INTRODUCTION
The uses of ionizing radiation to graft the macromolecules with monomeric molecules
were the subject of several early studies. Special concern was paid by other
studies to those macromolecules which have industrial applications such as polyethylene,
polypropylene, polystyrene, cellulose and others. Some times used gamma irradiation
in grafting process in the presence of atmospheric oxygen using different parameters
i.e., temperature, solvents and catalyst variations, it was suggested that the
degree of grafting of monomer increases with the increasing of the dose and
the concentration of the monomer to certain limits. It is well known that physico
chemical properties of some polymers can be verified to accommodate certain
industrial and other applied demands (Kurilenk, 1980;
Imai, 1982; Dole, 1973; Dongming
et al., 2009; Fydelor, 1971; Chapiro,
1962; Nicholas, 1997).
The study of polystyrene (PS)/acrylonitrile-butadiene-styrene (ABS) grafted
copolymer/ cyclohexanone or methylene chloride system compatibility both in
concentrated solutions and solid state has been carried out by phase separation,
viscosimetrical measurements and thermal behavior (Cornelia
et al., 1981).
It is possible to graft vinyl monomers, such as acrylonitrile, on to polystyrene
via anionic processes but not by a radical process. Both homopolymerization
of the added acrylonitrile and graft copolymerization in which acrylonitrile
units are added to the para position on the benzene ring in styrene occur; the
conversion of acrylonitrile into polymer depends upon the time and temperature
of the reaction and on the concentration of the anionic initiator, butyllithium.
A constant 15-20% of the acrylonitrile is converted to graft copolymer while
the remainder is homopolymerized (Thomas and Wilkie, 1997).
Poly (styrene-co-acrylonitrile)-graft-poly (propylene oxide), the stabilizer
formed in situ in the dispersion polymerization of styrene, acrylonitrile
and macromonomer was separated from ungrafted copolymer by liquid chromatography.
After the determination of the separation conditions by thin-layer chromatography,
the effective separation of the graft polymer from copolymer was achieved by
liquid column chromatography. The graft efficiency and the composition of the
graft polymer was determined by UV and 1H NMR (Guo et
al., 2001).
Gamma radiation-induced graft copolymerization of styrene onto poly (ethylene
terephthalate) films was studied using simultaneous irradiation technique. The
effects of grafting conditions on the degree of grafting were investigated.
The grafting conditions include monomer concentration, irradiation dose, dose
rate and the type of solvent (Mohamed, 2000).
The effects of γ irradiation on polymers used in food packaging have been
studied by NMR. In order to assess the presence of a threshold dose for an observable
effect, the whole range of 1-100 KGy was investigated. Polystyrene, poly-butadiene,
styrene-acrylonitrile, high-impact polystyrene and acrylonitrile-butadiene-
tyrene were studied before and after the γ irradiation treatment and in
the presence or in the absence of antioxidants and stabilizers (Pentimalli
et al., 2000).
The gamma radiation-induced surface graft copolymerizations of styrene-acrylonitrile
and styrene-methyl acrylate to Teflon were studied. It was observed that the
compositions of the various grafted copolymers are richer in the more polar
monomer. These results were interpreted in terms of a preferential solvation
of the relatively immobile growing graft polymer free radicals by the polar
monomers (George et al., 2003).
An evaluation of the flory-huggins interaction parameter was determined of
poly (styrene-co-acrylo-nitrile) and poly (methyl-methacrylate) blend from the
thermodynamic properties as enthalpy of mixing measurements to make a comparison
for each temperature in accordance with the behavior of these mixtures (Frezzotti
and Ravanetti1, 1994).
In the present study a polystyrene polymer was grafted by acrylonitrile using gamma-irradiation, with chloroform as a solvent and FAS as a catalyst. The new grafted polymer obtained was investigated and characterized.
MATERIALS AND METHODS
Chemicals and materials: Polystyrene (Sigma Aldrich, Germany, 2009). Acrylonitrile a commercial form was purchased from Merck, Germany 2009 and used without any laboratory interferences.
Dimethyl formamide DMF (BDH Limited Poole England). Ferrous ammonium Sulphate FAS a grade of Fluka-Garantic was used. Chloroform and Ethanol (Scharlau).
