الفهرس 
Absorbent Hydrogels Based on cellulose Derivatives from Concept to ImplementationOnly 14 pages are availabe for public view
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Abstract
In this thesis , Synthesis, characterization and applications of cellulosic products with high water absorbing capacity will be discussed. This work was divided into three parts :
First Part :
Synthesis and characterization of Superabsorbent hydrogels based on carboxymethyl cellulose
In current work, trials are made to introduce carboxymethyl groups into the molecular structure of cellulose and the CMC, so formed will act as a backbone into the hydrogel for keeping its appearance when it absorbs large amounts of water. Moreover, CMC was used as hydrophilic filler in the hydrogel network to increase the absorption of water. Silver nitrate (AgNO3) was incorporated in the hydrogel with a view of inducing antimicrobial activity to the CMC based superabsorbent hydrogel. The structure and properties of the superabsorbent materials are evaluated, that is,the intermolecular interaction and morphological change of the hydrogels are characterized using Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and scanning electron microscope (SEM).Given below are the main conclusions arrived at with this part :
1.1.1. Synthesis of Carboxymethyl Cellulose (CMC)
Cotton fibers were pretreated with sodium hydroxide solution. Active alkali cellulose was reacted with monochloro acetic acid solution. The primary treatment of pure cellulose fiber with variable weight percentage of NaOH in static solution and cotton fiber was conducted. The amount of adsorbed NaOH for the Cotton fiber was 39% higher than that in the static solution. The results revealed that the amount of adsorbed NaOH was proportional to concentration of NaOH solution as shown in figure 1 & eqn.3. The range of DS obtained was from 0.7 to 2.173 as shown in Table 1.
1.1.2. Preparation of CMC hydrogels and Silver CMC hydrogel
The 3 wt% CMC solution was prepared as follows: 3 g was dispersed into 97 g of 6 wt% NaOH/4 wt% urea/90 wt% water mixture with stirring for 5 min followed by storing in the refrigeration (-20 °C) for 12 h
The frozen solid was thawed and stirred extensively at room temperature to obtain a transparent CMC solution having a 3 wt% polymer concentration. The CMC solution was mixed with AgNO3 solution(0,1, 2 ml)(0.1mmol). ECH (98%) was added to the mixture as crosslinker, stirred at 30 °C for 2 h to obtain a homogeneous solution. The latter was kept at 60 °C for different duration(3, 6, 10, 12 h) whereby gels could be achieved. Gels were washed with water to obtain hydrogels.
II. characterization of CMC hydrogels and Silver CMC hydrogel
The CMC hydrogels and Silver CMC hydrogel were analyzed using FTIR-spectra, Differential scanning calorimetry ( DSC) and Thermogravimetric Analysis (TGA). The CMC hydrogels and Silver CMC hydrogel were confirmed by Scanning Electron Microscope (SEM). The silver particles formation is characterized by measuring the Energy Dispersative X-Ray Analysis.
III. Factor affecting on Swelling properties of the hydrogels
1. Effect of time on CMC hydrogel formation
2. Effect of AgNo3 Solution on CMC hydrogel
3. Effect of ECH as crossliner on CMC hydrogel
Second Part :
Novel Superabsorbent Hydrogels Using Carboxymethyl Cellulose/ Hydroxyethyl Cellulose/Citric Acid Aqueous System
In the present work, citric acid (CA) is used in preparation of hydrogels based on CMCNa /HEC mixture.
Citric acid is used in hydrogel preparation for the first time. This together with its nontoxicity advocate preparation and characterization along with the properties of the hydrogels in queotion.
The work in future extended to include Ag in the hydrogel using AgNO3 .State of the art tools are used for detailed investigation of the hydrogel.
Given below are the main conclusions arrived at with this part :
I. Synthesis of Hydrogels
Hydrogel samples were obtained by reacting, in water, CMCNa and HEC with CA as a crosslinking agent according the following procedure. First, a total polymer concentration of 2% by weight of water, using a mixture of CMCNa and HEC, with weight ratio equal to 3/1 was dissolved in distilled water by stirring gently at room temperature until a clear solution was obtained. The presence of HEC is necessary to promote intermolecular rather than intramolecular crosslinking. In fact, poor crosslinking efficiency is reported if only CMCNa is used, due to the electrostatic repulsion between polyelectrolyte chains and to the high degree of substitution of hydroxyl groups at C6 most reactive position(Sannino& Nicolais,2005). In accordance with this, CMCNa dissolution is slow at the concentration adopted; thus, first HEC was added to water till, after 5 min, a clear solution was obtained with a slight increase of viscosity; then, CMCNa was added, and the stirring was kept on till a clear solution was obtained (24 h), with a significant increase of viscosity.Finally, CA was added at different concentrations (1.75%, 2.75%, 3.75%, 10% and 20% w/w polymer) to obtain samples with various crosslinking degrees. This final solution was used to mold 10-mm thick samples. All samples were first predried at 30°C for 24 h to remove absorbed water and then kept at 80°C for the crosslinking reaction to occur within (24 h).
