POLYPROPYLENE

EC / List no.: 680-353-0 / 618-352-4
CAS no.: 26063-22-9 / 9003-07-0

Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. 
Polypropylene (PP) is produced via chain-growth polymerization from the monomer propylene.

Polypropylene belongs to the group of polyolefins and is partially crystalline and non-polar. 
Its properties are similar to polyethylene, but it is slightly harder and more heat resistant. 
Polypropylene (PP) is a white, mechanically rugged material and has a high chemical resistance.

Bio-Polypropylene (PP) is the bio-based counterpart of polypropylene (PP).

Polypropylene is the second-most widely produced commodity plastic (after polyethylene). 
In 2019, the global market for polypropylene was worth $126.03 billion.
Revenues are expected to exceed US$145 billion by 2019. 
The sales of this material are forecast to grow at a rate of 5.8% per year until 2021.

History
Phillips Petroleum chemists J. Paul Hogan and Robert Banks first demonstrated the polymerization of propylene in 1951.
The stereoselective polymerization to the isotactic was discovered by Giulio Natta and Karl Rehn in March 1954.
This pioneering discovery led to large-scale commercial production of isotactic polypropylene by the Italian firm Montecatini from 1957 onwards.
Syndiotactic polypropylene was also first synthesized by Natta.

Chemical and physical properties
Polypropylene is in many aspects similar to polyethylene, especially in solution behaviour and electrical properties. 
The methyl group improves mechanical properties and thermal resistance, although the chemical resistance decreases.
The properties of polypropylene depend on the molecular weight and molecular weight distribution, crystallinity, type and proportion of comonomer (if used) and the isotacticity.
In isotactic polypropylene, for example, the methyl groups are oriented on one side of the carbon backbone. 
This arrangement creates a greater degree of crystallinity and results in a stiffer material that is more resistant to creep than both atactic polypropylene and polyethylene.

Mechanical properties
The density of (PP) is between 0.895 and 0.92 g/cm3. 
Therefore, Polypropylene (PP) is the commodity plastic with the lowest density. 
With lower density, moldings parts with lower weight and more parts of a certain mass of plastic can be produced. 
Unlike polyethylene, crystalline and amorphous regions differ only slightly in their density. 
However, the density of polyethylene can significantly change with fillers.

The Young's modulus of Polypropylene (PP) is between 1300 and 1800 N/mm².

Polypropylene 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 acrylonitrile butadiene styrene (ABS). 
Polypropylene is reasonably economical.

Polypropylene has good resistance to fatigue.

Thermal properties
The melting point of polypropylene occurs in a range, so the melting point is determined by finding the highest temperature of a differential scanning calorimetry chart. 
Perfectly isotactic Polypropylene (PP) has a melting point of 171 °C (340 °F). 
Commercial isotactic Polypropylene (PP) has a melting point that ranges from 160 to 166 °C (320 to 331 °F), depending on atactic material and crystallinity. 
Syndiotactic Polypropylene (PP) with a crystallinity of 30% has a melting point of 130 °C (266 °F).
Below 0 °C, Polypropylene (PP) becomes brittle.
The thermal expansion of Polypropylene (PP) is very large, but somewhat less than that of polyethylene.

Chemical properties
Polypropylene at room temperature is resistant to fats and almost all organic solvents, apart from strong oxidants. Non-oxidizing acids and bases can be stored in containers made of PP.
At elevated temperature, Polypropylene (PP) can be dissolved in nonpolar solvents such as xylene, tetralin and decalin. Due to the tertiary carbon atom Polypropylene (PP) is chemically less resistant than PE (see Markovnikov rule).

Most commercial polypropylene is isotactic and has an intermediate level of crystallinity between that of low-density polyethylene (LDPE) and high-density polyethylene (HDPE). 
Isotactic & atactic polypropylene is soluble in p-xylene at 140 °C. 
Isotactic precipitates when the solution is cooled to 25 °C and atactic portion remains soluble in p-xylene.

The melt flow rate (MFR) or melt flow index (MFI) is a measure of molecular weight of polypropylene. 
The measure helps to determine how easily the molten raw material will flow during processing. 
Polypropylene with higher MFR will 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 polypropylene: homopolymer, random copolymer, and block copolymer. 
The comonomer is typically used with ethylene. 
Ethylene-propylene rubber or EPDM added to polypropylene homopolymer increases its low temperature impact strength.
Randomly polymerized ethylene monomer added to polypropylene homopolymer decreases the polymer crystallinity, lowers the melting point and makes the polymer more transparent.

Polypropylene can be categorized as atactic polypropylene (PP-at), syndiotactic polypropylene (PP-st) and isotactic polypropylene (PP-it). 
In case of atactic polypropylene, the methyl group (-CH3) is randomly aligned, alternating (alternating) for syndiotactic polypropylene and evenly for isotactic polypropylene. 
This has an impact on the crystallinity (amorphous or semi-crystalline) and the thermal properties (expressed as glass transition point Tg and melting point Tm).

The term tacticity describes for polypropylene how the methyl group is oriented in the polymer chain. Commercial polypropylene is usually isotactic. 
This article therefore always refers to isotactic polypropylene, unless stated otherwise. 
The tacticity is usually indicated in percent, using the isotactic index (according to DIN 16774). 
The index is measured by determining the fraction of the polymer insoluble in boiling heptane. Commercially available polypropylenes usually have an isotactic index between 85 and 95%. 
The tacticity effects the polymers physical properties. 
As the methyl group is in isotactic propylene consistently located at the same side, it forces the macromolecule in a helical shape, as also found in starch. 
An isotactic structure leads to a semi-crystalline polymer. 
The higher the isotacticity (the isotactic fraction), the greater the crystallinity, and thus also the softening point, rigidity, e-modulus and hardness.

