Cellulose Plastics: Cellulose is a natural polymer produced from wood via wood pulp. Woven grade cotton contains about 90% cellulose while an average wood has about 50% and the balance is composed of lignin and polysaccharides. Cellulose resins include four organic esters, cellulose acetate (CA), cellulose acetate butyrate (CAB), cellulose acetate propionate (CAP) and cellulose acetate triacetate (CAT).
Polymerization: The cellulose esters are prepared by reacting chemical cellulose with organic acids and anhydrides using sulfuric acid as a catalyst. In the standard synthesis of CA, the reaction proceeds with acetic acid and acetic anhydride to the trimester stage. CA is prepared by hydrolyzing the trimester to remove some of its acetyl groups. Plastic grade CA contains 38 to 40% acetyl. The propionate and butyrate esters are made by substituting prop ionic acid and prop ionic anhydride or butyric acid and butyric anhydride for some of the acetic acid and acetic anhydride. Plastic granules of CAP contain 39 to 47% propionyl and 2 to 9% acetyl. CAB contains 26 to 39% butyric and 12 to 15% acetyl.
Cellulose Esters: Cellulose Acetate: Manufacturing of cellulose acetate was done in 1865 using a process in which cotton was heated with acetic anhydride in sealed tube at 130-1400C but the process was difficult to control. With further research various new techniques of manufacturing of cellulose acetate are developed. One of the methods available today is homogenous acetylating. In this process cellulose is pretreated with glacial acetic acid to open up the cellulosic matter. After pretreating, acetylating is done by mixing pretreated cellulose with acetylating agent like acetic anhydride, a catalyst like
concentrated sulphuric acid and acetic acid as diluents.
Properties:
1. High water absorption
2. Poor electrical insulation characteristics
3. Limited aging resistance
4. Limited heat resistance
5. Dissolved by wide variety of reagents.
Cellulose Acetate Butyrate (CAB):
1. Good toughness
2. Excellent appearance
3. Giving good coating with hard glossy surface
4. Lower water absorption
5. Better flow properties
6. Lower density
Applications:
Toys, tools handles, tabular keys, telephone housing, pipes for conveying water, outdoor display signs, vacuum formed products and protective coating for metals.
Cellulose Acetate Propionate: Cellulose Acetate Propionate having shorter side chain and it is harder stiffer, and posse’s higher tensile strength than Cellulose Acetate Butyrate. Easy to vacuum form and also tend to be used for applications like tool handles, safety lockers, steering wheels, etc.
Properties: Cellulose Acetate Propionate has shorter side chain and it is harder, stiffer and possesses higher tensile strength than Cellulose Acetate Butyrate. Like cellulose acetate butyrate, this is easy to vacuum form and also tends to be used for applications like tool handles, safety lockers, steering wheels, etc.
Cellulose Nitrate: Cellulose Nitrate is manufactured by the reaction between cellulose, nitric acid and sulphuric acid. It is possible to vary degree of etherification according to the root hydroxyl group which is replaced by nitrate group. Fully nitrated cellulose, cellulose tri-nitrate is an explosive. Cellulose nitrate is precipiticised with camphor in order to make it easy process able.
Properties:
1. Good rigidity
2. Water white transparency
3. Poor chemical resistance
4. Reasonable toughness
5. Capable of forming highly attractive multi-colored sheeting
6. Highly inflammable.
Applications: The one time important application was in photographic film. Today the principal outlet are knife handles, table tennis ball and spectacle frames.
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