Polypropylene applications

Electrical grade polymer films have now largely replaced the Kraft paper that was previously used in capacitor applications. Polypropylene and poly(ethylene terephthalate) are both used in capacitors as free films or metallized with a thin layer of aluminum. Other, newer materials for capacitor applications are made by metallizing polysulfone and polycarbonate films. 

A variety of foams can be produced from various types of polyethylenes and cross-linked systems having a very wide range of physical properties, and foams can be tailor-made to a specific application. Polypropylene has a higher thermostability than polyethylene. The production volume of polyolefin foams is not as high as that of polystyrene, polyurethane, or PVC foams. This is due to the higher cost of production and some technical difficulties in the production of polyolefin foams. The structural foam injection molding process, described previously for polystyrene, is also used for polyethylene and polypropylene structural foams (see Figure 2.61). 

Polypropylene accounted for about half of the nonwoven products in industrial uses in 2001. Its share in ropes and nets was 55-60%, and 70-80% in civil construction, where polyester claimed 20-24%. In automotive applications, polypropylene shared 26-30%, nylon almost 50%, and polyester about 20%. Polypropylene contributed to over 86% of agricultural nonwoven, 100% of packaging cloth, 85% of sanitary items, and 64-70% of medical applications. The world consumption of industrial nonwoven products was 1.329 MT in 2000. Polypropylene topped all synthetic fibers with a share of over 40% in this market segment. 

In the early 1960s, an industry started to develop around the modification of polymers. This industry originally started as a way to simply modify polymer for improvements of impact resistance, color, or thermal stability. It initially used many tools of the rubber industry to modify polymers for specific end-use applications. Polypropylene with its useful balance of properties has found interesting utility in the automotive industry. This market penetration of PP was primarily due to its good thermal resistance for under-the-hood applications, its ease of colorability for applications on the interior of the car, and its low raw material cost. Today, the modification of PP is a large industry, often associated with the PP production or in some cases completely independent of the polymerization steps itself. 

Unfilled polypropylene generally is not recommended for use in load-bearing applications, because the plastic creeps rapidly even under moderate stresses. Glass-reinforced grades, however, can be used in high-load applications. Polypropylene also has good unnotched and excellent notched impact strength. Polypropylene s heat resistance is much superior to that of polyethylene. 

Polypropylene is one of the most widely used polymers in the world because of the widespread availability and low cost of monomer, low manufacturing cost, and attractive polymer properties. These properties can be modified to be suitable for a wide variety of applications. Polypropylene can be processed by almost all commercial fabrication techniques. Approximately 30,000,000 ton was consumed worldwide in 2001. 

PBT has been replacing polyamide in some new models in electrical switches, connectors and motor housings because of its better dimensional stability. OEMs are also becoming more demanding in applications such as window lift motor housing. There is a small threat from polypropylene in some interior applications. Polypropylene has a cost advantage in some areas, and PBT s key properties of strength, low water absorption, temperature and chemical resistance, are not often required for interior applications. 

J. Park, D. Lewis, C. Yoon, Vibration Weldability Study for Automotive Interior Application Polypropylenes , Proc. of ANTEC, SPE (2006)... 

The major uses of ethylene and propene are as starting materials for the preparation of polyethyl ene and polypropylene plastics fibers and films These and other applications will be described in Chapter 6... 

Lamination Inks. This class of ink is a specialized group. In addition to conforming to the constraints described for flexo and gravure inks, these inks must not interfere with the bond formed when two or more films, eg, polypropylene and polyethylene, are joined with the use of an adhesive in order to obtain a stmcture that provides resistance properties not found in a single film. Laminations are commonly used for food applications such as candy and food wrappers. Resins used to make this type of ink caimot, therefore, exhibit any tendency to retain solvent vapor after the print has dried. Residual solvent would contaminate the packaged product making the product unsalable. 

Polypropylene polymers are typically modified with ethylene to obtain desirable properties for specific applications. Specifically, ethylene—propylene mbbers are introduced as a discrete phase in heterophasic copolymers to improve toughness and low temperature impact resistance (see Elastomers, ETHYLENE-PROPYLENE rubber). This is done by sequential polymerisation of homopolymer polypropylene and ethylene—propylene mbber in a multistage reactor process or by the extmsion compounding of ethylene—propylene mbber with a homopolymer. Addition of high density polyethylene, by polymerisation or compounding, is sometimes used to reduce stress whitening. In all cases, a superior balance of properties is obtained when the sise of the discrete mbber phase is approximately one micrometer. Examples of these polymers and their properties are shown in Table 2. Mineral fillers, such as talc or calcium carbonate, can be added to polypropylene to increase stiffness and high temperature properties, as shown in Table 3. 

Polyethylene is sometimes blended with ethylene-propylene rubber (see Chapter 11). In this application it is most commonly used as an additive to the rubber, which in turn is added to polypropylene to produce rubber-modified... 

The application of metallocene catalysis to the preparation of polypropylenes reached a commercial stage with the production by Exxon of their Achieve range in 1996 and in 1997 by Targor, the BASF-Hoechst joint venture with the introduction of Metocene. Such metallocene polypropylenes are, however, only a small proportion of the total polypropylene market, predicted at only about 3% of the total in 2005. 

One unfortunate characteristic property of polypropylene is the dominating transition point which occurs at about 0°C with the result that the polymer becomes brittle as this temperature is approached. Even at room temperature the impact strength of some grades leaves something to be desired. Products of improved strength and lower brittle points may be obtained by block copolymerisation of propylene with small amounts (4-15%) of ethylene. Such materials are widely used (known variously as polyallomers or just as propylene copolymers) and are often preferred to the homopolymer in injection moulding and bottle blowing applications. 

The higher transparency coupled with the rigidity expected of a conventional polypropylene homopolymer is of particular interest in thin-wall moulding applications. 

An important application for polypropylene is film tape. This is made by slitting unoriented film (cast or blown) into tapes 2 or 3.5 mm wide and stretching under heat about seven-fold. With cast film the orientation is more completely monoaxial and there is a tendency for the film to split along its length (fibrillate). Tubular film does not self-split so easily and also has a somewhat softer feel. Such tapes may be woven into sacks and these have... 

Polypropylene monofilaments combine low density with a high tenacity and good abrasion resistance and are finding some application in ropes and netting. 

The polymer has found some small-scale outlets in other directions such as sheet, pipe and wire coating. Consumption of the polymer in these directions is, however, dependent on finding applications for which polypropylene is the most suitable material. 

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