Polypropylene or polypropene (PP) is a thermoplastic polymer, 
made by the chemical industry and used in a wide variety of applications, including packaging, textiles (e.g. ropes, thermal underwear and carpets), stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids. In 2007, the global market for polypropylene had a volume of 45.1 million tons which led to a turnover of about 65 billion US $ (47,4 billion €).
made by the chemical industry and used in a wide variety of applications, including packaging, textiles (e.g. ropes, thermal underwear and carpets), stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids. In 2007, the global market for polypropylene had a volume of 45.1 million tons which led to a turnover of about 65 billion US $ (47,4 billion €). Chemical and physical properties
Micrograph of polypropylene
Most commercial polypropylene is isotactic and has an intermediate level of crystallinity between that of low density polyethylene (LDPE) and high density polyethylene (HDPE); its Young's modulus is also intermediate. PP is normally tough and flexible, especially when copolymerized with ethylene. This allows polypropylene to be used as an engineering plastic, competing with materials such as ABS. Polypropylene is reasonably economical, and can be made translucent when uncolored but is not as readily made transparent as polystyrene, acrylic or certain other plastics. It is often opaque or colored using pigments. Polypropylene has good resistance to fatigue. Polypropylene has a melting point of ~160 °C (320 °F), as determined by Differential scanning calorimetry (DSC).
The MFR (Melt Flow Rate) or MFI (Melt Flow Index) is a measure of PP's molecular weight. This helps to determine how easily the molten raw material will flow during processing. Higher MFR PPs fill the plastic mold more easily during the injection or blow molding production process. As the melt flow increases, however, some physical properties, like impact strength, will decrease.
There are three general types of PP: homopolymer, random copolymer and block copolymer. The comonomer used is typically ethylene. Ethylene-propylene rubber or EPDM added to PP homopolymer increases its low temperature impact strength. Randomly polymerized ethylene monomer added to PP homopolymer decreases the polymer crystallinity and makes the polymer more transparent.
Degradation
Polypropylene is liable to chain degradation from exposure to UV radiation such as that present in sunlight. Oxidation usually occurs at the secondary carbon atom present in every repeat unit. A free radical is formed here, and then reacts further with oxygen, followed by chain scission to yield aldehydes and carboxylic acids. In external applications, it shows up as a network of fine cracks and crazes which become deeper and more severe with time of exposure.
For external applications, UV-absorbing additives must be used. Carbon black also provides some protection from UV attack. The polymer can also be oxidized at high temperatures, a common problem during molding operations. Anti-oxidants are normally added to prevent polymer degradation.
Polypropylene is commonly recycled
Source : http://en.wikipedia.org/wiki/Polypropylene
Micrograph of polypropylene
Most commercial polypropylene is isotactic and has an intermediate level of crystallinity between that of low density polyethylene (LDPE) and high density polyethylene (HDPE); its Young's modulus is also intermediate. PP is normally tough and flexible, especially when copolymerized with ethylene. This allows polypropylene to be used as an engineering plastic, competing with materials such as ABS. Polypropylene is reasonably economical, and can be made translucent when uncolored but is not as readily made transparent as polystyrene, acrylic or certain other plastics. It is often opaque or colored using pigments. Polypropylene has good resistance to fatigue. Polypropylene has a melting point of ~160 °C (320 °F), as determined by Differential scanning calorimetry (DSC).
The MFR (Melt Flow Rate) or MFI (Melt Flow Index) is a measure of PP's molecular weight. This helps to determine how easily the molten raw material will flow during processing. Higher MFR PPs fill the plastic mold more easily during the injection or blow molding production process. As the melt flow increases, however, some physical properties, like impact strength, will decrease.
There are three general types of PP: homopolymer, random copolymer and block copolymer. The comonomer used is typically ethylene. Ethylene-propylene rubber or EPDM added to PP homopolymer increases its low temperature impact strength. Randomly polymerized ethylene monomer added to PP homopolymer decreases the polymer crystallinity and makes the polymer more transparent.
Degradation
Polypropylene is liable to chain degradation from exposure to UV radiation such as that present in sunlight. Oxidation usually occurs at the secondary carbon atom present in every repeat unit. A free radical is formed here, and then reacts further with oxygen, followed by chain scission to yield aldehydes and carboxylic acids. In external applications, it shows up as a network of fine cracks and crazes which become deeper and more severe with time of exposure.
For external applications, UV-absorbing additives must be used. Carbon black also provides some protection from UV attack. The polymer can also be oxidized at high temperatures, a common problem during molding operations. Anti-oxidants are normally added to prevent polymer degradation.
Polypropylene is commonly recycled
Source : http://en.wikipedia.org/wiki/Polypropylene
![[Valid Atom 1.0]](valid-atom.png "Validate my Atom 1.0 feed")
No comments:
Post a Comment