What is the difference between polyethylene and polypropylene packaging bags?
The production process of polyethylene and polypropylene raw materials is similar, and the products can be used for plastic film, injection molding products, plastic pipes, etc, in many cases, the two raw materials have great similarities in nature and use.
But in fact, there are still many differences in the use of polypropylene raw materials and polyethylene raw materials: Product heat resistance rigidity (Tensile strength)
Low temperature resistance, aging resistance, flexibility, polypropylene, good, good, weak, good, good, remarks: the above comparison is compared with polypropylene and polyethylene, from the perspective of heat resistance, the heat resistance of polypropylene is higher than that of polyethylene. Under normal circumstances, the melting temperature of polypropylene is about 40% higher than that of polyethylene-50%, about 160-
170 ℃, so the product can be disinfected and sterilized at a temperature above 100 ℃, and will not deform at 150 ℃ without external force.
In life, we will find that the '5' polypropylene lunch box is often used for heating food in microwave ovens (The general temperature of microwave heating is 100-140 ° C)
However, polyethylene cannot be used as a plastic for microwave ovens due to poor heat resistance, including lunch boxes and plastic wrap.
Similarly, in the field of common packaging films, polyethylene packaging bags are more suitable for use below 90℃, while polypropylene packaging bags can also be used at relatively high temperatures.
From the perspective of rigidity and tensile strength, polypropylene is mainly characterized by low density, better mechanical properties than polyethylene, and outstanding rigidity.
From the perspective of low temperature resistance, the low temperature resistance of polypropylene is weaker than that of polyethylene, and the impact strength at 0℃ is only half of that at 20℃, while the brittle temperature of polyethylene can generally reach below-50℃;
With the increase of relative molecular mass, the lowest can reach-140 ℃.
Therefore, if the product needs to be used in a low temperature environment, polyethylene should be selected as the raw material as far as possible.
From the point of view of aging resistance, the aging resistance of polypropylene is weaker than that of polyethylene. The Structure of polypropylene is similar to that of polyethylene, but because it has a side branch composed of methyl, therefore, it is easier to oxidize and degrade under the action of ultraviolet light and heat energy.
The most common aging polypropylene product in daily life is woven bag, which is easy to break when exposed to the sun for a long time.
In fact, although the aging resistance of polyethylene is higher than that of polypropylene, its performance is not very prominent compared with other raw materials, because polyethylene molecules contain a small amount of double bonds and ether bonds, its weather resistance is not good, and sun exposure and rain can also cause aging.
From the perspective of flexibility, although polypropylene has high strength, it has poor flexibility, which is technically 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 printing surface packaging.
Polypropylene and polyethylene, as two important products in general plastics, have great similarities in their uses, so they are often replaced by each other.
However, in fact, in some cases, products have their own special application areas, which cannot be changed by price advantages.