Industrial processes can be used to produce an endless variety of polypropylene products, whose properties vary depending on the length of the polymer chains (molecular weight), their polydispersity, the comonomers that may be incorporated, and so on. These basic characteristics define the material’s mechanical properties and its end uses. We literally speak of different types or grades of polypropylene. For all these reasons, the wide variety of products manufactured from this polyolefin allows it to be used in applications as diverse as:
- Auto Parts
- Buckets, containers, bottles
- Furniture
- Toys
- Films for food packaging
- Fibers and Filaments
- Bags and Tote Bags
- Carpet Collection
- Diapers, sanitary pads, clothing
Thin-Wall Containers
One of the strongest trends in today’s injection molding industry is the design of parts with wall thicknesses less than 0.8 mm, generally referred to as “thin-wall.” Working with these wall thicknesses increases the process’s profitability in two distinct ways. On the one hand, it reduces the weight per part, and on the other, it shortens cycle times, thereby increasing productivity. The main applications of polypropylene in this field include items such as dessert cups, margarine tubs, and ice cream buckets, among others. For example, in cycles of up to 3 seconds, it is possible to produce 250 cm³ margarine containers weighing only 10 grams and 0.4 mm thick.
A very important variable is the ratio of total flow length to part thickness, which, in the case of polypropylene, must not exceed a value of 330. In other words, a part that is 1 mm thick can have a flow length of 330 mm. If the thickness is reduced to 0.8 mm, the flow length must be reduced by the same proportion; otherwise, the ratio would increase to 412, and there would be severe difficulties in filling the mold.
Working with such thin wall thicknesses poses a challenge for the material, which must strike a good balance between mechanical properties in the solid state and good flow properties in the molten state. The material, in turn, must ensure high rigidity and good impact resistance. Furthermore, it must have sufficient fluidity to fill a mold that offers significant resistance to flow.
Thanks to its properties in the molten state, polypropylene can be molded using most plastic processing methods, including the following:
Injection molding
This process involves melting the material, along with colorants or additives, and then forcing it under pressure into a mold. The mold is cooled, the material solidifies, and the final product is removed. This method is used to make many types of products, such as jars, lids, plastic furniture, appliance housings, household appliances, and automotive parts. Polypropylene is valued for its ease of processing and its excellent final properties, which include low density, high gloss and rigidity, and thermal and chemical resistance, among others.
Blow Molding
It is used for the production of jars, bottles, vehicle tanks, etc. In this process, a tube of molten material is blown into a mold and takes the shape of the cavity. When cooled, the mold is opened and the item is removed.
Polypropylene Films
These films are widely used in the packaging of food and other items. They are manufactured by extrusion, forcing the molten material through a tubular or flat die. The film produced in this way can be oriented afterward, resulting in a stronger film.
Extrusion
This process can be used to produce a wide variety of continuous products, including tubes, sheets, fibers, and more. Polypropylene sheets are made by passing the molten material through a flat die and then cooling it on parallel rollers. Sheets can be used to produce various items by cutting and bending them, or they can be thermoformed to make containers, cups, etc. Fibers are produced by cutting and then stretching a sheet; they are subsequently used in looms to produce fabrics, bags, etc.
polypropylene fibers
They are used in the production of carpets, rugs, and yarns, among other products. To manufacture them, the molten material is plasticized in an extruder and forced through tiny holes, forming the fibers. Polypropylene nonwovens are produced in a similar manner and are widely used in disposable hygiene products, protective clothing, and more. These products benefit from the strength and flexibility of these new materials.
Applications in the Automotive Industry
The automotive industry is evolving rapidly. In their quest for optimization, the search for materials that meet the greatest number of specific requirements has become one of the goals of major international companies. This search has identified polypropylene as one of the key materials within the broad family of plastics. In polypropylene, design and properties (art and technology) combine to bring increasingly innovative, competitive, and reliable products to the market.
In such a demanding industry, polypropylene and its compounds have found new applications by providing visual and tactile comfort in vehicle interiors, dimensional stability in engine compartments, optimal performance against environmental factors on the vehicle’s exterior, and good suitability for decorative surface treatments (paints). The fact that a single material meets such diverse primary requirements has established polypropylene as the most important plastic in automotive engineering today.
Source: http://www.textoscientificos.com/polimeros/polipropileno/aplicaciones