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Friday, April 13

  1. page Cellulose acetate edited Cellulose acetate is produced by modifying cellulose and thus is a semi-synthetic polymer. A major …
    Cellulose acetate is produced by modifying cellulose and thus is a semi-synthetic polymer. A major component of plant cell walls, cellulose is found in virtually all types of plants. Chemically, cellulose consists of D-glucose units linked by β(1->4) glycosidic bonds and is classified as a polysaccharide. In nature, it mostly exists in semi-crystalline fibre forms. Along with other polymers, such as lignin and hemicellulose, cellulose forms what is commonly known as the wood. The exact composition of wood varies tremendously between species.
    {http://upload.wikimedia.org/wikipedia/commons/thumb/0/07/Cellulose_Sessel.svg/500px-Cellulose_Sessel.svg.png}
    Figure
    Figure 1: Structure
    To produce cellulose acetate, cellulose is firstly extracted from plant sources such as wood pulp and cotton. Purified cellulose is then esterfied under acidic conditions, followed by partial hydrolysis. As the name suggests, cellulose acetate contains acetyl groups in place of the hydroxyl groups found in natural sugars. Cellulose is mixed with acetic acid and acetic anhydride to induce acetylation. Acidic conditions are provided by adding catalytic quantities of sulfuric acid. The level of acetylation can be varied through partial hydrolysis, which re-creates free hydroxyl groups. This changes the degrees of substitution, which in itself is an indicator of the amount of free hydroxyl groups. Along with the desired product, partial hydrolysis produces acetic acid, which can be used in the previous esterification step.
    {esterification_of_cellulose.png}
    Figure
    Figure 2. Esterification
    Various plasticizers can be used to produce thermoplastic with cellulose acetate. Materials such as diethylene diacetate, sucrose octaacetate and diethyl phthalate were tested for their use as plasticizers. The characteristics of resulting plastics were found to depend on the plasticizer used and the volume of plasticizer used. Currently, phthalate-based plasticizers are commonly used but, unfortunately, these plasticizers are not biodegradable. Consequently, more environmentally friendly plasticizers are under consideration. An example of such alternative is triethyl citrate.
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Thursday, April 12

