Polypropylene
IUPAC name	poly(1-methylethylene)
Other names	Polypropylene; Polypropene; Polipropene 25 [USAN];Propene polymers; Propylene polymers; 1-Propene homopolymer
Identifiers
CAS number	[9003-07-0]
Properties
Molecular formula	(C3H6)x
Density	0. IUPAC Nomenclature is a system of naming Chemical compounds and of describing the science of Chemistry in general CAS registry numbers are unique numerical identifiers for Chemical compounds Polymers biological sequences mixtures and Alloys They are also referred to A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different 855 g/cm3, amorphous 0. 946 g/cm3, crystalline
Melting point	~ 165 °C
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Polypropylene lid of a Tic Tacs box, with a living hinge and the resin identification code under its flap

Micrograph of polypropylene

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. The melting point of a solid is the temperature range at which it changes state from solid to Liquid. In Chemistry, the standard state of a material is its state at 1 bar (100 Kilopascals exactly Tic Tac (officially styled as "tic tac" is the brand name of small hard sweets manufactured by the Italian confectioner Ferrero A living hinge is a thin flexible Hinge ( Flexure bearing) made from Plastic (rather than Cloth, Leather, or some other substance The symbols in the table below belong to the SPI resin identification coding system, developed by the Society of the Plastics Industry in 1988 A thermoplastic is a Plastic that Melts to a liquid when heated and freezes to a Brittle, very Glassy state when cooled sufficiently A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds The chemical industry comprises the companies that produce industrial chemicals Packaging is the science art and technology of enclosing or protecting products for distribution storage sale and use A textile is a flexible material comprised of a network of natural or artificial Fibres often referred to as thread or Yarn. g. , ropes, thermal underwear and carpets), stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. A rope is a length of Fibers twisted or Braided together to improve strength for pulling and Connecting. Stationery has historically meant a wide gamut of materials Paper and Office supplies, Writing implements Greeting cards etc For the Marty Friedman album see Loudspeaker (album A loudspeaker, speaker, or speaker system is an electroacoustical Polymer banknotes were developed by the Reserve Bank of Australia (RBA Commonwealth Scientific and Industrial Research Organisation (CSIRO and The University An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids. An addition polymer is a polymer which is formed by an Addition reaction, where many Monomers bond together via rearrangement of bonds without the loss of any atom Propene, also known as propylene, is an unsaturated organic compound having the Chemical formula C 3 H 6 Its resin identification code is . The symbols in the table below belong to the SPI resin identification coding system, developed by the Society of the Plastics Industry in 1988 Melt processing of polypropylene can be achieved via extrusion and molding.

Common extrusion methods include production of melt blown and spun bond fibers to form long rolls for future conversion into a wide range of useful products such as face masks, filters, diapers and wipes.

The most common shaping technique is injection molding, which is used for parts such as cups, cutlery, vials, caps, containers, housewares and automotive parts such as batteries. Injection molding (British moulding The related techniques of blow molding and injection-stretch blow molding are also used, which involve both extrusion and molding. Blow molding (blow forming is a manufacturing process by which hollow Plastic parts are formed Extrusion is a process used to create objects of a fixed cross-sectional profile

The large number of end use applications for PP are often possible because of the ability to tailor grades with specific molecular properties and additives during its manufacture. For example, antistatic additives can be added to help PP surfaces resist dust and dirt. Many physical finishing techniques can also be used on PP, such as machining. Conventional Machining, one of the most important material removal methods is a collection of material-working processes in which power-driven Machine tools, such as lathes Surface treatments can be applied to PP parts in order to promote adhesion of printing ink and paints.

Chemical and physical properties

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. In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating Polyethylene or polythene ( IUPAC name poly(ethene) is a Thermoplastic commodity heavily used in consumer products (notably the Properties LDPE is defined by a density range of 0910 - 0940 g/cm³ High-Density Polyethylene ( HDPE) or PolyEthylene High-Density ( PEHD) is a Polyethylene Thermoplastic made from Petroleum In Solid mechanics, Young's modulus (E is a measure of the Stiffness of an isotropic elastic material Through the incorporation of rubber particles, PP can be made both tough and flexible, even at low temperatures. This allows polypropylene to be used as a replacement for engineering plastics, such as ABS. Engineering plastics are a group of Plastic materials that exhibit superior mechanical and thermal properties in a wide range of conditions over and above more commonly used Acrylonitrile butadiene styrene or ABS, ( Chemical formula (C8H8· C4H6·C3H3Nn is Polypropylene is rugged, often somewhat stiffer than some other plastics, reasonably economical, and can be made translucent when uncolored but is not as readily made transparent as polystyrene, acrylic or certain other plastics. In Optics, transparency (also called pellucidity) is the Material property of allowing Polystyrene ˌpɒliˈstaɪriːn ( IUPAC Polyphenylethene is an aromatic Polymer made from the aromatic Monomer Styrene Poly(methyl methacrylate ( PMMA) or poly(methyl 2-methylpropenoate is a Thermoplastic and transparent Plastic. It can also be made opaque and/or have many kinds of colors through the use of pigments. Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation especially visible Light. Polypropylene has very good resistance to fatigue, so that most plastic living hinges, such as those on flip-top bottles, are made from this material. A living hinge is a thin flexible Hinge ( Flexure bearing) made from Plastic (rather than Cloth, Leather, or some other substance Very thin sheets of polypropylene are used as a dielectric within certain high performance pulse and low loss RF capacitors. A dielectric is a nonconducting substance ie an insulator. The term was coined by William Whewell in response to a request from Michael Faraday. Pulsed power is the term used to describe the science and technology of accumulating Energy over a relatively long period of time and releasing it very quickly thus increasing Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors

