الفهرس 
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Abstract
monomers together. Polymers have extremely large molecules, and therefore have very strong covalent intramolecular bonding, and weak vander Waals intermolecular binding forces [1].
1.1 Classification of polymers
A polymer can be classified according to its source, method of polymerization, structure, shape, thermal processing behavior and mode of polymerization. Fig (1.1) summarizes the classification of polymers[1].
Fig. 1.1: Classification of polymers.
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1.1.1. Classification according to the source
Polymers which are synthesized by organisms are known biopolymer such as: Cellulose, Starch and Chitin, while polymers which are synthesized by scientists are known synthetic polymers.
1.1.2. Classification according to polymerization Process
Polymerization process is the joining of many small molecules together to form very large molecules, it can be classified into:
1.1.2.1. Addition Process: It consists of a series of reactions which consumes a reactive particle and produces the same particle; each individual reaction depends upon the previous one. The reactive particles can be Free radicals, Cations, or anions. Addition Process consists of three Processes (1) Initiation process (2) Propagation Process and (3) Termination Process[2].
1.1.2.2. Condensation Process: It consists of a series of reactions each reaction is independent of the preceding one. In which monomer molecules combine with other by losing simple molecules like water [2].
During polymerization, monomer react with each other to form dimmers, dimmers react to form tetramers; tetramers react with monomers to form pentamers, and so on.
This stepwise construction of polymer chains has important consequences for both their molecular weights and molecular weight distribution [3].
1.1.3. Classification according to structural shape of polymer molecule
1.1.3.1. Linear polymer: It has a definite backbone and does not have long chain branches but it may have short chain branches. Most commercial polymers are linear polymers. Fig. (1.2) shows the shape of linear polymer molecule.
Fig.1.2: Shape of linear polymer molecule.
1.1.3.2. Branched polymer: its unique backbone has short chains branches. Fig. (1.3) shows the shape of branched polymer molecule.
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Fig.1.3: Shape of branched polymer molecule.
1.1.3.3. Networks polymer: All molecules in a cross linked polymer are chemically
bonded together, forming a three dimensional network. Fig.(1.4) shows the shape of
net work polymer molecule.. The bonding is usually covalent but other types such
as ionic bonds are possible. Cross linked polymers are produced from linear or
branched polymers, or directly from chemical precursors. All rubbers are soft cross
linked polymers with low degrees of cross linking produced from linear polymers.
Epoxies are rigid cross linked polymers with very high degrees of cross linking
produced by mixing two chemical precursors [4].
Fig. 1.4: Shape of network polymer molecule.
1.1.4. Classification according to thermal processing behavior
Polymers can be classified into thermoplastics polymers which melt while heating
and resolidfy while cooling. It comprises essentially linear or lightly branched polymer
molecules. On the other hand thermosets polymers, do not melt while heating but at they
decompose at sufficiently high temperatures. They are substantially cross linked
materials, consisting of an extensive three dimensional network of covalent chemical
bonding [5].
1.1.5. Classification of polymers according to mode of polymerization
Polymers can be classified according to mode of polymerization into homopolymers
which are synthesized by polymerization of only one type of monomer such as Cellulose
which its monomers is β- Glucose and polyethylene which its monomer is ethylene.
Polymers can be also classified into Copolymers which are synthesized by polymerization
of more than one type of monomer [6].
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1.2 Polysaccharides
There is a growing interest in the production and use of new materials from renewable sources. Natural polymers replace synthetic polymers in different applications because the waste from natural polymers is normally biodegradable [7].
Polysaccharides are examples of natural polymers and they also can be synthesized of monosaccharide of different chemical structures arranged in specific sequence and joined together by different types of glycoside linkages. The chain of Polysaccharide may possess numerous side chains of monosaccharide [8].
1.2.1. Chitin
Chitin is a polysaccharide which is the most abundant polysaccharide in nature after Cellulose. The structure of Chitin is essentially the structure of Cellulose, where hydroxyl group at C-2 of the D-glucopyranose residue is substituted with an N-acetyl aminoز