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Polypropylene

Physical and chemical properties
Micrograph of polypropylene
Most commercial polypropylene is isotactic and has a crystallinity intermediate between that of low density polyethylene (LDPE) and high density polyethylene (HDPE), and Young's modulus is also intermediate. PP is usually resistant and flexible, especially when copolymerized with ethylene. This allows polypropylene to be used as an engineering plastic, competing materials such as ABS. Polypropylene is reasonably economical, and can be made transparent when no distortion, but it is not so easy to make transparent as polystyrene, acrylic or certain plastics. Often opaque or colored 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) or MFI (melt flow rate) is a measure of molecular weight PP. The measure helps determine the ease with molten material will flow through the process. MFR polypropylene filled with more plastic mold more easily during injection blow molding or production process. As the melt increases the flow, however, some physical properties such as resistance to impact is reduced.
There are three general types of PP: homopolymer, random copolymer and block copolymer. The comonomer used is ethylene. ethylene-propylene rubber or EPDM added PP homopolymer increases its strength, low temperature impact. Randomly polymerized ethylene monomer added PP homopolymer decreases the crystallinity of the polymer and does the most transparent polymer.
Degradation
Polypropylene is responsible for the degradation of the chain of exposure to UV radiation, such as present in sunlight. Oxidation usually occurs in the secondary carbon atom present in each repeat unit. A free radical is formed here, and then reacts with oxygen, followed by chain scission to produce aldehydes and carboxylic acids. In external applications, is shown as a network of hairline cracks and fashion that become more and more severe with exposure time.
For outdoor applications, UV-absorbing additives should be used. Carbon black also offers some protection against UV attack. The polymer can also be oxidized at high temperatures, a common problem during molding operations. Antioxidants are normally added to prevent degradation of polymers.
History
Polypropylene was polymerized first by Giulio Natta Karl Rehn and March 1954, serving as a groundwork for large-scale synthesis since 1957. At first he thought it would be cheaper than polyethylene.
Synthesis
Short segments polypropylene, showing examples of isotactic (above) and syndiotactic (below) tacticity.
An important concept in understanding the relationship between structure polypropylene and its properties are tacticity. The relative orientation of each methyl group (CH3 in the figure on the left) in relation 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 limited flexion backbone.
Like most vinyl polymers, useful polypropylene can not be made by radical polymerization due to the higher reactivity of allylic hydrogen (leading to dimerization) during polymerization. Moreover, the material that would result from this process would have methyl groups arranged randomly, so called atactic PP. The lack of order long range that prevents any crystallinity in a material, giving an amorphous material with very little force and specialized skills only suitable for niche end uses.
A Ziegler-Natta catalyst is able to limit incoming monomers to a specific orientation, only added to the polymer chain if they face the right direction. Most commercially available polypropylene is made with Ziegler-Natta these catalysts, which produce mostly isotactic polypropylene (the upper chain in previous figure). With the methyl group consisting of one hand, these molecules tend to coil into a helical shape, these helices then line up side by side to form the crystals that give commercial polypropylene its many desirable properties.
A ball and stick model of syndiotactic polypropylene.
More precisely engineered Kaminsky catalysts have been made, offering a much greater level of control. Based on metallocene molecules, these catalysts use organic groups control of the monomers to be added, so that a proper choice of catalyst can produce isotactic, syndiotactic, or atactic polypropylene, or even a combination thereof. In addition to this quality control, allowing a better quantitative control, with a much larger proportion of the desired tacticity than Ziegler-Natta previous techniques. They also produce more narrow molecular weight distribution of Ziegler-Natta catalysts traditional, which can further improve properties.
To produce a paste of polypropylene, a catalyst can cause yields isotactic polypropylene, but with organic groups tacticity influence in place by a relatively weak link. After the catalyst has a short length of polymer that is capable of crystallization, since account of the proper frequency is used to break the weak link, and remove the selectivity of the catalyst for the remaining length of the chain is atactic. The result is a mostly amorphous material with small crystals embedded in it. Because each chain has one end in a crystal, but most of its length in most soft and amorphous, the crystalline regions have the same function as vulcanization.