Atactic polypropylene, on the other hand, lacks any regularity which makes it unable to crystallize and amorphous.

Crystal structure of polypropylene
Isotactic polypropylene has a high degree of crystallinity, in industrial products 30–60%. 
Syndiotactic polypropylene is slightly less crystalline, atactic Polypropylene (PP) is amorphous (not crystalline).

Isotactic polypropylene (iPP)
Isotactic polypropylene can exist in various crystalline modifications which differ by the molecular arrangement of the polymer chains. 
The crystalline modifications are categorized into the α-, β- and γ-modification as well as mesomorphic (smectic) forms.
The α-modification is predominant in iPP. 
Such crystals are built from lamellae in the form of folded chains. 
A characteristic anomaly is that the lamellae are arranged in the so-called "cross-hatched" structure. The melting point of α-crystalline regions is given as 185 to 220 °C, the density as 0.936 to 0.946 g·cm−3.
The β-modification is in comparison somewhat less ordered, as a result of which it forms faster and has a lower melting point of 170 to 200 °C
The formation of the β-modification can be promoted by nucleating agents, suitable temperatures and shear stress.
The γ-modification is hardly formed under the conditions used in industry and is poorly understood. 
The mesomorphic modification, however, occurs often in industrial processing, since the plastic is usually cooled quickly. 
The degree of order of the mesomorphic phase ranges between the crystalline and the amorphous phase, its density is with 0.916 g·cm−3 comparatively. 
The mesomorphic phase is considered as cause for the transparency in rapidly cooled films (due to low order and small crystallites).

Syndiotactic polypropylene (sPP)
Syndiotactic polypropylene was discovered much later than isotactic Polypropylene (PP) and could only be prepared by using metallocene catalysts. 
Syndiotactic Polypropylene (PP) has a lower melting point, with 161 to 186 °C, depending on the degree of tacticity.

Atactic polypropylene (aPP)
Atactic polypropylene is amorphous and has therefore no crystal structure. 
Due to its lack of crystallinity, it is readily soluble even at moderate temperatures, which allows to separate it as by-product from isotactic polypropylene by extraction. 
However, the aPolypropylene (PP) obtained this way is not completely amorphous but can still contain 15% crystalline parts. 
Atactic polypropylene can also be produced selectively using metallocene catalysts, atactic polypropylene produced this way has a considerably higher molecular weight.

Atactic polypropylene has lower density, melting point and softening temperature than the crystalline types and is tacky and rubber-like at room temperature. 
Polypropylene (PP) is a colorless, cloudy material and can be used between −15 and +120 °C. 
Atactic polypropylene is used as a sealant, as an insulating material for automobiles and as an additive to bitumen.

Copolymers
Polypropylene copolymers are in use as well. 
A particularly important one is polypropylene random copolymer (PPR or PP-R), a random copolymer with polyethylene used for plastic pipework.

PP-RCT
Polypropylene random crystallinity temperature (PP-RCT), also used for plastic pipework, is a new form of this plastic. 
Polypropylene (PP) achieves higher strength at high temperature by β-crystallization.

Degradation
Polypropylene is liable to chain degradation from exposure to temperatures above 100 °C. Oxidation usually occurs at the tertiary carbon centers leading to chain breaking via reaction with oxygen. 
In external applications, degradation is evidenced by cracks and crazing. 
Polypropylene (PP) may be protected by the use of various polymer stabilizers, including UV-absorbing additives and anti-oxidants such as phosphites (e.g. tris(2,4-di-tert-butylphenyl)phosphite) and hindered phenols, which prevent polymer degradation.

Microbial communities isolated from soil samples mixed with starch have been shown to be capable of degrading polypropylene.
Polypropylene has been reported to degrade while in the human body as implantable mesh devices. The degraded material forms a tree bark-like layer at the surface of mesh fibers.

Optical properties
Polypropylene (PP) can be made translucent when uncolored but is not as readily made transparent as polystyrene, acrylic, or certain other plastics. 
Polypropylene (PP) is often opaque or colored using pigments.

Production
Polypropylene is produced by the chain-growth polymerization of propene:

The industrial production processes can be grouped into gas phase polymerization, bulk polymerization and slurry polymerization. 
All state-of-the-art processes use either gas-phase or bulk reactor systems.
In gas-phase and slurry-reactors, the polymer is formed around heterogeneous catalyst particles. 
The gas-phase polymerization is carried out in a fluidized bed reactor, propene is passed over a bed containing the heterogeneous (solid) catalyst and the formed polymer is separated as a fine powder and then converted into pellets. 
Unreacted gas is recycled and fed back into the reactor.
In bulk polymerization, liquid propene acts as a solvent to prevent the precipitation of the polymer. 
The polymerization proceeds at 60 to 80 °C and 30–40 atm are applied to keep the propene in the liquid state. 
For the bulk polymerization, typically loop reactors are applied. 
The bulk polymerization is limited to a maximum of 5% ethene as comonomer due to a limited solubility of the polymer in the liquid propene.
In the slurry polymerization, typically C4–C6 alkanes (butane, pentane or hexane) are utilized as inert diluent to suspend the growing polymer particles. 
Propene is introduced into the mixture as a gas.
The properties of Polypropylene (PP) are strongly affected by its tacticity, the orientation of the methyl groups (CH3) relative to the methyl groups in neighboring monomer units (see above). 
The tacticity of polypropylene can be chosen by the choice of an appropriate catalyst.