  1. page Enhancement of properties of Biodegradable Polymers edited ... The biodegradable polymers used in electrical wires can be modified so as to promote electrica…
    ...
    The biodegradable polymers used in electrical wires can be modified so as to promote electrical insulation. This is done so that so electrical energy is wasted to the surroundings. The specific polymer can be modified by not allowing the conducting groups of the polymer interact with each other. This is best explained using band gap theory in conjunction with molecular orbital theory.[3] Band theory tells us that in order to achieve electrical conductivity that there must be a close enough separation of a conducting band and a valence band of the insulator. When one then applies molecular orbital theory you see a large separation of conducting band and the valence band. This is best evidenced by the strength of a carbon-carbon bond. The carbon-carbon bond has such a large separation between it's HOMO and LUMO that an electron cannot be promoted to the conducting gap, stopping any electrical conductivity.
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    Polymers (previous page)
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    Matkó S, Toldy A, Keszei S, Anna P, Bertalan G, Marosi G. 2005. Flame retardancy of biodegradable polymers and biocomposites. Polym Degrad Stab 88(1):138-45.
    Li F, Hu K, Li J, Zhao B. 2001. The friction and wear characteristics of nanometer ZnO filled polytetrafluoroethylene. Wear 249(10–11):877-82.
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    7:56 am
  2. page Enhancement of properties of Biodegradable Polymers edited ... of ways. Sometimes, biodegradable polymers are so easily degradable that they are unable …
    ...
    of ways.
    Sometimes, biodegradable polymers are so easily degradable that they are unable to fulfill their use. In these cases, the polymers have extremely low thermal stability, and therefore measures can be taken to increase the usefulness of the biodegradable polymer. One example to increase the stability is by the addition of various additives. Alcohol groups are added in order to increase the intermolecular or hydrogen bonding interactions between the polymer. This results in the polymer being more stable and more resistant to decompostion. Another specific additive that has been used is ammonium polyphospahte.
    ...
    surface with nanoparticles.Thesenanoparticles. These nanoparticles enhance
    {Biopolymer_shapes.jpg} Figure 1 : Biodegradable polymers can be moulded into various shapes in order to enhance its properties for different applications.
    The biodegradable polymers used in electrical wires can be modified so as to promote electrical insulation. This is done so that so electrical energy is wasted to the surroundings. The specific polymer can be modified by not allowing the conducting groups of the polymer interact with each other. This is best explained using band gap theory in conjunction with molecular orbital theory.[3] Band theory tells us that in order to achieve electrical conductivity that there must be a close enough separation of a conducting band and a valence band of the insulator. When one then applies molecular orbital theory you see a large separation of conducting band and the valence band. This is best evidenced by the strength of a carbon-carbon bond. The carbon-carbon bond has such a large separation between it's HOMO and LUMO that an electron cannot be promoted to the conducting gap, stopping any electrical conductivity.
    Return to Home Page
    Go to Degradation of Biodegradable Polymers (previous page)
    ...
    (next page)
    Matkó S, Toldy A, Keszei S, Anna P, Bertalan G, Marosi G. 2005. Flame retardancy of biodegradable polymers and biocomposites. Polym Degrad Stab 88(1):138-45.
    Li F, Hu K, Li J, Zhao B. 2001. The friction and wear characteristics of nanometer ZnO filled polytetrafluoroethylene. Wear 249(10–11):877-82.
    (view changes)
    7:54 am
  3. page Enhancement of properties of Biodegradable Polymers edited ... variety of ways.[3] ways. Sometimes, biodegradable polymers are so easily degradable tha…
    ...
    variety of ways.[3]ways.
    Sometimes, biodegradable polymers are so easily degradable that they are unable to fulfill their use. In these cases, the polymers have extremely low thermal stability, and therefore measures can be taken to increase the usefulness of the biodegradable polymer. One example to increase the stability is by the addition of various additives. Alcohol groups are added in order to increase the intermolecular or hydrogen bonding interactions between the polymer. This results in the polymer being more stable and more resistant to decompostion. Another specific additive that has been used is ammonium polyphospahte.
    ...
    surface with nanoparticles. Thesenanoparticles.These nanoparticles enhance
    {Biopolymer_shapes.jpg} Figure 1 : Biodegradable polymers can be moulded into various shapes in order to enhance its properties for different applications.
    The biodegradable polymers used in electrical wires can be modified so as to promote electrical insulation. This is done so that so electrical energy is wasted to the surroundings. The specific polymer can be modified by not allowing the conducting groups of the polymer interact with each other. This is best explained using band gap theory in conjunction with molecular orbital theory.[3] Band theory tells us that in order to achieve electrical conductivity that there must be a close enough separation of a conducting band and a valence band of the insulator. When one then applies molecular orbital theory you see a large separation of conducting band and the valence band. This is best evidenced by the strength of a carbon-carbon bond. The carbon-carbon bond has such a large separation between it's HOMO and LUMO that an electron cannot be promoted to the conducting gap, stopping any electrical conductivity.
    (view changes)
    7:54 am
  4. page Enhancement of properties of Biodegradable Polymers edited ... variety of ways. ways.[3] Sometimes, biodegradable polymers are so easily degradable tha…
    ...
    variety of ways.ways.[3]
    Sometimes, biodegradable polymers are so easily degradable that they are unable to fulfill their use. In these cases, the polymers have extremely low thermal stability, and therefore measures can be taken to increase the usefulness of the biodegradable polymer. One example to increase the stability is by the addition of various additives. Alcohol groups are added in order to increase the intermolecular or hydrogen bonding interactions between the polymer. This results in the polymer being more stable and more resistant to decompostion. Another specific additive that has been used is ammonium polyphospahte.
    For some applications, such as knee joints, polymers need to flexible and have the ability to slide. A commonly used method to lower the coefficient of friction is to fuse the polymer surface with nanoparticles. These nanoparticles enhance the sliding properties of the polymer. Also, these particles are not easily degraded and therefore, they increase the stability and the rigidity of the polymer.
    ...
    Return to Home Page
    Go to Degradation of Biodegradable Polymers (previous page)
    ...
    (next page)
    Matkó S, Toldy A, Keszei S, Anna P, Bertalan G, Marosi G. 2005. Flame retardancy of biodegradable polymers and biocomposites. Polym Degrad Stab 88(1):138-45.
    Li F, Hu K, Li J, Zhao B. 2001. The friction and wear characteristics of nanometer ZnO filled polytetrafluoroethylene. Wear 249(10–11):877-82.
    (view changes)
    7:52 am
  5. page Enhancement of properties of Biodegradable Polymers edited ... of ways. Sometimes, biodegradable polymers are so easily degradable that they are unable …
    ...
    of ways.
    Sometimes, biodegradable polymers are so easily degradable that they are unable to fulfill their use. In these cases, the polymers have extremely low thermal stability, and therefore measures can be taken to increase the usefulness of the biodegradable polymer. One example to increase the stability is by the addition of various additives. Alcohol groups are added in order to increase the intermolecular or hydrogen bonding interactions between the polymer. This results in the polymer being more stable and more resistant to decompostion. Another specific additive that has been used is ammonium polyphospahte.
    For some applications, such as knee joints, polymers need to flexible and have the ability to slide. A commonly used method to lower the coefficient of friction is to fuse the polymer surface with nanoparticles. These nanoparticles enhance the sliding properties of the polymer. Also, these particles are not easily degraded and therefore, they increase the stability and the rigidity of the polymer.
    ...
    Return to Home Page
    Go to Degradation of Biodegradable Polymers (previous page)
    ...
    (next page)
    Matkó S, Toldy A, Keszei S, Anna P, Bertalan G, Marosi G. 2005. Flame retardancy of biodegradable polymers and biocomposites. Polym Degrad Stab 88(1):138-45.
    Li F, Hu K, Li J, Zhao B. 2001. The friction and wear characteristics of nanometer ZnO filled polytetrafluoroethylene. Wear 249(10–11):877-82.
    (view changes)
    7:51 am

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