Techniques
Gamma irradiation technique: Irradiation procedure was carried out by introducing
polystyrene in a pyrex tubes with acrylonitrile as monomer using chloroform
as solvent and FAS as a catalyst. The irradiation performed in the presence
of atmospheric air. The resulting of grafted polymer was dissolved in DMF solvent,
precipitated by ethanol then filtered using funnel. Precipitation process was
repeated three times and then the yield was kept under reduced pressure in order
to ensure complete removal of solvent. The gamma-irradiation was obtained with
dosing rate 1.1 Mrad h-1 using gamma cell 220 of Co60
Canadian type. Figure 1 show the distribution of the dose
in the gamma cell (Belchior et al., 2008).
FTIR technique: The FTIR spectra were obtained from the perkin elmer
FTIR 1650 spectrophotometer at room temperature using KBr disc method for characterizing
the polymer. To prepare the disc method, the sample was dried and grounded with
the KBr powder until they were in a well mixed, powdered form. The powder was
then pressed at 8 tons for 1 min to produce the disc. The sample was scanned
at 16 scans at wavenumber range of 4000-400 cm-1.
|
| Fig. 1: | The
isodose distribution in the irradiation chamber |
Viscosity technique: Viscometery measurement of viscosity was performed
by a viscometer. The grafted polymer was dissolved by DMF solvent, the reduced
viscosity values (ηred) were calculated and plotted versus concentrations
to give a straight line in accordance with Flory-Huggin,s equation
(Ovejero et al., 2007; Huggins,
1942; Fabio et al., 2006).
Where:
| to |
: |
Time flow of the solvent |
| t |
: |
Time flow of the solution |
| C |
: |
Concentration in g 100 mL-1 |
| ηred |
: |
Reduce viscosity |
Quantitative determination of grafting yield
Where:
| W1 |
: |
Film weight of polystyrene before grafting |
| W2 |
: |
Film weight of polystyrene after grafting |
TGA and DTGA techniques: The TG and DTG analysis using perkin elmer
model TGA 7 thermalgravimetry analyzer was used to measure the weight loss of
the samples. The samples were heated from 30-600°C with the heating rate
of 10°C min-1 under nitrogen atmosphere with a nitrogen flow
rate of 20 mL min-1.
RESULTS
Synthesis of polystyrene grafted with acrylonitrile using gamma-irradiation was proved by many identification methods:
| • |
FTIR methods: Table 1 shows the assignment
of the polystyrene, acrylonitrile and new grafted polymer (polystyrene grafted
with acrylonitrile) as illustrate with the three spectra of FTIR in (Fig.
2) |
| • |
Grafting study: Figure 3-5
show the relationship between the percentage of grafting (w/w%) with gamma
dose (Mrad), catalyst percentage (FAS w/w%) and monomer percentage (acrylonitrile
w/w%), respectively |
| • |
Viscosity study: Figure 6 shows the
viscosity relationship with grafted percentage for three different grafting
percent samples to produce the intrinsic viscosity from intercept of linear
relationship |
| Table 1: | FTIR
Assignment of Grafted Polystyrene, Polystyrene and Acrylonitrile |
 |
| s: Strong, m: Medium, w: Weak and v: Very |
| • |
Thermal degradation properties (TGA and DTG): Figure
7 is the TGA thermograms curve for polystyrene only and polystyrene
grafted with acrylonitrile. Figure 8a and b
of DTG for polystyrene only and polystyrene grafted with acrylonitrile,
respectively |
|
| Fig. 2: | FTIR
spectra of (a) polystyrene, (b) grafted polymer and (c) acrylonitrile |
|
| Fig. 3: | Variation
of grafting percent (w/w%) as a function of gamma dose of constant FAS
concentration 2% (w/w%) and monomer concentration 90% (w/w%) |
|
| Fig. 4: | Variation
of grafting percent (w/w%) as a function of FAS concentration (w/w%) of
constant dose 1.25 Mrad and monomer concentration 90% (w/w%) |
|
| Fig. 5: | Variation
of grafting percent (w/w%)as a function of monomer concentration of constant
dose 1.25 Mrad and FAS concentration 2% (w/w%) |
|
| Fig. 6: |
Variation of reduced viscosities (mL g-1) of grafted
polymer as function of concentration (g mL-1) of grafted polymer
in different grafted percentage (a) grafted polymer (%) = 21.68 (b) grafted
polymer (%) = 42 and (c) grafted polymer (%) = 54.1 |
|
| Fig. 7: | TGA
thermograms curve for (a) Polystyrene and (b) Grafted polymer |
The concentration of the catalyst (FAS) is 2% and the monomer concentration
is 90%, at 1.25 Mrad dose.
|
| Fig. 8: |
(a) TGA and DTG thermogram curves for Polystyrene at a heating
rate of 10°C min-1, (b) TGA and DTG thermogram curves for
Grafted Polymer at a heating rate of 10°C min-1 |
These results designate that best grafting percentage ratio could be exposed.
