Abstract

1
(No Transcript)
2

• Abstract
• We have prepared polystyrene/clay nanocomposites
  using an emulsion polymerization technique.
• The nanocomposites were exfoliated at up to a 3
  wt content of pristine clay relative to the
  amount of polystyrene (PS).
• We used two different surfactants for the
  montmorillonite the aminopropylisobutyl
  polyhedral oligomeric silsesquioxane (POSS) and
  the ammonium salt of cetylpyridinium chloride
  (CPC).

3

• Both surfactants can intercalate into the layers
  of the pristine clay dispersed in water prior to
  polymerization.
• Although the d spacing of the POSS-intercalated
  clay is relatively smaller than that of the
  CPC-intercalated clay, PS more easily
  intercalates and exfoliates the POSS-treated clay
  than the CPC-treated clay.
• IR spectroscopic analysis further con?rms the
  intercalation of POSS within the clay layers.

4

• We used X-ray diffraction (XRD) and transmission
  electron microscopy (TEM) to characterize the
  structures of the nanocomposites.
• The nanocomposite prepared from the clay treated
  with the POSS containing surfactant is
  exfoliated, while an intercalated clay was
  obtained from the CPC-treated surfactant.
• The molecular weights of polystyrene (PS)
  obtained from the nanocomposite is slightly lower
  than the virgin PS formed under similar
  polymerization conditions.

5

• The value of Tg of the PS component in the
  nanocomposite is 8 C higher than the virgin PS
  and its thermal decomposition temperature (21 C
  ) is also higher signi?cantly.
• The presence of the POSS unit in the MMT enhances
  the thermal stability of the polystyrene.
• Keywords Montmorillonite Nanocomposites
  Polystyrene

6

• 1. Introduction
• Nanoclay-?lled polymeric systems offer the
  prospect of greatly improving many of the
  properties of their mother polymers.
• In the recent literature, there have been
  reports of nanoclay-?lled polymeric systems that
  display signi?cant improvements in tensile and
  thermal properties 19, heat distortion
  temperatures 16, and resistance to ?ammability
  12 and reduced permeability to small molecules
  5,10,11 and reduced solvent uptake 13.

7

• The nanocomposite typically comprises the
  organically modi?ed clay and the mother polymer.
• Montmorillonite (MMT), which is an
  aluminosilicate mineral with sodium counterions
  present between the layers, is the most commonly
  used clay.
• The space between these clay layers is referred
  to as the clay gallery.
• To make this inorganic clay compatible with
  organic polymers, the sodium counterions are
  usually ion-exchanged with an organic ammonium or
  salt to convert the material into hydrophobic
  ammonium-treated clays.

8

• PS/clay nanocomposites were prepared through
  emulsion polymerization by suspending the
  surfactant-treated clay in styrene monomer.
• IR spectroscopic analysis con?rmed the existence
  of POSS in the intercalated clay samples.
• We used both X-ray diffraction (XRD) and
  transmission electron microscopy (TEM) to
  characterize the clay structure.
• The properties of these PS/clay nanocomposites
  were characterized by thermogravimetric analysis
  (TGA), differential scanning calorimetry (DSC),
  and gel permeation chromatography (GPC).

9

• 2. Experimental
• 2.1. Materials
• Most of chemicals used in this study, including
  monomeric styrene, chemically pure acetone,
  methanol, tetrahydrofuran, and potassium
  hydroxide (KOH) were acquired from the Aldrich
  Chemical Co.
• 2.2. Preparation of CPC-modi?ed clays
• The organically modi?ed clay was obtained by
  combining sodium montmorillonite (5 g) and the
  desired quantity (1, 1.5, 2, or 2.5 g) of the
  ammonium salt (CPC), as previously described
  19.

10

• 2.3. Preparation of POSS-modi?ed clays
• The prewashed clay (1 g) and water (50 ml) were
  placed into a 100 ml two-neck round-bottom ?ask
  and stirred continuously for 4 h.
• POSS (0.4 g) in THF (1 ml) was placed into
  another ?ask and then 10 hydrochloric acid (1
  ml) was added and then stirring for 1 h.
• This POSS solution was then added into the
  suspended clay and the mixture was stirred
  overnight.
• The mixture was ?ltered, washed several times
  with deionized water, and then dried overnight in
  a vacuum oven at room temperature.

11

• 2.5. Instrumentations
• IR spectroscopy was performed on a Nicolet Avatar
  320 FTIR Spectrophotometer, 32 scans were
  collected at a spectral resolution of 1 cm-1.
• Infrared spectra of the organic-modi?ed clay
  were obtained using the conventional KBr pellet
  method.
• XRD spectra were collected on an M18XHF-SPA X-ray
  diffraction instrument (MacScience Co., Japan),
  using Co K? radiation Braggs law (?2dsin ?)
  was used to calculate the spacing.

12

• TEM images of the composites were obtained at 100
  kV using a Hitachi H-7500 Electron Microscope.
• Thermogravimetric analyses were performed on a TA
  Instruments Thermal Analyzer under a 40 ml/min
  ?ow of nitrogen gas at a scan rate of 20 C /min
  from 30 to 800 C .
• A Du-Pont (DSC-9000) differential scanning
  calorimeter (DSC) was used to measure the glass
  transition temperature (Tg) of the PS/clay.

13
3. Results and discussion

• 3.1. X-ray diffractions
• We used XRD to characterize the layered
  structures of the modi?ed clays and polymer/clay
  nanocomposites, since changes in 2? indicate
  changes in the gallery distance of the clay.
• Fig. 1 shows XRD patterns of organic-modi?ed
  clays containing different CPC/clay ratios.

14
(No Transcript)
15

• The basal space indicates the interlayer spacing
  of the silicate layers, which is calculated from
  the peak position using the Bragg equation.
• The pristine clay has this peak at 6.94 , which
  corresponds to a basal space of 1.26 nm.
• The insertion of the CPC surfactant between the
  galleries of the clay increases the d spacing as
  the CPC/clay ratio increases.

16

• When the CPC/clay ratio is greater than 0.4, the
  d spacing remains constant, which implies that
  oversaturation of the surfactant has occurred.
• This result indicates that the CPC surfactant
  becomes successfully intercalated into the
  galleries of the clay nanoparticles.

17
PS
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)