Heat resistance: The heat resistance of PP Polypropylene is higher than that of polyethylene. Under normal circumstances, the melting temperature of polypropylene is about 40%-50% higher than that of polyethylene, which is about 160-170℃, so the product can be at 100℃ The above temperature is disinfected and sterilized, and it will not deform at 150°C without external force. In daily life, we will find that "5" polypropylene lunch boxes are often used to heat food in microwave ovens (the general temperature of microwave heating is 100-140℃), and polyethylene cannot be used as plastic for microwave ovens due to poor heat resistance , Including lunch boxes, plastic wrap. Similarly, in the field of ordinary packaging films, polyethylene packaging bags are more suitable for use at temperatures below 90°C, while polypropylene packaging bags can be used at relatively high temperatures.
Rigidity and tensile strength: The main characteristics of polypropylene are its low density, better mechanical properties than polyethylene, and outstanding rigidity. For example, polypropylene has gradually begun to compete with engineering plastics (PA/PC) and is widely used Electronic appliances, automotive fields. At the same time, because polypropylene has high tensile strength and good bending resistance, it is called "100-fold plastic". It is folded and bent 1 million times and does not become white when bent. This also provides a clue for us to distinguish polypropylene products. Hidden signs for recycling and sorting of products.
Low temperature resistance: Polypropylene has weaker low temperature resistance than polyethylene, and its impact strength at 0°C is only half of that at 20°C, while the brittleness temperature of polyethylene can generally reach below -50°C; and with the increase of relative molecular weight, the lowest It can reach -140℃. Therefore, if the product needs to be used in a low temperature environment, it is still necessary to choose polyethylene as the raw material. Generally, trays used for refrigerated food are made of polyethylene materials.
Aging resistance: The aging resistance of polypropylene is weaker than that of polyethylene. The structure of polypropylene is similar to that of polyethylene, but due to the presence of a side branch composed of methyl groups, it is more prone to oxidative degradation under the action of ultraviolet light and heat. The most common polypropylene product that is prone to ageing in daily life is the woven bag. The woven bag is easily broken when exposed to the sun for a long time. In fact, although the aging resistance of polyethylene is higher than that of polypropylene, compared with other raw materials, its performance is not very outstanding, because the polyethylene molecule contains a small amount of double bonds and ether bonds, and its weather resistance is not good. , Sun and rain can also cause aging.
Flexibility: Although polypropylene has high strength, it has poor flexibility, and technically speaking, it has poor impact resistance. Therefore, when it is used to make film products, its application field is still different from that of polyethylene. Polypropylene film is more used for surface packaging printing. In terms of pipes, simple polypropylene is rarely used for production, and cross-linked polypropylene, which is a common PPR pipe, is needed. Because ordinary polypropylene has poor impact resistance and is easy to crack, it is necessary to add impact modifiers in practical applications, and additives should be used to improve impact resistance in applications such as bumpers.