What is the difference Polypropylene（pp）and Polyethylene（PE）？
The production process of Polyethylene（PE） and Polypropylene（pp） raw materials is relatively similar, and the products can be used to make plastic film, injection molding products, plastic pipes and so on. In many cases, we find that the two raw materials have great similarities in nature and use. But in fact, Polypropylene（pp） raw materials and Polyethylene（PE） raw materials in the use of many differences.
- From the point of view of heat resistance analysis, the heat resistance of Polypropylene（pp）is higher than Polyethylene（PE）, under normal circumstances, the melting temperature of Polypropylene（pp）is about 40%-50% higher than Polyethylene（PE）, about 160-170℃, so the products can be sterilized at more than 100℃ temperature, under the condition of external force, 150℃ also does not deformation. And Polyethylene（PE） can not be used as a microwave plastic due to poor heat resistance, including lunch boxes, plastic wrap. Similarly, in the field of ordinary packaging film, Polyethylene（PE） bags are more suitable for use below 90℃, and Polypropylene（pp） bags can be used at relatively high temperatures.
- From the Angle of rigidity and tensile strength analysis, Polypropylene（pp）is mainly characterized by low density, mechanical properties better than Polyethylene（PE）, and has a very outstanding rigidity, widely used in electronic appliances, automotive fields. At the same time, due to the high tensile strength of Polypropylene（pp）, and then good bending resistance, known as "100 fold glue", folding bending 1 million times by the bending unchanged white, which also provides clues for us to identify Polypropylene（pp）products, at the same time become a recessive symbol of product recycling classification.
- From the perspective of low temperature resistance, the low temperature resistance of Polypropylene（pp）is weaker than Polyethylene（PE）, the impact strength at 0℃ is only half of that at 20℃, and the brittleness temperature of Polyethylene（PE）can generally reach below -50℃; And with the increase of relative molecular weight, the lowest can reach -140℃. Therefore, if products need to be used in low temperature environment, or try to choose Polyethylene（PE） as raw material. The trays used for refrigerating food are generally made of Polyethylene（PE）.
- From the point of view of aging resistance, the aging resistance of Polypropylene（pp）is weaker than that of Polyethylene（PE）. The structure of Polypropylene（pp）is similar to that of Polyethylene（PE）, but due to the existence of a methyl side chain, it is easier to be oxidized and degraded under the action of ultraviolet light and thermal energy. In daily life, the most common Polypropylene（pp） products that are easy to age are woven bags, which are easy to break under the sun for a long time. In fact, although the aging resistance of Polyethylene（PE） is higher than Polypropylene（pp）, but compared with other raw materials, its performance is not very outstanding, because the Polyethylene（PE） molecule contains a small number of double bonds and ether bonds, its weather resistance is not good, sun, rain can also cause aging.
- From the point of view of flexibility, although the strength of Polypropylene（pp）is high, but the flexibility is poor, from the technical point of view, that is, the impact resistance is poor. So when it is used to make film products, its application field is different from the application field of Polyethylene（PE）, Polypropylene（pp）film is more used for surface packaging printing. On the pipe side, simple Polypropylene（pp） is rarely used for production. Instead, cross-linked Polypropylene（pp）, commonly known as PPR, is used. Because ordinary Polypropylene（pp） has poor impact resistance and is easy to crack, it is necessary to add impact modifier in practical application and use auxiliaries to improve impact resistance in bumper and other applications.