How do the stretching rate and puncture performance of PE stretch film affect its packaging effect?

The stretching rate and puncture performance of PE stretch film are the core technical indicators of its packaging effect, and they jointly affect the economy, reliability, and applicability of the packaging system through different mechanisms of action. The stretching rate, as a quantitative expression of the material's extensibility, directly determines the coverage efficiency and tension distribution of the film in wrapping operations. When a tensile force is applied to the film, the molecular chains align along the direction of the applied force, forming an elastic network structure similar to a spring. The degree of molecular orientation is closely related to the stretching rate. The initial stretching ratio of industrial grade PE stretch films is usually controlled at 2-2.5 times, while films using pre stretching technology can achieve a stretching amplitude of 200-300% on packaging machines. In practical operation, high stretching rate endows the film with stronger deformation adaptability. For example, when wrapping goods with concave convex structures on the surface, the film can compensate for stress concentration through local extension, avoiding film fracture caused by local overload. The ordered arrangement of molecular chains can significantly enhance the elastic modulus of the film, and the pre stress layer formed in the cold stretching process can effectively offset the vibration energy during transportation, which is crucial for the stability of cargo stacks with a height exceeding 2.5 meters.

The puncture performance is directly related to the toughness and energy absorption capacity of the film. The ratio of crystalline and amorphous regions in PE materials, the dispersion state of additives, and processing parameters jointly affect this indicator. In multi-layer co extrusion technology, the synergistic effect of each functional layer is particularly crucial: the outer layer is formed by adding linear low-density polyethylene (LLDPE) or metallocene polyethylene (mPE) to form a puncture resistant surface layer, the middle layer is provided with rigid support by high-density polyethylene (HDPE), and the inner layer is reinforced with ethylene vinyl acetate copolymer (EVA) to enhance adhesion. This composite structure enables the puncture fracture force of OPET/PE composite film to reach 15.3N, which is more than three times higher than traditional single-layer films. It is worth noting that the biaxially oriented stretching process (BOPE) forms a three-dimensional network structure of molecular chains through synchronous stretching in both longitudinal and transverse directions, which can maintain higher puncture resistance even with a 20% reduction in thickness. This lightweight characteristic is particularly suitable for fields such as air transportation that are sensitive to packaging weight.

The synergistic effect of the two types of performance is more evident in specific application scenarios. Taking the transportation of automotive parts as an example, the sharp edges of metal castings such as engine cylinder blocks require the film to have a puncture strength of at least 12N. At the same time, due to the large weight of the goods (usually exceeding 800kg), a pre stretching rate of over 300% is required to ensure that the friction between the film layers is sufficient to resist sliding. The stress-strain curve shape of the film becomes a key parameter - the ideal stretching process should maintain a sufficiently long linear elastic deformation stage and complete the wrapping operation before entering the plastic deformation stage. This can not only avoid the loosening of the wrapping caused by residual stress relaxation, but also utilize the energy dissipation mechanism of the plastic deformation stage to absorb sudden impacts. Modern intelligent stretching packaging machines monitor tension changes in real-time through a closed-loop control system. When the elongation rate of the film reaches a critical value, the stretching roller speed is automatically adjusted. This dynamic adjustment capability increases the comprehensive performance utilization rate of the film by more than 40%.

At the level of materials science, there is a subtle balance between tensile strength and puncture performance. Increasing the elongation rate usually requires reducing the material density to enhance ductility, but this may weaken crystallinity and lead to a decrease in puncture strength. To solve this contradiction, the industry has developed a nano calcium carbonate filling modification technology, which adds CaCO3 particles with a particle size of 50-80nm to the PE matrix. This can not only increase the puncture strength by 25% through the rigidity enhancement effect of the nanoparticles, but also reduce the tensile friction coefficient by utilizing the ball rolling effect of the particles, breaking through the technical bottleneck of 350% mechanical tensile rate. The application of molecular chain cross-linking technology has opened up a new optimization path. Radiation cross-linked PE film maintains a 200% elongation rate while its puncture energy absorption value is 2.8 times that of ordinary film. This characteristic exhibits unique advantages in cold chain logistics: at -18 ℃ low temperature environment, the cross-linking structure can effectively suppress material brittleness and maintain the integrity of the packaging system.

From the perspective of packaging engineering, the combination selection of these two indicators requires a systematic consideration of logistics environment parameters. For sea container transportation, in addition to requiring the film to have salt spray corrosion resistance, it is also necessary to focus on evaluating the long-term creep characteristics - high tensile rate films are prone to stress relaxation under continuous static loads, which requires the material to have a steeper initial slope of the creep curve. Experimental data shows that the modified PE film with 2% nano clay added can increase the pre tension retention rate from 63% of the ordinary film to 82% under continuous tension for 30 days. This characteristic is particularly important for transportation cycles of several weeks in cross-border shipping. In the e-commerce logistics scenario, packages need to withstand 8-10 sorting impacts per day, and the film's ability to resist multiple punctures becomes crucial. By introducing self-healing elastic components, the new PE film can maintain 90% of its original strength after 5 punctures, significantly reducing the risk of progressive damage during transportation.