 2 records the tensile properties
of PA-6, PA-6,6, flexible PA-6/
PA-6,6 blend; and of PPTA[(PA6/
PA-6,6)] 5/[(47.5/47.5)], 10/[(45/45)]
and 15/[(42.5/42.5)] tercet molecular
nanocomposite. Table 2 shows that
compared to the tensile modulus of
0.97 GPa of the flexible 50/50 PA-6/
PA-6,6 blend, with the amount of
reinforcing rigid PPTA macromolecule
in the tercet molecular nanocomposites
increasing to 5, 10, and 15%; the tensile
modulus of the formed PPTA[(PA6/
PA-6,6)] 5/[(47.5/47.5)], 10/[(45/45)]
and 15/[(42.5/42.5)] tercet molecular
nanocomposites increases by
approximately 1.51, 1.78 and 2.01 GPa
respectively. Thus, with the amount of
reinforcing rigid PPTA macromolecule
in the tercet molecular nanocomposites
increasing to 5, 10, and 15%; the tensile
modulus of the formed PPTA[(PA6/
PA-6,6)] 5/[(47.5/47.5)], 10/[(45/45)]
and 15/[(42.5/42.5)] tercet molecular
nanocomposites increases by about 56,
84 and 107% respectively. Similarly,
with the amount of reinforcing rigid
PPTA macromolecule in the tercet
molecular nanocomposites increasing
to 5, 10 and 15%; the tensile strength
of the formed PPTA[(PA6/PA-6,6)]
- 5/[(47.5/47.5)] and 10/[(45/45)]
tercet molecular nanocomposites
increases by approximately 63, 80 and
98% respectively. In absolute terms,
compared to the tensile strength of
26 MPa of the flexible 50/50PA-6/
PA-6,6 blend; with the amount of
reinforcing rigid PPTA macromolecule
in the tercet molecular nanocomposites
increasing to 5, 10 and 15%; the tensile
strength of the formed PPTA[(PA6/
PA-6,6)] - 5/[(47.5/47.5)], 10/
[(45/45)] and 15/[(42.5/42.5)] tercet
molecular nanocomposites increases
to approximately 42.3, 46.8, and 51.4
MPa respectively. The considerable
improvement in tensile properties of
PPTA[(PA6/PA-6,6)] 5/[(47.5/47.5)],
10/[(45/45)] and 15/[(42.5/42.5)]
tercet molecular nanocomposites
compared to those of the constituent
flexible PA-6/PA-6,6 blend, and
the increase in tensile properties of
tercet molecular nanocomposites in
proportion to increasing amounts
of PPTA in the tercet molecular
nanocomposite compositions,
establishes the reinforcement of the
flexible PA-6/PA-6,6 blend by rigid-rod
PPTA macromolecule and formation
of composite in the form of tercet
molecular nanocomposite.
6. Conclusions:
Formation of
Tercet Molecular
NanoComposite
According to the concept and
the principle, a tercet molecular
nanocomposite is a ternary miscible
polymer system, in which a miscible
blend of two flexible polymers
is molecularly reinforced at the
nanometre level by a rigid-rod
macromolecule, and the resultant
tercet molecular nanocomposite
demonstrates properties better than
those of the constituent flexible
polymer blend due to its miscible
nature, homogeneous interface, and
Figure 5. FTIR spectra in the range 4000 cm-1 – 2500 cm-1
Table 2. Mechanical properties of 50/50 PA6/PA66 and tercet molecular nanocomposites of PPTA/[PA6/PA66]
Blend or Tercet Molecular Nano
Composite
Tensile
Modulus (GPa)
Tensile Strength
(MPa)
Blend of PA-6/PA-6,6
0.97
26
-
-
PPTA/[(PA-6/PA-6,6)] [5/(47.5/47.5)]
1.51
42.3
55.67
62.69
PPTA/[(PA-6/PA-6,6)] [10/(45/45)]
1.78
46.8
83.51
80.00
PPTA/[(PA-6/PA-6,6)] [15/(42.5/42.5)]
2.01
51.4
107.22
97.69
Polymers & Polymer Composites, Vol. 23, No. 6, 2015
Improvement in
Improvement in
Tensile Modulus in % Tensile Strength in %
413
Sanjay Palsule, Anuja Baijal, and Sampat Singh Bhati
nanometre-level dispersion of the
rigid-rod macromolecules. The higher
glass transition temperatures of
all the PPTA [PA-6 / PA – 6,6)]
tercet molecular nanocomposite
compositions, compared to that of
the constituent flexible PA-6/PA-6,6
blend and increase in glass transition
temperatures of the tercet molecular
nanocomposite compositions in
proportion to the amounts of rigidrod PPTA in them, confirms the
miscible nature of the tercet molecular
nanocomposites. The scanning
electron micrographs showing well
dispersed and intermingled flexible
and rigid-rod polymers with no phase
separation confirm homogeneous
morphology of the tercet molecular
nanocomposite and dispersion of
PPTA below 5 nanometres. FTIR
study confirms that intermolecular
hydrogen bonding, along with similar
solubility parameters, imparts a
miscible homogeneous nature to the
tercet molecular nanocomposites.
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