Polypropylene is a thermoplastic polymerized from propylene gas, being, besides polyethylene, one of main polyolefins existing on the market.
We can say that polypropylene is a "improved polyethylene (PE)", since PP replaces PE in applications where the excellent chemical resistance of polyethylene isn't requested or priority being necessary a superior mechanical strength of the final product. Is a resin of low density that offers a good balance of thermal, chemical and electrical properties together a moderate resistance. The resistance properties can be substantially increased or improved through the incorporation of glass fiber, although it isn't very common in this polymer, because when this is required usually it using a engineering plastic like the polyamide, for example. One of reinforcements more used is talc, that provides dimensional stability, acts as nucleating agent (increasing the melt index of the polymer) and improves the superficial aspect of the part.
The electrical properties of polypropylene are affected in a wide range of operating temperatures. With increase of temperature, the dielectric constant remains reasonably constant; however, the resistance or dielectric power increases, while the volume resistivity is reduced.
One peculiarity of PP is its "hinge effect", in other words, we can make parts with hinges in the material itself (e.g.: foldable bottle caps, spectacle cases).
One great disadvantage of polypropylene is its poor weatherability, so sun-exposed parts will discolor and probably lose properties.
In this case, there is a need to add some antioxidant and UV stabilizer in the polymer to delay this kind of degradation.
Polypropylene can easily be processed from various methods such as injection molding, films and sheets extrusion, thermoforming and blow molding.
Features:
- Low cost
- High chemical resistance
- Easy molding
- Easy coloring
- Non-toxic
- High fracture strength in bending
- Good impact resistance above 59°F (15°C)
- Low moisture absorption
- Sensitive to UV and oxidizing agents
Applications:
Water tanks, pipes for chemicals, toys, beer box, films, cosmetics and food packaging, flip-top caps.
Note:
¹ - Polyolefins are polymers with general formula CnH2n
Bibliografia:
HARPER, Charles A.; PETRIE, Edward M. Plastics Materials and Process: A Concise Encyclopedia. Hoboken: John Wiley & Sons, Inc., 2003.
CANEVAROLO JR., Sebastião V. Ciência dos Polímeros: Um texto básico para tecnólogos e engenheiros. 2.ed. São Paulo: Artliber Editora, 2002.
Notes: the data of the properties listed below are taken from our database, thus, they are found in commercial resins. In the cases where the values are presented in interval form, these data represent the lowest and highest value found to the material type. In some cases, where the propertie doesn't have as much variation from resin to resin, we present only the arithmetic mean. It is also important to note that the existance of a certain value here is not representative of all resins, for example, the indication of classification V0 (flameproof) doesn't mean that all materials of the same type are classified V0, but that there are resins with this classification.
About the author: Daniel Tietz Roda is Plastics Technologist graduated from the FATEC/ZL and Mechanical Design Technician from ETEC Aprígio Gonzaga, in São Paulo, Brazil. Roda worked 5 years with technical assistance and development of plastics in industries and nowadays is the publisher of this website.
