Polymeric Composite Materials Based On Silicate; I-Synthesis, Characterization And Formation Mechanism

Magneso-silicate has been synthesized by precipitation technique. Polyacrylamide acrylic acid and polyacrylamide acrylonitrile impregnated with inorganic ion exchanger, magneso-silicate,have beensynthesized by subjected co-monomers to gamma radiation initiated polymerization at radiation doses 25, 65 and 90KGy. The structure features of composites were investigated by sequential x-ray fluorescence spectrometer, x-ray diffraction, differential thermal-thermogravemetric analyses andinfrared spectroscopy.Formation mechanismfor these composites were conducted and the results obtained showed thatthe polymerization process were carried out in the hydrocarbon chain by addition polymerization whereas impregnation of magneso-silicate into the polymeric composites were carried out by condensation polymerization.


1-INTRODUCTION
Now inorganic ion exchange materials play an important role in analytical chemistry, based originally on their resistance to chemical attack as well as their thermal and radiation resistance [1,2]. Polymers can be synthesized through various techniques such as radical, cationic and anionic polymerization [3]. The structural,mechanical and thermal properties can be investigated through different kinds of characterization methods to determination of structure property relationships [3,4]. Recently were analyzedby different analytical techniques and a new ion exchange character was represented compared to the original ones.

2-EXPERIMENTAL
All chemicals and reagents used were of analytical grade.

2.1-SYNTHESIS OF MAGNESO-SILICATE COMPOSITE
Magneso-silicate ion exchange material was synthesized as reported earlier by Abou-Mesalam et al. [1,11,14] by the addition of equimolar solutions (0.5M) of magnesium chloride to sodium metasilicate dropwisely with volumetric ratio for (Mg/Si) equal 1.5 with continuous stirring in a water bath adjusted at 60±1 • C. The mixed solutions were immediately hydrolyzed in demineralized water. Diluted ammonia solution was added to the mixture until complete precipitation attained. The precipitate formed was kept in the mother solution to overnight standing. The precipitate was washed several times with distilled water, and then washed by 0.1M HNO3 to remove impurities and Cl − ions. The precipitate rewashed by distilled water to remove NO3 − ions. After drying at 60±1 • C, solid was poured in near boiling distilled water heated at 70±1 • C to break the solid and remove air trapped inside the solid, then redried at 60±1 • C. The obtained solid was ground and store at room temperature.

2.2-SYNTHESIS OF MONOMER SOLUTIONS
The investigated monomer solutions, acrylamide (AM), acrylic acid (AA) and acrylonitrile (AN) were prepared by dissolving 10% of each monomer in deoxygenated water.

2.3-SYNTHESIS OF CO-MONOMER SOLUTIONS
The acrylamide (AM) monomer solution was mixed with an aqueous solutions of acrylic acid (AA) and acrylonitrile (AN) by dropwith addition at constant stirring and room temperature with volumetric ratio equal unity for the preparation of (AM+AA) and (AM+AN) co-monomers, respectively. Then the (AM+AA) and (AM+AN) co-monomers were mixed with equimolar solutions (0.5M) of sodium metasilicate and magnesium chloride hexahydrate by dropwith addition at constant stirring and room temperature with volumetric ratio (AM-AA-Mg-Si) and (AM-AN-Mg-Si) equal 1:1:1.5:1, respectively. co-monomers to gamma radiation at radiation doses 25, 65 and 90KGy with dose rate 1.05KGy/h. After irradiation, the obtained hydrogel was cut into small pieces with a stainless steel scissors, soaked in acetone for removal of unreacted monomers, washed with water [17],dried at 50 o C, grained, sieved for different mesh sizes and stored at room temperature [18]. compositesprepared at different radiation doses were carried out by mixing of the solid with KOH in ratio 1:5 and ground to a very fine powder. A transparent disc was formed in a moisture free atmosphere. The IR spectra were recorded using BOMEM FTIR spectrometer in the range 400-4000 cm −1 . The stoichiometry of the constituents in MgSi and polymericcomposites based tosilicate prepared at different radiation doseswere determined using Philips sequential x-ray spectrometer-2400. The solid samples were ground to very fine powders and then mixed with H3BO3 as a binder to facilitate the pressing process. The mixture was pressed in a sample holder of 40mm diameter aluminum cups and pressed on pressing machine at 20 psi to produce a sample with the diameter of 40mm and 5 mm thickness. The concentrations of magnesium and silicone were measured according to Super-Q quantitative application program . X-ray diffraction patterns of prepared composites were carried out using a Shimadzu XD-D1, X-ray diffractometer with Cu-Kα radiation tube source (λ=1.5406A°) and graphite monochromator operating at 30kV and 30mA. The measurements were done in 2θ ranges from 4 to 90 with scan speed 2 • /min. Prepared composites (20mg) were analyzed for DTA and TGA with sample holder made of Pt in N2 atmosphere using a Shimadzu DTG-60H. The heating rate was maintained at 10 • C/min with using alumina powder as reference material.

