The Science of Fiberglass Entry Doors

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A composite material

What do we know about the principal properties of the main material in fiberglass entry doors? Fiberglass, as its name implies, is composed of very thin filaments of glass. Less known is that it is usually combined with plastic polymer and resins to form a bonded, composite structure. At the heart of fiberglass properties is the fact that it is primarily made of glass.

What are the properties of glass when it is stretched and spun into filaments?

Molecular composition

The glass in fiberglass entry doors itself is a noncrystalline solid. The molecular composition is silicon dioxide (or SiO2 in science-speak). Usually, solid forms of small molecules like SiO2 in fiberglass entry doors, for example CO2 or H2O, form crystalline structures. H2O, which is water, when frozen becomes a tetrahedrally coordinated solid that is highly ordered but also energetically stable. Unusually, SiO2 can exist in a noncrystalline state at low temperatures. When heated to very high temperatures and cooled very slowly however, SiO2 forms quartz, which is the crystalline state.

Non-crystalline but stable

But when heated to high temperatures and cooled quickly, it forms the vitreous, unordered form known as glass . For centuries, glass-making has followed this temperature cycling: (1) heat to high temperatures (over 1000 c elsius) and then (2) quick cooling. The resulting material is noncrystalline, therefore seems to have molecular properties of a liquid. Unlike a conventional liquid, glass is pretty solid and shows almost no flow over common human time scales. Interestingly, physics simulations of molecules show that quartz and glass are both energetically very stable. Therefore, even though glass is not an ordered crystal, its molecular structure is stable.

Stretching glass

When glass is heated again, it becomes quite malleable and can be drawn into long thin fibers. In 7th grade science, you may have done this experiment yourself by heating up a thin tube of glass and then stretching it over the bunsen burner. The principle remains the same: heated, softened glass can form thin fibers when stretched quickly. These thin fibers can then be woven by machine methods, then reinforced with plastic resins. The molecular structure of the thin fibers stays unordered as in the bulk glass form in products such as fiberglass entry doors.

Rich properties

Fiberglass is a narrow strand of glass, which makes it have a high surface area to volume ratio. As a result, it displays a lot of surface area which can react with chemicals. Because it can react so easily with volatile compounds, the protection of fiberglass entry doors from corrosive chemicals is important. But another advantage of fiberglass is that it can be bundled so that much air becomes trapped between the fibers, making fiberglass entry doors one of the best insulators. Glass is also one of those substances that do not conduct electricity, such that it forms the basis of materials which are water proof, and electrically and thermally non conductive. The various properties of fiberglass that derive from glass make it ideal for making many useful items because it resists water, insulates, has great strength and yet is flexible, and can be shaped into many materials. Many familiar items in our lives are made of fiberglass, such as surfboards, ski poles, tent poles, electrical insulation, boats and roofing materials, and fiberglass entry doors.