1. Bio-Degradable Polymers
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2. CORPORATE TRAINING AND PLANNING
Introduction
Although there certainly has never been a great incentive for making unstable polymers, the idea of making degradable polymers has long existed due to its environmental significance, and quite a bit of effort has gone into research along these lines.
There are three important ways of making a degradable to polymeric material.
1.Thermal degradation
2.photo degradation
3.Biodegradation
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Degradation:
Degradation is nothing but loose the properties of polymer due to external sources.
Thermal Degradation:
Polymaric materials will loose the properties because of over thermal conditions.
Photodegradation
One is to make the polymer sensitive to sunlight, which fractures its chemical bonds and breaks it down by photodegradation. To make plastics photodegradable, a material can be implanted that will absorb sunlight and becomes sufficiently reactive to attack the polymer molecules from which the material is composed.
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One other means of photodegradation is to incorporate in the polymer backbone suitable groups, e.g., carbonyl groups that absorb the ultraviolet (UV) component of the sunlight to form excited states energetic enough to undergo bond cleavage. .
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Bio-degradation
Biodegradation lies in the possibility to create an environment (as in a landfill) completely different from that encountered under normal storage conditions; e.g., microorganisms that can destroy organic polymers may be added to a landfill.
Biodegaradation is understood about the molecular-level interaction between polymers and microorganisms.
For example Esterases (ester hydrolyzing enzymes) and some microorganisms are known to biodegrade polyester at a reaction rate depending upon the polyester structure.
While many aliphatic polyesters, specifically poly(hydroxy fatty acids), are suited for biodegradation, the aromatic polyester (e.g., PET) do not possess this property.
Poly(vinyl alcohol) is the most readily biodegraded, compared to other vinyl polymers
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Natural Bio-degradable polymers:
Example for natural biodegradable polymers are Cellulose, Polysaccharides, Starch, PVOH etc.
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.
The cellulose are prepared by reacting chemical cellulose with organic acids and anhydrides using sulfuric acid as a catalyst.
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POLYVINYL ALCOHOL:
Vinyl alcohol does not exist in the free state and all attempts to prepare it have led instead to the production from acetaldehyde.
Poly(viny1 alcohol) is thus prepared by alcoholysis of a poly(viny1 ester) and methonal is used
The presence of hydroxyl groups attached to the main chain has a number of significant effects. The first effect is that the polymer is hydrophilic and will dissolve in water to a greater or lesser extent according to the degree of ‘hydrolysis’ and the temperature.
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8. CORPORATE TRAINING AND PLANNING
Water Soluble polymers:
Water soluble polymers cover a wide range of highly varied families of products of natural or synthetic origin, and have numerous uses.
The separation of solids in a liquid medium takes place rapidly when the density of the particles is markedly different from that of the liquid medium. Either the particles settle out or they float on top of the liquid.
Among these families, synthetic polymers, and more particularly coagulants and flocculants, are used mainly for facilitating the separation of materials in suspension in aqueous media.
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Synthetic Polymers
Degradable, synthetic polymers that are commonly known in the medical field include poly(a-hydroxy esters), poly(3-caprolactone), poly(ortho esters), polyanhydrides, poly(3-hydroxy butyrate), polyphosphazenes, polydioxanones, polyoxalates, and poly(amino acids).
The linear aliphatic polyester, PLA (XIV) is chemically synthesized by condensation polymerization of the free acid or catalytic ring-opening polymerization of the lactide (dilactone of lactic acid).
The ester linkages in the polymer are sensitive to both enzymatic and chemical hydrolysis. PLA is hydrolyzed by many enzymes including pronase, proteinase K, bromalin, ficin, esterase, and trypsin.
The degradation rate of PLA also varies with varying pH.
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The amount of lactic acid released during the course of PLA degradation is very small but increases rapidly as PLA is broken down to low molecular weight oligomers.
PLA is primarily considered for medical implants and drug delivery, but broader applications in packaging and consumer goods are also targeted.
An attractive feature of this material is the relatively low cost of the monomer, lactic acid, which can be derived from biomass (fermentation), coal, petroleum, or natural gas.
