Introduction
Thermal conductivity is a crucial component of everyday life. Understanding the thermal conductivity of materials enables more efficient use of these materials. Materials with low thermal conductivity make great thermal insulators, whereas high thermal conductivity materials are better thermal conductors as they move heat quickly and efficiently.
Fiberglass composites are materials made up of glass Fibers embedded within a thermosetting plastic matrix like polyester, epoxy and polyurethane. The reinforced material is strong, lightweight, and flexible. Perfect for rugged products like sporting equipment and boat hulls yet delicate enough for applications such as circuit boards.
Varying the composition of the material by including additives and fillers can alter physical and mechanical properties, such as fire resistance and thermal conductivity, allowing the composites to be widely used in various industries for many applications. So why is understanding the thermal conductivity of these composites so important?
Figure 1. Glass Fibers
Understanding Thermal Conductivity
Thermal conductivity, often denoted by k, λ, or ĸ, refers to a material's ability to transfer or conduct heat. We commonly express the thermal conductivity of a material in units of W · m-1 · K-1.
Conduction is one of the three modes of heat transfer; the other two are convection and radiation. Heat moves along a temperature gradient, from an area of high temperature to an area of lower temperature, until thermal equilibrium is reached.
The rate at which heat transfers depends on the material's composition, structure, and temperature. Therefore, the thermal conductivity of different materials varies. For example, a highly conductive material such as copper has a thermal conductivity of 398 W/m·K, whereas an insulative material like cellulose insulation has a thermal conductivity of 0.040 W/m·K.
Generally, polymers and foams have lower thermal conductivity, whereas metals have higher conductivities. Some materials may even vary in conductivity based on the composition of their counterparts or the manufacturing method.
Fiberglass Composites: Composition and Properties
Composite materials are formed by combining reinforcement (Fiber) with a matrix (resin). Fiberglass composites typically consist of a thermosetting plastic matrix containing desired additives, combined with glass Fibers as reinforcement.
Composite materials are typically more robust, lightweight, and flexible than their constituent materials.
A unique property that makes Fiberglass so versatile is that it can easily be moulded into any desired shape and size (at a relatively low cost), allowing for the incorporation of Fiberglass into many industrial products. Another reason to choose Fiberglass composites over wood or metal materials is their corrosion resistance. This material is not prone to rust like iron or steel, nor will it be invaded by pests or mold when exposed to moisture like wood.
Fiberglass composites exhibit high tensile strength and require minimal maintenance, thereby costing less over time than other materials. Custom fillers or additives can be incorporated into the material's composition to enhance properties such as fire resistance and thermal conductivity.
Factors Affecting the Thermal Conductivity of Fiberglass Composites
The thermal conductivity of composite material depends on the Fiber type, resin material, and orientation of the Fibers. As mentioned, fillers or additives can also be incorporated into the composites to enhance properties such as thermal conductivity.
Fiber is the reinforcing phase of composite materials. Glass Fibers are widely used as reinforcing materials due to their excellent mechanical properties. Different types of glass Fiber are used depending on the composite's application. Some are more insulative, while others help the structural integrity of the composite, for example, E-glass vs S-glass. Glass Fibers can also be arranged in different orientations and densities, which influences the overall thermal conductivity of the composite.
Resin is considered the matrix, or body, of the composite, providing the product's shape. As with the types of Fiber used, different resins yield distinct final product properties. Polyester is the most widely used due to its low cost, rapid curing time, and strength.
Fillers and additives such as aluminum or graphene can be incorporated into the composite to enhance specific properties. Fillers can improve thermal conductivity, tensile strength, cost, and temperature resistance in reinforced Fiberglass. The fillers' size and morphology also influence the heat transfer inside the composites.
Common fillers include metals, carbon-based materials, and ceramics. Metal and carbon-based fillers enhance the thermal conductivity of composites due to their high intrinsic thermal conductivities. Ceramic fillers may be used to increase the thermal resistance of fiberglass composites.
Figure 2. Additives and fillers.
Applications of Fiberglass Composites in Thermal Insulation
Fiberglass composites are durable, have a high strength-to-weight ratio, are highly corrosion-resistant, and are simple and inexpensive. These unique characteristics ensure that this material remains one of the most versatile and easy-to-use composites for the foreseeable future.