Mechanism of metallocene catalysts
The reaction of many metallocene catalysts requires a catalyst for the activation of cooperation. One co common catalyst for this purpose is Methylaluminoxane (MAO). Other catalysts cooperation include, Al (C2H5) 3.There are many metallocene catalysts that can be used for the polymerization of propylene. (Some metallocene catalysts are used to industrial process, while others are not, due to its high cost.) One of the simplest is Cp2MCl2 (M = Zr, Hf). catalyst may lead to different polymer different molecular weights and properties. Active research is still underway in a metallocene catalyst.
In the mechanism of the first metallocene catalyst reacts with the catalyst co. If the catalyst is MAO co, the first step is to replace one of the Cl atoms in the catalyst with a methyl group of the MAO. The methyl group is replaced Cl by the catalyst. The then removes another MAO catalyst Cl. This causes the positively charged catalyst and propylene susceptible to attack.
Once the catalyst activates the double bond in propene coordinated with the metal catalyst. The methyl group in 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 propylene and other reforms can coordinate with the metal. The second coordinates propene and carbon chain formed moving towards propene. The coordination process and the migration continues and a polymer chain is grown outside the metallocene catalysts.
Manufacturing
Melt processing of polypropylene can be achieved via extrusion and molding. The most common methods include the production of extrusion blown merger and textile fibers bond to form long rolls for future conversion into a wide range of useful products such as masks, filters, diapers, diapers () and wipes.
The most common technique is the configuration of injection molding, which is used for parts such as cups, cutlery, cups, lids, packaging items home and automotive parts such as batteries. The related technical blow molding and injection molding-stretch blow also used, which involve both extrusion and molding.
The large number of end use applications for PP are often made possible by the ability to tailor degrees to molecular properties and additives during manufacture. For example, antistatic additives can be added to help PP surfaces resist dust and dirt. Many physical finishing techniques can also be used in the PP, such as machining. Surface treatments can be applied to parts of PP in order to promote adhesion of printing ink and paints.
Applications
Polypropylene lid of a Tic Tac box, with a living hinge and the resin identification code on the flap
Since polypropylene is resistant to fatigue most living plastic hinges, such as those in the flip-top bottles are made from this material. However, it is important to ensure that the molecules are directed through the chain of the hinge for maximum strength.
Very thin sheets of polypropylene are used as a dielectric within certain impulses high performance, low loss RF capacitors.
piping systems are constructed using high purity polypropylene. Stronger, more piping systems rigid, for use in potable plumbing, hydronic heating and cooling systems, and applications of reclaimed water are also produced using polypropylene. This material is often chosen for its resistance to corrosion and chemical leaching, their resistance against most forms of physical harm, including the impact and freezing, and its ability to be joined by heat fusion rather than gluing citation. [Edit]
A chair made of polypropylene
Many articles plastics for medical or laboratory can be made from polypropylene because it can withstand the heat in an autoclave. Its heat resistance also allows you to use as material for manufacturing boilers consumer grade. Food containers made from it will not melt in the dishwasher, and does not melt during industrial processes hot filling. For this reason, most plastic tubs for dairy products are polypropylene sealed with aluminum foil (both material heat resistant). After the product has cooled, the tubs have lids made of a material less resistant to heat, such as LDPE or polystyrene. These containers provide a good hands-on example of the difference in the module, since the rubber softer (more flexible) feeling of LDPE with respect to PP of the same thickness is evident. Tough, translucent, reusable plastic containers manufactured in a wide variety of sizes and shapes to consumers of various companies like Rubbermaid and Sterilite are commonly made of polypropylene, although the covers are often made somewhat more flexible LDPE so they can add to the container to close it. Polypropylene also can be done in disposable bottles for containing liquids, powders or similar consumer products, despite the high density polyethylene and polyethylene terephthalate commonly is also used to make bottles. plastic buckets, car batteries, bins, containers, refrigerator, dishes and pitchers are often made of polypropylene or high density polyethylene, which typically have a very similar appearance, feel and properties at room temperature.
