FIBER Dr. AL? DEM?R – Asst. Prof. Dr.

 

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REVIEW
PAPER:

PROPERTIES
OF POLYMER LAYERED SILICA NANOCOMPOSITES                      ————————————————-

 

 

 

 

 

 

Prof.
Dr. AL? DEM?R – Asst. Prof. Dr. AL? KILIÇ
——————————————–

 

 

 

BEYZA
NUR TEPEKIRAN                                                                                                               
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513171003
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REVIEW
PAPER

PROPERTIES
OF POLYMER LAYERED SILICA NANOCOMPOSITES

 

INTRODUCTION

Composites
are widely used in various fields such as transportation, construction,
electronics and consumer products. It offers combinations of rigidity, strength
and weight that are difficult to achieve separately from individual components.
1 In brief, composites are generally 2 or 
more closely interacting materials which have different physical and
chemical properties in intimate contact with each other. Polymer science uses
the concept of a composite as a material formed by combining different phases.
In composite materials, one phase is usually continuous called the matrix;
while the other phase is a reinforcing material called the dispersed phase.

 

Figure
1. General
shape of composite (https://goo. gl/images/29fRHQ)

 

Nanocomposites
on the other hand is a relatively new class of materials with handheld,
ultra-thin phase sizes, typically at a few nanometers level.2 In nanotechnology,
polymer nanocomposites (PNC) have attracted academic and industrial interest
due to exceptional electrical, mechanical and permeability properties. 3 Because
of the nanometer size features of nanocomposites, they typically have unique properties
that are not shared by more conventional microcomposite replacements, for this
reason, it offers new technology and business opportunities. 4

Also,
much works have focused on developing polymer/clay nanocomposites. The most
popular or practical layered silicates of clay are of three types: Kaolinite,
MMT (sodium montmorillonite) which has a low content of alumina and high content
of silica and illinite that depends on application areas, appropriate clay type
can be used to synthesize polymer/clay composites. 5

Generally,
in these papers polymer nanocomposites with layered silicates (PLS) as an
inorganic phase (reinforcement) are discussed. For PLS (polymer layered
silicate) material design and synthesis is based on the ability to incorporate
a wide variety of monomers and polymers in the galleries between the layers of
the layered silicates. PLS nanocomposites in particullarly demonstrate higher
properties in terms of strenght, stiffness, mechanical and thermal properties
even flammability 6 and gas permeability 7 decrease. Also, it is more
lighter in weight. 8 In general, polymer layered silica nanocomposites are
fabricated via such two methods these are called either intercalated or
delaminated – exfoliated. 9

 

Figure
2. Schematic
image of composite structures obtained using layered silicates. The rectangular
bars represent the silicate layers. (a) Single polymer layers intercalated in
the silicate galleries (intercalated hybrids); (b) composites obtained by
delamination of the silicate particles and dispersion in a continuous polymer
matrix (delaminated hybrids).

 

 

PRODUCING
PLS NANOCOMPOSITES

The
composites were first reported in the literature in 1961 when Blumstein showed
the polymerization of vinyl monomers intercalated into montmorillonite (MMT) clay.
10 Polymer nanocomposites, particularly polymer layered silicate (PLS)
nanocomposites, are an alternative to conventional (macroscopically) filled
polymers. Depending on nanometer size distributions, nanocomposites significantly
improved properties when compared to conventional composites. 11 ” For example, the mechanical properties
of a Nylon-6-layered-silicate nanocomposite, with a silicate mass fraction of
only 5%, show excellent improvement over those for pure Nylon-6. ” 12

 

Figure
3. Representation
of different methods (solution blending, melt blending, and in situ
polymerization) use to prepare polymer-layered-silicate nanocomposites and the delaminated
(or exfoliated) and intercalated morphologies.

 

Most
synthesis methods of clay-based PNCs(polymer nanocomposites) are produced
include that in situ polymerization, the solution method and melt
intercalation. 13 However, the most versatile method for PLS nanocomposites
is melt intercalation from the point of the easiest and cost effective method.
14 J.-H. Lee et al 15 explained that for solution blending method, huge
solvent tank systems sholud be provided. Wang et al 16 also studied on the
PE/clay nanocomposites which were produced by melt blending method and as a
result of this one they succeded to produce intercalated nanocomposites whereas
they could not obtain fully exfoliated composites. 17

Figure
4. General
illustration of (a) in situ polymerization, (b) melt intercalation, (c) solution
intercalation

                                                                                                                                                                                                                               

Silicate
layered nanocomposites are called 2:1 layered silicates 18. Their crystal
structures consist of two layered silicates and between the layers the gallery
or interlayer is occured due to Vanderwalls gap.19  Delaminated and intercalated both of these
terms are used to explain nanocomposite morphology. 20 In general, two types
of hybrid structures are possible: first one is an intercalated single continuous
extended polymer chain intercalated between silicate layers, resulting in a
multi-layered array of alternating polymer / inorganic layers; and second one
is delaminated or exfoliated silicate layers (1 nm thick) into a continuous
polymer matrix. 21 Also, The silicate layers in the delaminated composites
that possess radius gyration of polymers might not be as good as in the
intercalated structure. 22

