الفهرس 
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Abstract
The present study focused on the synthesis and characterization of PVA/PVP nanocomposites which prepared by gamma irradiation. The current research includes PVA/PVP nanocomposites for possible application in biomedical, nanomaterials - based system for wound dressing. A new approach to the synthesis of a higher degree of biocompatibility and long-term antibacterial activity can be achieved with PVA/PVP/silver nanoparticles and PVA/PVP/clay nanocomposite. The results obtained in this study can be summarized as follows:
I. Radiation synthesis and characterization of PVA/PVP based hydrogl containing silver nanoparticles.
A- Prepration of PVA/PVP hydrogels
PVA/PVP blended hydrogels were prepared by using gamma irradiation. The effect of the composition and irradiation dose on the blended hydrogels gelation percent was investigated.
1-The gelation (%) decreased with increasing the ratio of PVP in the composition from 20 up to 80. The gelation (%) of PVA/PVP hydrogels was found to be sharply increased with increasing irradiation dose up to 30 KGy then showed a slight increase at 40 kGy. The interchain hydrogen bonding between the hydroxyl group on the PVA chains and carbonyl groups on PVP chains increased the stability of the polymer network.
2-The swelling of PVA/PVP (60:40) hydrogel nearly tends to increase with increasing PVP concentration from (0 to 60) %. The addition of PVP with PVP/PVA blend hydrogels absorbed more water than pure PVA and the water content increased with increasing PVP content. The relationship between swelling (%) and the time of immersion for different doses are showed that, the swelling (%) decrease as the irradiation dose increase up to 40 kGy.
B- Synthesis of hydrogel-Ag nanoparticles
Highly stable and uniformly distributed silver nanoparticles (PVA/PVP)-Ag have been obtained with hydrogel networks as nanoreactors. The swollen PVA/PVP hydrogels were immersed in AgNO3 then transferred to sodium borohydride to be reduced.
1-Swelling properties of the prepared hydrogel nanocomposite have been investigated. Considerable variation in the swelling capacity of hydrogels was noted when the hydrogels were modified or loaded with AgNO3 and Ag nanoparticles. The order of swelling capacity values was found to be hydrogel < hydrogel- Ag+ < hydrogel-Ag nanocomposite. The gels treated with silver nitrate formed Ag+ ions loaded throughout the gel networks. These ions present in the gel are responsible for a moderate increase of the swelling (%) of Ag loaded gels. The reduction of silver ions formed silver nanoparticles having different amounts of silver nanoparticles surface charges in the hydrogels causes an expansion of hydrogel network and more free spaces in hydrogel networks are present.
2-The formation of silver nanoparticles in PVA/PVP hydrogel has been demonstrated by X- ray diffraction studies. XRD data indicate well defined characteristics patterns of the silver nanoparticles present in the hydrogel. The observed diffraction peaks of PVA/PVP silver nanoparticles hydrogels found at 2 values of 38.46, 44.51, 64.77 and 77.74 are attributed to the diffraction planes (111), (2 0 0), (2 2 0) and (3 1 1) of face cubic center ( f c c) silver nanoparticles confirming the presence of silver nanoparticle in the hydrogel nanocomposite. According to Scherrer equation, the size of the silver nanoparticles in the (PVA/PVP)-Ag nanoparticles found was 8 nm, 12 nm, 14 nm.
3-To probe the possibility of chemical interaction between PVA/PVP molecules and Ag nanoparticles, FT-IR spectra of the pure PVA/PVP and the PVA/PVP stabilized Ag nanoparticles were obtained. The presence of the silver in PVA/PVP samples leads to the decreasing of all bands measure the interaction between PVP and PVA and its shift to lower energies should be due to the chemical interaction between PVA/PVP molecules and Ag nanoparticles.
4-The existence of silver nanoparticles in the gel networks is tested by UV–vis spectral analysis. all the UV-vis spectra of silver nanoparticles embedded in PVA/PVP hydrogel networks have shown a distinct characteristic absorption peaks around 420 nm. This must be due to the characteristic surface plasmon resonance effect of quantum –size silver nanoparticles present in the hydrogel networks.
5-The examination of the surface morphology of (PVA/PVP) hydrogel, (PVA/PVP) Ag+ and (PVA-PVP)-Ag nanocomposite by SEM was occurred. the (PVA/PVP) hydrogel has a relatively wider pore structure but a distinguished aggregation of the silver ions are observed as somewhat as a dark particles in case of PVA/PVP hydrogel loaded silver nitrate. No serious aggregation of the nanoparticles is observed and this can be explained as a stable network structure formed in the hydrogels and the strong interaction of the silver particles with the PVA and PVP molecules.
