Polypropylene

• Polypropen
• Poly (1- methylethylene ),
• Abbreviation: PP

Thermoplastic

Fixed

0.90 .. 0915 kg / l

Polypropylene (abbreviated PP) is a partially crystalline thermoplastic and belongs to the group of polyolefins. Polypropylene is obtained by polymerization of the monomer propene with the aid of catalysts. According to IUPAC is the preferred source material related name Polypropen; according to the repeating unit is the name poly (1- methylethylene ). In 2001, 30 million tons of polypropylene were produced. In 2007, the production volume was already at 45.1 million tons with a value of about 65 billion ( € 47.4 billion ) $.

Historical Information

Polypropylene was first synthesized in 1954 by Karl Rehn in the color Höechst and at the same time by Giulio Natta at the Politecnico di Milano. Natta, who first filed for a patent polypropylene, began in 1957 the large-scale synthesis in the Italian Montecatini. Today polypropylene according to the PE (after sales) world's second most important plastic.

Production

PP is produced by the polymerization of propene. For the production of PP about two-thirds of the propene produced in the world are consumed.

The methyl side group may be incorporated isotactic, syndiotactic or atactic. This arrangement has consequences for the physical properties. The isotactic structure, which can be produced, for example, with the aid of Ziegler -Natta catalysts, resulting in a semi-crystalline structure of the PP. This can be attributed to the methyl radical that is always on one side of the molecular chain, which forces the macromolecule in a helix form (see: cellulose). The ataxic variant of the PP, however, is completely amorphous.

Properties

PP is odorless and hypoallergenic, for applications in the food industry and the pharmaceutical industry, it is appropriate, it is physiologically harmless.

Since, in contrast to many other plastics, and vary the molecular structure, the mean molar mass, its distribution, copolymers, and other parameters, and thus the strong properties can be influenced, there is a plurality of PP grades.

The density of PP is between 0.895 g / cm ³ and 0.92 g / cm ³.

The E-modulus of PP is between 1300 N / mm ² and 1800 N / mm ².

PP has a higher stiffness, hardness and strength than polyethylene, however, they are lower than that of other plastics such as polyamide.

PP has a glass transition temperature of 0 to -10 ° C and is therefore brittle at low temperatures. The upper service temperature is 100 to 110 ° C. The crystallite melting range is 160 to 165 ° C.

The speed of sound is 2650-2740 m / s longitudinal and 1300 m / s transversal.

PP may be filled with mineral fillers such as talc, chalk or glass fibers. Thereby, the spectrum of the mechanical properties ( rigidity, operating temperatures, etc. ) is significantly expanded.

Polypropylene at room temperature to fats and almost all organic solvents, apart from strong oxidizing agents, resistant. Non-oxidizing acids and bases may be stored in a container made ​​of PP. At elevated temperature, PP can be solved in less polar solvents (eg xylene, tetralin and decalin ).

Processing

The world market price for unprocessed polypropylene in 2006 was about 950 Euro / ton.

PP is suitable for injection molding, extrusion, blow molding, hot stamping, welding, deep drawing, for metal processing or for the production of particle foam (EPP). Due to its low surface energy, it can be very bad glue and printed.

In medicine it is also used for hernia networks, while it contains biological resorbing shares. The chemical constituents are apparently easily integrated in the biological environment ( VIPRO II networks).

Approx. 5 million tonnes per year will be drawn into fibers (such as Polycolon ® filament or staple fibers). This, inter alia, non-wovens and fabrics are produced.

Types

Expanded Polypropylene

Expanded Polypropylene (EPP) was developed in the 1980s. This is a particle foam based on polypropylene. ( Porous expanded polypropylene is abbreviated PEPP. ) Unlike EPS EPP is delivered without propellant so that a propellant- based post- expansion is not possible.

The EPP - production there are two principle methods: The autoclave technology (standard) and the direct foam extrusion ( rare).

The processing in the so-called molding process takes place in special molding machines. These differ in their stable operation of conventional EPS machines. The actual processing step is by means of steam, the foam particles ( vapor temperature about 140 ° to 165 ° C - depending on the type of raw material ) to soften so they sinter. A subsequent processing (eg deburring ) is, unlike PU foam parts, in EPP molded parts not common.

