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• Time of issue:2020-09-22
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(Summary description)The raw materials in environmentally friendly plastic packaging bags are divided into two categories: polypropylene, homopolypropylene (all derived from the polymerization of propylene monomer) and copolypropylene (in addition to propylene, there are also a small amount of other monomers). Random co-polypropylene and block co-polypropylene are two major products. So what are the advantages and disadvantages and uses of these PP?



The main characteristics of homopolypropylene in plastic packaging bags:



①Small density (only 0.90g/m³, which is the least dense variety among common plastics).



②High rigidity (the rigidity is significantly higher than that of polyethylene, and for products with greater rigidity, when using polypropylene, the wall thickness of the product can be at least 10% lower than when using HDPE).



③High strength (the tensile yield strength reaches 30MPa).



④Good heat resistance (can withstand high temperature sterilization at 120～135℃).



⑤ It has good water and moisture resistance, and has outstanding barrier properties to water vapor. It is an ideal moisture and moisture-proof material.



⑥ Good transparency, and after adding a nucleating agent or stretching processing, the transparency of its parts can be significantly improved, even reaching a level similar to PVC transparent materials.



⑦Good chemical resistance, polypropylene has good chemical resistance, acid, alkali, salt and many chemical substances.



⑧Poor low-temperature impact, showing greater brittleness at around 5℃.



⑨Polypropylene has poor barrier properties to gases such as oxygen and carbon dioxide.



The main features of random co-polypropylene in plastic packaging bags:



Compared with homopolypropylene, the main characteristics of random copolymer polypropylene are as follows.



①The gloss is improved.



②The cold resistance and low temperature impact performance are improved, and the low temperature embrittlement temperature can be reduced to 0～-15℃.



③The tensile yield strength, rigidity and heat resistance decrease.



Block copolypropylene:



Compared with homopolypropylene, the main characteristics of block copolypropylene have the following three points.



①The impact strength is improved, especially the low temperature impact performance is significantly improved, and it can still show good impact performance at -30°C.



②The mechanical properties such as tensile yield strength and rigidity are not as good as homopolypropylene, but higher than random copolypropylene.



③Good transparency is not good.



Comparison of three polypropylene properties



①Tensile yield strength: homopolypropylene>block copolypropylene>random copolypropylene.



②Rigidity: homopolypropylene>block copolypropylene>random copolypropylene.



③Impact strength: block copolypropylene>random copolypropylene>homopolypropylene.



④Transparency: random copolypropylene>homopolypropylene>block copolypropylene.



⑤ Low temperature toughness: block copolymer polypropylene> random copolymer polypropylene> homopolypropylene.