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11. CORPORATE TRAINING AND PLANNING
In 1927, Eastman Kodak Co. commercialized cellulose acetate into photographic film base.
Molding grade of CA was introduced in 1935.
In 1938, Eastman introduced CAB.
CAP was introduced in 1960.
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12. CORPORATE TRAINING AND PLANNING
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 triester stage. CA is prepared by hydrolyzing the triester to remove some of its acetyl groups. Plastic grade CA contains 38 to 40% acetyl.
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The propionate and butyrate esters are made by substituting propionic acid and propionic 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% butyryl and 12 to 15% acetyl.
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When A is and B is Plastic is
H H Cellulose
—C—CH3 —C—CH3 Cellulose acetate
|| ||
O O
—C—CH —C—CH2—CH3 Cellulose acetate propionate
—C—CH —C—CH2—CH2—CH3 Cellulose acetate butyrate
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O O
—C—CH2—CH —C—CH2—CH3 Cellulose propionate
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O O
—CH2—CH —CH2—CH3 Ethyl cellulose
—NO —NO2 Cellulose Nitrate
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Cellulose Esters
Cellulose Acetate
Introduction
Manufacturing of cellulose acetate was done in 1865 using a process in which cotton was heated with acetic anhydride in sealed tube at C but the process was difficult to control.
With further research various new techniques of manufacturing of cellulose acetate are developed.
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One of the methods available today is homogenous acetylation.
In this process cellulose is pretreated with glacial acetic acid to open up the cellulosic matter.
After pretreating, acetylation is done by mixing pretreated cellulose with acetylating agent like acetic anhydride, a catalyst like concentrated sulphuric acid and acetic acid as diluent.
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Properties
- High water absorption
- Poor electrical insulation characteristics
- Limited aging resistance
- Limited heat resistance
- Dissolved by wide variety of reagents
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18. Properties of Cellulose acetate
Name
Value
Unit
Specific gravity
1.28 --
Tensile Strength 40
MPa
Tensile modulus
2174
Flexural modulus
1794
Elongation at break 38 %
Impact Strength (Izod )
160
J/m
Hardness
R62
---
HDT (under 1.82 MPa load.) 61 °C
Melting point
Glass transition temperature
157
Dielectric Strength
13.4
KV/mm
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Applications
CA Different applications
Spectacles
CA Different applications
Tool handles
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20. Cellulose Acetate Butyrate (CAB)
Bleached Wood Pulp
% H2SO4
Pretreated for 12 hours
Drying with Acetic acid
Etherification of treated cellulose with mixture of Butyric acid and acetic anhydride H2SO4 ( Catalyst)
Cellulose acetate butyrate
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Properties
- Good toughness
- Excellent appearance
- Giving good coating with hard glossy surface
- Lower water absorption
- Better flow properties
- Lower density
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22. Properties of Cellulose Acetate Butyrate
Name
Value
Unit
Specific gravity
1.19 --
Tensile Strength
34.5
MPa
Tensile modulus
1725
Flexural modulus
1449
Elongation at break 50 %
Impact Strength (Izod )
187
J/m
Hardness
R75
---
HDT (under 1.82 MPa load.) 65 °C
Dielectric Strength
13.4
KV/mm
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23. CORPORATE TRAINING AND PLANNING
Applications
- Toys, tools handles, tabular keys, telephone housing, pipes for conveying water, outdoor display signs, vacuum formed products and protective coating for metals.
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24. Cellulose Acetate Propionate
- Cellulose Acetate Propionate having shorter side chain and it is harder stiffer, and posses 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.
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Properties
- Cellulose Acetate Propionate have shorter side chain and it is harder, stiffer and possess 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.
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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-nitriate is an explosive.
- Cellulose nitrate is precipiticised with camphor in order to make it easy processable.
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27. Properties of Cellulose Nitrate
Good rigidity
Water white transparency
Poor chemical resistance
Reasonable toughness
Capable of forming highly attractive multi-coloured sheeting
Highly inflammable.
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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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