Polyvinyl chloride (PVC) glass fiber sleeves are key materials for electrical insulation and thermal protection, and their contact thermal resistance directly affects the heat dissipation efficiency and operational stability of equipment. Contact thermal resistance mainly stems from the microscopic gaps between the sleeve and the contact surface and differences in the thermal conductivity of the materials. Process improvements require a coordinated breakthrough in three aspects: material surface treatment, structural optimization, and interface filling.
Surface treatment is a fundamental step in reducing contact thermal resistance. The interfacial bonding strength between PVC and glass fiber directly affects heat transfer efficiency. In traditional processes, the smooth surface of glass fiber and its adsorbed water film result in poor adhesion to PVC, easily forming a thermal conduction barrier. Surface modification of glass fiber using silane coupling agents can introduce active groups to form chemical bonds with the PVC molecular chains, significantly improving interfacial bonding. For example, glass fiber treated with KH550 silane coupling agent exhibits significantly improved tensile and impact strength with PVC, reduced interfacial gaps, and consequently lower thermal resistance. Furthermore, plasma treatment technology can bombard the glass fiber surface with high-energy particles, increasing surface roughness and active sites, further strengthening the mechanical bonding with PVC.
Structural optimization needs to focus on the fiber distribution and orientation design within the sleeve. While glass fiber has better thermal conductivity than polyvinyl chloride (PVC), disordered fiber arrangement can easily block heat conduction paths. Controlling the orientation of glass fibers through melt spinning or molding processes can create directional heat conduction channels. For example, applying a magnetic field or shear force during sleeve fabrication can align the glass fibers axially, forming a continuous "fiber-matrix-fiber" heat conduction network. This structure reduces thermal resistance while maintaining the sleeve's electrical insulation properties. Furthermore, using a composite of chopped glass fibers and long fibers allows for both filling matrix gaps with short fibers and constructing dominant heat conduction paths with long fibers, achieving a balance between thermal resistance and mechanical strength.
Interface filling is a key technology for reducing contact thermal resistance. The microscopic gaps between the sleeve and the contact surface are filled with air, which has extremely low thermal conductivity and is a major source of thermal resistance. Applying thermally conductive silicone grease or a phase change material to the sleeve surface can eliminate gap air and fill it with a highly thermally conductive medium. Thermal grease's fluidity allows it to adapt to minute deformations at the contact surface, maintaining stable thermal conductivity over the long term. Phase change materials (PCMs), on the other hand, fill gaps during endothermic melting and solidify during exothermic solidification, providing both shock absorption and thermal conductivity. For example, adding paraffin-based PCMs between the sleeve and the radiator contact surface can significantly reduce contact thermal resistance. For high-temperature applications, inorganic thermally conductive fillers such as boron nitride and alumina can be used to prepare thermally conductive coatings, creating a low-thermal-resistance interface through the high thermal conductivity of the fillers.
Precise control of process parameters has a significant impact on contact thermal resistance. Plasticizing temperature and time are key factors affecting the density of polyvinyl chloride glass fiber sleeves. Too low a temperature leads to incomplete plasticization of the matrix, resulting in loose bonding between the fiber and matrix; too high a temperature may cause glass fiber degradation or polyvinyl chloride decomposition, damaging the thermally conductive network. Optimizing the plasticizing temperature range through experiments ensures that the matrix fully encapsulates the glass fiber, reducing interface defects. Simultaneously, controlling the mixing time and shear rate prevents excessive glass fiber breakage or agglomeration, maintaining the continuity of the thermally conductive channels.
The morphological matching design of the sleeve and the contact surface is a hidden key to reducing contact thermal resistance. Microscopic roughness of the contact surface can lead to localized stress concentration and increased gaps. Micro- and nano-structural treatment of the contact surface using CNC machining or chemical etching techniques can increase the actual contact area. For example, fabricating a micron-scale groove array on the heat sink surface, forming a mechanical interlock with the protrusions on the sleeve surface, enhances the bonding strength and reduces gap volume. This design allows the contact thermal resistance to decrease exponentially with increasing contact area.
The thermal resistance stability under long-term service conditions needs to be ensured through material aging resistance modification. Polyvinyl chloride (PVC) is prone to degradation under high temperature or ultraviolet radiation, leading to matrix shrinkage or cracking and damaging the interfacial bond with glass fiber. Adding heat stabilizers and ultraviolet absorbers can slow down the material aging rate and maintain the integrity of the thermal conductivity network. For example, using a calcium-zinc composite stabilizer instead of a traditional lead salt stabilizer can improve environmental performance while extending the thermal aging life of the sleeve.
Reducing the contact thermal resistance of polyvinyl chloride glass fiber sleeves requires collaborative innovation across multiple dimensions, including surface treatment, structural optimization, interface filling, process control, morphology matching, and aging resistance modification. These improvements not only enhance the thermal conductivity of the sleeve but also extend equipment lifespan, providing a reliable solution for thermal management of high-power electrical equipment.
