The flexibility of PP woven fabric at low temperatures is significantly affected by the raw material ratio. Adjusting the blending ratio of polypropylene (PP) and polyethylene (PE), adding elastomer toughening agents, optimizing filler selection, and controlling the amount of processing aids can effectively improve its low-temperature brittleness resistance while maintaining a balance between material strength and processing performance. The following analysis focuses on the core aspect of raw material ratio:
The blending of PP and PE is a fundamental method for improving low-temperature flexibility. PP itself is a crystalline polymer; at low temperatures, its molecular chain mobility decreases, making it prone to brittle fracture. PE (especially linear low-density polyethylene LLDPE) has lower crystallinity and a lower glass transition temperature, maintaining good flexibility even at low temperatures. Blending PP and PE forms a two-phase continuous structure, with PE distributed as a dispersed phase within the PP matrix, forming a "tough network." When the material is subjected to external force, the PE phase can absorb some energy and prevent crack propagation, thereby improving overall impact resistance. It is important to note that the amount of PE added must be controlled within a reasonable range; excessive amounts can lead to a significant decrease in PP crystallinity, affecting material strength and even causing delamination. It is generally recommended that the PE addition amount be 5%-15%, which can significantly improve low-temperature performance while maintaining the mechanical stability of PP woven fabric.
The introduction of elastomer toughening agents can further optimize low-temperature flexibility. Elastomers such as ethylene propylene diene monomer (EPDM) and ethylene-octene copolymer (POE) have excellent low-temperature resistance and high elasticity. The unsaturated bonds or flexible segments in their molecular chains can remain mobile at low temperatures, effectively absorbing impact energy. For example, the glass transition temperature of EPDM can be as low as -50℃. After addition, PP woven fabric can maintain good flexibility at -20℃, and the impact strength can be increased several times. POE, due to its excellent compatibility with PP, can achieve a significant toughening effect with a small addition amount, and has little impact on the transparency of the material. Elastomer toughening agents are usually used in combination with PE to form a multiphase toughening system, which further improves low-temperature performance through synergistic effects.
The choice of fillers also has an important impact on the low-temperature performance of PP woven fabric. While traditional inorganic fillers (such as calcium carbonate and talc) can reduce costs, they disrupt the continuity of PP, leading to increased low-temperature brittleness. Therefore, in applications requiring improved flexibility, the amount of inorganic fillers should be reduced, or fillers with toughening properties, such as nano-silica and wollastonite, should be selected. These fillers have small particle sizes and large specific surface areas, forming a uniformly dispersed reinforcing phase within the PP matrix. They transfer stress through interfacial interactions, reducing crack initiation. Furthermore, some organic fillers (such as wood flour and straw fiber) can also be used as toughening agents; their natural fibrous structure can create a "bridging" effect within the material, improving tear resistance.
The appropriate use of processing aids is crucial for ensuring low-temperature flexibility. Lubricants (such as calcium stearate and polyethylene wax) can reduce the viscosity of the PP melt, improve processing fluidity, and prevent stress concentration caused by melt fracture, thereby improving material uniformity. Antioxidants (such as hindered phenols and phosphites) can inhibit the thermal oxidative degradation of PP during processing, preventing increased brittleness caused by molecular chain breakage. Light stabilizers (such as UV absorbers and hindered amines) can delay the photoaging of PP during outdoor use, maintaining its long-term flexibility. While these additives do not directly contribute to toughening, they indirectly improve the reliability of PP woven fabric in low-temperature environments by stabilizing material properties.
Optimizing the raw material ratio requires balancing flexibility with other properties. For example, increasing flexibility may lead to a decrease in strength, which needs to be compensated for by adjusting the PP to PE ratio or introducing reinforcing fillers; the addition of toughening agents may affect the material's heat-sealing performance, requiring process adjustments (such as increasing the heat-sealing temperature). Furthermore, different applications have different performance requirements for PP woven fabric; for example, packaging bags require tear resistance, while geotextiles emphasize weather resistance. Therefore, the raw material ratio needs to be designed specifically for each application.
