The performance of PE plastic bags is determined by the molecular structure and aggregation characteristics of its raw material, polyethylene (PE), and further refined during processing to meet diverse needs. Its performance encompasses mechanical properties, chemical stability, thermal properties, barrier properties, processing adaptability, and safety, collectively contributing to its dominant position in the packaging industry.
Regarding mechanical properties, the tensile strength, tear strength, and impact resistance of PE plastic bags vary with the density and molecular structure of the raw material. Low-density polyethylene (LDPE), due to its highly branched molecular chains and low crystallinity, exhibits softness and good ductility, making it suitable for packaging lightweight and fragile items. Linear low-density polyethylene (LLDPE), while maintaining flexibility, significantly improves tensile strength and puncture resistance due to the uniform distribution of short branches, making it suitable for frozen foods and heavy-duty logistics bags. High-density polyethylene (HDPE), with its nearly linear molecular chains, fewer branches, and high crystallinity, offers superior rigidity and load-bearing capacity, commonly used in shopping bags and industrial packaging.
Chemical stability is a prominent advantage of PE plastic bags. Their saturated carbon-carbon backbone structure exhibits good resistance to most acids, alkalis, and common organic solvents, making them less prone to chemical reactions with their contents. This allows them to maintain the stability of materials in the packaging of chemical raw materials, food, and daily necessities. Simultaneously, PE possesses excellent electrical insulation properties, providing a certain degree of barrier against static electricity and moisture, making it suitable for protective packaging of electronic components, etc.
Regarding thermal properties, PE plastic bags have a wide operating temperature range, generally maintaining their basic physical properties between -50℃ and 80℃. They are not easily brittle at low temperatures, making them suitable for cold chain transportation and frozen storage; however, they soften and deform easily at high temperatures, thus their heat resistance is not as good as some engineering plastics, requiring appropriate selection based on operating conditions.
In terms of barrier properties, PE offers some barrier effect against moisture, slowing down the penetration of moisture in humid environments. However, its barrier effect against oxygen and some aromatic hydrocarbon gases is limited. Therefore, in food and pharmaceutical packaging requiring high barrier protection, this is often improved through multi-layer co-extrusion or surface coating with high-barrier materials.
In terms of processing adaptability, PE has good melt flowability, allowing for efficient molding through blow molding, casting, and hot pressing. It is also easy to heat-seal, print, and laminate, facilitating strong seals, clear patterns, and functional integration. Its raw materials are widely available and cost-effective, which is conducive to large-scale production.
Regarding safety, food-grade PE is non-toxic and odorless, meeting relevant hygiene standards for contact materials, and can be safely used for packaging fresh and cooked foods.
Overall, PE plastic bags offer a balanced advantage in mechanical, chemical, thermal, and processing properties. Coupled with adjustable raw material structures and process selection, they can reliably perform protective, load-bearing, and display functions in numerous fields, becoming an indispensable basic material in modern packaging systems.