الفهرس Only 14 pages are availabe for public view
 |  | from | 136 |  |  |
| | | from | 136 | | |
Abstract
These thesis works aimed at prepare hydrophilic hydrogels by electron beam irradiation based on different ratios of poly (vinyl alcohol) and acrylamide monomer (AM). The hydrogels were compounded with different contents of sodium montmorillonite clay (MMT) or Organo-montmorillonite clay. Composites with sodium montmorillonite (MMT) and Organo-montmorillonite clays were also prepared. The research work covered the following points:
(A) Characterization of Poly(vinyl alcohol/Acrylamide Hydrogels (PVA/AM) Prepared by Electron Beam Irradiation.
(B) Characterization of Poly(vinyl alcohol)/Acrylamide/Sodium Montmorillonite Clay Composites Prepared by Electron Beam Irradiation.
(C) Characterization of Poly(vinyl alcohol)/Acrylamide/ Organo-Montmorillonite Clay Composites Prepared by Electron Beam Irradiation.
The composites were characterized by XRD spectroscopy and thermogravimetric analysis (TGA). The effect of both temperature and pH on the degree of swelling of PVA/AM hydrogels were also studied. The results obtained through this work can be summarized through the following points:
(A) Characterization of Poly (vinyl alcohol/ِِِAcrylamide Hydrogels (PVA/AM) Prepared by Electron Beam Irradiation.
In this part, we study the gel fraction of crosslinking polymer and the effect of radiation dose on gel fraction. The gel fraction increases with increasing irradiation dose up to 40 kGy of electron beams due to the increased free radicals upon electron beam irradiation.
While the X-ray diffraction is an important for examining the crystalline structure of polymer composites it gives valuable information about the changes of structure, intensity and width of polymer crystals.
Thermogravimetric analysis (TGA) was used to investigate experimentally the thermal stability of the hydrogels based on pure PVA and PVA/AM hydrogels of different composition. However, the thermal stability was found to increase with increasing the ratio of AM monomer in the initial solutions. The derivative of the rate of reaction (DTGA) curves for the hydrogels illustrated the multiple stages of thermal decomposition of the hydrogels based on either pure PVA polymer hydrogel or PVA/AM copolymer hydrogels. The values of Tmax clearly indicated that the thermal stability of PVA/AM copolymer hydrogels increases with increasing the ratio of AM component in the initial solutions.
In the Equilibrium swelling with different temperatures and different pH, it can be seen that the degree of swelling of all the hydrogels increases with increasing swelling time, regardless of temperature. However, the degree of swelling was found to increase by increasing both the temperature up to 60oC, and with increasing the ratio of AM in the initial solutions meanwhile, it was found to decrease with increasing electron beam irradiation dose. Moreover, the degree of swelling was found to increase with increasing the pH value up to 11, and at low pH values, the copolymers are in a relatively collapsed state.
(B) Characterization of Poly (vinyl alcohol)/Acrylamide/Sodium Montmorillonite Clay Composites Prepared by Electron Beam Irradiation.
Gel Fraction of the hydrogels based on PVA/AM of different ratios and PVA/AM/MMT composites with different contents of MMT with different dose of electron beam irradiation. It can be seen that the gel fraction of PVA/AM hydrogels increased with increasing the irradiation dose up to 40 kGy, but decrease with increase of the content of MMT clay. It seems that MMT particles block limited number of sites leading to a decrease in gel fraction.
X-ray diffraction XRD reports that the effect of PVA/AM hydrogel composition increase with increasing of AM monomer ratio in the initial solution was associated with an increase of the intensity of the basal peak while with increase of the irradiation dose an increase of the intensity of the basal peak and an increase in the value of 2. The increase of MMT content was associated with an increase in the value of 2 up to 2% and then tended to decrease; this is due to increasing the AM ratio in hydrogel.
The thermogravimetric analysis (TGA) was used to investigate the thermal decomposition behavior of PVA/ AM/MMT composites, crosslinked at different doses of electron beam irradiation. It was observed that, PVA polymer displayed the lowest thermal stability. The thermal stability of PVA/MMT nanocomposites was found to increase with increasing the MMT content.
In the Equilibrium swelling at different temperatures and different pH, it can be seen that the degree of swelling of all the hydrogels increases with increasing swelling time, regardless of temperature. However, the degree of swelling was found to increase by increasing the temperature up to 60oC, and also found the degree of swelling increase with increasing the ratio of AM in the initial solutions meanwhile, the degree of swelling was found to decrease with increasing both electron beam irradiation dose, and the pH value up to 11. The degree of swelling was found also to increase with increasing the content of MMT clay due to the higher hydrophilic character of MMT clay.
The change in color intensity (E*) and the different color parameters (L*, a*, and b*) as a function of hydrogel composition for the hydrogel based on PVA/AM and PVA/AM/MMT composites films PVA/AM hydrogels at any composition are transparent on the basis of the L* values. The proportion of red color component (a*) was found to be low and the proportion of blue color component (b*) is high, in accordance with the values of the L* intercept. The proportions of the red and blue colors decrease systematically with increasing the MMT contents in the hydrogel composition. It may be concluded that PVA/AM hydrogels are miscible in any proportions even after compounding with MMT clay.
(C) Characterization of Poly (vinyl alcohol)/Acrylamide/ Organo-Montmorillonite Clay Composites Prepared by Electron Beam Irradiation.
The gel fraction of the hydrogels based on PVA/AM of different ratios and PVA/AM/SMMT composites with different contents of SMMT. It was observed that the gel fraction of PVA/AM hydrogels increased slightly with increasing the irradiation dose up to 40 kGy, irrespective of hydrogel ratio. The gel fraction decreased with increasing the content of SMMT organoclay due to the presence of SMMT clay in the network structure. It seemed that SMMT particles block limited number of sites leading to a decrease in gel fraction.
XRD patterns for pure organoclay (SMMT), PVA/AM hydrogels of different compositions modified by different contents of organoclay (SMMT), showed partially crystalline structure of PVA with increasing SMMT content, in which the peaks became narrower suggesting an induction of crystallinity in the polymer by inclusion of SMMT in the polymer matrix. This is due to, SMMT particles acting as seeds for crystallization to occur.
The initial TGA thermograms of reaction curves for the composites based on different compositions of PVA/AM and different contents of SMMT clay prepared at different doses of electron beam irradiation. The rate of reaction curves showed an increase of the content of SMMT had led to an increase in thermal stability. The increase of irradiation dose and the ratio of AM monomer have led to an increasing the thermal stability in terms of the values of Tmax.
The equilibrium swelling of PVA/AM/SMMT composites showed an increase in the ratio of AM monomer in the initial solution and found in all stages of swelling due to the higher hydrophilic character of PAM than PVA. The degree of swelling was found to increase with increasing the content of SMMT clay due to the higher hydrophilic character of MMT clay. The degree of swelling of all the hydrogels increased with increasing the temperature up to 60oC. It also can be seen that the degree of swelling increased slightly with increasing the pH up to 4, and then tends to increase promptly up to the pH of 11, but at low pH values, the copolymers are in a relatively collapsed state.