The new grafted polymer was proved by FTIR, TGA and Viscosity techniques, which
was analyzed and studied with a suggested presented mechanism.
The above results confirm that the adding of acrylonitrile to polystyrene was successfully grafted.
DISCUSSION
FTIR study: Figure 2 shows the FTIR spectra that grafting
occur of the acrylonitrile on to the polystyrene specially when the spectrum
of polystyrene alone has no indication of (-CN) absorption band, this band 2230
cm-1 appears in the grafted polymer at 2245 cm-1 for CN.
Moreover, the band of C=N appeared at 1615 cm-1 corresponding to
the resonance of the nitrile group when it was in the acrylonitrile form. However,
it disappears when the group is grafted with polystyrene. Moreover, a strong
band appears at 1220 cm-1 for -CN of grafted polymer only. Then the
very strong broad band appears in the spectrum of acrylonitrile at 965 cm-1
which indicating that C=C-H2 of the carbon closed to C=C group was
disappeared in the grafted polymer and polystyrene which proved this band is
for acrylonitril only. The detailed information of FTIR spectra are shown in
Table 1 (Radhi and EL-Bermani, 1990;
Colthup et al., 1975).
Grafting study: It was found that the percent of grafting increased
with the dose of gamma irradiation throughout the dose range from 0.4-1.5 Mrad
as show in Fig. 3. It explain the type of variation when keeping
the concentration of the catalyst FAS and the monomer at 2 and 90% (w/w%), respectively.
It was also found that the percent of grafting in it ,s higher value
is occur when the concentration of the catalyst FAS is about 2% (Fig.
4), although that at constant gamma dose (1.25 Mrad) and monomer concentration
(90%) the grafting percent was in high value. Another study was the effect of
monomer concentration on grafting percent which is found at 90% as in Fig.
5.
Viscosity study: The effect of grafted lateral chains was studied by determination of intrinsic viscosity [η] at different grafted polymer, up to 54.1% grafting, the [η] increased linearly as in (Fig. 6) with increasing grafting percent which prove the simple effect of lateral chains on the original macromolecule of polystyrene and the absent of network formation. The values of intrinsic viscosity of grafted polymer are high of the high grafted percentage as shown in Fig. 6.
Thermal degradation properties (TGA and DTG): The TGA curve and DTG
curve obtained for Polystyrene is shown in Fig. 7a and 8a,
respectively. Degradation commences near 395.96°C and continues rapidly
until about 440.89°C.
The TGA curve and DTG curve for grafted polymer (polystyrene grafted with acrylonitrile)
are presented in Fig. 7b and 8b, respectively.
Degradation proceeds in double steps commencing the first step at 169.45°C
and ending at 267.39°C indicating to traces of poly(acrylonitrile) ungrafted
in polymer, while the second step begin at 432.64°C and ended at 480.09°C
for the Grafted Polymer (polystyrene-acrylonitrile) (Ahmad
et al., 2007).
Polymerization methods: Free radicals used to initiate polymerization
can be generated in two ways: by temperature-sensitive catalysts or radiation
curing. Chemical curing is a cheaper method with small-scale productions, whereas,
gamma radiation is more economical on a larger scale, the suggest mechanism
of polystyrene by free radical as the following steps Manas
(2006). The mechanism of grafted polystyrene with acrylonitrile was proposed
at Scheme 1 in the following four steps.
| • | A
free radical catalyst or gamma-irradiated polymer generates the free radicals
(R• + R•.). Polystyrene• + Polystyrene• |
| • |
 |
|
|
Scheme 1: |
The proposal mechanism of polystyrene with acrilonitrile |
| • |
 |
| • |
 |
| • |
 |
Our literature review show that no information regarding grafting of polystyrene
by gamma radiation.
CONCLUSIONS
It was possible to graft onto polystyrene by a radical process as, used acrylonitrile (monomer) with gamma irradiation. The extent of grafted polymer formation depends upon:
| • | The
percentage of the monomer was about 90% (w/w%) |
| • | The
percentage of the catalyst (FAS) was about 2% (w/w%) |
| • | The
total gamma dose was around 1.25 Mrad |
The formation of a grafted polymer was successfully carried out using gamma irradiation with FAS as a catalyst. The new grafted polymer was characterized by FTIR spectroscopy and TG analyzer.
ACKNOWLEDGMENT
The authors wish to express their thanks to Professor Muhie R. Hamoud, Department of Chemistry, College of Education 2, University of Baghdad-Iraq.
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