Catalysts
The properties of Polypropylene (PP) are strongly affected by its tacticity, the orientation of the methyl groups (CH
3 in the figure) relative to the methyl groups in neighboring monomer units. 
A Ziegler–Natta catalyst is able to restrict linking of monomer molecules to a specific orientation, either isotactic, when all methyl groups are positioned at the same side with respect to the backbone of the polymer chain, or syndiotactic, when the positions of the methyl groups alternate. 
Commercially available isotactic polypropylene is made with two types of Ziegler-Natta catalysts. 
The first group of the catalysts encompasses solid (mostly supported) catalysts and certain types of soluble metallocene catalysts. 
Such isotactic macromolecules coil into a helical shape; these helices then line up next to one another to form the crystals that give commercial isotactic polypropylene many of its desirable properties.

Another type of metallocene catalysts produce syndiotactic polypropylene.
These macromolecules also coil into helices (of a different type) and crystallize.
Atactic polypropylene is an amorphous rubbery material. 
Polypropylene (PP) can be produced commercially either with a special type of supported Ziegler-Natta catalyst or with some metallocene catalysts.

Modern supported Ziegler-Natta catalysts developed for the polymerization of propylene and other 1-alkenes to isotactic polymers usually use TiCl4 as an active ingredient and MgCl2 as a support.
The catalysts also contain organic modifiers, either aromatic acid esters and diesters or ethers. 
These catalysts are activated with special cocatalysts containing an organoaluminum compound such as Al(C2H5)3 and the second type of a modifier. 
The catalysts are differentiated depending on the procedure used for fashioning catalyst particles from MgCl2 and depending on the type of organic modifiers employed during catalyst preparation and use in polymerization reactions. 
Two most important technological characteristics of all the supported catalysts are high productivity and a high fraction of the crystalline isotactic polymer they produce at 70–80 °C under standard polymerization conditions. 
Commercial synthesis of isotactic polypropylene is usually carried out either in the medium of liquid propylene or in gas-phase reactors.

Commercial synthesis of syndiotactic polypropylene is carried out with the use of a special class of metallocene catalysts. 
They employ bridged bis-metallocene complexes of the type bridge-(Cp1)(Cp2)ZrCl2 where the first Cp ligand is the cyclopentadienyl group, the second Cp ligand is the fluorenyl group, and the bridge between the two Cp ligands is -CH2-CH2-, >SiMe2, or >SiPh2.
These complexes are converted to polymerization catalysts by activating them with a special organoaluminum cocatalyst, methylaluminoxane (MAO).

Manufacturing from polypropylene
Melting process 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. 
The related techniques of blow molding and injection-stretch blow molding are also used, which involve both extrusion and molding.

The large number of end-use applications for polypropylene 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 polypropylene surfaces resist dust and dirt. 
Many physical finishing techniques can also be used on polypropylene, such as machining. 
Surface treatments can be applied to polypropylene parts in order to promote adhesion of printing ink and paints.

Expanded Polypropylene (EPP) has been produced through both solid and melt state processing. 
EPP is manufactured using melt processing with either chemical or physical blowing agents. 
Expansion of Polypropylene (PP) in solid state, due to its highly crystalline structure, has not been successful. 
In this regard, two novel strategies were developed for expansion of PP. 
Polypropylene (PP) was observed that Polypropylene (PP) can be expanded to make EPP through controlling its crystalline structure or through blending with other polymers.

Biaxially oriented polypropylene (BOPP)

When polypropylene film is extruded and stretched in both the machine direction and across machine direction it is called biaxially oriented polypropylene. 
Two methods are widely used for producing BOPP films, namely, the tenter process and tubular process.
Biaxial orientation increases strength and clarity.
BOPP is widely used as a packaging material for packaging products such as snack foods, fresh produce and confectionery. 
Polypropylene (PP) is easy to coat, print and laminate to give the required appearance and properties for use as a packaging material. 
This process is normally called converting. 
Polypropylene (PP) is normally produced in large rolls which are slit on slitting machines into smaller rolls for use on packaging machines.
BOPP is also used for stickers and labels, including by commercial sellers such as Sticker Mule.
Polypropylene (PP) is non-reactive which makes BOPP suitable for safe use in the pharmaceutical and food industry. 
Polypropylene (PP) is one of the most important commercial polyolefin films. 
BOPP films are available in different thicknesses and widths. 
They are transparent and flexible.

Applications
As polypropylene is resistant to fatigue, most plastic living hinges, such as those on flip-top bottles, are made from this material. 
However, it is important to ensure that chain molecules are oriented across the hinge to maximise strength.

Polypropylene is used in the manufacturing of piping systems, both ones concerned with high purity and ones designed for strength and rigidity (e.g., those intended for use in potable plumbing, hydronic heating and cooling, and reclaimed water).
This material is often chosen for its resistance to corrosion and chemical leaching, its resilience against most forms of physical damage, including impact and freezing, its environmental benefits, and its ability to be joined by heat fusion rather than gluing.

Many plastic items for medical or laboratory use can be made from polypropylene because it can withstand the heat in an autoclave. 
Its heat resistance also enables it to be used as the manufacturing material of consumer-grade kettles. 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 aluminum 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. 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 polypropylene 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 onto 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. 
Plastic pails, car batteries, wastebaskets, pharmacy prescription bottles, 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. 
A diversity of medical devices are made from PP.

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.

Polypropylene, highly colorfast, is widely used in manufacturing carpets, rugs and mats to be used at home.

Polypropylene is widely used in ropes, distinctive because they are light enough to float in water.
For equal mass and construction, polypropylene rope is similar in strength to polyester rope. Polypropylene costs less than most other synthetic fibers.

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. 
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.

Polypropylene is most commonly used for plastic moldings, wherein 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.

Polypropylene (PP) can also be produced in sheet form, widely used for the production of stationery folders, packaging, and storage boxes. 
The wide color range, durability, low cost, and resistance to dirt make it ideal as a protective cover for papers and other materials. 
Polypropylene (PP) is used in Rubik's Cube stickers because of these characteristics.

