Biomedical Engineering Reference
In-Depth Information
their use for wide range of applications and therefore, need to be explored fully for the
commercialization of PHB.
It is easily degradable both aerobically and anaerobically by wide variety of bacte-
ria and can also be produced from renewable resources. Due to these and many other
useful properties, it has found technical, commercial and biomedical significance.
syNthetiC PlastiC
Vs.
Natural PlastiC
The production and use of natural plastic is generally regarded as a more sustainable
activity when compared with plastic production from petroleum (petroplastic), be-
cause it relies less on fossil fuel as a carbon source and also introduces fewer, net-new
greenhouse emissions if it biodegrades. They significantly reduce hazardous wastes
caused by oil-derived plastics, which remain solid for hundreds of years, and open a
new era in packing technology and industry.
While production of most bioplastics results in reduced carbon dioxide emissions
compared to traditional alternatives, there are some real concerns that the creation of a
global bioeconomy could contribute to an accelerated rate of deforestation if not man-
aged effectively. There are associated concerns over the impact on water supply and
soil erosion and bioplastics represent a 42% reduction in carbon footprint. On the other
hand, bioplastic can be made from agricultural byproducts and also from used plastic
bottles and other containers using microorganisms.
syNthetiC PlastiC
A synthetic plastic material is a wide range of synthetic or semi-synthetic organic
solids used in the manufacture of industrial products and daily living purpose. They
are typically polymers of high molecular mass and monomers of plastics are synthetic
organic compounds.
types of synthetic Plastic
There are two types of plastics, thermoplastics and thermosetting polymers. Thermo-
plastics are the plastics that do not undergo chemical change in their composition
when heated and can be molded again and again, examples are polyethylene, polysty-
rene, polyvinyl polystyrene, polyvinyl chloride, and polytetrafluroethylene (PTFE).
The raw materials needed to make most plastics come from petroleum and natural gas.
Plastics can be classified by chemical structure, namely the molecular units that
make up the polymer's backbone and side chains. Some important groups in these
classifications are the acrylics, polyesters, silicones, polyurethanes, and halogenated
plastics. Common thermoplastics range from 20,000 to 500,000 MW. These chains
are made up of many repeating molecular units, known as repeat units, derived from
monomers; each polymer chain will have several thousand repeating units. The vast
majority of plastics are composed of polymers of carbon and hydrogen alone or with
oxygen, nitrogen, chlorine or sulfur in the backbone. Some plastics are partially crys-
talline and partially amorphous in molecular structure, giving them both a melting
point and one or more glass transitions. The so-called semi-crystalline plastics include
polyethylene, polypropylene, poly (vinyl chloride), polyamides (nylons), polyesters,
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