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Polypropylene

The chemical and physical properties
Micrograph of polypropylene
Most commercial polypropylene is isotactic and at an intermediate level of crystallinity between the low density polyethylene (LDPE) and high density polyethylene (HDPE), its Young modulus is also intermediate. PP is usually resilient and flexible, especially when copolymerized with ethylene. The polypropylene can be used as an engineering plastic, in competition with materials such as ABS. Polypropylene is reasonably economical, and can be transparent and colorless, but when it is not so easy to make transparent as polystyrene, acrylic or another. Often pigments opaque or using colors. Polypropylene has good resistance to fatigue.
Polypropylene has a melting point of 160 ° C (320 F.) as determined by calorimetry differential scanning (DSC).
The MFR (melt flow) or MFI (melt index) is a measure of molecular weight PP. The test measures the ease with which the first material melts during the process. MFR polypropylene plastic mold fill more easier in the process of injection or blow molding production. As melting increases the flow, however, certain physical properties such as impact resistance, is reduced.
There are three general types of PP homopolymer, random copolymer and block copolymer. The comonomer Ethylene is generally used. EPDM rubber or added to PP homopolymer increases its impact strength at low temperature. Random polymerized ethylene monomer added PP homopolymer decreases the crystallinity of the polymer and makes the most transparent polymer.
The degradation
Polypropylene is responsible for breaking the chain of exposure to UV radiation as found in sunlight. Oxidation typically occurs in the secondary carbon atom in each unit time of repetition. A free radical is formed here, and then reacts with more oxygen, followed by chain scission aldehydes and carboxylic acids. In applications outside, it looks like a network of fine cracks and fissures that become increasingly severe with time of exposure.
For outdoor applications, UV-absorbing additives should be used. Carbon black also provides some protection against attack by UV rays. The polymer can be oxidized high temperatures, a common problem during molding operations. Antioxidants are usually added to prevent degradation of the polymer.
History
Polypropylene was polymerized by Giulio Natta Karl Rehn and March 1954, serving as a preliminary to synthesize large scale from 1957. At first we thought it would less expensive than polyethylene.
Summary
Short segments of polypropylene, showing examples of isotactic (above) and syndiotactic (below) tacticity.
An important concept in understanding the relationship between structure and properties of polypropylene tacticity. The relative orientation of each methyl group (CH3 in Figure left) compared to the methyl groups of neighboring monomers has a significant effect on the ability of polymer crystals finished form, as each methyl group takes up space and limit dorsiflexion.
Like most other vinyl polymers, useful polypropylene can not be made by polymerization radicals due to the higher reactivity allyl hydrogen (leading to dimerization) during polymerization. In addition, materials that would result from a process which methyl groups arranged randomly, called atactic PP. The lack of long-range order prevents any crystallinity in a material, giving an amorphous material with little resistance and suitable only for special qualities to niche applications.
A catalyst Ziegler-Natta catalyst is able to limit incoming monomers to a specific orientation, only adds to the polymer chain if they face the right direction. Most commercially available polypropylene is made with Ziegler-Natta such that occur in mostly isotactic polypropylene (string greater than in the previous figure). With the methyl group is constantly on one side, the molecules tend to coil in a spiral; these helices then line next to each other to form crystals that give commercial polypropylene its many desirable properties.
A ball and stick model of syndiotactic polypropylene.
Designed specifically Kaminsky catalysts have been offering a much higher level of control. Based on metallocene molecules, these catalysts clusters used for the control of the monomers being added, while an appropriate choice of catalyst can produce isotactic, syndiotactic, or polypropylene atactic, or even a combination of both. In addition to this control Qualitatively, allow better quantitative control, with a significantly higher proportion of tacticity want the above techniques of Ziegler-Natta. They also produce narrow molecular weight distributions than traditional Ziegler-Natta catalysts, which can further improve more properties.
To produce a paste made of polypropylene, a catalyst can be made to give isotactic polypropylene, but with organic groups that influence tacticity held by a relatively weak link. After the catalyst has been a small piece of polymer that is capable of crystallization, light the correct frequency is used to break the weakest link, and remove the selectivity of the catalyst and the rest of the chain is atactic. The result is a material amorphous with many small crystals embedded in it. Because each chain has one end in a crystal, but most of its length in the soft, loose amorphous, the crystalline regions serve the same purpose as vulcanization.
Mechanism of metallocene catalysts
The reaction of many catalysts metallocene catalyst requires cooperation activation. One of the catalysts of cooperation for this purpose is common methylaluminoxane (MAO). Other cooperation are catalysts, Al (C2H5) 3.There many metallocene catalysts that can be used for the polymerization of propylene. (Some metallocene catalysts are used for industrial processes, while others they are, because of its high cost.) One of the most Cp2MCl2 is very easy (M = Zr, Hf). catalyst can give rise to different polymers with different molecular weights and properties. Active search is still ongoing in the metallocene catalyst.