Control samples containing neat HEC or neat CMCNa samples crosslinked with CA were also prepared following exactly the same experimental conditions used for HEC/CMCNa mixtures.
II. Characterization of superabsorbent Hydrogel
The superabsorbent Hydrogel was analyzed using FTIR-spectra, Differential scanning calorimetry ( DSC) and Thermogravimetric Analysis (TGA). The superabsorbent Hydrogel was confirmed by Scanning Electron Microscope (SEM). The silver particles formation is characterized by measuring the Energy Dispersative X-Ray Analysis.
III. Factor affecting the preparation of carboxymethyl cellulose hydrogel
1. Effect of Concentration of CA.
2. Effect of Time.
3. Effect of Temperature.
4. Effect of molar ratio.
Third part:
Synthesis and Properties of Carboxymethyl Cellulose graft- Poly(acrylic acid-co-acrylamide)
This work is undertaken with a view to synthesize a newcellulose- based superabsorbent by simultaneously grafting two kinds of hydrophilic monomers, AA and AM, onto CMC in the presence of the crosslinker NMBA, combining the high absorption capacity of poly(acrylic acid) and the strong resistance to metallic ions and fast swelling rate of polyacrylamide. The effects of various reaction parameters, such as the bath temperature, AA/AM molar ratio,monomer/CMC mass ratio, and crosslinker, on the water absorbency of the products, as well as their water retention and resistance to aqueous NaCl solutions, are investigated.
Given below are the main conclusions arrived at with this part :
I. synthesis of Hydrogels
AA was first dissolved in distilled water to obtain an aqueous AA solution, and the solution was neutralized to 85% by the dropwise addition of a 5 mol/L aqueous NaOH solution to form a mixture of AA and sodium acrylate. The whole process was performed in an ice– water bath to avoid possible polymerization of AA due to the increasing temperature caused by the neutralization reaction. An aqueous solution of CMC was placed in a 250-mL, four-necked flask equipped with a mechanical stirrer, a reflux condenser, a thermometer at room temperature to remove the dissolved oxygen from the solution. After a redox couple of sodium perborate and thiourea was added to the solution. it was gently stirred for 15 min to facilitate free-radical formation on the CMC backbone, AM and the partially neutralized AA were added to the flask. The crosslinker NMBA was added just after the addition of the monomers.
The reaction solution was heated in a water bath to desired temperatures to start the polymerization with constant stirring in an atmosphere of N2 for a certain time and then transferred to a stainless steel reactor for further reaction at 80°C for 2 h. The obtained product was cut into small pieces and dried in vacuum at 70°C for 24 h. The dry product was milled and sieved through a 40-mesh sieve. To remove soluble CMC, monomers, homopolymers, and other uncrosslinked copolymers from the products, these small pieces of copolymer were soaked in hot, distilled water, reaching equilibrium swelling under continuous stirring, then filtered. The process was repeated several times.
The product is refered to as carboxymethyl cellulose-graft poly( acrylic acid-co-acrylamide) [CMC-g-poly(AA-co-AM)]. Unless otherwise stated, the basic composition was as follows: the molar ratio of AA to AM was 3 : 1; the total weight of the two monomers with respect to the CMC weight was 4 : 1; the weight percentages of the crosslinker and initiator with respect to the monomers were 0.70 and 1%, respectively; the total weight percentage of AA, AM, and CMC with respect to distilled water was 11.6%; and the volume of the reaction system was 100 mL.
II. Characterization of carboxymethyl cellulose-graft poly( acrylic acid-co-acrylamide)
The [CMC-g-poly(AA-co-AM)] was analyzed using FTIR-spectra, Differential scanning calorimetry ( DSC) and Thermogravimetric Analysis (TGA). The [CMC-g-poly(AA-co-AM)] was confirmed by Scanning Electron Microscope (SEM).
III. Factor affecting the Swelling Ratio
1. Effect of the crosslinker content.
2. Effect of the AA/AM molar ratio.
3. Effect of the monomer/CMC weight ratio.
4. Effect of the bath Temperature.
5. Effect of the concentration of NaCl aqueous solution on the swelling ratio.
Comparsion among the three synthesized Hydrogels with different crosslinker
Hydrogel
crosslinker
Max.SR in dist.H2O
Max.SR in NaCl
CMC
ECH
775.931
353.468
CMCNa/HEC
CA
645.25
-
CMC-g-poly(AA-co-AM)
NMBA
850.540
375.