Thermal properties of fiberglass: excellent thermal insulation and high-temperature resistance.
The comprehensive performance of glass fiber is shaped by its chemical composition, production process, heat treatment process, and surface impregnation agents. Among many key properties, its thermal performance makes it stand out in fields such as high-temperature insulation and fire safety, becoming an indispensable basic material.
Core Thermal Performance Characteristics:
1. Excellent Thermal Insulation (Low Thermal Conductivity)
Glass fiber has extremely low thermal conductivity. At room temperature (approximately 25°C), its typical thermal conductivity is approximately 0.027 W/(m·K).
This value is far lower than most metallic materials (e.g., steel approximately 50 W/(m·K), aluminum approximately 237 W/(m·K)), and also significantly lower than many commonly used building and industrial materials (e.g., concrete approximately 1.7 W/(m·K), wood approximately 0.1-0.2 W/(m·K)).
This extremely low thermal conductivity means that glass fiber can effectively impede heat transfer, making it a high-performance thermal insulation material.
Temperature Influence: While the thermal conductivity of glass fiber increases slightly with rising ambient temperature, its fundamental low thermal conductivity is maintained over a fairly wide temperature range, making it suitable for insulation in medium to high temperature conditions.
2. Excellent High-Temperature Resistance and Non-combustibility
Compared to organic fibers (such as cotton, wool, polyester, nylon, aramid, etc.), glass fiber exhibits extremely high heat resistance.
Its softening temperature is as high as 550°C - 750°C. This means that below this temperature range, glass fiber maintains sufficient structural strength and morphological stability without softening or deforming.
Key Advantage: Non-combustible. Glass fiber is an inorganic silicate material that does not burn at high temperatures and does not release toxic fumes. This characteristic makes it ideal for fire safety applications (such as fireproof insulation in buildings, fire blankets, fire curtains, and high-temperature pipe cladding).
3. Thermal Shrinkage and its Impact on Composite Materials
Although the mechanical properties of glass fiber itself do not change significantly when heated at temperatures far below its softening point, thermal shrinkage occurs.
Composite Interface Risks: This thermal shrinkage behavior is crucial for resin-based composites (fiberglass reinforced plastics) reinforced with fiberglass. If the interfacial bonding between the glass fiber and the resin matrix is poor (e.g., inappropriate sizing agent selection or uneven coating leading to poor coupling), during repeated heating and cooling cycles (thermal cycling):
The fiber and resin deform differently due to their different coefficients of thermal expansion/contraction.
A poor interface cannot effectively transfer stress or coordinate deformation.
This can ultimately lead to interfacial debonding (separation) between the fiber and the resin matrix.
Consequences: Interfacial debonding severely weakens the integrity of the composite material, becoming a stress concentration point and crack initiation source, resulting in a significant decrease in the mechanical strength of the product (especially interlaminar shear strength and fatigue strength), affecting its long-term reliability and durability.
Application Areas: Solutions for High-Temperature and Thermal Insulation Needs
Based on the aforementioned unique thermal properties, glass fiber is widely used in:
Building Thermal Insulation: Glass wool, insulation felt/boards, used for wall, roof, and pipe insulation, saving energy and reducing consumption.
Industrial High-Temperature Insulation: Insulation layers for high-temperature kilns, pipelines, and equipment; thermal system insulation; energy saving.
Fire Safety: Fireproof door core materials, fireproof partitions, fire blankets, insulation layers for fire suits, and fireproof cable wrapping.
Aerospace and Transportation: Thermal insulation, sound insulation, and fireproofing materials for aircraft, ships, and high-speed trains.
Household Appliances: Thermal insulation pads for high-temperature appliances such as ovens, grills, and dryers.
Summary: Glass fiber, with its extremely low thermal conductivity (excellent insulation), ultra-high softening temperature, and non-combustibility (excellent high-temperature resistance and fire safety), has established its core position in high-temperature insulation and fireproofing. However, its inherent heat shrinkage characteristics also remind us that ensuring a strong interfacial bond between fibers and resin is crucial in composite material applications (especially those subjected to thermal cycling). Strengthening the interface through optimized impregnating agent formulations (especially coupling agents) and process control is key to fully utilizing the reinforcing effect of glass fiber and ensuring the long-term performance stability of composite materials under thermal conditions.