Although the use of composite materials is currently uncommon, these materials are increasingly present in all types of industries and applications without us realizing it. Composites have been around for more than 3,000 years, when Egypt and Mesopotamia used a mixture of mud and straw to create strong and durable adobe bricks. But how has the evolution of these materials been until today?
First of all, it is necessary to remember what is understood as a composite material.
A composite material is known as the heterogeneous union of two or more materials in order to create a uniform material with a synergistic sum of properties. To understand this we can use the previous example of adobe bricks: on the one hand, a mud brick is a brittle and fragile piece, like any clay vase. On the other hand, strands of straw are not capable of supporting the weight of a building. However, when these two materials are mixed evenly, they result in a much more resistant and tough brick.
First applications of composite materials
From what we see, the association of certain materials with properties that are at first glance antagonistic can create other products with improved characteristics. The Mongols arrived at this same reflection when they invented the first composite material bows around 1200 AD .
These tools were made using a combination of bamboo to provide flexibility characteristics with pine resin to stiffen the product. These small, light and powerful bows were the most feared weapon until the introduction of firearms in the 14th century.
It would be necessary to wait until the end of the 19th century for advances in the chemical industry to allow resins to be transformed from a liquid state to a solid state by cross-linking the molecular structure with the process known as polymerization. This scientific milestone allowed composite materials to become what we know today. Since, until then, the only sources of glues and binders were natural resins derived from plants and animals.
Materials such as vinyl, polystyrene, phenols and polyester were created and soon surpassed resins derived solely and directly from nature.
Evolution during the 20th century
In 1907, Belgian-American Leo Baekeland created the first fully synthetic plastic substance, Bakelite. This thermostable polymer with insulating and heat-resistant capabilities made the compound widely used in both industrial and consumer applications. However, plastics as such are not capable of providing sufficient resistance for any structural application. Therefore, the reinforcements were necessary to provide the necessary additional strength and rigidity.
In 1935, Owens Corning introduced the first fiberglass. Fiberglass when combined with a plastic polymer created an incredibly strong yet lightweight structure. In this way, the Fiber Reinforced Polymers (FRP) industry emerged, extended and modernized to this day. At this time, unsaturated polyester resins (dominantly used today due to their curing properties) were also patented, as well as other higher-performance resin systems such as epoxies years later.
As with Mongolian bows before, World War II took the FRP industry from laboratories to actual production. Alternative materials were needed for lightweight military aviation applications. Soon engineers realized other benefits of composites in addition to their good strength-to-weight ratio. Fiberglass composites were found to be radiofrequency transparent and thermal insulating. More than three thousand tons of fiberglass were used primarily for military applications during World War II.
After the war, fiberglass began to be incorporated into the nautical industry, drastically transforming it. In 1946 the first commercial fiberglass boat was introduced. In turn, Brandt Goldsworthy developed several novel processes and products such as pultrusion.
In the 1950s, the use of composites grew rapidly as boats, trucks, sports cars, storage tanks, pipes and many other products were produced using composite materials. Other production processes were developed, such as vacuum bag molding or large-scale filament winding. The latter was used as a basis for the construction of large rocket boosters that enabled space exploration in the 1960s and later.
In 1961 the first carbon fiber was patented and years later commercialized. Carbon fiber allowed the improvement of the stiffness-to-weight ratio of the thermoset parts. Therefore it was used in cutting-edge applications, such as aerospace. It wasn’t until 1981 when McLaren built the first F1 with a carbon fiber monocoque.
DuPont chemist Stephanie Kwolek invented the famous Kevlar in 1966, a fiber derived from aramid with high tensile strength, high density and lightweight. This fiber is mainly known for its use in ballistic and anti-sting material for protection.
In the 1970s, the automotive industry surpassed the nautical industry in the use of composite materials . Thanks in part to the introduction of the first commercial car to use all-fiberglass paneling in mass production, the Corvette. Furthermore, before the arrival of the 1980s, infrastructure applications arrived in Europe and Asia, including the first highway bridge using composite tendons.
The technology continued to develop at high speed in the 1990s. Composite materials became more common in conventional manufacturing and construction as a cost-effective replacement for traditional materials such as metal and engineering thermoplastics.
21st century: growth and innovation
This exponential growth was notable in the aviation industry, since in the late 2000s it already had a 50% weight percentage of FRP in some of its newest aircraft.
Nanotechnology began to be used in commercial products. Composites play an important role in carbon nanotubes to improve mechanical, thermal and electrical properties. A decade later, composite materials were adapted for 3D printing technology. In 2014 MarkForged announced the first carbon 3D printer.
Currently, the most recent studies investigate the automation of large-scale manufacturing processes of composite materials , to reduce production costs and bring them closer to everyday products. As well as the application of this type of materials to intelligent products, capable of adapting external parameters.
In addition, efforts are being made to improve the recyclability of composite materials to make them more sustainable and environmentally responsible products. Natural fibers such as hemp, linseed, jute, agave or coir are being used to develop green composites.