What Is Polypropylene?
Polypropylene is a plastic synthesized by polymerizing propylene (molecular formula: C3H6, structural formula: CH2=CH-CH3).
Polypropylene was discovered in 1954 by Mr. Natta of Italy, who discovered that it could be synthesized using a titanium-based organometallic compound called Ziegler-Natta catalyst. In Japan, industrial mass production began in 1962.
Among commodity resins, polypropylene can be produced at a lower cost and is second only to polyethylene in production volume. With a specific gravity of 0.9, it is small, scratch-resistant, strong, and chemical-resistant. It is used in a wide range of applications, from household materials such as packaging materials and food containers to automotive and medical supplies.
Polypropylene is classified as a thermoplastic resin that softens when heated above its glass transition point or melting point.
Uses of Polypropylene
Polypropylene is used in an extremely wide range of applications, taking advantage of its characteristics.
1. Food Containers
Food containers are a typical application for polypropylene. Polypropylene is a crystalline resin with high heat resistance and low dielectric constant, so it does not generate heat even when exposed to high frequencies in microwave ovens. This feature is used not only in general-purpose food containers but also in Tupperware for storing food ingredients for repeated use.
2. Automotive Applications
Next, automotive applications are attracting attention. Polypropylene is beginning to be used for bumpers and lamp housings, where metal materials have been used in the past, due to its low specific gravity and high strength. In the future, the replacement of electric vehicles with electric vehicles is expected to accelerate the development of lightweight automotive parts made of polypropylene.
3. Physical and Chemical Equipment and Medical Equipment
Polypropylene is a nonpolar polymer composed only of carbon and hydrogen, making it highly resistant to organic solvents, acids, and alkalis. Therefore, polypropylene is used in laboratory equipment and measuring instruments that come in contact with solvents, as well as syringes for syringes in the medical field.
4. Medical and Carpet Fibers
Polypropylene is nonpolar, as mentioned above, and therefore has poor dyeability and printability. However, recent technological advances such as surface treatment have made this possible, and polypropylene is increasingly being used as a quick-drying material.
Properties of Polypropylene
Polypropylene can be easily crystallized and has excellent heat resistance and mechanical strength. Molded products have high surface hardness and are not easily scratched. It is also possible to make grades with the desired strength by blending glass fibers and fillers.
Water resistance is as low as 0.01%, making it suitable for use in food containers, pipes, and other applications that are exposed to water for long periods of time. On the other hand, it has several drawbacks, the first of which is poor adhesion and printability. As a non-polar resin, it is incompatible with polar adhesives and does not wet well with inks.
The second problem is low weather resistance.
Polypropylene deteriorates and oxidizes when exposed to ultraviolet rays, resulting in a decrease in mechanical strength and bleaching. However, the addition of UV absorbers and antioxidants can compensate for these shortcomings.
Other Information on Polypropylene
Polypropylene Molding Methods
Polypropylene is a thermoplastic resin, which means that it becomes fluid when heated above its melting point. There are a wide variety of molding methods, including injection molding, extrusion, blow molding, and vacuum molding. Injection molding using molds enables mass production of products at a lower cost than other methods.
Polypropylene crystallizes easily, so if a flat product is desired, ribs should be placed where performance is not a problem, or the mold temperature and cooling conditions should be carefully controlled. Polypropylene sheets produced by extrusion molding or press molding can be easily bent or cut, making it possible to manufacture parts with a variety of shapes.
In recent years, it has also been used as a material for 3D printers that do not require molds.