In the mechanism of metallocene catalyst reacts with the catalyst of cooperation. If the catalyst is MAO co, the first step is to replace one of the chlorine atoms in the catalyst with a methyl group from MAO. The methyl group is replaced by Cl catalyst. The MPCA then removes another catalyst Cl This causes the positive charge of the catalyst and propylene susceptible to attack.
Once the catalyst is activated twice link to propene coordinated with the metal catalyst. The methyl group in the catalyst and then migrates propylene, and the double bond is broken. This starts the polymerization. Once methyl migration positively charged catalyst was discharged and another propene can coordinate the metal. Propylene second coordinates and the carbon chain formed migrates propene. The process coordination and continuous migration and a polymer chain is grown outside the metallocene catalysts.
Manufacturing
Melt processing of polypropylene can be obtained by extrusion and molding. common extrusion processes include the production of meltblown fibers and yarns together to form long rolls for future conversion a wide range of useful products such as masks, filters, nappies (diapers) and wipes.
The most common technique is to establish a molded injection, which is used for parts such as glasses, bottles, caps, containers, utensils and items such as batteries for cars. techniques Related blow molding and injection blow molding, which extends also used, which involve both extrusion and molding.
The large number of applications end use for PP are often due to the ability of qualifications measures 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. Treatments surface can be applied to PP parties to promote the adhesion of inks and paints.
Applications
Polypropylene cover with a box of Tic Tac, with a hinge and the identification code of the resin on his lapel
Since polypropylene is resistant to a fatigue, most of the plastic hinges, as in the flip-top bottles are made of this material. However, it is important to ensure that the chain molecules are oriented through the hinge for maximum strength.
Very thin sheets of polypropylene are used as dielectric in the pulse of some high-performance, low loss RF capacitors.
piping systems high purity are constructed from polypropylene. Stronger, more rigid piping systems, intended for use in potable plumbing, heating and cooling and recycled water applications, are also made of polypropylene. This material is often chosen for their resistance to leaching and chemical corrosion resistance against most forms of physical harm, including the impact and freezing, and its ability to bind heat fusion Instead of sticking. [Citation needed]
A chair made of polypropylene
Many plastic items for medical or laboratory can be made of polypropylene and can withstand heat in an autoclave. Heat resistance can also be used as material for the manufacture of boilers for the quality of consumption. Packaged foods are coming not melt in the dishwasher, and do not melt during the hot filling process industries. For this reason, most plastic tubs for products dairy products are polypropylene / aluminum (both heat-resistant materials). After the product is cooled, the tubs are often given the lids in less than a material resistant to heat, such as LDPE or polystyrene. These containers are a good practical example of the difference in the module, because the softer rubber (softer feeling) PP LDPE compared to the same thickness is evident. Robust, transparent containers, reusable plastic made in a variety of shapes and sizes to customers of various companies, such as Rubbermaid and Sterilite are usually made of polypropylene, although the covers are often of low density polyethylene more flexible so that the pressure container closed. Polypropylene can also be made of PET bottles for consumer products containing liquid, powder or the like, in spite of high density polyethylene and polyethylene terephthalate are also commonly used for the manufacture of bottles. plastic buckets, car batteries, bins, containers, refrigerators, plates and pitchers are often made of polypropylene or high density polyethylene which are generally quite similar in appearance, feel and properties at room temperature.
Polypropylene Important is a polymer used in nonwovens, with more than 50% used [citation needed] for diapers or sanitary products which absorb water is (Hydrophilic) than for natural water repellent (hydrophobic). Other interesting applications as non-woven air filter, gas and liquids where the fibers can be formed in sheets or strips can be folded to form layers or filter cartridges in different efficiency in the range of 0.5 to 30 microns. These requests could be seen at home and filters water or air conditioning filter type. The large surface area and polypropylene nonwoven ideal, of course, are the shock absorbers of hydrophobic oil spill booms family about oil spills in rivers.
A common application for polypropylene is biaxially oriented polypropylene (BOPP). These sheets are used to BOPP make a wide variety of materials, including transparent bags. When polypropylene is bi pragmatic, clear and is an excellent packaging material for products to retail and the arts.
Polypropylene, great complexion, is widely used in the manufacture of carpets and rugs used in the country.
In New Zealand United States Army, and elsewhere, polypropylene, or polypropylene (Polyprop New 'Zealand) was used for the manufacture of base layer in cold weather, such as long sleeved shirts or clothing Long (More recently, polyester, polypropylene replaced in these applications in the Army U.S., as in the ECWCS). Polypropylene is also used in warm weather team as a lingerie armor, you can easily transport the sweat from skin. Although polypropylene garments are highly flammable, which can melt, which can cause serious burns if the army is involved in an explosion or fire of any kind.