Designers, builders, and homeowners have widely adopted Fiberglass composites as lower-cost, more energy-efficient options for applications such as window reinforcements, exterior trim, and doors. One key advantage is its thermal insulation and its fire resistance. Fiberglass bars are commonly used as insulation, cladding, and raw roofing materials. The high thermal insulation of Fiberglass composites plays a vital role in reducing building energy consumption by minimizing heat transfer between adjacent zones.
Thermal insulation in aircraft, trains, and automobiles is critical for the transportation industry. Glass Fiber composites are widely used due to their high thermal insulation performance and low weight.
Limited thermal and electrical conductivity makes glass Fiber composites well-suited for motor, transformer, and electrical manufacturing, as well as recreational products such as sporting equipment and high-performance prosthetic limbs. Thanks to its superior strength, fast production time, and variability in size and shape, the possibilities of this material are nearly endless.
Comparative Analysis of Thermal Conductivity
Using the Thermtest Guarded Heat Flow Meter (GHFM-01), the thermal conductivity of a 6.4 mm thick sample of fiberglass was determined to be 0.36 W/m·K. Compared to the thermal properties of other commonly used construction and insulation materials, it is clear why Fiberglass has significant advantages.
|
Material |
Thermal Conductivity (W/m·K) |
|
Aluminum |
225.94 |
|
Steel |
16.10 |
|
Polyethylene (PE) |
0.50 |
|
Fiberglass Composite |
0.36 |
|
Wood |
0.21 |
The higher the thermal conductivity, the worse the material's insulating properties. These data show that Fiberglass composites exhibit significantly better insulating performance while maintaining the stiffness and strength of highly conductive materials such as aluminum and steel, making fiberglass composites more appealing for window and door reinforcements due to their thermal efficiency and strength.
Fiberglass outperforms aluminum and steel when alternating temperatures, leading to better energy conservation when the material expands or contracts.
Figure 3. Windows and doors are the main cause of energy loss in buildings and homes.
Reinforced Fiberglass is lightweight, high-strength, corrosion- and chemical-resistant, electrically insulating, thermally insulating, easy to work with, requires minimal maintenance, and is more sustainable than other commonly used materials. There is no question why this material is becoming increasingly popular in many industries.
Enhancing Thermal Conductivity in Fiberglass Composites
As mentioned above, there are various ways to enhance the thermal conductivity of a composite material. Fiber type, resin type, Fiber volume, Fiber orientation, fillers, and additives can affect conductivity. The thermal conductivity of Fiberglass composites depends directly on the types of Fiber and resin used and on their spatial orientation. The volume of glass Fibers in the composite will also affect the material's thermal conductivity. Different types of glass and resin offer distinct advantages depending on the product's intended use.
For example, using thermosetting plastic resins rather than thermoplastic resins will lead to better performance at elevated temperatures. Glass Fibers are available in continuous, chopped, or woven forms, each with different thermal properties due to the nature of the composition. The manufacturing method is another critical factor that alters the thermal properties of these composites. Fiberglass may be manufactured by pultrusion, compression molding, resin transfer molding, and casting, each yielding distinct thermal and physical properties.
The main advantage of using a filler material is to gain desirable thermal properties while maintaining low cost. Fillers can improve thermal conductivity, crack resistance, shrinkage, and fire resistance. Additives may decrease or increase the total cost of the product but enhance durability, electrical and thermal conductivity.
In recent years, significant advancements have been made in altering the thermal and physical properties of Fiberglass composite materials. Mahmud et al. (2023) highlighted the environmental concerns associated with the use of inorganic materials in composites. To address these concerns, the research group developed a new hybrid-style composite using coir and glass Fibers.
Coir is a natural Fiber extracted from coconut husks. The strong synthetic glass Fibers are used as the top and bottom layers, and the lower-strength natural coir Fibers comprise the center. These hybrid composites exhibit the same strength and durability but lower thermal conductivity, thereby creating a more sustainable future for reinforced Fiber composites.
Figure 4. Coir fibers
Conclusion
With the growing demand for high-performing structures and products, it is clear why Fiberglass composites have been continuously replacing traditional simple materials. Fiberglass is quickly becoming the leading material in home construction due to its high strength-to-weight ratio and low thermal conductivity. The ability to readily alter this material's thermal and physical properties to meet product requirements enables broader applications of Fiberglass composites.
This material is advantageous for reducing carbon emissions and improving the energy efficiency of buildings by enhancing thermal insulation, thereby contributing to a more sustainable future. Continued advancements in Fiberglass composites open exciting opportunities for residential, commercial, and industrial applications. The versatility of this composite is astounding and will only improve from here on out.
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