3-RESULTS AND DISCUSSION
The scope of this study is the attempt to synthesize a high chemical stable inorganic, organic and composite ion exchange materials with high selectivity for some heavy metals and {P(AM-AN)-MgSi} composites were prepared as mentioned before in the experimental part by gamma radiation initiated co-polymerization of (AAM+AA), (AM+AN), (AM+AA+Mg+Si) and (AM+AN+Mg+Si) co-monomers at radiation doses 25, 65 and 90KGy. In gamma radiation initiated, the co-polymerization polymer complexes were formed which may be attributed to the possible steps [19]: preparation of the polymer by thegenerated radicals from the co-monomers, and the propagation of the co-monomer associated with the polymer by free radicals generated in the system [16,20]. The formationmechanism of P(AM-AA) copolymers can be represented as shown in scheme(2),when (AM+AA) comonomer subjected to gamma radiation, breaking down was carried out for double bond of (AM) and (AA) to form covalent bond between C atoms of (AM) and (AA), the polymerization in the chain occurred by addition polymerization [21]. (AM+AA) free radical was obtained. (AM+AA) free radical react with (AM+AA) co-monomer to form chain propagation. Finally, the chains were coupled with another (AM-AA) free radicals to obtain P(AM-AA) copolymer. The formation mechanism of P(AM-AN) copolymers can be shown in scheme (3), from this scheme;when(AM+AN) comonomersubjected to gamma radiation, breaking down was carried out for double bond of (AM), (AN) to form covalent bond between C atoms of (AM) and (AN), the polymerization in the chain occurred by addition polymerization [21].(AM+AN) free radical was obtained. (AM+AN) free radical react with (AM-AN) co-monomer to form chain propagation. Finally, the chains were coupled with another (AM-AN) free radicals to obtain P(AM-AN) copolymer.
The formationmechanism of {P(AM-AA)-MgSi} composite can be represented as shown in scheme (4),the reaction started by converting of (AM) monomer to imine form in solution. Then imine form react with (AA+Mg+Si) to form (AM-AA-Mg-Si) co-monomer, and subjected to gamma radiation, breaking down was carried out for double bond of (AM) and (AA) and formation of covalent bond between C atoms of (AM) and (AA), the polymerization in the chain between (AM) and (AA) occurred by addition polymerization, where polymerization of (Mg-Si) in the chain was occurred by condensation polymerization The formation mechanism of {P(AM-AN)-MgSi} composite was shown in scheme (5), the reaction started by converting of (AM) monomer to imine form in solution. Then imine form reacted with (AN+Mg+Si) to form (AM-AN-Mg-Si) co-monomer, and subjected to gamma radiation, breaking down carried out for double bond of (AM), and (AN), the polymerization in the chain between (AM) and (AN) occurred by addition polymerization, where polymerization of (Mg-Si) in the chain was occurred by condensation polymerization [29], by elimination of OH − of imine form with Na + of Na2SiO3 with formation of ionic bond between C atom of imine form and Si atom of Na2SiO3 and elimination Na + from Na2SiO3 with Cl − of MgCl2.  [27]. Two bands appeared at 2960 and 2875cm -1 may be due to the stretching mode of C-H of acrylamide and acrylic acid [29][30][31]. Weak band appeared at 2245cm -1 due to the stretching mode of C≡C bond may be present by rearrangement in the structure [29,36]. Two bands appeared at 1725 and 1675cm -1 ,the former band may be due to the stretching mode ofcarbonylgroup of acrylic acid  [34,36].Strong band appeared at 2244cm -1 due to the stretching mode of C≡N bond of acrylonitrile [36]. Two bands appeared at 1661 and 1605cm -1 , the first band may be attributed to the bending mode C=O group of acrylamide or due to presence of imine group [32], and the second band may be due to bending vibration of N-H bond of acrylamide or O-H bonded water molecules absorbed on the composite [1,36].Two bands appeared at 1455 and 1413cm -1 attributed toC-Hof acrylamide and acrylonitrile [30].Band appeared at 1571cm -1 may be attributed to the bending mode ofN-H bond of acrylamide [32]. Two bands appeared at 1451 and 1413cm -1 may be attributed to the bending mode of C-H of acrylamide and acrylic acid     that P(AM-AA) copolymers have amorphous structure and these results were similar to the data obtained from XRD of polyacrylamide-coacrylic acid prepared by Hassan, et al. [31]. In addition, the crystalline character of the prepared samples was increased with radiation doses from 25 to 90KGy. Figure 3. (b) shows XRD patterns for P(AM-AN) copolymers preparedat radiation doses 25, 65 and 90KGy.From this figure it is clear that the sample prepared at radiation dose 25 KGy has crystalline structure, and these results were similar to the data obtained from XRD of potassium hexacyano cobalt (II) ferrate (II) polyacrylonitrile (KCFC-PAN) [41],where samples prepared at radiation doses 65 and 90KGy have amorphous structure.  Differential thermal and thermogravimetric analyses (DTA&TGA) play a vital role in studying the structure and the properties of any materials where it has been widely used to investigate the decomposition characteristics of materials. DTA and TGA data were used here to provide an alternative model for the kinetics of the composite degradation. For all investigation studies of the composites the rate of heating is 10°C/min [17,34,42,43], and the data were tabulated in Tables 1 and 2.  Table  2.The data in Table 2  The elemental analysesofmagneso-silicate and polymeric composites based on silicateprepared at different radiation doses were measured using XRF and tabulated in Table (3); the measured data is confirmed that impregnation of magneso-silicate in the{P(AM-AA)-MgSi} and{P(AM-AN)-MgSi} [45].