The low-temperature toughness of PE film needs to be analyzed comprehensively considering its material properties, molecular structure, and actual application scenarios. As a film material based on polyethylene (PE), its low-temperature toughness is mainly affected by molecular chain mobility, crystallinity, and additives. Different types of PE film exhibit varying low-temperature performance, but overall, they maintain good flexibility within reasonable usage ranges.
The low-temperature toughness of PE film is closely related to its molecular chain structure. Polyethylene molecular chains are composed of carbon-carbon single bonds, resulting in weak intermolecular forces, which endows it with good flexibility. At low temperatures, the mobility of the molecular chains decreases, but PE has a low glass transition temperature; for example, the glass transition temperature of low-density polyethylene (LDPE) is approximately -78°C. This means that even in environments tens of degrees below zero, its molecular chains can still maintain a certain degree of mobility and are not easily completely solidified due to temperature drops. Therefore, ordinary PE film does not become brittle rapidly at low temperatures like some crystalline plastics; instead, it exhibits a gradual decrease in toughness but still maintains basic flexibility.
The crystallinity of PE film is a key factor affecting its low-temperature toughness. Polyethylene can be classified into high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE), among others. HDPE has a tightly packed molecular chain and higher crystallinity, while LDPE and LLDPE have more branched molecular chains and lower crystallinity. Higher crystallinity results in greater rigidity but relatively lower toughness at low temperatures; conversely, low-crystallinity PE films maintain good flexibility at low temperatures. For example, LDPE film retains its toughness and is less prone to embrittlement at -45°C, while HDPE film may experience a decrease in toughness under the same conditions due to its higher crystallinity, but it is still superior to some other plastic materials.
The use of additives significantly improves the low-temperature toughness of PE films. Plasticizers are common additives that enhance the flexibility of plastics; they reduce the intermolecular forces and increase the mobility of the molecular chains. Adding an appropriate amount of plasticizer to PE film can effectively delay the decrease in toughness at low temperatures, allowing the film to remain flexible even at lower temperatures. Furthermore, while antioxidants and light stabilizers do not directly improve low-temperature performance, they can prevent the film's performance from deteriorating due to aging during long-term use, indirectly maintaining its low-temperature toughness. For example, plasticized PE film exhibits significantly better toughness than similar products without plasticizers at -50°C.
In practical applications, the low-temperature toughness of PE film is also affected by processing technology and structural design. By optimizing processing techniques such as blow molding and extrusion, the crystallinity and molecular chain arrangement of the film can be controlled, thereby improving its low-temperature performance. A reasonable structural design, such as uniform wall thickness and rounded corner transitions, can reduce stress concentration and lower the risk of low-temperature brittleness. For example, PE film produced using multi-layer co-extrusion technology, through the composite of PE films with different densities, can balance strength and toughness, exhibiting greater stability in low-temperature environments.
Compared to other plastic films, PE film has a significant advantage in low-temperature toughness. For example, polypropylene (PP) film, due to its high glass transition temperature, is prone to embrittlement at low temperatures; polystyrene (PS) film transitions from a glassy state to a brittle state at low temperatures, resulting in a significant decrease in toughness. PE film, with its low glass transition temperature and adjustable crystallinity, maintains good flexibility even in low-temperature environments, making it particularly suitable for frozen food packaging and low-temperature storage.
While the toughness of PE film gradually decreases with decreasing temperature, its low glass transition temperature, adjustable crystallinity, and the improving effects of additives allow it to maintain good flexibility within reasonable usage ranges. By optimizing material selection, processing technology, and structural design, its low-temperature performance can be further improved to meet the needs of different applications.