Polypropylene is a polymer of greater use in nonwovens, with more than 50% used [citation needed] for diapers and medical devices where it is to absorb water (hydrophilic) instead of repelling natural water (hydrophobic). Other interesting applications of nonwoven air filters, gas and liquids where the fibers can be formed into sheets or webs can be folded to form cartridges or layers that are filtered to different efficiency in the range of 0.5 to 30 microns. These applications could be seen in the house as water filters or air conditioning filters type. The large surface area and, of course, non-woven polypropylene are ideal hydrophobic absorbent oil spill with floating barriers near relatives spills oil on rivers.
A common application for polypropylene is biaxially oriented polypropylene (BOPP). These BOPP sheets are used for a variety of materials including transparent bags. When polypropylene is biaxially oriented, it becomes crystal clear and serves as an excellent packaging material and artistic products retail.
Polypropylene, high fade, is widely used in manufacturing carpets and rugs used in the home.
In New Zealand, in the army U.S., and elsewhere, polypropylene, or polypropylene (polyprops New Zealand), has been used for the manufacture of base layers of cold weather, such as long sleeved shirts or long underwear (More recently, polyester, polypropylene replace these applications in the U.S. military, as in the ECWCS). Polypropylene It is also used in running warm as some Under Armour clothing, which can easily transport the sweat from the skin. Although the clothes are not easily polypropylene flammable, which can melt, which can result in severe burns if the service member is involved in an explosion or fire of any kind.
Polypropylene is widely used in ropes, distinctive because they are light enough to float in water. For the same mass, polypropylene rope is the same force as a plow steel cable. polypropylene rope is stronger than nylon, but not as strong as polyester. Similarly, it is more UV resistant than nylon, but not as much as polyester. By usually costs less than polyester and is not as elastic as nylon.
Polypropylene is also used as an alternative to polyvinyl chloride (PVC) as insulation for electrical cables LSZH cable in poorly ventilated environments, especially tunnels. This is because it emits less smoke and no toxic halogens, that can lead to acid production at high temperature.
Polypropylene is also used in particular roofing membranes as the waterproofing top layer of a single system layer as opposed to slightly modified systems.
Its medical use is more common in the Prolene synthetic non-absorbable suture, made from Ethicon Inc.
Polypropylene is most commonly used for plastic moldings where it is injected into a mold while casting, the formation of complex forms with a relatively low cost and high volume, examples include bottle tops, bottles and accessories.
Recently on the blade shape and has been widely used for the production of stationary folders, packaging and storage boxes. The wide range of colors, durability and resistance to dirt make it ideal as a protective cover for papers and other materials. Tag is used Rubik's Cube, because of these characteristics.
The availability of sheet polypropylene has an opportunity for the use of the material by designers. Lightweight, durable and colorful plastic makes an ideal medium for the creation of tones and a number of designs have been developed using interlocking sections to create elaborate designs.
Polypropylene sheets are a popular choice for collectors of trading cards, which come with pockets (nine for standard size cards) for cards that are inserted and used to protect their status and are intended to be stored in a folder.
Polypropylene has been used in operations for hernia and pelvic organ prolapse repair the hernia protect the body again in the same place. A small piece of material is placed on the field of hernia, under the skin, and is painless and rarely, if ever, rejected by the body. However, the FDA has issued several warnings about the use of polypropylene mesh medical kits that are used for certain applications in pelvic organ prolapse, specifically when introduced into the vagina near the wall due a steady increase in the number of mesh erosion is reported by patients in recent years.
The material has been introduced recently in the industry fashion through the work of designers such as Anoush Waddington who have developed specialized techniques to create jewelry and clothing, made of polypropylene.