6-The diameter distribution of silver nanoparticles was determined by dynamic light scattering DLS. the particle size found to be ranged from 38 to 98 nm. Transmission electron microscope (TEM) showed almost spherical and uniform distribution of silver nanoparticles through the hydrogel network and the mean size of silver nanoparticles ranging was about 23 nm.
The improved properties as well as the cheapness of the materials suggest that (PVA/PVP)-Ag can be a good candidate as wound dressing.
II-Preparation and characterization of Poly Vinyl Alcohol/Poly Vinyl Pyrrolidone/Clay Based Nanocomposite by Gamma Irradiation:-
A series of PVA/PVP/clay nanocomposite were prepared by gamma irradiation with different clay contents of (0.15, 0.3, 1, 1.5, 3 and 5 wt %). The gelation content and swelling behavior were investigated.
7-The distribution of clay nanoparticles with the interchain hydrogen bonding between the hydroxyl group of the PVA chains and carbonyl groups of PVP chains leading to higher gel fractions by the irradiation dose up to 25 kGy due to the formation of insoluble and entangled polymeric network. As the radiation dose increase more than 25 kGy the gelation percent decreased.
8-The swelling percent decrease as the irradiation dose increase up to 40 kGy. The decreasing of the swelling percent by increasing the irradiation dose, may be due to the increasing of the crosslinking percentage in the hydrogels.
9-The increase of clay content causes a decrease of the swelling (%) for the clay concentrations (1, 3 and 5 %). The decrease of the swelling (%) is directly related to the packing effect caused by the clay on the matrix, therefore reducing the available free volume for swelling. Moreover, clay acting as co-crosslinking points of the PVA/PVP chains causes the overall decrease on the swelling behavior of the PVA/PVP/clay hydrogels and decrease the diffusion rate of water molecules.
10-The PVA/PVP/clay nanocomposite samples were characterized by FT-IR spectroscopy. The FT-IR results confirm the presence of hydrogen bonding between PVA/PVP hydrogels and clay, since the interactions between –OH groups are strongest in the bulk PVA/PVP hydrogels than PVA/PVP/clay hydrogels.
11-Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used for a thermal analysis study of the prepared P(PVA/PVP) hydrogels, P(PVA/PVP/Clay) nanocomposit. The thermal stability studies confirmed that the introduction of clay lead to an increase in the thermal stability.
12-The introduction of clay into polymer matrix was investigated by X-ray diffraction pattern. The crystalline behavior is suppressed by the introduction of clay into polymer matrix in the form of an intercalated or exfoliated layer structure.
13-The morphological image of the PVA/PVP/clay nanocomposite samples was studied by SEM. The SEM images of (PVA/PVP/clay) showed that the clay particles were finely dispersed through the interconnecting pours of the PVA/PVP polymer. The increasing of the clay content leads to a decrease on the size of the porous.
14-The TEM results showed that the clay nanoparticles are intercalated and exfoliated in the polymeric matrix. The improved properties of the materials suggested that PVA/PVP/clay nanocomposite can be a good candidate as a wound dressing.
Conclusion
In conclusion, we have demonstrated a highly facile and simple methodology for preparing hydrogel–silver nanoparticles. For this purpose, a series of (PVA/PVP) hydrogels were prepared by gamma irradiation with different compositions (wt%). Highly stable and uniformly distributed silver nanoparticles (PVA/PVP)-Ag have been obtained with hydrogel networks as nanoreactors. The developed nanocomposite swelling properties are dependent on the internal network structure. The order of swelling capacity values were found to be hydrogel < hydrogel-Ag+ < hydrogel-Ag nanocomposite. The formation of silver nanoparticles has been confirmed by ultraviolet visible (UV–vis) spectroscopy and X-ray diffraction pattern. The diameter distribution of silver nanoparticles was determined by dynamic light scattering DLS and Transmission electron microscope (TEM). The results showed that, a spherical and uniform distribution of silver nanoparticles of mean size ranging 23 nm. The improved properties of the materials suggested that (PVA/PVP)-Ag confirmed as excellent antibacterial materials and a good candidate as wound dressing.
On the other hand, the formation of nanocomposites gels based on hybrid films of PVA/PVP and calcium bentonite clay at various contents under the effect of gamma irradiation has been occurred. The swelling (%) is directly related to the packing effect caused by the clay on the matrix, therefore reducing the available free volume for swelling. It is observed that, the increase of the clay content causes a decrease in the swelling percent. The thermal stability studies confirmed that, the introduction of clay lead to an increase in the thermal stability. The exfoliation and intercalation affect the thermal properties in terms of glass transition and melting transition properties. The introduction of clay into polymer matrix was investigated by X-ray diffraction pattern and Transmission electron microscope (TEM). The TEM results showed that the clay nanoparticles are interchelated or exfoliated in the polymeric matrix. The improved properties of the materials suggested that PVA/PVP/clay nanocomposite can be a good candidate as a wound dressing.