In
the J.-H. Lee et al paper,23 PE (polyethylene)/clay nanocomposites were
synthesized by melt-intercalation using PP-g-MA compatibilizer. The pristine
clay was first modified with a swelling agent (octadecylamine) in solution to
obtain an organophilic clay before being melt blended with a compatibilizer:
PP-g-MA. These compounds were melt intercalated with PE to synthesis the
PE/clay nanocomposite. 24

Table 1.
Materials used for PE/clay nanocomposites

In
the J.-H. Lee et al. the experimant section initially start with modification
of the montmorillonite. 25 ” The purified sodium montmorillonite (MMT) was
initially treated to make it organophilic clay. The MMT (21 g) was dispersed
uniformly into hot water (1330 ml/80° C) using a mechanical stirrer and a homogeneous
suspension was obtained. Octadecylamine (8.3 g) was dissolved in hot water (670
ml) at 80°C with a small amount of hydrochloric acid for the Na+ ion exchange
reaction and poured into the MMT–water suspension while stirring the solution
vigorously. The MMT intercalated with octadecylamine (abbreviated OMMT) was
freeze-dried. The freeze-dried OMMT was ground with a mortar and pestle and
particles smaller than 160 micron were collected.” 26 First of all, briefly
was produced;

MMT
+ OCTADECYLAMINE = OMMT

Second
processes is preparation of pre-intercalated compounds. ”The OMMT was
melt-blended with a compatibilizer at 180°C for 10 min and at a speed of 50 rpm
with a internal mixer to obtain a pre-intercalated compound (PIC). Two
compatibilizers (PP-g-MA and PE-g-MA) were used to investigate the effects
of  the compatibilizer on PE/clay
nanocomposites. The PIC was ground with a mortar and pestle to obtain smaller
particles and hence better dispersion in the resin 27 and briefly can be
explained;

OMMT
+ COMPATIBILIZER = PIC

The
final step is preparation of PE/clay nanocomposites. ”The PIC was mixed with
PE resin at 180 ° C for 10 min to obtain a PE/clay nanocomposite (PECN). To
investigate the effects of clay content on the PECN, PE/clay nanocomposites
with various clay contents were prepared. The amount of compatibilizer (both
PP-g-MA and PE-g-MA) in the PECN was kept constant for all the composites by
adding the compatibilizer during the melt mixing. ” 28 J.-H. Lee et al.
finally obtained that;

PIC
+ PE resin = PECN

Gilman
et al. 29 reports their paper in conjunction with recent results of
polypropylene-graft-maleic anhydride (PPGMA) and polystyrene layered silicate
nanocomposites using montmorillonite in our continuous research on the
mechanism of reducing the flammability of polymeric-layered silicate
nanocomposites and fluorohectyl. ” PS-layered-silicate nanocomposite samples
were prepared using one of the following three techniques. First one is  solvent intercalation. A mixture of a
PS-toluene solution (Dow Styron-612, Mn27 100 000 g/mol, PS mass fraction 3-10%)
and an organically treated layered silicate (mass fraction of layered silicate
3%, relative to PS) was ultrasonicated for up to 5 min until a good suspension
was created. The solvent was then evaporated for several hours at temperature
in a fume hood, yielding a very viscous gel. The gel was placed in a vacuum oven
at 70 °C for 2-5 h to evaporate the remaining solvent.  Second production method is also; static melt
intercalation. PS (dried, powdered) and organically treated layered-silicate
(dried) were mixed and ground together in a mortar and pestle. The mixed powder
was heated at 170 °C for 2-6 h in a vacuum. The material was stirred once
halfway through the annealing/melt intercalation process. Final step for PLS
nanocomposites is extrusion melt intercalation. PS (dried, powdered) and organically
treated layered silicate (dried) were premixed and blended/extruded using a DSM
miniextruder under N2 at 150- 170 °C for 2-4 min. 30

 

 

 

 

 

 

CONCLUSIONS

J.-H.
Lee et al 31 the materials were characterized using X-RD, TEM, SEM, and TGA. Physical
properties were observed with DMA and stress tests. Also, permeability tests of
nanocomposites were performed. X-RD analysis and TEM observations partially
depicted intercalation / exfoliation and well-dispersed nanocrystals in the
composite. Polymer has developed a lot of mechanical and gas barrier properties
to load with nanoclay. The tensile modulus increased by about 49% with 7% clay
and the tensile strength increased by about 15% when compared to pure
polyethylene. DMA tests also showed good reinforcing effects of nanocells and
good machinability of the nanocomposites. Introducing nanoclaves reduced the
temperature for the onset of thermal decomposition.

TEM
observation of the PLS nanocomposites morphology for J.-H. Lee et al. 32

 

 

Figure 5. TEM
images of (a) and (b) nanocomposites
with 3% clay 100 k and nanocomposites with 7% clay 100 k, respectively.

 

                                (a)                                                                   
(b)

Figure
6. (a) Explain TGA curves of PE/clay nanocomposites for
various clay contents. Also (b) is explain DSC curves of PE/clay nanocomposites
for various clay contents.