Polypropylene has a typical peak melting point of ~160°C (320°F), as determined by Differential Scanning Calorimetry (DSC). Many plastic items for medical or laboratory use can be made from polypropylene because it can withstand the heat in an autoclave. An autoclave is a pressurized device designed to heat aqueous solutions above their Boiling point at normal atmospheric pressure to achieve sterilization Food containers made from it will not melt in the dishwasher, and do not melt during industrial hot filling processes. For this reason, most plastic tubs for dairy products are polypropylene sealed with aluminium foil (both heat-resistant materials). After the product has cooled, the tubs are often given lids made of a less heat-resistant material, such as LDPE or polystyrene. Polystyrene ˌpɒliˈstaɪriːn ( IUPAC Polyphenylethene is an aromatic Polymer made from the aromatic Monomer Styrene Such containers provide a good hands-on example of the difference in modulus, since the rubbery (softer, more flexible) feeling of LDPE with respect to PP of the same thickness is readily apparent. Rugged, translucent, reusable plastic containers made in a wide variety of shapes and sizes for consumers from various companies such as Rubbermaid and Sterilite are commonly made of polypropylene, although the lids are often made of somewhat more flexible LDPE so they can snap on to the container to close it. Polypropylene can also be made into disposable bottles to contain liquid, powdered or similar consumer products, although HDPE and polyethylene terephthalate are commonly also used to make bottles. Uses PET can be semi-rigid to rigid depending on its thickness and is very lightweight Plastic pails, car batteries, wastebaskets, cooler containers, dishes and pitchers are often made of polypropylene or HDPE, both of which commonly have rather similar appearance, feel, and properties at ambient temperature.

The MFR (Melt Flow Rate) or MFI (Melt Flow Index) is an indication of PP's molecular weight. The Melt Flow Index is a measure of the ease of flow of the melt of a Thermoplastic Polymer. This helps to determine how easily the melted 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 impact or block copolymer. The comonomer used is typically ethylene. Ethylene-propylene rubber 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

The polymer is however, liable to chain degradation from exposure to UV radiation such as that present in sunlight. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun. For external applications, UV-absorbing additives must be used. Carbon black also provides some protection from UV attack. Carbon black is a material produced by the incomplete Combustion of heavy Petroleum products such as FCC tar coal tar ethylene cracking tar and a small amount from The polymer can also be oxidised at high temperatures, a common problem during moulding operations. Anti-oxidants are normally added to prevent polymer degradation. An antioxidant is a Molecule capable of slowing or preventing the oxidation of other molecules Polymer degradation is a change in the properties - Tensile strength, Colour, shape etc - of a Polymer or polymer based product under the influence of

Synthesis

Short segments of polypropylene, showing examples of isotactic (above) and syndiotactic (below) tacticity. Tacticity (from Greek 'taktikos' of or relating to arrangement or order is the relative Stereochemistry of adjacent chiral centers within a Macromolecule

An important concept in understanding the link between the structure of polypropylene and its properties is tacticity. Tacticity (from Greek 'taktikos' of or relating to arrangement or order is the relative Stereochemistry of adjacent chiral centers within a Macromolecule The relative orientation of each methyl group (CH₃ in the figure at left) relative to the methyl groups on neighboring monomers has a strong effect on the finished polymer's ability to form crystals, because each methyl group takes up space and constrains backbone bending. In Chemistry, a methyl group is a Hydrophobic Alkyl Functional group named after Methane (4