The availability of sheet polypropylene has provided an opportunity for the use of the material by designers. 
The light-weight, durable, and colorful 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.

Expanded polypropylene (EPP) is a foam form of polypropylene. 
EPP has very good impact characteristics due to its low stiffness; this allows EPP to resume its shape after impacts. 
EPP is extensively used in model aircraft and other radio controlled vehicles by hobbyists. 
This is mainly due to its ability to absorb impacts, making this an ideal material for RC aircraft for beginners and amateurs.

Polypropylene is used in the manufacture of loudspeaker drive units. 
Its use was pioneered by engineers at the BBC and the patent rights subsequently purchased by Mission Electronics for use in their Mission Freedom Loudspeaker and Mission 737 Renaissance loudspeaker.

Polypropylene fibres are used as a concrete additive to increase strength and reduce cracking and spalling.
In some areas susceptible to earthquakes (e.g., California), Polypropylene (PP) fibers are added with soils to improve the soil's strength and damping when constructing the foundation of structures such as buildings, bridges, etc.

Polypropylene fibres are also used in drywall joint compound for reinforcement. 
Polypropylene (PP) can increase the flexibility and dimensional stability of the joint compound and reduce shrinkage and cracking when it dries.

Polypropylene is used in polypropylene drums.

In June 2016, a study showed that a mixture of polypropylene and durable superoleophobic surfaces created by two engineers from Ohio State University can repel liquids such as shampoo and oil. 
This technology could make it easier to remove all of the liquid contents from polypropylene bottles, particularly those that have high surface tension such as shampoo or oil.

Clothing
Polypropylene is a major polymer used in nonwovens, with over 50% used for diapers or sanitary products where it is treated to absorb water (hydrophilic) rather than naturally repelling water (hydrophobic). 
Other non-woven uses include filters for air, gas, and liquids in which the fibers can be formed into sheets or webs that can be pleated to form cartridges or layers that filter in various efficiencies in the 0.5 to 30 micrometre range. 
Such applications occur in houses as water filters or in air-conditioning-type filters. 
The high surface-area and naturally oleophilic polypropylene nonwovens are ideal absorbers of oil spills with the familiar floating barriers near oil spills on rivers.

Polypropylene, or 'polypro', has been used for the fabrication of cold-weather base layers, such as long-sleeve shirts or long underwear. 
Polypropylene is also used in warm-weather clothing, in which it transports sweat away from the skin. 
Polyester has replaced polypropylene in these applications in the U.S. military, such as in the ECWCS.
Although polypropylene clothes are not easily flammable, they can melt, which may result in severe burns if the wearer is involved in an explosion or fire of any kind.
Polypropylene undergarments are known for retaining body odors which are then difficult to remove. The current generation of polyester does not have this disadvantage.

Some fashion designers have adapted polypropylene to construct jewelry and other wearable items.

Medical
Its most common medical use is in the synthetic, nonabsorbable suture Prolene, manufactured by Ethicon Inc.

Polypropylene has been used in hernia and pelvic organ prolapse repair operations to protect the body from new hernias in the same location. 
A small patch of the material is placed over the spot of the hernia, below the skin, and is painless and rarely, if ever, rejected by the body. 
However, a polypropylene mesh will erode the tissue surrounding it over the uncertain period from days to years.

A notable application was as a transvaginal mesh, used to treat vaginal prolapse and concurrent urinary incontinence.
Due to the above-mentioned propensity for polypropylene mesh to erode the tissue surrounding it, the FDA has issued several warnings on the use of polypropylene mesh medical kits for certain applications in pelvic organ prolapse, specifically when introduced in close proximity to the vaginal wall due to a continued increase in number of mesh-driven tissue erosions reported by patients over the past few years.
On 3 January 2012, the FDA ordered 35 manufacturers of these mesh products to study the side effects of these devices. 
Due to the outbreak of the COVID-19 pandemic in 2020, the demand for Polypropylene (PP) has increased significantly because it's a vital raw material for producing meltblown fabric, which is in turn the raw material for producing facial masks.

Niche
Very thin sheets (≈2–20 µm) of polypropylene are used as a dielectric within certain high-performance pulse and low-loss RF capacitors.

Expanded polypropylene (EPP) foam is a structural material in hobbyist radio control model aircraft. 
Unlike expanded polystyrene foam (EPS) which is friable and breaks easily on impact, EPP foam is able to absorb kinetic impacts very well without breaking, retains its original shape, and exhibits memory form characteristics which allow it to return to its original shape in a short amount of time.

When the cathedral on Tenerife, La Laguna Cathedral, was repaired in 2002–2014, it turned out that the vaults and dome were in a rather bad condition. 
Therefore, these parts of the building were demolished, and replaced by constructions in polypropylene. 
This was reported as the first time this material was used in this scale in buildings.

Under the trade name Ulstron polypropylene rope is used to manufacture scoop nets for whitebait. 
Polypropylene (PP) has also been used for sheets of yacht sails.

Polymer banknotes are made from BOPP, where it provides a durable base and allows for the use of transparent security features by omitting opaque inks in the desired areas.