 

Figure 7. Explain
gas permeability of the nanocomposites for various clay contents.

 

 

 

 

Figure 8.
Explain Tensile properties of modulus and strength.

And
also another mechanical test is DMA

                                                     

                                 (a)                                                                       
(b)

 (c)

Figure
9. Explain
the dynamic (a) storage modulus, (b) loss modulus and (c) is the Tan d of the
nanocomposites.

Gilman
et al. expressed that 33  the XRD, TEM
and cone calorimetry test to measure the flammability of the PLS
nanocomposites. The cone calorimetry is the most effective method to measure of
the PLS nanocomposites. The cone calorimeter was used to measure heat release
rate and other flammability properties.nanocomposites under well controlled
combustion conditions. Both polymer-layered silicate nanocomposites and
combustion residues were studied by transmission electron microscopy and X-ray
diffraction. We found evidence for a common mechanism combustibility is
reduced. We have found that the layered silicate species is an effect on the burning
and processing of the nanopisperse. PS and PPgMA-layered-silicate
nanocomposites showed similar reductions in flammability. 34

 Figure 10. Comparison of
the heat release rate with a mass fraction of only 2% or 4% layered silicate,
respectively

 

 

Figure
11. Nanocornposite
containing 7. 5 vol. % silicate (on the right) and unfilled polycaprolactone
(left) after being exposed to an open flame for 30 s. 35

After
the flame was removed, the nanocomposite continued to burn and retained its integrity.
In contrast, unfilled the polymer continued to burn, causing it to be
destroyed. In nanocomposites, the silicate layers are most likely to be
effective as a barrier to diffusion of gaseous products and protection of the
polymer from heat flow. 36

As
a results, all of papers demonstrate that, PLS particullarly enhances the
mechanic and thermal properties which possess significant increase as a thermal
stability of nanocomposites whereas gas permeability is decreased. Also, nanocomposites
are lighter in weight than other conventional prepared counterparts. Moreover
polymer layered silica nanocomposites dramatically increase the degree of
stiffness, strenght, barrier properties.

 

Briefly
as an annotation, DMA (Dynam?c Mechan?c Analys?s) is 37 is an important
technique used to measure the dynamic mechanical and viscoelastic properties of
materials. The force and displacement amplitudes and phase shift are analyzed
as a function of temperature, time and frequency when they are exposed to
periodic stress. DMA measures viscoelastic properties that depend on the
temperature.

Figure
Expression schema of the DMA.

In
DMA, the sample is subjected to a periodic stress in one of several different
modes of deformation such as shear, 3 point bending, tension or comprassion,
single cantilever and dual cantilever.  Processes
and events measured by the DMA include secondary relaxations, glass
transitions, crystallization, solid-solid transitions, crosslinking reactions,
melting, flow behavior and the rubbery. 38

Figure
Testing methods of DMA such as shearing, pressure, 3-Point blending and single
dual cantilever. (https://goo.gl/images/f3Q7pc)

The
DMA technique is based on a rather simple principle; when a sample is subjected
to a sinusoidal oscillating stress, its response is a sinusoidal oscillation
with similar frequency provided the material stays within its elastic
limits.  When the material responds to
the applied oscillating stress perfectly elastically, the responding strain
wave is in-phase (storage or elastic response), while a viscous material
responds with an out-of-phase strain wave (loss or a viscous response). 39

Figure
Working principles of DMA (https://goo.gl/images/NWPL8U)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

REFERENCES

 

1,2,4,7,35,36 Giannelis,
E. P. (1996). Polymer layered silicate nanocomposites. Advanced materials,
8(1), 29-35.

3,7  Cui, Y., Kumar, S., Kona, B. R., & van
Houcke, D. (2015). Gas barrier properties of polymer/clay nanocomposites. Rsc
Advances, 5(78), 63669-63690.

5  Chen, B., Evans, J. R., Greenwell, H. C.,
Boulet, P., Coveney, P. V., Bowden, A. A., & Whiting, A. (2008). A critical
appraisal of polymer–clay nanocomposites. Chemical Society Reviews, 37(3),
568-594.

6,9,10,12,20,22,29,30,33,34
 Gilman, J. W., Jackson, C. L., Morgan,
A. B., Harris, R., Manias, E., Giannelis, E. P., … & Phillips, S. H.
(2000). Flammability properties of polymer? layered-silicate nanocomposites.
Polypropylene and polystyrene nanocomposites. Chemistry of Materials, 12(7),
1866-1873.

11,18,19,21
Giannelis, E. P. (1998). Polymer-layered silicate nanocomposites: synthesis,
properties and applications.

13,14,15,16,17,23,24,25,26,27,28,31,32
 Lee, J. H., Jung, D., Hong, C. E., Rhee,
K. Y., & Advani, S. G. (2005). Properties of polyethylene-layered silicate nanocomposites
prepared by melt intercalation with a PP-g-MA compatibilizer. Composites
science and technology, 65(13), 1996-2002.

37,38,
39 Menard, K. P. (2008). Dynamic mechanical analysis: a practical
introduction. CRC press.

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