Polypropylene is widely used in the strings, distinctive because they are light enough to float in water. For the same mass, rope Polypropylene is the same force that cut through steel cables. polypropylene rope is stronger than nylon, but not as strong as polyester. Similarly, it is more resistant UV than nylon, but not as much as polyester. In general, costs less and polyester is not as elastic as nylon.
Polypropylene is also used as a alternative to polyvinyl chloride (PVC) as insulation for electrical cables LSZH cable in environments with low ventilation, especially tunnels. This is because it emits less toxic smoke and halogen-free, which can lead to the production of acid in high temperature conditions.
Polypropylene is also used in membrane roofing systems as the sealing layer high single layer as opposed to systems that are not modified.
Most common medical use is Prolene synthetic thread non-absorbable suture, made by Ethicon Inc.
Polypropylene is most commonly used for plastic molding material is injected into a casting mold, the formation of complex shapes at relatively low cost and high volume include bottle caps, bottles and accessories.
Recently, it has become a leaf, which has been widely used for production of file folders, packaging and storage boxes. The wide range of colors, durability and resistance to dirt, is ideal as a protective cover for the paper and other materials. Label is used Rubik cube, because of these characteristics.
The availability of sheet polypropylene has provided an opportunity for the use of the material by designers. Plastic is light, durable and colors is an ideal medium to create shades of light and a series of models sections were developed with safety device to create intricate patterns.
polypropylene sheets are a popular choice for collectors of trading cards, come with pockets (Nine cards of standard size) for card insertion and are used to protect their status and are intended to be stored in a book.
Polypropylene has been used in operations for hernia and repair of pelvic organ prolapse to protect the body against hernias in the same place again. A particle of matter placed at the site of the 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 equipment used for some applications in pelvic organ prolapse, especially when introduced near the vaginal wall due to a steady increase erosion mesh is reported by patients in recent years.
The material was presented recently in the fashion industry through the work of designers such as Anoush Waddington who have developed specialized techniques for creating jewelry and portable polypropylene.
Polypropylene is used in the manufacture of the unit speaker units. Its use has been developed by BBC engineers and patent rights later acquired by the Mission Electronics to use their mission speakers of freedom and speaker 737 Mission Renaissance.
In 2008, Canadian researchers found that the biocidal quaternary ammonium and oleamide were laboratory equipment leaks Polypropylene some refer to the experimental results. Since polypropylene is used in many food containers such as yogurt, the media spokesman of Health Canada Paul Duchesne said the department will review the results to determine whether measures are necessary to protect consumers.
Expanded Polypropylene (EPP) is a polypropylene foam shape. PEP has features very good impact because their low stiffness, which allows the PPE to recover its shape after impact. CPE is widely used in aircraft and radio control vehicles by other fans. This is mainly due to its ability to absorb shocks, that the ideal material for RC planes beginners and enthusiasts.
Recycling
Polypropylene is often recycled, and the number "5" as a code identifying the resin.
References
^ Peter Morris JT (2005). Polymer Pioneers: A People's History of 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 ^ euros. Polym. J. Vol 34, No. 04/03, p. 577-580, 1998
Session 6 ^
^ Song (2004). "The polymerization of propylene catalyzed by zirconocene: kinetics, mechanism, and the role of anion Macromol Symp 213: … 173,185 doi:. 10.1002/masy.200450917.
^ P. Mercandelli, Sironi, Angelo; RESCON, Luigi; Camurati, Isabella (2007). "The polymerization of propylene in comparison with 1-butene polymerization catalyzed by MAO-activated zirconocene C2 and C1-symmetrical: an experimental study and calculation of the influence of size on stereoselectivity Journal of Organometallic olefin. Chemistry 692: 47844791. doi: 10.1016/j.jorganchem.2007.06.021.
ASTM F2389 ^ 2007, "Standard Specification for Polypropylene (PP) piping systems rated pressure ", ASTM International, West Conshohocken, PA, 2007, DOI: 10.1520/F2389-07E01, www.astm.org.
Carpet fibers ^
^ The general III ECWCS
^ USAF flight Magazine. Security. November 2002.
^ Rope materials
^ Plastic additives leaching experiments medical research shows Physorg.com November 10, 2008
^ Scientific evidence distorted by leaching plastics November 6, 2008.
^ Plastics recycling information sheet, waste online
External Links
Wikimedia Commons has media related to polypropylene
chain polypropylene structure
Technical properties and applications
Polypropylene is listed on the London Metal Exchange
EV
Plastics
Acid polyacrylic (PAA), cross-linked polyethylene (PEX or XLPE), polyethylene (PE) polyethylene terephthalate (PET or PETE)
polyphenyl ether polyvinyl chloride (PPE) (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), maleic anhydride styrene (SMA)
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