Repairing
Many objects are made with polypropylene precisely because it is resilient and resistant to most solvents and glues. 
Also, there are very few glues available specifically for gluing PP. 
However, solid Polypropylene (PP) objects not subject to undue flexing can be satisfactorily joined with a two-part epoxy glue or using hot-glue guns. 
Preparation is important and it is often helpful to roughen the surface with a file, emery paper or other abrasive material to provide better anchorage for the glue. 
Also it is recommended to clean with mineral spirits or similar alcohol prior to gluing to remove any oils or other contamination. 
Some experimentation may be required. 
There are also some industrial glues available for PP, but these can be difficult to find, especially in a retail store

Polypropylene (PP) can be melted using a speed tip welding technique. 
With speed welding, the plastic welder, similar to a soldering iron in appearance and wattage, is fitted with a feed tube for the plastic weld rod. 
The speed tip heats the rod and the substrate, while at the same time it presses the molten weld rod into position. 
A bead of softened plastic is laid into the joint and the parts and weld rod fuse.
With polypropylene, the melted welding rod must be "mixed" with the semi-melted base material being fabricated or repaired. 
A speed tip "gun" is essentially a soldering iron with a broad, flat tip that can be used to melt the weld joint and filler material to create a bond.

What is Polypropylene (PP), and What is it Used For?
Polypropylene (PP) is a thermoplastic “addition polymer” made from the combination of propylene monomers. 
Polypropylene (PP) is used in a variety of applications to include packaging for consumer products, plastic parts for various industries including the automotive industry, special devices like living hinges, and textiles.

Polypropylene was first polymerized in 1951 by a pair of Phillips petroleum scientists named Paul Hogan and Robert Banks and later by Italian and German scientists Natta and Rehn. 
Polypropylene (PP) became prominent extremely fast, as commercial production began barely three years after Italian chemist, Professor Giulio Natta, first polymerized it.

Natta perfected and synthesized the first polypropylene resin in Spain in 1954, and the ability of polypropylene to crystallize created a lot of excitement. 
By 1957, its popularity had exploded and widespread commercial production began across Europe. 
Today it is one of the most commonly produced plastics in the world.

According to some reports, the current global demand for the material generates an annual market of about 45 million metric tons and it is estimated that the demand will rise to approximately 62 million metric tons by 2020.

The major end users of polypropylene are the packaging industry, which consumes about 30% of the total, followed by the electrical and equipment manufacturing, which uses about 13% each. Household appliances and automotive industries both consume 10% each and construction materials follows with 5% of the market.

Other applications together make up the rest of the global polypropylene consumption.

Polypropylene has a relatively slippery surface which can make it a possible substitute for plastics like Acetal (POM) in low friction applications like gears or for use as a contact point for furniture.

Perhaps a negative aspect of this quality is that it can be difficult to bond Polypropylene to other surfaces (i.e. it does not adhere well to certain glues that work fine with other plastics and sometimes has to be welded in the event that forming a joint is required).

Although polypropylene is slippery at the molecular level, it does have a relatively high coefficient of friction - which is why acetal, nylon, or PTFE would be used instead. 
Polypropylene also has a low density relative to other common plastics which translates to weight savings for manufacturers and distributors of injection molded Polypropylene parts.

Polypropylene (PP) has exceptional resistance at room temperature to organic solvents like fats but is subject to oxidation at higher temperatures (a potential issue during injection molding).

One of the major benefits of Polypropylene is that it can be manufactured (either through CNC or injection molding, thermoforming, or crimping) into a living hinge. 
Living hinges are extremely thin pieces of plastic that bend without breaking (even over extreme ranges of motion nearing 360 degrees).

They are not particularly useful for structural applications like holding up a heavy door but are exceptionally useful for non load-bearing applications such as the lid on a bottle of ketchup or shampoo. 
Polypropylene is uniquely adept for living hinges because it does not break when repeatedly bent.

One of the other advantages is that polypropylene can be CNC machined to include a living hinge which allows for faster prototype development and is less expensive than other prototyping methods. 
Creative Mechanisms is unique in our ability to machine living hinges from a single piece of polypropylene. 

Another advantage of Polypropylene is that it can be easily copolymerized (essentially combined into a composite plastic) with other polymers like polyethylene. 
Copolymerization changes the material properties significantly, allowing for more robust engineering applications than are possible with pure polypropylene (more of a commodity plastic on its own).

The characteristics mentioned above and below mean that polypropylene is used in a variety of applications: dishwasher safe plates, trays, cups, etc, opaque to-go containers, and many toys.

What are the Characteristics of Polypropylene?
Some of the most significant properties of polypropylene are:

Chemical Resistance: 
Diluted bases and acids don’t react readily with polypropylene, which makes it a good choice for containers of such liquids, such as cleaning agents, first-aid products, and more.  

Elasticity and Toughness: 
Polypropylene will act with elasticity over a certain range of deflection (like all materials), but it will also experience plastic deformation early on in the deformation process, so it is generally considered a "tough" material. Toughness is an engineering term which is defined as a material's ability to deform (plastically, not elastically) without breaking..

Fatigue Resistance: 
Polypropylene retains its shape after a lot of torsion, bending, and/or flexing. This property is especially valuable for making living hinges.

Insulation: 
polypropylene has a very high resistance to electricity and is very useful for electronic components.

Transmissivity: 
Although Polypropylene can be made transparent, it is normally produced to be naturally opaque in color.
Polypropylene can be used for applications where some transfer of light is important or where it is of aesthetic value. 
If high transmissivity is desired then plastics like Acrylic or Polycarbonate are better choices.
Polypropylene is classified as a “thermoplastic” (as opposed to “thermoset”) material which has to do with the way the plastic responds to heat. 
Thermoplastic materials become liquid at their melting point (roughly 130 degrees Celsius in the case of polypropylene).

A major useful attribute about thermoplastics is that they can be heated to their melting point, cooled, and reheated again without significant degradation. 
Instead of burning, thermoplastics like polypropylene liquefy, which allows them to be easily injection molded and then subsequently recycled.

By contrast, thermoset plastics can only be heated once (typically during the injection molding process). 
The first heating causes thermoset materials to set (similar to a 2-part epoxy) resulting in a chemical change that cannot be reversed. 
If you tried to heat a thermoset plastic to a high temperature a second time it would simply burn.
This characteristic makes thermoset materials poor candidates for recycling.