Like most other vinyl polymers, useful polypropylene cannot be made by radical polymerization due to the higher reactivity of the allylic hydrogen (leading to dimerization) during polymerization. A vinyl compound is any Organic compound that contains a vinyl group (also called ethenyl) &minus C[[Hydrogen H]] =CH sub>2 Radical polymerization is a type of Polymerization in which the Reactive center of a polymer chain consists of a radical. Moreover, the material that would result from such a process would have methyl groups arranged randomly, so called atactic PP. The lack of long-range order prevents any crystallinity in such a material, giving an amorphous material with very little strength and only specialized qualities suitable for niche end uses. An amorphous solid is a Solid in which there is no Long-range order of the positions of the Atoms (Solids in which there is long-range atomic order are

A Ziegler-Natta catalyst is able to limit incoming monomers to a specific orientation, only adding them to the polymer chain if they face the right direction. A Ziegler-Natta catalyst is a Reagent or a mixture of reagents used in the production of Polymers of 1-alkenes (α-olefins Most commercially available polypropylene is made with such Ziegler-Natta catalysts, which produce mostly isotactic polypropylene (the upper chain in the figure above). Tacticity (from Greek 'taktikos' of or relating to arrangement or order is the relative Stereochemistry of adjacent chiral centers within a Macromolecule With the methyl group consistently on one side, such molecules tend to coil into a helical shape; these helices then line up next to one another to form the crystals that give commercial polypropylene many of its desirable properties.

A ball-and-stick model of syndiotactic polypropylene. Tacticity (from Greek 'taktikos' of or relating to arrangement or order is the relative Stereochemistry of adjacent chiral centers within a Macromolecule

More precisely engineered Kaminsky catalysts have been made, which offer a much greater level of control. A Kaminsky is a catalytic system for Olefin Polymerization discovered by Walter Kaminsky and coworkers in 1980 Based on metallocene molecules, these catalysts use organic groups to control the monomers being added, so that a proper choice of catalyst can produce isotactic, syndiotactic, or atactic polypropylene, or even a combination of these. A metallocene is a compound with the general formula (C5R52M consisting of two cyclopentadienyl anions (Cp bound to a metal center in the oxidation Tacticity (from Greek 'taktikos' of or relating to arrangement or order is the relative Stereochemistry of adjacent chiral centers within a Macromolecule Aside from this qualitative control, they allow better quantitative control, with a much greater ratio of the desired tacticity than previous Ziegler-Natta techniques. They also produce narrower molecular weight distributions than traditional Ziegler-Natta catalysts, which can further improve properties.

To produce a rubbery polypropylene, a catalyst can be made which yields isotactic polypropylene, but with the organic groups that influence tacticity held in place by a relatively weak bond. After the catalyst has produced a short length of polymer which is capable of crystallization, light of the proper frequency is used to break this weak bond, and remove the selectivity of the catalyst so that the remaining length of the chain is atactic. The result is a mostly amorphous material with small crystals embedded in it. Since each chain has one end in a crystal but most of its length in the soft, amorphous bulk, the crystalline regions serve the same purpose as vulcanization. Vulcanization (or Vulcanisation refers to a specific curing process of Rubber involving high heat and the addition of Sulfur or other equivalent curatives

Mechanism of metallocene catalysts

The reaction of many metallocene catalysts requires a co catalyst for activation. One of the most common co catalysts for this purpose is Methylalmuinoxane (MAO)^[1]. Other co catalysts include, Al(C₂H₅)₃^[2]. There are numerous metallocene catalysts that can be used for propylene polymerization. (Some metallocene catalysts are used for industrial process, while others are not, due to their high cost. ) One of the simplest is Cp₂MCl₂ (M = Zr, Hf). Different catalyst can lead to polymers with different molecular weights and properties. Active research is still being conducted on metallocene catalyst.

In the mechanism the metallocene catalyst first reacts with the co catalyst. If MAO is the co catalyst, the first step is to replace one of the Cl atoms on the catalyst with a methyl group from the MAO. The methyl group on the MAO is replaced by the Cl from the catalyst. The MAO then removes another Cl from the catalyst. This makes the catalyst positively charged and susceptible to attack from propylene^[3].

Once the catalyst is activated, the double bond on the propene coordinates with the metal of the catalyst. The methyl group on the catalyst then migrates to the propene, and the double bond is broken. This starts the polymerization. Once the methyl migrates the positively charged catalyst is reformed and another propene can coordinate to the metal. The second propene coordinates and the carbon chain that was formed migrates to the propene. The process of coordination and migration continues and a polymer chain is grown off of the metallocene catalyst. ^{[4] [5]}

History

Polypropylene was first polymerized on March 11 1954 by Giulio Natta. Giulio Natta ( February 26 1903, Imperia - Bergamo, 2 May 1979) was an Italian Chemist, who won At first it was thought that it would be cheaper than polyethylene. Polyethylene or polythene ( IUPAC name poly(ethene) is a Thermoplastic commodity heavily used in consumer products (notably the ^[6]