EPP is also becoming increasingly outside the initial application areas (automotive and high-quality reusable packaging ) in importance. Thus one finds EPP eg more often in the areas of sports, logistics, furniture and design, but also in the RC model, where for beginners due to its crash resistance is becoming increasingly popular.

A new development is the use of EPP in automotive interiors. Thus, the VW Touareg and the Porsche Cayenne, the rear seat bench made ​​of EPP.

CPP (cast polypropylene )

Cast polypropylene ( CPP designation, also known as UPP film or unstretched polypropylene) is a versatile packaging material.

As well as polypropylene (PP) is CPP, a partially crystalline thermoplastic and belongs to the group of polyolefins. Compared to conventional PE films, CPP is characterized by an extremely high transparency, stiffness and abrasion resistance. These properties make CPP, OPP next (Oriented Polypropylene) to the most frequently used polymer in the packaging industry. Main application areas are the packaging of food, textiles or medical articles and as lamination layer in multilayer films.

Stretching of PP ( OPP and BOPP)

You can do much more stable polypropylene films by stretching. For this purpose, the extruded film is passed over rollers, the increase in speed in the machine direction. This leads to a stretching of the plastic in the longitudinal direction. To obtain a BOPP film which is then also stretched in the transverse direction.

The advantages of this process are, inter alia, in a reduced water vapor. The mechanical strength increases, the films expand less, the appearance (transparency) is improved. The tear strength also increases.

Disadvantages are, inter alia, the decreasing sealability and printability. The sunscreen is low and the oxygen barrier properties decreases.

OPP (oriented polypropylene )

The extruded PP granules can also be along only this stretched to obtain OPP ( oriented PP). It is used for the production of high strength films, packaging tapes, yarns or composite films.

BOPP ( biaxially oriented polypropylene )

This oriented PP is additionally stretched in the transverse direction, to obtain maximum strength of this type of plastic. This is done in a stretching system ( Preheating - routes - stabilizing - cooling). In order to minimize stresses the film heat-set at the end of the manufacturing process by re- heating.

This plastic film is used in the packaging mainly to fill and seal machines ( horizontal and vertical), as a single film or a component of a composite film.

Application Examples

The above-mentioned special properties of PP and EPP permit a very broad use of this plastic.

• It is used in machinery and transport equipment for interiors for cars, dashboards and battery case. Also crash absorbing elements for the automotive industry, child safety seats, bicycle helmets.
• In electrical engineering, it is used for transformer casing, wire and cable jacketing and insulating films. A particularly outstanding significance of the BOPP oriented polypropylene film obtained as a dielectric of plastic film capacitors and power capacitors.
• In the building industry it is used for valves, fittings and piping; in ventilation and air conditioning systems in corrosion conditions favoring and promoting corrosive gases, usually in the form of PP-S (S = fire-resistant ).
• In concrete ( Stahl-/Spannbeton ) the concrete polypropylene fibers can be added to meet the requirements of fire protection. The molten / burned fibers pore space becomes free, which serves for the expansion of the water vapor or the escape.
• Fireplaces of condensing boilers can be built from PP pipes.
• In the textile industry it is used as worsted in Polycolon. PP fibers are inter alia to home textiles, carpets, sports textiles, packaging materials, hygiene products, medical products, ropes, geotextiles and auto parts processed.
• In the food industry, in the household and in the packaging technology, many products are used: cups ( for dairy products), bottle caps, internal parts for dishwashers, for heat resistant films, reusable containers, thermal transport boxes or warming trays (EPP), packing materials, drinking straws, adhesive film, ...
• In humid regions it is also used for plastic bills like the Australian dollar and the New Zealand Dollar.
• In the EPP model airplane is used for the production of very resistant, beginner-friendly model aircraft, the significantly better cope with a crash as a classic balsa wood model airplanes.
• In orthopedics, PP is used as a more common good material to work with.
• For iPP very durable fibers can be drawn for spinning.
• In the general medical surgery in elderly patients and recurrence ( recurrence ), nets made ​​of polypropylene for closure of hernias, eg hernias, used to strengthen the abdominal wall and to prevent a recurrence of the hernia.
• Also in boat building will use polypropylene, especially in small dinghies such as the topper.
• It can be processed into low-cost, floating ropes.