Why is Polypropylene used so often?
Polypropylene is used in both household and industrial applications. 
Its unique properties and ability to adapt to various fabrication techniques make it stand out as an invaluable material for a wide range of uses.

Another invaluable characteristic is polypropylene’s ability to function as both a plastic material and as a fiber (like those promotional tote bags that are given away at events, races, etc).

Polypropylene’s unique ability to be manufactured through different methods and into different applications meant it soon started to challenge many of the old alternative materials, notably in the packaging, fiber, and injection molding industries. 
Its growth has been sustained over the years and it remains a major player in the plastic industry worldwide.

At Creative Mechanisms, we have used polypropylene in a number of applications across a range of industries.
Perhaps the most interesting example includes our ability to CNC machine polypropylene to include a living hinge for prototype living hinge development.

Polypropylene is a very flexible, soft material with a relatively low melting point. 
These factors have prevented most people from being able to properly machine the material. 
Polypropylene (PP) gums up. 
Polypropylene (PP) doesn’t cut clean. 
Polypropylene (PP) starts to melt from the heat of the CNC cutter. 
Polypropylene (PP) typically needs to be scraped smooth to get anything close to a finished surface.

Polypropylene is a tough, rigid and crystalline thermoplastic produced from propene (or propylene) monomer. 
Polypropylene (PP) is a linear hydrocarbon resin. 
The chemical formula of polypropylene is (C3H6)n. 
PP is among the cheapest plastics available today.

Polypropylene (PP) is a linear hydrocarbon polymer, expressed as CnH2n. 
PP, like polyethylene (see HDPE, L/LLDPE) and polybutene (PB), is a polyolefin or saturated polymer. 
Polypropylene is one of those most versatile polymers available with applications, both as a plastic and as a fibre, in virtually all of the plastics end-use markets.

The properties of Polypropylene include...

Semi-rigid
Translucent
Good chemical resistance
Tough
Good fatigue resistance
Integral hinge property
Good heat resistance
PP does not present stress-cracking problems and offers excellent electrical and chemical resistance at higher temperatures. 
While the properties of PP are similar to those of Polyethylene, there are specific differences. 
These include a lower density, higher softening point (PP doesn't melt below 160oC, Polyethylene, a more common plastic, will anneal at around 100oC) and higher rigidity and hardness. 
Additives are applied to all commercially produced polypropylene resins to protect the polymer during processing and to enhance end-use performance.

Chemical Structure 

Linear hydrocarbon polymer, little or no unsaturation. 
Similar to polyethylene in many properties, especially solution and electrical. 
However, the presence of the methyl group attached to every alternate backbone chain carbon atom can alter the properties in a number of ways:  

(i) Polypropylene (PP) can cause a slight stiffening of the chain - increasing the crystalline melting point (Tm);  

(ii) Polypropylene (PP) can interfere with the molecular symmetry - depressing crystallinity and hence Tm.

Manufacture

Production of polypropylene takes place by slurry, solution or gas phase process, in which the propylene monomer is subjected to heat and pressure in the presence of a catalyst system. 
Polymerisation is achieved at relatively low temperature and pressure and the product yielded is translucent, but readily coloured. 
Differences in catalyst and production conditions can be used to alter the properties of the plastic.

Propylene is obtained, along with ethylene, by cracking naphtha (crude oil light distillate). 
Ethylene, propylene, and higher alkenes are separated by low temperature fractional distillation. 
From being a byproduct of ethylene in the early 1950's, propylene is now an important material in its own right.

Polypropylene is a major tonnage polymer with a growth rate higher than the norm for such thermoplastics. 
This growth rate is partially because of the versatility of polypropylene, and hence the wide range of application areas as indicated above. 
However, in the UK we have always used more polypropylene than in other European countries, e.g. West Germany. 
This is particularly the case in injection mouldings, which elsewhere might well be made from high density polyethylene.

What’s polypropylene, and what’s it used for? 
Polypropylene is a plastic. Of the commercial plastics on the market today, polypropylene is considered one of the safest.

It’s FDA-approved for food contact, so you’ll find polypropylene in food containers like those that hold yogurt, cream cheese, and butter products. Because it has a high heat tolerance, it’s also often used in packaging of food that can be heated in a microwave.

Some surgical devices and implants are also made of polypropylene, and polypropylene fibers are commonly used to weave area rugs for indoor and outdoor use.

polypropylene, a synthetic resin built up by the polymerization of propylene. 
One of the important family of polyolefin resins, polypropylene is molded or extruded into many plastic products in which toughness, flexibility, light weight, and heat resistance are required. 
Polypropylene (PP) is also spun into fibres for employment in industrial and household textiles. 
Propylene can also be polymerized with ethylene to produce an elastic ethylene-propylene copolymer.

Propylene is a gaseous compound obtained by the thermal cracking of ethane, propane, butane, and the naphtha fraction of petroleum. 
Like ethylene, it belongs to the “lower olefins,” a class of hydrocarbons whose molecules contain a single pair of carbon atoms linked by a double bond. 
The chemical structure of the propylene molecule is CH2=CHCH3. 
Under the action of polymerization catalysts, however, the double bond can be broken and thousands of propylene molecules linked together to form a chainlike polymer (a large, multiple-unit molecule).

Polypropylene Plastic
Polypropylene (PP) is one of the most commonly used thermoplastics in the world.
Polypropylene uses range from plastic packaging, plastic parts for machinery and equipment and even fibres and textiles. 
Polypropylene (PP) is a rigid, semi-crystalline thermoplastic that was first polymerised in 1951 and is used widely today in a range of domestic and industrial applications. 
Today, global demand for polypropylene is estimated at around 45 metric tons and this figure continues to rise exponentially.