Practical applications

A common application for polypropylene is as Biaxially Oriented polypropylene (BOPP). These BOPP sheets are used to make a wide variety of materials including clear bags. When polypropylene is biaxially oriented, it becomes crystal clear and serves as an excellent packaging material for artistic and retail products. Packaging is the science art and technology of enclosing or protecting products for distribution storage sale and use In India, polypropylene is used in manufacturing mats to be used at home. In New Zealand and also in the US military, polypropylene, or 'polypro' (New Zealand 'polyprops'), is the material used for the fabrication of cold-weather gear, such as a long-sleeve shirt or long underwear, in addition to warm-weather gear such as Under Armour clothing, which can easily wick away sweat. Under Armour is a brand of clothing headquartered in Baltimore, Maryland, designed for use in Sports It was originally created to be worn underneath These polypro clothes are not easily flammable, however, they can melt, which may result in severe burns if the service member is involved in an explosion or fire of any kind. ^[7] Polypropylene is also used as an alternative to polyvinyl chloride (PVC) as insulation for electrical cables for LSZH cable in low-ventilation environments, primarily tunnels. Low smoke zero halogen (LSZH or LSOH is a type of cable jacketing used in the manufacture of industrial and network cabling This is because it emits less smoke and no toxic halogens, which may lead to production of acid in high temperature conditions.

Polypropylene is also used in particular roofing membranes as the waterproofing top layer of single ply systems as opposed to modified bit systems. Its most common medical use is in the synthetic, nonabsorbable suture Prolene, manufactured by Ethicon Inc.

Polypropylene is most commonly used for plastic moldings where it is injected into a mold while molten, forming complex shapes at relatively low cost and high volume, examples include bottle tops, bottles and fittings. Prolene is a Synthetic, nonabsorbable Polypropylene suture. It is indicated for skin closure and general soft tissue approximation and ligation Ethicon Inc is a subsidiary of Johnson & Johnson. It was incorporated as a separate company under the Johnson & Johnson umbrella in 1949 to expand and diversify the Johnson

Recently it has been produced in sheet form and this has been widely used for the production of stationary folders, packaging and storage boxes. The wide colour range, durability and resistance to dirt make it ideal as a protective cover for papers and other materials. It is used in Rubik's cube stickers because of these characteristics. The Rubik's Cube is a Mechanical puzzle invented in 1974 by Hungarian Sculptor and Professor of Architecture Ernő Rubik

The availability of sheet polypropylene has provided an opportunity for the use of the material by designers. The light weight, durable and colourful plastic makes an ideal medium for the creation of light shades and a number of designs have been developed using interlocking sections to create elaborate designs.

Polypropylene sheets are a popular choice for trading card collectors; these come with pockets (nine for standard size cards) for the cards to be inserted and are used to protect their condition and are meant to be stored in a binder. A trading card (or collectible card) is a small Card, usually made out of Cardboard or thick Paper, which usually contains an image of a

Polypropylene has been used in hernia repair operations to protect the body from new hernias in the same location. A hernia is a protrusion of a tissue, structure or part of an organ through the muscular tissue or the membrane by which it is normally contained A small patch of the material is placed over the spot of the hernia, below the skin, and is painless and is rarely, if ever, rejected by the body.

The material has recently been introduced into the fashion industry through the work of designers such as Anoush Waddington who have developed specialized techniques to create jewellery and wearable items from polypropylene. Anoush Waddington is a leading designer in Art jewelry. Anoush’s work can be found in a significant number of private collections around the world

Expanded Polypropylene: EPP

Future Applications

Recent development of a specialty extruded polypropylene called Innegra S has produced a high modulus thread that is 66% lighter than comparably deniered fiberglass. Dr. Brian Morin patented a process that creates a high modulus fiber that has potential in specialty applications ranging from marine ropes, marine hulls, kayak paddles, aircraft pallets, ballistic applications and other lightweight structral applications. ^[8]

References

1. ^ R. Kleinschmidt et al. rJournal of Molecular Catalysis A: Chemical 157(2000)83–90
2. ^ Kyung-Jun Chu. Eur. Polym. J. Vol. 34, No. 3/4, pp. 577-580, 1998
3. ^ Session 6
4. ^ Song et al. Macromol. Symp. 2004, 213, 173-185
5. ^ P. Mercandelli et al. / Journal of Organometallic Chemistry 692 (2007) 4784–4791
6. ^ This week 50 years ago in New Scientist, 28 April, 2007, p. New Scientist is a weekly International science magazine and website covering recent developments in science and technology for a general English -speaking 15
7. ^ USAF Flying Magazine. Safety. Nov. 2002.
8. ^ High Modulus Thermoplastic Fibers for Use in Thermoset Composites

External links

• Chain structure of Polypropylene
• Technical Properties & Applications
• Polypropylene is traded on the London Metals Exchange