Polypropylene is used in the manufacture of speaker units. Its use was pioneered by engineers at the BBC and the patent rights later acquired by Electronic Mission for use in its mission speaker and Mission Freedom 737 Renaissance speaker.
In 2008, Canadian researchers said quaternary ammonium biocides and oleamide leaking out of polypropylene laboratory equipment specified, that affect experimental results. Since polypropylene is used in a wide range of food containers, such as yogurt, the media spokesman Paul Duchesne Health Canada, said the department will review the results to determine whether measures are needed to protect consumers.
Expanded Polypropylene (EPP) is a form of polypropylene foam. PPE has excellent impact characteristics due to its low rigidity, this PPE allows to resume their shape after impact. EPP is widely used in model airplanes and other vehicles controlled by radio amateurs. This is mainly due to ability to absorb shock, making this ideal material for RC airplanes for beginners and enthusiasts.
Recycling
Polypropylene is commonly recycled, and has the number "5" resin identification code:.
References
^ Peter Morris JT (2005). Polymer Pioneers: A History popular science and technology of large molecules. Chemical Heritage Foundation. p. 76. ISBN 0941901033. http://books.google.com/books?id=GjtJfmxvSWgC&pg=PA76.
^ This week 50 years ago in New Scientist, April 28, 2007, p. 15
^ R. Kleinschmidt et al. Journal of Molecular Catalysis A: Chemical, 157 (2000) 8390
Kyung-Jun Chu ^ Eur Polym. J. vol. 34, No. 3 / 4, pp. 577-580, 1998
^ Session 6
^ Song (2004). "Zirconocene catalyzed propene polymerization: kinetic mechanism and the role of the anion. "Macromol. Symp. 213: 173 185. doi: 10.1002/masy.200450917.
^ P. Mercandelli, Sironi, Angelo; Resconi, Luigi; Camurati, Isabella (2007). "Comparing propene polymerization with 1-butene polymerization catalyzed by MAO-activated C2 and C1-symmetric zirconocenes: Study experimental and computational size effect on the stereoselectivity of olefins. "Journal of Organometallic Chemistry 692: 47,844,791. doi: 10.1016/j.jorganchem.2007.06.021.
ASTM F2389 ^ 2007, "Standard Specification for Pressure-rated Polypropylene (PP) Piping Systems", ASTM International, West Conshohocken, PA, 2007, DOI: 10.1520/F2389-07E01, www.astm.org.
Carpet fibers ^
^ General III ECWCS
^ USAF Flight Magazine. Security. November 2002.
String ^ Materials
^ Leach plastic additives in medical experiments, research shows, Physorg.com, November 10, 2008
^ Tests biased scientific leaching plastic, November 6, 2008.
^ Plastics Recycling newsletter, online waste
Links External
Wikimedia Commons has media related to: Polypropylene
Polypropylene chain structure
Technical properties and applications
Polypropylene is quoted on the London Metal Exchange
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Plastics
Polyacrylic acid (PAA) cross-linked polyethylene (PEX or XLPE) polyethylene (PE) terephthalate polyethylene (PET or PETE)
polyphenyl ether (PPE) with polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) Polylactic acid (PLA) Polypropylene (PP), polybutylene (PB), polybutylene terephthalate (PBT) Polyamide (PA) Polyimide (PI) Polycarbonate (PC), polytetrafluoroethylene (PTFE) Polystyrene (PS) polyurethane (PU) Polyester (PEs) Acrylonitrile-butadiene-styrene (ABS) of poly (methyl methacrylate) (PMMA) Polyoxymethylene (POM) polysulfone (PES) Styrene-acrylonitrile (SAN) Ethylene vinyl acetate (EVA) of styrene maleic anhydride (SMA)
Categories: Dielectrics | Plastics | | Polymers | Polyolefins | Specialty Films | ThermoplasticsHidden categories: Chemboxes containing changes to the fields, Viewed | All articles lacking sources | Articles Featured in wa from June 2009 | Articles with unsourced statements March 2009 About the Author

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