Uses for polypropylene
plastic packaging is a use of polypropylene
Polypropylene has a slippery, tactile surface, making it ideal for

plastic furniture
low friction applications, such as gears in machinery and vehicles.
Polypropylene (PP) is highly resistant to chemical corrosion, making it an excellent choice for packaging for

cleaning products
bleaches and
first-aid products

Polypropylene (PP) offers excellent fatigue resistance and elasticity, securing it a well-deserved reputation for toughness and durability.
Polypropylene has high insulation properties too, making it safe to use for plastic casing in electrical goods and cables. 
In its fibre form, polypropylene uses are not limited to not only useful for tote bags but also encompass a much wider range of other products, including ropes, twine, tape, carpets, upholstery, clothing and camping equipment. 
Its waterproof properties make it especially effective for the marine sector. 
In the automotive industry, polypropylene is also used widely, for example in for battery casings, trays and drink holders, bumpers, interior details, instrumental panels and door trims.

Finally, the medical world appreciates the waterproof properties of polypropylene too, as well as its flexible strength, resistance to mould, bacteria and chemical corrosion. 
Polypropylene (PP) cleans well a sit can stand up to steam sterilisation methods. 
Some medical applications include,

syringes
medical vials
Petri dishes
pill containers
specimen bottles

Material properties and types of polypropylene

This versatile thermoplastic and polymer are popular due to its highly flexible properties, lighter density and ability to adapt to a range of fabrication techniques. 
The different variations in polypropylene have led the material to be known as the ‘steel’ of the plastic industry, as it can be used and manipulated a number of ways.

There are two main types of polypropylene thermoplastics:
homopolymers
copolymers
Homopolymers contain only propylene monomers in semi-crystalline form Main uses include textiles, packaging, pipes, medical components and electrical applications.

Copolymers are divided into random copolymers and block copolymers, produced by polymerising propene and ethene together. 
Copolymers contain higher amounts of ethylene, which result in an increase in desirable properties within the polypropylene.
They are softer than homopolymers but have better impact strength.

Polypropylene can function as both a plastic and fibre type of thermoplastic. 
This allows for a vastly increased range of uses. 
Polypropylene (PP) can be used as a fibre, such as in the manufacture of promotional tote bags and ‘bag for life’ shopping carriers. 
Polypropylene (PP) is soft, malleable and has a relatively low melting point, making it very easy to be used in the injection moulding process, where it is supplied in pellets. 
Polypropylene (PP) flows well too, due to its low melt viscosity.

Advantages to Polypropylene
Due to the fact that polypropylene adapts well to the injection moulding process, it can be used to make incredibly thin layers of plastic.
Polypropylene (PP) is very suited to applications such as

hinges on medication pots,
lids on shampoo bottles
and other containers that will be bent and manipulated a lot and mustn’t break.
application of Polypropylene is plastic shampoo bottle caps
Polypropylene can even withstand twisting motions of up to 360 degrees without snapping and is very hard to snap as a result. 
Polypropylene (PP) is relatively low cost and straightforward to produce and readily available in multiple countries and communities.

High chemical and fatigue resistance add to its durability and versatility as a packaging material and option for hinges and bottle tops attached to the main bottle by a thin layer of plastic. 
Polypropylene (PP) can offer great versatility in colour, as it can be produced as an opaque or transparent thermoplastic and used when some transfer of light is desired. 
Its lighter density allows it to be used in applications where weight saving has to be a key consideration.

Polypropylene is waterproof and extremely resistant to moisture absorption, which adds to its packaging benefits and flexibility as a packaging material. 
Its semi-crystalline nature offers high flexural strength too, making it resilient to general wear and tear and ideal for items that must undergo higher levels of physical stress. Polypropylene (PP) is also resilient against mildew, mould, rot and bacteria.

Chemical Properties    
Translucent, white solid.
Tensile strength 5000 psi, flexural strength 7000 psi, usable up to 121C. 
Insoluble in cold organic solvents; softened by hot solvents. 
Maintains strength after repeated flexing. 
Degraded by heat and light unless protected by antioxidants. 

Readily colored; good electrical resistance; 
low water absorption and moisture permeability; 
poor impact strength below ?9.4C; 
not attacked by fungi or bacteria; 
resists strong acids and alkalies up to 60C, but is attacked by chlorine, fuming nitric acid, and other strong oxidizing agents. 
Combustible, but slow-burning. 
Fair abrasion and good heat resis- tance if properly modified. 
Can be chrome-plated, injectionand blow-molded, and extruded.

Chemical Properties    
Polypropylene is a low-density resin that offers a good balance of thermal, chemical, and electrical properties, along with moderate strength. 
Strength can be significantly increased by using reinforcing agents such as glass fiber. 
Polypropylene has limited heat resistance, but it can be used in applications that must withstand boiling water or steam sterilization.
Polypropylenes can resist chemical attack and are unaffected by aqueous solutions of inorganic salts or mineral acids and bases, even at high temperatures. 
They are not attacked by most organic chemicals, and there is no solvent for these resins at room temperature.
The resins are attacked, however, by halogens, fuming nitric acid, other active oxidizing agents, and by aromatic and chlorinated hydrocarbons at high temperatures .
Polypropylene is translucent and autoclavable. 
Properties can be improved by compounding with fillers, by blending with synthetic elastomers, and by copolymerizing with small amounts of other monomers.

