How does the glass transition temperature of vitrified polyolefin cable material affect its temperature resistance?
Release Time : 2025-10-08
The glass transition temperature (Tg) of vitrified polyolefin cable material is a key indicator of its temperature resistance, directly determining its operating limits in high or low temperature environments. Tg is essentially the critical temperature at which polyolefin molecular chains transition from a "frozen" state to an "active" state. This transition accompanies the material's transition from a hard, brittle glassy state to a soft, highly elastic state, significantly impacting its mechanical properties, thermal stability, and long-term reliability.
When the ambient temperature approaches or exceeds the Tg of a vitrified polyolefin cable material, the molecular chains gain sufficient energy to begin moving, causing the material's hardness to decrease and its elasticity to increase. However, this also leads to a sharp increase in the thermal expansion coefficient, resulting in poor dimensional stability. For example, in high-temperature operating conditions, a low Tg may cause excessive softening and creep in the cable material, causing relative displacement between the insulation and conductor, and even localized overheating. Conversely, a properly designed Tg allows the material to maintain rigidity within the target temperature range, effectively resisting thermal deformation.
The Tg of a vitrified polyolefin cable material is closely related to its molecular structure. Introducing rigid groups (such as aromatic rings and heteroatoms) into the polyolefin backbone or enhancing intermolecular forces (such as hydrogen bonds and ionic bonds) can significantly increase the Tg. For example, embedding benzene rings into polyethylene chains through copolymerization can create a steric hindrance effect, restricting chain segment movement and thereby increasing the Tg. Adding nano-inorganic fillers (such as montmorillonite) can further constrain the thermal motion of molecular chains through physical crosslinking, enhancing high-temperature stability.
The crosslinking process significantly influences the Tg of vitrified polyolefin cable materials. Chemical crosslinking forms a three-dimensional network structure, reducing free volume and hindering molecular segment movement, thereby increasing the Tg. For example, radiation crosslinking can raise the Tg of standard polyolefins from 90°C to over 150°C, significantly extending their temperature resistance range. However, excessive crosslinking can lead to increased brittleness, necessitating a balance between increasing the Tg and maintaining toughness.
The addition of plasticizers can lower the Tg of vitrified polyolefin cable materials. Plasticizer molecules insert between polyolefin chains, increasing free volume and weakening intermolecular forces, making the chains more mobile. For example, adding 45% plasticizer to polyvinyl chloride can reduce its Tg from 78°C to -30°C. However, excessive use can compromise the material's heat resistance and mechanical strength. Therefore, the choice of plasticizer must be carefully regulated based on the temperature requirements of the application.
Dynamic thermomechanical analysis (DMA) is a key method for assessing the Tg of vitrified polyolefin cable materials. By measuring the temperature-dependent changes in the storage modulus, loss modulus, and dissipation factor, the Tg point can be precisely determined. Near the Tg, the storage modulus drops sharply and the loss modulus peaks, indicating the material's transition from a glassy state to a highly elastic state. The sensitivity of this transition directly impacts the cable material's performance stability under temperature fluctuations.
In practical applications, the Tg of vitrified polyolefin cable materials must be tailored to the application. For example, in high-temperature environments like automotive engine compartments or industrial motors, materials with a Tg above 120°C are required to ensure long-term reliability. In low-temperature regions, however, the Tg must be lowered or the filler system optimized to prevent embrittlement and cracking. In the future, with the advancement of nanocomposite technology, bio-based polyolefins, and intelligent responsive materials, the Tg of vitrified polyolefin cable materials will be more precisely controlled, providing a more reliable solution for power transmission in extreme environments.