Uses: 
Polypropylene (PP) is a thermoplastic material used in a wide variety of applications including packaging, labeling, textiles, etc. 
Due to high processability and low cost, PP is one of the most extensively produced polymers, especially, for auto industry. 
Pristine PP is resistant to photo-oxidation and thermal oxidation at moderate temperatures. 
However, PP is sensitive to various external aging environments (such as heat, light, and radiation), and, hence, has a relatively low service temperature.
When PP is exposed to high temperatures or to an irradiation environment, the tertiary hydrogen atoms present in PP chains are susceptible to be attacked by oxygen. 
It is well known that PP oxidation depends on both light and temperature in outdoor aging conditions.
PP can also be photo-degraded because several molecular chains are affected in the wavelength range from 310 to 350 nm.
    
Used with ram- and screw-injection machines. 
For automotive, housewares, general molding products and multi- and monofiliment fiber.

General extrusion grade polymer.

Base polymer in hot melt adhesives and paper-laminating, extender and viscosity modifier in caulks and sealants and waterproofing agent in wire and cable applications.

Modifier for waxes to reduce blocking, scuffing and abrasion. 
Improves pigment dispersion in polypropylene films and fibers.

Definition    
ChEBI: A polymer compose of repeating propane-1,2-diyl units.

polypropylene: Anisotactic polymer existing in bothlow and high formula-weight forms.
The lower-formula-weight polymer ismade by passing propene at moderatepressure over a heated phosphoricacid catalyst spread on aninert material at 200°C. 
The reactionyields the trimer and tetramer. 
Thehigher-formula-weight polymer isproduced by passing propene into aninert solvent, heptane, which containsa trialkyl aluminium and a titaniumcompound. 
The product is amixture of isotactic and atacticpolypropene, the former being themajor constituent. Polypropene isused as a thermoplastic mouldingmaterial.

Production Methods
In PP production, propylene monomer is polymerized to make the homopolymer by using a Ziegler–Natta type coordination catalyst. 
This catalyst results from the reaction and interaction of a transition metal compound and an organometallic compound, usually an alkylaluminum compound. 
Halide atoms are involved in most such catalyst systems .
Polypropylene can be made by solution, slurry (or solvent), bulk (or liquid propylene), or gas-phase polymerization, or a combination of these processes . 
The most widely used is the slurry process; however, the current trend is toward the gas-phase process. In the solution, slurry, and bulk processes, the catalyst system is mixed with propylene and a hydrocarbon diluent (usually hexane, heptane, or liquid propylene) in a reactor. 
After polymerization, the reaction mixture enters a flash tank where unreacted propylene is removed and recycled. 
Propylene–ethylene copolymers [9010-79-1] can be manufactured when ethylene is fed along with propylene to the polymerization reactor or by adding ethylene and propylene to a postpolymerization reactor that contains PP. 
This mixture may then be purified to remove lowmolecular weight and atactic fractions and washed to remove catalyst residues. 
The polypropylene resin is then dried and pelletized. 
During this time, additivesmay be incorporated in the gas-phase process; no liquid diluent is used .

General Description    
Tan to white odorless solid. Less dense than water and insoluble in water. 
Hence floats on water.

Industrial Uses    
Polypropylene is similar in structure to polyethylene,but every other carbon atom has oneof its H2 atoms replaced by a CH2group.
Although electrically similar to polyethylene,polypropylene can be made in thinner films, say 5μm as against about 25 μm for polyethylene.
These films replace paper for impregnatedcapacitors, with reduced loss.

Uses at Household & Commercial/Institutional Products
• Auto Products
• Commercial / Institutional
• Home Maintenance
• Inside the Home
• Personal Care
• Pesticides

IUPAC NAMES:
Polypropylene
1-Propene, homopolymer
12-[(2S,3R)-3-octyloxiran-2-yl]dodecanoic acid
poly(propene)
polypropene
POLYPROPYLENE
Polypropylene
polypropylene
Polypropylene homopolymer

SYNONYMS:
PROPYLENE RESIN
PROPYLENE, ISOTACTIC RESIN
POLYPROPYLENE
POLYPROPYLENE, ATACTIC
POLYPROPYLENE, PSS NANOREINFORCED
POLYPROPYLENE, ISOTACTIC
Polypropylene master batch,flame retarding
Polypropylene,film grade
Polypropylene FDY
Polypropylene full drawn yarn
Modified polypropylene for automobile
Polypropylene,flame retarding
Polypropylene filter silk oil for tobacco
Polypropylene,powder
Polypropylene,homopolymerization
Polypropylene resin, inorganic filler
Polypropylene fiber
Polypropylene,anti-weathering
Polypropylene,reinforced
RPP
Polypropylene,fiber grade
Polypropylene,modified
enjaye11s
Epolene N-15
epolenem5h
epolenem5k
epolenem5w
escon622
esconcd44a
esconex375
f080pp
Fiberfil J-60/30/E8
Fiberfil J-60/30/FR
Fiberfil PP-60/TC/40
Fiberil M-1492
Fortilene
Fortilene 1001
Fortilene 1602
Fortilene 1802
Fortilene 2104
Fortilene 3151
Fortilene 4104, 4109
Fortilene 4209
Fortilene 5801
Fortilene 9000
Fusabond MZ-109D
Fusabond MZ-203D
gerfil
gpcd398
Hercoflat texturing pigments and flatting agent
hercoflat135
Hercotuf
hercotuf110a
hercotufpb681
hercules6523
herculon
hf20
Hifax AB 6023
POLYPROPYLENE
9003-07-0
12-[(2s,3r)-3-octyloxiran-2-yl]dodecanoic acid
Oxiranedodecanoic acid, 3-octyl-, cis-
2-Oxiranedodecanoic acid, 3-octyl-, (2R,3S)-rel-
3420-36-8
N-Fmoc-5-aminolevulinicacid
Oxiranedodecanoic acid, 3-octyl-, (2R,3S)-rel-
ZINC111391968
3beta-Octyloxirane-2beta-dodecanoic acid
12-(3-Octyl-2-oxiranyl)dodecanoic acid #